According to research published in Nature Medicine, housing mice at thermoneutral temperatures to promote metabolic homeostasis results in improved experimental modelling of NAFLD, including several features that are often poorly recapitulated in other models of the disease.

Credit: Laura Marshall/Macmillan Publishers Limited

NAFLD is a common chronic liver disease, encompassing a spectrum of disorders ranging from steatosis to cirrhosis, and often leading to hepatocellular carcinoma (HCC). Although obesity, dysbiosis and various inflammatory processes are thought to have a role in disease development, few specific therapies for NAFLD exist and the pathogenesis of this disease remains underdefined.

“The lack of an in-depth definition of the mechanistic underpinnings regulating NAFLD pathogenesis ... is in part due to the absence of a relevant, murine model of NAFLD that more fully recapitulates human disease,” explains author Senad Divanovic. Current mouse models of NAFLD fail to simulate human disease features such as hepatic fibrosis and, in part, gene expression and gut microbiota composition. Furthermore, current mouse models are associated with a sex bias not seen in human NAFLD that precludes using female mice to investigate pathogenesis.

To address these issues, the investigators sought to develop a novel and improved mouse model of NAFLD that uses thermoneutral housing to promote physiological and metabolic homeostasis in mice. “Mice are normally housed at a suboptimal temperature that is comfortable for their human handlers (∼20–23°C),” says Divanovic. “Housing mice at thermoneutrality (30–32°C) reverses multiple physiological effects of cold stress, including reduction in heart rate and overall energy expenditure.”

The researchers housed mice at both standard and thermoneutral temperatures and found that the thermoneutral housing relieved stress-driven corticosterone production in mice and augmented pro-inflammatory immune responses. To investigate obesity-induced hepatic steatosis, the investigators then fed differently housed animals a high-fat diet (HFD) or standard chow for 24 weeks. Across multiple strains of mice, the pathogenesis of HFD-driven NAFLD was found to be exacerbated in animals housed at thermoneutrality compared with those housed at standard temperatures, as shown by increased hepatic steatosis and hepatocellular damage, as well as increased expression of genes associated with hepatic fibrosis and HCC. Disease exacerbation in thermoneutrally housed HFD-fed mice was also associated with increased intestinal permeability and an altered gut microbiota similar to that observed in patients with NASH.

Furthermore, measurable hepatic fibrosis was demonstrated using trichrome staining in thermoneutrally housed AKR mice fed a HFD, and in female C57BL/6 mice, who are typically resistant to HFD-induced obesity and NAFLD, thermoneutrality led to full disease characteristics. Together, these data suggest that thermoneutral housing provides a sex-independent model of exacerbated NAFLD that could improve our knowledge of the mechanisms regulating NAFLD.

“Comparing disease progression at thermoneutral, as opposed to standard, temperatures should allow for the identification of key mediators of disease that have previously gone unrealized,” concludes Divanovic. “This model might enable improved discovery and testing of potential therapeutics,” he adds. The researchers also plan to investigate thermoneutral housing of obese, pregnant mice, which could reveal how obesity contributes to transgenerational transfer of metabolic disease susceptibility.