Role of Autophagy in Osteogenic Differentiation of Mesenchymal Stem Cells Under Simulated Microgravity

Microgravity-induced bone loss is a significant problem for astronauts during spaceflight, and will limit the potential for future long duration spaceflight. The increased bone resorption by osteoclasts and the reduced bone formation by osteoblasts are largely responsible for this problem. Mesenchymal stem cells (MSCs) are multipotent cells that are capable of osteogenic, chondrogenic, adipogenic, and myogenic differentiation. MSCs play important roles in the regeneration of connective tissues, including bone. Microgravity has been shown to inhibit osteogenic differentiation of MSCs while increasing adipogenic differentiation. Autophagy is a key catabolic process that targets cellular contents for degradation in cellular stress responses and survival. Autophagy plays important roles in the maintenance of pluripotency and the commitment of MSCs to different lineages, especially in the osteoblastic lineage. Therefore, we hypothesized that modulation of autophagy regulates microgravity-induced inhibition of osteogenic differentiation of MSCs and manipulation of autophagy levels can promote MSC differentiation into osteoblasts. We examined autophagy levels MSCs and the effect of autophagy modulation on MSC differentiation into osteoblasts under simulated microgravity using custom-made Clinostat. Osteoblast formation was assessed by Real-Time Quantitative Reverse Transcription Polymerase Chain Reaction (RT-qPCR), Next Generation RNA Sequencing (NGS) and Quantitative Shotgun Proteomics