Thy1 (CD90) Expression Is Elevated in Radiation-Induced Periprosthetic Capsular Contracture: Implication for Novel Therapeutics

Abstract

Background Capsular contracture is a devastating complication of post-mastectomy implant-based breast reconstruction. Unfortunately, capsular contracture rates are drastically increased by targeted radiotherapy, a standard post-mastectomy treatment. Thy1 (also called CD90) is important in myofibroblast differentiation and scar tissue formation. However, the impact of radiotherapy on Thy1 expression and the role of Thy1 in capsular contracture are unknown. Methods We analyzed Thy1 expression in primary human capsular tissue and primary fibroblast explants by RT-qPCR, Western blotting, and immunohistochemistry. Thy1 was depleted using RNA interference to determine if Thy1 expression was essential for the myofibroblast phenotype in capsular fibroblasts. Furthermore, human capsular fibroblasts were treated with a new anti-scarring compound, salinomycin to determine if Thy1 expression and myofibroblast formation were blocked by salinomycin. Results Herein, we show that radiation therapy significantly increased Thy1 mRNA and protein expression in peri-implant scar tissue. Capsular fibroblasts explanted from scar tissue retained the ability to make the myofibroblast produced scar forming components collagen I and α-smooth muscle actin (αSMA). Depletion of Thy1 decreased the fibrotic morphology of capsular fibroblasts and significantly decreased αSMA and collagen levels. Furthermore, we show for the first time that salinomycin decreased Thy1 expression and prevented myofibroblast formation in capsular fibroblasts. Conclusions These data reveal that ionizing radiation-induced Thy1 over-expression may contribute to increased capsular contracture severity, and fibroblast scar production can be ameliorated through targeting Thy1 expression. Importantly, our new results show promise for the anti-scarring ability of salinomycin in radiation-induced capsular contracture.

Thy1 (CD90) expression is regulated by DNA methylation during adipogenesis

“…While we show that 5-aza-dC treatment decreased methylation in the Thy1-CGI1 region and blunted adipogenesis, it is possible that hypomethylating the Thy1 gene at the same time could affect other cell types, such as, fibroblasts (involved in fibrosis); it has been established that Thy1 expression is up-regulated during and involved in myofibroblast differentiation 55 . Future studies could examine other CpG islands in the traditional promoter region and downstream regions to investigate whether methylation of these sites is also essential for Thy1's involvement in adipogenesis, fibrosis, and other functions.…”

Defining Skin Fibroblastic Cell Types Beyond CD90

“…The expression of matrix metalloproteinase inhibitor Timp1 is found to be upregulated in CD90 + fibroblasts near the portal vein, suggesting these cells inhibit collagen degradation and promote accumulation of extracellular matrix (Katsumata et al, 2017 ). In line with these observations, CD90 expression is elevated in the capsular contracture and scar tissue after the implant-based breast reconstruction, and CD90 expression is essential for the myofibroblast phenotype in capsular fibroblasts (Hansen et al, 2017 ). In addition, higher CD90 expression is found to be accompanied by the increment of α-SMA + stromal component in hepatocellular carcinoma (Sukowati et al, 2013 ), implying for fibrotic and tumor promoting functions of CD90.…”

Thy1 (CD90) expression is regulated by DNA methylation during adipogenesis

“…Although we show that 5-aza-dC treatment decreased methylation in the Thy1-CGI1 region and blunted adipogenesis, it is possible that loss of methylation at the Thy1 gene could affect other cell types, such as fibroblasts or T lymphocytes, in a different manner. For example, it has been established that Thy1 expression is up-regulated in myofibroblasts from radiation-induced scarring compared with normal skin fibroblasts (59). Additionally, several types of malignant cells, including cancer stem cells, show increased expression of Thy1 (60,61).…”