Cathelicidin‐related antimicrobial peptide mediates skeletal muscle degeneration caused by injury and Duchenne muscular dystrophy in mice

Abstract

Background Cathelicidin, an antimicrobial peptide, plays a key role in regulating bacterial killing and innate immunity; however, its role in skeletal muscle function is unknown. We investigated the potential role of cathelicidin in skeletal muscle pathology resulting from acute injury and Duchenne muscular dystrophy (DMD) in mice. Methods Expression changes and muscular localization of mouse cathelicidin-related antimicrobial peptide (Cramp) were examined in the skeletal muscle of normal mice treated with chemicals (cardiotoxin and BaCl 2 ) or in dystrophic muscle of DMD mouse models (mdx, mdx/Utrn +/À and mdx/Utrn À/À ). Cramp penetration into myofibres and effects on muscle damage were studied by treating synthetic peptides to mouse skeletal muscles or C2C12 myotubes. Cramp knockout (KO) mice and mdx/Utrn/Cramp KO lines were used to determine whether Cramp mediates muscle degeneration. Muscle pathophysiology was assessed by histological methods, serum analysis, grip strength and lifespan. Molecular factors targeted by Cramp were identified by the pull-down assay and proteomic analysis. ResultsIn response to acute muscle injury, Cramp was activated in muscle-infiltrating neutrophils and internalized into myofibres. Cramp treatments of mouse skeletal muscles or C2C12 myotubes resulted in muscle degeneration and myotube damage, respectively. Genetic ablation of Cramp reduced neutrophil infiltration and ameliorated muscle pathology, such as fibre size (P < 0.001; n = 6) and fibrofatty infiltration (P < 0.05). Genetic reduction of Cramp in mdx/Utrn +/À mice not only attenuated muscle damage (35%, P < 0.05; n = 9-10), myonecrosis (53%, P < 0.05), inflammation (37-65%, P < 0.01) and fibrosis (14%, P < 0.05) but also restored muscle fibre size (14%, P < 0.05) and muscle force (18%, P < 0.05). Reducing Cramp levels led to a 63% (male, P < 0.05; n = 10-14) and a 124% (female, P < 0.001; n = 20) increase in the lifespan of mdx/Utrn À/À mice. Proteomic and mechanistic studies revealed that Cramp cross-talks with Ca 2+ signalling in skeletal muscle through sarcoplasmic/endoplasmic reticulum Ca 2+ -ATPase1 (SERCA1). Cramp binds and inactivates SERCA1, leading to the activation of Ca 2+ -dependent calpain proteases that exacerbate DMD progression. Conclusions These findings identify Cramp as an immune cell-derived regulator of skeletal muscle degeneration and provide a potential therapeutic target for DMD.

A Novel MAO-B/SSAO Inhibitor Improves Multiple Aspects of Dystrophic Phenotype in mdx Mice

“…Also, recent results showed how a murine cathelicidin-related antimicrobial peptide (Cramp), which has chemotactic effects on neutrophil recruitment during muscle damage, was strongly increased in dystrophic muscle compared to control animals. Loss of Cramp reduces the presence of Ly6G-positive neutrophils in dystrophic muscle and significantly reduces the fibrosis, as measured by Sirius red staining [ 38 ]. Interestingly, one of the mechanisms leading to these beneficial effects passes through the modulation of Sarco-Endoplasmic Reticulum Calcium ATPase (SERCA) activity, linking inflammation to intracellular calcium homeostasis, which is a well-known modulator of muscle physiology and its increase is sufficient to induce a muscular pathology [ 39 ].…”

LL-37 Might Promote Local Invasion of Melanoma by Activating Melanoma Cells and Tumor-Associated Macrophages

“…CXCL5 is a chemokine that promotes tumor formation by triggering the migration of CXCR2+ immune cells to tumors [ 29 , 30 ]. Not only recruiting immunosuppressive cells, such as precursors of TAMs, neutrophils, and myeloid-derived suppressor cells in the tumor microenvironment [ 30 ], CXCL5 can recruit endothelial cells (ECs) via its highly conserved glutamic acid-leucine-arginine ‘ELR’ motif [ 29 , 31 ], promoting cancer progression in various cancer types [ 20 ]. For example, the interaction between ECs and cancer cells enhances EC recruitment and promotes cancer progression through the EGFR-NF-kB-CXCL5-CXCR2 pathway in bladder cancer [ 32 ].…”

“…LL-37 stimulates these skin-resident cells to produce various chemokines, leading to recruit further immune cells to develop inflammatory microenvironment in the lesional skin of cutaneous disorders [ 18 , 19 ]. Notably, genetically lack of CRAMP (the mouse ortologe of LL-37) significantly reduces the neutrophils recruitment in muscle in the mouse Duchenne muscular dystrophy model [ 20 ], though its effects on skin inflammatory disorder is still controversial [ 21 ]. In addition to immunomodulatory effects, LL-37 promotes angiogenesis in the skin by the induction of vascular endothelial growth factor (VEGF) and matrix metalloproteinases (MMPs) [ 19 ].…”