Simulated microgravity attenuates skin wound healing by inhibiting dermal fibroblast migration via F-actin/YAP signaling pathway.

Skin and its cell components continuously subject to extrinsic and intrinsic mechanical forces and are mechanical sensitive. Disturbed mechanical homeostasis may lead to changes in skin functions. Gravity is the integral mechanical force on the earth, however, how gravity contributes to the maintenance of skin function and how microgravity in space affects the wound healing are poorly understood. Here, using microgravity analogs, we show that simulated microgravity (SMG) inhibits the healing of cutaneous wound and the accumulation of dermal fibroblasts in the wound bed. In vitro, SMG inhibits the migration of human foreskin fibroblast cells (HFF-1), and decreases the F-actin polymerization and YAP (yes-associated protein) activity. The SMG-inhibited migration can be recovered by activating YAP or F-actin polymerization using lysophosphatidic acid (LPA) or jasplakinolide (Jasp), suggesting the involvement of F-actin/YAP signaling pathway in this process. In SMG rats, LPA treatment improves the cutaneous healing with increased dermal fibroblasts in the wound bed. Together, our results demonstrate that SMG attenuates the cutaneous wound healing by inhibiting dermal fibroblast migration, and propose the crucial role of F-actin/YAP mechano-transduction in the maintenance of skin homeostasis under normal gravity, and YAP as a possible therapeutic target for the skin care of astronauts in space.

Simulated Microgravity Inhibits Rodent Dermal Fibroblastic Differentiation of Mesenchymal Stem Cells by Suppressing ERK/ß-Catenin Signaling Pathway.

Studies have shown that bone marrow-derived mesenchymal stem cells (BMSCs) can differentiate into dermal fibroblasts to participate in skin-repairing. However, at present, little is known about how microgravity affects dermal fibroblastic differentiation of BMSCs in space. The aim of this study was to investigate the effect of simulated microgravity (SMG) on the differentiation of BMSCs into dermal fibroblasts and the related molecular mechanism. Here, using a 2D-clinostat device to simulate microgravity, we found that SMG inhibited the differentiation and suppressed the Wnt/ß-catenin signaling and phosphorylation of extracellular regulated protein kinases 1/2 (ERK1/2). After upregulating the Wnt/ß-catenin signaling with lithium chloride (LiCl) treatment, we found that the effect of the differentiation was restored. Moreover, the Wnt/ß-catenin signaling was upregulated when phosphorylation of ERK1/2 was activated with tert-Butylhydroquinone (tBHQ) treatment. Taken together, our findings suggest that SMG inhibits dermal fibroblastic differentiation of BMSCs by suppressing ERK/ß-catenin signaling pathway, inferring that ERK/ß-catenin signaling pathway may act as a potential intervention target for repairing skin injury under microgravity conditions.

[Mesenchymal stem cells and skin injury repair].

Mesenchymal stem cells (MSCs) are pluripotent stem cells with high self-proliferation and multidirectional differentiation potential. They also have other functions including immune regulation, paracrine and so on, playing an important role in repairing injured tissues. In recent years, a lot of research has been done on how MSCs promote skin injury repair, and a lot of progress has been made. Compared with direct injection of MSCs in the wound area, some special treatments or transplantation methods could enhance the ability of MSCs to repair skin injury. This paper mainly discusses the role of MSCs in skin injury repair and technical ways to improve its repairing capacity, and discusses the existing problems in this field and prospects for future research directions.

Simulated Microgravity Suppresses Osteogenic Differentiation of Mesenchymal Stem Cells by Inhibiting Oxidative Phosphorylation.

Studies showed that energy metabolism plays a pivotal role in the differentiation of stem cells. Previous studies revealed that simulated microgravity (SMG) inhibits osteogenic differentiation of mesenchymal stem cells (MSCs). However, the underlying relationship between osteogenesis and energy metabolism under SMG conditions is not fully understood. In the present study, we investigated mitochondrial oxidative phosphorylation (OXPHOS) by assessing the level of peroxisome proliferator activated receptor γ coactivator 1α (PGC-1α), mitochondrial DNA (mtDNA) copy number, mitochondrial mass and oxygen consumption rate (OCR) during osteogenesis of MSCs under SMG conditions. We found that SMG inhibited osteogenic differentiation and OXPHOS of MSCs. Moreover, the expression of sirtuin 1 (Sirt1), an important energy sensor, significantly decreased. After upregulating the expression of Sirt1 using resveratrol, an activator of Sirt1, SMG-inhibited OXPHOS and osteogenic differentiation of MSCs were recovered. Taken together, our results suggest that SMG suppresses osteogenic differentiation of MSCs by inhibiting OXPHOS, indicating that OXPHOS might serve as a potential therapeutic target for repairing bone loss under microgravity conditions.