Glial Cell Line-Derived Neurotrophic Factor Protects Against High Fat Diet-Induced Hepatic Steatosis

28 Glial cell line derived neurotrophic factor (GDNF) protects against high fat diet (HFD)-induced hepatic 29 steatosis in mice, however, the mechanisms involved are not known. In this study we investigated the effects of 30 GDNF overexpression and nanoparticle delivery of GDNF in mice on hepatic steatosis and fibrosis and the 31 expression of genes involved in the regulation of hepatic lipid uptake and de novo lipogenesis. Transgenic 32 overexpression of GDNF in liver and other metabolically active tissues was protective against HFD-induced 33 hepatic steatosis. Mice overexpressing GDNF had significantly reduced P62/sequestosome 1 protein levels 34 suggestive of accelerated autophagic clearance. They also had significantly reduced peroxisome proliferator 35 activated receptor-γ (PPAR-γ) and CD36 gene expression and protein levels, and lower expression of mRNA 36 coding for enzymes involved in de novo lipogenesis. GDNF loaded nanoparticles were protective against short37 term HFD-induced hepatic steatosis and attenuated liver fibrosis in mice with long-standing HFD-induced 38 hepatic steatosis. They also suppressed the liver expression of steatosis-associated genes. In vitro, GDNF 39 suppressed triglyceride accumulation in HepG2 cells through enhanced p38 MAPK-dependent signaling and 40 inhibition of PPAR-γ gene promoter activity. These results show that GDNF acts directly in the liver to protect 41 against HFD-induced cellular stress and that GDNF may have a role in the treatment of NAFLD. 42 43