Reduced Myogenic and Increased Adipogenic Differentiation Capacity of Rotator Cuff Muscle Stem Cells

Abstract

Background: Fat accumulation commonly occurs in chronically torn rotator cuff muscles, and increased fat within the rotator cuff is correlated with poor clinical outcomes. The extent of lipid deposition is particularly pronounced in injured rotator cuff muscles compared with other commonly injured muscles such as the gastrocnemius. Satellite cells, which are a tissue-resident muscle stem-cell population, can differentiate into fat cells. We hypothesized that satellite cells from the rotator cuff have greater intrinsic adipogenic differentiation potential than do gastrocnemius satellite cells, and this difference is due to variations in epigenetic imprinting between the cells. Methods: Satellite cells from gastrocnemius and rotator cuff muscles of mice were cultured in adipogenic media, and the capacity to differentiate into mature muscle cells and adipogenic cells was assessed (n ‡ 9 plates per muscle group). We also performed DNA methylation analysis of gastrocnemius and rotator cuff satellite cells to determine whether epigenetic differences were present between the 2 groups (n = 5 mice per group). Results: Compared with the gastrocnemius, satellite cells from the rotator cuff had a 23% reduction in myogenic differentiation and an 87% decrease in the expression of the differentiated muscle cell marker MRF4 (myogenic regulatory factor 4). With respect to adipogenesis, rotator cuff satellite cells had a 4.3-fold increase in adipogenesis, a 12-fold increase in the adipogenic transcription factor PPARg (peroxisome proliferator-activated receptor gamma), and a 65-fold increase in the adipogenic marker FABP4 (fatty-acid binding protein 4). Epigenetic analysis identified 355 differentially methylated regions of DNA between rotator cuff and gastrocnemius satellite cells, and pathway enrichment analysis suggested that these regions were involved with lipid metabolism and adipogenesis. Conclusions: Satellite cells from rotator cuff muscles have reduced myogenic and increased adipogenic differentiation potential compared with gastrocnemius muscles. There appears to be a cellular and genetic basis behind the generally poor rates of rotator cuff muscle healing. Clinical Relevance: The reduced myogenic and increased adipogenic capacity of rotator cuff satellite cells is consistent with the increased fat content and poor muscle healing rates often observed for chronically torn rotator cuff muscles. For patients undergoing rotator cuff repair, transplantation of autologous satellite cells from other muscles less prone to fatty infiltration may improve clinical outcomes. R otator cuff tears are a common upper-extremity disorder, with >250,000 surgical repairs performed annually in the U.S. 1. Achieving positive clinical outcomes following repair can be limited by fatty infiltration or myosteatosis, which is the combined atrophy, fibrosis, and fat accumulation within and around myofibers 2-4. The relative amount of fat in torn rotator cuff muscles is often greater than in other injured muscle groups 5-7 , and many patients devel...

Widespread diversity in the transcriptomes of functionally divergent limb tendons

“…Furthermore, gaining a greater understanding of the nature of how mechanical signals transmitted to tendons result in transcriptional changes would have important implications in the treatment of tendon injuries and diseases. In addition to mechanical signalling events, there are likely to be epigenetic factors that regulate gene expression, as skeletal muscles with different anatomical and functional roles display divergence in their transcriptomes and epigenomes (Terry et al 2018;Gumucio et al 2019;Schubert et al 2019). We found that even though tendons across the body share a common anatomical definition based on their physical location between skeletal muscle and bone, tendon is a surprisingly genetically heterogeneous tissue.…”

“…2019; Schubert et al . 2019). We found that even though tendons across the body share a common anatomical definition based on their physical location between skeletal muscle and bone, tendon is a surprisingly genetically heterogeneous tissue.…”

Overexpression of DGAT2 Stimulates Lipid Droplet Formation and Triacylglycerol Accumulation in Bovine Satellite Cells

“…There are three types of differentiated adipogenic cells, including white, brown, and beige adipocytes, and the three types are morphologically difficult to recognize; however, a common feature of all adipoblasts is the expression of FABP4 [ 38 , 39 , 40 ]. A study by Schubert et al [ 41 ] on the differentiation capacity of satellite cells from the rotator cuff revealed that all FABP4+ cells were also Pax7-tdTomato+, suggesting that these adipocytes originate from a myogenic progenitor population. Furthermore, in adipogenic media, satellite cells have reduced myogenic differentiation potential, and the expression of the differentiated myocyte marker MRF4 is decreased; accompanied by a significant upregulation of the adipogenesis transcription factor PPAR and FABP4 expression, and increased adipogenic differentiation potential.…”

Rotator cuff muscle stem cells: the double-edged sword in the skeletal muscle

“…In "The Journal of Bone and Joint Surgery (American volume)", Schubert et al reported that rotator cuff satellite cells are more disinclined to myogenic differentiation, rather prone to adipogenic differentiation compared with that from gastrocnemius muscles (17). By isolation of the specifically labeled satellite cells from rotator cuff muscle and gastrocnemius muscles in tamoxifen-stimulated Pax7 CreERT2 :R26R tdTomato mice, they evaluated the potential of satellite cells to differentiating into myogenic or adipogenic lineage.…”