Skeletal muscle healing by M1-like macrophages produced by transient expression of exogenous GM-CSF

Martins, Leonardo; Gallo, Camila Congentino; Honda, Tamisa Seeko Bandeira; Alves, Patricia Terra; Stilhano, Roberta Sessa; Rosa, Daniela Santoro; Koh, Timothy Jon; Han, Sang Won

doi:10.1186/S13287-020-01992-1

Title

Skeletal muscle healing by M1-like macrophages produced by transient expression of exogenous GM-CSF

Author

Martins, Leonardo

Gallo, Camila Congentino

Honda, Tamisa Seeko Bandeira

Alves, Patricia Terra

Stilhano, Roberta Sessa

Rosa, Daniela Santoro

Koh, Timothy Jon

Han, Sang Won

Abstract

Background After traumatic skeletal muscle injury, muscle healing is often incomplete and produces extensive fibrosis. The sequence of M1 and M2 macrophage accumulation and the duration of each subtype in the injured area may help to direct the relative extent of fibrogenesis and myogenesis during healing. We hypothesized that increasing the number of M1 macrophages early after traumatic muscle injury would produce more cellular and molecular substrates for myogenesis and fewer substrates for fibrosis, leading to better muscle healing. Methods To test this hypothesis, we transfected skeletal muscle with a plasmid vector to transiently express GM-CSF shortly after injury to drive the polarization of macrophages towards the M1 subset. C57BL/6 mouse tibialis anterior (TA) muscles were injured by contusion and electroporated with uP-mGM, which is a plasmid vector that transiently expresses GM-CSF. Myogenesis, angiogenesis, and fibrosis were evaluated by histology, immunohistochemistry, and RT-qPCR; subpopulations of macrophages by flow cytometry; and muscle functioning by the maximum running speed on the treadmill and the recovery of muscle mass. Results Muscle injury increased the number of local M1-like macrophages and decreased the number of M2-like macrophages on day 4, and uP-mGM treatment enhanced this variation. uP-mGM treatment decreased TGF-beta 1 protein expression on day 4, and the Sirius Red-positive area decreased from 35.93 +/- 15.45% (no treatment) to 2.9% +/- 6.5% (p < 0.01) on day 30. uP-mGM electroporation also increased Hgf, Hif1 alpha, and Mtor gene expression; arteriole density; and muscle fiber number during regeneration. The improvement in the quality of the muscle tissue after treatment with uP-mGM affected the increase in the TA muscle mass and the maximum running speed on a treadmill. Conclusion Collectively, our data show that increasing the number of M1-like macrophages immediately after traumatic muscle injury promotes muscle recovery with less fibrosis, and this can be achieved by the transient expression of GM-CSF.

Language

English

Source (journal)

Stem cell research & therapy

Publication

2020

ISSN

1757-6512

DOI

10.1186/S13287-020-01992-1

Volume/pages

11 :1 (2020) , p. 1-12