Fibrotic transformation of the liver is a major cause of death worldwide. The generation of reactive oxygen species (ROS) is a typical feature of chronic liver disease, causing protein damage and lipid peroxidation and leading to formation of toxic aldehydes. Mitochondrial aldehyde dehydrogenase-2 (ALDH2) detoxifies these aldehydes. My recent pilot study showed that Alda-1, a novel small-molecule activator of ALDH2, decreased fibrosis after bile duct ligation (BDL). Accordingly, I seek to validate ALDH2 as a drug target to decrease fibrosis by detoxification of toxic aldehydes. I hypothesize that activation of ALDH2 aids in the detoxification of aldehydes and decreases activation of hepatic stellate cells, thereby suppressing fibrosis and promoting recovery. Success of this study will identify a novel therapeutic target against fibrosis for development of much needed antifibrotic drugs to treat hepatic fibrosis/cirrhosis. I will test this hypothesis through two Specific Aims. 1) Elucidate the anti-fibrotic role of ALDH2 in a mouse model of cholestatic injury. The role of toxic aldehydes in fibrosis remains unclear. Therefore, I will explore whether toxic aldehydes play a critical role in liver fibrosis and if ALDH2 activation attenuates fibrosis after BDL. I will assess time- dependent changes of toxic aldehydes generation (4-hydroxynonenal [4-HNE] and malondialdehyde [MDA]), ALDH2 expression/activity, and fibrotic markers and signals (e.g., alpha-smooth muscle actin [?-SMA], TGF?- 1, PDGF, Smad 2/3, ERK, and NF-?B p65 subunit), and epigenetic control by microRNAs. I will directly image HSC activation and procollagen deposition using intravital multiphoton/second harmonic generation (SHG) microscopy. Fibrotic liver injury is a complex, multicellular process, so I will also determine the effect of ALDH2 activation and deficiency on hepatocellular injury (necrosis and apoptosis) and inflammation after BDL. I expect that ALDH2-deficiency will increase toxic aldehydes and exacerbate hepatic injury and fibrotic activation, whereas ALDH2 activation will mitigate these adverse events. I expect that these studies will validate ALDH2 as a new drug target against ROS-associated liver fibrosis. 2) Determine whether ALDH2 activation inhibits activation of hepatic stellate cells (HSC) and/or causes reversion of activated HSCs to a quiescent state. In addition to my pilot study, previous studies show that aldehydes activate cultured HSCs. I will assess whether ALDH2 activation in HSCs prevents/decreases activation by both exogenous and endogenous aldehydes at early stages and promotes reversion of activated HSCs at later stages. I will verify through ALDH2 knockdown that the effect of Alda-1 is ALDH2 dependent. I expect: 1) Toxic aldehydes will accumulate as HSCs become activated in culture; 2) ALDH2 knockdown will increase, whereas ALDH2 activation by Alda- 1 will delay/decrease spontaneous and exogenous aldehyde-induced HSC activation; and 3) Late administration of Alda-1 will blunt and even reverse HSC activation. These data serve to demonstrate a direct relationship between aldehyde metabolism and activation of HSCs, the primary fibrotic effector cells.
Liver fibrosis leads to cirrhosis and liver failure, requiring transplantation, and is one of the leading causes of death worldwide. My project proposes to evaluate aldehyde dehydrogenase-2 (ALDH2), an enzyme that detoxifies aldehydes generated in liver injury, as a potential drug target to prevent and possibly reverse liver fibrosis using the small molecule activator of ALDH2, Alda-1, in a mouse model of bile duct ligation and in cultured hepatic stellate cells.
