KIOM-79 protects AGE-induced retinal pericyte apoptosis via inhibition of NF-kappaB activation in vitro and in vivo

IL-1β-induced pericyte dysfunction with a secretory phenotype exacerbates retinal microenvironment inflammation via Hes1/STAT3 signaling pathway

Retinal pericytes are mural cells surrounding capillaries to maintain the integrity of blood-retina barrier and regulate vascular behaviors. Pericyte loss has been considered as the hallmark of diabetic retinopathy (DR), which is a major complication of diabetes and the leading cause of blindness in adults. However, the precise function of pericytes in regulating the retinal microenvironment and the underlying mechanism remains largely unknown. In this study, we observed a secretory phenotype of pericytes with elevated inflammatory cytokines in response to Interleukin-1β (IL-1β), a canonical inflammatory cytokine which significantly increases during the initial stages of diabetic retinopathy. This phenotype is also accompanied by reduced expression of adherent junction proteins and contractile proteins. Paracrine cytokines derived from pericytes further induce the chemotaxis of microglia cells and trigger detrimental changes in endothelial cells, including reduced expression of tight junction protein Occludin and increased apoptosis. Mechanically, the secretion potential in pericytes is partially mediated by Hes1/STAT3 signaling pathway. Moreover, co-injection of stattic, an inhibitor targeting STAT3 activation, could effectively attenuate IL-1β-induced retinal inflammation and microglial activation in retina tissues. Collectively, these findings demonstrate the potential of retinal pericytes as an initial inflammatory sensor prior to their anatomical pathological loss, via undergoing phenotypic changes and secreting paracrine factors to amplify local inflammation and damage endothelial cells in vitro. Furthermore, inhibition of STAT3 activation by inhibitors significantly ameliorates IL-1β-induced retinal inflammation, suggesting STAT3 in retinal pericytes as a promising target for alleviating DR and other IL-1β-induced ocular diseases.

Antioxidants and Mechanistic Insights for Managing Dry Age-Related Macular Degeneration

Age-related macular degeneration (AMD) severely affects central vision due to progressive macular degeneration and its staggering prevalence is rising globally, especially in the elderly population above 55 years. Increased oxidative stress with aging is considered an important contributor to AMD pathogenesis despite multifaceted risk factors including genetic predisposition and environmental agents. Wet AMD can be managed with routine intra-vitreal injection of angiogenesis inhibitors, but no satisfactory medicine has been approved for the successful management of the dry form. The toxic carbonyls due to photo-oxidative degradation of accumulated bisretinoids within lysosomes initiate a series of events including protein adduct formation, impaired autophagy flux, complement activation, and chronic inflammation, which is implicated in dry AMD. Therapy based on antioxidants has been extensively studied for its promising effect in reducing the impact of oxidative stress. This paper reviews the dry AMD pathogenesis, delineates the effectiveness of dietary and nutrition supplements in clinical studies, and explores pre-clinical studies of antioxidant molecules, extracts, and formulations with their mechanistic insights.

C1q/tumor necrosis factor-related protein-3 (CTRP3) activated by forkhead box O4 (FOXO4) down-regulation protects retinal pericytes against high glucose-induced oxidative damage through nuclear factor erythroid 2-related factor 2 (Nrf2)/Nuclear factor-kappaB (NF-κB) signaling

Diabetic retinopathy (DR) remains a major cause of blindness among diabetes mellitus patients. C1q/tumor necrosis factor-related protein-3 (CTRP3) is a novel adipokine which is associated with multiple types of metabolism. Nevertheless, little is known about the role of CTRP3 in high glucose (HG)-induced human retinal pericytes (HRPs). This study set out to assess the influence of CTRP3 on HG-induced HRPs and elucidate the latent regulatory mechanism. RT-qPCR and Western blot were to analyze CTRP3 and forkhead box O4 (FOXO4) expression. Western blot was also utilized to detect the protein levels of apoptosis-related factors and nuclear factor erythroid 2-related factor 2 (Nrf2)/Nuclear factor-kappaB (NF-κB) signaling-related factors. CCK-8 was to measure cell proliferation while TUNEL assay was to estimate cell apoptosis. Levels of oxidative stress biomarkers including manganese (MnSOD), catalase (CAT) and malonedialdehyde (MDA) were evaluated by the corresponding kits. JASPAR database, ChIP and luciferase reporter assay were to verify the interaction between FOXO4 and CTRP3 promoter. The experimental results uncovered that CTRP3 expression was decreased in HG-stimulated HRPs. Moreover, CTRP3 overexpression strengthened the viability while abrogated the apoptosis and oxidative stress of HG-induced HRPs. Furthermore. FOXO4 was up-regulated in HG-induced HRPs. Besides, FOXO4 bond to CTRP3 promoter and inhibited CTRP3 transcription to modulate the Nrf2/NF-κB signaling pathway. FOXO4 up-regulation reversed the influence of CTRP3 elevation on the proliferation, apoptosis and oxidative stress of HG-induced HRPs. To be summarized, CTRP3 negatively modulated by FOXO4 prevented HG-induced oxidative damage in DR via modulation of Nrf2/NF-κB signaling.

Diabetic Retinopathy: From Animal Models to Cellular Signaling

Diabetic retinopathy (DR) is an ocular complication of diabetes mellitus (DM), a metabolic disorder characterized by elevation in blood glucose level. The pathogenesis of DR includes vascular, neuronal, and inflammatory components leading to activation of complex cellular molecular signaling. If untreated, the disease can culminate in vision loss that eventually leads to blindness. Animal models mimicking different aspects of DM complications have been developed to study the development and progression of DR. Despite the significant contribution of the developed DR models to discovering the mechanisms of DR and the recent achievements in the research field, the sequence of cellular events in diabetic retinas is still under investigation. Partially, this is due to the complexity of molecular mechanisms, although the lack of availability of models that adequately mimic all the neurovascular pathobiological features observed in patients has also contributed to the delay in determining a precise molecular trigger. In this review, we provide an update on the status of animal models of DR to help investigators choose an appropriate system to validate their hypothesis. We also discuss the key cellular and physiological events of DR in these models.

Insulin protects against type 1 diabetes mellitus-induced ultrastructural abnormalities of pancreatic islet microcirculation

Pancreatic islet microcirculation, consisting of pancreatic islet microvascular endothelial cells (IMECs) and pericytes (IMPCs), provides crucial support for the physiological function of pancreatic islet. Emerging evidence suggests that pancreatic islet microcirculation is impaired in type 1 diabetes mellitus (T1DM). Here, we investigated the potential ultrastructural protective effects of insulin against streptozotocin (STZ)-induced ultrastructural abnormalities of the pancreatic islet microcirculation in T1DM mouse model. For this purpose, pancreatic tissues were collected from control, STZ-induced T1DM and insulin-treated mice, and a pancreatic IMECs cell line (MS1) was cultured under control, 35 mM glucose with or without 10⁻⁸ M insulin conditions. Transmission and scanning electron microscopies were employed to evaluate the ultrastructure of the pancreatic islet microcirculation. We observed ultrastructural damage to IMECs and IMPCs in the type 1 diabetic group, as demonstrated by destruction of the cytoplasmic membrane and organelles (mainly mitochondria), and this damage was substantially reversed by insulin treatment. Furthermore, insulin inhibited collagenous fiber proliferation and alleviated edema of the widened pancreatic islet exocrine interface in T1DM mice. We conclude that insulin protects against T1DM-induced ultrastructural abnormalities of the pancreatic islet microcirculation.

Long noncoding RNA MIAT regulates primary human retinal pericyte pyroptosis by modulating miR-342-3p targeting of CASP1 in diabetic retinopathy

Diabetic retinopathy (DR) is the leading cause of visual impairment and acquired blindness among adults worldwide. Retinal microvascular pericyte deficiency is one of the earliest pathological changes associated with DR, and long noncoding RNA myocardial infarction-associated transcript (MIAT) has been implicated as a crucial regulator of microvascular dysfunction in DR. Pyroptosis is a caspase-1-dependent proinflammatory form of cell death, and in the present study, we investigated the potential pyroptosis of primary human retinal pericytes (HRPCs) and the mechanism by which MIAT is involved in this process. We applied advanced glycation end product modified bovine serum albumin (AGE-BSA) to simulate the DR environment. The results suggested that AGE-BSA induced the active cleavage of caspase-1 and gasdermin D, the release of IL-1β, IL-18 and LDH, and reduced cell viability, which was prevented by the inhibition of caspase-1, indicating the occurrence of caspase-1-mediated pyroptosis in HRPCs. Immunofluorescence images revealed the phenotypic characteristics of pyroptosis, including pyknosis, swelling and hyperpermeability in plasmolemma. MIAT and CASP1 expression were substantially increased, while that of miR-342-3p was decreased in AGE-BSA-treated HRPCs. MIAT knockdown inhibited pyroptosis in HRPCs, which was reinforced by cotreatment with miR-342-3p mimic but relieved by cotreatment with miR-342-3p inhibitor. Furthermore, HRPC pyroptosis was inhibited by treatment with the miR-342-3p mimic alone but enhanced by the miR-342-3p inhibitor. Luciferase reporter assay results demonstrated binding between MIAT and miR-342-3p, as well as between miR-342-3p and CASP1. MIAT antagonized the effect of miR-342-3p on the depression of its target CASP1 and promoted AGE-BSA-induced pericyte pyroptosis. These findings may promote a better understanding of retinal pericyte depletion pathogenesis and the development of new therapeutic strategies for the treatment of diabetic retinopathy.

Recent Update on the Role of Chinese Material Medica and Formulations in Diabetic Retinopathy

Diabetes mellitus is one of the most frequent endocrine disorders, affecting populations worldwide. Diabetic retinopathy (DR) is the most frequent microvascular complication of diabetes in patients aged 20 and over. Major complications of DR include intraocular neovascularization, inter-retinal edema, hemorrhage, exudates and microaneurysms. Therefore, timely medical attention and prevention are required. At present, laser-assisted therapy and other operational procedures are the most common treatment for DR. However, these treatments can cause retinal damage and scarring. Also, use of the majority of traditional medicines is not supported by clinical evidence. However, due to accumulating scientific evidence, traditional natural medications may assist in delaying or preventing the progression of DR. This review focuses on evidence for the role of traditional natural medicines and their mechanisms of action and pharmacological test results in relation to the progression of DR.

iRAGE as a novel carboxymethylated peptide that prevents advanced glycation end product-induced apoptosis and endoplasmic reticulum stress in vascular smooth muscle cells

Advanced glycation end-products (AGE) and the receptor for AGE (RAGE) have been linked to numerous diabetic vascular complications. RAGE activation promotes a self-sustaining state of chronic inflammation and has been shown to induce apoptosis in various cell types. Although previous studies in vascular smooth muscle cells (VSMC) showed that RAGE activation increases vascular calcification and interferes with their contractile phenotype, little is known on the potential of RAGE to induce apoptosis in VSMC. Using a combination of apoptotic assays, we showed that RAGE stimulation with its ligand CML-HSA promotes apoptosis of VSMC. The formation of stress granules and the increase in the level of the associated protein HuR point toward RAGE-dependent endoplasmic reticulum (ER) stress, which is proposed as a key contributor of RAGE-induced apoptosis in VSMC as it has been shown to promote cell death via numerous mechanisms, including up-regulation of caspase-9. Chronic NF-κB activation and modulation of Bcl-2 homologs are also suspected to contribute to RAGE-dependent apoptosis in VSMC. With the goal of reducing RAGE signaling and its detrimental impact on VSMC, we designed a RAGE antagonist (iRAGE) derived from the primary amino acid sequence of HSA. The resulting CML peptide was selected for the high glycation frequency of the primary sequence in the native protein in vivo. Pretreatment with iRAGE blocked 69.6% of the increase in NF-κB signaling caused by RAGE activation with CML-HSA after 48h. Preincubation with iRAGE was successful in reducing RAGE-induced apoptosis, as seen through enhanced cell survival by SPR and reduced PARP cleavage. Activation of executioner caspases was 63.5% lower in cells treated with iRAGE before stimulation with CML-HSA. To our knowledge, iRAGE is the first antagonist shown to block AGE-RAGE interaction and we propose the molecule as an initial candidate for drug discovery.

Protective effect of a Chinese Medicine formula He-Ying-Qing-Re Formula on diabetic retinopathy

ETHNOPHARMACOLOGY RELEVANCE

He-Ying-Qing-Re Formula (HF) is a formula modified from "Si-Miao-Yong-An Decoction", a traditional Chinese medical classic emerged in the Qing dynasty and has been reported for treatment of vascular diseases. HF, containing 8 herbs, has been used in local hospital for decades as a complementary method for diabetic retinopathy (DR) with retinal vascular dysfunction. Clinical reports revealed HF could ameliorate vision defects, microaneurysms, hemorrhages and macular edema. The aim of this study is to investigate the anti-DR action of HF and its underlying mechanism experimentally.

METHODS

Chromatographic fingerprinting of HF and rodent model of DR were established; hypoglycemic effect of HF was measured by fasting, random blood glucose and glucose tolerance test; vascular degeneration was measured by retinal digestion; blood-retina-barrier (BRB) permeability was assessed with Evans Blue leakage assay. Advanced glycation end products (AGEs) were measured in vitro and in vivo level; Migration of retinal vascular endothelial cells were determined by wound healing and transwell chamber assays; permeability of endothelial monolayer was monitored with dextran transport. AGEs-related proteins and signaling were measured with immunoblotting and immunohistochemistry.

RESULTS

Chlorogenic acid, ferulic acid and arctin were identified as major components in HF; HF suppresses retinal vasculature degeneration and BRB permeability damage without significant inhibition on hyperglycemia; HF reduces in vitro and in vivo formation of AGEs and AGEs-induced migration as well as permeability of retinal vascular endothelial cells. Expression of tight junction proteins Zo-1 and Claudin-1 was increased while activation of AGEs receptor and downstream signaling Akt were suppressed upon HF treatment.

CONCLUSIONS

HF exhibits protective effect against diabetic retinopathy, which may be associated with inhibition on AGEs and recovery on endothelial dysfunction via modulation of tight junction and AGEs downstream signaling.

Animal Models of Diabetic Retinopathy

Diabetic retinopathy (DR) is one of today's main causes of blindness in numerous developed countries worldwide. The underlying pathogenesis of DR is complex and not well understood, thus impeding development of specific, effective treatment modalities. Consequently, the use of animal models of DR is of critical importance for investigating the pathogenesis of and treatment for DR. While rats and mice are the most commonly used animal models of DR, the zebrafish now appears to be a promising model. Nonhuman primates and humans have similar eye structures, and both can develop spontaneous diabetes mellitus (DM). Although various traditionally used animal models of DR undergo a number of pathological changes similar to those of human DR, several human variations, e.g. retinal neovascularization, cannot yet be fully mimicked in any existing animal model of DM. Since both the animal models and the methods chosen for inducing DR have great influence on experimental results, a clear understanding of available animal models is vital for planning an experimental design. In this review, we summarize the mechanisms, methodologies and pros and cons of the most commonly used animal models of DR.

Advanced glycation end products (AGEs) and their receptor (RAGE) induce apoptosis of periodontal ligament fibroblasts

Diabetics have an increased prevalence of periodontitis, and diabetes is one of the causative factors of severe periodontitis. Apoptosis is thought to be involved in this pathogenic relationship. The aim of this study was to investigate apoptosis in human periodontal ligament (PDL) fibroblasts induced by advanced glycation end products (AGEs) and their receptor (RAGE). We examined the roles of apoptosis, AGEs, and RAGE during periodontitis in diabetes mellitus using cultured PDL fibroblasts that were treated by AGE-modified bovine serum albumin (AGE-BSA), bovine serum albumin (BSA) alone, or given no treatment (control). Microscopy and real-time quantitative PCR indicated that PDL fibroblasts treated with AGE-BSA were deformed and expressed higher levels of RAGE and caspase 3. Cell viability assays and flow cytometry indicated that AGE-BSA reduced cell viability (69.80±5.50%, P<0.01) and increased apoptosis (11.31±1.73%, P<0.05). Hoechst 33258 staining and terminal-deoxynucleotidyl transferase-mediated nick-end labeling revealed that AGE-BSA significantly increased apoptosis of PDL fibroblasts. The results showed that the changes in PDL fibroblasts induced by AGE-BSA may explain how AGE-RAGE participates in and exacerbates periodontium destruction.

Peroxisome proliferator-activated receptor α protects capillary pericytes in the retina

Pericyte degeneration is an early event in diabetic retinopathy and plays an important role in progression of diabetic retinopathy. Clinical studies have shown that fenofibrate, a peroxisome proliferator-activated receptor α (PPARα) agonist, has robust therapeutic effects on diabetic retinopathy in type 2 diabetic patients. We evaluated the protective effect of PPARα against pericyte loss in diabetic retinopathy. In streptozotocin-induced diabetic mice, fenofibrate treatment significantly ameliorated retinal acellular capillary formation and pericyte loss. In contrast, PPARα(-/-) mice with diabetes developed more severe retinal acellular capillary formation and pericyte dropout, compared with diabetic wild-type mice. Furthermore, PPARα knockout abolished the protective effect of fenofibrate against diabetes-induced retinal pericyte loss. In cultured primary human retinal capillary pericytes, activation and expression of PPARα both significantly reduced oxidative stress-induced apoptosis, decreased reactive oxygen species production, and down-regulated NAD(P)H oxidase 4 expression through blockade of NF-κB activation. Furthermore, activation and expression of PPARα both attenuated the oxidant-induced suppression of mitochondrial O2 consumption in human retinal capillary pericytes. Primary retinal pericytes from PPARα(-/-) mice displayed more apoptosis, compared with those from wild-type mice under the same oxidative stress. These findings identified a protective effect of PPARα on retinal pericytes, a novel function of endogenous PPARα in the retina.

Effect of KIOM-79 on Diabetes-Induced Myocardial Fibrosis in Zucker Diabetic Fatty Rats

KIOM-79, a herbal mixture of parched Puerariae radix, gingered Magnoliae cortex, Glycyrrhizae radix, and Euphorbiae radix, has a strong inhibitory effect on advanced glycation end products (AGEs) formation. We investigated the beneficial effects of KIOM-79 on cardiac fibrosis in Zucker diabetic fatty (ZDF) rats. KIOM-79 (50 or 500 mg/kg/day) was orally administered for 13 weeks. AGEs formation and collagen expression in the myocardium were assessed by immunohistochemistry. The expression levels of the receptor for AGEs (RAGE), transforming growth factor- β 1 (TGF- β 1), collagen IV, fibronectin, urotensin II, and urotensin II receptor were examined in the myocardial tissue of ZDF rats. KIOM-79 treatment at 500 mg/kg inhibited the accumulation of AGEs, reduced RAGE mRNA and protein expression, and reduced the upregulation of cardiac fibrogenic factors, such as fibronectin and collagen IV, in heart of ZDF rats. Additionally, KIOM-79 ameliorated urotensin II/receptor gene expression in the cardiac tissue of ZDF rats. Our findings indicate that KIOM-79 diminishes cardiac fibrosis in ZDF rats by preventing AGEs accumulation and RAGE overexpression and by modulating the cardiac urotensin II/receptor pathway, which decreases the amount of profibrotic factors, such as TGF- β 1, fibronectin, and collagen in cardiac tissue.