Sinha-Hikim Indrani, Taylor Wayne E, Gonzalez-Cadavid Nestor F, Zheng Wei, Bhasin Shalender
Division of Endocrinology, Metabolism, and Molecular Medicine, Charles R. Drew University of Medicine and Science, Los Angeles, California 90059, USA.
J Clin Endocrinol Metab. 2004 Oct;89(10):5245-55. doi: 10.1210/jc.2004-0084.
Androgens stimulate myogenesis, but we do not know what cell types within human skeletal muscle express the androgen receptor (AR) protein and are the target of androgen action. Because testosterone promotes the commitment of pluripotent, mesenchymal cells into myogenic lineage, we hypothesized that AR would be expressed in mesenchymal precursor cells in the skeletal muscle. AR expression was evaluated by immunohistochemical staining, confocal immunofluorescence, and immunoelectron microscopy in sections of vastus lateralis from healthy men before and after treatment with a supraphysiological dose of testosterone enanthate. Satellite cell cultures from human skeletal muscle were also tested for AR expression. AR protein was expressed predominantly in satellite cells, identified by their location outside sarcolemma and inside basal lamina, and by CD34 and C-met staining. Many myonuclei in muscle fibers also demonstrated AR immunostaining. Additionally, CD34+ stem cells in the interstitium, fibroblasts, and mast cells expressed AR immunoreactivity. AR expression was also observed in vascular endothelial and smooth muscle cells. Immunoelectron microscopy revealed aggregation of immunogold particles in nucleoli of satellite cells and myonuclei; testosterone treatment increased nucleolar AR density. In enriched cultures of human satellite cells, more than 95% of cells stained for CD34 and C-met, confirming their identity as satellite cells, and expressed AR protein. AR mRNA and protein expression in satellite cell cultures was confirmed by RT-PCR, reverse transcription and real-time PCR, sequencing of RT-PCR product, and Western blot analysis. Incubation of satellite cell cultures with supraphysiological testosterone and dihydrotestosterone concentrations (100 nm testosterone and 30 nm dihydrotestosterone) modestly increased AR protein levels. We conclude that AR is expressed in several cell types in human skeletal muscle, including satellite cells, fibroblasts, CD34+ precursor cells, vascular endothelial, smooth muscle cells, and mast cells. Satellite cells are the predominant site of AR expression. These observations support the hypothesis that androgens increase muscle mass in part by acting on several cell types to regulate the differentiation of mesenchymal precursor cells in the skeletal muscle.
雄激素可刺激肌生成，但我们并不清楚人类骨骼肌内哪些细胞类型表达雄激素受体（AR）蛋白以及是雄激素作用的靶点。由于睾酮可促进多能间充质细胞向肌源性谱系分化，我们推测AR会在骨骼肌的间充质前体细胞中表达。通过免疫组织化学染色、共聚焦免疫荧光和免疫电子显微镜，对健康男性在接受超生理剂量庚酸睾酮治疗前后的股外侧肌切片中的AR表达进行了评估。还对来自人类骨骼肌的卫星细胞培养物进行了AR表达检测。AR蛋白主要在卫星细胞中表达，卫星细胞可通过其位于肌膜外和基膜内的位置以及CD34和C-met染色来识别。肌纤维中的许多肌细胞核也显示出AR免疫染色。此外，间质中的CD34 +干细胞、成纤维细胞和肥大细胞表达AR免疫反应性。在血管内皮细胞和平滑肌细胞中也观察到了AR表达。免疫电子显微镜显示卫星细胞核仁和肌细胞核仁中有免疫金颗粒聚集；睾酮治疗增加了核仁AR密度。在富集的人类卫星细胞培养物中，超过95%的细胞CD34和C-met染色阳性，证实了它们作为卫星细胞的身份，并表达AR蛋白。通过逆转录聚合酶链反应（RT-PCR）、逆转录和实时PCR、RT-PCR产物测序以及蛋白质免疫印迹分析，证实了卫星细胞培养物中AR mRNA和蛋白的表达。用超生理浓度的睾酮和双氢睾酮（100 nM睾酮和30 nM双氢睾酮）孵育卫星细胞培养物，可适度增加AR蛋白水平。我们得出结论，AR在人类骨骼肌的几种细胞类型中表达，包括卫星细胞、成纤维细胞、CD34 +前体细胞、血管内皮细胞、平滑肌细胞和肥大细胞。卫星细胞是AR表达的主要部位。这些观察结果支持了以下假设，即雄激素部分通过作用于几种细胞类型来调节骨骼肌中间充质前体细胞的分化，从而增加肌肉质量。
