Skeletal muscle injury, whether acute or chronic, is characterized by influxes of pro- and anti-inflammatory cells that coordinate with muscle to precisely control the reparative process. This intricate coordination is facilitated by a signaling feedback loop between satellite cells and extravasated immune cells. Regulation of the cytokines and chemokines that…
Skeletal muscle injury, whether acute or chronic, is characterized by influxes of pro- and anti-inflammatory cells that coordinate with muscle to precisely control the reparative process. This intricate coordination is facilitated by a signaling feedback loop between satellite cells and extravasated immune cells. Regulation of the cytokines and chemokines that mediate healthy repair is critical for the overall success of fiber regeneration and thus provides a prospective direction for the development of therapeutics aimed at fine-tuning the local inflammatory response. This work describes (1) the contribution of non-myogenic cells in skeletal muscle regeneration, (2) the role of the transcription factor Mohawk (Mkx) in regulating inflammation following acute muscle injury and the identification of an overarching requirement for Mkx in the establishment of a pro-inflammatory response, and (3) characterization of eosinophils in acute and chronic muscle damage. Mice deficient for Mkx exhibited delayed muscle regeneration, accompanied by impaired clearance of necrotic fibers and smaller regenerated fibers. This diminished regenerative capacity was associated with a reduction in the recruitment of pro-inflammatory macrophages to the site of damage. In culture, Mkx-/- bone marrow-derived macrophages displayed reduced proliferative capacity but retained the ability to polarize in response to a pro-inflammatory stimulus. The necessity of Mkx in mounting a robust immune response was further confirmed by an immunological challenge in which Mkx-/- mice exhibited increased susceptibility to Salmonella enterica serovar Typhimurium infection. Significant downregulation of key cytokine and chemokine expression was identified throughout the course of muscle repair in Mkx-/- mice and represents one mechanism in which Mkx regulates the establishment of an inflammatory response. Previous research discovered that Mkx is highly expressed in eosinophils, a type of innate immune cell that participates in disease-fighting and inflammation, however the role of eosinophils in muscle repair is not well described. This work outlines the contribution of eosinophils in muscle repair following acute and chronic injury. In healthy mice, eosinophils were found to inhibit efficient muscle repair following acute injury. Utilizing the mdx-/-utrn-/- muscular dystrophy mouse model, eosinophil depletion via administration of anti-IL-5 antibody significantly improved diaphragm fiber diameter and increased the survival rate during the course of treatment.
MicroRNAs (miRNAs) regulate gene output by targeting degenerate elements in mRNAs and have undergone drastic expansions in higher metazoan genomes. The evolutionary advantage of maintaining copies of highly similar miRNAs is not well understood, nor is it clear what unique functions, if any, miRNA family members possess. Here, we study…
MicroRNAs (miRNAs) regulate gene output by targeting degenerate elements in mRNAs and have undergone drastic expansions in higher metazoan genomes. The evolutionary advantage of maintaining copies of highly similar miRNAs is not well understood, nor is it clear what unique functions, if any, miRNA family members possess. Here, we study evolutionary patterns of metazoan miRNAs, focusing on the targeting preferences of the let-7 and miR-10 families. These studies reveal hotspots for sequence evolution with implications for targeting and secondary structure. High-throughput screening for functional targets reveals that each miRNA represses sites with distinct features and regulates a large number of genes with cooperative function in regulatory networks. Unexpectedly, given the high degree of similarity, single-nucleotide changes grant miRNA family members with distinct targeting preferences. Together, our data suggest complex functional relationships among miRNA duplications, novel expression patterns, sequence change, and the acquisition of new targets.
