Exendin-4 improves ER stress-induced lipid accumulation and regulates lipin-1 signaling in HepG2 cells

Lipin1 ameliorates cognitive ability of diabetic encephalopathy via regulating Ca2+ transfer through mitochondria-associated endoplasmic reticulum membranes

Diabetic encephalopathy (DE) is a common central nervous system complication resulting from diabetes mellitus (DM). While the exact pathogenesis remains unclear, a homeostatic imbalance of mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) within neurons has been shown to be closely associated with the dysfunctional cognitive pathology of this condition. Our previous work has revealed that phosphatidate phosphatase Lipin1 plays a critical role in the cognitive processes of DE via regulating mitochondrial function. In this study, we reported that the integrity of neuronal MAMs was disrupted in DE mice, which was accompanied by a decrease in the expression of hippocampal Lipin1. With a knock-down of hippocampal Lipin1 in normal mice, ER stress was induced, MAMs structures were impaired and Ca2+ transfer was suppressed. Such effects resulted in mitochondrial dysfunction, synaptic plasticity impairments, and finally cognitive dysfunctions. In contrast, an up-regulation of hippocampal Lipin1 in the DE model partially alleviated these dysfunctions. These results suggest that Lipin1 may ameliorate the cognitive dysfunctions associated with DE via regulating Ca2+ transfers through MAMs. Therefore, targeting Lipin1 may serve as a therapeutic strategy for the clinical treatment of DE.

Kimchi attenuates endoplasmic reticulum stress-induced hepatic steatosis in HepG2 cells and C57BL/6N mice

Kimchi is a traditional fermented food that contains abundant nutrients and functional ingredients with various health benefits. We previously reported that kimchi active components suppress hepatic steatosis caused by endoplasmic reticulum (ER) stress in vitro and in vivo. Therefore, we assessed the effect of kimchi on the inhibition of hepatic steatosis caused by ER stress in HepG2 cells and C57BL/6N mice to verify the hypothesis that kimchi may potentially inhibit nonalcoholic fatty liver disease. We investigated the effect of kimchi on cell viability and triglyceride concentrations in cells and on lipid profile, lipid accumulation, and expression of related genes in cells and mice with hepatic steatosis. A mechanistic study was also performed using the liver X receptor α agonist T0901317 and the AMP-activated protein kinase agonist AICAR. Kimchi was noncytotoxic and effectively reduced triglyceride concentrations and suppressed hepatic steatosis-related gene expression in cells and mice. Additionally, kimchi recovered weight loss, lowered the serum and liver tissue lipid profiles, suppressed lipid accumulation, and reduced the effects of T0901317 and AICAR on lipogenic gene expression in tunicamycin-treated mice. Our results highlight that kimchi could prevent hepatic steatosis caused by ER stress in cells and mice.

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.

Emerging roles of Sirtuins in alleviating alcoholic liver Disease: A comprehensive review

Sirtuins (SIRTs), a NAD⁺ family of dependent deacetylases, are involved in the regulation of various human diseases. Recently, accumulating evidence has uncovered number of substrates and crucial roles of SIRTs in the pathogenesis of alcoholic liver disease (ALD). However, systematic reports are still lacking, so this review provides a comprehensive profile of the crucial physiological functions of SIRTs and its role in attenuating ALD, including alcoholic liver steatosis, steatohepatitis, and fibrosis. SIRTs play beneficial roles in energy/lipid metabolism, oxidative stress, inflammatory response, mitochondrial homeostasis, autophagy and necroptosis of ALD via regulating multiple signaling transduction pathways such as AMPK, LKB1, SREBP1, Lipin1, PGC-1α, PPARα/γ, FoxO1/3a, Nrf2/p62, mTOR, TFEB, RIPK1/3, HMGB1, NFATc4, NF-κB, TLR4, NLRP3, P2X7R, MAPK, TGF1β/Smads and Wnt/β-catenin. In addition, the mechanism and clinical application of natural/ synthetic SIRTs agonists in ALD are summarized, which provide a new idea for the treatment of ALD and basic foundation for further studies into target drugs.

The role of glutathione-mediated triacylglycerol synthesis in the response to ultra-high cadmium stress in Auxenochlorella protothecoides

Under ultra-high cadmium (Cd) stress, large amounts of glutathione are produced in Auxenochlorella protothecoides UTEX 2341, and the lipid content increases significantly. Glutathione is the best reductant that can effectively remove Cd, but the relationship between lipid accumulation and the cellular response to Cd stress has not been ascertained. Integrating analyses of the transcriptomes and lipidomes, the mechanism of lipid accumulation to Cd tolerance were studied from the perspectives of metabolism, transcriptional regulation and protein glutathionylation. Under Cd stress, basic metabolic pathways, such as purine metabolism, translation and pre-mRNA splicing process, were inhibited, while the lipid accumulation pathway was significantly activated. Further analysis revealed that the transcription factors (TFs) and genes related to lipid accumulation were also activated. Analysis of the TF interaction sites showed that ABI5, MYB_rel and NF-YB could further regulate the expression of diacylglycerol acyltransferase through glutathionylation/deglutathionylation, which led to increase of the triacylglycerol (TAG) content. Lipidomes analysis showed that TAG could help maintain lipid homeostasis by adjusting its saturation/unsaturation levels. This study for the first time indicated that glutathione could activate TAG synthesis in microalga A. protothecoides, leading to TAG accumulation and glutathione accumulation under Cd stress. Therefore, the accumulation of TAG and glutathione can confer resistance to high Cd stress. This study provided insights into a new operation mode of TAG accumulation under heavy metal stress.

TRB3 stimulates SIRT1 degradation and induces insulin resistance by lipotoxicity via COP1

Fatty acid-induced lipotoxicity plays an important role in the pathogenesis of diabetes mellitus. Our previous studies have documented that lipotoxicity contributes to the onset and development of diabetes via insulin resistance and/or compromised function of the pancreatic β-cells. However, the underlying molecular mechanisms associating lipotoxicity with insulin resistance remain to be fully elucidated. In this study, we explored the role of TRB3-COP1-SIRT1 in lipotoxicity leading to insulin resistance in hepatocytes. High fat diet (HFD)-fed mice and hepG2 cells stimulated with palmitate were utilized as models of lipid metabolism disorders. We analyzed the interactions of SIRT1 and COP1 with each other and with TRB3 using co-immunoprecipitation, western blotting. SIRT1 ubiquitination was also explored. Animal and cell experiments showed that lipotoxicity induced SIRT1 down-regulation at the protein level without altering the mRNA level, whereas, lipotoxicity led to up-regulation of TRB3 and COP1 at both the gene and protein levels. Mechanistic analysis indicated that COP1 functioned as an E3 Ub-ligase of SIRT1, responsible for its proteasomal degradation under lipotoxic conditions. TRB3 recruited COP1 to SIRT1 to promote its ubiquitination. Our data indicated for the first time that TRB3-COP1-SIRT1 pathway played an important role in lipotoxicity leading to insulin resistance in hepatocytes, and suggested that COP1 could be a potential therapeutic choice for the treatment of diabetes mellitus, with lipotoxicity being the important pathomechanism.

Dropping in on lipid droplets: insights into cellular stress and cancer

Lipid droplets (LD) have increasingly become a major topic of research in recent years following its establishment as a highly dynamic organelle. Contrary to the initial view of LDs being passive cytoplasmic structures for lipid storage, studies have provided support on how they act in concert with different organelles to exert functions in various cellular processes. Although lipid dysregulation resulting from aberrant LD homeostasis has been well characterised, how this translates and contributes to cancer progression is poorly understood. This review summarises the different paradigms on how LDs function in the regulation of cellular stress as a contributing factor to cancer progression. Mechanisms employed by a broad range of cancer cell types in differentially utilising LDs for tumourigenesis will also be highlighted. Finally, we discuss the potential of targeting LDs in the context of cancer therapeutics.