Role of microRNAs in osteoblasts differentiation and bone disorders.

Advanced studies of single stranded endogenous ~22 nt microRNAs (miRNAs) have demonstrated their diverse biological functions including control of cell differentiation, cell cycle and pathological conditions. Recent studies suggest the potential application of miRNAs in stem cell engineering. miRNAs play a vital role as post-transcriptional regulators of gene expression which controls osteoblasts-mediated bone formation and osteoclasts related bone remodeling. Transcriptional and post-transcriptional mechanisms regulate the differentiation of osteoblasts and osteogenesis. The differentiation of osteoblasts is a key step in the development of skeletal muscles and it is involved in triggering the signaling pathways. Signaling pathways like TGFβ, BMP and Wnt are regulated by miRNAs which in turn, are shown to be associated with bone dynamics and bone disorders. This recap highlights the role of miRNAs in osteoblasts differentiation and emphasizes their potential therapeutic role in metabolic bone disorders.

Physiological effects of microgravity on bone cells.

Life on Earth developed under the influence of normal gravity (1g). With evidence from previous studies, scientists have suggested that normal physiological processes, such as the functional integrity of muscles and bone mass, can be affected by microgravity during spaceflight. During the life span, bone not only develops as a structure designed specifically for mechanical tasks but also adapts for efficiency. The lack of weight-bearing forces makes microgravity an ideal physical stimulus to evaluate bone cell responses. One of the most serious problems induced by long-term weightlessness is bone mineral loss. Results from in vitro studies that entailed the use of bone cells in spaceflights showed modification in cell attachment structures and cytoskeletal reorganization, which may be involved in bone loss. Humans exposed to microgravity conditions experience various physiological changes, including loss of bone mass, muscle deterioration, and immunodeficiency. In vitro models can be used to extract valuable information about changes in mechanical stress to ultimately identify the different pathways of mechanotransduction in bone cells. Despite many in vivo and in vitro studies under both real microgravity and simulated conditions, the mechanism of bone loss is still not well defined. The objective of this review is to summarize the recent research on bone cells under microgravity conditions based on advances in the field.