B04

Higher serum levels of GPNMB are linked to type 2 diabetes mellitus (T2DM) and metabolic dysfunction-associated steatotic liver disease (MASLD). Disruption of circadian rhythms also influences the development and progression of MASLD. In this study, we investigated how GPNMB modulates hepatic glycogen metabolism and its potential interaction with the hepatic circadian clock. Male DBA/2 J mice, either wild-type (GP⁺) or carrying an inactivating Gpnmb mutation (GP⁻), were fed a high-fat diet (48.4% fat) supplemented with 30% fructose in drinking water for 12 weeks. Despite similar weight gain, GP⁻ mice displayed greater global fat mass accumulation and elevated serum triglyceride and cholesterol levels. Surprisingly, GP⁻ mice showed improved glucose tolerance, whereas GP⁺ mice developed impaired glycemic control. Indirect calorimetry under thermoneutral conditions (30°C) revealed loss of diurnal rhythmicity in energy expenditure (EE) in GP⁻ mice, which was independent of food intake. Despite its preserved rhythms, hepatic clock gene expression in GP⁻ mice showed increased MESOR (e.g., Per1, Per2, and Nr1d1) and increased amplitude (e.g., Nr1d1), indicating higher expression levels throughout the day. GPNMB deficiency further impaired hepatic glycogen storage dynamics, which was attributed to reduced AKT phosphorylation (indicative of defective insulin signaling), reduced FOXO1 phosphorylation, and increased PEPCK-M. Translating our findings to human MASLD patients, GPNMB expression obtained from liver biopsies showed a clear increase across MASLD progression. Importantly, patients with metabolic dysfunction-associated steatohepatitis (MASH) and diabetes who received anti-diabetic treatment showed a reduction in hepatic GPNMB expression. Collectively, our findings suggest that GPNMB plays a role in metabolic adaptation to obesogenic diets, as a Gpnmb loss-of-function model reveals an association with impaired hepatic insulin signaling and glycogen metabolism despite improved systemic glucose tolerance in mice, whereas hepatic GPNMB upregulation correlates with MASLD progression in humans.

Background & aims: The liver ensures organismal homeostasis through modulation of physiological functions over the course of the day. How liver diseases such as nonalcoholic steatohepatitis (NASH) affect daily transcriptome rhythms in the liver remains elusive.

Methods: To start closing this gap, we evaluated the impact of NASH on the diurnal regulation of the liver transcriptome in mice. In addition, we investigated how stringent consideration of circadian rhythmicity affects the outcomes of NASH transcriptome analyses.

Results: Comparative rhythm analysis of the liver transcriptome from diet-induced NASH and control mice showed an almost 3-hour phase advance in global gene expression rhythms. Rhythmically expressed genes associated with DNA repair and cell-cycle regulation showed increased overall expression and circadian amplitude. In contrast, lipid and glucose metabolism-associated genes showed loss of circadian amplitude, reduced overall expression, and phase advances in NASH livers. Comparison of NASH-induced liver transcriptome responses between published studies showed little overlap (12%) in differentially expressed genes (DEGs). However, by controlling for sampling time and using circadian analytical tools, a 7-fold increase in DEG detection was achieved compared with methods without time control.

Conclusions: NASH had a strong effect on circadian liver transcriptome rhythms with phase- and amplitude-specific effects for key metabolic and cell repair pathways, respectively. Accounting for circadian rhythms in NASH transcriptome studies markedly improves DEG detection and enhances reproducibility.

Keywords: Circadian Bioinformatics; Circadian Clock; Circadian RNAseq; Energy Metabolism; Nonalcoholic Fatty Liver Disease (NAFLD).

The circadian clock comprises a cellular endogenous timing system coordinating the alignment of physiological processes with geophysical time. Disruption of circadian rhythms has been associated with several metabolic diseases. In this review, we focus on liver as a major metabolic tissue and one of the most well-studied organs with regard to circadian regulation. We summarize current knowledge about the role of local and systemic clocks and rhythms in regulating biological functions of the liver. We discuss how the disruption of circadian rhythms influences the development of non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). We also critically evaluate whether NAFLD/NASH may in turn result in chronodisruption. The last chapter focuses on potential roles of the clock system in prevention and treatment of NAFLD/NASH and the interaction of current NASH drug candidates with liver circadian rhythms and clocks. It becomes increasingly clear that paying attention to circadian timing may open new avenues for the optimization of NAFLD/NASH therapies and provide interesting targets for prevention and treatment of these increasingly prevalent disorders.

Keywords: NAFLD; NASH; chronotherapy; circadian rhythms; clock genes; liver; metabolic-associated fatty liver disease (MAFLD).