A Non-Canonical Role for Hepatocyte MLKL in Promoting Mitochondrial Dysfunction and Senescence in the Aging Liver

Liver aging is characterized by chronic inflammation and metabolic dysfunction that drive progression of metabolic dysfunction-associated steatotic liver disease (MASLD). Necroptosis, a pro-inflammatory form of cell death via the Receptor-Interacting serine/threonine-Protein Kinase 1 (RIPK1)-RIPK3-Mixed Lineage kinase domain Like pseudokinase (MLKL) pathway, is activated in aging livers, and systemic inhibition of this pathway reduces hepatic inflammation and pathology. The cell type-specific role of necroptosis in liver aging, however, is unclear. Notably, RIPK3 is suppressed in hepatocytes under metabolic disease, suggesting necroptosis independent functions for MLKL. Here, we show that MLKL is elevated in aged hepatocytes and drives liver aging via a non-necroptotic mechanism. Using hepatocyte-specific MLKL-overexpressing mice (MLKL^HepOE), we find that MLKL overexpression does not induce necroptosis but instead promotes cellular senescence, evidenced by increased p16INK4a and p21WAF1/Cip1 and elevated senescence associated secretory phenotype (SASP). Mechanistically, MLKL induces hepatocyte mitochondrial dysfunction, with impaired respiration, altered mitochondrial dynamics, and increased reactive oxygen species, implicating oxidative stress as a contributing mechanism. This mitochondrial stress is associated with enhanced release of pro-inflammatory extracellular vesicles (EVs) and induction of senescence in hepatocytes and non-parenchymal cells. While hepatocytes contribute substantially to total senescent burden by abundance, macrophages emerge as a senescence-enriched population, indicating amplification of senescence through non-cell-autonomous signaling. Collectively, these findings reveal a non-lethal, non-necroptotic function of hepatocyte MLKL in promoting liver inflammaging via mitochondrial dysfunction and paracrine senescence signaling, identifying MLKL as a regulator of hepatic aging and a potential therapeutic target in age-associated liver disease.