BMP signaling is required for adult skeletal homeostasis and mediates bone anabolic action of parathyroid hormone.

Bmp2 and Bmp4 genes were ablated in adult mice (KO) using a conditional gene knockout technology. Bones were evaluated by microcomputed tomography (µCT), bone strength tester, histomorphometry and serum biochemical markers of bone turnover. Drill-hole was made at femur metaphysis and bone regeneration in the hole site was measured by calcein binding and µCT. Mice were either sham operated (ovary intact) or ovariectomized (OVX), and treated with human parathyroid hormone (PTH), 17ß-estradiol (E2) or vehicle. KO mice displayed trabecular bone loss, diminished osteoid formation and reduced biomechanical strength compared with control (expressing Bmp2 and Bmp4). Both osteoblast and osteoclast functions were impaired in KO mice. Bone histomorphomtery and serum parameters established a low turnover bone loss in KO mice. Bone regeneration at the drill-hole site in KO mice was lower than control. However, deletion of Bmp2 gene alone had no effect on skeleton, an outcome similar to that reported previously for deletion of Bmp4 gene. Both PTH and E2 resulted in skeletal preservation in control-OVX, whereas in KO-OVX, E2 but not PTH was effective which suggested that the skeletal action of PTH required Bmp ligands but E2 did not. To determine cellular effects of Bmp2 and Bmp4, we used bone marrow stromal cells in which PTH but not E2 stimulated both Bmp2 and Bmp4 synthesis leading to increased Smad1/5 phosphorylation. Taken together, we conclude that Bmp2 and Bmp4 are essential for maintaining adult skeletal homeostasis and mediating the anabolic action of PTH.

HIV-1 Nef breaches placental barrier in rat model.

The vertical transmission of HIV-1 from the mother to fetus is known, but the molecular mechanism regulating this transmission is not fully characterized. The fetus is highly protected by the placenta, which does not permit microbial pathogens to cross the placental barrier. In the present study, a rat model was established to observe the effect of HIV-1 protein Nef on placental barrier. Evans blue dye was used to assay permeability of placental barrier and fourteen day pregnant Sprague Dawley rats were injected intravenously with 2% Evans blue dye along with various concentrations of recombinant Nef. After an hour, animals were sacrificed and dye migration was observed through the assimilation of peripheral blood into fetus. Interestingly, traces of recombinant Nef protein were detected in the embryo as well as amniotic fluid and amniotic membrane along with placenta and uterus. Our study indicates that recombinant HIV-1-Nef protein breaches the placental barrier and allows the migration of Evans blue dye to the growing fetus. Further the concentration of Nef protein in blood is directly proportional to the intensity of dye migration and to the amount of Nef protein detected in uterus, placenta, amniotic membrane, amniotic fluid and embryo. Based on this study, it can be concluded that the HIV-1 Nef protein has a direct effect on breaching of the placental barrier in the model we have established in this study. Our observations will be helpful to understand the molecular mechanisms related to this breach of placental barrier by Nef in humans and may be helpful to identify specific Nef inhibitors.