Increased osteoblastogenesis and decreased bone resorption protect against ovariectomy-induced bone loss in thrombospondin-2-null mice.

Although bone is composed primarily of extracellular matrix (ECM), the dynamic role that the ECM plays in regulating bone remodeling secondary to estrogen loss is relatively unexplored. Previous studies have shown that mice deficient in the matricellular protein thrombospondin-2 (TSP2-null) form excess endocortical bone; thus, we postulated that enhanced bone formation in TSP2-null mice could protect against ovariectomy (OVX)-induced bone loss. Wild-type (WT) OVX mice showed a significant loss of both midfemoral endocortical and proximal tibial trabecular bone, but OVX did not significantly alter TSP2-null bone.

Analysis of muscle creatine kinase regulatory elements in recombinant adenoviral vectors.

Adenoviral gene transfer holds promise for gene therapy, but effective transduction of a large and distributed tissue such as muscle will almost certainly require systemic delivery. In this context, the use of muscle-specific regulatory elements such as the muscle creatine kinase (MCK) promoter and enhancer will avoid potentially harmful ectopic expression of transgenes. We describe here the development and testing of adenoviral vectors containing small, striated muscle-specific, highly active MCK expression cassettes.

Hypercalcemia during the osteogenic phase after rat marrow ablation coincides with increased bone resorption assessed by the NTx marker.

Marrow ablation is a model of bone turnover in which the excavated tibial intramedullary cavity is rapidly and reproducibly filled by osteoblasts with new woven bone (days 6-8), which is then rapidly resorbed by osteoclasts (days 10-15). We showed previously (Magnuson et al., 1997) that marrow ablation induces a dramatic hypercalcemia and hypercalciuria in rats that unexpectedly peaked at the time of maximal osteogenesis and continued throughout the subsequent resorption phase.

Osteoclasts generate cross-linked collagen N-telopeptides (NTx) but not free pyridinolines when cultured on human bone.

Urinary excretion of the cross-linked alpha 2(I) N-telopeptide (NTx) of type I collagen has proven in clinical studies to provide a highly responsive and specific index of bone resorption. In order to understand better the biological basis of the specificity and responsiveness of this marker, we examined whether osteoclasts cultured on human bone could generate immunoreactive NTx peptide. Mouse bone marrow cultures stimulated with 1,25 diliydroxyvitamin D3 (1,25(OH)2D3) and hydrocortisone to produce osteoclasts, were cocultured on human bone particles or dentin slices.

Muscle gene E-box control elements. Evidence for quantitatively different transcriptional activities and the binding of distinct regulatory factors.

The muscle creatine kinase gene enhancer contains two regulatory elements (MCK-R and MCK-L) with the consensus E-box sequence (CAnnTG). A myocyte specific protein complex, MEF1, binds the MCK-R site. MEF1 contains several basic H-L-H myogenic determination factors (MDFs), each dimerized with ubiquitous members of the bH-L-H family (e.