The Role of Exosomes in Pulmonary Hypertension: Mechanisms and Therapeutic Potential

Abstract

Pulmonary hypertension (PH) is a progressive vasculopathy characterized by pulmonary vascular remodeling, right ventricular maladaptation, and premature death. Exosomes, an endosome-derived subset of small extracellular vesicles, mediate intercellular communication through the transfer of selected RNAs, proteins, and lipids. In PH, they can modulate endothelial dysfunction, pulmonary artery smooth muscle cell proliferation and phenotypic switching, immune dysregulation, and right ventricular remodeling, implicating them in key aspects of disease pathobiology. These properties have prompted interest in exosomes as minimally invasive biomarkers and as candidates for cell-free therapeutic delivery. However, clinical translation remains at an early stage. Most evidence supporting exosome-based therapeutic strategies in PH is preclinical, whereas current clinical data are largely limited to exploratory biomarker studies. Important gaps also remain in distinguishing exosomes from other extracellular vesicle populations and in addressing methodological standardization, heterogeneity, cargo attribution, biodistribution, dosing, and clinical validation. This review summarizes current evidence on exosome biology in PH and discusses both translational opportunities and the major barriers to clinical implementation.

Graphical Abstract

Introduction

Pulmonary hypertension (PH) is a hemodynamic and clinical syndrome defined by a mean pulmonary artery pressure (mPAP) >20 mmHg at rest, as measured by right heart catheterization.^1–6 Importantly, PH is not a single disease entity but a heterogeneous group of disorders with distinct etiologies, pathobiological mechanisms, and clinical outcomes.⁷ This heterogeneity is reflected in the current clinical classification of PH, which includes five major groups: Group 1, pulmonary arterial hypertension (PAH); Group 2, PH associated with left heart disease; Group 3, PH associated with lung diseases and/or hypoxia; Group 4, chronic thromboembolic pulmonary hypertension (CTEPH) and other pulmonary artery obstructions; and Group 5, PH with unclear and/or multifactorial mechanisms.^5,8 Thus, PAH refers specifically to WHO Group 1 PH and should not be used interchangeably with PH as an umbrella term.⁸ This distinction is important when interpreting mechanistic studies, because findings from specific disease settings or experimental models—including hypoxia-induced PH, monocrotaline (MCT)-induced experimental PH, CTEPH, and PH associated with chronic lung disease—may not be uniformly generalizable across the full spectrum of PH.^9–11 A clearer appreciation of this heterogeneity is therefore essential for contextualizing emerging molecular mechanisms and evaluating their translational relevance. PH represents a substantial global health burden, affecting approximately 1% of the general population and up to 10% of individuals older than 65 years.^12,13 PH is associated with progressive clinical deterioration and increased mortality.^14,15 Therefore, further research is urgently needed to develop effective preventive and therapeutic strategies for different forms of PH.

Intercellular communication is essential for normal physiological homeostasis as well as pathological responses to tissue injury and repair.^16,17 Such communication occurs through several mechanisms, including direct cell-cell contact, paracrine signaling, and extracellular vesicles (EVs).^18,19 EVs are lipid-bilayer-delimited particles released from cells that cannot replicate on their own and are increasingly recognized as important mediators of physiological homeostasis and disease progression. They facilitate intercellular communication by transferring diverse bioactive cargo, including nucleic acids, proteins, lipids, and metabolites.^20–23 According to the Minimal Information for Studies of Extracellular Vesicles 2023 (MISEV2023) guidelines, “exosome” is a biogenesis-based term referring to EVs of endosomal origin and should not be assigned solely on the basis of vesicle size. In particular, small EVs and exosomes should not be considered synonymous, because EV populations within a similar size range may arise through different biogenetic pathways.²⁴ Accordingly, the generic term “EVs” or operational terminology such as “small EVs” is preferred when the subcellular origin of a vesicle population has not been rigorously demonstrated. Nevertheless, because the primary studies discussed in this review predominantly identify and report the investigated vesicle populations as “exosome”, we retain the term “exosome” when describing these published findings to maintain consistency with the original literature. Importantly, unless their endosomal origin has been specifically demonstrated, the use of “exosome” throughout this review should be understood as reflecting the terminology adopted in the original studies rather than as a definitive assignment of vesicle biogenesis. Where appropriate, the broader term “EVs” is used in accordance with the MISEV2023 recommendations.

As reported in the exosome literature, nearly all cell types can release vesicles containing diverse biomolecules, including DNA, RNA, lipids, metabolites, and cytoplasmic as well as membrane-associated proteins.²⁵ Their biological effects are highly context-dependent: exosomes derived from the same cell type may exert distinct, or even opposing, effects in different recipient cells because of differences in cargo composition, receptor expression, and intracellular signaling pathways.^26,27 In addition, exosomes display source-dependent heterogeneity in their composition and biological functions.²⁸ Their intrinsic biocompatibility and capacity to mediate intercellular signaling have attracted increasing attention to exosomes as potential biomarkers and therapeutic tools in cardiovascular and pulmonary vascular diseases, including PH.^29–31 However, the clinical assessment of PH still faces important limitations. Currently used circulating biomarkers, particularly B-type natriuretic peptide (BNP) and N-terminal pro-BNP (NT-proBNP), provide valuable prognostic information but primarily reflect myocardial stress, lack specificity for PH, and do not directly capture the underlying pulmonary vascular remodeling.⁵ Moreover, longitudinal assessment of pulmonary vascular remodeling and right ventricular (RV) involvement remains challenging, as it relies on the integration of functional, imaging, biochemical, and hemodynamic measurements, none of which alone provides a direct and dynamic readout of the molecular changes occurring within the pulmonary vasculature and the RV. Against this background, exosomes have attracted increasing interest as potential biomarkers because their molecular cargo may reflect disease-associated changes in their cells of origin and provide additional information on ongoing pathological processes.

Accumulating evidence indicates that exosomes contribute to the pathogenesis and progression of PH and hold promise as diagnostic biomarkers and therapeutic targets.^32–34 Exosomes released by various pulmonary vascular cell types, including pulmonary artery endothelial cells (PAECs), pulmonary artery smooth muscle cells (PASMCs), and pulmonary artery fibroblasts (PAFs), have been implicated in the development of PH.^35,36 In addition, mesenchymal stem cell (MSC)-derived exosomes have shown considerable therapeutic and translational potential for the treatment of PH.^37–40 Nevertheless, exosome-based biomarkers remain investigational, and their clinical utility will require further validation and methodological standardization. In this review, we summarize recent advances in the understanding of exosomes in PH, with particular emphasis on their roles in pulmonary vascular homeostasis and PH pathogenesis, as well as their potential applications as biomarkers and therapeutic agents.

The Biogenesis, Mechanisms, and Functions of Exosomes

The Origin of Exosomes

The biogenesis of exosomes generally follows a sequential process. It begins with plasma membrane invagination and endocytosis, leading to the formation of early sorting endosomes (ESEs). Subsequently, ESEs gradually mature into late sorting endosomes (LSEs), during which inward budding of the endosomal membrane generates intraluminal vesicles (ILVs) and ultimately forms multivesicular bodies (MVBs). Finally, MVBs fuse with the plasma membrane, releasing ILVs into the extracellular space as exosomes.^41–43 During the initial invagination process, the plasma membrane internalizes cell surface proteins and soluble extracellular components, thereby contributing to the de novo formation of ESEs. In some cases, newly formed endocytic vesicles may also fuse directly with pre-existing ESEs. In addition, the trans-Golgi network and the endoplasmic reticulum contribute to the formation and maturation of ESEs and influence their cargo composition. Subsequently, ESEs mature into LSEs and ultimately into MVBs.^44–46 The fate of MVBs is twofold: they can either fuse with lysosomes for degradation or fuse with the plasma membrane to release their ILVs into the extracellular space as exosomes.^47–50 The entire process is regulated by both ESCRT-dependent and ESCRT-independent pathways.^51–54 ESCRT-0, ESCRT-I, and ESCRT-II are responsible for recognizing and sorting ubiquitinated cargo, whereas ESCRT-III mediates membrane budding and scission.^55,56 By contrast, ESCRT-independent pathways involve tetraspanins such as CD9, CD63, and CD81, as well as ceramide-mediated membrane curvature.⁵⁷ Alterations in exosome biogenesis, cargo sorting, and secretion may influence intercellular communication within the pulmonary vasculature and thereby contribute to the pathogenesis of PH. The origin of exosomes have been summarized in Figure 1.

Figure 1.

The origin and biological mechanisms of action of exosomes. Exosomes biogenesis begins with plasma membrane invagination and endocytosis, forming early sorting endosomes (ESEs), which mature into late sorting endosomes (LSEs) and multivesicular bodies (MVBs) containing intraluminal vesicles (ILVs). MVBs either fuse with lysosomes for degradation or with the plasma membrane to release ILVs as exosomes. This process is regulated by both ESCRT-dependent and ESCRT-independent pathways, involving. ESCRT complexes, tetraspanins (CD9, CD63, and CD81), and ceramide-mediated membrane remodeling. After release, exosomes communicate with recipient cells through direct ligand–receptor interactions, soluble factor-mediated indirect signaling, or cellular uptake via clathrin-mediated endocytosis, caveolin-mediated endocytosis, macropinocytosis, phagocytosis, and lipid raft-dependent internalization. The black arrows indicate the direction of intracellular trafficking and material exchange involved in exosome biogenesis, secretion, and delivery to recipient cells. The figure was created with BioRender.com.

Molecular Basis of Exosome Mechanisms

Current evidence suggests that exosomes communicate with recipient cells mainly through three mechanisms: direct ligand-receptor interactions, indirect signaling mediated by soluble factors, and cellular internalization.^58–61 Direct ligand-receptor interactions involve specific binding between surface molecules on exosomes and corresponding receptors on recipient cells, including proteins, glycans, and lipids.^62–64 The soluble factor-mediated indirect signaling mechanism refers to a process in which exosomes, without coming into direct contact with target cells, release soluble protein components that bind to specific receptors on the surface of target cells, thereby indirectly inducing the activation of signaling pathways.⁶⁵ Internalization of exosomes occurs through several endocytic routes, including clathrin-mediated endocytosis, caveolae-mediated endocytosis, macropinocytosis, phagocytosis, and lipid raft-dependent uptake.^47,66,67 In clathrin-mediated endocytosis, exosomal surface proteins, such as tetraspanins (CD9, CD63, and CD81) and integrins, interact with receptors on the recipient cell membrane, triggering the formation of clathrin-coated pits and subsequent vesicle internalization.⁶⁸ Caveolae-mediated endocytosis depends on cholesterol-rich lipid rafts and caveolin proteins that generate flask-shaped membrane invaginations. This pathway may facilitate intracellular trafficking while, in some contexts, limiting direct lysosomal degradation and enabling transcytosis.^69–71 Macropinocytosis is driven by actin-dependent membrane ruffling and results in the nonspecific uptake of extracellular fluid and exosomes into large vesicles. In contrast, phagocytosis is a receptor-dependent process that mediates the engulfment of larger particles, including EVs, by specialized cell types. Lipid raft-dependent uptake involves cholesterol-rich membrane microdomains and provides another route for exosome internalization.^72,73 In the pulmonary vasculature, these interaction and uptake mechanisms are likely to determine how exosomal cargo is transferred among endothelial cells, smooth muscle cells, fibroblasts, and immune cells, thereby shaping pulmonary vascular remodeling in PH. The biological mechanisms of exosome action have been summarized in Figure 1.

The Biological Functions of Exosomes

Accumulating evidence indicates that exosomes play important roles in maintaining tissue homeostasis and in the initiation and progression of disease.^25,74 Exosomes function as natural nanocarriers that transfer bioactive cargo, including nucleic acids, proteins, lipids, and metabolites, to recipient cells, thereby altering their phenotype and function.^75,76 Among these cargo molecules, non-coding RNAs, particularly microRNAs (miRNAs), are considered major mediators of exosome-induced gene regulation.^22,77 In addition to cargo delivery, exosomes can directly mediate intercellular communication through membrane-associated proteins and lipids that activate signaling pathways in recipient cells. Through these mechanisms, exosomes influence diverse biological processes, including proliferation, apoptosis, inflammation, immune regulation, and tissue remodeling. The specific functional roles of exosomes in PH are discussed in the following section.

Introduction to the Pathological Mechanism of PH

PH is a severe cardiopulmonary vascular disorder characterized by pulmonary vascular remodeling and a progressive increase in pulmonary vascular resistance (PVR), ultimately leading to right heart failure and premature death, with poor prognosis.^78,79 Although vasodilator therapies have advanced over the past decades, PH-associated mortality remains high.⁸⁰ The central pathological feature of PH is the aberrant phenotypic transformation of multiple cell types within the injured pulmonary vascular wall and the complex intercellular network they establish.^44,81,82

During pulmonary vascular remodeling, injury and dysfunction of PAECs are generally regarded as initiating events.^83–85 Dysfunctional PAECs promote vascular dysregulation by decreasing the release of vasodilators, such as NO and PGI2, while increasing vasoconstrictors, such as endothelin-1. They also contribute to lesion formation through endothelial-to-mesenchymal transition (EndoMT) and acquisition of an abnormal hyperproliferative, apoptosis-resistant phenotype.^86–90 PASMCs subsequently switch from a quiescent contractile phenotype to a proliferative, apoptosis-resistant, tumor-like state, resulting in medial thickening and progressive luminal narrowing.^91–93 Meanwhile, PAFs in the adventitia are activated and further aggravate vascular remodeling through excessive extracellular matrix (ECM) deposition and differentiation into myofibroblasts.^94–97

In recent years, the perivascular immune microenvironment has been increasingly recognized as a critical driver of PH pathogenesis. Immune cells, including macrophages, T and B lymphocytes, and neutrophils, accumulate in the perivascular space and establish a chronic inflammatory milieu.^98–102 These cells not only directly injure vascular cells by releasing pro-inflammatory mediators, such as IL-6 and TNF-α, but also modulate the behavior of PAECs and PASMCs through complex intercellular crosstalk.^103,104 This dysregulated immune network drives pulmonary vascular remodeling from an initially adaptive response toward an irreversible pathological process.

In summary, PH is not driven by an abnormality in a single cell type, but by a dynamic multicellular process involving PAECs, PASMCs, and PAFs under the influence of immune cells and inflammatory signaling. Further elucidation of how exosomes mediate communication among these cell populations will deepen our understanding of PH pathobiology and may provide a basis for developing targeted therapies against vascular remodeling and immune dysregulation.

The Role of Exosomes from Different Pulmonary Vascular Cells Origins in PH

Interactions Between PAEC-Derived Exosomes and PASMC-Derived Exosomes

Accumulating evidence indicates that PAEC-derived exosomes, as nanoscale carriers of bioactive cargo, play a pivotal role in pulmonary vascular remodeling in PH. By transporting diverse molecular signals, these vesicles not only amplify remodeling cascades over time, but also mediate communication across the endothelial, medial, and adventitial layers of the pulmonary arterial wall.^105–108 For example, PAEC-derived exosomes have been identified as carriers of HCG20, which can be transferred to neighboring PASMCs and subsequently promote the proliferation of PASMCs, thereby accelerating vascular remodeling.¹⁰⁹ In contrast, exosomes derived from endothelial progenitor cells (EPCs) suppress PASMCs viability and migration, promote apoptosis, and attenuate pulmonary vascular remodeling under hypoxic conditions.¹⁰⁸ Endothelial exosomes have also been shown to transmit NEDD9-related signals to PASMCs, inducing excessive collagen production and aggravating vascular fibrosis, thus supporting a TGF-β-independent profibrotic mechanism in PH.¹¹⁰ In addition, our previous work demonstrated that PAEC-derived exosomes contribute to pulmonary vascular homeostasis through both autocrine and paracrine actions.¹¹¹ Notably, under pathological conditions, both exosome release and cargo composition are markedly altered. Exosomes secreted by hypoxia-treated mouse PAECs enhance DNA synthesis and migration in PASMCs, driving their phenotypic switch from a quiescent contractile state to a proliferative synthetic state and thereby promoting medial thickening.^112,113 Zhang et al further showed that hypoxic PAECs release exosomes enriched in 15-LO2, which are taken up by adjacent endothelial cells and activate STAT3 signaling, leading to excessive endothelial proliferation.¹¹⁴

Conversely, phenotypically altered PASMCs can also impair endothelial function through exosome-mediated signaling, thereby forming a pathogenic feedback loop that further accelerates vascular remodeling. Wang et al reported that, in hypoxic PH, aberrant activation of a super-enhancer in PASMCs drives marked upregulation of Syndecan-4 (SDC4), which promotes PASMC proliferation by regulating protein kinase C-α ubiquitination. Importantly, PASMC-derived exosomes can further transfer SDC4 to PAECs, inducing endothelial dysfunction and aggravating pulmonary vascular remodeling.¹¹⁵ In addition, PASMC-derived exosomes exert paracrine effects on PAECs by promoting endothelial migration and angiogenesis.¹¹⁶ Transcriptomic evidence has further shown that PASMC-derived exosomes can induce EndoMT in PAECs.³⁶ Together, these findings indicate that exosome-mediated crosstalk between PAECs and PASMCs is bidirectional and actively coordinates pathological changes across the entire vascular wall. Therefore, therapeutic strategies for PH should not be limited to lesions in a single cell type, but should also aim to disrupt this maladaptive intercellular communication by targeting exosome biogenesis, cargo loading, or vesicle transfer. The roles of PAEC-derived exosomes and PASMC-derived exosomes in PH have been summarized in Figure 2.

Figure 2.

The role of exosomes from different pulmonary vascular cells origins in Pulmonary hypertension (PH). Under hypoxic and inflammatory conditions, pulmonary artery endothelial cells (PAECs), pulmonary artery smooth muscle cells (PASMCs), and pulmonary artery fibroblasts (PAFs) release exosomes carrying distinct pathogenic cargoes that mediate intercellular communication across the intima, media, and adventitia. PAEC-derived exosomes promote PASMC phenotypic transition, proliferation, DNA synthesis, and migration, thereby contributing to medial thickening. Specifically, exosomal HCG20 enhances PASMC proliferation, whereas NEDD9-associated exosomal signaling promotes collagen production and vascular fibrosis through a TGF-β-independent profibrotic mechanism. In addition, exosomes derived from hypoxic PAECs and enriched in 15-LO2 can be taken up by adjacent endothelial cells, where they activate STAT3 signaling and further stimulate endothelial proliferation. Conversely, PASMC-derived exosomes exert pathogenic effects on PAECs, promoting endothelial migration, angiogenesis, and endothelial-to-mesenchymal transition (EndoMT). Among these, SDC4-containing exosomes derived from PASMCs with activated super-enhancers contribute to both PASMC hyperproliferation and endothelial dysfunction. In the adventitial compartment, PAF-derived C3-enriched exosomes induce macrophage polarization toward a pro-inflammatory M1-like phenotype and drive metabolic reprogramming toward glycolysis, thereby amplifying perivascular inflammation. Collectively, these exosome-mediated signaling networks integrate endothelial dysfunction, PASMC proliferation and phenotypic remodeling, fibrosis, and inflammation, ultimately promoting pulmonary vascular remodeling in PH. Red, purple, and yellow arrows denote the sequential mechanistic processes through which PAEC-, PASMC-, and PAF-derived exosomes, respectively, mediate PH progression. The figure was created with BioRender.com.

PAF-Derived Exosomes

Compared with PAEC-derived exosomes and PASMC-derived exosomes, the role of PAF-derived exosomes in PH has been far less explored, despite the recognized importance of PAFs in adventitial remodeling and fibrosis.^94,97,117 To date, only one study identified complement C3-enriched vesicles released by PAFs as critical mediators of complement-dependent perivascular inflammation. Mechanistically, these vesicles promote macrophage polarization toward a pro-inflammatory phenotype through a C3-dependent pathway and reprogram macrophage metabolism toward glycolysis, thereby fostering a local inflammatory microenvironment that contributes to PH progression.¹¹⁸ Although current evidence remains limited, these findings suggest that PAF-derived exosomes may serve as important paracrine regulators linking adventitial fibroblasts to immune activation in PH. Further studies are needed to define their cargo composition, including miRNAs and proteins, clarify their roles in vascular remodeling and immune dysregulation, and assess their potential as therapeutic targets in PH. The role of PAF-derived exosomes in PH has been summarized in Figure 2.

Key Cargoes of Exosomes in Molecular Signaling Pathways in PH

In the previous section, we highlighted the role of exosomes as mediators of intercellular communication among pulmonary vascular cells in PH. However, the function of exosomes extends beyond simple cargo transfer. Their biological effects are largely determined by the selective loading of specific molecular cargoes, which can reprogram transcriptional activity, metabolism, and signaling pathways in recipient cells. Therefore, understanding exosomal function in PH requires not only identifying their cellular sources and target cells, but also defining the pathogenic or protective roles of their bioactive contents.

Exosomal Cargoes Targeting the BMPR2/TGF-β Axis in PH

The BMPR2/TGF-β signaling axis is a central regulator of pulmonary vascular homeostasis and a well-established contributor to PH pathogenesis.^119–121 However, its regulation by exosome-mediated communication remains insufficiently defined. To date, only a single study has demonstrated a direct regulatory link, revealing that adipose stem cell (ASC)-derived exosomes can deliver miR-191 to injured PAECs, subsequently modulating intracellular BMPR2 protein expression to confer vascular protection.¹²² Over the past decade, several other studies have phenomenologically linked exosome administration to the modulation of the BMPR2/TGF-β axis in pulmonary vascular cells.^106,123 For example, MSC-derived exosomes attenuate PAEC injury and PASMC proliferation by rescuing hypoxia-induced BMPR2 downregulation and suppressing TGF-β upregulation. These effects are accompanied by modulation of related pathways, including Wnt5a/BMP, NF-κB/BMP, and TGF-β1/Smad2/3 signaling.^124,125 However, in most of these studies, the specific exosomal non-coding RNAs (ncRNAs) or other active cargoes responsible for these effects were not identified, which limits mechanistic interpretation. Although direct evidence remains limited, intracellular studies provide an important framework for understanding how exosomal cargoes may influence this signaling axis in PH. BMPR2 deficiency has been shown to reduce miR-124 expression, thereby promoting glycolytic reprogramming and hyperproliferation in PAECs.¹²⁶ In PASMCs, loss of BMPR2 increases miR-29 expression, leading to mitochondrial dysfunction and aggravated vascular remodeling.¹²⁷ In parallel, other ncRNA networks also regulate this axis. For instance, circ-Ntrk2 acts as a sponge for miR-296-5p, relieving repression of TGF-β1 and accelerating PH progression.¹²⁸ These observations suggest that ncRNAs linked to BMPR2/TGF-β dysregulation may also function through exosome-mediated intercellular transfer. This possibility is supported by evidence from other cardiovascular diseases, in which stress conditions promote the selective sorting of specific ncRNAs, such as miR-221 and miR-6516-5p, into exosomes.^129,130 By analogy, exosomes in PH may act as intercellular amplifiers of BMPR2/TGF-β imbalance by delivering regulatory ncRNAs between vascular cells. Further studies are therefore needed to define the exosomal ncRNA landscape targeting this axis, clarify the mechanisms governing selective cargo loading, and determine whether these pathways can be exploited for therapeutic intervention in PH. The role of exosomal cargoes in regulating the BMPR2/TGF-β signaling axis in PH has been summarized in Figure 3.

Figure 3.

The role of exosomal cargoes in regulating Crucial signaling pathways in Pulmonary hypertension (PH). Exosomes derived from distinct cellular sources modulate multiple pathogenic and protective pathways across the pulmonary vascular–right ventricular axis. In the BMPR2/TGF-β signaling module, adipose stem cell (ASC)-derived exosomes (ASC-exo) deliver miR-191 to injured pulmonary artery endothelial cells (PAECs), thereby modulating BMPR2, whereas mesenchymal stem cell (MSC)-derived exosomes (MSC-exo) have been associated with restoration of BMPR2/TGF-β signaling and regulation of the Wnt5a/BMP, NF-κB/BMP, and TGF-β1/Smad2/3 pathways. In the context of phenotypic remodeling, pulmonary microvascular endothelial cell (PVEC)-derived exosomes (PVEC-exo) enriched in miR-214-3p, miR-326-3p, and miR-125b-2-3p promote PASMC proliferation through FoxM1-related signaling, whereas hypoxia-associated exosomal signaling further sustains the proliferative phenotype via the CaMK1/PPAR-γ axis. By contrast, protective exosomes derived from MSCs, endothelial progenitor cells (EPCs), induced pluripotent stem cells (iPSCs), and KLF2-activated endothelial cells suppress EGFR/ErbB2, Mfn2/Ras-Raf-ERK1/2, HIF-1α, Runx2/PAK1/AKT, and Notch4/ETS1 signaling, thereby attenuating PASMC proliferation, restoring apoptosis sensitivity, and improving endothelial function. Exosomal regulation also extends to mitochondrial homeostasis, including reversal of glycolytic reprogramming, promotion of oxidative phosphorylation, and correction of excessive mitochondrial fission. In addition, exosomal miR-21-mediated mitochondrial protection in right ventricular (RV) cardiomyocytes is associated with restoration of mtDNA copy number, reduction of reactive oxygen species (ROS), and stabilization of mitochondrial membrane potential. Collectively, these findings indicate that exosomal cargoes act as active regulators of signaling and metabolic remodeling in PH rather than passive vehicles of intercellular communication. Solid arrows represent the mechanistic actions of ASC-, MSC-, EPC-, and iPSC-derived exosomes in PH. Black upward and downward arrows indicate upregulation or downregulation of the adjacent markers, respectively, whereas T-shaped black arrows denote inhibition. The figure was created with BioRender.com.

Exosomal Cargoes Drives PASMCs Phenotypic Switching and Endothelial Dysfunction in PH

The transition of PASMCs from a quiescent contractile phenotype to a hyperproliferative synthetic phenotype is a hallmark of pulmonary vascular remodeling in PH.¹³¹ Increasing evidence indicates that exosomes and their selectively loaded cargoes play an important role in this process by regulating proliferation, apoptosis resistance, and intercellular signaling. Under pathological conditions, microenvironmental stress can alter exosomal cargo composition and promote the transfer of pro-remodeling signals to recipient cells. For example, pulmonary microvascular endothelial cell (PVEC)-derived exosomes are enriched in miR-214-3p, miR-326-3p, and miR-125b-2-3p, which cooperatively target the non-coding region of FoxM1 and promote PASMC proliferation.¹³² Likewise, hypoxia enhances the release of miR-211-enriched exosomes, which suppress the peroxisome proliferator-activated receptor-γ (PPAR-γ) pathway by targeting calmodulin-dependent kinase 1 (CaMK1), thereby sustaining the proliferative phenotype of PASMCs.¹³³ By contrast, exosomes derived from stem or progenitor cells show protective effects against pulmonary vascular remodeling. At the membrane receptor level, MSC-derived exosomes inhibit EGFR/ErbB2 dimerization and thereby blunt upstream proliferative signaling.¹³⁴ At the intracellular signaling level, EPC-derived exosomes regulate mitofusin-2 (Mfn2) expression through delivery of miR-21-5p, which suppresses the Ras-Raf-ERK1/2 cascade and restores PASMCs susceptibility to apoptosis.¹⁰⁸ Exosomes can also modulate nuclear transcriptional programs in recipient cells. For instance, induced pluripotent stem cell (iPSC)-derived exosomes inhibit HIF-1α and, through regulation of the upstream PAK1/AKT pathway, suppress Runx2 activity, thereby attenuating both kinase-driven and transcription-dependent remodeling responses.¹³⁵

In addition to smooth muscle remodeling, endothelial dysfunction is another major determinant of PH progression.¹³⁶ This process is characterized by an imbalance between endothelial apoptosis and abnormal proliferation, which further disrupts vascular homeostasis. Notably, exosomal cargoes can coordinately regulate both endothelial and smooth muscle cells. Overexpression of the flow-responsive transcription factor KLF2 in PAECs induces the release of exosomes enriched in miR-181a-5p and miR-324-5p. These exosomal miRNAs have been reported to target Notch4 and ETS1, which may contribute to the preservation of PAEC function under injury conditions. Their transfer to PASMCs may also alleviate the apoptosis-resistant phenotype of these cells.¹³⁷ Taken together, these findings indicate that exosomal cargoes do not act as passive transferred molecules, but as active regulators of receptor signaling, kinase cascades, and transcriptional reprogramming in PH. The role of exosomal cargoes in regulating PASMC phenotypic switching and endothelial dysfunction in PH has been summarized in Figure 3.

Exosomal Cargoes Modulate Mitochondrial Homeostasis and Vascular Remodeling in PH

In addition to canonical receptor-mediated signaling, metabolic reprogramming has emerged as an important mechanism underlying pulmonary vascular remodeling in PH.¹³⁸ As central regulators of cellular bioenergetics and redox balance, mitochondria play a key role in this process. Mitochondrial dysfunction, including enhanced glycolysis, disturbed fission-fusion dynamics, and abnormal mitophagy, contributes to the proliferative and apoptosis-resistant phenotypes of pulmonary vascular cells.^139–141 Recent studies suggest that exosomes may participate in this process by transferring ncRNAs and metabolic regulators that modulate mitochondrial homeostasis in recipient cells. At the level of energy metabolism, exosomes can partially reverse the pathological shift toward glycolysis. For example, MSC-derived exosomes have been reported to increase the expression of pyruvate dehydrogenase (PDH) and glutamate dehydrogenase 1 (GLUD1) in hypoxic PASMCs, changes that may favor a metabolic shift from glycolysis toward oxidative phosphorylation and potentially improve mitochondrial substrate utilization.¹⁴² These findings suggest that exosomes can influence metabolic flux in pulmonary vascular cells and counteract bioenergetic abnormalities associated with PH. Exosomes also affect mitochondrial network dynamics, which are closely linked to cell fate.¹⁴³ Proliferating PASMCs are typically characterized by excessive mitochondrial fragmentation, whereas EPC-derived exosomes regulate mitofusin-2 (Mfn2) expression through delivery of miR-21-5p.¹⁰⁸ By modulating mitochondrial dynamics, these exosomes inhibit PASMC proliferation and restore susceptibility to apoptosis. Thus, exosome-mediated control of mitochondrial structure appears to be another mechanism by which intercellular communication contributes to vascular remodeling in PH. Importantly, mitochondrial dysregulation in PH is not confined to the pulmonary vasculature but also represents a key feature of RV adaptation and maladaptation.¹⁴⁴ In contrast to pulmonary vascular cells, in which mitochondrial reprogramming is closely associated with proliferative and apoptosis-resistant phenotypes, mitochondrial alterations in the pressure-loaded RV primarily reflect the changing bioenergetic demands and stress responses of cardiomyocytes. The transition from adaptive RV hypertrophy to maladaptive remodeling has been associated with altered substrate utilization, increased reliance on glycolysis, impaired oxidative metabolism, disturbed mitochondrial dynamics, and enhanced oxidative stress.^145,146 In experimental PH-associated right heart failure, exosome-delivered miR-21 promotes mitochondrial fusion and limits excessive fission in cardiomyocytes. This is accompanied by stabilization of mitochondrial membrane potential, restoration of mtDNA copy number, and reduction of reactive oxygen species (ROS), collectively supporting mitochondrial integrity under hypoxic stress.¹⁴⁷ Nevertheless, the pulmonary vascular and RV effects of exosomal miR-21 cannot yet be fully disentangled. Because alterations in pulmonary vascular remodeling and RV afterload can secondarily influence RV mitochondrial function, current in vivo evidence does not establish whether the observed RV effects arise predominantly from direct endothelial exosome–cardiomyocyte communication or partly from indirect hemodynamic effects.

Taken together, available evidence suggests that exosome-associated signaling may influence mitochondrial homeostasis at multiple levels, including metabolic flux, mitochondrial dynamics, and oxidative stress control. These effects are currently better characterized in pulmonary vascular cells, whereas evidence for direct exosome-mediated regulation of RV mitochondrial adaptation remains limited. Further studies are needed to identify the key vesicular cargoes involved, distinguish direct RV effects from those secondary to altered pulmonary vascular load, and determine whether mitochondria-targeted exosome engineering may offer therapeutic benefit in PH. The role of exosomal cargoes in regulating mitochondrial homeostasis and vascular remodeling in PH has been summarized in Figure 3.

Clinical Translational Applications of Exosomes in PH

The Therapeutic Potential of Stem Cell-Derived Exosomes in PH

Given the important role of exosomal signaling in pulmonary vascular remodeling, stem cell-derived exosomes have attracted increasing attention as potential therapeutic candidates for PH. MSCs, in particular, have long been investigated for their immunomodulatory and reparative properties.^148,149 However, accumulating evidence suggests that the beneficial effects of MSCs in PH may depend less on long-term engraftment and more on paracrine mechanisms mediated by EVs, especially exosomes.^150,151

Endothelial injury is considered an early event in PH pathogenesis. Several studies have shown that exosomes collected from MSC culture supernatants attenuate hypoxia-induced apoptosis in PAECs.¹⁵² In addition, in both in vitro models and MCT-induced PH models, MSC-derived exosomes inhibit EndoMT, thereby helping preserve endothelial integrity and barrier homeostasis.^122,153 In parallel, MSC-derived exosomes also affect the abnormal phenotypic switching of PASMCs, which contributes directly to medial thickening and luminal narrowing. Experimental studies indicate that MSC-derived exosomes can deliver functional cargoes to PASMCs and suppress hypoxia-induced proliferative and apoptosis-resistant phenotypes.^37,154 Mechanistically, these effects have been linked to inhibition of the Hsp90aa1/ERK/pERK pathway and the TGF-β1/Smad2/3 signaling axis, resulting in reduced PASMC proliferation and migration and attenuation of vascular remodeling.^125,155 Thus, stem cell-derived exosomes appear to target not only the endothelial component of disease initiation, but also the smooth muscle component of disease progression. Inflammation is another major contributor to PH progression, particularly through perivascular macrophage accumulation and sustained cytokine signaling.¹⁵⁶ In this context, human umbilical cord mesenchymal stem cell (HUCMSC)-derived exosomes have been reported to promote macrophage polarization toward an anti-inflammatory M2 phenotype and to increase IL-10 expression. At the same time, they suppress the IL-33/ST2 signaling axis and reduce M1-associated inflammatory activation, thereby attenuating the pro-inflammatory microenvironment that supports vascular remodeling.¹⁵⁷ These observations further support the concept that stem cell-derived exosomes may exert therapeutic effects through immunomodulation in addition to direct vascular cell regulation. The role of therapeutic potential of stem cell-derived exosomes in PH has been summarized in Figure 4.

Figure 4.

The role of exosomes in clinical translation in Pulmonary hypertension (PH). Exosomes derived from mesenchymal stem cells (MSCs) and human umbilical cord mesenchymal stem cells (HUCMSCs) target key cellular processes involved in PH. In pulmonary artery endothelial cells (PAECs), exosome therapy attenuates hypoxia- or monocrotaline (MCT)-induced apoptosis and endothelial-to-mesenchymal transition (EndoMT). In pulmonary artery smooth muscle cells (PASMCs), exosomes suppress hypoxia-driven phenotypic transition, proliferation, and migration, in part through inhibition of the Hsp90aa1/ERK/p-ERK and TGF-β1/Smad2/3 pathways. In macrophages, exosomes promote M2 polarization, increase IL-10, and inhibit IL-33/ST2-associated inflammatory signaling, thereby reducing inflammatory activation. Through these coordinated effects, stem cell-derived exosomes may alleviate pulmonary vascular remodeling and reduce luminal narrowing. In addition, circulating plasma exosomes may serve as liquid biopsy biomarkers in PH, as exosomal miR-122-5p is positively associated with the severity of pulmonary vascular remodeling, whereas elevated exosomal miR-596 is associated with poorer survival in idiopathic pulmonary arterial hypertension (IPAH). Solid arrows represent the mechanistic actions of MSC- and HUCMSC-derived exosomes in PH. Red upward and downward arrows indicate upregulation or downregulation of the adjacent markers, respectively, whereas red T-shaped arrows denote inhibition. The figure was created with BioRender.com.

In summary, available preclinical evidence suggests that stem cell-derived exosomes may exert pleiotropic protective effects across several disease-relevant pathways in PH, including endothelial homeostasis, smooth muscle cell phenotypic plasticity, and inflammatory signaling. These coordinated effects have been associated with attenuation of pulmonary vascular remodeling and improvement of PH-related hemodynamic and RV phenotypes in experimental models. However, the current evidence is derived predominantly from in vitro studies and animal models and therefore does not establish that stem cell-derived exosomes can reverse PH in patients. As a cell-free approach, stem cell-derived exosomes may offer practical advantages over viable-cell therapies, including greater flexibility in formulation and storage and avoidance of risks associated with uncontrolled cell proliferation. Nevertheless, they should currently be regarded as promising preclinical therapeutic candidates rather than established disease-modifying treatments for PH.

The Clinical Value of Exosomes in Early Screening and Continuous Monitoring of PH

The clinical management of PH would benefit from biomarkers that support earlier detection and more continuous disease monitoring, particularly given the invasive nature of right heart catheterization and the limited ability of current approaches to capture dynamic vascular changes.^158,159 In this context, exosomes have attracted growing interest as a liquid biopsy source. By carrying protected molecular cargoes, especially miRNAs, exosomes released into the circulation may reflect pathological changes in the pulmonary vascular microenvironment.^160,161 Their lipid bilayer structure enhances cargo stability in blood, making exosomal miRNAs promising candidates for non-invasive assessment of disease onset, progression, and prognosis.

Recent studies suggest that circulating exosomal miRNA profiles may provide clinically relevant information in selected PH populations, although the available evidence remains limited and should be interpreted according to the specific PH subgroup studied. Zhao et al reported that plasma exosomal miR-122-5p levels were positively associated with the degree of pulmonary vascular remodeling, supporting its potential value as an indicator of structural vascular injury.¹⁶² However, current evidence for this miRNA remains purely mechanistic, without established biomarker utility. In contrast, the prognostic evidence for plasma exosomal miR-596 is currently specific to idiopathic pulmonary arterial hypertension (IPAH). Yang et al confirmed in discovery and validation cohorts that elevated plasma exosomal miR‑596 levels independently predict overall survival in IPAH patients; however, the relatively small sample size and the absence of independent external validation currently limit its clinical applicability.¹⁶³ This finding provides proof-of-concept that exosome-associated miRNAs may contribute to risk stratification and prognostic assessment in a defined PAH population. However, whether this association extends to other PAH subtypes or other PH groups remains unknown. The potential biomarker roles of exosomes in PH are summarized in Figure 4.

Taken together, current evidence suggests that circulating exosomal miRNAs represent promising candidate biomarkers for disease characterization and prognostic assessment in PH, although their clinical applicability remains unestablished. Importantly, the strength of evidence varies among individual candidates. Future studies should focus on larger, multicenter, and longitudinal cohorts, standardized exosome and miRNA detection approaches, and evaluation of potential confounding factors and PH subtype-specific performance. The diagnostic and prognostic value of exosomal biomarkers should also be assessed in comparison with established PH biomarkers and risk stratification parameters. Therefore, circulating exosomal miRNAs remain promising candidate biomarkers, but further analytical and clinical validation is required before their incorporation into routine PH management.

Conclusion and Perspectives

Current evidence supports exosome-associated intercellular communication as an important component of PH pathobiology, particularly in the regulation of endothelial dysfunction, inflammatory signaling, smooth muscle cell phenotypic changes, and pulmonary vascular remodeling. However, the evidence supporting specific exosomal cargos as causal drivers of human PH, as well as the therapeutic efficacy of MSC-derived or engineered exosomes, remains predominantly preclinical. Likewise, circulating exosomes and their molecular cargos are promising candidate biomarkers, but their diagnostic, prognostic, and monitoring value has not yet been sufficiently validated for routine clinical use. Importantly, no exosome-based therapy is currently established as a standard treatment for PH. Thus, exosomes provide a valuable framework for understanding intercellular communication in PH and a promising platform for biomarker and therapeutic development, but their clinical application remains dependent on rigorous validation, methodological standardization, and demonstration of clinically meaningful benefit.

Taken together, the available evidence supports exosome-associated intercellular signaling as a biologically relevant component of PH pathobiology. However, the strength of evidence varies considerably across different applications. Altered vesicle-mediated communication and its effects on disease-relevant cellular phenotypes are supported by convergent experimental observations, whereas the causal roles of individual exosomal cargos and the therapeutic efficacy of specific exosome preparations remain predominantly supported by in vitro studies and experimental PH models. In particular, improvements in RV structure or function following exosome-based interventions should be interpreted cautiously, because they may partly result from reduced pulmonary vascular afterload rather than a direct myocardial effect. Similarly, although circulating exosomes and their molecular cargos are attractive candidate biomarkers, their clinical utility remains insufficiently established. Most reported signatures require validation in larger, independent, and longitudinal cohorts, together with demonstration of reproducibility and incremental diagnostic or prognostic value beyond established clinical, hemodynamic, imaging, and circulating biomarkers. These limitations highlight the need to distinguish biological plausibility and preclinical efficacy from demonstrated clinical utility when interpreting the current exosome literature in PH.

The next stage of exosome research in PH should move beyond the identification of additional candidate cargos in isolated experimental settings and instead prioritize rigorous biological and translational validation of the most reproducible findings. In accordance with current EV guidelines, greater standardization is required across pre-analytical procedures, EV separation and characterization, nomenclature, assessment of preparation heterogeneity, and exclusion of non-vesicular contaminants. Such standardization will be essential for determining whether apparently divergent findings across studies reflect true biological heterogeneity or methodological variability. For biomarker development, future studies should prioritize multicenter validation, longitudinal sampling, standardized analytical workflows, and assessment of whether exosome-associated signatures provide incremental information beyond established clinical, imaging, hemodynamic, and circulating biomarkers. For therapeutic applications, additional requirements include scalable and reproducible manufacturing, batch-to-batch consistency, definition of critical quality attributes and active components, validated potency assays, dose-response relationships, pharmacokinetics and biodistribution, optimized routes of administration, storage stability, and systematic evaluation of immunological and off-target effects. Carefully designed clinical studies will ultimately be required to determine whether the mechanistic and therapeutic effects observed in experimental PH can be translated into clinically meaningful benefit.

For an integrated overview of the evidence discussed above, Tables 1 and 2 categorize PH-associated exosomes into pathogenic/disease-associated and protective/therapeutic groups, respectively, and summarize their cellular sources or biofluids, key cargoes, recipient cells, signaling pathways, phenotypic effects, and translational relevance.

Table 1.

Pathogenic and Disease-Associated Exosomes in PH: Cellular Sources or Biofluids, Major Cargoes, Signaling Pathways, and Phenotypic Effects

Cellular Source/Biofluid	PH Context	Major Cargo	Recipient Cell	Signaling Axis	Main Phenotype	Effect in PH	Ref
PAECs	Hypoxia	HCG20	PASMCs	HCG20 target U2AF2	PASMCs proliferation/ migration ↑	Pro-PH	[109,112,113]
PAECs	Inflammation	NEDD9	PASMCs	NEDD9 target NKX2-5-COL3A1	PASMCs fibrosis↑	Pro-PH	[110]
PAECs	Hypoxia	15-LO2, miR-181, miR-324	PAECs	15-LO2 target STAT3, miR-181 target Notch4, miR-324 target ETS-1	Endothelial dysfunction↑	Pro-PH	[114,137]
PASMCs	Hypoxia	miR-143	PAECs	miR-143 target TGF-β1	PAECs proliferation/ migration↑	Pro-PH	[116]
PASMCs	TGF-β stimulation	/	PAECs	/	PAECs EndoMT↑	Pro-PH	[36]
PAFs	Inflammation	Complement C3	Macrophages	Complement C3 target metabolic reprogramming	Macrophage polarization↑	Pro-PH	[118]
PVECs	Intrauterine growth restriction	miR-214-3p, miR-326-3p, miR-125b-2-3p	PASMCs	miR-214-3p/miR-326-3p/miR-125b-2-3p target FoxM1	PASMCs proliferation↑	Pro-PH	[132]
Plasma	Idiopathic PH patient plasma	miR-122-5p, miR-596	PAECs, PASMCs	miR-122-5p target DLAT/RIMS1	PASMC/PAECs proliferation↑	P-cBM	[162,163]

Notes: For clinical studies, “plasma” denotes the biofluid from which circulating exosomes/EVs were isolated and does not imply a defined cellular origin. The upward-pointing black arrow indicates promotion.

Abbreviations: PH, Pulmonary hypertension; PAECs, Pulmonary artery endothelial cells; PASMCs, pulmonary artery smooth muscle cells; HCG20, HLA complex group 20; U2AF2, U2 small nuclear RNA auxiliary factor 2; NEDD9, neural precursor cell expressed, developmentally down-regulated 9; COL3A1, collagen type III alpha 1 chain;15-LO2, 15-lipoxygenase 2; Notch4, neurogenic locus notch homolog protein 4; ETS-1, estrogen sulfotransferase 1; PAFs, pulmonary artery fibroblasts; FoxM1, Forkhead box M1; P-cBM, Potential circulating biomarker.

Table 2.

Protective and Therapeutic Exosomes in PH: Cellular Sources or Biofluids, Major Cargoes, Signaling Pathways, and Phenotypic Effects

Cellular Source/Biofluid	PH Context	Major Cargo	Recipient Cell	Signaling Axis	Main Phenotype	Effect in PH	Ref
PVECs	Hypoxia	miR-21	Right ventricular cells	miR-21 target SPRY2/p-ERK and PTEN/AKT	Cardiomyocytes apoptosis↓	Anti-PH	[147]
MSCs	MCT	miR-191	PAECs	miR-191target BMPR2	PAECs proliferation/ apoptosis/ EndoMT↓	Anti-PH	[122,152,153]
MSCs	Hypoxia	miR-29a-3p	PASMCs	miR-29a-3p target ENPP2	PASMCs proliferation/ migration↓	Anti-PH	[37,125,134,154,155]

Notes: The downward-pointing black arrow indicates suppression.

Abbreviations: PH, Pulmonary hypertension; PAECs, Pulmonary artery endothelial cells; PASMCs, pulmonary artery smooth muscle cells; MSCs, mesenchymal stem cells; EndoMT, endothelial-to-mesenchymal transition; PVECs, pulmonary microvascular endothelial cells; MCT, monocrotaline; p-ERK, phosphorylated extracellular signal-regulated kinase; BMPR2, Bone Morphogenetic Protein Receptor Type 2; ENPP2, ectonucleotide pyrophosphatase/phosphodiesterase 2.

Funding Statement

This study was supported by grants from the National Natural Science Foundation of China (No.82372109).

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The author(s) report no conflicts of interest in this work.