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

ABSTRACT

BACKGROUND & AIMS: 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). METHODS: 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. RESULTS: 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. CONCLUSIONS: 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. LAY SUMMARY: Cyclin 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.