AAV mediated gene knockdown of PIK3C2B as a therapeutic strategy for X-linked myotubular myopathy and fatty liver disease

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PROJECT SUMMARY/ABSTRACT PIK3C2B encodes the class II PI3 kinase Phosphatidylinositol-4-phosphate 3-kinase C2 domain-containing beta (PIK3C2B) protein, a regulator of vesicle trafficking through the endosome. Mouse knockout of Pik3c2b has no overtly deleterious phenotype, but instead promotes a beneficial metabolic profile that includes reduced weight gain, improved insulin sensitivity, and, most relevant for this proposal, reduced fat deposition in the liver. In addition, we have previously shown that genetic reduction of Pik3c2b can both prevent and reverse the skeletal muscle phenotype, as well as extend survival, of the mouse model of X-linked myotubular myopathy (XLMTM). XLMTM is rare neurogenetic condition with onset in infancy that is associated with profound muscle related disabilities and early death. In addition to affecting the skeletal muscle, an emerging XLMTM phenotype is hepatobiliary disease, which progresses to liver failure in a subset of patients. There are no treatments for XLMTM. Importantly, liver disease has not previously been identified in pre-clinical models of XLMTM, a significant barrier for disease understanding and treatment. To overcome this barrier, in new data, we have developed the first mouse model of XLMTM liver disease. Non-alcoholic fatty liver disease (NAFLD) is a highly prevalent condition that affects nearly 25% of American adults. It can lead to non-alcoholic hepatosteatosis (NASH), which in turn can progress to cirrhosis, liver failure, liver cancer, and death. There are no adequate therapies for these common and severe conditions. The scientific premise of this proposal is that reduction of PIK3C2B in mice promotes reduction of diet induced fatty liver and amelioration of disease relevant XLMTM phenotypes. The overall goal of the project is to develop therapies for XLMTM and NAFLD/NASH using a RNA knockdown based gene therapy. We hypothesize the following: (1) PIK3C2B knockdown in muscle and liver can be specifically, lastingly, and safely achieved with a synthetic miRNA delivered in vivo with AAV8 (AAV-miR-PIK3C2B); (2) AAV-miR- PIK3C2B can ameliorate both muscle and liver and phenotypes of the XLMTM mouse model; and (3) AAV-miR- PIK3C2B can prevent the development and progression of diet induce mouse NAFLD/NASH. These hypotheses will be rigorously evaluated in 3 aims. Aim 1 will develop AAV-miR-PIK3C2B, Aim 2 will test it in XLMTM mice, and Aim 3 will study it in a diet induced model of NASH. If successful, this proposal will be of high significance and impact because it will identify a single therapy suitable for clinical translation for both a rare, fatal paediatric condition and for a prevalent disease affecting millions of adults.