Читать книгу Musculoskeletal Disorders - Sean Gallagher - Страница 100
Osteocytes—the mechanotransducers and maintainers of bone
ОглавлениеOsteocytes are mature bone cells that live within the substance of bone and comprise 90–95% of all bone cells (Bonewald, 2007). Osteocytes are embedded in spaces (lacunae) in the interior of bone and are connected to adjacent cells by long cytoplasmic processes radiating from the cell body that lie within channels (canaliculi) throughout the mineralized matrix of bone (Figure 3.17) (Hirose et al., 2007; Lian & Stein, 2008). The processes of adjacent osteocytes make contact via gap junctions as well as with the osteoblasts and bone lining cells, maintaining the vitality of osteocytes by passing nutrients and metabolites between blood vessels and distant osteocytes (Jiang, Siller‐Jackson, & Burra, 2007).
Osteocytes are believed to be the bone‐sensing cells involved in mechanotransduction and thus the key regulators of bone remodeling. The gap junctions mentioned earlier aid in this function. Also, the osteocyte cell membrane is surrounded by interstitial fluid and extracellular matrix in which microtubules are embedded in order to transmit extracellular matrix mechanical changes to the osteocyte’s actin filaments (Bakker et al., 2009). Osteocytes also communicate with surrounding cells via the release of biochemical factors and signaling molecules, such as bone morphogenetic proteins (BMPs), prostaglandin E2 (PGE2), and nitric oxide (NO) (Klein‐Nulend, Bacabac, & Bakker, 2012).
Osteocytes are also actively involved in maintaining the bony matrix. They express osteoblast stimulating factor‐1 after mechanical or muscular loading (Klein‐Nulend & Bonewald, 2008). Osteocytes send inhibitory signals to osteoclasts to prevent bone loss during normal loading (Nakashima et al., 2011). Local damage (microcracks) of the osteoid matrix can compromise the osteocyte environment, disrupting the fluid flow, consequently reducing nutrients and oxygen supply to the embedded cells and creating oxidative stress (Al‐Dujaili et al., 2011).