Page 116 - Physico-Chemical Niche Conditions for Bone Cells

Regulation of bone cell mitochondrial structure and dynamics
ABSTRACT
Although mechanical loading of bone is generally associated with proliferation and differentiation of osteoblasts, the latter highly depends on the cellular energy state, and as such mitochondrial function co-determines the osteoblast fate and function. However, very little is known about how mechanical loading affects mitochondrial network structure and dynamics. Physical factors that are exerted on eukaryotic cells are transmitted to mitochondria along cytoskeletal filaments including actin. Here, we aimed to determine the effects of mechanical loading by pulsating fluid flow (PFF) on bone cell mitochondrial network structure and dynamics. Prior to PFF treatment, MC3T3-E1 pre-osteoblasts were live stained for 4 h by for mitochondria and F-actin. Confocal microscopy was employed for live cell imaging (video; top and side view) of mitochondria and F-actin during 2 min PFF treatment to track speed and displacement of mitochondrial networks. During 2 min PFF, mitochondrial track speed ranged from 0-14.9 μm/s, and displacement from 0-62.7 μm. Moreover, the footprint and morphology of the mitochondrial network changed during PFF, particularly at 50 and 70 sec. Mean branch length of mitochondria was not affected by PFF. Side view imaging revealed that mitochondria and F-actin alternatingly moved up and down. Top view imaging revealed that mitochondria displaced, thereby following the flow direction, while F-actin fibers did not. In conclusion, both mitochondrial network structure and dynamics in pre-osteoblasts were affected by 2 min of mechanical loading, but F-actin was not. This mechanoresponse of mitochondria may contribute to changes in structure and function of bone cells. Mechanical loading-induced changes in mitochondria may drive signaling pathways involved in the regulation of cell function in aging and diseases.
Keywords
Mitochondria; Network structure; Dynamics; Cytoskeletal filaments; Mechanical loading; Mechanotransduction
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