UC San Diego

Non-alcoholic fatty liver disease (NAFLD) has rapidly emerged as the most prevalent liver disease in westernized countries, affecting approximately 1 in 3 adults in the US and roughly 25% of adults globally [1,2]. NAFLD can progress to nonalcoholic steatohepatitis (NASH), a progressive form of the disease characterized by inflammation, hepatocyte injury, and increased risk for hepatology-related morbidity and mortality [3]. It is unclear why only a subset of patients with NAFLD progress to NASH. One of the leading explanations is the “multiple parallel hits hypothesis”, which considers multiple insults such as hepatic steatosis, inflammation, and insulin resistance that act in unison to trigger the progression of NAFLD to NASH [4]. However, a very significant element of this hypothesis that is missing is circadian rhythms, which play a role in modulating every insult or “hit”. Our objective is to elucidate the role of circadian rhythms in the liver and intestines, which can be entrained by the gut microbiome, in the pathophysiology and progression of NAFLD to NASH. Previous research indicates that certain feeding patterns, such as time-restricted feeding (TRF), prevent a variety of NASH risk factors, including hepatic steatosis and circadian rhythm disruption in the liver and intestines [5,6]. We hypothesize that NASH onset results from altered gut microbiome dynamics and disrupted hepatic circadian rhythms, which can be manipulated with feeding pattern to ameliorate disease. To test this hypothesis, we used the streptozotocin + high-fat diet (STAM/HFD) murine model of NASH, which recapitulates key aspects of human NASH pathogenesis, including hepatic steatosis, inflammation, and fibrosis on a hyperglycemic background [7]. STAM/HFD mice underwent 8-hour TRF or had access to food ad libitum (adlib). Importantly, STAM/HFD mice are hypoinsulinemic and do not become insulin resistant [7]. This allowed us to specifically investigate whether TRF can prevent NASH via the modulation of circadian rhythms, without the confounding factor of TRF affecting insulin signaling. Our results demonstrate that TRF is not capable of preventing NASH in the STAM/HFD model. Surprisingly, STAM/HFD mice with adlib access to food have a maintenance of rhythmic feeding patterns, as well as a maintenance of ileal and hepatic gene expression patterns. TRF was capable of preventing disruptions to diurnal fluctuations in gut microbiome composition. However, this was not capable of preventing the onset of NASH in the STAM/HFD model. Results from this study suggest that STAM/HFD-induced NASH does not result from circadian rhythm disruption, and that insulin may be a crucial element to mediating the protective effects of TRF.