microRNA-133a as an Indicator of Disease Progression and Treatment Response in a Mouse Model of X-linked Myotubular Myopathy

Abstract

X-linked Myotubular myopathy (XLMTM) is a rare pediatric neuromuscular disease caused by loss-of-function variants in myotubularin (MTM1). XLMTM is associated with severe disabilities and early death and is at present, without effective therapy. As interventional clinical trials for XLMTM gather momentum, the discovery of robust biomarkers that reflect disease severity and therapeutic efficacy is critically required. Using high-throughput and directed approaches, I identified a decrease in miR-133a expression as a marker of XLMTM disease in skeletal muscle and plasma of a mouse model of XLMTM (Mtm1 KO). miR-133a is a muscle-enriched non-coding RNA that is involved in muscle development and has emerged as a treatment-effect biomarker and therapeutic candidate in other neuromuscular disorders. miR-133a is also a demonstrated negative regulator of DNM2, holding significant pathomechanistic and therapeutic implications for XLMTM. I show that miR-133a expression significantly and positively correlates with myofiber size and disease severity in Mtm1 KO mice and is upregulated in response to treatments that rescue XLMTM. Using predictive modelling, I show that miR-133a expression demonstrates a powerful therapeutic response and is a robust classifier for XLMTM with a classification accuracy of 70-90% by linear discriminant analysis in both treated and untreated conditions. Receiver operating characteristic (ROC) curve analysis further demonstrated that miR-133a has high discrimination accuracy for XLMTM (AUC >0.80). Moving beyond correlation to test causation, I show that miR-133a overexpression in Mtm1 KO mice using an AAV9-based construct significantly improves survival, myofiber size, muscle strength and modulates overall body composition in XLMTM. In this work, I identify the first small RNA based non-invasive biomarker for XLMTM that reflects both disease severity and treatment response. I also introduce a novel treatment strategy for XLMTM with excellent potential for clinical translation. This work results in completely new knowledge of disease pathogenesis and sets the stage for future biomarker validation and treatment development for XLMTM at a time of great clinical need.