The PI3K/AKT signaling pathway represents a pivotal intracellular cascade that governs various cellular processes, such as inhibition of apoptosis, facilitation of proliferation (19) and safeguarding against injury-induced loss of RGCs in the context of glaucoma (21,22). Its complex orchestration involves several key molecular components, including receptor tyrosine kinases (RTKs), PI3K, phosphatidylinositol-4,5-bisphosphate (PIP2), phosphatidylinositol-3,4,5-bisphosphate (PIP3) and protein kinase B (PKB)/AKT (23-25). RTKs serve as a principal upstream regulator of the PI3K/AKT signaling cascade, instigated by extracellular growth factors to initiate signaling events and activate PI3K (25,26). Within the cell membrane, PIP2 and PIP3 are minor phospholipid constituents. In PI3K/AKT-mediated apoptosis, PIP2 is converted to PIP3, which accumulates as a pivotal docking phospholipid within the plasma membrane. Subsequently, PIP3 binds to specific structural domains, facilitating the recruitment of AKT to its kinase PDK1, thereby activating PKB/AKT (27). This activation event culminates in the attenuation of RGCs apoptosis, thereby impeding glaucoma (28). Ultimately, this complex regulatory network contributes to a reduction in RGCs apoptosis and a subsequent delay in the onset and progression of glaucoma pathology (Fig. 2).

In addition, previous studies have shown that Caveolins play a significant role in regulating several signal transduction pathways in ocular diseases including glaucoma (29,30). There are three subtypes of Caveolins in vertebrates, namely Cav-1, Cav-2 and Cav-3 (31). Among them, Cav-1 exhibits strong immunoreactivity in the RGC layer, and has been identified as a gene locus associated with glaucoma in genome-wide association studies (15). Experiments have found that the expression of Cav-1 is downregulated in the induced glaucoma mouse model, and the mice showed ocular hypertension, further indicating the protective role of Cav-1 in glaucoma (32). It has been found that Cav-1 has been proven to play a positive role in the PI3K/AKT signaling pathway, and can inhibit apoptosis, inflammation and oxidative stress by upregulating the PI3K/AKT signal transduction pathway (33-35), thereby preventing the induced degeneration of RGCs in glaucoma. Moreover, studies have suggested that acteoside, the main ingredient of Yunnan purple taro, and baicalin, the dry root of the Chinese herbal medicine Scutellaria baicalensis, have significant effects in preventing and treating glaucoma, reducing the loss, autophagy and oxidative stress of RGCs, and thus preventing the occurrence and development of glaucoma (36-38). Experiments have demonstrated that Acteoside can prevent the autophagic apoptosis of RGCs and delay the optic nerve atrophy induced by glaucoma by activating the PI3K/AKT signaling pathway (16,38). A recent study found that the protective effect of Acteoside on glaucoma is affected by Cav-1 (16). Cav-1-deficient mice not only reverse the effects of Acteoside on the oxidative stress and autophagy of RGCs, but also reverse the inhibitory effect of Acteoside on RGCs loss and its activation effect on the PI3K/AKT signaling pathway. This indicates that Acteoside relies on the positive regulation of Cav-1 to activate the PI3K/AKT pro-survival signaling pathway, thereby preventing the deterioration of glaucoma (16). Furthermore, in a study by Zhao et al (39), RGCs were stimulated with N-methyl-D-aspartate (NMDA) to establish an in vitro glaucoma model. Methyl-thiazolyl-tetrazolium assay indicated a decline in RGCs' viability and an increase in apoptotic rates with increasing NMDA concentrations. Concurrently, there was a decrease in the expression of phosphorylated (p-)AKT and p-PI3K in RGCs. Subsequent administration of baicalin, a compound found to counteract the promoting effect of NMDA on RGCs apoptosis, restored the diminished levels of p-AKT and p-PI3K proteins, further corroborating the involvement of the PI3K/AKT pathway in alleviating apoptosis and injury in NMDA-treated RGCs. Additionally, treatment with LY294002, a PI3K inhibitor, reversed the beneficial effects of baicalein on viability and expression of RGCs, underscoring the crucial role of the PI3K/AKT signaling pathway in modulating survival and function of RGCs. Collectively, these findings highlight the significant association between the PI3K/AKT pathway and RGCs, highlighting its potential as a therapeutic target for impeding RGCs' apoptosis and delaying glaucoma progression.

MAPK constitutes a group of serine-threonine kinases that serve as pivotal elements in intracellular signal transduction mechanisms and orchestrate a diverse array of cellular processes, including differentiation, proliferation, apoptosis, inflammation and responses to various stress stimuli (40). The MAPK signaling cascade delineates a sequential series of kinase events involving MAP3K, MAP2K and MAPK. Initially, MAP3K, a Ser/Thr protein kinase, is activated through phosphorylation, which subsequently catalyzes the activation of MAP2K at its activation site. Consequently, MAP2K increases MAPK activity by affecting dual phosphorylation events at Thr and Tyr residues situated within specific motifs (41). The MAPK pathway, in its complex network, diverges into three principal routes: Extracellular signal-regulated kinase (ERK), p38 MAPK and c-Jun N-terminal kinase (JNK) (40) (Fig. 2). Activation of ERK promotes cell survival, whereas the activation of p38 MAPK and JNK plays a critical role in mediating apoptosis in RGCs (41,42).

The apoptosis of RGCs has been associated with the activation of microglia and the subsequent release of inflammatory mediators such as tumor necrosis factor-alpha (TNF-α), interleukin (IL)-16 and IL-6 (5,43). Moreover, canonical inducers of p38 MAPK activation encompass inflammatory cytokines such as TNF-α, IL-6 and IL-1β (44). Osteopontin (OPN) serves not only as a phosphorylated glycoprotein but also as a pro-inflammatory cytokine in various tissues and cellular contexts (45-47). Its involvement extends to the pathogenesis of numerous neurodegenerative disorders and is closely associated with the regulation of autophagy and its ramifications on neuronal function (48). In the retina, knockout of OPN in mice revealed that microglia showed no signs of activation, such as migration from the inner retina to the subretinal space, or morphological changes in the amoeboid microglia (49). It was deduced that OPN may promote the transition of microglia to the amoeboid phenotype and activate microglia (50). A study conducted by Yu et al (51) established a rat model characterized by chronic ocular hypertension (COH), revealing microglial activation, upregulated expression of microglia-derived OPN and changes in inflammatory cytokine levels (TNF-α, IL-1β and IL-6). Treatment with an inhibitor targeting the p38 MAPK pathway in activated microglia led to diminished production of TNF-α, IL-1β and IL-6. Additionally, intravitreal administration of anti-OPN antibodies in COH-afflicted rats resulted in a significant reduction in p38 expression compared with that in the untreated COH cohort. These findings highlight the potential of OPN to induce apoptosis of RGCs via microglial activation, with the p38 MAPK pathway playing a pivotal role in this complex cascade of events.

The JNK pathway plays a pivotal role in the pathogenesis of diverse diseases, including Alzheimer's disease, Parkinson's disease and glaucoma (52-54). Its significance as a prospective target for neuroprotective intervention has attracted considerable attention (55). Among the proteins implicated in JNK activation and the regulation of neuronal apoptosis, JNK interacting protein 1 (JIP1) emerges as a noteworthy scaffolding protein (42). In the specific context of glaucoma, the complex interplay between mitochondrial dysfunction, oxidative stress and apoptosis in RGCs is well-established (56). Notably, Rotenone, a lipid-soluble environmental toxin, induces RGCs' apoptosis by impeding mitochondrial complex I (57). In a study conducted by Liu et al (42), the suppression of JIP1 in mice exposed to rotenone led to diminished JNK activation, reduced caspase-3 cleavage, and a decrease in TUNEL-positive RGCs within the retina. This attenuation of rotenone-induced RGCs electrophysiological dysfunction highlights the potential therapeutic relevance of the JIP1-JNK signaling axis in alleviating RGCs degeneration. Furthermore, thioredoxin 1 (Trx1), a 12 kDa oxidoreductase, assumes a critical role in antioxidant and anti-apoptotic processes during periods of oxidative stress (58,59). Melatonin, renowned for its protective effects against H₂O₂-induced apoptosis and oxidative stress, functions by preserving the expression of Trx1 and thioredoxin reductase 1 (TrxR1), and the activity of TrxR1 in RGC-5 cells. The significance of Trx1 in melatonin-mediated protection against oxidative stress-induced apoptosis is highlighted by observations indicating compromised protective effects of Trx1 knockdown. Intriguingly, the alleviating effect of Trx1 silencing in RGC-5 cells was partially counteracted by the administration of a JNK signaling inhibitor (60). This suggests a complex interaction between JNK signaling and Trx1 in modulating apoptosis and oxidative damage in RGC-5 cells, implicating the JNK signaling pathway in safeguarding RGC-5 cells against detrimental effects.

Indirect traumatic optic neuropathy (ITON) shares a pathological resemblance with glaucoma, characterized by apoptosis of RGCs and subsequent optic nerve atrophy (61). Experimental induction of an ITON model coupled with the activation of JNK/c-Jun signaling revealed concurrent microglial and NLRP3 inflammasome activation. Conversely, inhibition of JNK/c-Jun signaling was found to forestall NLRP3 inflammasome activation in microglia, thereby protecting against RGCs' death and axonal degeneration (62). This elucidated the complex interaction among JNK signaling, microglial activation and RGCs' survival pathways, suggesting a potential approach for therapeutic intervention in conditions characterized by optic nerve damage.

Apoptosis typically occurs via two distinct pathways: The intrinsic pathway, which is mediated by mitochondria, and the extrinsic pathway, which is mediated by death receptors. The Bcl-2 family of proteins plays a critical role (63). In RGCs, mitochondrial dysfunction and oxidative stress are closely associated with apoptosis, suggesting the involvement of the Bcl-2 family of proteins in RGCs' death (64). This family is comprised of three main types: Pro-apoptotic BH3 proteins (BIM, BID, PUMA, BMF, NOXA, BIK, BAD and HRK), pro-survival proteins (BCL-2, BCL-XL, BCL-W, MCL-1 and A1/BFL-1), and apoptotic effectors (BAX, BAK and BOK) (65-67). Notably, BAX and BAK play pivotal roles in triggering apoptosis and exhibit a strong affinity for BH3 structural domains (67). Under conditions such as nutrient deprivation, lack of growth factors, oxidative stress, exposure to γ-irradiation, or treatment with cytotoxic drugs, BH3 activator proteins selectively bind to the BH3 structural domain-binding groove in BAX/BAK, prompting their activation through structural changes. This triggers the formation of BAX and BAK oligomers in the outer mitochondrial membrane, leading to the creation of pores that permeabilize the membrane. Consequently, cytochrome, an apoptotic factor residing within the mitochondria, is released, which subsequently activates caspase-9 and caspase-3. Activated caspases initiate the breakdown and elimination of RGCs (66-68) (Fig. 2).

In cases of glaucoma resulting from damage to the optic nerve, there is a significant increase in the levels of genes that promote cell death, such as BAX and BAD, in both the affected retina and optic nerve (20). This increase led to the widespread death of RGCs. Extensive research has revealed that activating the cAMP-response element binding protein (CREB)/BCL-2 pathway can prevent mitochondrial cell death. Conversely, the disruption of CREB function tends to worsen cell death, resulting in a decreased BCL-2/BAX ratio, ultimately leading to the loss of mitochondrial function (69). Pituitary adenylate cyclase-activating polypeptide (PACAP) has emerged as a powerful protector of nerve cells, exhibiting significant neuroprotective properties (70). PACAP is important in preventing RGCs' death, as well documented in various animal models of retinal damage (71). After optic nerve injury, there is a significant increase in PACAP and its receptor PAC1R in the layer of RGCs, indicating the prevention of cell death mediated by caspase-3 in RGCs. This series of events is further characterized by an increase in the activation of cAMP-responsive CREB and an elevation in the levels of BCL-2 (70). Altogether, these findings highlight the crucial role of the CREB/BCL-2 pathway in reducing cell death in RGCs and emphasize its importance in maintaining retinal health and function.

BDNF constitutes a critical neurotrophic element pivotal in the processes of neuronal development, differentiation and survival (74). Its principal synthesis occurs in the brain and retina, where it exerts considerable neuroprotective effects in conjunction with other neurotrophic factors. This protective mechanism operates by alleviating the loss of RGCs following optic nerve trauma through its interaction with receptor tyrosine kinases (Trk family) located in the ONH (75). Specifically, the binding of nerve growth factor to TrkA, BDNF to TrkB, and neurotrophic factor-3 to TrkC has been established (74). Among them, furthermore, the BDNF/TrkB signaling pathway plays a crucial role in the health of RGCs and the prevention of apoptosis (14). BDNF administration has been proven to delay the apoptosis of RGCs and extend the survival of neurons under various stress conditions (76). As aforementioned, Cav-1 participates in signaling pathways, and its deficiency will impair retinal function. However, a recent study proposed that Cav-1 negatively regulates the BDNF/TrkB signal transduction in RGCs through its interaction with the tyrosine phosphatase 2 (Shp2) (14). It has been reported that the dysregulation of Shp2 is related to neurodegenerative diseases in the brain and eyes (77,78). Abbasi et al (15) demonstrated through experiments that the silencing of Shp2 has a protective effect on retinal function under chronic experimental glaucoma conditions, and this protective effect depends on Cav-1 in the retina. Cav-1 may use raft microdomains as a platform to recruit Shp2, and then transfer Shp2 to the vicinity of its target TrkB receptor through this platform for interaction (79). TrkB is a high-affinity receptor for BDNF and can support the long-term survival of RGCs (75). Under stress conditions, Cav-1 will be hyperphosphorylated in RGCs, and the number of its bindings with Shp2 will increase significantly, leading to the activation of Shp2 and then the negative phosphorylation of the TrkB receptor (80). The long-term dephosphorylation of TrkB will result in the loss of axonal integrity and hinder the axonal regeneration and other neuroprotective effects of BDNF and neurotrophic factor-4 (NT-4) (14). Therefore, in-depth exploration of the complex interactions among BDNF, TrkB, Shp2 and Cav-1 is of great significance for the treatment of glaucoma. Targeting this pathway is expected to increase the survival probability of neurons, protect the optic nerve and relieve vision problems, bringing new hope for the clinical treatment of glaucoma.

Activation of the PI3K/AKT signaling cascade and ERK, accompanied by CREB phosphorylation (Fig. 2), plays a pivotal role in fostering cellular survival and thwarting mitochondrial apoptosis, thereby conferring neuroprotection (81). In glaucoma, noteworthy deviations in the functional dynamics and expression patterns of BDNF and TrkB have been observed, particularly within the retinal milieu. In this context, the interaction between BDNF and TrkB elicits the activation of the PI3K/AKT and ERK pathways, culminating in CREB phosphorylation and consequently enhancing retinal resilience (75,82). Furthermore, engagement of the p75 neurotrophic factor receptor (p75NTR), acting as a BDNF receptor, with the brain-derived neurotrophic factor precursor (pro-BDNF) induces apoptosis, thus presenting a counterpoint to the effects induced by TrkB binding (75,83). Consequently, strategic interventions targeting the proBDNF/p75NTR signaling axis have emerged as a promising approach for increasing neuronal sustenance and proliferation.

A previous study has revealed the capacity of lithium to increase the population density of RGCs in a dose-dependent manner, concomitant with the upregulation of BDNF observed at both the mRNA and protein tiers (84). The protein Dock3, belonging to the Dock family and known for its involvement in cellular adhesion and neurite elongation, has been delineated as a facilitator of axonal regeneration and neuroprotection in vivo (85,86). Notably, the signaling cascade mediated by Dock3 is activated by BDNF, and conversely, Dock3 reciprocally enhances the stimulatory influence of BDNF on neurite extension (74).

Furthermore, BDNF levels consistently decreased in patients with glaucoma having ONH damage (81). Patients with primary open-angle glaucoma (POAG) and normotensive glaucoma exhibit significantly lower serum BDNF levels than controls, with even lower levels observed in early-stage glaucoma than in moderate glaucoma. These findings suggest that BDNF can potentially serve as a biomarker for glaucoma.

PTEN is a phosphatase that acts on lipids and proteins and has been implicated in the pathogenesis of neurodegenerative diseases. Notably, in murine models with a PTEN knockout, substantial enhancement of axonal regeneration following optic nerve injury has been observed (87). This phenomenon underscores the pivotal role of PTEN in the modulation of cellular responses to injury. Mechanistically, PTEN exerts its inhibitory effect on cell proliferation by impeding the phosphorylation of PIP2 to PIP3, thereby thwarting the activation of the PI3K pathway and its downstream effectors, including AKT and the mTOR cascade (88) (Fig. 2). Conversely, the downregulation of PTEN promotes the activation of the PI3K/AKT/mTOR axis, which promotes axon regeneration in the optic nerve and augments the survival of RGCs post-injury (89). Furthermore, the suppressor of cytokine signaling 3 (SOCS3) is a pivotal regulator of signaling pathways associated with fundamental cellular processes such as proliferation, survival, migration and genomic stability (90). Comparative analyses revealed markedly reduced RGCs' survival in murine models featuring either pure optic nerve injury or SOCS3 knockout, compared with those with PTEN deficiency alone or in combination with SOCS3 (91). Additionally, investigations of optic nerve compression have revealed dendrite and axon retention and regeneration (91).

The miR-200 family plays a critical role in regulating cellular proliferation and apoptosis (92). PTEN has been identified as a co-target of the miR-200 family, indicating a regulatory interplay between them (93,94). Current investigations on POAG have shifted attention toward the involvement of trabecular meshwork (TM) cells and apoptosis of RGCs. Shen et al (93) elucidated the interaction between PTEN and miR-200c in TM cells, with oxidative stress-inducing decreased expression of miR-200c-3p, consequently leading to elevated PTEN levels and heightened cellular apoptosis (95). Additionally, miR-200c-3p has been shown to negatively regulate PTEN expression, cleaved caspase-3 and Bax, while concurrently enhancing the expression of p-AKT, AKT and mTOR, thereby promoting cell proliferation and inhibiting apoptosis, which can be reversed by PTEN (93).

Furthermore, genes associated with mitochondrial function, such as Dynlt1a and Lars2, have been implicated in facilitating axon regeneration, and PTEN inhibition upregulates their expression (96). Moreover, PTEN inhibition was found to induce the dedifferentiation of intrinsically light-sensitive RGCs, thereby activating the intrinsic peripheral axon regeneration capacity (96).

In summary, PTEN has emerged as a pivotal regulator in both the upstream and downstream pathways governing optic nerve axons and survival and regeneration of RGCs. Consequently, PTEN inhibition has emerged as a promising therapeutic target for optic nerve protection and regeneration in patients with glaucoma.

Rho, a constituent of the cytoplasmic Rho family of small GTP-binding proteins, belongs to the Ras superfamily of GTPases and encompasses three distinct isoforms: RhoA, RhoB and RhoC (97). Notably, RhoA exhibits a marked increase in the ONH of individuals with glaucoma (98). Acting as a pivotal downstream effector of Rho GTPases, ROCK (Rho-associated protein kinase) represents a serine/threonine kinase, existing in two isoforms, namely ROCK1 and ROCK2 (98,99). Pertinently, microglia, acknowledged for their significance in the pathogenesis of glaucoma, are implicated in neurotoxicity under the influence of activated ROCK, thereby contributing to optic neuropathy (100,101). Significantly, the administration of ROCK inhibitors, including Y-27632, Y-39983, netarsudil and ripasudil, inhibits ROCK activation, consequently facilitating the axonal regeneration of RGCs (102-105). Hence, the use of ROCK inhibitors has emerged as a promising approach for the advancement of optical neuroprotective strategies in glaucoma.

ROCK inhibitors have been proposed to slow down optic nerve damage by lowering IOP in glaucoma (99), ROCK can improve cell proliferation, inhibit apoptosis, and lower IOP by blocking the Rho kinase cascade activation response (106). Moreover, ROCK inhibitors can provide optic neuroprotection by targeting the cytoskeleton in the TM and Schlemm's canal (SC) cells, increasing aqueous humor (AH) outflow and reducing IOP (99). In glaucoma, ischemia leads to progressive damage to retinal tissue and optic nerves (107). The Rho/ROCK signaling pathway is present in vascular smooth muscle and promotes relaxation, suggesting that ROCK inhibitors could offer neuroprotection by inducing vasodilation to improve blood flow to the retina and optic nerve, thereby supporting axonal regeneration and survival of RGCs (108). Shaw et al (104) discovered that RGCs survival and optic nerve axon regeneration were significantly higher in mice treated topically with a Rock/norepinephrine transporter protein (Net) inhibitor than in mice administered a placebo. This topical treatment also resulted in reduced ROCK target protein phosphorylation in the retina and proximal optic nerve. RGCs play a crucial role in optic nerve damage in glaucoma, with the expression of Rho-kinase significantly increased in apoptotic RGCs. Liu et al (109) conducted in vitro experiments by treating RGCs with siRhoA, and found that this treatment effectively downregulated RhoA expression, protecting cells from H₂O₂-induced damage. They also observed a reduction in the expression of ROCK1, the ROCK2 receptor and Casepase-3, along with an elevation in Bcl-2 expression at both the mRNA and protein levels. In conclusion, blocking the Rho/ROCK signaling pathway could be a promising approach for developing new strategies for optic nerve protection and axon regeneration in glaucoma treatment.

Ca²⁺ enter cells and interact with various Ca²⁺-binding proteins, serving as pivotal signaling entities in the regulation of numerous physiological processes (115). Perturbation of Ca²⁺ homeostasis has been implicated in various pathological conditions, including oxidative stress-induced cell death in glaucoma (116). Notably, cytoplasmic Ca²⁺ levels are aberrantly elevated in LC cells in models of oxidative stress-induced glaucoma (117). This elevation comprises two distinct components: The direct influx of extracellular calcium into the cytoplasm in response to the stress stimulus, and release from intracellular stores, namely the endoplasmic reticulum and sarcoplasmic reticulum, mediated by the Inositol 1,4,5-trisphosphate receptor (IP3R) and ryanodine receptor (118,119). The increase in intracellular Ca²⁺ in glaucomatous LC cells promotes the expression of ECM genes, thereby instigating excessive ECM deposition, as shown in Fig. 3. Consequently, fibroblasts undergo phenotypic alterations and differentiate into myofibroblasts, driving connective tissue fibrosis, and exacerbating glaucomatous optic neuropathy (120). Additionally, other studies have also demonstrated that the synthesis and secretion processes of ECM-related molecules are also regulated by Cav-1 (121,122). The decrease in Cav-1 expression contributes to the disruption of ECM remodeling, thus protecting the microenvironment around RGCs and maintaining the integrity of the structure and normal physiological functions of ocular tissues (122).

In the context of fibrosis, protein kinase C (PKC), p38, p42/44-MAPK and the PI3K/mTOR axis were proposed as pivotal signaling transduction mediators downstream of Ca²⁺ signaling (120). Experimental simulation of glaucoma through hypo-osmotic-induced cell swelling has revealed notable upregulation in the expression and activity of PKCα, p38 and p42/p44-MAPKs (120). Additionally, increased mRNA expression of PI3K, IP3R, mTOR and Ca²⁺-calmodulin protein kinase II was observed in LC under such conditions. The calcium-modulated phosphatase-NFAT signaling pathway plays a significant role in promoting fibroblast proliferation, activation and contraction. Notably, Cyclosporin A, an inhibitor of NFAT activity, has shown significant suppression of NFATc3 expression induced by oxidative stress, as well as elevation of pro-fibrotic ECM genes in both normal and glaucomatous LC cells (123). Hence, targeting PKCα, p38, p42/p44-MAPKs, PI3K/mTOR and the calmodulin phosphatase-NFATc3 signaling pathways emerges as a potential therapeutic strategy for addressing glaucoma-associated LC fibrosis.

Besides, L-type Ca²⁺ channels are increased in glaucomatous LC cells, and the administration of verapamil, a blocker of L-type Ca²⁺ channels, reduces the mechanical strain-induced ECM gene response in human LC cells (124). Blocking Ca²⁺ signaling has been hypothesized to attenuate the fibrotic response in glaucomatous optic neuropathy. It has been found that voltage-independent, stretch-activated cation channels and transient receptor potentials typical of TRPC1 and TRPC6 are highly expressed in glaucomatous LC cells and are also involved in abnormally high levels of Ca²⁺ in glaucomatous LC cells (125). Hu et al (126) established a mouse model of COH and found that the increase in ATP levels and Ca²⁺ endocytosis in response to hydrostatic pressure was accompanied by upregulation of Transient Receptor Potential Vanilloid 1 (TRPV1, encoded by the TRPV1 gene) and 1-phosphatidylinositol 4,5-bisphosphate phosphodiesterase γ-1 (PLCγ1, encoded by the PLCG1 gene) expression. In the same study, knockdown of TRPV1 and PLCG1 genes resulted in a significant reduction in ATP levels and intracellular Ca²⁺, as well as a significant attenuation of apoptosis and autophagy in RGCs. In addition, the expression and activity of the Ca²⁺-dependent potassium channel maxi-K were significantly elevated in glaucomatous LC cells (127). In summary, Ca²⁺ homeostasis is a critical factor for cell function and survival, and the maintenance of Ca²⁺ homeostasis helps attenuate LC cell injury and ECM remodeling, providing a potential target for the treatment of persistent optic neuropathy (128).

TGF-β belongs to the dimeric peptide growth factor family and plays pivotal roles in various signaling cascades associated with cellular processes such as differentiation, proliferation, chemotaxis and fibrosis. It encompasses three primary isoforms, namely TGF-β1, TGF-β2 and TGF-β3, among which TGF-β2 exhibits a particularly close association with glaucoma (88,129). TGF-β orchestrates ECM remodeling, which contributes to the deposition of fibrotic material in the retina, consequently instigating glaucomatous conditions (130). Elevated levels of TGF-β have been detected in glaucomatous AH (131), underscoring its involvement in the pathogenesis of glaucoma. Additionally, TGF-β2 has been shown to activate Src signaling by upregulating the Src scaffolding protein CasL, thereby impeding the expression of tissue plasminogen activator and attenuating ECM degradation (132). It has been proposed that TGF-β exerts its influence on ECM generation and remodeling in tandem with the classical Smad pathway (88). Within this pathway, TGF-β binds to TGF-β type II receptor (TβRII), initiating a cascade wherein the TβRII phosphorylates TGF-β type I receptor (133,134), leading to downstream phosphorylation of Smad2 and Smad3. These phosphorylated Smads form a complex with Smad4, translocate to the nucleus, and modulate gene transcription, thereby promoting ECM production within the ONH and precipitating glaucoma (88,135). Moreover, members of the TGF-β superfamily can induce glaucoma development by activating PI3K/AKT and MAPK signaling pathways (134). The above content is clearly presented in Fig. 2.

Recent investigations have revealed a significant elevation of TGF-β2 levels in glaucomatous ONH and LC, as evidenced in a non-human primate glaucoma model, highlighting the involvement of TGF-β2 in glaucoma pathogenesis (136). TGF-β signaling exerts a direct influence on the expression of microRNAs (miRNAs), which in turn regulate protein translation. Specifically, dysregulation of miRNA-29 family expression, attributed to TGF-β2 signaling, may contribute to glaucomatous pathology by modulating ECM deposition and remodeling within the LC (137). Furthermore, TGF-β signaling has been implicated in the differentiation of myoblasts into myofibroblasts through Smad3-mediated downregulation of miRNA-29 expression (138). Aberrant miRNA-29 expression, which results in dysregulated TGF-β2 signaling, may promote glaucoma by exacerbating ECM deposition and remodeling within the LC (137). Additionally, upregulation of the long non-coding RNA (lncRNA) series NR_003923 has been observed in glaucomatous tissues, with knockdown experiments revealing inhibition of TGF-β signaling and reduced cell migration, fibrosis and autophagy (139). To summarize, targeting TGF-β signaling emerges as a promising therapeutic approach for the treatment of glaucoma.