The microRNA miR‐133b functions to slow Duchenne muscular dystrophy pathogenesis

Abstract

Impairment of muscle biogenesis contributes to the progression of Duchenne muscular dystrophy (DMD). r As a muscle enriched microRNA that has been implicated in muscle biogenesis, the role of miR-133b in DMD remains unknown. r To assess miR-133b function in DMD-affected skeletal muscles, we genetically ablated miR-133b in the mdx mouse model of DMD. r We show that deletion of miR-133b exacerbates the dystrophic phenotype of DMD-afflicted skeletal muscle by dysregulating muscle stem cells involved in muscle biogenesis, in addition to affecting signalling pathways related to inflammation and fibrosis. r Our results provide evidence that miR-133b may underlie DMD pathology by affecting the proliferation and differentiation of muscle stem cells.

Argonaute 2 is lost from neuromuscular junctions affected with amyotrophic lateral sclerosis in SOD1G93A mice

“…Using AAV-mediated expression of Cre-recombinase to temporally knockdown Ago2 in skeletal muscles of juvenile mice, we found that reduced levels of Ago2 caused an increased presence of thickened interstitial space, moderately altered the morphology of AChR clusters, but did not impact the size of muscle fibers or their NMJ endplates. The absence of an overtly deleterious phenotype following Ago2 knockdown is in line with previous studies that found that otherwise healthy skeletal muscles are minimally impacted by deletion of individual miRNAs 13 , 35 , 36 . For example, global deletion of miR-133b did not produce an observable effect on the health of juvenile or adult skeletal muscle fibers, their NMJs or their transcriptome 36 .…”

“…The absence of an overtly deleterious phenotype following Ago2 knockdown is in line with previous studies that found that otherwise healthy skeletal muscles are minimally impacted by deletion of individual miRNAs 13 , 35 , 36 . For example, global deletion of miR-133b did not produce an observable effect on the health of juvenile or adult skeletal muscle fibers, their NMJs or their transcriptome 36 . By contrast, deletion of miR-133b in the mdx mouse model of Duchenne muscular dystrophy exacerbated dystrophic muscle pathology and induced widespread transcriptomic changes 36 .…”

“…For example, global deletion of miR-133b did not produce an observable effect on the health of juvenile or adult skeletal muscle fibers, their NMJs or their transcriptome 36 . By contrast, deletion of miR-133b in the mdx mouse model of Duchenne muscular dystrophy exacerbated dystrophic muscle pathology and induced widespread transcriptomic changes 36 . These findings suggest that miRNAs, and Ago2, may serve as emergency responders that largely remain on standby in healthy skeletal muscles.…”

“…Mice were maintained on a mixed genetic background, appeared healthy and were not subjected to non-related procedures prior to the study. Sample size determination was based on previous gene expression and IHC studies in skeletal muscles performed by our laboratory 19 , 22 , 36 with the goal of minimizing research animal use and detecting robust effects; a power analysis was not used. Ninety-four mice were used for this study.…”

“…The number of muscle fibers per TA muscle was approximated by dividing the cross-sectional area of the TA muscle by the average muscle fiber cross-sectional area following laminin IHC. Enlarged interstitial areas were identified by the presence of thickened laminin + regions between muscle fibers that contained at least one nucleus that was not immediately adjacent to a muscle fiber, as described previously 36 . Cross-sectional area and minimum Feret’s diameter measurements were performed with ImageJ (RRID:SCR_003070).…”