Mechanisms and therapeutic potential of blocking the mitochondrial Mg2+ channel Mrs2 in obesity and NAFLD

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ABSTRACT Aberrant hepatic glucose and lipid metabolism is a feature of several prevalent metabolic disorders, including obesity, type 2 diabetes (T2DM) and nonalcoholic fatty liver disease (NAFLD). Increased hepatic glucose production directly contributes to hyperglycemia in patients with T2DM, and hepatic steatosis is the defining feature of NAFLD. The increased prevalence of T2DM and NAFLD present a significant threat to public health, and treatment strategies that address the underlying pathological processes are urgently needed. Although Ca2+ signaling in metabolic disease is emerging, the potential reciprocal role of Mg2+ dynamics on mitochondrial bioenergetics is much less understood and is the focus of the current proposal. In preliminary studies, we generated a global KO model of the mitochondrial Mg2+ transporter Mrs2 using CRISPR/Cas9 and examined the impact on hepatic metabolism (Daw et al Cell 2020). Interestingly, loss of Mrs2 impairs mMg2+ uptake and prevents hepatic steatosis in vivo. This is associated with increased mitochondrial respiratory capacity in hepatocytes and markedly enhanced browning of white adipose tissue, indicative of increased capacity for energy expenditure. Using innovative, unbiased RNA-seq, animal physiology studies, molecular, cell biological, biochemistry and biophysical approaches, we have identified candidate pathways linking Mrs2-mediated mMg2+ uptake to mitochondrial suppression of OXPHOS and fatty acid oxidation under WD. Remarkably, the elevation of de novo lipogenesis precursor citrate is blunted in Mrs2 KO mice and thus controls diet induced obesity. Based on these preliminary data, we hypothesize that Mrs2-mediated mMg2+ uptake is a key determinant of mitochondrial bioenergetic failure in the liver during disease progression, and that mitigating excess mMg2+ uptake using a small molecule blocker of the Mrs2 channel activity will prevent the development of NAFLD through restoration of signaling and mitochondrial bioenergetics. The overall aim of the current proposal is to identify molecular signals that are controlled by mMg2+ dynamics, and their impact on bioenergetics and mitochondrial quality control, and to describe the molecular mechanisms linking Mrs2 to key hepatic metabolic pathways that are dysregulated in metabolic diseases. Using a combination of integrative in vitro and in vivo approaches, we will perform mechanistic studies to determine the impact of disrupted intracellular Mg2+ signals on mitochondrial function, hepatic lipid and glucose metabolism, whole-body energy homeostasis, and the progression of NAFLD. Given these preliminary findings, in Specific Aim 1 of the proposal we will employ our unique mouse model to examine the role of Mrs2 and mMg2+ uptake on mitochondrial function in hepatocytes and will determine the impact of impaired mMg2+ uptake on hepatic and whole-body glucose and lipid metabolism. In Specific Aim 2, we will investigate the role of citrate in Hif-1α dependent signaling that is altered in Mrs2 KO, which ultimately restores mitochondrial energetics and quality control. Finally, in Specific Aim 3, we will use both genetic and pharmacologic interventions to evaluate the significance of MRS2 in NAFLD models.