The Possible Link Between the Clock Gene Bmal1 and Eye Disease

Photoreceptors, comprising cone and rod cells, are specialized sensory neurons in the retina which are responsible for converting light stimuli into nerve impulses [51]. Rod cells exhibit higher sensitivity to low light conditions, facilitating night vision, whereas cone cells excel in color discrimination and visual perception during daylight [52]. The functional differences between rods and cones are caused by the varied expressions of specific light‐sensing opsins that regulate the key signaling pathways of visual function [53, 54]. Rod cells only express one opsin, known as rhodopsin, while cone cells possess a variety of opsins and are classified based on their spectral sensitivity. The mammalian retina displays a wide array of daily rhythms in biochemical and cellular processes, allowing visual function to adapt to the light/dark (LD) cycle [38]. The rhythmic processes encompass the mRNA expression of photopigments and genes related to phototransduction in both rods and cones [55]. Additionally, targeted deletion of Bmal1 specifically in the retina, similar to the knockout of Bmal1 in the entire organism, leads to a reduction in both scotopic and ERG b‐wave amplitudes. Therefore, disruption of Bmal1 is likely to impact the transmission of light information from rods and cones to bipolar cells and/or its processing in the inner retina. The researchers found that at 26 months, Chx10Cre; Bmal1^fl/fl mice had about a 60% reduction in the number of cone outer segments and cone nuclei compared to younger mice [56]. Specifically, in the cone pathway, significant effects include diminished viability of cones, shortened lengths of OS and IS, as well as disruption in both structure and function of cones. Moreover, these features would be accentuated in aging mice. In the rod pathway, the dendritic processes of rod bipolar cells were notably stunted at both ages, while the dendrites of cone bipolar cells appeared to develop normally. These findings indicate that the effects of Bmal1 deletion on the rod and cone visual pathways are likely mediated by distinct mechanisms. Researchers also specifically demonstrated the significance of Bmal1 in the light‐adapted ERG, wherein the b‐wave exhibits greater amplitude during the subjective day compared to the subjective night [57]. Interestingly, a study observed diurnal variations in ERG a‐ and b‐waves in control mice carrying one allele of Bmal1 specifically in rods, with higher amplitudes during the subjective night. Together, these data demonstrated the fundamental role of retinal clocks in the structural integrity and functional performance of retinal tissue. However, the molecular pathways that link cell specific clocks to retinal health and function remain to be elucidated. Recently, researchers knocked out Bmal1 in the rod photoreceptors of the P23H mutant mouse model (P23H Rho) [7]. The results reveal that conditional, rod‐specific KO of Bmal1 markedly exacerbates the retinal RP phenotype in P23H mice. Compared with P23H Rho mutant mice, double mutant mice display a significantly greater number of differentially expressed genes in the retina, involving pathways such as neurogenesis, phototransduction cascades, and metabolic processes. This not only elucidates a connection between circadian clock dysfunction and retinal degeneration but also potentially promises an avenue for the restoration of vision in retinal degeneration through the targeted manipulation of the clock gene Bmal1.

Recently, the clock gene Bmal1 that controls thyroid hormone‐mediated spectrum recognition and cone cell photosensitivity is studied [23]. Thyroid hormone (TH) signaling exerts regulatory control over numerous physiological functions, encompassing the modulation of dorso‐ventral cone gradient distribution and cone apoptosis [58, 59]. The study demonstrates that disruption of the circadian clock gene Bmal1 leads to a perturbation of the dorso‐ventral gradient of S and M opsins, resulting in the upregulation of S opsin expression across the entire retina. Additionally, the transcript levels encoding the thyroid‐activating enzyme Dio2 exhibit oscillations within the retina throughout the circadian day, and it is noteworthy that the circadian clock protein BMAL1 binds to the promoter region of Dio2, thereby providing compelling evidence for a persistent involvement of thyroid hormone signaling in maintaining cone photoreceptors [23]. Bmal1 also has a close connection with Complex proteins (Cplxs), which function as regulators of the soluble N‐ethylmaleimide‐sensitive factor attachment protein receptors (SNARE) complex and govern the velocity and calcium ion sensitivity of SNARE‐mediated synaptic vesicle fusion [60]. All four Cplx isoforms have been identified in the mouse retina, with Cplx3 and Cplx4 being localized at the synapses of cone photoreceptor ribbons that exhibit relatively lower expression in rods [61]. Depletion of Bmal1 in cone cells leads to decreased levels of Cplx3 in both cones and rods [62]. In cone‐specific Bmal1 knockout mice, Cplx3 expression decreases during the day, while Cplx4 expression in the outer plexiform layer remains unaffected after Bmal1 knockout. Furthermore, a study identifies three E‐boxes within the promoter region of Cplx3, one of which serves as a binding site for CLOCK:BMAL1 complex to control Cplx3 expression [63]. Thereby, the straightforward explanation is that Cplx3 transcription is enhanced through the circadian clock via CLOCK:BMAL1 binding to these E‐boxes. In conclusion, Cplx3/4 acts as a regulator in the adaptation‐dependent availability of synaptic vesicles, especially at photoreceptor ribbon synapses. Given the essential role of Bmal1 in maintaining cone functionality, it is imperative to develop future therapeutic strategies targeting these genes to restore retinal circuit function; however, further experimental evidence is required to validate this hypothesis.

Melatonin is a hormone that is physiologically synthesized in the pineal gland and retina via a well‐defined biosynthetic pathway [64]. In the retina, melatonin production follows a circadian rhythm and predominantly occurs in the photoreceptor layer (Figure 3A). To date, multiple studies have substantiated the existence of a circadian rhythm in retinal melatonin synthesis [65]. Melatonin functions as an exceptional free radical scavenger in nature, playing a pivotal role in regulating the human sleep–wake cycle and modulating inflammatory responses [66]. Melatonin exerts its effects through binding to MT1 (melatonin receptor type 1) and MT2 (melatonin receptor type 2), which are members of the G protein‐coupled Euphorbia receptor family [67]. In rats, MT1 receptors are found in retinal horizontal cells, inner plexiform layer, photoreceptors, and RGCs [68]. The synthesis of melatonin involves a multi‐step pathway with the participation of numerous enzymes, starting from tryptophan. The sequential order of these participating enzymes includes tryptophan hydroxylase (TPOH), aromatic amino acid decarboxylase (AAAD), arylalkylamine‐N‐acetyltransferase (AA‐NAT), and hydroxyindole‐O‐methyltransferase (HIOMT, also known as acetylserotonin‐O‐methyltransferase [ASMT]) [69]. A significant portion of the research on melatonin synthesis regulation has primarily focused on elucidating the regulatory mechanism of AA‐NAT due to its substantial circadian variations in activity, which give rise to an ∼10‐fold melatonin rhythm within the pineal gland [64]. Research has shown that the activity of CLOCK:BMAL1 is dynamically consistent with increased AANAT mRNA transcription in mice [70]. Cyclic adenosine monophosphate (cAMP) stimulates AANAT gene expression by activating protein kinase A (PKA) and phosphorylating the cAMP‐responsive element‐binding protein (CREB), allowing it to interact with the cAMP response element (CRE) on the AANAT gene promoter [71]. Additionally, the elevation of cAMP and PKA activity leads to phosphorylation of AANAT, facilitating its binding to the corresponding protein [72]. Within the retina, the promoter region of the AANAT gene contains an E‐box sequence that serves as a binding site for the CLOCK:BMAL1 heterodimer, regulating the rhythmicity of AANAT enzyme [73]. CLOCK:BMAL1 rhythmically controls the expression of type 1 adenylyl cyclase (AC1) mRNA through an E‐box in its promoter region to govern cAMP synthesis [74]. Melatonin synthesis is exclusively regulated in darkness under multiple regulatory mechanisms. Conversely, melatonin can also modulate the Bmal1 expression. Several studies have shown that the scotopic ERG in melatonin‐deficient mice (C57/Bl6 mice) is not regulated by the circadian clock; this lack of circadian regulation may be attributed to the absence of melatonin signaling [75]. Removal of melatonin signaling affects the Bmal1 expression and other clock genes in the GCL. A study utilizing melatonin receptor knockout mice shows that melatonin signaling can influence the circadian rhythm of Per1 and Cry2 in the inner retina through MT1 receptors, as well as these same genes in RGCs layer via both MT1 and MT2 receptors; it also affects PER1 and CRY2 protein levels through post‐transcriptional mechanisms rather than mRNA expression [76]. On the basis of our current understanding, it is plausible that melatonin exerts both dependent and independent effects on the clock gene Bmal1 to modulate retinal physiology.

Dopamine (DA) is a pivotal neurotransmitter involved in numerous physiological functions, encompassing motor control, modulation of affective and emotional states, reward mechanisms, reinforcement of behavior, selected higher cognitive functions, and mid‐day contrast sensitivity (Figure 3B) [77, 78]. It has been demonstrated that dopamine release and synthesis follow a circadian rhythm, with both dopamine levels and its primary retinal metabolite 3,4‐dihydroxyphenylacetic acid (DOPAC) being higher under light conditions than under dark conditions [79, 80]. Dopamine regulates intracellular changes through two metabolic dopamine receptor (DR) families that are G protein‐coupled receptors. Activation of D1 receptors (including D1R and D5R) stimulates cAMP production and protein kinase A activity. Conversely, activation of D2 receptors (including D2R, D3R, and D4R) exerts an inhibitory effect on cAMP production and protein kinase A activity [81]. A previous study demonstrated that the nuclear staining intensity of dopamine cells in the retina of Bmal1^−/− mice was significantly reduced compared to wild‐type controls, suggesting the presence of BMAL1 protein expression in dopamine cells [82]. Moreover, activation of D2R‐dependent signaling stimulates the MAPK transduction cascade and enhances recruitment of CREB Binding Protein (CBP) to CLOCK:BMAL1 complex, thereby promoting CBP phosphorylation. Consequently, D2R‐mediated signaling potentiates CLOCK:BMAL1‐driven circadian regulation. Notably, both CLOCK:BMAL1‐dependent activity and light‐induced mPer1 gene transcription are significantly attenuated in retinas lacking D2R [80]. Therefore, dopamine could potentially serve as an intermediary for transmitting signals from the central to peripheral circadian clock within the retina.

The retinal circadian clock exerts an indirect influence on dopamine levels in the retina through modulating the hormone melatonin. Arguably, one of the extensively investigated effects of melatonin in the vertebrate retina pertains to its modulation of dopamine release, with melatonin acutely inhibiting this process across all vertebrate species [83]. For instance, the circadian rhythm of dopamine release in the mouse retina is likely dependent on MT2 receptors, as it persists even in MT1 knockout animals [75]. The melatonin/dopamine system has been extensively investigated as one of the most prominent clock pathways in the vertebrate retina. In Xenopus and fish, the melatonin release rate is high during the night, while the dopamine release rate is high during the subjective day [84]. Endogenous activation of melatonin receptors at night inhibits dopamine release, supporting the view that the circadian melatonin generates the rhythm of dopamine release. However, the exact mechanism/circuit through which melatonin inhibits dopamine remains unclear. The clock genes are believed to account for the clock‐related effects of melatonin and dopamine on retinal physiology. Future investigations into the role of the clock gene Bmal1 in regulating the circadian release patterns of melatonin and dopamine may hold great potential for advancing our understandings of retinal physiology.

The clock gene Bmal1 exhibits a correlation with insulin receptor substrate‐1 (IRS‐1) and the K⁺ channel (Kir4.1), in regulating pathological changes within DR mice. Various ion channels, ligand receptors, and transmembrane transporter molecules are presented on the membrane of Müller cells, including IRS‐1. DR downregulates the expression of Kir4.1 protein while altering K⁺ conductance, resulting in Müller cells swelling and dysfunction [46, 47]. The diurnal rhythm of Kir4.1 in Müller cells has been previously reported, and it has been demonstrated that BMAL1 directly modulates this rhythm, potentially through its interaction with E‐box elements [47]. Moreover, the functionality of Kir4.1 channels in Müller cells relies on insulin signaling mediated by IRS‐1, and the diurnal rhythm of Kir4.1 is synchronized with that of IRS‐1. Researchers have demonstrated that Bmal1 maintains the intrinsic rhythm of insulin secretion, while IRS‐1 potentially modulates Kir4.1 channels via the circadian clock gene Bmal1, thereby implicating their significant involvement in Müller cell dysfunction [47, 90]. Furthermore, silencing of IRS‐1 in rat Müller cells (rMC‐1) results in a reduction in Bmal1 mRNA, BMAL1 protein, and Kir4.1 protein levels. Additionally, rMC‐1 cells administered with siRNA targeting the clock gene Bmal1 exhibits decreased expression of Kir4.1 [90]. Additionally, the circadian regulatory protein BMAL1 plays a crucial role in connecting IRS‐1 and Kir4.1, thereby revealing a novel mechanism underlying the decrease of Kir4.1 in diabetes and providing new insights into the involvement of circadian dysrhythmia in Müller cell dysfunction observed in diabetes.

NF‐κB is a family of transcription factors that are of central significance in several immunity processes, including development, cell growth and survival [91]. Experimental models have shown that there exists an inflammatory environment in the DR retina with the upregulation of IL‐6 and TNF‐α, and Bmal1 can indirectly amplify the NF‐κB signaling pathway in mice with DR [92]. Studies have demonstrated that Bmal1 deficiency results in CLOCK release, promoting p65 phosphorylation to amplify the NF‐κB signaling pathway [93]. Notably, overexpression of Bmal1 could enhance CBP levels to activate the NF‐κB pathway, which subsequently inducing inflammatory cytokine release through enhancing p65 activity. The downstream target genes regulated by activated NF‐κB pathway further facilitate the invasion and metastasis in breast cancer cells [94]. Intriguingly, the pro‐inflammatory transcription factor NF‐κB subunit RELA, like the clock repressor CRY1, represses the transcriptional activity of CLOCK:BMAL1 on the cis‐element of the circadian E‐box [95]. NF‐κB exerts a remodeling effect on the BMAL1/CLOCK‐E‐box complex. Further investigations are warranted to elucidate the coordinated regulation of E‐box transcription by BMAL1, CLOCK, and NF‐κB.

Melatonin (N‐acetyl‐5‐methoxytryptamine), primarily synthesized by the pineal gland, is also endogenously produced in the retina of various vertebrate species. AANAT serves as the principal regulatory enzyme in melatonin synthesis, exhibiting a pronounced circadian variation in both its mRNA expression level and enzymatic activity within the rat retina. Recently, there has been significant attention focused on melatonin and DR. Melatonin plays a pivotal role in the pathogenesis of DR, encompassing the maintenance of iBRB, modulation of autophagy, regulation of inflammatory responses, and attenuation of oxidative stress [96]. It has been demonstrated that a significant decrease in pineal melatonin synthesis is observed in diabetic rats induced by alloxan or STZ (Amaral FG, personal communication, 2010), as well as in hamsters [97]. Interestingly, STZ‐induced diabetic rats exhibited disrupted rhythmicity in AANAT activity, thereby providing a highly plausible hypothesis that the reduction in melatonin synthesis is attributed to perturbations in the circadian regulation of the AANAT enzyme. Moreover, the involvement of the CLOCK:BMAL1 complex in the regulation of AC1 and AANAT gene expression, along with the crucial role of the cAMP signaling pathway in maintaining AANAT stability, is well established. In the diabetic retinas, the diurnal variation in Bmal1 expression is abolished compared to that observed in the control retinas [65]. It is plausible to hypothesize that the downregulation of Bmal1 expression may potentially impede AC1 levels, leading to the observed decline in cAMP concentration and subsequent reduction in AANAT activity. Additionally, the flattened expression of Bmal1 may exert an influence on AANAT gene expression. This further emphasizes the crucial importance of investigating the intricate correlation among Bmal1, melatonin, and DR. These explorations mark an epoch‐making milestone in clock gene research and cast unprecedented insights into comprehending the retinal circadian rhythms in DR.

Endothelial dysfunction with reduced vascularity is the central pathology of DR vascular disease, which is largely mediated by bone marrow progenitor cells (BMPCs) expressing the Bmal1 gene [98, 99]. Current research indicates that mice lacking Bmal1 in their endothelial cells exhibit exacerbated retinal damage following I/R injury compared with WT mice, accompanied by an accelerated increase in the folding of cellular capillaries. The deletion of endothelial BMAL1 orchestrates the progression of microvascular injury, and the absence of Bmal1 in BMPCs further exacerbates endothelial dysfunction due to their inadequate participation in vascular repair [98]. According to a previous research, the Bmal1 gene in RGCs owns a robust correlation with retinal neovascularization [89]. The intense diurnal expression of Bmal1 in the mouse embryo retina is stable after exposure to light stimulus. Retinal neurons can influence the growth of retinal blood vessels in part through light‐mediated signaling pathways, and deletion of Bmal1 and Per2 from retinal neurons leads to defects in neovascularization [53, 100, 101, 102]. The deficiency of Bmal1 and Per2 in embryonic mouse retinas results in impaired angiogenic function [9, 56, 103]. Specific knockout of Bmal1 in endothelial cells would exacerbate retinal microvascular damage and induce pathology closely resembling DR. Moreover, systemic deletion of Bmal1 can promote the production of superoxide radicals in mouse retina [98]. Under hypoxic conditions, Bmal1 is involved in the proliferation of superficial retinal vessels, while Per2 contributes to the growth of deep retinal vessels [9]. These findings suggest that the Bmal1 and Per2 are closely associated with ectopic retinal angiogenesis. The deficiency of the clock gene Bmal1 may facilitate the progression of diabetic retinopathy from NPDR to PDR, while its normal expression is likely to mitigate this pathological process. However, future in‐depth experimental studies are warranted to elucidate the precise mechanisms through which the clock gene Bmal1 functions at different DR stages. Generally, the findings highlight the significance of the circadian clock system in maintaining vascular homeostasis, and suggest that the mammalian circadian clock is a pivotal regulator implicated in diverse retinopathies. As our comprehension of the critical role of circadian clock genes in disease pathophysiology continues to expand, future interventions targeting the pathways that govern mammalian circadian rhythms may offer a promising approach for developing innovative therapies against aging‐related disorders, retinopathies, neurodegenerative diseases, and tumorigenesis.

Overall, while direct evidence explicitly linking Bmal1 to DR remains limited, its well‐documented role in modulating oxidative stress, inflammation, and vascular homeostasis highlights its potential as a pivotal therapeutic target. Additionally, the development of specific Bmal1 inhibitors and their integration with other therapeutic strategies may represent a promising avenue for the prevention and treatment of DR. Future research should prioritize unraveling the underlying mechanisms and performing rigorous clinical validation to fully exploit the therapeutic potential of Bmal1.

Glaucoma, characterized by a group of chronically progressive disorders of the optic nerve, acts as the leading cause of irreversible blindness worldwide [104]. RGCs damage caused by elevated intraocular pressure (IOP) is a major etiologic factor for glaucoma [44]. Numerous studies have demonstrated that IOP exhibits an inherent circadian rhythm regulated by the light/dark cycle; interestingly, this IOP circadian rhythm is modulated by a combination of central and peripheral clock genes [105]. The circadian rhythm of IOP has a sinusoidal pattern which shows trough during subjective daytime and peak during subjective nighttime [106]. The central circadian clock genes of the SCN are subjected to the glucocorticoid‐mediated regulation. The Bmal1 gene, whether expressing in SCN neurons or the paraventricular nucleus neurons, commit to controlling the daily rhythms of glucocorticoid release [107]. Glucocorticoids bind to and activate glucocorticoid receptors (GRs), enabling them to combine with response elements in DNA that are present at the promoter regions of clock genes such as Per1 and Per2 [108]. Extensive evidences have indicated that the disruption of either impaired central circadian clocks in SCN or glucocorticoid signaling removal results in the abrogation of circadian rhythm in IOP [109]. On the contrary, other components of the circadian clock genes such as CLOCK and CRY can inhibit the activation of GRs through interacting with them [110]. In the iris‐ciliary complex of mice, Bmal1 gene expression is negatively correlated with IOP, but Cry1, Cry2, Per1, and Per2 are positive correlated with IOP. Furthermore, it is worth noting that the alteration in Bmal1, Cry, and Per expression occurred prior to the change in IOP, suggesting that circadian clock genes may regulate the diurnal variation in IOP [111]. However, a separate study demonstrates that the IOP rhythm in ciliary epithelium‐specific Bmal1 knockout mice remains intact, suggesting that the regulation of IOP rhythm may not be governed by the ciliary clock [112]. Hence, it is highly possible that the regulation of IOP rhythms is directly mediated by glucocorticoids rather than being governed by the circadian clock of the ciliary body. Whether peripheral clock genes are involved in the production of atrial water remains to be investigated. It is imperative to acknowledge that the central clock genes exert a substantial influence on the synthesis of aqueous humor. Although direct evidence is still limited, the regulatory roles of Bmal1 in IOP, oxidative stress, and neuroinflammation highlight its potential as a promising therapeutic target for glaucoma. Integrating circadian biology with chronotherapeutics may provide novel strategies to preserve vision in this neurodegenerative condition.

Myopia is the most prevalent consequence of refractive error [113]. Myopia can cause various retinopathies, cataracts, and glaucoma, all of which are extremely blinding [114, 115, 116]. Recently, an increasing body of evidence has established a correlation between the circadian rhythms of ocular activity and refractive development. A myopia mouse model was generated by disrupting the circadian clock gene Bmal1, as embodied by a significant increase in both axial length and vitreous chamber depth of Bmal1 knockout mice [117]. Mice with Bmal1 defects also demonstrate a noticeable reduction in the amplitude of both scotopic and photopic full‐field ERG examinations, specifically in the b‐wave response. As it stands, circadian rhythms are associated with ocular growth and the development of refractive error and could offer a novel avenue for investigating the pathogenesis of myopia [113]. On the basis of these experimental results, it is reasonable to speculate that there may be a potential correlation between refractive development and the retinal circadian clock. Refractive dysgenesis or myopia in mammals, particularly humans, necessitates future research to substantiate the role of Bmal1.

Age‐related macular degeneration (AMD), characterized by accumulation of extracellular deposits (namely drusen), progressive degeneration of photoreceptors and adjacent tissue, is a debilitating ocular disease that leads to severe visual impairment and legal blindness [118]. The relationship between AMD and circadian rhythms remains incompletely elucidated; nevertheless, there are several compelling reasons to posit a connection between them. RPE cells degeneration resulting from circadian rhythm dysregulation may be implicated in the progression of AMD. In the retina, RPE cells phagocytose photoreceptor outer segments (POS) to maintain photoreceptor function [39]. Phagocytosis of POS exhibits a circadian rhythm, with its peak occurring within 1–2 h of after light exposure [119]. Deletion of Bmal1 from the RPE abolishes the daily peak of phagocytosis [26]. Another study demonstrates that the senescent RPE cells exhibit an upregulated phagocytic activity, a downregulated level of Bmal1 mRNA, and an elevated level of Rev‐erbα mRNA [40]. Consequently, it is postulated that the dysregulation of circadian clock leading to enhanced RPE phagocytic activity may detrimentally impact retinal function in association with AMD [40]. Furthermore, claudin‐5, which is under regulation of the BMAL1 protein, exhibits the highest level of enrichment among a series of up to 30 interacting proteins within endothelial cells [120]. When the expression of claudin‐5 is persistently suppressed, it will induce significant atrophy in RPE cells. In the retina, iBRB plays an important role in maintaining retinal homeostasis [121]. Knockout of Bmal1 in endothelial cells impedes claudin‐5 circulation in vivo and diminishes the levels of claudin‐5. The dysregulated circulation of claudin‐5 disturbs the iBRB's function in regulating substance exchange, thereby increasing the daily phagocytic load of RPE cells and leading to RPE atrophy and drusen deposition [122]. These findings suggest a critical role of an inner retina–derived factor in the early pathophysiological changes associated with AMD [122]. Therefore, restoring the integrity of the iBRB could potentially serve as a promising therapeutic strategy for preventing and treating geographic atrophy (GA) secondary to dry AMD. The maintenance of stable expression of clock genes and five proteins in the retina may be effective in the prevention or halting of the progression of AMD.

Additionally, the activation of Vegf has been implicated in the pathogenesis of choroidal neovascularization (CNV) [123, 124]. In zebrafish, researchers have discovered that the CLOCK:BMAL1 heterodimer can enhance the expression of Vegf via targeting the promoter region of Vegf gene. Conversely, deletion of these E‐boxes in the promoter region results in the inactivation of Vegf gene promoter activity [125]. In light of the highly conserved nature of the clock genes, these results can be reasonably extrapolated to mammals. The results of another study demonstrate that stable silencing of BMAL1 can mitigate the expression of VEGF [126]. Furthermore, it has been observed that the Bmal1 gene exerts an indirect regulatory effect on VEGF expression through modulation of the WNT/β‐catenin pathway [123, 124]. Dysregulation of circadian rhythm may result in the activation of the WNT/β‐catenin pathway, which subsequently contributes to wet AMD [127, 128]. Specifically, BMAL1 regulates multiple genes involved in WNT signaling [128]. Moreover, Bmal1 is implicated in both transcription and degradation of β‐catenin [129]. The WNT/β‐catenin pathway directly upregulates the VEGF expression in wet AMD [130]. Conversely, the WNT/β‐catenin pathway activates the PI3K/Akt pathway through inhibiting GSK‐3β [124]. The activition of PI3K/Akt pathway has been demonstrated in wet AMD, leading to subsequent upregulation of Vegf expression [131, 132, 133]. Therefore, it is reasonable to hypothesize that the dysregulation of Bmal1 may be associated with the increased in VEGF level in wet AMD. Retinoic Acid 6 (STRA6) is a multi‐transmembrane protein that serves as a specific membrane receptor for retinol binding protein (RBP) and demonstrates high affinity in binding to RBP [134, 135]. The disruption of circadian rhythms has been shown to facilitate the development of CNV. Studies have shown that patients with AMD, exhibit significantly elevated levels of STRA6 expression compared with healthy controls [8]. Furthermore, STRA6 is found to be enriched in pathways associated with angiogenesis. STRA6 expression is under the control of the promoters CLOCK and BMAL1, which regulates the circadian cycle. In vivo experiments demonstrated that STRA6 knockdown reversed the CNV formation induced by circadian rhythm disruption. STRA6 knockdown has been shown to significantly impair the proliferation, migration, and VEGF secretion of RPE cells in vitro. Additionally, the STRA6‐induced CNV formation in asynchronous RPE cells is found to be mediated through the activation of the JAK2/STAT3/VEGFA pathway. These studies elucidate the importance of circadian rhythms in AMD‐associated neovascularization, providing new pathways and targets for anti‐VEGF therapy.