AAV8 gene therapy and dietary insults together precipitate cholestatic liver disease in a mouse model of X-linked myotubular myopathy.

Adeno-associated virus (AAV)-mediated liver injury is the primary off-target toxicity observed with viral gene therapy. Understanding of the underlying mechanisms has been hindered by the fact that murine studies poorly model AAV toxicity. The X-linked myotubular myopathy (XLMTM) gene therapy program epitomizes this therapeutic discordance, because a subset of participants treated with AAV8-driven myotubularin (MTM1) gene replacement developed fatal liver injury that was not predicted by preclinical models. Here, we investigated a multihit hypothesis whereby loss of Mtm1 interacts with the postweaning environment to precipitate liver injury in XLMTM mouse models. Mtm1 knockout (KO) mice fed purified ingredient diets manifested liver dysfunction that mirrored patient clinical presentations, including elevated plasma transaminases, altered bile acid composition, and histological features of cholestasis. We further demonstrated a role for MTM1 in maintaining hepatocyte structure and localization of the bile salt export pump. Liver-specific deletion of Mtm1 recapitulated many of these features, supporting a liver-autonomous role for Mtm1. Treatment of diet-sensitized mice with AAV8-driven gene therapy increased the susceptibility of cholestasis in global KO mice and induced liver injury in wild-type mice. Last, as a proof of concept, we treated global KO mice with lipid nanoparticle MTM1 gene replacement, which prevented development of key histopathological liver abnormalities. These findings provide critical insights into the environmental precipitants and molecular mechanisms of liver dysfunction in XLMTM and the adverse events seen in viral gene therapy studies and more broadly offer a framework to model AAV-associated toxicity and identify potential therapeutic interventions.