C3 and metabolic dysfunction-associated steatotic liver disease: Because C3 is the key molecule in the pathway of complement system activation (7), several hypotheses are proposed that C3 plays an important role in lipid metabolism in the pathogenesis of NAFLD (Figure 2): Firstly, C3 is mainly synthesized by hepatocytes and identified to appear in lipoprotein particles such as high density lipoprotein and chylomicron (20, 21).