Skeletal muscle healing by M1-like macrophages produced by transient expression of exogenous GM-CSF
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(2020) 11:473
RESEARCH
Open Access
Skeletal muscle healing by M1-like macrophages produced by transient expression of exogenous GM-CSF Leonardo Martins1, Camila Congentino Gallo1, Tâmisa Seeko Bandeira Honda1, Patrícia Terra Alves1, Roberta Sessa Stilhano2, Daniela Santoro Rosa3, Timothy Jon Koh4 and Sang Won Han1,5*
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 GMCSF 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-β1 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, Hif1α, 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. Keywords: Fibrosis, Skeletal muscle, Injury, Myogenesis, GM-CSF, Macrophage, Arteriogenesis, Contusion
* Correspondence: [email protected] 1 Interdisciplinary Center for Gene Therapy, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil 5 Department of Biophysics, Escola Paulista de Medicina, Universidade Federal de São Paulo, Rua Mirassol 207, São Paulo, SP 04044-010, Brazil Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduc
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