SIRT1/HSF1/HSP pathway is essential for exenatide-alleviated, lipid-induced hepatic endoplasmic reticulum stress

Glucagon-Like Peptide-1: New Regulator in Lipid Metabolism

Glucagon-like peptide-1 (GLP-1) is a 30-amino acid peptide hormone that is mainly expressed in the intestine and hypothalamus. In recent years, basic and clinical studies have shown that GLP-1 is closely related to lipid metabolism, and it can participate in lipid metabolism by inhibiting fat synthesis, promoting fat differentiation, enhancing cholesterol metabolism, and promoting adipose browning. GLP-1 plays a key role in the occurrence and development of metabolic diseases such as obesity, nonalcoholic fatty liver disease, and atherosclerosis by regulating lipid metabolism. It is expected to become a new target for the treatment of metabolic disorders. The effects of GLP-1 and dual agonists on lipid metabolism also provide a more complete treatment plan for metabolic diseases. This article reviews the recent research progress of GLP-1 in lipid metabolism.

SIRT1 regulates endoplasmic reticulum stress-related organ damage

Endoplasmic reticulum (ER) stress plays a key role in the pathogenesis of several organ damages. Studies show that excessive ER stress (ERS) can destroy cellular homeostasis, causing cell damage and physiological dysfunction in various organs. In recent years, Sirtuin1 (SIRT1) has become a research hotspot on ERS. Increasing evidence suggests that SIRT1 plays a positive role in various ERS-induced organ damage via multiple mechanisms, including inhibiting cellular apoptosis and promoting autophagy. SIRT1 can also alleviate liver, heart, lung, kidney, and intestinal damage by inhibiting ERS. We discuss the possible mechanism of SIRT1, explore potential therapeutic targets of diseases, and provide a theoretical basis for treating ERS-related diseases.

GLP-1/GLP-1RAs: New Options for the Drug Treatment of NAFLD

Non-alcoholic fatty liver disease (NAFLD) has recently emerged as a global public health concern. Currently, the cornerstone of NAFLD treatment is lifestyle modification and, if necessary, weight loss. However, compliance is a challenge, and this approach alone may not be sufficient to halt and treat the more serious disease development, so medication is urgently needed. Nevertheless, no medicines are approved to treat NAFLD. Glucagon-like peptide-1 (GLP-1) is an enteropeptide hormone that inhibits glucagon synthesis, promotes insulin secretion, and delays gastric emptying. GLP-1 has been found in recent studies to be beneficial for the management of NAFLD, and the marketed GLP-1 agonist drugs have different degrees of effectiveness for NAFLD while lowering blood glucose. In this article, we review GLP-1 and its physiological roles, the pathogenesis of NAFLD, the correlation between NAFLD and GLP-1 signaling, and potential strategies for GLP-1 treatment of NAFLD.

A crosstalk between epigenetic modulations and non-alcoholic fatty liver disease progression

Non-alcoholic fatty liver disease (NAFLD) has recently emerged as a major public health concern worldwide due to its rapidly rising prevalence and its potential to progress into end-stage liver disease. While the precise pathophysiology underlying NAFLD remains incompletely understood, it is strongly associated with various environmental triggers and other metabolic disorders. Epigenetics examines changes in gene expression that are not caused by alterations in the DNA sequence itself. There is accumulating evidence that epigenetics plays a key role in linking environmental cues to the onset and progression of NAFLD. Our understanding of how epigenetic mechanisms contribute to NAFLD pathophysiology has expanded considerably in recent years as research on the epigenetics of NAFLD has developed. This review summarizes recent insights into major epigenetic processes that have been implicated in NAFLD pathogenesis including DNA methylation, histone acetylation, and microRNAs that have emerged as promising targets for further investigation. Elucidating epigenetic mechanisms in NAFLD may uncover novel diagnostic biomarkers and therapeutic targets for this disease. However, many questions have remained unanswered regarding how epigenetics promotes NAFLD onset and progression. Additional studies are needed to further characterize the epigenetic landscape of NAFLD and validate the potential of epigenetic markers as clinical tools. Nevertheless, an enhanced understanding of the epigenetic underpinnings of NAFLD promises to provide key insights into disease mechanisms and pave the way for novel prognostic and therapeutic approaches.

Pioglitazone-Enhanced Brown Fat Whitening Contributes to Weight Gain in Diet-Induced Obese Mice

INTRODUCTION

Pioglitazone is an insulin sensitizer used for the treatment of type 2 diabetes mellitus (T2DM) by activating peroxisome proliferator-activated receptor gamma. This study aimed to investigate the effects of pioglitazone on white adipose tissue (WAT) and brown adipose tissue (BAT) in diet-induced obese (DIO) mice.

METHODS

C57BL/6 mice were treated with pioglitazone (30 mg/kg/day) for 4 weeks after a 16-week high-fat diet (HFD) challenge. Body weight gain, body fat mass, energy intake, and glucose homeostasis were measured during or after the treatment. Histopathology was observed by hematoxylin and eosin, oil red O, immunohistochemistry, and immunofluorescence staining. Expression of thermogenic and mitochondrial biogenesis-related genes was detected by quantitative real-time PCR and western blotting.

RESULTS

After 4-week pioglitazone treatment, the fasting blood glucose levels, glucose tolerance, and insulin sensitivity were significantly improved, but the body weight gain and fat mass were increased in DIO mice. Compared with the HFD group, pioglitazone did not significantly affect the weights of liver and WAT in both subcutaneous and epididymal regions. Unexpectedly, the weight of BAT was increased after pioglitazone treatment. Histological staining revealed that pioglitazone ameliorated hepatic steatosis, reduced the adipocyte size in WAT, but increased the adipocyte size in BAT.

CONCLUSION

Though pioglitazone can promote lipolysis, thermogenesis, and mitochondrial function in WAT, it leads to impaired thermogenesis, and mitochondrial dysfunction in BAT. In conclusion, pioglitazone could promote the browning of WAT but led to the whitening of BAT; the latter might be a new potential mechanism of pioglitazone-induced weight gain during T2DM treatment.

SIRT1-dependent deacetylation of Txnip H3K9ac is critical for exenatide-improved diabetic kidney disease

Glucagon-like peptide 1 receptor agonist exenatide (exendin-4) has potential protective capabilities against diabetic kidney disease (DKD). However, the underlying mechanism has not been fully elucidated. The expression of thioredoxin-interacting protein (Txnip) is upregulated during DKD progression by histone acetylation. Sirtuin 1 (SIRT1) is a deacetylase and is decreased in DKD, which indicates that it may regulate Txnip in this disease. Here, we used whole-body heterozygous Sirt1 knockout (Sirt1+/-) and kidney-specific Sirt1 knockout (KSK) mice to investigate whether SIRT1 regulates Txnip via histone deacetylation in DKD and exenatide-alleviated DKD. Exenatide substantially improved renal pathological damage, decreased the albumin-to-creatinine ratio (ACR), upregulated SIRT1 expression, and downregulated Txnip expression in kidneys of high-fat diet-treated C57BL/6J mice. However, these effects diminished in Sirt1+/- and KSK mice under exenatide treatment. The downregulation of Txnip expression by exendin-4 in high-glucose-treated SV40 MES13 cells was hampered during Sirt1 knockdown. These results demonstrate that kidney SIRT1 is indispensable in exenatide-improved DKD and downregulation of Txnip expression. Exendin-4 mechanistically downregulated Txnip histone 3 lysine 9 acetylation (H3K9ac) in a SIRT1-dependent manner and decreased spliced X-box binding protein 1 (XBP1s) recruitment to the Txnip promoter. These findings provide epigenetic evidence elucidating the specific mechanism for exenatide-mediated DKD alleviation and highlight the importance of Txnip as a promising therapeutic target for DKD.

Toxic effects of copper on duck cerebrum: a crucial role of oxidative stress and endoplasmic reticulum quality control

To study the effects of Cu overload on ER quality control in duck cerebrums, 144 ducks were treated with 8 mg/kg, 100 mg/kg, 200 mg/kg and 400 mg/kg Cu added in the feed for 45 days. From histopathological examination, we found that excessive Cu increased the amount of microglia and disintegrated neuron, decreased the number of Nissl bodies, perturbed nerve fibers in duck cerebrums. Cu poisoning also increased Cu, H2O2, T-SOD, and MDA levels, decreased Fe and CAT contents in duck cerebrums. Furthermore, Cu treatment upregulated the mRNA levels of the unfolded protein response genes (PERK, ATF6, and IRE1), ER-associated degradation genes (CNX, Derlin1, and Derlin2), autophagy genes (ATG5, ATG7, ATG10, Beclin1, LC3A, LC3B, and P62), and heat shock response genes (Hsp70 and Hsp90) in duck cerebrums; elevated the protein levels of p-PERK, CNX, SEL1L, Beclin1, P62, and LC3BII/LC3BI in duck cerebrums; increased the numbers of SEL1L and LC3B puncta in duck cerebrums. Thus, our data showed that excessive Cu could cause histopathological damage to duck cerebrums, disrupt the balance of the trace elements, induce oxidative stress and activation of ER quality control, thereby resulting in duck cerebrums damage.

Resveratrol‑mediated activation of SIRT1 inhibits the PERK‑eIF2α‑ATF4 pathway and mitigates bupivacaine‑induced neurotoxicity in PC12 cells

Endoplasmic reticulum (ER) stress and apoptosis play significant roles in the development of neurotoxicity caused by bupivacaine (BUP). By activating sirtuin 1 (SIRT1), resveratrol (RSV) can regulate various cellular processes associated with anti-oxidative stress, anti-apoptosis and anti-inflammatory responses, thereby exerting neuroprotective effects. However, it remains unknown whether the activation of SIRT1 by RSV is able to attenuate BUP-induced ER stress and apoptosis. Therefore, the present study aimed to explore the effect of RSV on BUP-induced cytotoxicity in PC12 cells and the underlying mechanism. Cell Counting Kit-8 assays, flow cytometry and inverted phase-contrast microscopy were used to assess the viability, apoptosis rate and morphological changes of the cells, respectively. Western blotting and immunofluorescence staining were used to analyze the levels of SIRT1, the apoptosis-related proteins Bax, Bcl-2 and cleaved caspase-3, the ER stress-related proteins glucose-regulated protein 78, caspase-12 and CHOP, and the protein kinase RNA-like ER kinase (PERK)-eukaryotic translation initiation factor 2 α (eIF2α)-activating transcription factor 4 (ATF4) pathway-associated proteins phosphorylated (p)-PERK, PERK, p-eIF2α, eIF2α and ATF4. The results revealed that BUP induced cell apoptosis and decreased cell viability, accompanied by the downregulation of SIRT1. However, RSV restored SIRT1 protein expression, downregulated the expression of the pro-apoptotic protein Bax, upregulated the expression of the anti-apoptotic protein Bcl-2, decreased the apoptosis rate of the cells and increased cell viability. Furthermore, the anti-apoptotic effects exhibited by RSV were associated with inhibition of the PERK-eIF2α-ATF4 pathway of ER stress. However, the protective effect of RSV was significantly mitigated by the SIRT1 inhibitor EX527. These results indicate that the activation of SIRT1 by RSV alleviates BUP-induced PC12 cell ER stress and apoptosis via regulation of the PERK-eIF2α-ATF4 pathway. These findings offer insights into the molecular mechanism underlying BUP-induced apoptosis and suggest the potential of RSV as a therapeutic agent against the neurotoxicity caused by BUP.

Targeting protein modifications in metabolic diseases: molecular mechanisms and targeted therapies

The ever-increasing prevalence of noncommunicable diseases (NCDs) represents a major public health burden worldwide. The most common form of NCD is metabolic diseases, which affect people of all ages and usually manifest their pathobiology through life-threatening cardiovascular complications. A comprehensive understanding of the pathobiology of metabolic diseases will generate novel targets for improved therapies across the common metabolic spectrum. Protein posttranslational modification (PTM) is an important term that refers to biochemical modification of specific amino acid residues in target proteins, which immensely increases the functional diversity of the proteome. The range of PTMs includes phosphorylation, acetylation, methylation, ubiquitination, SUMOylation, neddylation, glycosylation, palmitoylation, myristoylation, prenylation, cholesterylation, glutathionylation, S-nitrosylation, sulfhydration, citrullination, ADP ribosylation, and several novel PTMs. Here, we offer a comprehensive review of PTMs and their roles in common metabolic diseases and pathological consequences, including diabetes, obesity, fatty liver diseases, hyperlipidemia, and atherosclerosis. Building upon this framework, we afford a through description of proteins and pathways involved in metabolic diseases by focusing on PTM-based protein modifications, showcase the pharmaceutical intervention of PTMs in preclinical studies and clinical trials, and offer future perspectives. Fundamental research defining the mechanisms whereby PTMs of proteins regulate metabolic diseases will open new avenues for therapeutic intervention.

Malonylation of Acetyl-CoA carboxylase 1 promotes hepatic steatosis and is attenuated by ketogenic diet in NAFLD

Protein post-translational modifications (PTMs) participate in important bioactive regulatory processes and therefore can help elucidate the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Here, we investigate the involvement of PTMs in ketogenic diet (KD)-improved fatty liver by multi-omics and reveal a core target of lysine malonylation, acetyl-coenzyme A (CoA) carboxylase 1 (ACC1). ACC1 protein levels and Lys1523 malonylation are significantly decreased by KD. A malonylation-mimic mutant of ACC1 increases its enzyme activity and stability to promote hepatic steatosis, whereas the malonylation-null mutant upregulates the ubiquitination degradation of ACC1. A customized Lys1523ACC1 malonylation antibody confirms the increased malonylation of ACC1 in the NAFLD samples. Overall, the lysine malonylation of ACC1 is attenuated by KD in NAFLD and plays an important role in promoting hepatic steatosis. Malonylation is critical for ACC1 activity and stability, highlighting the anti-malonylation effect of ACC1 as a potential strategy for treating NAFLD.

SIK2 protects against renal tubular injury and the progression of diabetic kidney disease

Despite optimal medical therapy, many patients with diabetic kidney disease (DKD) progress to end-stage renal disease. The identification of new biomarkers and drug targets for DKD is required for the development of more effective therapies. The apoptosis of renal tubular epithelial cells is a key feature of the pathogenicity associated with DKD. SIK2, a salt-inducible kinase, regulates important biological processes, such as energy metabolism, cell cycle progression and cellular apoptosis. In our current study, a notable decrease in the expression of SIK2 was detected in the renal tubules of DKD patients and murine models. Functional experiments demonstrated that deficiency or inactivity of SIK2 aggravates tubular injury and interstitial fibrosis in diabetic mice. Based on transcriptome sequencing, molecular mechanism exploration revealed that SIK2 overexpression reduces endoplasmic reticulum (ER) stress-mediated tubular epithelial apoptosis by inhibiting the histone acetyltransferase activity of p300 to activate HSF1/Hsp70. Furthermore, the specific restoration of SIK2 in tubules blunts tubular and interstitial impairments in diabetic and vancomycin-induced kidney disease mice. Together, these findings indicate that SIK2 protects against renal tubular injury and the progression of kidney disease, and make a compelling case for targeting SIK2 for therapy in DKD.

Emerging role of aging in the progression of NAFLD to HCC

With the aging of global population, the incidence of nonalcoholic fatty liver disease (NAFLD) has surged in recent decades. NAFLD is a multifactorial disease that follows a progressive course, ranging from simple fatty liver, nonalcoholic steatohepatitis (NASH) to liver cirrhosis and hepatocellular carcinoma (HCC). It is well established that aging induces pathological changes in liver and potentiates the occurrence and progression of NAFLD, HCC and other age-related liver diseases. Studies of senescent cells also indicate a pivotal engagement in the development of NAFLD via diverse mechanisms. Moreover, nicotinamide adenine dinucleotide (NAD⁺), silence information regulator protein family (sirtuins), and mechanistic target of rapamycin (mTOR) are three vital and broadly studied targets involved in aging process and NAFLD. Nevertheless, the crucial role of these aging-associated factors in aging-related NAFLD remains underestimated. Here, we reviewed the current research on the roles of aging, cellular senescence and three aging-related factors in the evolution of NAFLD to HCC, aiming at inspiring promising therapeutic targets for aging-related NAFLD and its progression.

Nutri-stress, mitochondrial dysfunction, and insulin resistance-role of heat shock proteins

Excess nutrient flux into the cellular energy system results in a scenario of cellular metabolic stress in diseases involving insulin resistance, such as type 2 diabetes, referred to as nutri-stress and results in cellular bioenergetic imbalance, which leads to insulin resistance and disease. Under nutri-stress, the heat shock response system is compromised due to metabolic abnormalities that disturb energy homeostasis. Heat shock proteins (HSPs) are the chief protectors of intracellular homeostasis during stress. Heat shock response (HSR) impairment contributes to several metabolic pathways that aggravate chronic hyperglycaemia and insulin resistance, highlighting a central role in disease pathogenesis. This article discusses the role of nutri-stress-related molecular events in causing insulin resistance and the nature of the roles played by heat shock proteins in some of the crucial checkpoints of the molecular networks involved in insulin resistance. Ample evidence suggests that the heat shock machinery regulates critical pathways in mitochondrial function and energy metabolism and that cellular energy status highly influences it. Weakening of HSPs, therefore, leads to loss of their vital cytoprotective functions, propagating nutri-stress in the system. Further research into the mechanistic roles of HSPs in metabolic homeostasis will help widen our understanding of lifestyle diseases, their onset, and complications. These inducible proteins may be crucial to attenuating lifestyle risk factors and disease management.

Integrating Network Pharmacology and Transcriptomic Strategies to Explore the Pharmacological Mechanism of Hydroxysafflor Yellow A in Delaying Liver Aging

Aging affects the structure and function of the liver. Hydroxysafflor yellow A (HSYA) effectively improves liver aging (LA) in mice, but the potential mechanisms require further exploration. In this study, an integrated approach combining network pharmacology and transcriptomics was used to elucidate the potential mechanisms of HSYA delay of LA. The targets of HSYA were predicted using the PharmMapper, SwissTargetPrediction, and CTD databases, and the targets of LA were collected from the GeneCards database. An ontology (GO) analysis and a Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotation of genes related to HSYA delay of LA were performed using the DAVID database, and Cytoscape software was used to construct an HSYA target pathway network. The BMKCloud platform was used to sequence mRNA from mouse liver tissue, screen differentially expressed genes (DEGs) that were altered by HSYA, and enrich their biological functions and signaling pathways through the OmicShare database. The results of the network pharmacology and transcriptomic analyses were combined. Then, quantitative real-time PCR (qRT-PCR) and Western blot experiments were used to further verify the prediction results. Finally, the interactions between HSYA and key targets were assessed by molecular docking. The results showed that 199 potentially targeted genes according to network pharmacology and 480 DEGs according to transcriptomics were involved in the effects of HSYA against LA. An integrated analysis revealed that four key targets, including HSP90AA1, ATP2A1, NOS1 and CRAT, as well as their three related pathways (the calcium signaling pathway, estrogen signaling pathway and cGMP-PKG signaling pathway), were closely related to the therapeutic effects of HSYA. A gene and protein expression analysis revealed that HSYA significantly inhibited the expressions of HSP90AA1, ATP2A1 and NOS1 in the liver tissue of aging mice. The molecular docking results showed that HSYA had high affinities with the HSP90AA1, ATP2A1 and NOS1 targets. Our data demonstrate that HSYA may delay LA in mice by inhibiting the expressions of HSP90AA1, ATP2A1 and NOS1 and regulating the calcium signaling pathway, the estrogen signaling pathway, and the cGMP-PKG signaling pathway.

The Value of SIRT1/FOXO1 Signaling Pathway in Early Detection of Cardiovascular Risk in Children with β-Thalassemia Major

Background: Atherosclerosis represents one of the major causes of morbidity in children with β-thalassemia major (β-TM). Aim: This study was designed to investigate SIRT1-FOXO1 signaling in β-TM children and their role in early detection of premature atherosclerosis. Methods: We equally subdivided 100 Egyptian children aged 6−14 years with β-TM according to carotid intima media thickness (CIMT) into 50 with CIMT < 0.5 mm and 50 with CIMT ≥ 0.5 mm, and 50 healthy children of matched age were included. They were subjected to evaluation of SIRT1, heat shock protein 72 (HSP72), and hepcidin levels via ELISA and forkhead box protein 1 (FOXO1) mRNA expression using real-time PCR in PBMCs; meanwhile, malondialdehyde (MDA), superoxide dismutase (SOD), and catalase activities were evaluated spectrophotometrically. Results: Our results show significantly high values for CIMT, β-stiffness, atherogenic index of plasma (AIP), MDA, HSP72 and FOXO1, ferritin with significantly low hepcidin, SOD, catalase, and SIRT1 in β-TM as compared to controls with a more significant difference in β-TM with CIMT ≥ 0.5 mm than those with CIMT < 0.5 mm. A significant positive correlation between CIMT and MDA, HSP72, and FOXO1 gene expression was found, while a significant negative correlation with hepcidin, SOD, catalase, and SIRT1 was found. FOXO1 gene expression and HSP72 levels were the strongest independent determinants of CIMT. Conclusion: In β-TM, FOXO1 signaling is activated with low levels of SIRT1, and this is attributed to accelerated atherosclerosis in β-TM, which would be crucial in prediction of atherosclerosis.

Trichloroethylene induces immune renal tubular injury through SIRT 1/HSP 70/TLR 4 pathway in BALBc mice

Trichloroethylene (TCE) is a volatile chlorinated solvent widely used for cleaning and degreasing industrial metal parts. Due to the widespread use and improper disposal of TCE, exposure to TCE causes a variety of adverse effects on human and animal health. However, the underlying mechanism of the damage remains unclear. The purpose of this study is to investigate the role of Sirtuin-1 (SIRT 1) in TCE-induced immune renal tubular injury. 6-8-week-old female BALB/c mice were used to construct a TCE sensitized mouse model. SIRT 1 activator, SRT 1720 (0.1 ml, 5 mg/kg) and toll like receptor 4 (TLR 4) inhibitor, TAK-242 (0.1 ml, 3 mg/kg) were used for treatment. Results show that SIRT 1 and heat shock protein 70 (HSP 70) levels are significantly down-regulated in renal tubules, serum and urine HSP 70 levels are significantly increased, and inflammatory cytokines levels are significantly increased in renal tubules in TCE-sensitized positive mice. After SRT 1720 treatment, intracellular HSP 70 level is significantly increased and extracellular HSP 70 level is decreased, and inflammatory cytokines levels get alleviated. In addition, HSP 70 and Toll-like Receptor 4 (TLR 4) proteins exist an interaction that can be significantly attenuated by SIRT 1. Subsequently, inflammation of the renal tubules mediated by SIRT 1 downregulation is attenuated after TAK-242 treatment. In conclusion, SIRT 1 alleviates renal tubular epithelial cells immune injury by inhibiting the release of HSP 70 and thereby weakening interaction with HSP 70 and TLR 4.

SIRT1 mediates nutritional regulation of SREBP-1c-driven hepatic PNPLA3 transcription via modulation of H3k9 acetylation

Background

Patatin-like phospholipase domain containing 3 (PNPLA3) is the main nonalcoholic fatty liver disease (NAFLD) susceptibility. Its expression is regulated tightly by nutritional and energy status, but the mechanism of epigenetic regulation of PNPLA3 gene by nutritional dietary factors has not been reported. Here, we investigated the effect and mechanism of Sirtuin 1 (SIRT1) regulated H3K9 deacetylation on PNPLA3 transcriptional expression in vivo and in vitro.

Methods

Mouse models of fasting/re-feeding transition and nonalcoholic fatty liver induced by high Sucrose diet were constructed; and HepG2 cells were treated with serum- and glucose-free medium or exposed to high glucose and high insulin, to generate fasting and high-glucose-induced lipid deposition cell states. Enrichment levels of histone H3K9 acetylation and sterol responsive element binding protein-1c (SREBP-1c) at the PNPLA3 promoter were observed by ChIP-qPCR. PNPLA3 gene expression was detected by real-time PCR; SIRT1 protein expression was detected by western blot. And lipid deposition was detected by Oil Red O.

Results

H3K9ac levels at SRE regions of PNPLA3 promoter were found to be decreased in mice during fasting and increase during refeeding, and increased in mice with NAFLD induced by high-sucrose diet. The change pattern of PNPLA3 promoter H3K9Ac physiologically (fasting/refeeding) and pathologically was consistent with that of PNPLA3 gene expression, but opposite to that of SIRT1 protein expression. In HepG2 cells, overexpression of SIRT1 inhibited high-glucose induced hyper-acetylation of H3K9 at PNPLA3 promoter, and silent expression of SIRT1 suppressed fasting-induced hypo-acetylation of H3K9. Overexpression of SIRT1 prevented basal and SREBP-1c-driven PNPLA3 gene expression and also prevented the endogenous binding of SREBP-1c to PNPLA3.

Conclusions

We first preliminarily revealed SIRT1 may regulate PNPLA3 gene expression by affecting SREBP-1-driven transcription via acetylation modification of H3K9.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41021-022-00246-1.

The Role of Glucagon-Like Peptide-1 Receptor Agonists (GLP-1 RA) in Diabetes-Related Neurodegenerative Diseases

Recent clinical guidelines have emphasized the importance of screening for cognitive impairment in older adults with diabetes, however, there is still a lack of understanding about the drug therapy. Glucagon-like peptide 1 receptor agonists (GLP-1 RAs) are widely used in the treatment of type 2 diabetes and potential applications may include the treatment of obesity as well as the adjunctive treatment of type 1 diabetes mellitus in combination with insulin. Growing evidence suggests that GLP-1 RA has the potential to treat neurodegenerative diseases, particularly in diabetes-related Alzheimer’s disease (AD) and Parkinson’s disease (PD). Here, we review the molecular mechanisms of the neuroprotective effects of GLP-1 RA in diabetes-related degenerative diseases, including AD and PD, and their potential effects.

Preventive Effect of Apple Polyphenol Extract on High-Fat Diet-Induced Hepatic Steatosis in Mice through Alleviating Endoplasmic Reticulum Stress

In this work, the protective effect of apple polyphenol extract (APE) on hepatic steatosis was investigated. Thirty-two C57BL/6J mice were assigned randomly to control group, hepatic steatosis group, lovastatin group, and APE group. After 8 weeks of intervention, APE supplementation markedly decreased the body weight gain, liver weight, liver index, epididymal adipose weight, epididymal adipose index, serum, and hepatic lipid levels. Hematoxylin and eosin staining revealed that APE supplementation alleviated histopathological changes of hepatic steatosis. Western blot revealed that APE downregulated the protein levels of GRP78, IRE1α, p-IRE1α, XBP1, PERK, p-PERK, p-eIF2α, ATF6, PPAR-γ, SREBP-1c, FAS, and ACC1. In conclusion, this study found that APE inhibited IRE1α-XBP1, PERK-eIF2α, and ATF6 signaling pathways to alleviate endoplasmic reticulum stress, thereby improving HFD-induced hepatic steatosis.

Hepatic Fibroblast Growth Factor 21 Is Involved in Mediating Functions of Liraglutide in Mice With Dietary Challenge

BACKGROUND AND AIMS

Several studies have shown that expression of hepatic fibroblast growth factor 21 (FGF21) can be stimulated by glucagon-like peptide 1 (GLP-1)-based diabetes drugs. As GLP-1 receptor (GLP-1R) is unlikely to be expressed in hepatocytes, we aimed to compare such stimulation in mice and in mouse hepatocytes, determine the involvement of GLP-1R, and clarify whether FGF21 mediates certain functions of the GLP-1R agonist liraglutide.

APPROACH AND RESULTS

Liver FGF21 expression was assessed in mice receiving a daily liraglutide injection for 3 days or in mouse primary hepatocytes (MPHs) undergoing direct liraglutide treatment. The effects of liraglutide on metabolic improvement and FGF21 expression were then assessed in high-fat diet (HFD)-fed mice and compared with the effects of the dipeptidyl-peptidase 4 inhibitor sitagliptin. Animal studies were also performed in Glp1r^-/- mice and liver-specific FGF21-knockout (lFgf21-KO) mice. In wild-type mouse liver that underwent RNA sequencing and quantitative reverse-transcription PCR, we observed liraglutide-stimulated hepatic Fgf21 expression and a lack of Glp1r expression. In MPHs, liraglutide did not stimulate Fgf21. In mice with HFD-induced obesity, liraglutide or sitagliptin treatment reduced plasma triglyceride levels, whereas their effect on reducing body-weight gain was different. Importantly, increased hepatic FGF21 expression was observed in liraglutide-treated mice but was not observed in sitagliptin-treated mice. In HFD-fed Glp1r^-/- mice, liraglutide showed no beneficial effects and could not stimulate Fgf21 expression. In lFgf21-KO mice undergoing dietary challenge, the body-weight-gain attenuation and lipid homeostatic effects of liraglutide were lost or significantly reduced.

CONCLUSIONS

We suggest that liraglutide-stimulated hepatic Fgf21 expression may require GLP-1R to be expressed in extrahepatic organs. Importantly, we revealed that hepatic FGF21 is required for liraglutide to lower body weight and improve hepatic lipid homeostasis. These observations advanced our mechanistic understanding of the function of GLP-1-based drugs in NAFLD.

Metformin Alleviates Steatohepatitis in Diet-Induced Obese Mice in a SIRT1-Dependent Way

Metformin is the first-line anti-diabetic drug for type 2 diabetes. It has been found to significantly reduce liver aminotransferase in nonalcoholic fatty liver disease (NAFLD). However, whether metformin improves NAFLD progression remains controversial. Sirtuin 1 (SIRT1), an NAD⁺-dependent deacetylase, plays a vital role in hepatic steatosis and inflammation. Here, we investigated the effect of metformin on steatohepatitis and the role of SIRT1 in diet-induced obese (DIO) mice. The results showed that metformin significantly reduced body weight and fat mass of DIO mice. In addition, metformin also alleviated adiposity and hepatic steatosis, and greatly upregulated uncoupling protein 1 (UCP1) expression in adipose tissues of DIO mice. Unexpectedly, the effects of metformin on reducing body weight and alleviating hepatic steatosis were not impaired in Sirt1 heterozygous knockout (Sirt1^+/−) mice. However, SIRT1-deficiency remarkably impaired the effects of metformin on lowering serum transaminases levels, downregulating the mRNA expression of proinflammatory factors, and increasing the protein level of hepatic Cholesterol 25-Hydroxylase (CH25H), a cholesterol hydroxylase in cholesterol catabolism. In summary, we demonstrated that metformin alleviates steatohepatitis in a SIRT1-dependent manner, and modulation of M1 polarization and cholesterol metabolism may be the underlying mechanism.

Shift of Glucose Peak Time During Oral Glucose Tolerance Test is Associated with Changes in Insulin Secretion and Insulin Sensitivity After Therapy with Antidiabetic Drugs in Patients with Type 2 Diabetes

INTRODUCTION

Delay in peak blood glucose during an oral glucose tolerance test (OGTT) predicts declining β-cell function and poor ability to regulate glucose metabolism. Glucose peak time has not been used as a comparative indicator of the improvement in islet function after treatment with exenatide, insulin, or oral antidiabetic drugs (OADs). We evaluated the efficacy of three types of antidiabetic drugs on the basis of blood glucose peak time in patients with non-newly diagnosed type 2 diabetes.

METHODS

The data from 100 patients with diabetes who completed two OGTTs within 6 months were collected. Thirty-seven of them with type 2 diabetes were treated with Humalog Mix25, 28 patients with OADs (metformin, acarbose, and gliclazide), and 35 patients with exenatide.

RESULTS

Glycated hemoglobin improved in all three groups after treatment (P < 0.05). Subcutaneous adipose tissue (P < 0.01) and visceral adipose tissue (P < 0.0001) significantly decreased in the exenatide group. The insulinogenic index (IGI) (P = 0.01) and IGI × oral glucose insulin sensitivity (OGIS) (P = 0.01) improved in the exenatide group only. Homeostatic assessment of β-cell function (HOMA-β) and OGIS were greater in the exenatide and OAD groups than in the Humalog Mix25 group (all P < 0.05). A shift to an earlier peak was observed in 57.1%, 35.7%, and 27.0% of patients in the exenatide, OAD, and Humalog Mix25 groups, respectively (P = 0.029). OGIS (odds ratio [OR] 0.54, 95% confidence interval [CI] 0.33-0.89, P = 0.026) and IGI × OGIS (OR 1.72, 95% CI 0.44-6.68, P = 0.012) were independently related to shifts in glucose peak time.

CONCLUSION

Exenatide, Humalog Mix25, and OADs improved glycemic metabolism. However, exenatide exhibited superior efficacy in shifting blood glucose peak time to an earlier point, while it improved insulin secretion and insulin sensitivity. Hence, the shift of glucose peak time may be considered an indicator for the evaluation of the effect of hypoglycemic drugs.

Sirtuin 1 as the mechanism of action of agents used in the diabetes mellitus pharmacotherapy

SIRT1 (sirtuin 1, a member of histone deacetylase III family) is responsible for deacetylation of lysine in histones and the conservation of DNA in the state of transcriptionally inactive heterochromatin. SIRT1 is also capable of deacetylation of transcription factors, as well as other regulatory proteins. The SIRT1 activity plays a unique role in the prevention of metabolic memory, reducing many pathways leading to chronic diabetic complications or diseases concomitant with diabetes. Factors modifying expression and/or activity of SIRT1 may be especially helpful for patients with diabetes. This article attempts to sum up the current state of knowledge about agents commonly used in the treatment of type 2 diabetes which might have an impact on the SIRT1 expression and activity. It is the review of several studies regarding drug-induced pleiotropic activity and the way in which their interference with cellular pathways gives us better understanding of this activity, as well as the influence of therapy on the course of the disease.

Antioxidative Potentials of Incretin-Based Medications: A Review of Molecular Mechanisms

Glucagon-like peptide 1 receptor agonists and dipeptidyl-peptidase 4 inhibitors are medications used for managing diabetes, mimicking the metabolic effects of incretin hormones. Recent evidence suggests that these medications have antioxidative potentials in the diabetic milieu. The pathophysiology of most diabetic complications involves oxidative stress. Therefore, if incretin-based antidiabetic medications can alleviate the free radicals involved in oxidative stress, they can potentially provide further therapeutic effects against diabetic complications. However, the molecular mechanisms by which these medications protect against oxidative stress are not fully understood. In the current review, we discuss the potential molecular mechanisms behind these pharmacologic agents' antioxidative properties.

Inonotsuoxide B regulates M1 to M2 macrophage polarization through sirtuin-1/endoplasmic reticulum stress axis

We explored the effect of tetracyclic triterpenoid inonotsuoxide B (IB) extracts of Inonotus obliquus on M1 to M2 macrophage polarization and its possible underlying mechanism. Lipopolysaccharide (LPS)-activated M1 macrophages exert pro-inflammatory effects and release inflammatory cytokines including interleukin (IL)-1β and tumor necrosis factor (TNF)-α. The model and various groups were treated with different IB concentrations (2.5, 5, and 10 μg/mL) to observe changes in the M1 and M2 phenotypes, gene expression of NAD-dependent deacetylase sirtuin-1 (Sirt1), and endoplasmic reticulum stress (ERS). SIRT1-siRNA and thapsigargin (TG), an ERS agonist, were used to examine the relationship between SIRT1/ERS and the effect of IB on M1 to M2 RAW264.7 macrophage phenotypic changes. We found that IB had no effect on RAW264.7 cell proliferation at 10 μg/mL. Increasing concentrations of IB (2.5, 5, and 10 μg/mL) decreased the number of phenotypic M1 macrophages and, consequently, decreased the release of the inflammatory cytokines, IL-1β and TNF-α. Furthermore, IB treatment increased the level of phenotypic M2 macrophages, which increased the release of anti-inflammatory cytokines such as arginase (Arg)-1 and found in inflammatory zone 1 (FIZZ1) in a dose-dependent manner. Further, we found that IB increased the expression of SIRT1 and inhibited that of ERS. Inhibition of Sirt1 expression by siRNA significantly increased that of ERS marker genes and IL1β. Excessive ERS levels inhibited the IB-induced transformation of phenotypic M1 macrophage to the M2 macrophage phenotype. Therefore, IB, an extract of I. obliquus, may regulate macrophage polarization through the SIRT1/ERS signaling pathway.

Homocysteine in Neurology: A Possible Contributing Factor to Small Vessel Disease

Homocysteine (Hcy) is a sulfur-containing amino acid generated during methionine metabolism, accumulation of which may be caused by genetic defects or the deficit of vitamin B12 and folate. A serum level greater than 15 micro-mols/L is defined as hyperhomocysteinemia (HHcy). Hcy has many roles, the most important being the active participation in the transmethylation reactions, fundamental for the brain. Many studies focused on the role of homocysteine accumulation in vascular or degenerative neurological diseases, but the results are still undefined. More is known in cardiovascular disease. HHcy is a determinant for the development and progression of inflammation, atherosclerotic plaque formation, endothelium, arteriolar damage, smooth muscle cell proliferation, and altered-oxidative stress response. Conversely, few studies focused on the relationship between HHcy and small vessel disease (SVD), despite the evidence that mice with HHcy showed a significant end-feet disruption of astrocytes with a diffuse SVD. A severe reduction of vascular aquaporin-4-water channels, lower levels of high-functioning potassium channels, and higher metalloproteinases are also observed. HHcy modulates the N-homocysteinylation process, promoting a pro-coagulative state and damage of the cellular protein integrity. This altered process could be directly involved in the altered endothelium activation, typical of SVD and protein quality, inhibiting the ubiquitin-proteasome system control. HHcy also promotes a constant enhancement of microglia activation, inducing the sustained pro-inflammatory status observed in SVD. This review article addresses the possible role of HHcy in small-vessel disease and understands its pathogenic impact.

ER stress-induced adipocytes secrete-aldo-keto reductase 1B7-containing exosomes that cause nonalcoholic steatohepatitis in mice

Nonalcoholic steatohepatitis (NASH) is an increasingly prevalent liver disease linked to obesity and associated complications. Endoplasmic reticulum (ER) stress provokes dysfunction in lipid metabolism, which often leads to a progression of obesity-induced hepatic steatosis to NASH. However, the underlying mechanisms in which ER stress in adipose tissue induces hepatic pathology remain elusive. Here, we used male C57BL/6J mice to develop an animal model of NASH induced by a high fat (HFD) diet and methionine- and choline-deficient (MCD) diets. Using a gene-silencing approach with a recombinant lentiviral vector and extensive LC-MS/MS-based proteomics and lipidomics, we demonstrate that the ER stress-induced adipocyte-secreted exosome (ATEx) orchestrates lipid dynamics in the liver. We also noted that ATEx causes hepatic steatosis, inflammation, and fibrosis that lead to NASH through initial accumulation of glycerol and triglycerides in hepatocytes. We also determined that aldo-keto-reductase 1B7 (Akr1b7), a key mediator in liver lipid metabolism, is involved in ATEx-mediated NASH induction. Of note, Akr1b7 deficiency in ER stress-induced ATEx strongly protected the murine liver against HFD and MCD-induced NASH. Our results indicated that ER stress-induced, adipocyte-secreted ATEx triggers NASH by delivering exosomal AKR1B7 to, and elevating glycerol level, in hepatocytes. These findings suggest potential therapeutic strategie that target ATEx to prevent or manage obesity-induced NASH.

Caveolin-1 Is Essential for the Improvement of Insulin Sensitivity through AKT Activation during Glargine Treatment on Diabetic Mice

Insulin treatment was confirmed to reduce insulin resistance, but the underlying mechanism remains unknown. Caveolin-1 (Cav-1) is a functional protein of the membrane lipid rafts, known as caveolae, and is widely expressed in mammalian adipose tissue. There is increasing evidence that show the involvement of Cav-1 in the AKT activation, which is responsible for insulin sensitivity. Our aim was to investigate the effect of Cav-1 depletion on insulin sensitivity and AKT activation in glargine-treated type 2 diabetic mice. Mice were exposed to a high-fat diet and subject to intraperitoneal injection of streptozotocin to induce diabetes. Next, glargine was administered to treat T2DM mice for 3 weeks (insulin group). The expression of Cav-1 was then silenced by injecting lentiviral-vectored short hairpin RNA (shRNA) through the tail vein of glargine-treated T2DM mice (CAV1-shRNA group), while scramble virus injection was used as a negative control (Ctrl-shRNA group). The results showed that glargine was able to upregulate the expression of PI3K and activate serine phosphorylation of AKT through the upregulation of Cav-1 expression in paraepididymal adipose tissue of the insulin group. However, glargine treatment could not activate AKT pathway in Cav-1 silenced diabetic mice. These results suggest that Cav-1 is essential for the activation of AKT and improving insulin sensitivity in type 2 diabetic mice during glargine treatment.

GLP-1 Receptor Agonists: Beyond Their Pancreatic Effects

Glucagon like peptide-1 (GLP-1) is an incretin secretory molecule. GLP-1 receptor agonists (GLP-1RAs) are widely used in the treatment of type 2 diabetes (T2DM) due to their attributes such as body weight loss, protection of islet β cells, promotion of islet β cell proliferation and minimal side effects. Studies have found that GLP-1R is widely distributed on pancreatic and other tissues and has multiple biological effects, such as reducing neuroinflammation, promoting nerve growth, improving heart function, suppressing appetite, delaying gastric emptying, regulating blood lipid metabolism and reducing fat deposition. Moreover, GLP-1RAs have neuroprotective, anti-infectious, cardiovascular protective, and metabolic regulatory effects, exhibiting good application prospects. Growing attention has been paid to the relationship between GLP-1RAs and tumorigenesis, development and prognosis in patient with T2DM. Here, we reviewed the therapeutic effects and possible mechanisms of action of GLP-1RAs in the nervous, cardiovascular, and endocrine systems and their correlation with metabolism, tumours and other diseases.

Gut Akkermansia muciniphila ameliorates metabolic dysfunction-associated fatty liver disease by regulating the metabolism of L-aspartate via gut-liver axis

The gut bacterium Akkermansia muciniphila has been increasingly recognized for its therapeutic potential in treating metabolic disorders, including obesity, diabetes, and metabolicdysfunction-associated fatty liver disease (MAFLD). However, its underlying mechanism involved in its well-known metabolic actions needs further evaluation. The present study explored the therapeutic effect and mechanism of A. muciniphila in intervening MAFLD by using a high-fat and high-cholesterol (HFC) diet induced obese mice model. Mice treated with A. muciniphila efficiently reversed MAFLD in the liver, such as hepatic steatosis, inflammatory, and liver injury. These therapeutic effects persisted after long-term drug withdrawal and were slightly weakened in the antibiotics-treated obese mice. A. muciniphila treatment efficiently increased mitochondrial oxidation and bile acid metabolism in the gut-liver axis, ameliorated oxidative stress-induced cell apoptosis in gut, leading to the reshaping of the gut microbiota composition. These metabolic improvements occurred with increased L-aspartate levels in the liver that transported from the gut. The administration of L-aspartate in vitro or in mice displayed the similar beneficial metabolic effects mentioned above and efficiently ameliorated MAFLD. Together, these data indicate that the anti-MAFLD activity of A. muciniphila correlated with lipid oxidation and improved gut-liver interactions through regulating the metabolism of L-aspartate. A. muciniphila could be a potential agent for clinical intervention in MAFLD.

Liraglutide Alleviates Hepatic Steatosis by Activating the TFEB-Regulated Autophagy-Lysosomal Pathway

Liraglutide, a glucagon-like peptide-1 receptor agonist (GLP-1RA), has been demonstrated to alleviate non-alcoholic fatty liver disease (NAFLD). However, the underlying mechanism has not been fully elucidated. Increasing evidence suggests that autophagy is involved in the pathogenesis of hepatic steatosis. In this study, we examined whether liraglutide could alleviate hepatic steatosis through autophagy-dependent lipid degradation and investigated the underlying mechanisms. Herein, the effects of liraglutide on NAFLD were evaluated in a high-fat diet (HFD)-induced mouse model of NAFLD as well as in mouse primary and HepG2 hepatocytes exposed to palmitic acid (PA). The expression of the GLP-1 receptor (GLP-1R) was measured in vivo and in vitro. Oil red O staining was performed to detect lipid accumulation in hepatocytes. Electron microscopy was used to observe the morphology of autophagic vesicles and autolysosomes. Autophagic flux activity was measured by infecting HepG2 cells with mRFP-GFP-LC3 adenovirus. The roles of GLP-1R and transcription factor EB (TFEB) in autophagy-lysosomal activation were explored using small interfering RNA. Liraglutide treatment alleviated hepatic steatosis in vivo and in vitro. In models of hepatic steatosis, microtubule-associated protein 1B light chain-3-II (LC3-II) and SQSTM1/P62 levels were elevated in parallel to blockade of autophagic flux. Liraglutide treatment restored autophagic activity by improving lysosomal function. Furthermore, treatment with autophagy inhibitor chloroquine weakened liraglutide-induced autophagy activation and lipid degradation. TFEB has been identified as a key regulator of lysosome biogenesis and autophagy. The protein levels of nuclear TFEB and its downstream targets CTSB and LAMP1 were decreased in hepatocytes treated with PA, and these decreases were reversed by liraglutide treatment. Knockdown of TFEB expression compromised the effects of liraglutide on lysosome biogenesis and hepatic lipid accumulation. Mechanistically, GLP-1R expression was decreased in HFD mouse livers as well as PA-stimulated hepatocytes, and liraglutide treatment reversed the downregulation of GLP-1R expression in vivo and in vitro. Moreover, GLP-1R inhibition could mimic the effect of the TFEB downregulation-mediated decrease in lysosome biogenesis. Thus, our findings suggest that liraglutide attenuated hepatic steatosis via restoring autophagic flux, specifically the GLP-1R-TFEB-mediated autophagy-lysosomal pathway.

Triclosan inhibits the activation of human periodontal ligament fibroblasts induced by lipopolysaccharide from Porphyromonas gingivalis

Periodontitis is a highly prevalent, chronic, non-specific, and immunologically devastating disease of periodontal tissues, caused by microbial infection. This study aims to examine the efficacy and protective mechanism of triclosan (TCS), a bisphenolic, non-cationic component of oral care products, against periodontal inflammation induced by lipopolysaccharide purified from Porphyromonas gingivalis (LPS-PG). TCS markedly downregulated interleukin-6 (IL-6), IL-8, and IL-15 in human periodontal ligament fibroblasts (HPDLFs) treated with LPS-PG. By using a liquid chromatography-tandem mass spectrometry (LC-MS/MS) approach, 318 differentially expressed proteins (161 upregulated and 157 downregulated) were identified in TCS-pretreated HPDLFs. TCS upregulated HSPA5 and HSP90B1 but downregulated HSPA2. Besides, TCS upregulated miR-548i in HPDLFs, which downregulated IL-15. These results indicate that TCS attenuates the activation of HPDLFs and downregulates the inflammatory cytokines through various mechanisms, thus highlighting its protective role in periodontal inflammation.

Glucagon-like peptide-1 receptor agonists in non-alcoholic fatty liver disease: An update

Non-alcoholic fatty liver disease (NAFLD) is the predominant cause of chronic liver disease worldwide. NAFLD progresses in some cases to non-alcoholic steatohepatitis (NASH), which is characterized, in addition to liver fat deposition, by hepatocyte ballooning, inflammation and liver fibrosis, and in some cases may lead to hepatocellular carcinoma. NAFLD prevalence increases along with the rising incidence of type 2 diabetes mellitus (T2DM). Currently, lifestyle interventions and weight loss are used as the major therapeutic strategy in the vast majority of patients with NAFLD. Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are used in the management of T2DM and do not have major side effects like hypoglycemia. In patients with NAFLD, the GLP-1 receptor production is down-regulated. Recently, several animal and human studies have emphasized the role of GLP-1RAs in ameliorating liver fat accumulation, alleviating the inflammatory environment and preventing NAFLD progression to NASH. In this review, we summarize the updated literature data on the beneficial effects of GLP-1RAs in NAFLD/NASH. Finally, as GLP-1RAs seem to be an attractive therapeutic option for T2DM patients with concomitant NAFLD, we discuss whether GLP-1RAs should represent the first line pharmacotherapy for these patients.

SIRT1 is a key regulatory target for the treatment of the endoplasmic reticulum stress-related organ damage

Endoplasmic reticulum (ER) stress is an evolutionarily conserved adaptive response that contributes to deal with the misfolded or unfolded protein in the lumen of the ER and restore the ER homeostasis. However, excessive and prolonged ER stress can trigger the cell-death signaling pathway which causes cell death, usually in the form of apoptosis. It is generally accepted that inappropriate cellular apoptosis and a series of the subsequent inflammatory response and oxidative stress can cause disturbance of normal physiological functions and organ damage. A lot of evidence shows that the excessive activation of the ER stress contributes to the pathogenesis of many kinds of diseases and inhibiting the inappropriate stress is of great significance for maintaining the normal physiological function. In recent years, Sirtuin1 (SIRT1) has become a research hotspot on ER stress. As a master regulator of ER stress, increasing evidence suggests that SIRT1 plays a positive role in a variety of ER stress-induced organ damage via multiple mechanisms, including inhibiting cellular apoptosis and promoting autophagy. Furthermore, a lot of factors have shown effective regulation of SIRT1, which indicates the feasibility of treating SIRT1 as a target for the treatment of ER stress-related diseases. We summarize and reveal the molecular mechanisms underlying the protective effect of SIRT1 in multiple ER stress-mediated organ damage in this review. We also summed up the possible adjustment mechanism of SIRT1, which provides a theoretical basis for the treatment of ER stress-related diseases.

Effect of glucagon-like peptide-1 receptor agonists on adipokine level of nonalcoholic fatty liver disease in rats fed high-fat diet

Background

Nonalcoholic fatty liver disease (NAFLD) is the leading cause of liver disease worldwide, and no effective treatment exists until now. Glucagon-like peptide-1 receptor agonists are becoming the preferred therapeutic option for the management of obesity and are becoming the preferred treatment options for the management of both NAFLD and type 2 diabetes mellitus, but the molecular mechanisms are still unclear.

Methods

Forty-five healthy male Wistar rats were divided into three groups: normal control, high-fat diet (HFD) group, HFD + liraglutide (100 mg/kg body weight) group. Biochemical parameters and adipokine levels were examined in the serum of rats. In order to judge the degree of steatosis of NAFLD, the magnetic resonance imaging and histopathology of the liver were also studied.

Results and conclusion

Liraglutide caused a significant decrease in the serum fasting glucose and improved the insulin resistance, dyslipidemia, and liver enzymes. It reduced the adipokine level, and alleviated the histopathology of liver of rats in the steatosis, ballooning, and lobular inflammation when compared to the HFD group. Thus, liraglutide demonstrated amelioration of NAFLD by decreasing the adipokine levels in this animal model and seems to be a promising molecule for the management of NAFLD.

Autophagy protects HUVECs against ER stress-mediated apoptosis under simulated microgravity

Astronauts exposed to a gravity-free environment experience cardiovascular deconditioning that causes post-spaceflight orthostatic intolerance and other pathological conditions. Endothelial dysfunction is an important factor responsible for this alteration. Our previous study showed enhanced autophagy in endothelial cells under simulated microgravity. The present study explored the cytoprotective role of autophagy under microgravity in human umbilical vein endothelial cells (HUVECs). We found that clinorotation for 48 h induced apoptosis and endoplasmic reticulum (ER) stress in HUVECs. ER stress and the unfolded protein response (UPR) partially contributed to apoptosis under clinorotation. Autophagy partially reduced ER stress and restored UPR signaling by autophagic clearance of ubiquitin-protein aggregates, thereby reducing apoptosis. In addition, the ER stress antagonist 4-phenylbutyric acid upregulated autophagy in HUVECs. Taken together, these findings indicate that autophagy plays a protective role against apoptosis under clinorotation by clearing protein aggregates and partially restoring the UPR.

LncRNA-Malat1 is Involved in Lipotoxicity-Induced ß-cell Dysfunction and the Therapeutic Effect of Exendin-4 via Ptbp1

Increasing evidence indicates that long noncoding RNAs (lncRNAs) have crucial roles in various biological processes. However, the contribution of lncRNAs to β-cell dysfunction and their roles in diabetes therapeutics remain poorly understood. The aim of this study was to identify the lncRNAs dysregulated in diabetic islets and to explore the lncRNAs involved in β-cell function as potential therapeutic targets. By using RNA sequencing and real-time PCR, we identified thousands of lncRNAs in the islets of db/db mice and db/m littermate mice. Among the differentially expressed lncRNAs, lncRNA-Malat1 (metastasis-associated lung adenocarcinoma transcript 1) was reduced in the islets of db/db mice and palmitate-treated MIN6 cells. The results of TUNEL, Western blot and flow cytometric analyses, and GSIS assays revealed that Malat1 knockdown significantly induced β-cell apoptosis and inhibited insulin secretion. Mechanistically, RNA immunoprecipitation showed that Malat1 enhanced polypyrimidine tract-binding protein 1 (Ptbp1) protein stability by direct interaction, thereby adjusting the ratio of pyruvate kinase muscle (PKM) isoforms 1 and 2 (PKM1/PKM2). Moreover, luciferase assay and chromatin immunoprecipitation indicated that Malat1 was transcriptionally activated by pancreatic and duodenal homeobox 1 (Pdx1), through which exendin-4 alleviated lipotoxicity-induced β-cell damage. In summary, our findings suggested the involvement of Malat1 in β-cell dysfunction under diabetic conditions via the Malat1/Ptbp1/PKM2 pathway. In addition, exendin-4 ameliorated β-cell impairment by Pdx1-mediated Malat1 upregulation. Hence, Malat1 may serve as a therapeutic target for the treatment of type 2 diabetes.

SIRT1 Mediates Effects of FGF21 to Ameliorate Cisplatin-Induced Acute Kidney Injury

Acute kidney injury (AKI) is a common complication in cancer patients. Kidney function is closely related to patients’ quality of life and tumor prognosis. Cisplatin is a highly effective anti-tumor drug. However, the use of cisplatin is limited by its nephrotoxicity. It has been reported that FGF21 has a renal-protective function, but the mechanisms by which it does so remain unclear. In this study, we show that the expression of FGF21 is significantly upregulated in both in vitro and in vivo cisplatin-induced AKI models. Administration of recombinant FGF21 to cisplatin-induced AKI mice resulted in significantly decreased blood urea nitrogen (BUN) and serum creatinine levels, as well as significantly reduced protein levels of kidney injury molecule-1 (TIM-1), C-caspase 3, and Bax. H&E-stained kidney sections from cisplatin-induced AKI mice treated with recombinant FGF21 showed a relatively normal renal tissue structure, a reduced number of necrotic sites and vacuolar changes, and decreased casts, suggesting alleviated renal tubular injury. Experiments with an AKI cell model (cisplatin-treated HK-2 cells) yielded similar results as the mouse model; recombinant FGF21 significantly downregulated protein expression levels of TIM-1, C-caspase 3, and Bax. Furthermore, administration of recombinant FGF21 to cisplatin-treated AKI models significantly increased SIRT1 expression, and the beneficial effects of FGF21 on kidney injury were reversed by SIRT1 knockdown. Collectively, our results suggest that SIRT1 mediates the protective effect of FGF21 on cisplatin-induced kidney injury.

Protection of retinal function and morphology in MNU-induced retinitis pigmentosa rats by ALDH2: an in-vivo study

Background

Retinitis pigmentosa (RP) is a kind of inherited retinal degenerative diseases characterized by the progressive loss of photoreceptors. RP has been a conundrum without satisfactory countermeasures in clinic until now. Acetaldehyde dehydrogenase 2 (ALDH2), a major enzyme involved in aldehyde detoxification, has been demonstrated to be beneficial for a growing number of human diseases, such as cardiovascular dysfunction, diabetes mellitus and neurodegeneration. However, its protective effect against RP remains unknown. Our study explored the impact of ALDH2 on retinal function and structure in N-methyl-N-nitrosourea (MNU)-induced RP rats.

Methods

Rats were gavaged with 5 mg/kg Alda-1, an ALDH2 agonist, 5 days before and 3 days after MNU administration. Assessments of retinal function and morphology as well as measurement of specific proteins expression level were conducted.

Results

Electroretinogram recordings showed that Alda-1 administration alleviated the decrease in amplitude caused by MNU, rendering protection of retinal function. Mitigation of photoreceptor degeneration in MNU-treated retinas was observed by optical coherence tomography and retinal histological examination. In addition, Western blotting results revealed that ALDH2 protein expression level was upregulatedwith increased expression of SIRT1 protein after the Alda-1 intervention. Besides, endoplasmic reticulum stress (ERS) was reduced according to the significant downregulation of GRP78 protein, while apoptosis was ameliorated as shown by the decreased expression of PARP1 protein.

Conclusions

Together, our data demonstrated that ALDH2 could provide preservation of retinal function and morphology against MNU-induced RP, with the underlying mechanism at least partly related to the modulation of SIRT1, ERS and apoptosis.

Araloside C attenuates atherosclerosis by modulating macrophage polarization via Sirt1-mediated autophagy

Atherosclerosis-related cardiovascular disease is still the predominant cause of death worldwide. Araloside C (AsC), a natural saponin, exerts extensive anti-inflammatory properties. In this study, we explored the protective effects and mechanism of AsC on macrophage polarization in atherosclerosis in vivo and in vitro. Using a high-fat diet (HFD)-fed ApoE-/- mouse model and RAW264.7 macrophages exposed to ox-LDL, AsC was evaluated for its effects on polarization and autophagy. AsC significantly reduced the plaque area in atherosclerotic mice and lipid accumulation in ox-LDL-treated macrophages, promoted M2 phenotype macrophage polarization, increased the number of autophagosomes and modulated the expression of autophagy-related proteins. Moreover, the autophagy inhibitor 3-methyladenine and BECN1 siRNA obviously abolished the antiatherosclerotic and M2 macrophage polarization effects of AsC. Mechanistically, AsC targeted Sirt1and increased its expression, and this increase in expression was associated with increased autophagy and M2 phenotype polarization. In contrast, the effects of AsC were markedly blocked by EX527 and Sirt1 siRNA. Altogether, AsC attenuates foam cell formation and lessens atherosclerosis by modulating macrophage polarization via Sirt1-mediated autophagy.

Short-term GLP-1 receptor agonist exenatide ameliorates intramyocellular lipid deposition without weight loss in ob/ob mice

OBJECTIVE

Ectopic lipid deposition is closely associated with type 2 diabetes (T2D). Accumulating evidence shows that GLP-1 receptor agonists (GLP-1 RAs) improve obesity and liver steatosis. However, it remains unknown whether and how they ameliorate lipid deposition in skeletal muscle. This study aimed to investigate the effect of exenatide (a GLP-1 RA) on intramyocellular lipid deposition in the skeletal muscle of T2D models and its dependence on weight loss.

METHODS

Ob/ob mice and diet-induced obese (DIO) mice were treated with exenatide (24 nmol/kg), leptin (1 mg/kg), or saline control intraperitoneally once daily for 4 weeks. Phenotypic evaluations were performed during and after the intervention. PA-induced myoblast C2C12 cells were used as an in vitro model. The expression of key enzymes involved in lipid metabolism was assessed in the skeletal muscle of ob/ob mice and DIO mice.

RESULTS

In ob/ob mice, 4-week exenatide treatment did not improve the body weight and fat mass, but modestly ameliorated intramyocellular lipid deposition and lipid profiles. In DIO mice, it remarkably alleviated the body weight, lipid profiles, and intramyocellular lipid deposition. In the skeletal muscle of these two models, exenatide treatment activated the AMP-activated protein kinase (AMPK) signaling pathway, stimulated lipid oxidation enzymes, and upregulated the insulin signaling pathway. In vitro, exendin-4 activated the AMPK signaling pathway and stimulated lipid metabolism to improve lipid accumulation in palmitate-induced myoblast C2C12 cells.

CONCLUSIONS

Exenatide ameliorated intramyocellular lipid deposition without body weight reduction in ob/ob mice, but alleviated body weight and intramyocellular lipid deposition in DIO mice. The underlying mechanism included the activation of AMPK signaling pathway and improvement in insulin sensitivity, independent of weight loss in ob/ob mice.

Cytoplasmic SIRT1 inhibits cell migration and invasion by impeding epithelial-mesenchymal transition in ovarian carcinoma

Sirtuin1 (SIRT1) is a mammalian NAD⁺-dependent type III deacetylase that plays paramount roles in diverse cellular processes. The nucleocytoplasmic shuttling of SIRT1 was discovered more than a decade ago, but the roles of subcellular SIRT1 localization in tumor progression remain unclear. Here, we report that cytoplasmic SIRT1 acts as a tumor suppressor in ovarian carcinoma. By creating ovarian carcinoma cell lines overexpressing wild-type SIRT1 and nuclear localization signals (NLSs) mutated SIRT1 together with both unbiased proteomic and acetylomic approaches and Transwell assays, we identified that mutations in the NLS sequences prevented SIRT1 from entering the nucleus, resulting in the predominant cytoplasmic localization of SIRT1; the cytoplasmic localization of SIRT1 suppressed the mesenchymal program, activated the epithelial program, and inhibited the migration and invasion of tumor cells, thus providing experimental evidence that SIRT1 functions as a tumor suppressor or oncogene may depend on its subcellular localization. Altogether, our findings may highlight a novel role of cytoplasmic SIRT1 in ovarian carcinoma, providing new possible insights for studies investigating the role of SIRT1 in tumor progression.

Inhibition of microRNA-124a attenuates non-alcoholic fatty liver disease through upregulation of adipose triglyceride lipase and the effect of liraglutide intervention

AIM

Glucagon-like peptide-1 receptor agonists (GLP-1Ras) have been reported to prevent non-alcoholic fatty liver disease (NAFLD), but the potential mechanisms are still debated. MicroRNAs (miRNAs) play a prominent role in the field of metabolic disorders, including NAFLD. Our study was designed to further evaluate the effect of GLP-1Ra liraglutide on NAFLD in terms of miRNAs.

METHODS

MicroRNA expression was evaluated by clustering analysis of microRNA arrays in high fat diet-fed mice. The luciferase reporter assay was carried out to validate the cross-talk between adipose triglyceride lipase (ATGL) and miR-124a. MicroRNA-124a mimics and inhibitor plasmids were transfected to study the role of miR-124a in palmitate-treated normal human liver cell line (HL-7702). Liraglutide treatment was used to observe the effect of GLP-1Ra on the miR-124a/ATGL pathway.

RESULTS

Expression of ATGL decreased and miR-124a expression increased in hepatosteatosis in vivo and in vitro. Mechanistically, miR-124a interacted with the 3'-untranslated region of ATGL mRNA and induced its degradation. MicroRNA-124a overexpression antagonized the effect of liraglutide on NAFLD by inhibiting ATGL expression, whereas miR-124a knockdown led to elevated ATGL and sirtuin 1 (Sirt1) expression, and subsequently decreased lipid accumulation and inflammation in cells.

CONCLUSIONS

MicroRNA-124a overexpression contributes to the progression of NAFLD through reduction of ATGL expression, whereas miR-124a knockdown can reverse this trend, suggesting that miR-124a and its downstream target ATGL can be novel therapeutic targets of NAFLD. We reveal a novel mechanism by which liraglutide attenuates NAFLD by the miR-124a/ATGL/Sirt1 pathway.

Sirtuin-1 ameliorates cadmium-induced endoplasmic reticulum stress and pyroptosis through XBP-1s deacetylation in human renal tubular epithelial cells

Cadmium (Cd), an occupational and environmental pollutant, induces nephrotoxicity by primarily damaging renal proximal tubular cells. In this study, we hypothesized that pyroptosis, a caspase-1-dependent inflammatory programmed cell death mechanism, mediates Cd-induced nephrotoxicity. Human proximal tubular epithelial HK-2 cells were treated with 0-10 µM CdCl₂ for 48 h. We found that Cd dose-dependently caused cytotoxicity, which correlated with activation of the NLRP3 inflammasome, increases in the expression and secretion of pro-inflammatory cytokines and upregulation of pyroptosis-related genes in HK-2 cells or/and in kidneys of Cd-treated mice. These effects were significantly abrogated by inhibiting caspase-1 activity with inhibitor YVAD or silencing NLRP3 with siRNA in vitro, suggesting that Cd induces caspase-1- and NLRP3-inflammasome-dependent pyroptosis. Moreover, Cd treatment also activated three branches (ATF6, PERK and IRE-1α) of endoplasmic reticulum stress. Selective inhibition of the IRE-1α/XBP-1s branch by a pharmacological inhibitor STF-083010 or by genetic silencing of XBP-1 significantly attenuated Cd-induced NLRP3 inflammasome activation and pyroptosis. Mechanistically, Cd suppressed deacetylase Sirtuin-1 (SIRT-1) protein expression and activity leading to decrease in physical binding with XBP-1s protein, and thus the accumulation of acetylated XBP-1s levels. Activation of SIRT1 using a pharmacological agonist resveratrol or genetic SIRT1 overexpression significantly abolished Cd-induced activation of the IRE-1α/XBP-1s pathway and the NRLP3 inflammasome as well as pyroptosis, which were counteracted by co-overexpression of both SIRT1 and XBP-1s. Collectively, our findings indicate that SIRT1 activity protects against Cd-induced pyroptosis through deacetylating XBP-1s, and thus inhibiting the IRE-1α/XBP-1s pathway in HK-2 cells. These results provide a novel mechanism for Cd-induced nephrotoxicity.

HSF1/HSP pathway in the hippocampus is involved in SIRT1-mediated caloric restriction-induced neuroprotection after surgery in aged mice

Postoperative cognitive dysfunction is common in the elderly. Endoplasmic reticulum stress (ER-stress) increases neuronal apoptosis after surgery, and chaperone molecules, such as heat shock proteins (HSPs), help reduce unfolded protein reactions, thereby promoting protein homeostasis. Mammal sirtuin1 (SIRT1)-mediated deacetylation of heat shock factor 1 (HSF1) upregulates HSF1 binding to the HSP70 promoter. Caloric restriction (CR) improves cognition in many neurodegenerative models. In this study, we evaluated whether CR improves impaired learning and memory after surgery by attenuating ER-stress in an SIRT1-dependent manner. Male 18-month-old C57BL/6J mice receiving a 12-week CR or an ad libitum (AL) diet pre-intervention were challenged with tibial open fracture surgery and anesthesia or no treatment. We found a significant protective effect of CR on memory in contextual fear conditioning test after surgery compared with the AL group. CR alleviated ER-stress and neuronal apoptosis in the hippocampus induced by surgery. CR increased HSP70 expression through the HSF1/HSP pathway in a SIRT1-mediated manner, and inhibition of SIRT1 in the hippocampus by lentivirus injection partially reduced the benefits of CR (increased HSP70, deacetylated HSF1, reduced ER-stress, and improved memory). Taken together, our results showed that CR alleviates memory impairment postoperatively via attenuation of ER-stress in the hippocampus in an SIRT1-dependent manner, and the SIRT1/HSF1/HSP70 pathway is involved in this process.

Exenatide Protects Against Cardiac Dysfunction by Attenuating Oxidative Stress in the Diabetic Mouse Heart

Cardiovascular disease is the major cause of death in patients with diabetes. Current treatment strategies for diabetes rely on lifestyle changes and glucose control to prevent angiopathy and organ failure. Exenatide, a glucagon-like peptide-1 (GLP-1) receptor agonist, is used as an add-on therapy to insulin treatment. Exenatide also has multiple beneficial effects in addition to its hypoglycemic effects, such as preventing hepatic steatosis and protecting against cardiac injury from doxorubicin-induced cardiotoxicity or ischemic reperfusion. However, the mechanisms underlying the cardioprotective effects of exenatide in diabetes have not been fully clarified. To address this issue, we investigated the cardioprotective effects of exenatide in type 1 and type 2 diabetic mice. We found that exenatide simultaneously attenuated reactive oxidative species (ROS) production through increases in the antioxidant enzymes manganese dependent superoxide dismutase (MnSOD) and catalase. Moreover, exenatide decreased tumor protein P53 (p53) expression and prevented cell apoptosis in H9c2 cells. The presence of the catalase inhibitor 3-AT attenuated the effects of exenatide. Overall, the results strongly indicate that exenatide treatment may be protective against the development of diabetic cardiomyopathy.

Multiple target tissue effects of GLP-1 analogues on non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH)

Accumulating experimental and clinical evidences over the last decade indicate that GLP-1 analogues have a series of central nervous system and peripheral target tissues actions which are able to significantly influence the liver metabolism. GLP-1 analogues pleiotropic effects proved to be efficacious in T2DM subjects not only reducing liver steatosis and ameliorating NAFLD and NASH, but also in lowering plasma glucose and liver inflammation, improving cardiac function and protecting from kidney dysfunction. While the experimental and clinical data are robust, the precise mechanisms of action potentially involved in these protective multi-target effects need further investigation. Here we present a systematic review of the most recent literature data on the multi-target effects of GLP-1 analogues on the liver, on adipose and muscular tissue and on the nervous system, all capable of influencing significant aspects of the fatty liver disease physiopathology. From this analysis, we can conclude that the multi-target beneficial action of the GLP-1 analogues could explain the positive effects observed in animal and human models on progression of NAFLD to NASH.

Moderate weight loss attenuates chronic endoplasmic reticulum stress and mitochondrial dysfunction in human obesity

OBJECTIVE

In obese patients undergoing caloric restriction, there are several potential mechanisms involved in the improvement of metabolic outcomes. The present study further explores whether caloric restriction can modulate endoplasmic reticulum (ER) stress and mitochondrial function, as both are known to be mechanisms underlying inflammation and insulin resistance (IR) during obesity.

METHODS

A total of 64 obese patients with BMI ≥35 kg/m² underwent a dietary program consisting of 6 weeks of a very-low-calorie diet followed by 18 weeks of low-calorie diet. We evaluated changes in the metabolic and inflammatory markers -TNFα, hsCRP, complement component 3 (C3c), and retinol binding protein 4 (RBP4)-, in the ER stress markers and modulators -eIF2α-P, sXBP1, ATF6, JNK-P, CHOP, GRP78, and SIRT1-, and in mitochondrial function parameters -mitochondrial reactive oxygen species (mROS), glutathione peroxidase 1 (GPX1), cytosolic Ca²⁺, and mitochondrial membrane potential.

RESULTS

The dietary intervention produced an 8.85% weight loss associated with enhanced insulin sensitivity, a less marked atherogenic lipid profile, and a decrease in systemic inflammation (TNFα, hsCRP) and adipokine levels (RBP4 and C3c). Chronic ER stress was significantly reduced (ATF6-CHOP, JNK-P) and expression levels of SIRT1 and GRP78 - a Ca²⁺-dependent chaperone - were increased and accompanied by the restoration of Ca²⁺ depots. Furthermore, mROS production and mitochondrial membrane potential improvement were associated with the up-regulation of the antioxidant enzyme GPX1.

CONCLUSIONS

Our data provide evidence that moderate weight loss attenuates systemic inflammation and IR and promotes the amelioration of ER stress and mitochondrial dysfunction, increasing the expression of chaperones, SIRT1 and antioxidant GPX1.