Monoacylglycerol lipase reprograms hepatocytes and macrophages to promote liver regeneration

Background & aims: Liver regeneration is a repair process in which metabolic reprogramming of parenchymal and inflammatory cells plays a major role. Monoacylglycerol lipase (MAGL) is an ubiquitous enzyme at the crossroad between lipid metabolism and inflammation. It converts monoacylglycerols into free fatty acids and metabolises 2-arachidonoylglycerol into arachidonic acid, being thus the major source of pro-inflammatory prostaglandins in the liver. In this study, we investigated the role of MAGL in liver regeneration.

Methods: Hepatocyte proliferation was studied in vitro in hepatoma cell lines and ex vivo in precision-cut human liver slices. Liver regeneration was investigated in mice treated with a pharmacological MAGL inhibitor, MJN110, as well as in animals globally invalidated for MAGL (MAGL^-/-) and specifically invalidated in hepatocytes (MAGL^Hep-/-) or myeloid cells (MAGL^Mye-/-). Two models of liver regeneration were used: acute toxic carbon tetrachloride injection and two-thirds partial hepatectomy. MAGL^Mye-/- liver macrophages profiling was analysed by RNA sequencing. A rescue experiment was performed by in vivo administration of interferon receptor antibody in MAGL^Mye-/- mice.

Results: Precision-cut human liver slices from patients with chronic liver disease and human hepatocyte cell lines exposed to MJN110 showed reduced hepatocyte proliferation. Mice with global invalidation or mice treated with MJN110 showed blunted liver regeneration. Moreover, mice with specific deletion of MAGL in either hepatocytes or myeloid cells displayed delayed liver regeneration. Mechanistically, MAGL^Hep-/- mice showed reduced liver eicosanoid production, in particular prostaglandin E₂ that negatively impacts on hepatocyte proliferation. MAGL inhibition in macrophages resulted in the induction of the type I interferon pathway. Importantly, neutralising the type I interferon pathway restored liver regeneration of MAGL^Mye-/- mice.

Conclusions: Our data demonstrate that MAGL promotes liver regeneration by hepatocyte and macrophage reprogramming.

Impact and implications: By using human liver samples and mouse models of global or specific cell type invalidation, we show that the monoacylglycerol pathway plays an essential role in liver regeneration. We unveil the mechanisms by which MAGL expressed in both hepatocytes and macrophages impacts the liver regeneration process, via eicosanoid production by hepatocytes and the modulation of the macrophage interferon pathway profile that restrains hepatocyte proliferation.