Hyperlipidemia induces proinflammatory responses by activating STING pathway through IRE1α-XBP1 in retinal endothelial cells

Single-cell RNA sequencing in exploring the pathogenesis of diabetic retinopathy

Diabetic retinopathy (DR) is a leading cause of irreversible blindness in the working-age populations. Despite decades of research on the pathogenesis of DR for clinical care, a comprehensive understanding of the condition is still lacking due to the intricate cellular diversity and molecular heterogeneity involved. Single-cell RNA sequencing (scRNA-seq) has made the high-throughput molecular profiling of cells across modalities possible which has provided valuable insights into complex biological systems. In this review, we summarise the application of scRNA-seq in investigating the pathogenesis of DR, focusing on four aspects. These include the identification of differentially expressed genes, characterisation of key cell subpopulations and reconstruction of developmental 'trajectories' to unveil their state transition, exploration of complex cell‒cell communication in DR and integration of scRNA-seq with genome-wide association studies to identify cell types that are most closely related to DR risk genetic loci. Finally, we discuss the future challenges and expectations associated with studying DR using scRNA-seq. We anticipate that scRNA-seq will facilitate the discovery of mechanisms and new treatment targets in the clinical care landscape for patients with DR. KEY POINTS: Progress in scRNA-seq for diabetic retinopathy (DR) research includes studies on DR patients, non-human primates, and the prevalent mouse models. scRNA-seq facilitates the identification of differentially expressed genes, pivotal cell subpopulations, and complex cell-cell interactions in DR at single-cell level. Future scRNA-seq applications in DR should target specific patient subsets and integrate with single-cell and spatial multi-omics approaches.

Glucagon-like peptide-1 receptor agonists rescued diabetic vascular endothelial damage through suppression of aberrant STING signaling

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) protect against diabetic cardiovascular diseases and nephropathy. However, their activity in diabetic retinopathy (DR) remains unclear. Our retrospective cohort study involving 1626 T2DM patients revealed superior efficacy of GLP-1 RAs in controlling DR compared to other glucose-lowering medications, suggesting their advantage in DR treatment. By single-cell RNA-sequencing analysis and immunostaining, we observed a high expression of GLP-1R in retinal endothelial cells, which was down-regulated under diabetic conditions. Treatment of GLP-1 RAs significantly restored the receptor expression, resulting in an improvement in retinal degeneration, vascular tortuosity, avascular vessels, and vascular integrity in diabetic mice. GO and GSEA analyses further implicated enhanced mitochondrial gene translation and mitochondrial functions by GLP-1 RAs. Additionally, the treatment attenuated STING signaling activation in retinal endothelial cells, which is typically activated by leaked mitochondrial DNA. Expression of STING mRNA was positively correlated to the levels of angiogenic and inflammatory factors in the endothelial cells of human fibrovascular membranes. Further investigation revealed that the cAMP-responsive element binding protein played a role in the GLP-1R signaling pathway on suppression of STING signaling. This study demonstrates a novel role of GLP-1 RAs in the protection of diabetic retinal vasculature by inhibiting STING-elicited inflammatory signals.

ER: a critical hub for STING signaling regulation

The Stimulator of Interferon Genes (STING) has a crucial role in mediating the immune response against cytosolic double-stranded DNA (dsDNA) and its activation is critically involved in various diseases. STING is synthesized, modified, and resides in the endoplasmic reticulum (ER), and its ER exit is intimately connected with its signaling. The ER, primarily known for its roles in protein folding, lipid synthesis, and calcium storage, has been identified as a pivotal platform for the regulation of a wide range of STING functions. In this review, we discuss the emerging factors that regulate STING in the ER and examine the interplay between STING signaling and ER pathways, highlighting the impacts of such regulations on immune responses and their potential implications in STING-related disorders.

Protective effect of bromelain on some metabolic enzyme activities in tyloxapol-induced hyperlipidemic rats

Elevation of one or more plasma lipids, such as phospholipids, cholesterol esters, cholesterol, and triglycerides, is known as hyperlipidemia. In humans and experimental animals, bromelain, the primary active ingredient isolated from pineapple stems, has several positive effects, including anti-tumor growth, anticoagulation, and anti-inflammation. Hence, the purpose of this study was to determine the possible protective impact of bromelain on some metabolic enzymes (paraoxonase-1, glutathione S-transferase, glutathione reductase, sorbitol dehydrogenase [SDH], aldose reductase [AR], butyrylcholinesterase [BChE], and acetylcholinesterase [AChE]), activity in the heart, kidney, and liver of rats with tyloxapol-induced hyperlipidemia. Rats were divided into three groups: control group, HL-control group (tyloxapol 400 mg/kg, i.p. administered group), and HL+bromelain (group receiving bromelain 250 mg/kg/o.d. prior to administration of tyloxapol 400 mg/kg, i.p.). BChE, SDH, and AR enzyme activities were significantly increased in all tissues in HL-control compared to the control, whereas the activity of other studied enzymes was significantly decreased. Bromelain had a regulatory effect on all tissues and enzyme activities. In conclusion, these results prove that bromelain is a new mediator that decreases hyperlipidemia.

Hyperglycemia-induced STING signaling activation leads to aortic endothelial injury in diabetes

Hyperglycaemia-induced endothelial dysfunction is a key factor in the pathogenesis of diabetic microangiopathy and macroangiopathy. STING, which is a newly discovered regulator of innate immunity, has also been reported to play an important role in various metabolic diseases. However, the role of STING in diabetes-induced endothelial cell dysfunction is unknown. In this study, we established a diabetic macroangiopathy mouse model by streptozotocin (STZ) injection combined with high-fat diet (HFD) feeding and a glucotoxicity cell model in high glucose (HG)-treated rat aortic endothelial cells (RAECs). We found that STING expression was specifically increased in the endothelial cells of diabetic arteries, as well as in HG-treated RAECs. Moreover, genetic deletion of STING significantly ameliorated diabetes-induced endothelial cell dysfunction and apoptosis in vivo. Likewise, STING inhibition by C-176 reversed HG-induced migration dysfunction and apoptosis in RAECs, whereas STING activation by DMXAA resulted in migration dysfunction and apoptosis. Mechanistically, hyperglycaemia-induced oxidative stress promoted endothelial mitochondrial dysfunction and mtDNA release, which subsequently activated the cGAS-STING system and the cGAS-STING-dependent IRF3/NF-kB pathway, ultimately resulting in inflammation and apoptosis. In conclusion, our study identified a novel role of STING in diabetes-induced aortic endothelial cell injury and suggested that STING inhibition was a potential new therapeutic strategy for the treatment of diabetic macroangiopathy. Video Abstract.

Copper and Diabetes: Current Research and Prospect

Copper is an essential trace metal for normal cellular functions; a lack of copper is reported to impair the function of important copper-binding enzymes, while excess copper could lead to cell death. Numerous studies have shown an association between dietary copper consumption or plasma copper levels and the incidence of diabetes/diabetes complications. And experimental studies have revealed multiple signaling pathways that are triggered by copper shortages or copper overload in diabetic conditions. Moreover, studies show that treated with copper chelators improve vascular function, maintain copper homeostasis, inhibit cuproptosis, and reduce cell toxicity, thereby alleviating diabetic neuropathy, retinopathy, nephropathy, and cardiomyopathy. However, the mechanisms reported in these studies are inconsistent or even contradictory. This review summarizes the precise and tight regulation of copper homeostasis processes, and discusses the latest progress in the association of diabetes and dietary copper/plasma copper. Further, the study pays close attention to the therapeutic potential of copper chelators and copper in diabetes and its complications, and hopes to provide new insight for the treatment of diabetes.

Endoplasmic reticulum stress: molecular mechanism and therapeutic targets

The endoplasmic reticulum (ER) functions as a quality-control organelle for protein homeostasis, or "proteostasis". The protein quality control systems involve ER-associated degradation, protein chaperons, and autophagy. ER stress is activated when proteostasis is broken with an accumulation of misfolded and unfolded proteins in the ER. ER stress activates an adaptive unfolded protein response to restore proteostasis by initiating protein kinase R-like ER kinase, activating transcription factor 6, and inositol requiring enzyme 1. ER stress is multifaceted, and acts on aspects at the epigenetic level, including transcription and protein processing. Accumulated data indicates its key role in protein homeostasis and other diverse functions involved in various ocular diseases, such as glaucoma, diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, achromatopsia, cataracts, ocular tumors, ocular surface diseases, and myopia. This review summarizes the molecular mechanisms underlying the aforementioned ocular diseases from an ER stress perspective. Drugs (chemicals, neurotrophic factors, and nanoparticles), gene therapy, and stem cell therapy are used to treat ocular diseases by alleviating ER stress. We delineate the advancement of therapy targeting ER stress to provide new treatment strategies for ocular diseases.

Spotlight on iron and ferroptosis: research progress in diabetic retinopathy

Iron, as the most abundant metallic element within the human organism, is an indispensable ion for sustaining life and assumes a pivotal role in governing glucose and lipid metabolism, along with orchestrating inflammatory responses. The presence of diabetes mellitus (DM) can induce aberrant iron accumulation within the corporeal system. Consequentially, iron overload precipitates a sequence of important adversities, subsequently setting in motion a domino effect wherein ferroptosis emerges as the utmost pernicious outcome. Ferroptosis, an emerging variant of non-apoptotic regulated cell death, operates independently of caspases and GSDMD. It distinguishes itself from alternative forms of controlled cell death through distinctive morphological and biochemical attributes. Its principal hallmark resides in the pathological accrual of intracellular iron and the concomitant generation of iron-driven lipid peroxides. Diabetic retinopathy (DR), established as the predominant cause of adult blindness, wields profound influence over the well-being and psychosocial strain experienced by afflicted individuals. Presently, an abundance of research endeavors has ascertained the pervasive engagement of iron and ferroptosis in the microangiopathy inherent to DR. Evidently, judicious management of iron overload and ferroptosis in the early stages of DR bears the potential to considerably decelerate disease progression. Within this discourse, we undertake a comprehensive exploration of the regulatory mechanisms governing iron homeostasis and ferroptosis. Furthermore, we expound upon the subsequent detriments induced by their dysregulation. Concurrently, we elucidate the intricate interplay linking iron overload, ferroptosis, and DR. Delving deeper, we engage in a comprehensive deliberation regarding strategies to modulate their influence, thereby effecting prospective interventions in the trajectory of DR's advancement or employing them as therapeutic modalities.

High glucose-induced endothelial STING activation inhibits diabetic wound healing through impairment of angiogenesis

Chronic hyperglycemia-induced impairment of angiogenesis is important in diabetic foot ulcer (DFU). Additionally, the stimulator of interferon gene (STING), which is a key protein in innate immunity, mediates palmitic acid-induced lipotoxicity in metabolic diseases through oxidative stress-induced STING activation. However, the role of STING in DFU is unknown. In this study, we established a DFU mouse model with streptozotocin (STZ) injection and found that the expression of STING was significantly increased in the vascular endothelial cells of wound tissues from diabetic patients and in the STZ-induced diabetic mouse model. We further established high glucose (HG)-induced endothelial dysfunction with rat vascular endothelial cells and found that the expression of STING was also increased by high-glucose treatment. Moreover, the STING inhibitor, C176, promoted diabetic wound healing, whereas the STING activator, DMXAA, inhibited diabetic wound healing. Consistently, STING inhibition reversed the HG-induced reduction of CD31 and vascular endothelial growth factor (VEGF), inhibited apoptosis, and promoted migration of endothelial cells. Notably, DMXAA treatment alone was sufficient to induce endothelial cell dysfunction as a high-glucose treatment. Mechanistically, STING mediated HG-induced vascular endothelial cell dysfunction by activating the interferon regulatory factor 3/nuclear factor kappa B pathway. In conclusion, our study reveals an endothelial STING activation-mediated molecular mechanism in the pathogenesis of DFU and identifies STING as a novel potential therapeutic target for DFU.

Association between Systemic Immunity-Inflammation Index and Hyperlipidemia: A Population-Based Study from the NHANES (2015-2020)

The systemic immunity-inflammation index (SII) is a novel inflammatory marker, and aberrant blood lipid levels are linked to inflammation. This study aimed to look at the probable link between SII and hyperlipidemia. The current cross-sectional investigation was carried out among people with complete SII and hyperlipidemia data from the 2015-2020 National Health and Nutrition Examination Survey (NHANES). SII was computed by dividing the platelet count × the neutrophil count/the lymphocyte count. The National Cholesterol Education Program standards were used to define hyperlipidemia. The nonlinear association between SII and hyperlipidemia was described using fitted smoothing curves and threshold effect analyses. A total of 6117 US adults were included in our study. A substantial positive correlation between SII and hyperlipidemia was found [1.03 (1.01, 1.05)] in a multivariate linear regression analysis. Age, sex, body mass index, smoking status, hypertension, and diabetes were not significantly correlated with this positive connection, according to subgroup analysis and interaction testing (p for interaction > 0.05). Additionally, we discovered a non-linear association between SII and hyperlipidemia with an inflection point of 479.15 using a two-segment linear regression model. Our findings suggest a significant association between SII levels and hyperlipidemia. More large-scale prospective studies are needed to investigate the role of SII in hyperlipidemia.