Abstract
Dystrophin is an essential protein for regulating the transmission of intracellular force to the extracellular matrix within the skeletal muscle. The mammalian dystrophin gene (Dmd) is X-linked and has several isoforms with tissue-specific expression, including the large Dp427m muscle transcript found in heart and skeletal muscle, and the Dp427c transcript that encodes the brain-specific dystrophin cerebellar protein. Dystrophin-deficiency results in Duchenne muscular dystrophy (also abbreviated DMD) in patients and understanding the pathways and tissues that are affected by dystrophin loss will impact dystrophin replacement gene therapy and exon-skipping DMD correction strategies. We generated conditional Dystrophin knockout mice by targeting exon 52 of the mouse Dystrophin (Dmdflox52) locus. We then combinatorially generated dystrophin constitutive and inducible myofiber knockout (Dmd mKO; Dp427m) mice to evaluate the tissue-specific function of the large skeletal muscle dystrophin isoform (Dp427m). Constitutive embryonic deletion of the Dystrophin gene exclusively in skeletal myofibers resulted in a severe skeletal muscle myopathy as demonstrated using histopathology, physiological force assessments, and overall functional assessments compared to the mdx mouse model. Transcriptomic analysis of skeletal myofibers of the Dmd mKO mice revealed the dysregulation of key extracellular matrix and cytokine signaling pathways. Separately, we generated Purkinje neuron cerebellar dystrophin knockout (Dmd:Pcp2 KO; Dp427c) mice that displayed neurobehavioral deficits in social approach, social memory, and spatial navigation and working memory. These studies reveal the essential requirement for dystrophin within muscle development, growth, and regeneration in addition to normal neurobehavioral function.
Significance Statement Duchenne muscular dystrophy is caused by the lack of a functional dystrophin protein in muscle. The large dystrophin (Dp427m) isoform is expressed in skeletal, cardiac, and smooth muscle, but its tissue-specific requirements remain unknown. We generated and characterized a conditional skeletal muscle knockout mouse (Dmd mKO). Constitutive embryonic genetic ablation of skeletal muscle Dystrophin resulted in muscle histopathologies similar to the mdx mouse, while postnatal muscle Dystrophin ablation resulted in milder pathologies. Ablating cerebellar Dystrophin Dp427c using a Pcp2/L7-Cre driver resulted in sociobehavioral defects. Transcriptomic analysis of the Dmd mKO mice showed a severe reduction of extracellular matrix and cytokine signaling pathways. Our study reveals an essential role for skeletal muscle dystrophin and identifies essential pathways for modulation using dystrophin-replacement therapies.
Competing Interest Statement
L.M.K is a consultant for Pfizer, Dyne Therapeutics, and Myofinity for muscle disease drug therapies. All other authors declare no conflicts of interest.
Footnotes
Competing Interest Statement: L.M.K is a consultant for Pfizer, Dyne Therapeutics, and Myofinity for muscle disease drug therapies. All other authors declare no conflicts of interest.
Classification: Medical Sciences
https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE284723