Pancreatic β cells put the glutamine engine in reverse

Epigenetic crossroads in metabolic and cardiovascular health: the role of DNA methylation in type 2 diabetes and cardiovascular diseases

Type 2 diabetes (T2D) and cardiovascular diseases (CVD), part of the metabolic syndrome (MetS), are major contributors to the global health crisis today. A recent report from the World Health Organisation estimates that 17.9 million lives are lost each year to CVD, and one-third of these are premature. The international diabetes federation estimates that around 537 million adults aged between 20 and 79 years are living with diabetes. People with diabetes are suggested to have twice the risk of developing CVD. Epigenetic modifications are being increasingly recognised as the key mediators linking genetic and environmental conditions to metabolic dysfunction. Among these, DNA methylation plays a crucial role in modulating gene expression and influencing pathways involved in glucose homeostasis, inflammation, and vascular integrity. Despite the advances in our understanding of the role of epigenetic alterations in metabolic diseases, including that of T2D, the mechanisms driving selective methylation changes and their long-term impact on cardiovascular health are still not well understood. This review synthesises the current knowledge on DNA methylation dynamics in T2D and their role towards the progression of CVD and explores their potential as biomarkers and therapeutic targets. Understanding the interplay between metabolism and epigenetics in the pathogenesis of T2D and CVD could provide critical insights for early disease identification and the development of novel epigenome-targeted therapeutic strategies.

The Diabetes Gene Tcf7l2 Organizes Gene Expression in the Liver and Regulates Amino Acid Metabolism

TCF7L2 harbors the strongest genetic association with diabetes identified thus far. However, its function in liver has remained unclear. Here, we find using mice with liver-specific deletion, that Tcf7l2 plays a central role in maintaining hepatic zonation. That is, in the normal liver, many genes show gradients of expression across the liver lobule; in the absence of Tcf7l2 , these gradients collapse. One major consequence is the disorganization of glutamine metabolism, with a loss of the glutamine production program, ectopic expression of the glutamine consumption program, and a decrease in glutamine levels. In parallel, metabolomic profiling shows glutamine to be the most significantly decreased metabolite in individuals harboring the rs7903146 variant in TCF7L2 . Taken together, these data indicate that hepatic TCF7L2 has a secondary role in glycemic control, but a primary role in maintaining transcriptional architecture and glutamine homeostasis.

Metabolic regulation of mitochondrial morphologies in pancreatic beta cells: coupling of bioenergetics and mitochondrial dynamics

Cellular bioenergetics and mitochondrial dynamics are crucial for the secretion of insulin by pancreatic beta cells in response to elevated levels of blood glucose. To elucidate the interactions between energy production and mitochondrial fission/fusion dynamics, we combine live-cell mitochondria imaging with biophysical-based modeling and graph-based network analysis. The aim is to determine the mechanism that regulates mitochondrial morphology and balances metabolic demands in pancreatic beta cells. A minimalistic differential equation-based model for beta cells is constructed that includes glycolysis, oxidative phosphorylation, calcium dynamics, and fission/fusion dynamics, with ATP synthase flux and proton leak flux as main regulators of mitochondrial dynamics. The model shows that mitochondrial fission occurs in response to hyperglycemia, starvation, ATP synthase inhibition, uncoupling, and diabetic conditions, in which the rate of proton leakage exceeds the rate of mitochondrial ATP synthesis. Under these metabolic challenges, the propensities of tip-to-tip fusion events simulated from the microscopy images of the mitochondrial networks are lower than those in the control group and prevent the formation of mitochondrial networks. The study provides a quantitative framework that couples bioenergetic regulation with mitochondrial dynamics, offering insights into how mitochondria adapt to metabolic challenges.

Efficacy of Perioperative Infusion of N(2)-L-alanyl-L-glutamine in Glycemic Control for Patients With Uncontrolled Diabetes Mellitus Presented for Urgent Coronary Artery Bypass Surgery: A Randomized Controlled Trial

OBJECTIVES

To evaluate the efficacy of preoperative glutamine infusion in reducing insulin requirements in patients with uncontrolled type 2 diabetes, defined as glycated hemoglobin (HbA1c) >7%, undergoing urgent coronary artery bypass graft (CABG) surgery.

DESIGN

A randomized controlled trial.

SETTING

At Ain Shams University Hospital, Cardiothoracic Academy.

PARTICIPANTS

Ninety-three patients (of both sexes) with uncontrolled diabetes presenting for urgent CABG were categorized into 2 groups.

INTERVENTIONS

The dipeptiven group (n = 46) was given an infusion of dipeptiven 1.5 mL/kg body weight dissolved in normal saline (200 mL) over 3 hours before surgery. The control group (n = 47) received a normal saline infusion (200 mL).

MEASUREMENTS AND MAIN RESULTS

The dipeptiven group demonstrated statistically significant lower intraoperative (173.74 ± 19.97 mg/dL v 198.22 ±14.64 mg/dL) and postoperative (162.36 ±13.11 mg/dL v 176.13 ±14.86 mg/dL) mean blood glucose levels. In addition, dipeptiven infusion was found to reduce mean total insulin requirements intraoperatively by 3.64 ± 0.56 units/h and postoperatively by 37.109 ± 4.30 units/24 h in comparison to placebo (50.98 ± 16.55 units/24 h and 5.10 ± 2.28 units/h, respectively).

CONCLUSION

A preoperative infusion of dipeptiven can contribute to ameliorating stress hyperglycemia in uncontrolled diabetic patients undergoing urgent CABG.

Hispidin Inhibits Ferroptosis Induced by High Glucose via the miR-15b-5p/GLS2 Axis in Pancreatic Beta Cells

Type 2 diabetes mellitus (T2DM) is a global health issue that lacks effective treatments. Dysfunction and/or death of pancreatic β-cells (PBCs) are considered a major cause of T2DM. Therefore, elucidating the mechanisms underlying the death of PBCs might be helpful to develop novel strategies to treat T2DM. Ferroptosis is a newly identified form of cell death that has distinct features. However, knowledge regarding the role of ferroptosis in the death of PBCs remains limited. In the current study, we used high glucose (10 mM) (HG) levels to induce ferroptosis in PBC. We also observed that hispidin, a polyphenol compound that can be isolated from Phellinus linteus, could attenuate ferroptosis induced by HG in PBCs. Mechanistic investigations showed that hispidin led to the upregulation of miR-15b-5p, which directly inhibits the expression of glutaminase (GLS2) which plays an essential role in the glutamine metabolism. In addition, we found that overexpression of GLS2 could abrogate the protective effect of hispidin against ferroptosis caused by HG in PBCs. Therefore, our study provides novel insights into the mechanisms that regulate the death of PBCs.