Elevated circulating TGFβ1 during acute liver failure activates TGFβR2 on cortical neurons and exacerbates neuroinflammation and hepatic encephalopathy in mice

BackgroundAcute liver failure resulting from drug-induced liver injury can lead to the development of neurological complications called hepatic encephalopathy (HE). Hepatic transforming growth factor beta 1 (TGF1) is upregulated due to liver failure in mice and inhibiting circulating TGF reduced HE progression. However, the specific contributions of TGF1 on brain cell populations and neuroinflammation during HE are not known. Therefore, the aim of this study was to characterize hepatic and brain TGF1 signaling during acute liver failure and its contribution to HE progression using a combination of pharmacological and genetic approaches.MethodsC57Bl/6 or neuron-specific transforming growth factor beta receptor 2 (TGFR2) null mice (TGFR2(Neu)) were treated with azoxymethane (AOM) to induce acute liver failure and HE. The activity of circulating TGF1 was inhibited in C57Bl/6 mice via injection of a neutralizing antibody against TGF1 (anti-TGF1) prior to AOM injection. In all mouse treatment groups, liver damage, neuroinflammation, and neurological deficits were assessed. Inflammatory signaling between neurons and microglia were investigated in in vitro studies through the use of pharmacological inhibitors of TGF1 signaling in HT-22 and EOC-20 cells.ResultsTGF1 was expressed and upregulated in the liver following AOM injection. Pharmacological inhibition of TGF1 after AOM injection attenuated neurological decline, microglia activation, and neuroinflammation with no significant changes in liver damage. TGFR2(Neu) mice administered AOM showed no effect on liver pathology but significantly reduced neurological decline compared to control mice. Microglia activation and neuroinflammation were attenuated in mice with pharmacological inhibition of TGF1 or in TGFR2(Neu) mice. TGF1 increased chemokine ligand 2 (CCL2) and decreased C-X3-C motif ligand 1 (CX3CL1) expression in HT-22 cells and reduced interleukin-1 beta (IL-1 ss) expression, tumor necrosis factor alpha (TNF) expression, and phagocytosis activity in EOC-20 cells.ConclusionIncreased circulating TGF1 following acute liver failure results in activation of neuronal TGFR2 signaling, driving neuroinflammation and neurological decline during AOM-induced HE.