Toll-like receptors and metabolic (dysfunction)-associated fatty liver disease

Metabolic (dysfunction)-associated fatty liver disease (MAFLD) is characterized by the accumulation of lipids in the liver (steatosis). In predisposed individuals, liver steatosis can progress to inflammation, fibrosis, cirrhosis, and hepatocellular carcinoma. The pathogenesis of MAFLD is complex and incompletely understood, involving various steatogenic, pro-inflammatory, and fibrogenic processes. Hyperactivation of the innate immune system through hepatic toll-like receptors (TLRs) contributes to the pathogenesis of MAFLD. Products of intestinal microbiota and danger signals from damaged hepatocytes constitute key ligands of TLRs that promote MAFLD. Most TLRs promote development and progression of MAFLD by induction of pro-inflammatory and pro-fibrogenic cytokines. Several nutraceutical and therapeutic agents improve MAFLD partly through the inhibition of hepatic TLRs. Herein, we review the available literature on hepatic TLR expression and signaling; crosstalk between gut microbiota and hepatic TLRs; and the contribution of TLRs to the pathogenesis of MAFLD. We also highlight implications for therapeutic approaches for MAFLD based on modulation of TLR signaling.