Long non-coding RNA Gm15441 attenuates hepatic inflammasome activation in response to metabolic stress

Chad N. Brocker; Donghwan Kim; Tisha Melia; Kritika Karri; Thomas J. Velenosi; Shogo Takahashi; Jessica A. Bonzo; David J. Waxman; Frank J. Gonzalez

To ascertain whether PPARA regulates lncRNAs, RNA-seq was performed on livers from wild-type and Ppara -/mice treated with the specific PPARA agonist WY-14643. More than 400 liver-expressed lncRNAs, including many novel non-coding RNA transcripts, were significantly upregulated or downregulated in mouse liver 48 hours after WY-14643 treatment. Only six of these lncRNAs were similarly responsive to WY-14643 in Ppara -/mice, thus establishing the striking PPARA dependence of these non-coding RNA transcriptomic responses. PPARAdependent, liver-specific expression was verified for six non-coding RNAs, and detailed functional studies were carried out on one such gene, Gm15441, which showed an unusually strong induction in WY-14643-treated liver. Importantly, the genomic orientation of Gm15441 is antisense to that of Txnip, which codes for a ubiquitously-expressed protein that facilitates cellular responses to oxidative stress and inflammation (Watanabe et al., 2010) . TXNIP was originally identified as a negative regulator of thioredoxin (Muoio, 2007) , and subsequent studies found that TXNIP contributes to a wide array of processes in several tissues. Notably, TXNIP causes an increase in intracellular reactive oxygen species generation (Hong et al., 2016) that may inhibit hepatocellular carcinoma cell proliferation (Li et al., 2017a) . TXNIP is key regulator of NLRP3 inflammasome activation, which plays an important role in liver fibrosis and hepatocellular carcinoma (Ringelhan et al., 2018; Wree et al., 2017) , and its activation is associated with the NLRP3 inflammasome pathway in human diseases (Bai et al., 2019; Kim et al., 2019; Li et al., 2019) . TXNIP has also emerged as an important glucose sensor that regulates glucose uptake in response to insulin (Waldhart et al., 2017) and plays an important role in metabolic stress (Mandala et al., 2016; Wu et al., 2013) . Another study found that PPARA activation by fenofibrate downregulated Txnip mRNA and TXNIP protein in endothelial cells (Deng et al., 2017) , suggesting the Gm15441-Txnip regulatory axis described here for liver may also function in extrahepatic tissues. An earlier study found that Ppara mRNA and PPARA target gene mRNAs were elevated in Txnip-null mice, and that Txnip expression attenuated PPRE-luciferase response when co-transfected with PPARA/RXR and treated with WY-14643 (Oka et al., 2009) , suggesting a Txnip-Ppara feedback regulatory loop that may also involve Gm15441.