Thermoneutral housing does not accelerate metabolic dysfunction-associated fatty liver disease in male or female C57Bl/6J mice fed a Western diet

Metabolic dysfunction-associated fatty liver disease (MAFLD) represents a growing cause of mortality and morbidity and encom-passes a spectrum of liver pathologies. Although dozens of preclinical models have been developed to recapitulate stages of MAFLD, few achieve fibrosis using an experimental design that mimics human pathogenesis. We sought to clarify whether the combination of thermoneutral (TN) housing and consumption of a classical Western diet (WD) would accelerate the onset and progression of MAFLD. Male and female C57Bl/6J mice were fed a nutrient-matched low-fat control or Western diet (WD) for 16 wk. Mice were housed with littermates at either standard temperature (TS; 22 & DEG;C) or thermoneutral-like conditions (TN; -29 & DEG;C). Male, but not female, mice housed at TN and fed a WD were significantly heavier than TS-housed control animals. WD-fed mice housed under TN conditions had lower levels of circulating glucose compared with TS mice; however, there were select but mini-mal differences in other circulating markers. Although WD-fed TN males had higher liver enzyme and higher liver triglyceride levels, no differences in markers of liver injury or hepatic lipid accumulation were observed in females. Housing temperature had little effect on histopathological scoring of MAFLD progression in males; however, although female mice retained a level of pro-tection, WD-TN conditions trended toward a worsened hepatic phenotype, which was associated with higher macrophage tran-script expression and content. Our results indicate that interventions coupling TN housing and WD-induced MAFLD should be longer than 16 wk to accelerate hepatic steatosis and increase inflammation in both sexes of mice. NEW & NOTEWORTHY Mouse models leading to accelerated fatty liver onset are a useful translational tool. Here we show that coupling thermoneutral-like housing and Western diet feeding in mice for 16 wk does not lead to significant disease progression in either sex, though the molecular phenotype indicates priming of immune-related and fibrotic pathways.