RIG-I inhibits pancreatic β cell proliferation through competitive binding of activated Src

Hepatocyte-specific RIG-I loss attenuates metabolic dysfunction-associated steatotic liver disease in mice via changes in mitochondrial respiration and metabolite profiles

Pattern recognition receptor (PRR)-mediated inflammation is an important determinant of the initiation and progression of metabolic diseases such as metabolic dysfunction-associated steatotic liver disease (MASLD). In this study, we investigated whether RIG-I is involved in hepatic metabolic reprogramming in a high-fat diet (HFD)-induced MASLD model in hepatocyte-specific RIG-I-KO (RIG-I∆hep) mice. Our study revealed that hepatic deficiency of RIG-I improved HFD-induced metabolic imbalances, including glucose impairment and insulin resistance. Hepatic steatosis and liver triglyceride levels were reduced in RIG-I-deficient hepatocytes in HFD-induced MASLD mice, and this was accompanied by the reduced expression of lipogenesis genes, such as PPARγ, Dga2, and Pck1. Hepatic RIG-I deficiency alters whole-body metabolic rates in the HFD-induced MASLD model; there is higher energy consumption in RIG-I∆hep mice. Deletion of RIG-I activated glycolysis and tricarboxylic acid (TCA) cycle-related metabolites in hepatocytes from both HFD-induced MASLD mice and methionine-choline-deficient diet (MCD)-fed mice. RIG-I deficiency enhanced AMPK activation and mitochondrial function in hepatocytes from HFD-induced MASLD mice. These findings indicate that deletion of RIG-I can activate cellular metabolism in hepatocytes by switching on both glycolysis and mitochondrial respiration, resulting in metabolic changes induced by a HFD and stimulation of mitochondrial activity. In summary, RIG-I may be a key regulator of cellular metabolism that influences the development of metabolic diseases such as MASLD.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-024-00264-x.

Role of the Innate Immune Response in Glomerular Disease Pathogenesis: Focus on Podocytes

Accumulating evidence indicates that inflammatory and immunologic processes play a significant role in the development and progression of glomerular diseases. Podocytes, the terminally differentiated epithelial cells, are crucial for maintaining the integrity of the glomerular filtration barrier. Once injured, podocytes cannot regenerate, leading to progressive proteinuric glomerular diseases. However, emerging evidence suggests that podocytes not only maintain the glomerular filtration barrier and are important targets of immune responses but also exhibit many features of immune-like cells, where they are involved in the modulation of the activity of innate and adaptive immunity. This dual role of podocytes may lead to the discovery and development of new therapeutic targets for treating glomerular diseases. This review aims to provide an overview of the innate immunity mechanisms involved in podocyte injury and the progression of proteinuric glomerular diseases.

RIG-I contributes to keratinocyte proliferation and wound repair by inducing TIMP-1 expression through NF-κB signaling pathway

Epithelial keratinocyte proliferation is an essential element of wound repair, and chronic wound conditions, such as diabetic foot, are characterized by aberrant re-epithelialization. In this study, we examined the functional role of retinoic acid inducible-gene I (RIG-I), a key regulator of epidermal keratinocyte proliferation, in promoting TIMP-1 expression. We found that RIG-I is overexpressed in keratinocytes of skin injury and underexpressed in skin wound sites of diabetic foot and streptozotocin-induced diabetic mice. Moreover, mice lacking RIG-I developed an aggravated phenotype when subjected to skin injury. Mechanistically, RIG-I promoted keratinocyte proliferation and wound repair by inducing TIMP-1 via the NF-κB signaling pathway. Indeed, recombinant TIMP-1 directly accelerated HaCaT cell proliferation in vitro and promoted wound healing in Ddx58-/- and diabetic mice in vivo. In summary, we demonstrated that RIG-I is a crucial factor that mediates epidermal keratinocyte proliferation and may be a potential biomarker for skin injury severity, thus making it an attractive locally therapeutic target for the treatment of chronic wounds such as diabetic foot.

Transcriptomics of rhinovirus persistence reveals sustained expression of RIG-I and interferon-stimulated genes in nasal epithelial cells in vitro

BACKGROUND

Human rhinoviruses (HRVs) are frequently associated with asthma exacerbations, and have been found in the airways of asthmatic patients. While HRV-induced acute infection is well-documented, it is less clear whether the nasal epithelium sustains prolonged HRV infections along with the associated activation of host immune responses.

OBJECTIVE

To investigate sustainably regulated host responses of human nasal epithelial cells (hNECs) during HRV persistence.

METHODS

Using a time-course study, HRV16 persistence and viral replication dynamics were established using an in vitro infection model of hNECs. RNA sequencing was performed on hNECs in the early and late stages of infection at 3 and 14 days post-infection (dpi), respectively. The functional enrichment of differentially expressed genes (DEGs) was evaluated using gene ontology (GO) and Ingenuity pathway analysis.

RESULTS

HRV RNA and protein expression persisted throughout prolonged infections, even after decreased production of infectious virus progeny. GO analysis of unique DEGs indicated altered regulation of pathways related to ciliary function and airway remodeling at 3 dpi and serine-type endopeptidase activity at 14 dpi. The functional enrichment of shared DEGs between the two time-points was related to interferon (IFN) and cytoplasmic pattern recognition receptor (PRR) signaling pathways. Validation of the sustained regulation of candidate genes confirmed the persistent expression of RIG-I and revealed its close co-regulation with interferon-stimulated genes (ISGs) during HRV persistence.

CONCLUSIONS

The persistence of HRV RNA does not necessarily indicate an active infection during prolonged infection. The sustained expression of RIG-I and ISGs in response to viral RNA persistence highlights the importance of assessing how immune-activating host factors can change during active HRV infection and the immune regulation that persists thereafter.

Morus alba L. (Sangzhi) Alkaloids Promote Insulin Secretion, Restore Diabetic β-Cell Function by Preventing Dedifferentiation and Apoptosis

Background:Morus alba L. (Sangzhi) alkaloids (SZ-A), extracted from the Chinese herb Morus alba L. (mulberry twig), have been shown to ameliorate hyperglycemia in type 2 diabetes and have been approved for diabetes treatment in the clinic. However, their versatile pharmacologic effects and regulatory mechanisms are not yet completely understood.

Purpose: This study explored the protective effects of SZ-A on islet β cells and the underlying mechanism.

Methods: Type 2 diabetic KKA^y mice were orally administered SZ-A (100 or 200 mg/kg, once daily) for 11 weeks, and oral glucose tolerance, insulin tolerance, intraperitoneal glucose tolerance and hyperglycemia clamp tests were carried out to evaluate the potency of SZ-A in vivo. The morphology and β-cell dedifferentiation marker of KKA^y mouse islets were detected via immunofluorescence. The effect of SZ-A on glucose-stimulated insulin secretion was investigated in both the islet β-cell line MIN6 and mouse primary islets. Potential regulatory signals and pathways in insulin secretion were explored, and cell proliferation assays and apoptosis TUNEL staining were performed on SZ-A-treated MIN6 cells.

Results: SZ-A alleviated hyperglycemia and glucose intolerance in type 2 diabetic KKA^y mice and improved the function and morphology of diabetic islets. In both MIN6 cells and primary islets, SZ-A promoted insulin secretion. At a normal glucose level, SZ-A decreased AMPKα phosphorylation, and at high glucose, SZ-A augmented the cytosolic calcium concentration. Additionally, SZ-A downregulated the β-cell dedifferentiation marker ALDH1A3 and upregulated β-cell identifying genes, such as Ins1, Ins2, Nkx2.2 and Pax4 in KKA^y mice islets. At the same time, SZ-A attenuated glucolipotoxicity-induced apoptosis in MIN6 cells, and inhibited Erk1/2 phosphorylation and caspase 3 activity. The major active fractions of SZ-A, namely DNJ, FAG and DAB, participated in the above regulatory effects.

Conclusion: Our findings suggest that SZ-A promotes insulin secretion in islet β cells and ameliorates β-cell dysfunction and mass reduction under diabetic conditions both in vivo and in vitro, providing additional supportive evidence for the clinical application of SZ-A.

RIG-I Deficiency Promotes Obesity-Induced Insulin Resistance

Inflammation and immunity are linked to the onset and development of obesity and metabolic disorders. Pattern recognition receptors (PRRs) are key regulators of inflammation and immunity in response to infection and stress, and they have critical roles in metainflammation. In this study, we investigated whether RIG-I (retinoic acid-inducible gene I)-like receptors were involved in the regulation of obesity-induced metabolic stress in RIG-I knockout (KO) mice fed a high-fat diet (HFD). RIG-I KO mice fed an HFD for 12 weeks showed greater body weight gain, higher fat composition, lower lean body mass, and higher epididymal white adipose tissue (eWAT) weight than WT mice fed HFD. In contrast, body weight gain, fat, and lean mass compositions, and eWAT weight of MDA5 (melanoma differentiation-associated protein 5) KO mice fed HFD were similar to those of WT mice fed a normal diet. RIG-I KO mice fed HFD exhibited more severely impaired glucose tolerance and higher HOMA-IR values than WT mice fed HFD. IFN-β expression induced by ER stress inducers, tunicamycin and thapsigargin, was abolished in RIG-I-deficient hepatocytes and macrophages, showing that RIG-I is required for ER stress-induced IFN-β expression. Our results show that RIG-I deficiency promotes obesity and insulin resistance induced by a high-fat diet, presenting a novel role of RIG-I in the development of obesity and metabolic disorders.

Pattern recognition receptor-mediated inflammation in diabetic vascular complications

The innate immune system contains multiple classes of pattern recognition receptors (PRRs), which recognize pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs) in the intracellular and extracellular space. Although PRRs are indispensable for the detection and clearance of invading pathogens, dysregulated PRR activation by extrinsic and intrinsic factors leads to inflammatory diseases. PRR-mediated inflammation has been shown to play a pivotal role in the pathogenesis of diabetic vascular complications (DVCs), which are the leading causes of morbidity and mortality in diabetic patients. Upon sensing hyperglycemia-generated DAMPs, PRRs activate intracellular signaling pathways leading to the production of proinflammatory cytokines and chemokines in various cells of the kidney, brain, eye, and heart. The resulting chronic, low-grade inflammation contributes to DVCs. In this review, we summarize the role of PRRs in DVCs including diabetic nephropathy, neuropathy, retinopathy, and cardiomyopathy. We propose that targeting PRRs and associated signaling pathways may be beneficial for the management of DVCs.

Mechanisms of the Regulation and Dysregulation of Glucagon Secretion

Glucagon, a hormone secreted by pancreatic alpha cells, contributes to the maintenance of normal blood glucose concentration by inducing hepatic glucose production in response to declining blood glucose. However, glucagon hypersecretion contributes to the pathogenesis of type 2 diabetes. Moreover, diabetes is associated with relative glucagon undersecretion at low blood glucose and oversecretion at normal and high blood glucose. The mechanisms of such alpha cell dysfunctions are not well understood. This article reviews the genesis of alpha cell dysfunctions during the pathogenesis of type 2 diabetes and after the onset of type 1 and type 2 diabetes. It unravels a signaling pathway that contributes to glucose- or hydrogen peroxide-induced glucagon secretion, whose overstimulation contributes to glucagon dysregulation, partly through oxidative stress and reduced ATP synthesis. The signaling pathway involves phosphatidylinositol-3-kinase, protein kinase B, protein kinase C delta, non-receptor tyrosine kinase Src, and phospholipase C gamma-1. This knowledge will be useful in the design of new antidiabetic agents or regimens.

Underlying Mechanism of Insulin Resistance: A Bioinformatics Analysis Based on Validated Related-Genes from Public Disease Databases

Background

The underlying mechanism of insulin resistance is complex; bioinformatics analysis is used to explore the mechanism based differential expression genes (DEGs) obtained from omics analysis. However, the expression and role of most DEGs involved in bioinformatics analysis are invalidated. This study aimed to disclose the mechanism of insulin resistance via bioinformatics analysis based on validated insulin resistance-related genes (IRRGs) collected from public disease-gene databases.

Material/Methods

IRRGs were collected from 4 disease databases including NCBI-Gene, CTD, RGD, and Phenopedia. GO and KEGG analysis of IRRGs were performed by DAVID. Then, the STRING database was employed to construct a protein–protein interaction (PPI) network of IRRGs. The module analysis and hub genes identification were carried out by MCODE and cytoHubba plugin of Cytoscape based on the primary PPI network, respectively.

Results

A total of 1195 IRRGs were identified. Response to drug, hypoxia, insulin, positive regulation of transcription from RNA polymerase II promoter, cell proliferation, inflammatory response, negative regulation of apoptotic process, glucose homeostasis, cellular response to insulin stimulus, and aging were proposed as the crucial functions related to insulin resistance. Ten insulin resistance-related pathways included the pathways of insulin resistance, pathways in cancer, adipocytokine, prostate cancer, PI3K-Akt, insulin, AMPK, HIF-1, prolactin, and pancreatic cancer signaling pathway were revealed. INS, AKT1, IL-6, TP53, TNF, VEGFA, MAPK3, EGFR, EGF, and SRC were identified as the top 10 hub genes.

Conclusions

The current study presented a landscape view of possible underlying mechanism of insulin resistance by bioinformatics analysis based on validated IRRGs.

Innate Viral Sensor MDA5 and Coxsackievirus Interplay in Type 1 Diabetes Development

Type 1 diabetes (T1D) is a polygenic autoimmune disease characterized by immune-mediated destruction of insulin-producing β-cells. The concordance rate for T1D in monozygotic twins is ≈30-50%, indicating that environmental factors also play a role in T1D development. Previous studies have demonstrated that enterovirus infections such as coxsackievirus type B (CVB) are associated with triggering T1D. Prior to autoantibody development in T1D, viral RNA and antibodies against CVB can be detected within the blood, stool, and pancreata. An innate pathogen recognition receptor, melanoma differentiation-associated protein 5 (MDA5), which is encoded by the IFIH1 gene, has been associated with T1D onset. It is unclear how single nucleotide polymorphisms in IFIH1 alter the structure and function of MDA5 that may lead to exacerbated antiviral responses contributing to increased T1D-susceptibility. Binding of viral dsRNA via MDA5 induces synthesis of antiviral proteins such as interferon-alpha and -beta (IFN-α/β). Viral infection and subsequent IFN-α/β synthesis can lead to ER stress within insulin-producing β-cells causing neo-epitope generation, activation of β-cell-specific autoreactive T cells, and β-cell destruction. Therefore, an interplay between genetics, enteroviral infections, and antiviral responses may be critical for T1D development.

Melanoma Differentiation-Associated Gene 5 Positively Modulates TNF-α-Induced CXCL10 Expression in Cultured HuH-7 and HLE Cells

The molecular mechanisms of innate immunity are closely associated with the development of non-alcoholic fatty liver disease (NAFLD). TNF-α is a key cytokine involved in the pathogenesis of metabolic inflammation like NAFLD. Melanoma differentiation-associated gene 5 (MDA5) is a member of the intracellular RNA helicase family proteins that play a pivotal role in an antiviral immune response. Previous studies have demonstrated that TNF-α induces the expression of MDA5 in some types of cells. However, the correlation between TNF-α and the expression of MDA5 in hepatocytes remains unknown. In the present study, we used two human hepatocellular carcinoma cell lines, HuH-7 and HLE, and examined the expression of MDA5 in these cells upon stimulation with TNF-α. The expression of MDA5 induced by TNF-α was analyzed by quantitative real-time RT-PCR and western blotting. Next, RNA interference against MDA5 was performed and the expressions of CXCL10 and STAT1 were examined. We found that the expression of MDA5 had increased upon stimulation with TNF-α in a concentration-dependent manner. Gene silencing against MDA5 suppressed the expression of TNF-α-induced CXCL10 in both cells. In HLE cells, gene silencing of MDA5 impaired STAT1 phosphorylation 24 h after stimulation with TNF-α. On the other hand, TNF-α-induced STAT1 phosphorylation was not detected in HuH-7 cells. These results indicated that MDA5 positively modulated the TNF-α-induced expression of CXCL10 in both STAT1-dependent and -independent manner and may be associated with metabolic inflammation in the liver.

CD36 dependent redoxosomes promotes ceramide-mediated pancreatic β-cell failure via p66Shc activation

Altered metabolism is implicated in the pathogenesis of beta-cell failure in type 2 diabetes (T2D). Plasma and tissue levels of ceramide species play positive roles in inflammatory and oxidative stress responses in T2D. However, oxidative targets and mechanisms underlying ceramide signaling are unclear. We investigated the role of CD36-dependent redoxosome (redox-active endosome), a membrane-based signaling agent, in ceramide-induced beta-cell dysfunction and failure. Exposure of beta cells to C2-ceramide (N-acetyl-sphingosine) induced a CD36-dependent non-receptor tyrosine kinase Src-mediated redoxosome (Vav2-Rac1-NOX) formation. Activated Rac1-GTP-NADPH oxidase complex induced c-Jun-N-terminal kinase (JNK) activation and nuclear factor (NF)-kB transcription, which was associated with thioredoxin-interacting protein (TXNIP) upregulation and thioredoxin activity suppression. Upregulated JNK expression induced p66Shc serine36 phosphorylation and peroxiredoxin-3 hyperoxidation, causing beta-cell apoptosis via mitochondrial dysfunction. CD36 inhibition by sulfo-N-succinimidyl oleate (SSO) or CD36 siRNA blocked C2-ceramide-induced redoxosome activation, thereby decreasing JNK-dependent p66Shc serine36 phosphorylation. CD36 inhibition downregulated TXNIP expression and promoted thioredoxin activity via enhanced thioredoxin reductase activity, which prevented peroxiredoxin-3 oxidation. CD36 inhibition potentiated glucose-stimulated insulin secretion and prevented beta-cell apoptosis. Our results reveal a new role of CD36 during early molecular events that lead to Src-mediated redoxosome activation, which contributes to ceramide-induced pancreatic beta-cell dysfunction and failure.

Long non-coding RNA XLOC_006390 promotes cervical cancer proliferation and metastasis through the regulation of SET domain containing 8

The long non-coding RNA (lncRNA) XLOC_006390 is increased in various human cancer tissues and it plays important roles in cell growth and migration. However, the role of lncRNA XLOC_006390 in the progression and metastasis of cervical cancer has not been evaluated and remains unclear. In the present study, we hypothesized that lncRNA XLOC_006390 is also increased in cervical cancer, and upregulation of lncRNA XLOC_006390 contributes to cervical cancer metastasis. The expression of lncRNA XLOC_006390 in cervical cancer tissues and cell lines was analyzed using quantitative reverse-transcription-polymerase chain reaction (qRT-PCR). RNA interference approach and an overexpression system were used to investigate the cellular functions of XLOC_006390 and SET domain containing 8 (SET8). Cell Counting Kit-8 (CCK-8) assay was performed to detect cell proliferation. Cell migration and invasion abilities were evaluated by Transwell assays. Western blotting and immunofluorescence were performed to detect SET8 protein expression. The results revealed that XLOC_006390 was increased in cervical cancer tissues. Patients with high XLOC_006390 expression were associated with FIGO stages III and IV (P=0.0170), lymphatic metastasis (P=0.0078) and distant metastasis (P=0.0025). Furthermore, SET8 was also increased in cervical cancer tissues and its expression was positively associated with XLOC_006390, and XLOC_006390 regulated SET8 expression. In addition, knockdown or overexpression of XLOC_006390 and SET8 expression suppressed or promoted cervical cancer cell proliferation, migration and invasion in vitro, respectively. In conclusion, our data suggest that lncRNA XLOC_006390 promotes cervical cancer cell growth and metastasis through the regulation of SET8, at least partly, which indicate the critical roles of XLOC_006390 and SET8 in cervical cancer progression and metastasis.

An Activating Mutation in STAT3 Results in Neonatal Diabetes Through Reduced Insulin Synthesis

Neonatal diabetes mellitus (NDM) is a rare form of diabetes diagnosed within the first 6 months of life. Genetic studies have allowed the identification of several genes linked to the development of NDM; however, genetic causes for ∼20% of the cases remain to be clarified. Most cases of NDM involve isolated diabetes, but sometimes NDM appears in association with other pathological conditions, including autoimmune diseases. Recent reports have linked activating mutations in STAT3 with early-onset autoimmune disorders that include diabetes of autoimmune origin, but the functional impact of STAT3-activating mutations have not been characterized at the pancreatic β-cell level. By using whole-exome sequencing, we identified a novel missense mutation in the binding domain of the STAT3 protein in a patient with NDM. The functional analyses showed that the mutation results in an aberrant activation of STAT3, leading to deleterious downstream effects in pancreatic β-cells. The identified mutation leads to hyperinhibition of the transcription factor Isl-1 and, consequently, to a decrease in insulin expression. These findings represent the first functional indication of a direct link between an NDM-linked activating mutation in STAT3 and pancreatic β-cell dysfunction.

Metainflammation in Diabetic Coronary Artery Disease: Emerging Role of Innate and Adaptive Immune Responses

Globally, noncommunicable chronic diseases such as Type-2 Diabetes Mellitus (T2DM) and Coronary Artery Disease (CAD) are posing a major threat to the world. T2DM is known to potentiate CAD which had led to the coining of a new clinical entity named diabetic CAD (DM-CAD), leading to excessive morbidity and mortality. The synergistic interaction between these two comorbidities is through sterile inflammation which is now being addressed as metabolic inflammation or metainflammation, which plays a pivotal role during both early and late stages of T2DM and also serves as a link between T2DM and CAD. This review summarises the current concepts on the role played by both innate and adaptive immune responses in setting up metainflammation in DM-CAD. More specifically, the role played by innate pattern recognition receptors (PRRs) like Toll-like receptors (TLRs), NOD1-like receptors (NLRs), Rig-1-like receptors (RLRs), and C-type lectin like receptors (CLRs) and metabolic endotoxemia in fuelling metainflammation in DM-CAD would be discussed. Further, the role played by adaptive immune cells (Th1, Th2, Th17, and Th9 cells) in fuelling metainflammation in DM-CAD will also be discussed.