Targeting necroptosis in muscle fibers ameliorates inflammatory myopathies

Mari Kamiya,Shinsuke Yasuda,Hitoshi Kohsaka,Masahiro Nishibori,Kimito Kawahata,Jessica Day,Dengli Wang,Cynthia Louis,Fumitaka Mizoguchi,Ian P Wicks

doi:10.1038/s41467-021-27875-4

Abstract

Muscle cell death in polymyositis is induced by CD8+ cytotoxic T lymphocytes. We hypothesized that the injured muscle fibers release pro-inflammatory molecules, which would further accelerate CD8+ cytotoxic T lymphocytes-induced muscle injury, and inhibition of the cell death of muscle fibers could be a novel therapeutic strategy to suppress both muscle injury and inflammation in polymyositis. Here, we show that the pattern of cell death of muscle fibers in polymyositis is FAS ligand-dependent necroptosis, while that of satellite cells and myoblasts is perforin 1/granzyme B-dependent apoptosis, using human muscle biopsy specimens of polymyositis patients and models of polymyositis in vitro and in vivo. Inhibition of necroptosis suppresses not only CD8+ cytotoxic T lymphocytes-induced cell death of myotubes but also the release of inflammatory molecules including HMGB1. Treatment with a necroptosis inhibitor or anti-HMGB1 antibodies ameliorates myositis-induced muscle weakness as well as muscle cell death and inflammation in the muscles. Thus, targeting necroptosis in muscle cells is a promising strategy for treating polymyositis providing an alternative to current therapies directed at leukocytes.

Highlights

Muscle cell death in polymyositis is induced by CD8+ cytotoxic T lymphocytes
Immunofluorescence staining revealed that the dying muscle fibers, which are identified as cells with reduced eosin staining in the cytoplasm, expressed RIPK1, RIPK3, Mixed Lineage Kinase Domain Like Pseudokinase (MLKL) and phosphorylated MLKL, whereas the expression levels of these proteins in the intact muscle fibers were low or absent (Fig. 1b, Supplementary Fig. 1c–e, g)
We found some of the dying muscle fibers expressed phosphorylated MLKL, which localizes on the plasma membrane upon necroptosis[12,13,14]

Summary

Introduction

Muscle cell death in polymyositis is induced by CD8+ cytotoxic T lymphocytes. We hypothesized that the injured muscle fibers release pro-inflammatory molecules, which would further accelerate CD8+ cytotoxic T lymphocytes-induced muscle injury, and inhibition of the cell death of muscle fibers could be a novel therapeutic strategy to suppress both muscle injury and inflammation in polymyositis. Inhibition of necroptosis suppresses CD8+ cytotoxic T lymphocytes-induced cell death of myotubes and the release of inflammatory molecules including HMGB1. Muscle fibers express CASP8 and FADD Like Apoptosis Regulator (CFLAR)[8], which suppresses the apoptosis pathway by inhibiting the activation of Caspase 8 (CASP8) These results suggest that the pattern of cell death in muscle fibers induced by CTLs is not apoptosis, and has been assumed to be necrosis instead[9]. The necroptotic cells subsequently release inflammatory molecules including damage-associated molecular patterns (DAMPs) and cytokines, which cause tissue inflammation

Methods

Results

Conclusion