Annexin VIII is differentially expressed by chondrocytes in the mammalian growth plate during endochondral ossification and in osteoarthritic cartilage.
"Fetal bovine growth plate chondrocytes as opposed to epiphyseal chondrocytes [genetic expression was compared]. Annexin VIII [is] expressed by growth plate chondrocytes and not by epiphyseal chondrocytes. Immunohistochemistry of the fetal bovine growth plate identified a gradient of increasing annexin VIII protein from the proliferative to the hypertrophic zone. annexin VIII [is] largely [localized] to the chondrocyte cell membrane.
We examined the distribution of annexin VIII in normal and osteoarthritic (OA) articular cartilage. In OA cartilage, the protein was located in a subset of mid- to deep zone chondrocytes and in the matrix surrounding these cells; no annexin VIII was detected in normal articular cartilage. annexin VIII is a marker for chondrocyte differentiation during normal endochondral ossification."
"The annexin repeats form a planar cyclic structure with a central pore region. The pore is lined with hydrophilic residues and has been found to act as a calcium channel in vitro and in vivo."
"Annexin VIII is expressed by the differentiating chondrocytes of the growth plate but not by the phenotypically stable epiphyseal chondrocytes [suggesting] that it has a specific differentiation-associated role within the growth plate"
Bone matrix regulates osteoclast differentiation and annexin A8 gene expression.
"We cultured murine bone marrow-derived osteoclasts on either cell culture plastic or devitalized mouse calvariae. Annexin A8 (AnxA8) mRNA was markedly up-regulated by bone. AnxA8 protein was present at high levels in osteoclasts present in human tissues recovered from sites of pathological bone loss. The presence of bone mineral was required for up-regulation of AnxA8 mRNA since osteoclasts plated on decalcified bone express AnxA8 at low levels as did osteoclasts plated on native or denatured type I collagen. AnxA8-regulated cytoskeletal reorganization in osteoclasts generated on a mineralized matrix. Anxa8 [is] a gene strongly induced late in osteoclast differentiation and a protein that regulates formation of the cell's characteristic actin ring."
"AnxA8 has been shown to bind F-actin and phospholipids in a calcium-dependent manner, consistent with the idea that AnxA8 may regulate cytoskeletal reorganization, a process central to osteoclastic resorption"
"Mononuclear cells, stromal cells, and fibroblasts did not stain positively for AnxA8 expression"
"AnxA8 can disrupt the actin cytoskeleton and/or suppress lysosomal trafficking, leading to failure of osteoclast spreading and function"
"AnxA8 knockdown inhibits formation of actin rings"
"Osteoclasts on native or denatured type I collagen fail to express AnxA8."<-However AnnexinA8 was expressed on osteoclasts on bone so osteoclasts could have been the source of AnxA8 with LSJL.
Osteoclasts are responsive to fluid flow Fluid flow-induced calcium response in early or late differentiated osteoclasts., and the change in calcium response is consistent with alterations in AnxA8 expression.
"MLO-Y4 osteocyte-like cells were exposed to fluid flow-induced shear stress(12dyn/cm(2))for 0, 1, 2, 4, 6, 12, and 24 hours. Osteocyte exposed to shear stress at different time points were used in co-culture system for 9 days. On the 9(th) day the amount of positively stained osteoclasts were counted and compared. The expressions of osteoprotegerin (OPG) and receptor activator of nuclear factor-kappa (RANKL) were detected.
Compared with bone cells without stimulation with fluid flow-induced shear stress, the amount of osteocytes significantly decreased at all time points after the application of fluid flow-induced shear stress. The OPG expression at mRNA levels was significantly up-regulated in the first 12 hours, the RANKL mRNA expression was significantly down-regulated in the first 4 hours, and the RANKL/OPG ratio significantly decreased within 12 hours. However, all these indicators showed no significant difference at 24 hours when compared with the pre-stimulation level."
LSJL gene expression was done at 49 hours but one hour after the last stimulation so osteoclast activity could have influenced annexin a8 levels.
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