Renin‐Angiotensin Signaling and Vascular Function: Insights into Health and Disease

ABSTRACT

The renin‐angiotensin system (RAS) is an essential regulator of vascular structure and function, and dysregulation of angiotensin II (Ang II) signaling plays a critical role in the development of hypertension and associated vascular complications. Ang II exerts its vascular actions primarily through the angiotensin II type 1 receptor (AT1R), activating canonical and non‐canonical signaling pathways that extend beyond classical G‐protein‐dependent signaling mechanisms. Here, we review the literature on tissue‐specific RAS, Ang II‐dependent and Ang II‐independent signaling mechanisms of vascular Ang II receptors, and their contribution to vasoconstriction, endothelial dysfunction, vascular remodeling, and arterial stiffness in hypertension. We highlight the roles of mechanosensitive AT1R signaling, dysregulation of vascular ion channels, enhanced reactive oxygen species production, immune and inflammatory signaling, and mineralocorticoid receptor activation as key drivers of hypertensive vascular pathology. In addition, we discuss tissue‐specific expression of RAS components and separation between RAS pathways underlying blood pressure elevation and vascular remodeling in hypertension. Collectively, emerging research on vascular Ang II receptor signaling reveals novel regulatory mechanisms and therapeutic opportunities beyond conventional RAS inhibition. Targeting downstream pathways that mediate oxidative stress, mechanotransduction, ion channel activity, and profibrotic signaling may offer improved strategies to prevent or reverse Ang II receptor‐dependent vascular dysfunction in hypertension.

Practioner Points

• Angiotensin II (Ang II) is a central regulator of vascular function under healthy conditions, and a key driver of vascular dysfunction in cardiovascular disorders through coordinated actions on vascular smooth muscle, endothelium, and the extracellular matrix.

• Beyond the canonical angiotensin II type 1 receptor (AT1R)–G‐protein signaling, Ang II receptors activate non‐canonical mechanisms, including mechanosensitive and G‐protein‐independent mechanisms, that promote ion channel dysregulation, oxidative stress, and vascular inflammation in hypertension.

• A deeper mechanistic understanding of AT1R‐dependent mechanisms may reveal novel therapeutic strategies to prevent or reverse the vascular dysfunction in hypertension and other cardiovascular disorders.

Abbreviations

ACE

angiotensin converting enzyme

ADAM17

A disintegrin and metalloproteinase 17

AGT

angiotensinogen

AKAP5

A‐kinase anchoring protein 5

Ang II

angiotensin II

AT1R

angiotensin type 1 receptor

AT2R

angiotensin type 2 receptor

BK channel

large‐conductance Ca²⁺‐activated K⁺ channel

Cav1

Caveolin‐1

COX‐2

cyclooxygenase 2

DAG

diacylglycerol

EC

endothelial cell

ECM

extracellular matrix

EGFR

epidermal growth factor receptor

eNOS

endothelial nitric oxide synthase

ERK 1/2

extracellular signal–regulated kinase 1/2

GPCR

G protein‐coupled receptors

ICAM‐1

intercellular adhesion molecule‐1

IP3

inositol trisphosphate

IP3R

IP3 receptor

JAK2

Janus kinase 2

Kv channel

voltage‐gated K⁺ channel

LTCC

L‐type Ca²⁺ channels

MAPK

mitogen‐activated protein kinase

MLC

myosin light chain

MLCK

MLC kinase

MLCP

MLC phosphatase

MMP

matrix metalloproteinase

MR

mineralocorticoid receptor

NFATc3

nuclear factor of activated T cells 3

NF‐κB

nuclear factor kappa‐light‐chain‐enhancer of activated B cells

NKCC1

Na‐K‐Cl cotransporter 1

NLRP3

NLR family pyrin domain containing 3

NO

nitric oxide

NOX

NADPH oxidase

PKC

protein kinase C

PLC

phospholipase C

RAS

renin‐angiotensin system

ROCK

RhoA/Rho kinase

ROS

reactive oxygen species

SMC

smooth muscle cell

SOCE

store‐operated Ca²⁺ entry

SR

sarcoplasmic reticulum

STIEM1

stromal interaction molecule 1

TGFβ

transforming growth factor b

TMEM16A

TransMEMbrane protein 16A

TRPC6

transient receptor potential canonical 6

TRPM4

transient receptor potential melastatin 4

TRPV4

transient receptor potential vanilloid 4

VCAM‐1

vascular cell adhesion molecule‐1

1. Introduction

The renin‐angiotensin system (RAS) is a crucial regulator of several physiological functions from fluid volume, cardiac output, blood pressure, to vascular integrity and cell growth. The classical RAS pathway consists of a cascade of biologically active peptides that regulate cardiovascular and renal physiology through endocrine, paracrine, and autocrine mechanisms [1, 2, 3]. Renin, a proteolytic enzyme released by the chemo‐ and barosensitive juxtaglomerular cells of the kidney in response to alterations in blood pressure as well as extracellular fluid volume and composition, cleaves circulating angiotensinogen (AGT) at its N‐terminus to generate the inactive precursor Angiotensin I (Ang I). Ang I is subsequently converted into the biologically active octapeptide Angiotensin II (Ang II) by angiotensin‐converting enzyme (ACE), a widely distributed membrane‐associated metalloproteinase, with particularly high levels in endothelial cells of the lungs, intestine and testis [1, 4, 5]. In addition to the systemic and circulating RAS, it is now well established that local RAS systems also contribute to the regulation of organ function. Indeed, the expression of RAS‐related enzymes in tissues allows local synthesis of angiotensin, in addition to their uptake from plasma [6, 7], https://www.proteinatlas.org/search/angiotensin.

Ang II is the predominant vasoactive peptide of the RAS and exerts its actions primarily through two G‐protein‐coupled receptors, Ang II Type 1 (AT1R) and Type 2 (AT2R) receptors. Activation of AT1R mediates vasoconstriction, cellular growth, and aldosterone secretion, whereas AT2R signaling generally promotes vasodilation and anti‐inflammatory effects [8]. In addition to Ang II, several secondary angiotensin peptides are generated along the cascade and contribute to the overall complexity of RAS signaling. Briefly, Ang II can be further metabolized by ACE2 to produce Ang (1–7), a key component of the counter‐regulatory RAS axis that signals through Mas receptors and elicits vasodilatory, antihypertensive, and antifibrotic effects [1]. In parallel, ACE2 can process Ang I to form Ang (1–9), which preferentially activates AT2R via a low‐affinity interaction [9]. Additional enzymatic processing generates Ang III and Ang IV, which interact with angiotensin receptors or the AT4R, currently identified as the insulin‐regulated aminopeptidase (IRAP), thereby further expanding the regulatory and functional diversity of the RAS [1].

Beyond the canonical enzymatic cascade, several studies have proposed a renin‐independent mechanism for the generation of angiotensin, involving proteolytic cleavage of AGT into dodecapeptide Ang (1–12), which has been suggested to serve as a precursor of Ang II, either indirectly via ACE or directly as a substrate for the serine protease chymase [10, 11, 12]. However, this nonclassical mechanism has been recently disputed, since mass spectrometry‐based analyses of blood and tissues across different species failed to detect intact Ang (1–12). These findings suggest that earlier observations may reflect immunoassay cross‐reactivity with AGT rather than a bona fide circulating peptide [13].

In this review, we summarize the literature on tissue‐specific RAS, Ang II‐dependent and Ang II‐independent signaling mechanisms of vascular Ang II receptors, their physiological roles under healthy conditions, and contributions to hypertensive vasoconstriction and vascular remodeling. We discuss both canonical and non‐canonical Ang II receptor signaling pathways, emphasizing the critical involvement of vascular ion channels, reactive oxygen species, mineralocorticoid receptor signaling and tissue‐specific RAS, and the emerging links between RAS, immune signaling and vascular aging.

2. Tissue‐Specific Expression of RAS Components

2.1. Heart

Although distinguishing locally generated Ang II from circulating Ang II remains challenging, evidence indicates that part of the beneficial effects of ACE inhibitors and AT1R blockers on cardiac remodeling is attributable to inhibition of local cardiac RAS [14, 15]. Numerous studies in both human and animal models have demonstrated the presence of ACE activity in cardiac tissue [7, 16, 17], along with local synthesis of Angiotensin peptides [7, 18, 19]. While several reports have detected mRNA expression of AGT and renin in human and animal hearts [20, 21, 22], the capacity of cardiac cells to synthesize renin remains controversial. For example, cultured cardiac cells failed to produce renin [23], and cardiac renin expression was not detected in transgenic mice carrying a genomic human renin construct [24]. These findings support the concept that cardiac RAS may rely largely on the uptake of circulating renin or prorenin, or on renin‐independent mechanisms, rather than local renin synthesis.

2.2. Vasculature

The vascular wall represents a major effector site for circulating RAS, where AT1R signaling in SMCs promotes vasoconstriction. However, the recognition that multiple RAS components are expressed within the vascular wall has led to the concept of vascular RAS. The local generation of Ang II in the vascular wall has been documented [25, 26, 27] and evidence suggests a specific contribution of ECs, considering the reduction in Ang II production following endothelial denudation [28]. As with the heart, local generation of renin in the vascular wall has also been debated [7, 21, 29]. Current consensus favors a developmental role for renin in arterial morphogenesis during embryogenesis, with its expression in adult organisms becoming largely restricted to the juxtaglomerular region and the tips of renal arterioles, as reviewed recently [30]. In contrast, ACE1 and ACE2 have been clearly detected in the vasculature, with ACE1 specifically located in ECs and ACE2 ubiquitously expressed in both ECs and SMCs [31]. Notably, ACE2 has gained particular attention as a critical regulator of pulmonary vascular homeostasis and has been implicated in the pulmonary vascular dysfunction observed during SARS‐CoV‐2 infection [32, 33], further underscoring the physiological and pathological relevance of vascular RAS components.

3. Ang II Receptor Signaling

As a prototypical G‐protein coupled receptor, AT1R mediates most of the established physiological and pathological actions of Ang II on cardiovascular homeostasis and fluid balance [1, 34]. In contrast, AT2R signals mainly through Gi proteins and tyrosine phosphatases, producing inhibitory effects that counterbalance AT1R signaling and growth factor receptor‐driven cellular responses [35]. In addition to signaling as individual receptors, AT1R and AT2R can form homo‐ and heteromeric receptor complexes, adding a layer of structural regulation to their independent signaling axes [36]. AT1R and AT2R homodimers can form constitutively in a ligand‐independent manner and are localized in both the plasma membrane and perinuclear compartments [37]. Notably, Ang II stimulation induces internalization of AT1R homomers, whereas AT2R homomers remain localized at the plasma membrane [37]. Heteromerization adds further complexity, as angiotensin receptors can interact with each other and with other GPCRs, modifying receptor signaling, trafficking, ligand‐binding properties, and biological responses [38]. AT1R–AT2R heterodimerization inhibits AT1R‐mediated G‐protein signaling, providing a molecular basis for the counter‐regulatory actions of AT2R [39]. Both AT1R and AT2R can also form heterodimers with the bradykinin Type 2 receptor (B2R), modifying receptor signaling and G‐protein coupling [40, 41]; notably, AT1R–B2R heteromerization enhances Ang II responsiveness and has been implicated in hypertensive disorders, including preeclampsia [42]. Although we focus primarily on AT1R in this review, recent findings have advanced our understanding of vascular AT2R signaling, which is briefly discussed below.

3.1. AT1R Activation by Ang II

Ang II is the primary agonist of AT1R, and its binding to AT1R activates multiple heterotrimeric G proteins, including G_q/11, G_12/13, and G_i. Activation of these G‐proteins promotes the formation of second messengers inositol trisphosphate (IP3), diacylglycerol (DAG), arachidonic acid, and reactive oxygen species.

The functional outcomes of AT1R signaling are context‐dependent. In vascular smooth muscle cells (SMC), AT1R signaling predominantly induces contraction through G_q/11‐mediated phospholipase C β (PLCβ) activation, leading to IP3 receptor (IP3R)‐dependent Ca²⁺ release from the sarcoplasmic reticulum (SR) and subsequent activation of myosin light chain kinase (MLCK). In parallel, G_12/13‐driven RhoA/Rho kinase (ROCK) pathway inhibits myosin light chain phosphatase (MLCP) [43], enhancing actin‐myosin interaction through Ca²⁺ sensitization (Figure 1A).

FIGURE 1.

Ang II‐dependent and independent activation of AT1R signaling in vascular smooth muscle cells. In vascular smooth muscle cells (SMCs), angiotensin II type 1 receptor (AT1R) signaling can be activated either by angiotensin II (Ang II) or through Ang II‐independent mechanisms. (A) Ang II binding to AT1R triggers downstream pathways that converge on activation of the RhoA/Rho kinase (ROCK) cascade, promoting myosin light chain (MLC) phosphorylation and contraction. Ang II also stimulates inositol trisphosphate (IP3) production via AT1R, leading to IP3 receptor (IP3R) activation, Ca²⁺ release from the sarcoplasmic reticulum (SR), and enhanced MLC phosphorylation and contraction. In parallel, AT1R activation increases TRPV4 channel activity, which subsequently activates BK channels, causing membrane hyperpolarization and vasorelaxation as a negative feedback mechanism. (B) Independently of Ang II, AT1R can function as a mechanosensor, activating PLC and generating DAG and IP3. This signaling cascade promotes Ca²⁺ influx through TRPC6 channels, leading to TRPM4 activation and subsequent Na⁺ entry that depolarizes the SMC membrane, thereby activating L‐type Ca²⁺ channels (LTCC), enhancing Ca²⁺ influx, and ultimately driving MLC phosphorylation and contraction.

Beyond vasoconstriction, AT1R signaling plays a central role in vascular remodeling. Activation of the extracellular signal–regulated kinase (ERK1/2) represents a key downstream mechanism for AT1R‐induced hypertrophic and proliferative responses. ERK1/2 activation can occur directly via Gα_q‐dependent activation of protein kinase C (PKC), which stimulates Ras/Raf/MEK/ERK1/2 cascade or ROCK‐induced nuclear translocation of ERK1/2 [44]. Additionally, ERK activation in SMCs can also occur indirectly via AT1R‐transactivation of the platelet‐derived growth factor receptor (PDGFR) [45] and epidermal growth factor receptor (EGFR). Specifically, AT1R activates the metalloprotease ADAM17, which cleaves pro‐heparin‐binding EGF‐like growth factor (pro‐HB‐EGF) to generate HB‐EGF. HB‐EGF then binds and phosphorylates EGFR, initiating mitogen‐activated protein kinase (MAPK) signaling through recruitment of the Shc/Grb2/Sos complex, activation of the small GTPase Ras, and downstream activation of Raf‐1 and MEK, culminating in ERK1/2 phosphorylation and hypertensive, inflammatory, and profibrotic responses [46, 47].

In endothelial cells (ECs), Ang II mainly regulates the balance between nitric oxide (NO) and reactive oxygen species (ROS) [48]. AT1R signaling activates different NADPH oxidase (NOX) isoforms, catalyzing the production of ROS and influencing downstream MAP kinases, ROCK, transcription factors, protein tyrosine phosphatases, and tyrosine kinases [49]. Consequently, overproduction of ROS can lead to reduced NO bioavailability and vascular dysfunction.

In addition to classical G‐protein‐mediated pathways, AT1R activation can also trigger G‐protein‐independent pathways such as the β‐arrestin‐mediated MAPK activation [46]. Additionally, G protein‐coupled receptor (GPCR) kinase leads to phosphorylation of AT1R, increasing the receptor affinity for β‐arrestin, which results in functional uncoupling of G‐protein signaling and initiates ERK1/2 signaling. These non‐canonical pathways add further complexity to AT1R signaling and may differentially regulate vascular tone, remodeling, and inflammation.

3.2. Ang II‐Independent Activation of AT1R

Recent studies have demonstrated that AT1R functions as a mechanosensitive GPCR, capable of transducing mechanical stimuli into intracellular signaling independent of Ang II‐binding [50, 51, 52]. In vitro experiments revealed that mechanical stretch alone induces a conformational change in AT1R, converting it into an active state that associates with the non‐receptor tyrosine kinase Janus kinase 2 (JAK2), followed by dissociation and translocation of G proteins into the cytosol [50] (Figure 1B). This was further supported by structural studies showing that mechanical stress promotes a conformational rearrangement of AT1R transmembrane domain 7 (TM7) into the ligand‐binding pocket, thereby stabilizing AT1R in its active conformation and initiating downstream signaling [53].

As a mechanosensor, AT1R appears to play a critical role in intraluminal pressure‐induced vasoconstriction, or myogenic tone. This response is driven primarily by two key events: depolarization of SMCs and activation of voltage‐gated L‐type Ca²⁺ channels (LTCCs). Ligand‐independent activation of AT1R in response to increased intraluminal pressure has also been shown to stimulate Ca²⁺‐permeable transient receptor potential canonical 6 (TRPC6) channels in cerebral and renal arteries [54], leading to Ca²⁺ influx into SMCs. Pressure‐induced AT1R activation was linked with phospholipase Cγ1 (PLCγ1) signaling, resulting in the generation of IP3 and DAG, which, in turn, activate TRPC6 channels [55, 56] (Figure 1B). In addition, PLCγ1‐derived IP3 and Ca²⁺ influx though TRPC6 channels activated IP3R on the SR, leading to Ca²⁺ release and activation of TRP melastatin 4 (TRPM4) channels. Na⁺ entry through TRPM4 channels depolarized the SMC membrane, increasing LTCC activity, augmenting Ca²⁺ influx, and promoting SMC contraction [55] (Figure 1B). However, some studies have disputed the role of TRPC6 channels in AT1R mechanosensing and instead proposed that inhibition of voltage‐gated K⁺ (K_V) channel is a key downstream mechanism for AT1R‐initiated myogenic constriction [51]. These divergent findings highlight unresolved questions regarding AT1R mechanosignaling and underscore the need for further investigation to reconcile these mechanisms across vascular beds and experimental conditions.

3.3. AT2R Signaling

AT2R generally counterbalances AT1R signaling in the vasculature and is thought to contribute to the protective effects of RAS. Vascular AT2R is expressed in both endothelial and smooth muscle cells and can promote vasodilation through NO‐dependent mechanisms, while also activating phosphatases and other signaling pathways that oppose AT1R‐mediated vasoconstriction, proliferation, and remodeling [57]. AT2R‐mediated vasodilation becomes particularly evident following AT1R inhibition, and recent work has further implicated AT2R in the regulation of vascular tone in response to flow and in the preservation of endothelial function [57]. These vasoprotective properties have generated interest in AT2R as a therapeutic target, with selective agonists such as Compound 21 (C21) showing beneficial effects in experimental models of vascular dysfunction, including protection against endothelial dysfunction and arterial stiffening in obese mice [58]. Studies in AT2R‐deficient mice generally support this counter‐regulatory role, as receptor deletion enhances Ang II‐dependent pressor responses and vascular remodeling [59, 60].

However, AT2R actions are context‐dependent, with both vasodilatory and vasoconstrictor effects reported across vascular beds and disease states, and divergent effects on vascular remodeling and atherosclerosis [57, 61]. More recent studies indicate that the consequences of AT2R deficiency are highly dependent on the pathological context. AT2R deficiency reduced blood pressure in mice with elastin insufficiency, whereas it improved vascular recovery and endothelial function in diabetic ischemia, suggesting that loss of AT2R can have distinct, and even opposing, effects in different vascular disorders [62, 63]. Importantly, recent evidence suggests that AT2R does not contribute to beneficial effects of AT1R inhibition on the endothelium, as losartan and its metabolite EXP3179 retained effects on endothelial function in AT2R‐deficient mice [64]. Together, these findings highlight the context‐dependent actions of AT2R and challenge the concept that AT2R is a predominantly protective arm of vascular RAS signaling.

4. Ang II Receptor Signaling Mechanisms in Hypertensive Vasoconstriction

Ang II, acting through its receptors, plays a central role in the development and progression of multiple cardiovascular diseases, including hypertension [47, 65, 66]. In the vasculature, AT1R signaling promotes hypertensive pathology through several mechanisms, including increased vasoconstriction, vascular remodeling, fibrosis, and arterial stiffening [1]. In contrast, AT2R signaling generally counteracts these effects by promoting vasodilation and exerting anti‐inflammatory, antifibrotic, and antihypertensive actions [67].

4.1. Canonical and Non‐Canonical AT1R Signaling

As discussed above, Ang II‐induced vasoconstriction is mediated primarily through canonical AT1R–PLCβ signaling, leading to MLCK activation and MLCP inhibition in SMCs. However, accumulating evidence indicates that non‐canonical AT1R signaling also contributes significantly to hypertensive vasoconstriction. One key mechanism involves JAK2, which phosphorylates Rho guanine nucleotide exchange factor Arhgef1 in SMCs, activating RhoA and promoting Ang II‐induced vasoconstriction and blood pressure elevation in mice [68] (Figure 2). Consistent with these findings, SMC‐specific silencing of JAK2 reduced Rho kinase activity and intracellular Ca²⁺ levels, resulting in attenuated Ang II‐induced vasoconstriction [69], demonstrating the importance of JAK2‐dependent signaling. Notably, Ang II‐dependent activation of Arhgef1 has also been shown in human SMCs [70], indicating conservation of this signaling pathway across species. Additionally, Src family tyrosine kinases have also been implicated in Ang II‐induced vasoconstriction (Figure 2). Pharmacological inhibition of Src kinases prevented Ang II‐induced MLC phosphorylation and vasoconstriction [71]. Moreover, Ang II‐dependent hypertension, but not vascular remodeling, was attenuated in c‐Src⁺/⁻ mice [72], suggesting that Src activity is required for the acute pressor response to Ang II but may be dispensable for longer‐term structural changes in the vasculature.

FIGURE 2.

Ang II‐induced SMC contraction in hypertension. During hypertension, canonical and non‐canonical signaling pathways downstream of Ang II converge to promote MLC phosphorylation in SMCs, either directly or through elevations in intracellular Ca²⁺, thereby promoting vasoconstriction. Activation of JAK2 and SRC via Ang II–AT1R signaling enhances MLC phosphorylation and vasoconstriction, while ion channels often become dysfunctional during hypertension. In particular, TRPC6 and store operated Ca²⁺ entry (SOCE) significantly contribute to increased Ca²⁺ mobilization, which is further amplified by L type Ca²⁺ channels (LTCCs) whose activity is enhanced by membrane depolarization driven by NKCC1 and TMEM16A, while TRPV4 channels additionally support the rise in intracellular Ca²⁺. At the same time, Ang II signaling suppresses physiological negative feedback mechanisms by inhibiting BK channels via NFATc and K_V channels via PKC, both of which are activated downstream of AT1R, thereby promoting sustained vasoconstriction.

4.2. ROS Production

ROS production is a central component of Ang II‐induced vascular pathology. Ang II stimulates ROS production primarily through NOX, a mechanism implicated in excessive vasoconstriction, endothelial dysfunction, vascular remodeling, and hypertension [1, 73, 74]. The biological effects of ROS depend on the chemical species generated, their site of production, and the cellular context. Superoxide (O₂•−) is a highly reactive and short‐lived radical that can react with NO to form peroxynitrite, whereas H₂O₂ is more stable, can cross biological membranes, and can function as a redox‐signaling mediator. Excessive ROS levels can lead to oxidative modifications of proteins, lipids, and DNA, resulting in cellular dysfunction [75, 76]. ROS from both ECs and SMCs contributes to the development and maintenance of Ang II‐induced hypertension.

SMC‐specific overexpression of NOX1 increased oxidative stress, vasoconstrictor responses, and hypertrophic remodeling in response to Ang II, demonstrating that SMC‐derived NOX1 may participate in Ang II‐induced hypertension [77]. Consistent with this, Ang II‐induced hypertension was attenuated in NOX1‐deficient mice, although effects on vascular remodeling were less clear [78, 79]. Mice lacking the NOX regulatory subunit, p47^phox, likewise reduced Ang II‐induced hypertension [80] and blunted afferent arteriolar contraction [81], highlighting the requirement of NOX activity for Ang II vascular responses. In ECs, NOX2 deletion attenuated Ang II‐induced hypertension in mice [82], further illustrating the combined contributions of EC‐ and SMC‐derived ROS. Ang II can also regulate the activity of NOX4, which, unlike NOX1 and NOX2, predominantly generates H₂O₂ [83, 84]. NOX4 appears to exert cardioprotective effects, as loss of NOX4 in ECs or cardiomyocytes exacerbates cardiac remodeling in response to pressure overload, with activation of nuclear factor erythroid 2‐related factor 2 (NRF2), a transcription factor that promotes antioxidant defenses [83, 85, 86]. NOX4‐derived H₂O₂ can promote vasodilation through transient receptor potential melastatin 2 (TRPM2)‐dependent activation of eNOS and NO release [87]. However, increased NOX4 expression has been associated with SMC proliferation, vascular dysfunction, and remodeling in hypertension [88, 89]. Thus, the divergent findings across experimental studies highlight the context‐dependent and still unresolved roles of NOX4 in cardiovascular disease.

NOX5 represents another important component of RAS‐associated redox signaling. Unlike other vascular NOX isoforms, NOX5 is not expressed in mice and rats [90], limiting the use of conventional rodent models to study its contribution to cardiovascular disease. In human ECs, Ang II activates NOX5 through a Ca²⁺/calmodulin‐dependent mechanism, increasing O₂• − production and promoting endothelial proliferation and pro‐inflammatory responses [91, 92]. Ang II also regulates NOX5 in human SMCs, where NOX5‐derived ROS activates c‐Src and downstream pathways involved in contraction, growth, and cytoskeletal remodeling, linking NOX5 to vascular dysfunction in hypertension [92, 93]. NOX5 also contributes to RAS‐associated dysfunctions in other tissues, with renal NOX5 linked to oxidative stress and hypertension and cardiac NOX5 implicated in Ang II‐induced cardiac hypertrophy [94, 95, 96].

Mitochondria represent an additional source and target of Ang II‐induced redox signaling. Ang II promotes mitochondrial ROS production and disrupts mitochondrial redox homeostasis, reducing endothelial NO bioavailability and contributing to vascular dysfunction [97, 98]. Mitochondrial dysfunction may also promote vascular aging through oxidative DNA damage and cellular senescence. In SMCs, Ang II induces oxidative DNA damage and accelerates cellular senescence via AT1R signaling [99], which was also shown to contribute to atherosclerosis [100]. Similarly, in ECs, Ang II induces mitochondrial fission and cellular senescence, promoting a pro‐inflammatory environment that increases monocyte adhesion [101]. Senescent cells can further propagate inflammation through the senescence‐associated secretory phenotype (SASP), characterized by the release of pro‐inflammatory and tissue‐remodeling factors that contribute to hypertension‐associated premature vascular aging [102]. Consistent with these findings, chronic Ang II exposure was shown to induce SASP signaling and immune‐cell recruitment in the kidney [103].

Antioxidant defenses are also altered in hypertension, with reduced antioxidant enzyme expression and activity reported in experimental models [104]. Mice lacking the antioxidant superoxide dismutase 1 (SOD1) exhibit exacerbated Ang II‐induced hypertension [105], whereas SOD1 or catalase overexpression, as well as treatment with SOD mimetics or antioxidants such as resveratrol, attenuates blood pressure elevation, endothelial dysfunction, and cardiovascular remodeling [106, 107, 108, 109]. As a compensatory mechanism to increased oxidative stress, NRF2 activation has been reported in models of DOCA‐salt hypertension and chronic pressure overload [110, 111]. Similarly, ACE2 overexpression increased NRF2 levels and its downstream antioxidant response [112]. However, nuclear accumulation of NRF2 and expression of NRF2‐regulated antioxidants were reduced in two different models of hypertension [113, 114], suggesting that failure of this adaptive response may allow excessive ROS accumulation and contribute to vascular dysfunction and hypertension.

Beyond vascular cells, Ang II also stimulates ROS production in immune cells, which further amplifies hypertensive signaling. Lysozyme M‐positive monocytes and T cells have been shown to contribute to Ang II‐induced hypertension, vascular dysfunction, and ROS production [115, 116, 117], underscoring a critical interplay between vascular and immune‐derived oxidative pathways.

4.3. Vascular Ion Channels

Ang II infusion is a widely used rodent model of hypertension in which elevations of arterial pressure result from the combined effects of Ang II on the vasculature, kidney, adrenal glands, and brain [118, 119]. Within the vasculature, Ang II increases total peripheral resistance, thereby contributing directly to blood pressure elevation. Both SMCs and ECs rely heavily on ion channels to regulate membrane potential, intracellular Ca²⁺, vascular resistance, and ultimately blood pressure [120, 121, 122, 123, 124, 125, 126, 127, 128]. Accordingly, numerous studies have demonstrated that dysregulation of vascular ion channel activity plays a critical role in Ang II‐induced hypertension [123, 124, 125, 127, 129, 130, 131, 132, 133, 134, 135].

4.3.1. LTCCs

Smooth muscle LTCCs are essential for intraluminal pressure‐ and agonist‐induced vasoconstriction [121] (Figure 2), and serve as critical regulators of systemic arterial pressure under physiological and pathological conditions [120, 129, 136, 137, 138]. In a mouse model of Ang II‐induced hypertension, LTCC expression is increased in small arteries, an effect attributed to upregulation of the accessory β3 subunit [136]. Additionally, anchoring of PKC by A‐kinase anchoring protein 5 (AKAP5) in close proximity to LTCCs promoted channel phosphorylation and persistent opening, contributing to elevated blood pressure [129]. Phosphorylation of S1928 on α1C, the pore‐forming LTCC subunit, has also been shown to regulate channel activity and vascular tone in Ang II‐induced hypertension and may represent a potential therapeutic target [139].

4.3.2. TRP Vanilloid 4 (TRPV4) Channels

Smooth muscle TRPV4 channels regulate blood pressure under healthy conditions [123]. Importantly, TRPV4 channels in SMCs occur in two spatially distinct subpopulations—one promoting contraction and another one promoting relaxation [123, 140]. In Ang II‐induced hypertension, constrictor TRPV4 activity is increased while dilator TRPV4 activity is suppressed, shifting the balance toward excessive vasoconstriction [123] (Figure 2). Consistent with this, SMC‐specific TRPV4 deletion attenuated the increase in blood pressure after 2 weeks of Ang II infusion [123]. In cerebral parenchymal arterioles, however, AT1R‐mediated regulation of TRPV4 channels appears to serve a negative feedback role [141]. In this vascular bed, AT1R activation increases TRPV4 channel activity, which in turn activates large‐conductance Ca²⁺‐activated K⁺ (BK) channels. BK channel activation hyperpolarizes SMCs, leading to vasodilation and attenuation of Ang II‐induced constriction [141].

Endothelial ion channels are crucial regulators of endothelium‐dependent vasodilation and vascular resistance. A dysfunction of key endothelial ion channels has been observed in Ang II infusion‐induced hypertension. In mice infused with Ang II for 4 weeks, a loss of endothelium‐dependent vasodilation was attributed to disrupted cooperative opening of endothelial TRPV4 channels [127]. Under physiological conditions, endothelial AKAP5 promotes TRPV4 channel openings and vasodilation and maintains a low resting blood pressure [125, 127]. In Ang II‐infused mice, endothelial AKAP5–TRPV4 interaction was impaired, contributing to endothelial dysfunction and increase in blood pressure [127]. Ang II infusion for 4 weeks was also found to reduce the expression of endothelial TRPV4 channels [142].

4.3.3. Na‐K‐Cl Cotransporter 1 (NKCC1)

NKCC1 depolarizes SMCs, increasing LTCC activity and promoting vasoconstriction [143]. Ang II infusion increased NKCC1 expression in arteries from hypertensive rats, and NKCC1 inhibition with bumetanide reduced Ang II‐induced vasoconstriction [144], supporting a key role for NKCC1 in Ang II‐induced vasoconstriction. WNK (With‐No‐Lysine) kinases are important upstream regulators of NKCC activity [145]. Consistent with this regulatory pathway, Ang II‐induced hypertension and vasoconstriction are attenuated in WNK3‐knockout mice, identifying WNK3 as a key regulator of Ang II‐induced NKCC activation [146].

4.3.4. Cl⁻ Channels

Activation of Cl⁻ channels leads to Cl⁻ efflux, membrane depolarization, activation of LTCCs, elevated intracellular Ca²⁺, and SMC contraction (Figure 2) [147]. Among several Cl⁻ channel subtypes, Ca²⁺‐activated Cl⁻ channels (CaCCs) have garnered particular attention for coupling Ca²⁺ signaling to membrane excitability [147]. The Ca²⁺‐activated chloride channel TransMEMbrane protein 16A (TMEM16A) is a key component CaCC in SMCs [147] (Figure 2). Ang II increased the expression of TMEM16A in primary SMCs [148], and smooth muscle‐specific TMEM16A deletion markedly suppressed Ang II‐induced hypertension, demonstrating a critical role for this channel in Ang II‐induced hypertension [149].

4.3.5. K⁺ Channels (BK and K_V Channels)

K⁺ channels hyperpolarize SMC membrane and are major negative feedback regulators of SMC contraction and blood pressure. In Ang II‐infused mice, activation of calcineurin and Nuclear Factor of Activated T Cells 3 (NFATc3) downregulated the expression of accessory β1 subunit of the BK channel, reducing channel activity and contributing to hypertension [132]. In addition, Ang II stimulated internalization and degradation of BK channels in arterial myocytes, further augmenting vasoconstriction [150]. Ang II also activated PKC‐dependent pathways that promote degradation of voltage‐gated K⁺ channels (K_V1.5 channels) in mesenteric artery SMCs, decreasing surface K_V1.5 expression and whole‐cell K_V1.5 currents [151]. Loss of BK and K_V channel activity in Ang II‐dependent hypertension depolarizes SMC membrane, increasing Ca²⁺ influx and sustaining hypertensive vasoconstriction.

4.3.6. TRPC Channels and Store‐Operated Ca²⁺ Entry

TRP canonical (TRPC) and store‐operated Ca²⁺ entry (SOCE) channels constitute additional important Ca²⁺ influx pathways in SMCs in Ang II‐induced hypertension. Pharmacological inhibition of TRPC channels reduced Ang II infusion‐induced increase in myogenic constriction, supporting their contribution to pathological vasoconstriction. At the cellular level, Ang II‐induced increases in SMC Ca²⁺ were reduced by TRPC6 knockdown, but not by TRPC3 or TRPC7 knockdown [152]. Ang II‐induced hypertension was also attenuated in mice with smooth muscle‐specific IP3R knockout, suggesting a central role of AT1R–IP3R signaling in Ca²⁺ mobilization in this model of hypertension. Stromal interaction molecule 1 (STIM1), the SR Ca²⁺ sensor that activates Orai1 channels during SOCE, is also essential for Ang II‐induced hypertension. Accordingly, SMC‐specific STIM1‐deficient mice did not develop hypertension following Ang II infusion [153], establishing SOCE as a key contributor to blood pressure elevation in response to Ang II infusion.

4.4. Immune Signaling and Vascular Aging

RAS and immune system interact bidirectionally in hypertension and cardiovascular disease. Ang II can act directly on immune cells through AT1R, which is expressed by monocytes/macrophages, dendritic cells, and T lymphocytes, amplifying Ang II‐dependent vascular and renal injury [1, 154]. Beyond classical inflammatory signaling, Ang II can activate the NLRP3 (NLR family pyrin domain containing 3) inflammasome, linking AT1R signaling to innate immune activation and vascular injury. Ang II‐induced NLRP3 activation promotes caspase‐1 activation and IL‐1β maturation, while inhibition of inflammasome signaling attenuates Ang II‐induced vascular inflammation, remodeling, and endothelial dysfunction [155, 156]. These pathways may also intersect with vascular senescence and inflammaging, the chronic, low‐grade inflammation associated with aging [157]. Aging may further amplify Ang II‐dependent vascular inflammation through increased matrix metalloproteinase (MMP) activity, contributing to vascular remodeling [157]. An emerging concept is immunometabolism, whereby metabolic pathways within immune cells influence inflammatory activation and cardiovascular disease. In macrophages, Ang II suppresses cholesterol efflux through AT1R‐dependent downregulation of ATP‐binding cassette transporter A1 (ABCA1), promoting cholesterol accumulation and foam‐cell formation and linking RAS signaling to atherosclerosis [158, 159]. In addition, metabolic remodeling of immune cells, including increased glycolysis and altered mitochondrial metabolism, can shape inflammatory activation, suggesting that immunometabolism may represent an additional mechanism through which RAS signaling contributes to cardiovascular inflammation [160, 161].

4.5. Mineralocorticoid Receptor (MR) Signaling

Downstream of Ang II–AT1R signaling, SMC mineralocorticoid receptors (MRs) promote increases in blood pressure, oxidative stress, vasoconstriction, and expression of LTCCs. Crosstalk between AT1R signaling and MR signaling, independent of aldosterone (endogenous MR agonist), has been reported [162]. Consistent with this interaction, smooth muscle‐specific MR‐deficient mice showed significantly reduced systolic blood pressure and oxidative stress during Ang II infusion, supporting a critical role for MR signaling in the pathogenesis of Ang II‐induced hypertension [163].

5. Ang II Signaling Mechanisms in Endothelial Dysfunction in Hypertension

Endothelial dysfunction is an independent risk factor for the development of cardiovascular disorders. It is characterized primarily by impaired endothelium‐dependent vasodilation, particularly in small arteries that regulate vascular resistance. Endothelium‐dependent dilation is mediated largely through activation of endothelial nitric oxide synthase (eNOS), which generates nitric oxide (NO), or through Ca²⁺‐activated small‐ and intermediate‐conductance K⁺ channels (SK and IK channels, respectively), whose hyperpolarizing effects promote vasodilation.

Ang II promotes endothelial dysfunction through multiple interconnected pathways, most prominently via increased ROS production and endothelial inflammation [164]. Ang II‐induced ROS production has been attributed to NOX activation and mitochondrial ROS generation [98]. A direct consequence of enhanced ROS production in ECs is a reduced availability of NO. Superoxide radicals, a major ROS, rapidly react with NO to form peroxynitrite, which not only diminishes NO signaling but also exerts damaging oxidative effects on endothelial proteins and lipids [124, 125, 165, 166] (Figure 3). Reduced NO availability impairs endothelium‐dependent vasodilation, thereby increasing vasoconstriction and elevating blood pressure.

FIGURE 3.

Ang II‐induced endothelial dysfunction. In endothelial cells (ECs), Ang II‐induced dysfunction is mainly driven by NOX‐dependent ROS generation, which reduces nitric oxide (NO) bioavailability through rapid peroxynitrite formation, thereby impairing endothelium‐dependent vasodilation and increasing blood pressure. Ang II can also promote a pro‐inflammatory endothelial phenotype via NFκB activation and subsequent upregulation of VCAM‐1 and ICAM‐1, contributing to leukocyte adhesion and progression of hypertensive vascular dysfunction.

In addition to oxidative stress, Ang II exerts potent pro‐inflammatory effects on the endothelium. Ang II activated the nuclear factor kappa‐light‐chain‐enhancer of activated B cells (NF‐κB) pathway in ECs, leading to upregulation of vascular cell adhesion molecule‐1 (VCAM‐1) and intercellular adhesion molecule‐1 (ICAM‐1) [167] (Figure 3). Increased expression of these adhesion molecules promotes leukocyte‐endothelial interactions, endothelial activation, and vascular inflammation, all of which contribute to endothelial dysfunction and progression of hypertension.

6. Ang II Signaling Mechanisms in Hypertensive Vascular Remodeling and Arterial Stiffness

6.1. Vascular Remodeling

Smooth muscle AT1R signaling mediates vascular remodeling and inflammatory perivascular fibrosis independent of hypertension, indicating that Ang II‐induced blood pressure elevation and vascular remodeling occur through distinct mechanisms [168]. Among the downstream pathways, activation of ERK1/2 is one of the most widely studied contributors to Ang II‐induced vascular remodeling. Specifically, Ang II phosphorylates and activates a transmembrane metalloproteinase ADAM17, promoting EGFR transactivation, downstream ERK signaling, and endoplasmic reticulum (ER) stress [169]. Pharmacological inhibition of EGFR or ER/SR stress (Figure 4), as well as genetic deletion of EGFR, attenuated Ang II‐induced vascular wall thickening in mice, underscoring a central role of this signaling pathway in hypertensive vascular remodeling [170, 171]. The smooth muscle‐specific nature of this mechanism was supported by findings in smooth muscle‐specific ADAM17‐deficient mice, in which Ang II‐induced EGFR transactivation and vascular remodeling, but not hypertension, were reduced [172].

FIGURE 4.

Ang II‐induced vascular remodeling and arterial stiffness in hypertension. In SMCs, AT1R signaling mediates vascular remodeling and arterial stiffness, promoting vascular dysfunction. The main downstream pathway involves ERK1/2 activation, which can occur through direct AT1R signaling or via Ang II‐induced activation of ADAM17, leading to Epidermal Growth Factor Receptor (EGFR) transactivation and subsequent ERK 1/2 activation. ERK 1/2 can also be activated through NADPH oxidase 1 (NOX1) via reactive oxygen species (ROS) generation, as well as through JAK2 signaling downstream of AT1R. Vascular remodeling is further exacerbated by TGFβ and mineralocorticoid receptor (MR) pathways, which contribute particularly to vascular fibrosis. In addition, Ang II promotes arterial stiffness by upregulating Matrix metalloproteinase 2 (MMP2) and cyclooxygenase (COX), leading to extracellular matrix degradation and collagen deposition, respectively.

Scaffolding protein caveolin‐1 (Cav1) has also emerged as a key regulator of Ang II‐induced vascular remodeling. Ang II infusion increased Cav1 expression in mouse aorta [173], and Cav1^−/− mice were protected from Ang II‐induced vascular remodeling and perivascular fibrosis [173, 174]. ADAM17 colocalizes with Cav1 in SMC lipid rafts [175] (Figure 4), and Cav1 silencing in SMCs attenuated Ang II‐induced ADAM17 activation, EGFR transactivation, protein synthesis, and collagen deposition. Furthermore, deletion of Cav1 or ADAM17 [172, 173] suppressed vascular remodeling without altering hypertension, reinforcing the concept that Ang II‐induced remodeling can occur independently of hypertension.

Beyond EGFR signaling, JAK2 functions as a key upstream tyrosine kinase mediating Ang II‐induced vascular remodeling (Figure 4). Studies in SMC‐specific JAK2‐deficient mice infused with Ang II demonstrated a crucial role for JAK2 in promoting ROS generation and vascular wall thickening [69].

Nox1‐derived ROS also plays a central role in Ang II‐induced vascular remodeling (Figure 4). In NOX1‐knockout mice, Ang II‐induced hypertension and vascular hypertrophy were significantly reduced [78]. In contrast, NOX2 deficiency did not affect Ang II‐induced hypertension [176]. Moreover, an inducible deletion of NOX4 exacerbated vascular hypertrophy in response to Ang II without affecting blood pressure. Together, these findings support NOX1 as a key mediator of Ang II‐dependent vascular remodeling.

6.2. Arterial Stiffness

Arterial stiffness is a hallmark of vascular aging and frequently precedes the onset of hypertension. It results from increased collagen deposition, elastin fiber fragmentation, vascular calcification, and enhanced cross‐linking of collagen molecules—changes that collectively promote fibrosis and reduce arterial elasticity. Among various contributing factors, Ang II is a central mediator of vascular profibrotic responses [177].

Ang II‐mediated arterial stiffness and vascular fibrosis arise from coordinated contributions of adventitial fibroblasts, SMCs, immune cells, and dynamic extracellular matrix (ECM) remodeling, all of which interact with inflammatory mediators to promote progression of vascular stiffening. MMPs and their endogenous inhibitors, tissue inhibitors of metalloproteinases (TIMPs), are key regulators of ECM homeostasis (Figure 4). Enhanced ECM degradation facilitates SMC migration and proliferation, as well as infiltration of inflammatory cells, thereby promoting vascular remodeling [178]. Notably, Ang II infusion increased vascular MMP2 activity, and MMP2 siRNA lowered Ang II‐induced hypertension in mice [179], highlighting the importance of MMP‐dependent ECM remodeling.

Ang II also induces cyclooxygenase 2 (COX‐2) and COX‐2‐derived prostanoids (Figure 4), and both COX‐2 deletion and COX‐2 inhibition reduce Ang II‐induced vascular stiffness and collagen deposition [180]. Moreover, transforming growth factor β (TGF‐β) and downstream Smad3 are also required for Ang II‐induced vascular fibrosis [181] (Figure 4).

In addition to these mechanisms, mice lacking smooth muscle MR developed less vascular fibrosis from aging and were protected from Ang II‐induced vascular oxidative stress and hypertension [163]. These findings underscore the importance of MR signaling as a downstream amplifier of Ang II‐mediated profibrotic and stiffening responses within the vasculature (Figure 4).

7. Limitations and Future Directions

Despite advances in defining RAS‐dependent signaling in cardiovascular disease, the translational relevance of several mechanisms remains uncertain. Evidence for AT1R/AT2R‐mediated signaling, redox and Ca²⁺ regulation, inflammatory responses, and senescence‐associated pathways is largely derived from rodent models and cultured cells, highlighting the need to validate these mechanisms in human disease and determine their therapeutic relevance. Nevertheless, as recently reviewed, therapeutic targeting of the RAS is expanding beyond conventional ACE inhibition and AT1R blockade toward more selective modulation of the cascade, including AGT suppression, aldosterone synthase inhibition, and activation of ACE2/Ang (1–7)/Mas axis [182]. Importantly, these therapeutic approaches are increasingly being evaluated in clinical trials, including studies of Ang (1–7) in obesity‐associated hypertension and aging (unique identifiers: NCT06482853 and NCT05301192). Recent evidence further highlights RAS modulation as a potential strategy for age‐related disease, with potential applications in frailty, sarcopenia, cardiovascular and renal disease, and neurodegenerative disorders [183].

8. Conclusion

In conclusion, Ang II is a central regulator of vascular function under healthy conditions, and a key driver of vascular dysfunction in hypertension through coordinated actions on SMCs, ECs, and the extracellular matrix. Beyond the canonical AT1R–G‐protein signaling, Ang II receptors activate non‐canonical mechanisms, Ang II‐independent mechanosensitive pathways, and G‐protein‐independent mechanisms that lead to ion channel dysregulation, oxidative stress, MR activation, and proinflammatory signaling in hypertension. These mechanisms collectively promote vasoconstriction, endothelial dysfunction, vascular remodeling, and arterial stiffening. Importantly, Ang II‐induced vascular remodeling appears to occur independently of systemic blood pressure elevation. Emerging evidence also highlights tissue‐specific and context‐dependent Ang II receptor signaling, as well as links between RAS signaling, vascular inflammation, redox balance and aging, underscoring the complexity of the vascular RAS. A deeper mechanistic understanding of these pathways may reveal novel therapeutic strategies for Ang II‐dependent hypertension, including selective targeting of downstream signaling mechanisms in the vasculature including redox signaling, ion channels, mechanotransduction mechanisms, and MR signaling. These approaches may enable more effective strategies to prevent or reverse the vascular dysfunction in Ang II‐dependent hypertension and associated cardiovascular disease.

Author Contributions

Giovanni Bertoldi: conceptualization, methodology, software, writing – original draft, writing – review and editing, investigation, validation. Swapnil K. Sonkusare: conceptualization, methodology, software, investigation, validation, supervision, funding acquisition, project administration, resources, writing – original draft, writing – review and editing.

Funding

This work was supported by grants from the National Institutes of Health to SKS (HL142808, HL146914, EY034238, and HL167208).

Ethics Statement

The authors have nothing to report.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

Data sharing not applicable to this article as no datasets were generated or analysed during the current study.