Magnesium accumulation upon cyclin M4 silencing activates microsomal triglyceride transfer protein improving NASH

•CNNM4 acts as a magnesium exporter in the liver. Its upregulation in NASH leads to elevated magnesium levels in serum.•Liver-specific CNNM4 targeting alleviates steatosis, inflammation, and fibrosis in preclinical NASH models.•siRNA-mediated CNNM4 downregulation promotes hepatic magnesium accumulation and reduces endoplasmic reticulum stress.•Silencing CNNM4 enhances microsomal triglyceride transfer protein activity leading to VLDL assembly and secretion. Background & AimsPerturbations of intracellular magnesium (Mg2+) homeostasis have implications for cell physiology. The cyclin M family, CNNM, perform key functions in the transport of Mg2+ across cell membranes. Herein, we aimed to elucidate the role of CNNM4 in the development of non-alcoholic steatohepatitis (NASH).MethodsSerum Mg2+ levels and hepatic CNNM4 expression were characterised in clinical samples. Primary hepatocytes were cultured under methionine and choline deprivation. A 0.1% methionine and choline-deficient diet, or a choline-deficient high-fat diet were used to induce NASH in our in vivo rodent models. Cnnm4 was silenced using siRNA, in vitro with DharmaFECT and in vivo with Invivofectamine® or conjugated to N-acetylgalactosamine.ResultsPatients with NASH showed hepatic CNNM4 overexpression and dysregulated Mg2+ levels in the serum. Cnnm4 silencing ameliorated hepatic lipid accumulation, inflammation and fibrosis in the rodent NASH models. Mechanistically, CNNM4 knockdown in hepatocytes induced cellular Mg2+ accumulation, reduced endoplasmic reticulum stress, and increased microsomal triglyceride transfer activity, which promoted hepatic lipid clearance by increasing the secretion of VLDLs.ConclusionsCNNM4 is overexpressed in patients with NASH and is responsible for dysregulated Mg2+ transport. Hepatic CNNM4 is a promising therapeutic target for the treatment of NASH.Lay summaryCyclin M4 (CNNM4) is overexpressed in non-alcoholic steatohepatitis (NASH) and promotes the export of magnesium from the liver. The liver-specific silencing of Cnnm4 ameliorates NASH by reducing endoplasmic reticulum stress and promoting the activity of microsomal triglyceride transfer protein. Perturbations of intracellular magnesium (Mg2+) homeostasis have implications for cell physiology. The cyclin M family, CNNM, perform key functions in the transport of Mg2+ across cell membranes. Herein, we aimed to elucidate the role of CNNM4 in the development of non-alcoholic steatohepatitis (NASH). Serum Mg2+ levels and hepatic CNNM4 expression were characterised in clinical samples. Primary hepatocytes were cultured under methionine and choline deprivation. A 0.1% methionine and choline-deficient diet, or a choline-deficient high-fat diet were used to induce NASH in our in vivo rodent models. Cnnm4 was silenced using siRNA, in vitro with DharmaFECT and in vivo with Invivofectamine® or conjugated to N-acetylgalactosamine. Patients with NASH showed hepatic CNNM4 overexpression and dysregulated Mg2+ levels in the serum. Cnnm4 silencing ameliorated hepatic lipid accumulation, inflammation and fibrosis in the rodent NASH models. Mechanistically, CNNM4 knockdown in hepatocytes induced cellular Mg2+ accumulation, reduced endoplasmic reticulum stress, and increased microsomal triglyceride transfer activity, which promoted hepatic lipid clearance by increasing the secretion of VLDLs. CNNM4 is overexpressed in patients with NASH and is responsible for dysregulated Mg2+ transport. Hepatic CNNM4 is a promising therapeutic target for the treatment of NASH.