Effects of alpha/beta-androstenediol immune regulating hormones on bone remodeling and apoptosis in osteoblasts.

A large body of evidence suggests that the immune system directly impacts bone physiology. We tested whether immune regulating hormones (IRH), 17beta-androstenediol (beta-AED), 7beta,17beta-androstenetriol (beta-AET) or the 17alpha-androstenediol (alpha-AED), and 7alpha,17beta-androstenetriol (alpha-AET) metabolites could directly influence bone remodeling in vitro using human fetal osteoblasts (FOB-9). The impact on bone remodeling was examined by comparing the ratio of RANKL/OPG gene expression in response to AED and AET compounds.

Expression of RANKL in osteolytic membranes: association with fibroblastic cell markers.

Background: Aseptic loosening is often mentioned as the primary reason for costly revision of total joint arthroplasties. Receptor activator of nuclear factor-kappaB ligand (RANKL) appears to be a major factor in the bone resorption observed in periprosthetic osteolysis. RANKL plays an essential role in the recruitment, differentiation, and survival of the osteoclasts implicated in periprosthetic osteolysis.

Regulation of smooth muscle calcium sensitivity: KCl as a calcium-sensitizing stimulus.

KCl has long been used as a convenient stimulus to bypass G protein-coupled receptors (GPCR) and activate smooth muscle by a highly reproducible and relatively "simple" mechanism involving activation of voltage-operated Ca2+ channels that leads to increases in cytosolic free Ca2+ ([Ca2+]i), Ca2+-calmodulin-dependent myosin light chain (MLC) kinase activation, MLC phosphorylation and contraction. This KCl-induced stimulus-response coupling mechanism is a standard tool-set used in comparative studies to explore more complex mechanisms generated by activation of GPCRs. One area where this approach has been especially productive is in studies designed to understand Ca2+ sensitization, the relationship between [Ca2+]i and force produced by GPCR agonists.

K+ depolarization induces RhoA kinase translocation to caveolae and Ca2+ sensitization of arterial muscle.

KCl causes smooth muscle contraction by elevating intracellular free Ca2+, whereas receptor stimulation activates an additional mechanism, termed Ca2+ sensitization, that can involve activation of RhoA-associated kinase (ROK) and PKC. However, recent studies support the hypothesis that KCl may also increase Ca2+ sensitivity. Our data showed that the PKC inhibitor GF-109203X did not, whereas the ROK inhibitor Y-27632 did, inhibit KCl-induced tonic (5 min) force and myosin light chain (MLC) phosphorylation in rabbit artery.