Mitochondrial homeostasis imbalance-triggered PANoptosis in traumatic brain and spinal cord injury: from mechanism to therapeutic strategies

Abstract

Traumatic injury to the central nervous system (CNS), also known as traumatic brain injury (TBI) and spinal cord injury (SCI), is characterized by high disability and mortality worldwide. PANoptosis is a newly identified cell death mode that synergistically initiates pyroptosis, apoptosis and necroptosis via activation of PANoptosome. It is closely associated with oxidative stress, neuroinflammation, and secondary injury following TBI and SCI, yet the key pathogenic factors and mechanisms underlying PANoptosis remain incompletely elucidated. Mitochondria, as a central organelle for energy synthesis and oxidative stress, its health and homeostasis are the cornerstone of cell survival and biological function. Emerging evidence suggests that the loss of mitochondrial homeostasis plays a fundamental role in the activation and execution of PANoptosis across various cell types. Here, we review the detailed manifestations of mitochondrial homeostasis imbalance in TBI and SCI, such as impaired biogenesis, abnormal dynamics, mitophagy dysfunction, and mitochondria-derived vesicles. Meanwhile, we systematically analyze the characteristics and pathological effects of PANoptosis cascade following TBI and SCI, with a focus on the regulatory patterns, mechanisms, and potential targets of injured mitochondria driving PANoptosis. In addition, we discuss the advancements and future perspectives of mitochondria-based strategies for modulating PANoptosis in TBI and SCI. Taken together, despite considerable challenges in governing post-traumatic mitochondria homeostasis, its multiple targeting of the upstream PANoptosome and downstream cell death signaling offers a promising approach to improve the outcome of CNS trauma.

1. Introduction

Central nervous system (CNS) trauma, including traumatic brain injury (TBI) and spinal cord injury (SCI), is a severe and life-threatening disease with high incidence, disability, and mortality [1]. Although significant advances have been made in clinical management of TBI and SCI, considerable challenges persist in mitigating neurological deficits and improving long-term outcomes. During the post-traumatic pathophysiology, programmed cell death (PCD) is the hallmark of secondary injury that exacerbates neuroinflammation and neurological deficits [2]. Therefore, further investigation into the factors and mechanisms involved in cellular PCD is of paramount significance for developing novel therapeutic strategies.

PANoptosis, a cascade of integrated inflammatory cell death modality, is mediated by PANoptosome and incorporates the features of pyroptosis, apoptosis, and necroptosis, yet it cannot be characterized exclusively by any one of these individual pathways [3,4]. Increasing evidence indicates that PANoptosis plays a crucial role in the pathogenesis of various CNS diseases, including trauma, stroke, and degeneration [[5], [6], [7]]. In PANoptosis cascade, the upstream PANoptosome is assembled and activated by damage/pathogen-associated molecular patterns (DAMPs/PAMPs), serving as a master switch for the downstream pyroptosis, apoptosis, and necroptosis pathways [8,9]. Unlike individual PCD pathways, PANoptosis enables a single stimulus to coordinately activate a multidimensional death response that drives neuroinflammation, representing a highly regulated and sophisticated program [9]. In CNS trauma, this may partly explain why microglial activation by DAMPs/PAMPs yields a hybrid death phenotype that cannot be fully rescued through inhibition of any single PCD pathway. Consequently, targeting PANoptosome holds greater therapeutic promise than targeting individual PCD components.

Mitochondria, as highly dynamic organelles responsible for cellular energy synthesis and metabolism, maintain their homeostasis through a coordinated quality control system that includes biogenesis, dynamics, mitophagy, and mitochondrial-derived vesicles (MDVs) [10,11]. Under physiological conditions, the survival and biological function of CNS cells are highly dependent on the stable number, structure, and activity of mitochondria [12]. In pathological conditions, the mitochondrial homeostasis is disrupted by mitochondrial membrane potential (MMP) loss, abnormal opening of permeability transition pore, calcium overloading, reactive oxygen species (ROS) burst, mitochondrial DNA (mtDNA) damage and leakage, as well as oxidative stress response [11,12]. Recent studies have revealed that mitochondrial dysfunction is involved in the assembly and initiation of PANoptosome, consequently amplifying the PANoptosis cascade following TBI and SCI [13,14]. During the process, numerous inflammatory mediators are generated, compromising neural cell viability and function, ultimately leading to irreversible neurological impairment. Therefore, a comprehensive understanding of the detailed manifestation of mitochondrial homeostasis imbalance following CNS trauma, as well as its regulatory effect on PANoptosis cascade, is essential for novel therapeutic avenues to restore the associated neurological function.

Accordingly, this review aims to elucidate the mechanism underlying mitochondrial homeostasis disruption and PANoptosis in CNS trauma, and to discuss emerging evidence that damaged mitochondria act as a central driver of PANoptosis in neuroinflammation. Moreover, we evaluate the efficacy of current mitochondria-based therapeutic strategies in mitigating neural injury and facilitating neurological recovery via PANoptosis modulation.

2. Mitochondrial homeostasis imbalance and CNS trauma

Mitochondria are energy factories present in almost all types of cells, playing a fundamental role in cellular activities. They are composed of the outer mitochondrial membrane (OMM), inner mitochondrial membrane (IMM), intermembrane space, and matrix. With the assistance of diverse enzymes, mitochondria host the tricarboxylic acid cycle in matrix and oxidize the metabolic products of pyruvate to generate nicotinamide and flavin adenine dinucleotide. These electron carriers then fuel the electron transport chain in IMM, establishing a proton gradient that drives oxidative phosphorylation (OXPHOS) and adenosine triphosphate (ATP) synthesis [15]. In CNS, the mitochondrial quality control system is orchestrated through various mechanisms to preserve structural integrity and functional homeostasis, ensuring continuous energy supply for the brain and spinal cord [16]. To date, several biological processes involved in homeostasis maintenance have been characterized, including mitochondrial biogenesis, fission and fusion, mitophagy, and MDVs [[17], [18], [19]]. Following TBI and SCI, perturbation of these processes compromises mitochondrial homeostasis and energy metabolism, precipitating neuronal PCD and neurological deficits [20].

2.1. Mitochondrial biogenesis alteration in TBI and SCI

Mitochondrial biogenesis is a highly dynamic process that produces new mitochondria to replace the injured and aged ones, thereby ensuring cell survival and metabolism (Fig. 1). The process relies on the coordinated regulation of both nuclear and mitochondrial genes. Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) stands as a master regulator that governs the intricate modulatory network [21]. It can activate peroxisome proliferator-activated receptors (PPARs) and nuclear factor erythroid 2-related factor 2 (Nrf2) to enhance the transcription of nuclear genes involved in adenosine ATP generation and utilization, mtDNA transcription and modification, as well as the mitochondrial protein synthesis and assembly [21,22]. Meanwhile, PGC-1α also drives mitochondrial renewal through the transcriptional activation of mitochondrial transcription factor A (TFAM), cytochrome c oxidase subunit 1(COX1), and mtDNA-encoded genes [23]. During the early phase of TBI, neuronal PGC-1α levels exhibit transient upregulation induced by primary mechanical injury [24]. However, the levels rapidly decrease in the phase of secondary brain injury, accompanied by reduced mitochondrial DNA copy number and downregulated expression of electron transport chain complex I [25]. Therefore, activation of PGC-1α has been considered as a promising strategy to repair mitochondrial biogenesis following TBI.

Fig. 1.

Schematic diagram of mitochondrial quality control system. Mitochondrial biogenesis, mitochondrial dynamics, mitophagy and MDVs work together to preserve mitochondrial homeostasis.

In addition, AMP-activated protein kinase (AMPK) and Sirtuin 1 have been identified as two critical upstream activators of PGC-1α, mediating mitochondrial biogenesis-dependent microglial polarization, astrocytic phenotype transition, and neuronal survival [[26], [27], [28], [29]]. These processes collectively contribute to attenuating the blood-brain barrier (BBB) permeability, behavioral alterations, and cognitive deficits after TBI [30]. Moreover, PGC-1α is essential for the neuroprotective effect of various therapeutic agents, such as melatonin and dexmedetomidine, on mitochondrial biogenesis and anti-oxidative damage following TBI [[31], [32], [33]]. Notably, the PGC-1α/Nrf2 axis serves as a key pathway mediating the anti-inflammatory effects of tannic acid and quercetin by rescuing impaired mitochondria biogenesis in microglia following TBI [[34], [35], [36]]. Thus, pharmacological activation of PGC-1α-mediated mitochondrial biogenesis holds considerable potential for ameliorating neurological deficits after TBI.

Similar to TBI, PGC-1α-driven mitochondrial biogenesis is downregulated in injured neurons after SCI; Conversely, its upregulation reprograms ATP production to promote neuronal survival and axonal regeneration through Ras homolog family member A signaling [37,38]. Photobiomodulation could activate the AMPK/PGC-1α pathway, thereby enhancing mitochondrial energy metabolism and boosting electron respiratory chain activity via TFAM, which in turn facilitates motor and sensory recovery after SCI [39]. In addition, genetic deletion of tumor necrosis factor-α (TNF-α) elevates PGC-1α levels, resulting in improved mitochondrial morphology and metabolic activity, along with a concurrent increase in M2 phenotype of microglia in the injured spinal cord [40].

Recently, emerging evidence indicates that PGC-1α-mediated mitochondrial biogenesis is also involved in neuropathic pain following SCI [41,42]. The histone deacetylase 2 (HDAC2)-induced deacetylation and suppression of PGC-1α promoter are closely associated with mitochondrial homeostasis imbalance, which in turn contributes to neuronal dysfunction, microglial pro-inflammatory polarization, and the progression of neuropathic pain [42]. However, the pain relief can be achieved by promoting mitochondrial biogenesis and protein synthesis via the PGC-1α/Nrf2 axis [43].

2.2. Mitochondrial dynamics alteration in TBI and SCI

Mitochondrial dynamics, which include the cyclical fusion and fission, are one of the core mechanisms for maintaining mitochondrial homeostasis (Fig. 1). The balance between fusion and fission not only determines mitochondrial number and morphology but also modulates their functional state, ensuring precise energy supply for cell activities. The fusion involves OMM and IMM fusion, enabling two granular mitochondria to connect and merge into a single tubular mitochondrion. Studies have shown that mitofusin 1 and 2 (MFN1/2), optic atrophy 1 (OPA1), and phospholipids collectively facilitate mitochondrial content exchange and homeostasis restoration [44]. Conversely, mitochondrial fission refers to the division of a tubular mitochondrion into two granular mitochondria, accompanied by the segregation of mtDNA and matrix. The process is mediated by the specific proteins such as mitochondrial fission factor (MFF), fission 1 (FIS1), mitochondrial dynamics proteins of 49 kDa (MID49) and 51 kDa (MID51), and dynamin-2 (DNM2). These factors recruit dynamin-related protein 1 (DRP1) to the OMM and initiate fission via GTP hydrolysis. This enables removal of depolarized regions while preserving healthy components within mitochondria, thereby preventing accumulation of mtDNA mutation and enhancing mitochondrial function [44].

Following TBI, the disturbed mitochondrial dynamics are characterized by reduced fusion capacity and increased fission. This leads to the accumulation of non-functional or dysfunctional mitochondria fragments within neurons, which are unable to produce sufficient energy to meet the demands of cellular stress responses to injury, thereby triggering PCD [45,46]. Administration of mitochondrial division inhibitor-1 (Mdivi-1), a pharmacological DRP1 inhibitor that blocks excessive mitochondrial fission and attenuates hippocampal neuronal loss after TBI, thereby ameliorating acute learning and memory deficits and limiting long-term neurodegeneration [46,47]. At the same time, Mdivi-1 also confers neuroprotection by restoring mitochondrial transport along the injured axons and enhancing synaptic transmission after intracerebral hemorrhage [48]. In addition, studies have shown that blockade of poly (ADP-ribose) polymerase-1 (PARP-1) induces the expression of mitochondrial fusion markers MFN1/2 and OPA1, together with the antioxidant enzymes superoxide dismutase 1 and glutathione peroxidase 1/4, indicating PARP-1 as a potential therapeutic target for restoring mitochondrial dynamics after CNS trauma [49]. Interestingly, a few studies reported that the expression of genes involved in mitochondrial fusion was upregulated in mild TBI but downregulated in severe TBI, whereas those involved in mitochondrial fission were downregulated in mild TBI and upregulated in severe TBI. The findings suggest that mitochondrial dynamics alteration may correlate with trauma severity, highlighting the need for tailored therapeutic interventions [50].

Following SCI, activated microglia exhibit upregulated FIS1 and downregulated MFN1/2, reflecting a shift toward mitochondrial fission during neuroinflammation. Importantly, the impaired mitochondrial dynamics and microglial pro-inflammatory polarization can be reversed by 17β-estradiol [51]. In addition, DRP1-dependent mitochondrial fission is significantly increased in neurons of the injured spinal cord, accompanied by persistent mitochondrial swelling and fragmentation in axons [52,53]. Li et al. [54] have found that photobiomodulation ameliorates the excessive fission of mitochondria, consequently reducing neuronal PCD and improving hindlimb motor function following SCI. Therefore, restoration of mitochondrial dynamics represents a promising therapeutic approach for SCI-induced neuroinflammation and neurological deficits.

The alterations in mitochondrial cristae number and surface area under various physiological or pathological conditions are termed cristae remodeling, which serves as an adaptive mechanism for cells to cope with energy fluctuations [55]. Meanwhile, it represents an additional mode of mitochondrial dynamics modulation that is closely linked to mitochondrial fission, fusion, and matrix density. Studies have demonstrated that mitochondrial contact site and cristae organizing system (MICOS), OPA1, and ATP synthase play crucial roles in cristae remodeling, thereby modulating OXPHOS, ATP synthesis, cell survival, and cycle progression [56,57]. Particularly, OPA1 emerges as an attractive therapeutic target for restoring cristae remodeling and IMM dynamics in swollen mitochondria of injured neurons after TBI [50,58]. In addition, mitochondrial cristae damage and fragmentation in dorsal horn neurons contribute to secondary neuropathic pain following SCI. Administration of cobra venom factor could attenuate the pain progression by targeting complement C3-mediated cristae remodeling [59].

2.3. Mitophagy alteration in TBI and SCI

Mitophagy, another mechanism of regulating mitochondrial homeostasis, encapsulates damaged or dysfunctional mitochondria into autophagosomes that subsequently fuse with lysosomes for degradation (Fig. 1). This process not only maintains physiological function in healthy cells but also serves as a self-protective mechanism in injured cells, facilitating their response to damage-associated stress [60]. In CNS, mitophagy dysregulation has been implicated in the pathogenesis of various diseases, including Parkinson's disease, Alzheimer's disease, and ischemia reperfusion injury [61]. Although multiple proteins, kinases, and post-translational modifications regulate mitophagy, their functions are primarily mediated through ubiquitination or non-ubiquitination pathways [62]. The ubiquitination signaling is triggered by PTEN-induced putative kinase 1 (PINK1), which recruits Parkin and other ubiquitin ligases to OMM, thereby activating the mitophagy protein. In contrast, the non-ubiquitination signaling is initiated when light chain 3 (LC3) engages autophagy receptors on OMM, such as BCL2-interacting protein 3, FUN14 domain containing 1 (FUNDC1), and Nip3-like protein X (NIX) [63,64].

Following TBI, MMP alterations trigger mitophagy to selectively eliminate the injured mitochondria via the PINK1/Parkin axis, consequently mitigating neuroinflammation and cognitive impairments [65,66]. However, elevated copper levels in the injured cortex and hippocampus impair synaptic mitophagy, leading to the accumulation of damaged mitochondria and subsequent release of ROS and mtDNA. These DAMPs, in turn, aggravate PCD storm and synaptic dysfunction post-trauma [67]. Notably, a few studies support that excessive mitophagy amplifies the secondary brain injury and BBB disruption following TBI [68,69]. Likewise, aberrant activation of NIX-LC3 complex-dependent mitophagy exacerbates neuronal PCD and neurological deficits in SCI [70]. These findings suggest that the function of mitophagy highly depends on its activation status in the CNS. A moderate level of mitophagy may act as a safeguard against neural injury and confer neuroprotective benefits. Either excessive or insufficient mitophagy is detrimental to mitochondrial homeostasis and impede neurological recovery post trauma. Future research is required to clarify the underlying spatial-temporal patterns and mechanisms of mitophagy following CNS trauma.

2.4. MDVs alteration in TBI and SCI

As a novel degradative mechanism of dysfunctional mitochondria, MDVs participate in the regulation of mitochondrial homeostasis in concert with mitophagy, fission, and fusion [71]. The vesicles originate from OMM with a diameter of 60-150 nm and deliver abundant bioactive cargoes to targeted organelles or cells, including mtDNA, RNA, lipids, and proteins [72]. It provides an initial defense against mitochondrial injury at the early stage, whereas mitophagy takes on a more prominent role when injury becomes more severe [73]. Physiologically, the xanthine oxidase/xanthine is responsible for the generation of MDVs enriched in translocase of outer mitochondrial membrane 20 (TOM20⁺ MDVs) (Fig. 1). The interaction between Toll-interacting protein and the ubiquitin-like domain of Parkin promotes vesicle maturation. Rab7 plays a crucial role in transporting these vesicles to the lysosome for degradation [72,74]. Pathologically, MDVs derived from stressed mitochondria are enriched in the matrix protein pyruvate dehydrogenase (PDH⁺ MDVs) (Fig. 1). Their transport and degradation are modulated by the PINK1/Parkin axis [75].

Since MDVs formation and trafficking are closely associated with mitochondria status, the abundance and composition of cargo within these vesicles can be monitored as biomarkers for diseases, including neurotrauma, neurodegeneration, and aging [76]. Remote ischemic preconditioning has been found to attenuate mitochondria dysfunction-induced apoptosis in cerebral ischemia and reperfusion injury by enhancing neuronal MDVs generation [77]. During the acute stage of TBI, MDVs enriched in TFAM and mtDNA drive the release of inflammatory cytokines and aggravate neuroinflammation induced by perturbed mitochondria [78,79]. Brain proteomics reveals that MDVs transport ATP synthase, OXPHOS proteins, and IMM translocase 9/10, which are essential for fine-tuning mitochondrial homeostasis and cellular function [80,81]. In addition, it has been found that β-hydroxybutyrate (BHB) promotes the secretion of PDH⁺ MDVs through hydroxybutyrylation of sorting nexin 9 (SNX9), thereby contributing to mitochondrial homeostasis in alcohol-induced liver injury [82]. These findings lay a foundation for developing MDV-based strategies to improve neurological recovery after CNS trauma.

3. PANoptosis cascade and CNS trauma

3.1. Overview of PANoptosome

PCD represents the primary mode of cell death in the injured brain and spinal cord, including pyroptosis, apoptosis, necroptosis, ferroptosis, and cuproptosis [2]. Each type of PCD is governed by specific signaling pathways that play crucial roles in neural injury and restoration after CNS trauma. However, the emerging evidence of inter-pathway crosstalk has challenged the long-standing paradigm that different PCD signaling pathways operate independently. In 2019, Malireddi et al. [3] uncovered a novel inflammatory cell death modality that incorporates features of pyroptosis, apoptosis, and necroptosis, and coined the term “PANoptosis” from the initials of these processes. Recently, the integrated death modality has been verified in the pathophysiology of various CNS diseases, offering a novel dimension to elucidate the interaction among pyroptosis, apoptosis, and necroptosis following trauma.

The PANoptosome, an essential polymeric complex in PANoptosis cascade, is assembled by a series of sensors, adaptors, and effectors. It functions not only as a switch for perceiving upstream stimuli but also as a platform that coordinates the activation of downstream cascades [83]. Currently, five types of PANoptosomes have been identified: Z-DNA binding protein 1 (ZBP1) PANoptosome, absent in melanoma 2 (AIM2) PANoptosome, receptor-interacting protein kinase 1 (RIPK1) PANoptosome, Nod-like receptor protein 12 (NLRP12) PANoptosome, and NLR family CARD domain-containing 5 (NLRC5) PANoptosome. By sensing PAMPs, DAMPs, and cytokines, they act as molecular scaffolds that couple key proteins in pyroptosis, apoptosis, and necroptosis pathways, and initiate PANoptosis cascade in a programmed manner [84].

By sensing nucleic acid damage signals, ZBP1 PANoptosome activates the PANoptosis cascade during pathogen infection and immune responses [85]. It initiates pyroptosis through nod-like receptor protein 3 (NLRP3) inflammasome and GSDMD, while simultaneously inducing caspase-8-dependent apoptosis and RIPK3-mediated necroptosis. This multimodal activation ultimately leads to lytic cell death and robust inflammation [86,87]. Emerging evidence identifies Ninjurin-1 as a key downstream executor of plasma membrane rupture in ZBP1 PANoptosome-induced cell death. Its absence substantially blocks the three PCD pathway in PANoptosis cascade, underscoring its therapeutic potential for diseases [88].

The assembly and activation of RIPK1 PANoptosome correlate with suppression of transforming growth factor-β-activated kinase 1 (TAK1) during Yersinia infection [89]. Genetic ablation of RIPK1 attenuates both pyroptosis and apoptosis, yet unleashes necroptosis through unchecked activation of RIPK3 and mixed lineage kinase domain-like protein (MLKL) [89,90]. Conversely, caspase-8 could suppress necroptosis by restraining RIPK3 kinase activity in sepsis-like syndrome [87,89,91]. The findings reveal the mutually antagonistic yet interdependent roles of RIPK1 PANoptosome components in orchestrating the PANoptosis cascade.

AIM2 PANoptosome serves as a critical orchestrator of inflammatory responses to cellular injury in CNS development. Its dysregulation causes accumulation of damaged neuronal DNA, leading to developmental retardation and neurobehavioral deficits [92]. In addition, evidence indicates that ZBP1 and pyrin collaboratively promote AIM2-driven PANoptosis in lung macrophages during herpes simplex virus 1 (HSV1) and F.novicida infection [93,94]. The PANoptosome also contributes to cardiomyocyte PANoptosis in doxorubicin-induced injury by recognizing mtDNA damage and leakage [95]. Thus, AIM2 PANoptosome functions both in host defense against infection and in response to injury across various diseases.

NLRP12 and NLRC5 PANoptosomes are two newly identified complexes in hemolytic diseases. Hematopoietic cell kinase (HCK) binds the pyrin-NACHT junction to promote NLRP12 PANoptosome assembly, which is further activated by heme via interferon regulatory factor 1 (IRF1) and TLR2/4 signaling [96,97]. Knockout of NLRP12 attenuates the PANoptosome-driven inflammation and reduces mortality in hemolytic reactions [96,97]. Additionally, upon stimulation with heme plus LPS or TNF-α, the NLRC5 PANoptosome participates in various cellular metabolic processes, including ROS production and nicotinamide adenine dinucleotide depletion [98]. Notably, nicotinamide administration reverses NLRC5-induced macrophage PANoptosis, thereby mitigating inflammatory cytokine release and organ damage [98,99]. Collectively, as pattern recognition receptors (PRRs), NLRP12 and NLRC5 represent promising therapeutic targets for hemolytic diseases.

3.2. Pathological effects of PANoptosis in TBI and SCI

During the secondary injury process of CNS trauma, a series of oxidative damage and pathophysiological changes occur in mitochondria, including ROS burst, mtDNA leakage, calcium overload, and MMP loss [100]. Activated by these damage patterns, PANoptosome triggers pyroptosis, apoptosis, and necroptosis within the PANoptosis cascade, thereby exacerbating post-traumatic edema, inflammation, and BBB disruption. Among these processes, pyroptosis is characterized by NLRP3 inflammasome activation and GSDMD cleavage, which induces the formation of plasma membrane pores and the release of inflammatory cytokines in the CNS [101]. Apoptosis is initiated by extrinsic death receptors and intrinsic mitochondrial cytochrome C, which converge to activate caspase-3 and caspase-7 to cleave specific substrates, causing non-lytic cell death [102]. Necroptosis is mediated by RIPK3 phosphorylation and MLKL oligomerization, leading to cellular swelling and rupture, thereby inducing inflammatory damage following CNS trauma [103].

Given the highly pro-inflammatory characteristics of PANoptosis, unraveling its role and mechanism in CNS trauma is of great significance. It has been found that mechanical stretch to neurons elicits a significant upregulation of key molecules in PANoptosis cascade, including the pyroptosis executioner proteins NLRP3 and GSDMD, apoptosis-related proteases caspase-3 and caspase-8, and necroptosis activators phosphorylated RIPK1 and RIPK3 [[101], [102], [103]]. Administration of specific inhibitors targeting the three PCD pathways effectively rescues neuronal viability in vitro [13]. In parallel, the proteomic landscape of the injured cortex in TBI mice also exhibits a marked increase of apoptosis, pyroptosis, and necroptosis markers in PANoptosis cascade. Importantly, the in vivo alterations are correlated with the motor and cognitive impairments caused by brain injury [13]. Collectively, the findings suggest neuronal PANoptosis following TBI, yet the specific PANoptosome complex orchestrating this process remains to be elucidated.

It is noteworthy that evodiamine performs an inhibitory role in the survival and polarization of M1 microglia by activating PANoptosis in a mouse model of severe TBI [104]. The effect results in a decrease of acute brain edema and pro-inflammatory cytokines infiltration. The findings notably differ from other studies showing microglial PANoptosis exacerbates neuroinflammation and worsens neurological function following brain injury [5,13]. The discrepancy may arise from the severity of TBI and the time window employed for PANoptosis detection, in which the proportion of apoptosis is greater than that of pyroptosis and necroptosis in activated microglia. As a result, future investigations are required to elucidate the detailed effect of PANoptosis across diverse severities and phases of TBI. Therefore, the interaction among the three PCD modalities in PANoptosis cascade needs to be further investigated.

Following SCI, Y-box-binding protein 1 (YBX1) has been identified as a crucial initiator for neuronal PANoptosis, thereby contributing to motor and sensory deficits. At the same time, co-localization of ZBP1, caspase1, caspase3, and PIPK3 within NeuN⁺ cells is significantly increased in the injured spinal cord, implying that the neuronal PANoptosis is driven by ZBP1 PANoptosome [105]. Ubiquitination of M3 fragment in YBX1 by tripartite motif-containing protein 56 (TRIM56) promotes its degradation, thus counteracting ZBP1 PANoptosome activation and mitigating neurological deficits post injury [105]. Using a set of machine learning algorithms, Li et al. [7] screened several PANoptosis-related genes in SCI, including caspase-4, NLRP3, NLRC4, and Gasdermin B, and further verified that upregulation of these genes promotes the recruitment of γδ T and mast cells during the early inflammatory stage of SCI. In addition, another bioinformatic analysis has revealed that bone marrow X kinase is a promising biomarker of PANoptosis-mediated inflammation in the blood of SCI patients, yet the spatiotemporal expression pattern and detailed mechanism still need to be validated [106].

4. Mitochondrial homeostasis disruption-triggered PANoptosis in CNS trauma

Apart from serving as an energy-producing organelle for cellular metabolism and activity, mitochondria hold the switch between cell survival and death. Following CNS trauma, mitochondrial injury and disturbance impair cell fate by activating diverse PCD pathways. The DAMPs generated from damaged mitochondria are potent triggers of pyroptosis, apoptosis, and necroptosis. Importantly, disruption of mitochondrial homeostasis also acts as a central hub to amplify the PCD storm within the PANoptosis cascade following CNS trauma (Fig. 2).

Fig. 2.

Schematic diagram of mitochondria homeostasis imbalance acts as a central hub that triggers PANoptosis following TBI and SCI. As shown in the yellow box, CNS trauma induces mitochondrial injury and dysfunction, characterized by ROS burst, oxidative stress, compromised energy metabolism, Ca2⁺ overload, mtDNA damage and leakage, abnormal MPTP opening, and loss of MMP. As shown in the red box, mitochondrial injury leads to impaired biogenesis, abnormal dynamics, aberrant MDVs, and defective mitophagy, ultimately disrupting mitochondrial homeostasis. The purple box illustrates that upon mitochondrial homeostasis imbalance, the PANoptosome is activated by IRF1, PRR, MAPK, and cGAS signaling, which subsequently initiates pyroptosis, apoptosis, and necroptosis in PANoptosis cascade.

4.1. Association between mitochondrial dysfunction and PANoptosis in TBI

Following TBI, the upregulated proteasome 26S subunit, non-ATPase 14 (PSMD14) is able to mitigate mtROS-induced PANoptosis in neurons through activating PINK1/Parkin-mediated mitophagy. Mechanistic investigation reveals that PSMD14 prevents pyruvate kinase M1/2 (PKM1/2) degradation via removal of ubiquitination modification at Lys48 and thereby promotes PKM-dependent phosphorylation of PINK1 at Thr257. The process subsequently activates mitophagy to phagocytize the disturbed mitochondria and accumulated mtROS, leading to reduced PANoptosis and improved outcome of TBI. Conversely, inhibition of the PINK1/Parkin pathway abolishes the protective effect of PSMD14 by exacerbating neuronal PANoptosis [13]. In the acute phase of subarachnoid hemorrhage, elevated phosphoglycerate mutase family member 5 (PGAM5) phosphorylates RIPK1 at ser166 in damaged mitochondria, which triggers RIPK1 PANoptosome assembly and propels the injured neurons toward PANoptotic death [107]. Additionally, Snapin acts as an orchestrator of neuronal mitophagy through the hydrogen sulfide (H₂S)/cathepsin D (CTSD) pathway in the injured cortex, which restores mitochondrial homeostasis and attenuates neuronal PANoptosis after TBI [108]. Interestingly, evodiamine treatment suppresses the survival of M1-polarized microglia after severe TBI by promoting PANoptosis, thereby alleviating microglia-induced inflammation and mitigating its impact on mitochondrial homeostasis in neighboring neurons [104]. The findings indicate that under specific severities or conditions of TBI, PANoptosis might play a role in the clearance of activated microglia and influence their communication with neurons.

It is well known that cerebral edema, ischemia and hypoxia substantially contribute to the secondary injury and neurological deficits following TBI. The PANoptotic death is widely observed in neurons, microglia and astrocytes under oxygen-glucose deprivation [5]. PANoptosis is also detected in retinal neurons suffering from ischemic injury, which is induced by DRP1 phosphorylation-mediated excessive mitochondrial fission and mtROS production. Downregulation of extracellular signal-regulated kinase 1/2 (Erk1/2) inhibits the activation of PANoptosis by targeting DRP1/mtROS axis [109]. Moreover, intermittent hypoxia opens mitochondrial permeability transition pore (MPTP) in hippocampal neuron and induces mtDNA translocation to activate PANoptosis through cyclic GMP-AMP synthase/stimulator of interferon genes [110]. Accordingly, restoration of mitochondrial homeostasis represents a promising approach to alleviate ischemic brain injury. However, whether PANoptosis is involved in the ischemic and hypoxic processes following TBI remains to be investigated. Identifying specific PANoptosome initiators may yield new targets for neurological recovery.

Toll-like receptor 9 (TLR9) has been demonstrated to impair mitochondrial energy metabolism via p38 mitogen-activated protein kinase (MAPK) signaling, thereby initiating PANoptosis in cortical neurons. Pharmacological blockade of TLR9 markedly attenuates the three PCD modalities in PANoptosis cascade and mitigates inflammatory injury [111]. However, inhibition of p38 MAPK selectively abrogates neuronal apoptosis and pyroptosis while potentiating the necroptotic pathway, implying the existence of inter-conversion and regulatory mechanisms among the three PCD modalities [111]. Integrative multi-omics profiling and functional assay reveal that neutrophil extracellular traps drive microglial release of CCL3, CCL7, and CXCL10 in the injured brain. These cytokines contribute to mitochondrial homeostasis imbalance by disrupting OXPHOS and glycolysis. These processes further trigger metabolic-reprogramming-dependent PANoptosis in microglia, exacerbating the inflammatory response and neurological deficits [112]. Therefore, mitochondrial dysfunction serves as a multifaceted regulator of PANoptosis in neurons and microglia following TBI, highlighting its important role in neuroinflammation post-trauma.

The autonomic dysregulation, immune-cell dysfunction, and BBB disruption following TBI collaboratively predispose patient to a life-threatening systemic inflammation in multi-organ [113,114]. In turn, peripheral inflammation feeds back on the injured brain and amplifies the inflammatory response, thereby worsening the outcome of TBI [115]. The gut-brain connection is a recently uncovered bidirectional communication route between the CNS and the digestive system. Following TBI, the brain-to-gut route disrupts gut microbiota composition, altering immune homeostasis and intestinal barrier integrity. In contrast, the disturbed microbiota activates microglial polarization and causes neural circuit damage via gut-to-brain route, which amplifies neuroinflammation and cognitive impairment post-trauma [116]. Studies have shown that enterocyte mitophagy attenuates apoptosis and oxidative stress after TBI via Erk/Nrf2 signaling, thereby protecting mucosal and intestinal barrier function along the brain-to-gut axis [117]. Fecal microbiota transplantation not only reverses TBI-induced dysbiosis but also promotes mitophagy through Wipi1/PINK1/Parkin signaling, thereby attenuating microglial pyroptosis and neuroinflammation [118]. Knockout of mitochondrial PGAM5 facilitates the enrichment of Akkermansia muciniphila in the gut of TBI mice, leading to improved mucosal barrier function and reduced pyroptosis in cortical neurons [119]. However, the microbial metabolite trimethylamine-N-oxide has been found to induce mitochondrial swelling, vacuolization, and MPTP opening in hippocampal neurons via the gut-to-brain axis. This damage serves as an upstream trigger of neuronal PANoptosis and neurobehavioral abnormality [120]. Together, the involvement of gut-brain connection in mitochondria homeostasis imbalance-driven PANoptosis provides novel insights into central-peripheral crosstalk and unveils new therapeutic avenues for TBI.

4.2. Association between mitochondrial dysfunction and PANoptosis in SCI

In the early stage of SCI, mitochondrial homeostasis imbalance is the fundamental trigger for PANoptosis cascade across various cell types [121]. In neurons, restoration of mitophagy via the Lgals3/Bax pathway attenuates oxidative stress-induced PANoptosis following SCI [14]. Activation of melanocortin receptor 4 (MC4R) inhibits AIM2-driven pyroptosis and improves functional recovery by targeting DRP1-mediated mitochondrial fission [122]. In microglia, salt-inducible kinase 2 (SIK2) induces aberrant mitochondrial dynamics through DRP1 phosphorylation at ser616, leading to mtDNA leakage and AIM2 inflammasome activation in the inflammatory storm after SCI [123]. Signal regulatory protein α causes myelin debris accumulation by disrupting microglia phagocytosis, which subsequently triggers NLRP12-mediated PANoptosis in neurons [124]. In astrocytes, Fanconi anemia complementation group C promotes mitophagy by targeting Parkin to clear the injured mitochondria, thereby reducing mtROS-mediated necroptosis and improving motor function recovery after SCI [125].

In the subacute stage of SCI, the reperfusion of blood following the subsidence of acute edema produces massive free radicals and inflammatory mediators, which act synergistically to aggravate mitochondrial dysregulation and PANoptosis. Melatonin has been shown to inhibit cytochrome C release from damaged mitochondria via the PI3K/Akt pathway, consequently alleviating microglial pyroptosis as well as neuronal apoptosis and necroptosis induced by ischemia-reperfusion injury. However, the anti-PANoptotic effect is abolished upon the treatment of melatonin receptor antagonist Luzindole [126]. In addition, low-concentration H₂S has been found to ameliorate impaired mitochondrial homeostasis and attenuate PANoptosis cascade after SCI, thereby conferring protection to neurons and microglia against ischemia-reperfusion injury [127].

During the recovery period of SCI, the mammalian target of rapamycin (mTOR)-insensitive companion localized at the mitochondria-associated endoplasmic reticulum membrane repairs the inflammatory niche and suppresses necroptosis of endogenous neural stem cells (NSCs). This subsequently facilitates endogenous NSCs migration toward the injured site, thereby enhancing neural circuit reconstruction [128]. Exosomes derived from exogenous NSCs can inhibit necroptosis by blocking the RIPK1-RIPK3 interaction in injured neurons, which ultimately promotes functional recovery after SCI [129]. Additionally, it has been found that RIPK3 ablation prevents mitochondrial fission-induced necroptosis yet redirects cell death toward RIPK1-dependent apoptosis in fibroblasts [130]. Whether a similar conversion switch exists in the injured spinal cord remains unknown and warrants further investigation.

5. Mitochondria-based therapy for PANoptosis in CNS trauma

As described above, the close association between disrupted mitochondrial homeostasis and PANoptosis opens new broad avenues for therapeutic strategies in TBI and SCI. The mitochondria-based therapies are on the rise and have shown considerable potential for modulating PANoptosis. The emerging treatments encompass pharmacological agents, chemical compounds, gene editing, traditional Chinese herbal extracts, and metal ions. They regulate the PANoptosis cascade by acting on diverse facets of mitochondrial homeostasis following CNS trauma, including mitochondrial biogenesis, dynamics, and mitophagy (Table 1).

Table 1.

Mitochondria-based interventions for PANoptosis in CNS trauma.

Disease	Intervention Strategy	Targeted Cell	Molecular Mechanism	Regulation of Mitochondria Function	Influence on PANoptosis	Publication Year	Reference Number
TBI	Lactate	Neuron	PSMD14-dependent deubiquitination of PKM	Mitophagy	Reduce	2025	[13]
	Evodiamine	Microglia	Plorization phenotype	Mitochondrial biogenesis	Induce	2025	[104]
	H2S and Pepstatin A	Neuron	H2S-mediated s-sulfhydration of CTSD	Mitophagy	Reduce	2026	[108]
SCI	Zinc ions	Neuron	Lgals3/Bax pathway	Mitochondiral dynamics and mitophagy	Reduce	2024	[14]
	TRIM56 overexpression	Neuron	TRIM56-induced ubiquitination and degradation of YBX1	Mitochondrial biogenesis	Reduce	2024	[105]
	Sirpα inhibition	Neuron	Syk/PI3K/Akt pathway-mediated microglial phagocytosis	Mitophagy	Reduce	2026	[124]

5.1. Mitochondria-based therapy for PANoptosis in TBI

Both in vitro and in vivo evidence indicate that lactate potentiates PINK1-mediated mitophagy in neurons through H3 lysine 18 lactylation and PSMD14 upregulation, thus inhibiting mtROS production and subsequent PANoptosis activation following TBI [13]. Exogenous H₂S has been shown to compensate for insufficient mitochondrial H₂S synthesis in injured neurons, consequently suppressing persulfidation-induced cathepsin D (CTSD) maturation and PANoptosis activation [108]. Additionally, Pepstatin A treatment directly inhibits mature CTSD expression in dysfunctional mitochondria and PANoptotic neuronal death after TBI [108]. By modulating mitochondrial biogenesis and PANoptosome assembly, the bioactive alkaloid extracted from Evodia rutaecarpa exerts protective effects against neuroinflammation in severe TBI [104]. Taken together, the findings support mitochondria-based therapy as an effective and feasible strategy for the management of PANoptosis following TBI.

5.2. Mitochondria-based therapy for PANoptosis in SCI

It has been found that zinc ions attenuate mitochondrial damage and neuronal PANoptosis after SCI by restoring Lgals3/Bax-mediated mitophagy [14]. TRIM56 inhibits PANoptosis through promoting ubiquitination-dependent degradation of YBX1 in injured neurons [105]. MC4R mitigates AIM2-mediated neuronal pyroptosis following SCI via inhibition of aberrant mitochondrial dynamics [122]. Pharmacological or genetic inhibition of SIK2 also alleviates AIM2-induced pyroptosis by suppressing excessive mitochondrial fission and oxidative damage in microglia [123]. These studies indicate that, by targeting specific genes, a precise mitochondria-based approach can be achieved to govern PANoptosis in SCI. Notably, AIM2 acts as a central hub in SIK2- and MC4R-dependent regulation of mitochondria homeostasis and pyroptosis following SCI. Given that AIM2 serves as an essential sensor in AIM2 PANoptosome, whether targeted manipulation of these signaling pathways additionally modulates apoptosis and necroptosis in PANoptosis cascade remains to be further investigated.

5.3. Future perspectives of mitochondria-based therapy and PANoptosis

Although MDVs have not yet been adopted in mitochondria-related therapy for TBI and SCI, recent multicolor nanoscopic studies have characterized their ultrastructure, composition, and function in healthy neurons [131]. Beyond their role in mitochondrial biogenesis and oxidative cargo transport, the vesicles traffic across the BBB into peripheral circulation, serving as a biomarker of mitochondrial status and cellular fate. More importantly, the functional mitochondria carried by MDVs offer a promising strategy for mitochondrial transfer or transplantation to rescue cells from PCD following CNS trauma [132,133]. It has been reported that bone marrow mesenchymal stem cells (MSCs)-derived MDVs reduce neuronal apoptosis and improve axonal regeneration by preventing mitochondrial dysfunction in SCI [132]. MDVs from human umbilical cord MSCs confer a protective role against neuronal pyroptosis by delivering exogenous mitochondria to restore mitochondrial homeostasis in the injured brain [133]. Furthermore, the endogenous mitochondria transfer from astrocyte to neuron significantly ameliorates neuronal PANoptosis and neurological deficits after brain injury [134]. Collectively, these findings lay a preclinical foundation for developing MDV-based strategies to target mitochondrial dysfunction-mediated PANoptosis in CNS trauma.

PANoptosis cascade integrates apoptosis, pyroptosis, and necroptosis pathways through PANoptosome, offering an attractive target for mitochondria-based therapy in CNS trauma. However, the interventions exhibit differential inhibitory efficacy across the three PCD modalities and provoke inter-pathway compensatory resistance. For instance, intervention targeting the RIPK1 PANoptosome and caspase-8 ameliorates pyroptotic and apoptotic cell death but fails to inhibit necroptosis and even induces its compensatory activation [89,91]. Thus, a thorough understanding of the dynamic interconnections within PANoptosis cascade following TBI and SCI is critical for the development of multitargeted therapeutic strategies, ranging from upstream PANoptosome assembly to downstream PCD execution.

Another consideration is the intervention precision and approach of mitochondria-based strategies in CNS. The therapeutic drugs should be preferentially delivered to the injured brain or spinal cord while minimizing off-target distribution in surrounding tissues. In addition, selective recognition and modulation of specific cell populations following CNS trauma remains a challenge, such as the injured neurons, pro-inflammatory M1 microglia, and pluripotent neural stem cells, as well as the subcellular organelles. This should not be overlooked in future research.

6. Conclusion

As reviewed above, mitochondrial homeostasis imbalance and PANoptosis persist for months to years, contributing significantly to the secondary pathophysiological injury following CNS trauma. In acute phase, the PANoptosis cascade drives cellular PCD and amplifies inflammatory response. During the chronic phase, it exacerbates post-traumatic neurodegeneration and neurological deficits. However, the dynamic link between specific PANoptosome types and mitochondria homeostasis imbalance at different phases of CNS trauma remains unclear, highlighting the need for systematic research. In addition, future studies should focus on the novel PANoptosome putative in TBI and SCI, which has not been described in other diseases previously. Such findings may yield innovative therapeutic targets and strategies to promote neurological recovery post trauma.

CRediT authorship contribution statement

Yuqin Ye: Conceptualization, Formal analysis, Investigation, Writing – original draft, Writing – review & editing. Zhusheng Feng: Conceptualization, Investigation, Writing – original draft. PeiPei Huang: Investigation, Visualization, Writing – original draft. Xinhong Su: Investigation, Visualization, Writing – original draft. Chuanhao Lu: Investigation, Writing – original draft. Yang Yu: Investigation, Writing – original draft. Liang Li: Formal analysis, Writing – original draft. Jiayi Wang: Formal analysis, Supervision, Visualization, Writing – review & editing. Xia Li: Conceptualization, Supervision, Visualization, Writing – review & editing.

Declaration of competing interest

The authors have declared that no competing interests exist.

Data availability

No data was used for the research described in the article.