Mackey Abigail L, Magnan Mélanie, Chazaud Bénédicte, Kjaer Michael
Institute of Sports Medicine, Department of Orthopaedic Surgery M, Bispebjerg Hospital, and Center for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.
Center for Healthy Aging, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.
J Physiol. 2017 Aug 1;595(15):5115-5127. doi: 10.1113/JP273997. Epub 2017 May 23.
Accumulation of skeletal muscle extracellular matrix is an unfavourable characteristic of many muscle diseases, muscle injury and sarcopenia. The extent of cross-talk between fibroblasts, as the source of matrix protein, and satellite cells in humans is unknown. We studied this in human muscle biopsies and cell-culture studies. We observed a strong stimulation of myogenesis by human fibroblasts in cell culture. In biopsies collected 30 days after a muscle injury protocol, fibroblast number increased to four times control levels, where fibroblasts were found to be preferentially located immediately surrounding regenerating muscle fibres. These novel findings indicate an important role for fibroblasts in supporting the regeneration of muscle fibres, potentially through direct stimulation of satellite cell differentiation and fusion, and contribute to understanding of cell-cell cross-talk during physiological and pathological muscle remodelling.
Accumulation of skeletal muscle extracellular matrix is an unfavourable characteristic of many muscle diseases, muscle injury and sarcopenia. In addition to the indispensable role satellite cells play in muscle regeneration, there is emerging evidence in rodents for a regulatory influence on fibroblast activity. However, the influence of fibroblasts on satellite cells and muscle regeneration in humans is unknown. The purpose of this study was to investigate this in vitro and during in vivo regeneration in humans. Following a muscle injury protocol in young healthy men (n = 7), the number of fibroblasts (TCF7L2+), satellite cells (Pax7+), differentiating myogenic cells (myogenin+) and regenerating fibres (neonatal/embryonic myosin+) was determined from biopsy cross-sections. Fibroblasts and myogenic precursor cells (MPCs) were also isolated from human skeletal muscle (n = 4) and co-cultured using different cell ratios, with the two cell populations either in direct contact with each other or separated by a permeable membrane. MPC proliferation, differentiation and fusion were assessed from cells stained for BrdU, desmin and myogenin. On biopsy cross-sections, fibroblast number was seen to increase, along with myogenic cell number, by d7 and increase further by d30, where fibroblasts were observed to be preferentially located immediately surrounding regenerating muscle fibres. In vitro, the presence of fibroblasts in direct contact with MPCs was found to moderately stimulate MPC proliferation and strongly stimulate both MPC differentiation and MPC fusion. It thus appears, in humans, that fibroblasts exert a strong positive regulatory influence on MPC activity, in line with observations during in vivo skeletal muscle regeneration.
骨骼肌细胞外基质的积累是许多肌肉疾病、肌肉损伤和肌肉减少症的一个不利特征。作为基质蛋白来源的成纤维细胞与人类卫星细胞之间的相互作用程度尚不清楚。我们在人体肌肉活检和细胞培养研究中对此进行了研究。我们在细胞培养中观察到人类成纤维细胞对肌生成有强烈刺激作用。在肌肉损伤方案实施30天后采集的活检样本中，成纤维细胞数量增加到对照水平的四倍，发现成纤维细胞优先位于再生肌纤维周围。这些新发现表明成纤维细胞在支持肌纤维再生中起重要作用，可能是通过直接刺激卫星细胞分化和融合，并有助于理解生理和病理肌肉重塑过程中的细胞间相互作用。
骨骼肌细胞外基质的积累是许多肌肉疾病、肌肉损伤和肌肉减少症的一个不利特征。除了卫星细胞在肌肉再生中发挥的不可或缺的作用外，在啮齿动物中也有新证据表明其对成纤维细胞活性有调节作用。然而，成纤维细胞对人类卫星细胞和肌肉再生的影响尚不清楚。本研究的目的是在体外和人体体内再生过程中对此进行研究。在年轻健康男性（n = 7）中实施肌肉损伤方案后，从活检横截面确定成纤维细胞（TCF7L2+）、卫星细胞（Pax7+）、分化的肌原性细胞（肌细胞生成素+）和再生纤维（新生儿/胚胎肌球蛋白+）的数量。还从人类骨骼肌中分离出成纤维细胞和肌原性前体细胞（MPC）（n = 4），并以不同细胞比例进行共培养，两个细胞群体要么直接接触，要么由可渗透膜隔开。通过对BrdU、结蛋白和肌细胞生成素染色的细胞评估MPC的增殖、分化和融合。在活检横截面上，成纤维细胞数量与肌原性细胞数量一起在第7天增加，并在第30天进一步增加，此时观察到成纤维细胞优先位于再生肌纤维周围。在体外，发现与MPC直接接触的成纤维细胞的存在适度刺激MPC增殖，并强烈刺激MPC分化和MPC融合。因此，在人类中，成纤维细胞似乎对MPC活性有强烈的正向调节作用，这与体内骨骼肌再生过程中的观察结果一致。
