KUPFFER CELLS¿ MITOCHONDRIAL PLASTICITY AFFECTS SYSTEMIC IMMUNO-METABOLISM

BACKGROUND: Kupffer cells (KCs) are hepatic resident macrophages that are essential for liver physiology and contribute to the development of metabolic-associated fatty liver disease (MAFLD). Due to their high plasticity, KCs can maintain immunotolerance and mediate cell-cell interaction within the hepatic niche, playing both an immune and metabolic role. As a result, KCs require large amounts of energy to perform their functions, which is why mitochondria turn out to be critical for their functioning. Among the mitochondrial proteins that regulate their dynamism, OPA1 is the gatekeeper of mitochondrial fusion and thus modulates oxidative phosphorylation. AIM: The immunomodulatory role of mitochondria on the activity of antigen-presenting cells has been proposed and needs further investigation. This is a critical aspect of modulation that coordinates cell fate decisions and metabolic capacity in relation to the intracellular and extracellular environment. On this premises, this project aims to study how modulation of OPA1-driven mitochondrial fusion in KCs can influence lipid metabolism and immune response at the systemic and hepatic levels. RESULTS: Mice selectively lacking OPA1 in KCs were fed a Standard Diet or a High-Fat Diet for 20 weeks. The immune phenotype was assessed by cytofluorimetry while the metabolic profile was evaluated by in vivo indirect calorimetry and with plasma and tissue lipid profile analysis. Single cell RNA sequencing was also performed to profile the impact of OPA1 deficiency on KCs function and the paracrine effects on hepatocytes. Under standard dietary conditions, mice selectively lacking OPA1 in KCs exhibit a metabolic substrate preference toward carbohydrates, with an immunophenotype characterized by a higher proportion of pro-resolving KC2s than pro-inflammatory KC1s. Functionally, KCs also exhibit increased phagocytic and antigen-presenting ability, and a different proliferative capacity compared to controls which could be reconducted to a different cholesterol distribution within the plasma membrane. By challenging the system with a high-fat diet, we observed reversal of the phenotype in terms of metabolic preference and a significant reduction of KC percentage on total liver immune cells. CONCLUSIONS: Taken together, these data suggest that OPA1 plays a key role in the function of Kupffer cells and that the lack of OPA1, by causing intracellular remodeling and thus metabolic reprogramming, affects their interaction with resident liver cells, thereby influencing both the metabolic immunophenotype, the development and progression of MAFLD.