Nicotinamide riboside protects against liver fibrosis induced by CCl4 via regulating the acetylation of Smads signaling pathway

Aims: Increasing nicotinamide adenine dinucleotide (NAD(+)) by Nicotinamide riboside (NR) provides protective benefits in multiple disorders. However, the role of NR on liver fibrosis is unclear. We performed in vivo and in vitro experiments to test the hepatic protective effects of NR against liver fibrosis and the underlying mechanisms. Materials and methods: Mice were injected with CCl4 to establish liver fibrosis model. NR was given by gavage to explore the hepatic protection of NR. LX-2 cells were given a TGF-beta stimulation +/- NR, the activation of LX-2 cells and the acetylation of Smads were analyzed. To further confirm the role of Sirtl on the protective pathway of NR, we knockdown Sirtl in LX-2 cells. Key findings: We found NR could prevent liver fibrosis and reverse the existing liver fibrosis. NR inhibited the activation of LX-2 cells induced by TGF-beta, activated Sirtl and deacetylated Smad2/3. Sirtl knockdown diminished the inhibiting effect of NR on LX-2 cells activation, and increased expressions of acetylated Smads. In conclusion, NR could prevent liver fibrosis via suppressing activation of hepatic stellate cells (HSCs). This protective effect was mediated by regulating the acetylation of Smads signaling pathway. Significance: NR protected mice against liver fibrosis induced by CCl4. NR suppressed activation of hepatic stellate cells induced by TGF-beta. NR protects liver fibrosis via increasing the activity of Sirtl and decreasing the expression of P300, resulting in the deacetylation of Smads in stellate cells.