Circadian rhythms in diabetic retinopathy: an overview of pathogenesis and investigational drugs

The Effect of Partial Sleep Deprivation on Retinal Microvasculature in Myopia With Different Axial Lengths

Purpose

To investigate the effects of partial sleep deprivation (PSD) on the retinal microvasculature in individuals with myopia, using optical coherence tomography angiography (OCTA).

Methods

In total, 87 right eyes were categorized by axial length (AL) into three groups: A (AL < 24 mm, n = 20), B (24 ≤ AL < 26 mm, n = 41), and C (AL ≥ 26 mm, n = 26). Participants underwent macular (6 mm × 6 mm) and optic disc (4.5 mm × 4.5 mm) OCTA scans. Vessel density (VD) parameters-including superficial capillary plexus VD (SCP-VD), deep capillary plexus VD (DCP-VD), radial peripapillary capillary VD (RPC-VD), inside disc RPC VD (iVD), and peripapillary RPC VD (ppVD)-were compared at baseline, before and after PSD, and following 3 days of regular sleep.

Results

Compared with group A, groups B and C had lower baseline DCP-VD in all subregions (P < 0.05), except for the perifovea-inferior area, where only groups C and A showed significant differences (P = 0.001). After PSD, group C showed a decrease in SCP-VD in certain subregions of the parafovea (P = 0.013 and P = 0.022 for parafovea-temporal and parafovea-inferior, respectively), along with an increase in ppVD (P = 0.012). All VD parameters recovered after 3 days of regular sleep (P < 0.05).

Conclusions

The retinal microvasculature of myopic eyes with an AL of ≥26 mm show greater susceptibility to PSD than those with an AL of <26 mm. However, short-term PSD effects can be restored by setting a regular sleep schedule.

The role of melatonin and circadian rhythms in the pathogenesis of diabetic retinopathy: A systematic review

AIMS

This review investigates literature on systemic melatonin levels and circadian timing in diabetic retinopathy (DR), examining their associations with DR.

METHODS

Our search was conducted in March 14, 2024, and included the databases Medline, Web of Science, Scopus, ProQuest Health, Latin American and Caribbean Health Sciences Literature (LILACS), Cochrane, International Standard Randomised Controlled Trial Number (ISRCTN) registry, and International Clinical Trials Registry Platform (ICTRP).

RESULTS

Our review analysed twelve articles measuring melatonin concentration in saliva, blood serum, urine, or aqueous humour. Studies measuring melatonin levels in saliva found no significant differences in the average nocturnal or daytime melatonin levels between type 2 diabetes (T2D) patients with and without DR. The studies comparing serum melatonin levels in patients with different stages of DR and controls showed inconsistent results. Only two studies measured the endogenous onset of melatonin secretion, known as dim light melatonin onset (DLMO), a highly accurate biomarker for circadian regulation. These studies showed that only 33% and 57% of patients with DR had detectable DLMO in saliva and serum, respectively. All studies evaluating overnight melatonin production using urinary aMT6s (urinary 6-sulfaoxymelatonin) levels found that DR was associated with lower nocturnal melatonin production.

CONCLUSIONS

Our review results showed evidence of reduced nocturnal melatoin production in DR with no significant changes in melatonin circadian timing.

miRNAs, piRNAs, and lncRNAs: A triad of non-coding RNAs regulating the neurovascular unit in diabetic retinopathy and their therapeutic potentials

Diabetic Retinopathy (DR), a leading complication of diabetes mellitus, has long been considered as a microvascular disease of the retina. However, recent evidence suggests that DR is a neurovascular disease, characterized by the degeneration of retinal neural tissue and microvascular abnormalities encompassing ischemia, neovascularization, and blood-retinal barrier breakdown, ultimately leading to blindness. The intricate relationship between the retina and vascular cells constitutes a neurovascular unit, a multi-cellular framework of retinal neurons, glial cells, immune cells, and vascular cells, which facilitates neurovascular coupling, linking neuronal activity to blood flow. These interconnections between the neurovascular components get compromised due to hyperglycemia and are further associated with the progression of DR early on in the disease. As a result, therapeutic approaches are needed to avert the advancement of DR by acting at its initial stage to delay or prevent the pathogenesis. Non-coding RNAs (ncRNAs) such as microRNAs, piwi-interacting RNAs, and long non-coding RNAs regulate various cellular components in the neurovascular unit. These ncRNAs are key regulators of neurodegeneration, apoptosis, inflammation, and oxidative stress in DR. In this review, research related to alterations in the expression of ncRNAs and, correspondingly, their effect on the disintegration of the neurovascular coupling will be discussed briefly to understand the potential of ncRNAs as therapeutic targets for treating this debilitating disease.

Therapeutic Effects of Metformin on Central Nervous System Diseases: A Focus on Protection of Neurovascular Unit

Metformin is one of the most commonly used oral hypoglycemic drugs in clinical practice, with unique roles in neurodegeneration and vascular lesions. Neurodegeneration and vasculopathy coexist in many diseases and typically affect the neurovascular unit (NVU), a minimal structural and functional unit in the central nervous system. Its components interact with one another and are indispensable for maintaining tissue homeostasis. This review focuses on retinal (diabetic retinopathy, retinitis pigmentosa) and cerebral (ischemic stroke, Alzheimer's disease) diseases to explore the effects of metformin on the NVU. Metformin has a preliminarily confirmed therapeutic effect on the retinal NUV, affecting many of its components, such as photoreceptors (cones and rods), microglia, ganglion, Müller, and vascular endothelial cells. Since it rapidly penetrates the blood-brain barrier (BBB) and accumulates in the brain, metformin also has an extensively studied neuronal protective effect in neuronal diseases. Its mechanism affects various NVU components, including pericytes, astrocytes, microglia, and vascular endothelial cells, mainly serving to protect the BBB. Regulating the inflammatory response in NVU (especially neurons and microglia) may be the main mechanism of metformin in improving central nervous system related diseases. Metformin may be a potential drug for treating diseases associated with NVU deterioration, however, more trials are needed to validate its timing, duration, dose, clinical effects, and side effects.

Association between rest-activity rhythm and diabetic retinopathy among US middle-age and older diabetic adults

Background

The disruption of circadian rhythm has been reported to aggravate the progression of diabetic retinopathy (DR). Rest-activity rhythm (RAR) is a widely used method for measuring individual circadian time influencing behavior. In this study, we sought to explore the potential association between RAR and the risk of DR.

Methods

Diabetic participants aged over 40 from 2011-2014 National Health and Nutrition Examination Survey (NHANES) were enrolled. Data from the wearable device ActiGraph GT3X was used to generate RAR metrics, including interdaily stability (IS), intradaily variability (IV), most active 10-hour period (M10), least active 5-hour period (L5), and Relative amplitude (RA). Weighted multivariable logistic regression analysis and restricted cubic spline analysis were conducted to examine the association between RAR metrics and DR risk. Sensitivity analysis was also conducted to examine the robustness of the findings. An unsupervised K-means clustering analysis was conducted to identify patterns in IV and M10.

Results

A total of 1,096 diabetic participants were enrolled, with a DR prevalence of 20.53%. The mean age of participants was 62.3 years, with 49.57% being male. After adjusting covariates, IV was positively associated with DR (β: 3.527, 95%CI: 1.371-9.073). Compared with the lowest quintile of IV, the highest quintile of IV had 136% higher odds of DR. In contrast, M10 was negatively associated with DR (β: 0.902, 95%CI: 0.828-0.982), with participants in the highest M10 quintile showing 48.8% lower odds of DR. Restricted cubic spline analysis confirmed that these associations were linear. Meanwhile, sensitivity analysis confirmed the robustness. K-means clustering identified three distinct clusters, with participants in Cluster C (high-IV, low-M10) had a significantly higher risk of DR comparing with Cluster A (low-IV, high-M10).

Conclusion

A more fragmented rhythm and lower peak activity level might be associated with an increased risk of DR. These findings indicate that maintaining a more rhythmic sleep-activity behavior might mitigate the development of DR. Further research is necessary to establish causality and understand the underlying mechanisms, and focus on whether interventions designed to enhance daily rhythm stability and increase diurnal activity level can effectively mitigate the risk of progression of DR.

The Effects of STRA6 Regulation of the Circadian Rhythm on Choroidal Neovascularization

Purpose

This study aims to investigate the relationship among STRA6, circadian rhythm, and choroidal neovascularization (CNV) formation, as well as the regulatory mechanism of STRA6 in CNV under circadian rhythm disturbances.

Methods

C57BL/6J male mice (aged 6 weeks) were randomly divided into control and jet lag groups (using a time shift method every 4 days to disrupt the molecular clock's capacity to synchronize with a stable rhythm). A laser-induced CNV model was established in both the control and the jet lag group after 2 weeks of jet lag. The size of CNV lesions and vascular leakage were detected by morphological and imaging examination on the seventh day post laser. STRA6 was screened by full transcriptome sequencing. Bioinformatics analysis was conducted to assess the variation and association of STRA6 in the GSE29801 dataset. The effects of STRA6 were evaluated both in vivo and in vitro. The pathway mechanism was further elucidated and confirmed through immunofluorescence of paraffin sections and Western blotting.

Results

The disturbance of circadian rhythm promotes the formation of CNV. Patients with age-related macular degeneration (AMD) exhibited higher levels of STRA6 expression compared to the control group, and STRA6 was enriched in pathways related to angiogenesis. In addition, CLOCK and BMAL1, which are initiators that drive the circadian cycle, had regulatory effects on STRA6. Knocking down STRA6 reversed the promotion of CNV formation caused by circadian rhythm disturbance in vivo, and it also affected the proliferation, migration, and VEGF secretion of RPE cells without circadian rhythm in vitro, as well as impacting endothelial cells. Through activation of the JAK2/STAT3/VEGFA signaling pathway in unsynchronized RPE cells, STRA6 promotes CNV formation.

Conclusions

This study suggests that STRA6 reduces CNV production by inhibiting JAK2/STAT3 phosphorylation after circadian rhythm disturbance. The results suggest that STRA6 may be a new direction for the treatment of AMD.

Effects of photoperiod and food on glucose intolerance and subsequent ocular pathology in the fat sand rat

Type 2 diabetes mellitus (T2DM) and its ocular complications, such as cataract and diabetic retinopathy (DR) have been linked to circadian rhythm-disturbances. Using a unique diurnal animal model, the sand rat (Psammomys obesus) we examined the effect of circadian disruption by short photoperiod acclimation on the development of T2DM and related ocular pathologies. We experimented with 48 male sand rats. Variables were day length (short photoperiod, SP, vs. neutral photoperiod NP) and diet (standard rodent diet vs. low-energy diet). Blood glucose, the presence of cataract and retinal pathology were monitored. Histological slides were examined for lens opacity, retinal cell count and thickness. Animals under SP and fed standard rodent diet (SPSR) for 20 weeks had higher baseline blood glucose levels and lower glucose tolerance compared with animals kept under NP regardless of diet, and under SP with low energy diet (SPLE). Animals under SPSR had less cells in the outer nuclear layer, a lower total number of cells in the retina, and a thickened retina. Higher blood glucose levels correlated with lower number of cells in all cellular layers of the retina and thicker retina. Animals under SPSR had higher occurrence of cataract, and a higher degree of cataract, which correlated with higher blood glucose levels. Sand rats kept under SPSR develop cataract and retinal abnormalities indicative of DR, whereas sand rats kept under NP regardless of diet, or under SPLE, do not. These ocular abnormalities significantly correlate with hyperglycemia.

Preservation of Intrinsically Photosensitive Retinal Ganglion Cells (ipRGCs) in Late Adult Mice: Implications as a Potential Biomarker for Early Onset Ocular Degenerative Diseases

Purpose

Intrinsically photosensitive retinal ganglion cells (ipRGCs) play a crucial role in non-image-forming visual functions. Given their significant loss observed in various ocular degenerative diseases at early stages, this study aimed to assess changes in both the morphology and associated behavioral functions of ipRGCs in mice between 6 (mature) and 12 (late adult) months old. The findings contribute to understanding the preservation of ipRGCs in late adults and their potential as a biomarker for early ocular degenerative diseases.

Methods

Female and male C57BL/6J mice were used to assess the behavioral consequences of aging to mature and old adults, including pupillary light reflex, light aversion, visual acuity, and contrast sensitivity. Immunohistochemistry on retinal wholemounts from these mice was then conducted to evaluate ipRGC dendritic morphology in the ganglion cell layer (GCL) and inner nuclear layer (INL).

Results

Morphological analysis showed that ipRGC dendritic field complexity was remarkably stable through 12 months old of age. Similarly, the pupillary light reflex, visual acuity, and contrast sensitivity were stable in mature and old adults. Although alterations were observed in ipRGC-independent light aversion distinct from the pupillary light reflex, aged wild-type mice continuously showed enhanced light aversion with dilation. No effect of sex was observed in any tests.

Conclusions

The preservation of both ipRGC morphology and function highlights the potential of ipRGC-mediated function as a valuable biomarker for ocular diseases characterized by early ipRGC loss. The consistent stability of ipRGCs in mature and old adult mice suggests that detected changes in ipRGC-mediated functions could serve as early indicators or diagnostic tools for early-onset conditions such as Alzheimer's disease, Parkinson's disease, and diabetes, where ipRGC loss has been documented.

Identification of key genes modules linking diabetic retinopathy and circadian rhythm

Background

Diabetic retinopathy (DR) is a leading cause of vision loss worldwide. Recent studies highlighted the crucial impact of circadian rhythms (CR) on normal retinopathy in response to the external light cues. However, the role of circadian rhythms in DR pathogenesis and potential investigational drugs remains unclear.

Methods

To investigate the weather CR affects DR, differential expression analysis was employed to identify differentially expressed genes (DEGs) from the GEO database (GSE160306). Functional enrichment analysis was conducted to identify relevant signaling pathways. LASSO regression was utilized to screen pivotal genes. Weighted gene co-expression network anlaysis (WGCNA) was applied to identify different modules. Additionally, we use the Comparative Toxicogenomics Database (CTD) database to search key genes related to drugs or molecular compounds. The diabetic mouse model received three consecutive intraperitoneal injections of streptozotocin (STZ) during 3 successive days.

Results

We initially identified six key genes associated with circadian rhythm in DR, including COL6A3, IGFBP2, IGHG4, KLHDC7A, RPL26P30, and MYL6P4. Compared to normal tissue, the expression levels of COL6A3 and IGFB2 were significantly increased in DR model. Furthermore, we identified several signaling pathways, including death domain binding, insulin-like growth factor I binding, and proteasome binding. We also observed that COL6A3 was positively correlated with macrophages (cor=0.628296895, p=9.96E-08) and Th17 cells (cor=0.665120835, p=9.14E-09), while IGFBP2 showed a negatively correlated with Tgd (cor=-0.459953045, p=0.000247284) and Th2 cells (cor=-0.442269719, p=0.000452875). Finally, we identified four drugs associated with key genes: Resveratrol, Vitamin E, Streptozocin, and Sulindac.

Conclusion

Our findings revealed several key genes related to circadian rhythms and several relevant drugs in DR, providing a novel insight into the mechanism of DR and potential implications for future DR treatment. This study contributes to a better understanding of CR in DR and its implications for future therapeutic interventions.

Investigation of circadian rhythm gene Per3 in diabetic neuropathy

PURPOSE

Diabetic neuropathy (DN) is a serious complication of diabetes that affects peripheral and autonomic nerves, and it has been linked to irregularities in circadian rhythm. Several studies have demonstrated that disruptions in circadian rhythm and changes in expression of rhythm genes may play a role in the development and progression of diabetes, including the development of DN.

METHODS

In this study, the association between the VNTR polymorphism of the PER3 gene and diabetic neuropathy was investigated. The study included 84 patients with diabetes, 220 patients with diabetic neuropathy, and 218 healthy individuals as the control group.

RESULTS

Upon analyzing the data from the study, it was found that there was no significant difference in the PER3 VNTR polymorphism between the diabetic neuropathy patients, diabetes and control groups. However, there was a significant difference observed between the control group and the diabetes group, particularly in terms of the 5/5 genotype and 5 alleles. Moreover, a significant difference was observed between the patient group and the control group (p < 0.05).

CONCLUSIONS

In conclusion, first in the world, the relationship between PER3 gene VNTR polymorphism and diabetic neuropathy and diabetes, was investigated. Our results showed that PER3 may be associated with diabetes but not with diabetic neuropathy.

Diabetes Reshapes the Circadian Transcriptome Profile in Murine Retina

Purpose

Diabetic retinopathy (DR) is a common complication of diabetes and has a high prevalence. Dysregulation of circadian rhythmicity is associated with the development of DR. This research aimed to investigate rhythmical transcriptome alterations in the retina of diabetic mice.

Methods

C57BL/6J mice were used to establish a diabetes model by intraperitoneal injection of streptozotocin (STZ). After 12 weeks, retinas were collected continuously at 4-hour intervals over 1 day. Total RNA was extracted from normal and STZ-treated retinas and RNA sequencing was performed. Meta2d algorithm, Kyoto Encyclopedia of Genes, Phase Set Enrichment Analysis, and time-series cluster analysis were used to identify, analyze and annotate the composition, phase, and molecular functions of rhythmic transcripts in retinas.

Results

The retina exhibited powerful transcriptome rhythmicity. STZ-induced diabetes markedly modified the transcriptome characteristics of the circadian transcriptome in the retina, including composition, phase, and amplitude. Moreover, the diabetic mice led to re-organized temporal and clustering enrichment pathways in space and time and affected core clock machinery.

Conclusions

Diabetes impairs the circadian rhythm of the transcriptomic profile of retinas. This study offers new perspectives on the negative effects of diabetes on the retina, which may provide important information for the development of new treatments for DR.

Neuronal Bmal1 regulates retinal angiogenesis and neovascularization in mice

Circadian clocks in the mammalian retina regulate a diverse range of retinal functions that allow the retina to adapt to the light-dark cycle. Emerging evidence suggests a link between the circadian clock and retinopathies though the causality has not been established. Here we report that clock genes are expressed in the mouse embryonic retina, and the embryonic retina requires light cues to maintain robust circadian expression of the core clock gene, Bmal1. Deletion of Bmal1 and Per2 from the retinal neurons results in retinal angiogenic defects similar to when animals are maintained under constant light conditions. Using two different models to assess pathological neovascularization, we show that neuronal Bmal1 deletion reduces neovascularization with reduced vascular leakage, suggesting that a dysregulated circadian clock primarily drives neovascularization. Chromatin immunoprecipitation sequencing analysis suggests that semaphorin signaling is the dominant pathway regulated by Bmal1. Our data indicate that therapeutic silencing of the retinal clock could be a common approach for the treatment of certain retinopathies like diabetic retinopathy and retinopathy of prematurity.

Association Between Diabetic Retinopathy and Insomnia Risk: A Nationwide Population-Based Study

BACKGROUND

Previous studies have suggested a close link between sleep disturbances and diabetic retinopathy (DR). However, to date, no confirmatory findings have been reported. We aimed to explore the risk of insomnia in DR by considering demographic factors and diabetes mellitus (DM)-related variables.

METHODS

A nationwide population-based cohort of 2,206,619 patients with type 2 diabetes from the Korean National Insurance Service Database was followed up for insomnia incidence. DR, non-proliferative DR (NPDR), and proliferative DR (PDR) were defined according to ICD-10 codes. The interactive effects of sex, age, and DM-related variables were analyzed to evaluate their impact on insomnia risk in DR.

RESULTS

Compared with the non-DR group, insomnia risk was increased in the DR [(adjusted hazard ratio (aHR): 1.125, 95% confidence interval (CI):1.108-1.142), NPDR (aHR:1.117, 95% CI:1.099-1.134), and PDR (aHR:1.205, 95% CI: 1.156-1.256), even after controlling for comorbidities, lifestyle factors, and DM-related variables. The men and youngest age groups (<40 years) were most vulnerable to insomnia risk. Sex, age, DM duration, and chronic kidney disease (CKD) status exerted interactive effects with DR status in increasing the insomnia risk. In the PDR group, sex, age, DM duration, insulin therapy status, and CKD status exerted interactive effects that increased the risk of insomnia.

CONCLUSION

Insomnia risk is significantly higher in patients with DR, and clinical attention is warranted.