Association between endoplasmic reticulum stress and risk factors of diabetic retinopathy

Effects of medications on hypoxia-inducible factor in the retina: A review

Hypoxia-inducible factor (HIF) plays a critical role in the mechanisms that allow cells to adapt to various oxygen levels in the environment. Specifically, HIF-1⍺ has shown to be widely involved in cellular repair, survival, and energy metabolism. HIF-1⍺ has also been found in increased levels in cancer cells, highlighting the importance of balance in the hypoxic response. Promoting HIF-1⍺ activity as a potential therapy for degenerative diseases and inhibiting HIF-1⍺ as a therapy for pathologies with overactive cell proliferation are actively being explored. Digoxin and metformin, HIF-1⍺ inhibitors, and deferoxamine and ⍺-ketoglutarate analogues, HIF-1⍺ activators, are being studied for application in age-related macular degeneration, diabetic retinopathy, and retinitis pigmentosa. However, these same medications have retinal toxicities that must be assessed before implementation of therapeutic care. Herein, we highlight the duality of therapeutic and toxic potential of HIF-1⍺ that must be carefully assessed prior to its clinical application in retinal disorders.

Role of vitamin D in diabetic retinopathy: Pathophysiological and clinical aspects

Epidemiological data predict a dramatic increase in the prevalence of diabetes and of diabetic retinopathy (DR) - the most common complication of diabetes-for which however we do not have so far effective tools for prevention and treatment. Since hypovitaminosis D is very frequent in patients with diabetes and vitamin D (VD) has vascular protective properties, several studies have addressed the association of VD deficiency with DR and its severity and progression, whereas the effects of VD supplementation on its natural history are largely unknown. Here we review the available evidence that supports the possible protective role of VD in DR and suggests to determine the VD levels in DR patients calling for a definitive randomized clinical trial to ascertain whether VD supplementation could protect against DR.

Pyroptosis in the Retinal Neurovascular Unit: New Insights Into Diabetic Retinopathy

Diabetic retinopathy (DR) is prevalent among people with long-term diabetes mellitus (DM) and remains the leading cause of visual impairment in working-aged people. DR is related to chronic low-level inflammatory reactions. Pyroptosis is an emerging type of inflammatory cell death mediated by gasdermin D (GSDMD), NOD-like receptors and inflammatory caspases that promote interleukin-1β (IL-1β) and IL-18 release. In addition, the retinal neurovascular unit (NVU) is the functional basis of the retina. Recent studies have shown that pyroptosis may participate in the destruction of retinal NVU cells in simulated hyperglycemic DR environments. In this review, we will clarify the importance of pyroptosis in the retinal NVU during the development of DR.

New Insight into the Effects of Metformin on Diabetic Retinopathy, Aging and Cancer: Nonapoptotic Cell Death, Immunosuppression, and Effects beyond the AMPK Pathway

Under metabolic stress conditions such as hypoxia and glucose deprivation, an increase in the AMP:ATP ratio activates the AMP-activated protein kinase (AMPK) pathway, resulting in the modulation of cellular metabolism. Metformin, which is widely prescribed for type 2 diabetes mellitus (T2DM) patients, regulates blood sugar by inhibiting hepatic gluconeogenesis and promoting insulin sensitivity to facilitate glucose uptake by cells. At the molecular level, the most well-known mechanism of metformin-mediated cytoprotection is AMPK pathway activation, which modulates metabolism and protects cells from degradation or pathogenic changes, such as those related to aging and diabetic retinopathy (DR). Recently, it has been revealed that metformin acts via AMPK- and non-AMPK-mediated pathways to exert effects beyond those related to diabetes treatment that might prevent aging and ameliorate DR. This review focuses on new insights into the anticancer effects of metformin and its potential modulation of several novel types of nonapoptotic cell death, including ferroptosis, pyroptosis, and necroptosis. In addition, the antimetastatic and immunosuppressive effects of metformin and its hypothesized mechanism are also discussed, highlighting promising cancer prevention strategies for the future.

Visualizing the intellectual structure and recent research trends of diabetic retinopathy

AIM

To analyze the intellectual structure and recent research trends in diabetic retinopathy (DR) and unearth potential knowledge.

METHODS

English DR publication included in this study was exported from the Web of Science Core Collection, and Chinese DR publication was exported from China National Knowledge Infrastructure from the establishment time of the database to 2019. CiteSpace and Microsoft Excel were used to visually analyze DR research, including analysis of the number of publications, highly cited publication analysis, spatial distribution analysis, and keyword co-occurrence analysis.

RESULTS

A total of 23 795 English studies and 11 577 Chinese studies, including 2089 studies related to traditional Chinese medicine (TCM), were obtained. The data suggested the following: 1) The number of English and Chinese DR publications increased over time, and the growth rate of English publications was relatively fast. 2) The distribution of international scholars and institutions was close, while the distribution was scattered in China. Shanghai Jiao Tong University has the largest number of publications. Tien-Yin Wong was the core author with the largest number of publications. England and the United States are the core of international DR research cooperation. 3) Optical coherence tomography and risk factors are recent international research hot spots and trends. The difference is that TCM is a recent research trend under DR in China.

CONCLUSION

DR has drawn an increasing amount of attention worldwide. The focus of research in this field has shifted from tertiary type DR treatment to secondary prevention strategies which focus on the screening and monitoring of disease progression. The advantages of TCM in the prevention of DR have attracted attention, and it is worth incorporating this with Western medicine to address this challenge.

Characterization of Retinal Microvascular Complications and the Effects of Endoplasmic Reticulum Stress in Mouse Models of Diabetic Atherosclerosis

Purpose

Recent evidence suggests that there is a correlation between the micro- and macrovascular complications of diabetes mellitus. The aim of this study is to investigate the molecular mechanisms by which diabetes promotes the development of microvascular disease (diabetic retinopathy [DR]) through characterization of the effects of hyperglycemia in the retina of mouse models of diabetic atherosclerosis.

Methods

Hyperglycemia was induced in apolipoprotein E-deficient (ApoE-/-) mice, a model of accelerated atherosclerosis, either through streptozotocin (STZ) injection or introduction of the Ins2Akita mutation (ApoE-/-Ins2+/Akita). Another subset of ApoE-/- mice was supplemented with glucosamine (GlcN). To attenuate atherosclerosis, subsets of mice from each experimental group were treated with the chemical chaperone, 4-phenylbutyric acid (4PBA). Eyes from 15-week-old mice were either trypsin digested and stained with periodic acid-Schiff (PAS) or frozen for cryostat sectioning and immunostained for endoplasmic reticulum (ER) stress markers, including C/EBP homologous protein (CHOP) and 78-kDa glucose-regulated protein (GRP78). PAS-stained retinal flatmounts were analyzed for microvessel density, acellular capillaries, and pericyte ghosts.

Results

Features of DR, including pericyte ghosts and reduced microvessel density, were observed in hyperglycemic and GlcN-supplemented mice. Treatment with 4PBA reduced ER stress in the retinal periphery and attenuated DR in the experimental groups.

Conclusions

Mouse models of diabetic atherosclerosis show characteristic pathologies of DR that correlate with atherosclerosis. The increased magnitude of these changes and responses to 4PBA in the peripheral retina suggest that future studies should be aimed at assessing regional differences in mechanisms of ER stress-related pathways in these mouse models.

The Effects of Puerarin on Autophagy Through Regulating of the PERK/eIF2α/ATF4 Signaling Pathway Influences Renal Function in Diabetic Nephropathy

BACKGROUND AND PURPOSE

Autophagy is the main protective mechanism against aging in podocytes, which are terminally differentiated cells that have a very limited capacity for mitosis and self-renewal. Here, a streptozotocin-induced DN C57BL/6 mouse model was used to investigate the effects of puerarin on the modulation of autophagy under conditions associated with endoplasmic reticulum stress (ERS). In addition, this study aimed to identify the potential underlying molecular mechanisms.

METHODS AND RESULTS

DN C57BL/6 mouse model was induced by streptozotocin (150 mg/kg) injection. The mice were administered rapamycin and puerarin, respectively, daily for up to 8 weeks. After the serum and kidney samples were collected, the fasting blood glucose (FBG), parameters of renal function, histomorphology, and the podocyte functional proteins were analyzed. Moreover, the autophagy markers and the expressions of PERK/ATF4 pathway were studied in kidney. Results found that the FBG level in DN mice was significantly higher than in normal mice. Compared with DN model mice, puerarin-treated mice showed an increased expression of podocyte functional proteins, including nephrin, podocin, and podocalyxin. Furthermore, the pathology and structure alterations were improved by treatment with rapamycin and puerarin compared with the DN control. The results indicated an elevated level of autophagy in rapamycin and puerarin groups compared with the DN model, as demonstrated by the upregulated expression of autophagy markers Beclin-1, LC3II, and Atg5, and downregulated p62 expression. In addition, the levels of PERK, eIF2α, and ATF4 were reduced in the DN model, which was partially, but significantly, prevented by rapamycin and puerarin.

CONCLUSION

This study emphasizes the renal-protective effects of puerarin in DN mice, particularly in the modulation of autophagy under ERS conditions, which may be associated with activation of the PERK/eIF2α/ATF4 signaling pathway. Therefore, PERK may be a potential target for DN treatment.