TMEM97 links endoplasmic reticulum stress to hepatic stellate cell activation in experimental liver fibrosis: pharmacological attenuation by CT1812.

Liver fibrosis lacks broadly effective antifibrotic therapies, and activated hepatic stellate cells drive extracellular matrix deposition. We investigated whether transmembrane protein 97 (TMEM97), the σ-2 receptor, contributes to hepatic stellate cell (HSC) activation and whether the σ-2 receptor complex antagonist CT1812 attenuates experimental fibrosis. In male C57BL/6J mice, carbon tetrachloride (CCl4) was administered for 4 or 8 weeks, and a separate 8-week CCl4 model received daily oral CT1812 (10 mg/kg/day) or vehicle. Human LX-2 cells were stimulated with transforming growth factor-β1 (TGF-β1) and treated with TMEM97-targeting small interfering RNA (siTMEM97), CT1812, or both; confirmatory experiments used a second siRNA and GSK2606414. Hepatic TMEM97 mRNA, protein abundance, and fluorescence intensity increased progressively during CCl4-induced fibrosis and were preferentially associated with α-smooth muscle actin (α-SMA)-positive fibrotic cells. In LX-2 cells, TMEM97 knockdown and CT1812 reduced ACTA2, COL1A1, and CTGF expression and suppressed proliferation and migration without reducing cell viability over 72 h. Both interventions attenuated multiple unfolded protein response readouts, including p-eIF2α/eIF2α, ATF4, CHOP, BiP, nuclear ATF4, p-IRE1/IRE1, and ATF6 (p50). The second siRNA reproduced key phenotypes, while GSK2606414 reduced PERK-eIF2α signaling and fibrogenic readouts. In vivo, CT1812 reduced hepatic hydroxyproline accumulation, collagen staining, α-SMA and collagen I expression, ER-stress markers, liver-injury indices, inflammatory cytokines, and macrophage accumulation. These findings support TMEM97-associated σ-2 receptor complex signaling as a contributor to ER-stress-coupled HSC activation and identify CT1812 as a candidate pharmacological modulator of experimental liver fibrosis.