Gap junction mediated regulation of osteocytes to osteoblastic alkaline phosphatase activity is independent of microgravity

Abstract

Decreased bone formation is one of the main causes of bone loss under microgravity. As a mechanical perceiver, osteocyte regulates bone formation by sending mechanical signals to osteoblast. However, the regulation of osteoblastic bone formation by osteocytes is less known so far under the microgravity conditions. The aim of this study was to investigate the regulation of bone formation/loss by detection of the osteocytic regulatory effects on the bone-specific alkaline phosphatase (ALP) activity of osteoblasts under altered gravitational environment. The altered gravitational environment was provided by a large gradient high magnetic field that could produce high magneto-gravitational environment (HMGE) and provided three apparent gravity levels (µg, 1g, and 2g). After the MLO-Y4 and 2T3 cells were cocultured in direct physical contact for 24 h and established gap junction intercellular communication under HMGE, a highly significant rapid increase in ALP activity was observed in µg, 1g, 2g, and control group (p < 0.001). Conversely, application of 50-µM beta-glycyrrhetinic acid gap junction inhibitor or remote coculture significantly decreased the ALP activity. There were no obvious differences of osteoblastic 2T3 ALP activity among µg, 1g, 2g, and control groups. Based on these findings, we interpreted that gap junction was probably the main route of osteoblastic ALP activity regulation by osteocyte. Gravity had no significant impact on the osteoblastic ALP activity regulated by osteocyte in a short period of time.

Fucoidan Induces Cell Aggregation and Apoptosis in Osteosarcoma MG-63 Cells

“…These results suggested that fucoidan can be used in bone health supplements and as an additive for biomaterial-based scaffolds to promote bone regeneration. Efficient bone regeneration and repair is mediated by directed cell migration of osteoblasts to sites in need of bone formation (Pignolo & Kassem 2011;Dirckx et al 2013;Meng & Xie 2014;Song & Park 2014). Some controversial effects of fucoidan on cell migration have been reported in several types of cancer cells.…”

Development of bone cell microarrays in microfluidic chips for studying osteocyte-osteoblast communication under fluid flow mechanical loading

“…The more gentle parachute assay consists in incubating the donor cells with the reporter dye and dropping them on a monolayer of acceptor cells, which still leads to cell-cell contacts randomly distributed throughout the culture dishes [101]. The first structural organization of gap junctional coupling was reported with the use of porous membranes [20,102]. Two different cell types are seeded on the opposite sides of the membrane and gap junctions can only occur through the micropores.…”

“…Cx43 gap junctions can form between identical or different cell types, leading to homotypic and heterotypic interactions [14]. In order to unravel the cooperative action of the different bone cell types in response to mechanical stimuli, heterotypic communication between bone cells has been studied [19][20][21][22][23]. Mostly, gap junctional coupling in co-cultures of osteoblasts-osteocytes and osteoblasts-osteoclasts was probed using a standard dye transfer assay [19][20][21][22].…”

“…In order to unravel the cooperative action of the different bone cell types in response to mechanical stimuli, heterotypic communication between bone cells has been studied [19][20][21][22][23]. Mostly, gap junctional coupling in co-cultures of osteoblasts-osteocytes and osteoblasts-osteoclasts was probed using a standard dye transfer assay [19][20][21][22]. The co-cultures were created either by performing a parachute assay or using a porous membrane.…”