Review Article
Volume 5 Issue 2 - 2020
Melatonin Reduces Microgravity-Induced Bone Loss: Implications for the Challenges of Long-Term Spaceflight
Mu-Tai Liu1* and Russel J Reiter2
1Department of Radiology, Yuanpei University of Science and Technology, Taiwan
2Department of Cell Systems and Anatomy, The University of Texas Health Science Center, San Antonio, Texas, USA
*Corresponding Author: Mu-Tai Liu, Department of Radiology, Yuanpei University of Science and Technology, Taiwan.
Received: April 13, 2021; Published: April 21, 2021


Spaceflight, especially because of microgravity, critically affects the health of astronauts who participate in a long-term space mission. Microgravity exposure causes osteoporosis-like bone loss and muscle atrophy in astronauts. Bone mineral density (BMD) reduced at the rate of 1% per month at the lumbar spine and 1 - 1.6% per month at the hip in astronauts of the Russian/MIR space station and International Space Station (ISS). Bone remodeling is regulated primarily by the activity of bone-resorbing osteoclasts and bone-forming osteoblasts. Microgravity with reduced mechanical load on the weight-bearing bones leads to an increase in bone resorption and a reduction in bone formation. Microgravity inhibits bone formation through effects on the Wnt/β-catenin signaling pathway. Melatonin induces human mesenchymal stem cells (hMSC) differentiation into mature osteoblasts via multiple signal transduction mechanisms which include MEK/ERK1/2, runt-related transcription factor 2 (RUNX-2), osteocalcin, BMP-2 and Wnt/β-catenin. It promotes the synthesis and mineralization of new bone. It significantly inhibits the increase in the expression of genes for osteoclastogenesis, including Mmp‐9, cathepsin K, Trap and Rankl, in microgravity conditions compared to that on the ground. Conversely, it enhances the expression levels of osteoclast inhibitory genes, Opg and Calcitonin. Treatment with melatonin is a potential approach for inhibiting osteoclast activity in microgravity. Melatonin is recommended as a promising agent for the prevention of bone loss during space exploration. With the technological advancements in stem cell-based therapy, mesenchymal stem cells (MSCs) with the capacity to differentiate into osteoblasts may serve as a novel approach for the treatment of osteoporosis. Bone marrow mesenchymal stem cells (BM-MSCs) increase trabecular bone, inhibit the loss of BMD and prevents osteoporosis. The addition of strontium-containing hydroxyapatite nanoparticles (nSr-HAP) to human bone marrow mesenchymal stem cells (hBM-MSCs) may be a potential strategy to promote bone regeneration for microgravity-induced osteoporosis. Furthermore, combined melatonin and bone marrow mesenchymal stem cell therapy may serve as a promising regimen for the treatment of osteoporosis. The study suggests the possible prospective strategy for both preclinical and clinical studies of combined melatonin and mesenchymal stem cells in the treatment of microgravity-induced osteoporosis-like bone loss in order to provide advanced health care for astronauts on long-term space exploration missions.

Keywords: Spaceflight; Astronauts; Microgravity; Melatonin; Osteoclasts; Osteoblasts; Osteocytes; RANKL; Bone; Mesenchymal Stem Cells


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Citation: Mu-Tai Liu and Russel J Reiter. “Melatonin Reduces Microgravity-Induced Bone Loss: Implications for the Challenges of Long-Term Spaceflight”. EC Emergency Medicine and Critical Care 5.5 (2021): 18-28.

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