COL1A1 and metabolic dysfunction-associated steatohepatitis: In addition, macrophage-specific Pparγ deficiency showed significantly increased expression of liver fibrosis-related genes, such as transforming growth factor-beta 1 (TGF-β1), actin alpha 2, collagen type I alpha 1 (COL1A1), and tissue inhibitor of metalloproteinase (TIMP)-1, in MASH liver.