Myeloid Nrf2 deficiency aggravates non-alcoholic steatohepatitis progression by regulating YAP-mediated NLRP3 inflammasome signaling

Nuclear-erythroid-2-related factor 2 (Nrf2) is involved in the pathogenesis of different liver diseases. Herein, we first demonstrated that Nrf2 expression was diminished in nonalcoholic steatohepatitis (NASH) liver macrophages. In myeloid Nrf2-deficiency mice, aggravated liver steatosis and inflammation in high-fat-diet (HFD)-fed mice were observed compared with the chow-diet group. Moreover, the increasing inflammatory cytokines influenced the lipid metabolism in hepatocytes in vivo and in vitro. Further study showed Nrf2 regulated reactive-oxygen-species-mediated Hippo-yes-associated protein (YAP) signaling, which in turn modulated the NLRP3 inflammasome activation. Administration of YAP activator also significantly ablated the lipid accumulation and inhibited the NLRP3 activation in the Nrf2 deletion condition both in vitro and vivo. Overexpression Nrf2 in liver macrophages effectively alleviated steatohepatitis in wild-type mice fed with an HFD . Our data support that by modulating YAP-mediated NLRP3 inflammasome activity, macrophage Nrf2 slows down NASH progression.

Chronic cold exposure induces autophagy to promote fatty acid oxidation, mitochondrial turnover, and thermogenesis in brown adipose tissue

Autophagy plays an important role in lipid breakdown, mitochondrial turnover, and mitochondrial function during brown adipose tissue (BAT) activation by thyroid hormone, but its role in BAT during adaptive thermogenesis remains controversial. Here, we examined BAT from mice exposed to 72 h of cold challenge as well as primary brown adipocytes treated with norepinephrine and found increased autophagy as well as increased β-oxidation, mitophagy, mitochondrial turnover, and mitochondrial activity. To further understand the role of autophagy of BAT in vivo, we generated BAT-specific Atg5 knockout (Atg5cKO) mice and exposed them to cold for 72 h. Interestingly, BAT-specific Atg5cKO mice were unable to maintain body temperature after chronic cold exposure and displayed deranged mitochondrial morphology and reactive oxygen species damage in their BAT. Our findings demonstrate the critical role of autophagy in adaptive thermogenesis, fatty acid metabolism, and mitochondrial function in BAT during chronic cold exposure.

A human pluripotent stem cell model for the analysis of metabolic dysfunction in hepatic steatosis

Nonalcoholic fatty liver disease (NAFLD) is currently the most prevalent form of liver disease worldwide. This term encompasses a spectrum of pathologies, from benign hepatic steatosis to non-alcoholic steatohepatitis, which have, to date, been challenging to model in the laboratory setting. Here, we present a human pluripotent stem cell (hPSC)-derived model of hepatic steatosis, which overcomes inherent challenges of current models and provides insights into the metabolic rewiring associated with steatosis. Following induction of macrovesicular steatosis in hepatocyte-like cells using lactate, pyruvate, and octanoate (LPO), respirometry and transcriptomic analyses revealed compromised electron transport chain activity. 13C isotopic tracing studies revealed enhanced TCA cycle anaplerosis, with concomitant development of a compensatory purine nucleotide cycle shunt leading to excess generation of fumarate. This model of hepatic steatosis is reproducible, scalable, and overcomes the challenges of studying mitochondrial metabolism in currently available models.