Hepatic IDH2 regulates glycolysis and gluconeogenesis

Prepregnancy Obesity Reprograms Offspring Skeletal Muscle Fibre Transition Through H3K9me3

BACKGROUND

Maternal prepregnancy obesity predisposes offspring to obesity and metabolic disorders, yet its impact on skeletal muscle fibre transition remains unclear. Given that skeletal muscle plays a crucial role in systemic metabolism, we investigated how maternal prepregnancy high-fat diet (HFD) influences muscle fibre composition and metabolic function in offspring.

METHODS

We established mouse models with a prepregnancy chow diet (CD) and a prepregnancy high-fat diet (HFD) for 8 weeks to compare metabolic phenotypes in offspring. Skeletal muscles from offspring were analysed using RNA sequencing, quantitative reverse transcription polymerase chain reaction and western blot to understand the changes in metabolic and signalling pathways. siRNA knockdown and lentiviral-mediated overexpression experiments were conducted in vitro and in vivo to validate molecular mechanisms. Chromatin immunoprecipitation followed by qPCR (ChIP-qPCR) was used to assess histone modification levels at promoter regions.

RESULTS

Male and female offspring of prepregnancy obese dams (mHFD) exhibited a significant reduction in slow-twitch oxidative fibres (p < 0.001) and an increase in fast-twitch glycolytic fibres compared with controls. This was accompanied by impaired glucose tolerance (AUC increased by 12.87%, p < 0.01), insulin resistance and mitochondrial dysfunction (mtDNA copy number reduced by 31%, p < 0.01). RNA sequencing identified IDH2 as the most significantly downregulated gene (29.67% decrease, p < 0.001), with protein levels further reduced in male (30.15%, p < 0.01) and female (46.02%, p < 0.0001) offspring. IDH2 knockdown in C2C12 cells impaired mitochondrial biogenesis and led to higher oxidative stress (NADP+/NADPH ratio elevated by 32%, p < 0.01), while IDH2 overexpression restored mitochondrial integrity, enhanced slow-twitch fibre proportion (26.43 ± 0.6936% in mHFD-LV-IDH2, p < 0.01) and improved glucose metabolism (fasting glucose reduced by 14.7%, p < 0.01). ChIP-qPCR revealed increased H3K9me3 enrichment at the IDH2 promoter (2.54-fold in males, 2.55-fold in females, p < 0.0001), suggesting transgenerational epigenetic regulation.

CONCLUSIONS

Maternal prepregnancy obesity induces a metabolic shift in offspring skeletal muscle by promoting a slow-to-fast fibre transition and impairing mitochondrial biogenesis. This effect is mediated by IDH2 suppression via H3K9me3 histone modification, contributing to systemic insulin resistance. Targeting IDH2 may represent a potential therapeutic strategy to mitigate metabolic dysfunction in offspring exposed to maternal prepregnancy obesity.

Integration of proteomics and metabolomics reveals energy and metabolic alterations induced by glucokinase (GCK) partial inactivation in hepatocytes

AIMS

Glucokinase (GCK) acts as the glucose sensor in maintaining glucose homeostasis. The inactivating mutation of the GCK gene leads to glucokinase-maturity onset diabetes of the young (GCK-MODY). This study aims to gain further insights into the molecular alterations triggered by GCK partial inactivation in hepatocytes, potentially underlying the favorable prognosis of GCK-MODY.

MAIN METHODS

A GCK knockdown HepG2 cell model was established, and the integration of proteomics and metabolomics was used to gain a comprehensive understanding of the molecular pathway changes caused by GCK inactivation in the liver.

KEY FINDINGS

Proteomic analysis identified 257 differential proteins. KEGG pathway enrichment analysis showed that protein expression changes in the GCK knockdown group were significantly enriched in central carbon metabolism, the TCA cycle, amino acid metabolism and the oxidative phosphorylation pathway. Among them, enzymes in the TCA cycle (PC, IDH2, SDH) were significantly downregulated in GCK-knockdown group. Targeted metabolomics revealed that in the GCK knockdown hepatocytes, TCA cycle intermediates were significantly decreased, including pyruvate, oxaloacetate, citrate and succinic acid, and three metabolites increased including glycine, betaine and homocysteine. These metabolic alterations in turn reduced the accumulation of reactive oxygen species in GCK knockdown hepatocytes. Correlation analysis indicated that TCA cycle metabolites were positively correlated with proteins involved in the TCA cycle, carbon metabolism, glycolysis, Ras signaling, fibrosis and inflammation.

SIGNIFICANCE

In conclusion, GCK knockdown reduced TCA cycle flux and oxidative stress in hepatocytes by influencing the levels of key transcription factors and enzymes, providing a comprehensive understanding of the effects of GCK partial inactivation on liver metabolism and molecular mechanisms.

NADPH Dynamics: Linking Insulin Resistance and β-Cells Ferroptosis in Diabetes Mellitus

This review offers an in-depth exploration of Nicotinamide Adenine Dinucleotide Phosphate (NADPH) in metabolic health. It delves into how NADPH affects insulin secretion, influences insulin resistance, and plays a role in ferroptosis. NADPH, a critical cofactor in cellular antioxidant systems and lipid synthesis, plays a central role in maintaining metabolic homeostasis. In adipocytes and skeletal muscle, NADPH influences the pathophysiology of insulin resistance, a hallmark of metabolic disorders such as type 2 diabetes and obesity. The review explores the mechanisms by which NADPH contributes to or mitigates insulin resistance, including its role in lipid and reactive oxygen species (ROS) metabolism. Parallelly, the paper investigates the dual nature of NADPH in the context of pancreatic β-cell health, particularly in its relation to ferroptosis, an iron-dependent form of programmed cell death. While NADPH's antioxidative properties are crucial for preventing oxidative damage in β-cells, its involvement in lipid metabolism can potentiate ferroptotic pathways under certain pathological conditions. This complex relationship underscores the delicate balance of NADPH homeostasis in pancreatic health and diabetes pathogenesis. By integrating findings from recent studies, this review aims to illuminate the nuanced roles of NADPH in different tissues and its potential as a therapeutic target. Understanding these dynamics offers vital insights into the development of more effective strategies for managing insulin resistance and preserving pancreatic β-cell function, thereby advancing the treatment of metabolic diseases.

Differentially Expressed Genes Regulating Glutathione Metabolism, Protein-Folding, and Unfolded Protein Response in Pancreatic β-Cells in Type 2 Diabetes Mellitus

Impaired redox homeostasis in the endoplasmic reticulum (ER) may contribute to proinsulin misfolding and thus to activate the unfolded protein response (UPR) and apoptotic pathways, culminating in pancreatic β-cell loss and type 2 diabetes (T2D). The present study was designed to identify differentially expressed genes (DEGs) encoding enzymes for glutathione metabolism and their impact on the expression levels of genes regulating protein folding and UPR in β-cells of T2D patients. The GEO transcriptome datasets of β-cells of diabetics and non-diabetics, GSE20966 and GSE81608, were analyzed for 142 genes of interest using limma and GREIN software, respectively. Diabetic β-cells showed dataset-specific patterns of DEGs (FDR ≤ 0.05) implicated in the regulation of glutathione metabolism (ANPEP, PGD, IDH2, and CTH), protein-folding (HSP90AB1, HSP90AA1, HSPA1B, HSPA8, BAG3, NDC1, NUP160, RLN1, and RPS19BP1), and unfolded protein response (CREB3L4, ERP27, and BID). The GCLC gene, encoding the catalytic subunit of glutamate-cysteine ligase, the first rate-limiting enzyme of glutathione biosynthesis, was moderately down-regulated in diabetic β-cells from both datasets (p ≤ 0.05). Regression analysis established that genes involved in the de novo synthesis of glutathione, GCLC, GCLM, and GSS affect the expression levels of genes encoding molecular chaperones and those involved in the UPR pathway. This study showed for the first time that diabetic β-cells exhibit alterations in the expression of genes regulating glutathione metabolism, protein-folding, and UPR and provided evidence for the molecular crosstalk between impaired redox homeostasis and abnormal protein folding, underlying ER stress in type 2 diabetes.