Modulation of mitochondrial dynamism in kupffer cells impacts systemic metabolism

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): University of Milan Background Kupffer Cells (KC) are hepatic resident macrophages that are essential for liver physiology and contribute to the development of Non-Alcoholic Fatty Liver Disease (NAFLD). The liver of patients with NAFLD shows different expression of some key regulators of inner mitochondrial membrane fusion compared with healthy subjects, including OPA1 protein, which is a mitochondrial protein whose activity promotes mitochondrial fusion and positive modulation of oxidative phosphorylation. Aim Given that Kupffer Cells have both immune and metabolic roles, their mitochondria are critical for their and energy requirements and their functionality. This project aims to study how the inhibition of OPA1-driven mitochondrial fusion affects immune-metabolic response and progression of NAFLD by exploring the role of OPA1 in both a Standard and High-fat diet context. Methods mice selectively lacking OPA1 in Kupffer Cells were fed with either a Standard diet or a High-fat diet for 20 weeks. The metabolic phenotype was assessed by in vivo indirect calorimetry, measurement of plasma and tissue lipid profile, glucose and insulin sensitivity assays, and complete immunophenotype characterization. Single cell RNA sequencing was also performed to profile with higher resolution the impact of OPA1 deficiency on Kupffer Cell function and cross talk with other liver cells types within the hepatic niche. Results Under Standard diet conditions mice selectively lacking OPA1 in Kupffer Cells show a significant reduction in the KC1 pro-inflammatory subset, while the pro-resolutive KC2 increases significantly. In addition, mice lacking OPA1 in KCs show a metabolic preference towards carbohydrates, despite comparable energy expenditure, O2 consumption and CO2 production. The systemic immune profile was comparable between the two groups, with an expected reduction in KC total number under High-fat diet conditions, where no significant differences were observed between the two groups in plasma cholesterol and triglyceride levels, while a significant reduction in liver fibrosis was observed with liver histology. Conclusions Taken together these preliminary data suggest that OPA1-mediated inhibition of mitochondrial fusion in Kupffer Cells affects the systemic metabolic response under Standard diet with a reflection also on High-fat diet conditions, where systemic metabolism is comparable between the two groups, but the loss of OPA1 appears to influence the progression of NAFLD through a reduction in total liver fibrosis. Ongoing studies aim to understand the molecular mechanisms underlying these different immune-metabolic responses.