We have evaluated the role of the ADP-ribosyl cyclase, CD38, in bone remodeling, a process by which the skeleton is being renewed constantly through the coordinated activity of osteoclasts and osteoblasts. CD38 catalyzes the cyclization of its substrate, NAD+, to the Ca2+-releasing second messenger, cyclic ADP-ribose (cADPr). We have shown previously that CD38 is expressed both in osteoblasts and osteoclasts. Its activation in the osteoclast triggers Ca2+ release through ryanodine receptors (RyRs), stimulation of interleukin-6 (IL-6), and an inhibition of bone resorption. Here, we have examined the consequences of deleting the CD38 gene in mice on skeletal remodeling. We report that CD38-/- mice displayed a markedly reduced bone mineral density (BMD) at the femur, tibia, and lumbar spine at 3 months and at the lumbar spine at 4 months, with full normalization of the BMD at all sites at 5 months. The osteoporosis at 3 months was accompanied by a reduction in primary spongiosa and increased osteoclast surfaces on histomorphometric analysis. Hematopoetic stem cells isolated ex vivo from CD38-/- mice showed a dramatic approximately fourfold increase in osteoclast formation in response to incubation for 6 days with RANK-L and M-CSF. The osteoclasts so formed in these cultures showed a approximately 2.5-fold increase in resorptive activity compared with wild-type cells. However, when adherent bone marrow stromal cells were allowed to mature into alkaline phosphatase-positive colony-forming units (CFU-Fs), those derived from CD38-/- mice showed a significant reduction in differentiation compared with wild-type cells. Real-time RT-PCR on mRNA isolated from osteoclasts at day 6 showed a significant reduction in IL-6 and IL-6 receptor mRNA, together with significant decreases in the expression of all calcineurin A isoforms, alpha, beta, and gamma. These findings establish a critical role for CD38 in osteoclast formation and bone resorption. We speculate that CD38 functions as a cellular NAD+ "sensor," particularly during periods of active motility and secretion.

Background Porphyromonas gingivalis strains are shown to invade human cells in vitro with different invasion efficiencies, varying by up to three orders of magnitude.ObjectiveWe tested the hypothesis that invasion-associated interstrain genomic polymorphisms are present in P. gingivalis and that putative invasion-associated genes can contribute to P. gingivalis invasion.DesignUsing an invasive (W83) and the only available non-invasive P. gingivalis strain (AJW4) and whole genome microarrays followed by two separate software tools, we carried out comparative genomic hybridization (CGH) analysis.ResultsWe identified 68 annotated and 51 hypothetical open reading frames (ORFs) that are polymorphic between these strains. Among these are surface proteins, lipoproteins, capsular polysaccharide biosynthesis enzymes, regulatory and immunoreactive proteins, integrases, and transposases often with abnormal GC content and clustered on the chromosome. Amplification of selected ORFs was used to validate the approach and the selection. Eleven clinical strains were investigated for the presence of selected ORFs. The putative invasion-associated ORFs were present in 10 of the isolates. The invasion ability of three isogenic mutants, carrying deletions in PG0185, PG0186, and PG0982 was tested. The PG0185 (ragA) and PG0186 (ragB) mutants had 5.1×103-fold and 3.6×103-fold decreased in vitro invasion ability, respectively.ConclusionThe annotation of divergent ORFs suggests deficiency in multiple genes as a basis for P. gingivalis non-invasive phenotype.

Progressive ventricular dilatation commonly accompanies the transition to overt failure in chronically overloaded hearts; however, only recently have studies begun to elucidate underlying molecular alterations. In particular, the potential role of altered myocardial expression of the procollagenase gene in this process has not previously been examined. Biventricular hypertrophy and dilatation were produced in rats by creating an abdominal aortocaval fistula. The time courses of changes in expression of collagen I and III genes and of the procollagenase gene (matrix metalloproteinase-1, MMP-1) were assessed by Northern blot hybridization. Expression of all three genes increased promptly; however, collagenase gene expression peaked much earlier (8 h) than did expression of either of the collagen genes (7 days), and all returned to baseline levels by 45 days. These data corroborate earlier reports of increased collagen gene expression in this model, but more importantly, they provide the first evidence of concurrent activation of collagenase gene expression, suggesting that enhancement of collagen degradation may be a prerequisite for structural cardiac dilatation.

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