An Expanding Role for Nuclear Factor κB in Muscle Stem Cells: Implications for the Treatment of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a fatal disease characterized by progressive skeletal muscle degeneration. Inhibition of the transcription factor nuclear factor-κ B (NF-κB), and more specifically the p65 subunit, significantly improves the phenotype of mdx mice, a murine DMD model. However, the ubiquity of NF-κB stands as an obstacle to clinical translation. In this dissertation, we explore the roles of NF-κB/p65 in the regenerative capacity of muscle-derived stem cells (MDSCs) with the goal of identifying alternative approaches to DMD treatment. We found that both cell proliferation and myogenic potential were increased in MDSCs lacking one allele of p65 (p65+/-). In wild type MDSCs, in vitro pharmacologic inhibition of the upstream activating kinase, IKKβ, increased myotube formation in a dose-dependent manner. When transplanted into mdx hind limb muscle, p65+/- MDSCs resulted in significantly larger engraftments. Furthermore, engraftments in cardiotoxin (CTX) injured muscle were associated with reduced local host necrosis and inflammation. Not only were p65+/- MDSCs found to be more resistant to oxidative stress, but we found that p65 depletion improved the anti-inflammatory capacity of MDSCs in vitro and in vivo via upregulation of hepatocyte growth factor (HGF). Moreover, accelerated regeneration in p65 haploinsufficient mdx mice (mdx;p65+/-) coincided with HGF upregulation. Intraperitoneal injection of a musculotropic adeno-associated virus carrying shRNA targeting HGF reversed the phenotypic improvements of mdx;p65+/- mice, increasing both muscle inflammation and necrosis. These data implicate NF-κB/p65 in muscle stem cell proliferation, differentiation, survival, and growth factor gene expression, further underlining the danger of broadly targeting such an important pathway. Finally, this research has also identified HGF as a downstream effector of NF-κB/p65 inhibition in mdx mice. Thus, delivery of HGF or activation of its receptor, MET, may represent a new approach to reduce chronic inflammation and preserve muscle fiber integrity in DMD