Osteoporosis is a common aging-related disease diagnosed primarily using bone mineral density (BMD). We assessed genetic determinants of BMD as estimated by heel quantitative ultrasound (eBMD) in 426,824 individuals, identifying 518 genome-wide significant loci (301 novel), explaining 20% of its variance. We identified 13 bone fracture loci, all associated with eBMD, in ~1.2M individuals. We then identified target genes enriched for genes known to influence bone density and strength (maximum odds-ratio=58, p=10 −75 ) from cell-specific features, including chromatin conformation and accessible chromatin sites. We next performed rapid-throughput skeletal phenotyping of 126 knockout mice lacking target genes and found an increased abnormal skeletal phenotype frequency compared to 526 unselected lines (p<0.0001). In-depth analysis of one gene, DAAM2 , showed a disproportionate decrease in bone strength relative to mineralization. This genetic atlas provides evidence testing how to link associated-SNPs to causal genes, offers new insights into osteoporosis pathophysiology and highlights opportunities for drug development.

Vitamin D signaling regulates cell proliferation and differentiation, and epidemiological data suggest that it functions as a cancer chemopreventive agent, although the underlying mechanisms are poorly understood. Vitamin D signaling can suppress expression of genes regulated by c-MYC, a transcription factor that controls epidermal differentiation and cell proliferation and whose activity is frequently elevated in cancer. We show through cell-and animal-based studies and mathematical modeling that hormonal 1,25-dihydroxyvitamin D (1,25D) and the vitamin D receptor (VDR) profoundly alter, through multiple mechanisms, the balance in function of c-MYC and its antagonist the transcriptional repressor MAD1/MXD1. 1,25D inhibited transcription of c-MYC-regulated genes in vitro, and topical 1,25D suppressed expression of c-MYC and its target setd8 in mouse skin, whereas MXD1 levels increased. 1,25D inhibited MYC gene expression and accelerated its protein turnover. In contrast, it enhanced MXD1 expression and stability, dramatically altering ratios of DNA-bound c-MYC and MXD1. Remarkably, F-box protein FBW7, an E3-ubiquitin ligase, controlled stability of both arms of the c-MYC/MXD1 push-pull network, and FBW7 ablation attenuated 1,25D regulation of c-MYC and MXD1 turnover. Additionally, c-MYC expression increased upon VDR knockdown, an effect abrogated by ablation of MYC regulator β-catenin. c-MYC levels were widely elevated in vdr −/− mice, including in intestinal epithelium, where hyperproliferation has been reported, and in skin epithelia, where phenotypes of VDR-deficient mice and those overexpressing epidermal c-MYC are similar. Thus, 1,25D and the VDR regulate the c-MYC/MXD1 network to suppress c-MYC function, providing a molecular basis for cancer preventive actions of vitamin D.V itamin D is obtained naturally from limited dietary sources. It is also generated by cutaneous conversion of 7-dehydrocholesterol in the presence of adequate surface solar UV-B radiation, which varies with latitude and time of year (1). Vitamin D has attracted broad clinical interest because insufficiency or deficiency is widespread in several populations worldwide (2-4). Although initially identified as a regulator of calcium homeostasis, vitamin D is now known to have a broad spectrum of actions, driven by the virtually ubiquitous expression of the vitamin D receptor (VDR), a nuclear receptor and hormone-regulated transcription factor. For example, it acts as a chemopreventive agent in several animal models of cancer and induces cell-cycle arrest and nonmalignant and malignant cell differentiation (5-11). Epidemiological data have provided associations between lack of UV-B exposure, vitamin D insufficiency, and the prevalence of certain cancers (12). A large prospective study associated vitamin D sufficiency with reduced total cancer incidence and mortality, particularly in digestive cancers [head and neck squamous cell carcinoma (HNSCC), esophageal, pancreatic, stomach, and colorectal cancers] and leukemias (13). VDR gene polymorphi...

We examined the role of bone remodeling in the regulation of circulating concentrations of FGF23 using mouse models manifesting differing degrees of coupled and uncoupled bone turnover. Administration of the antiresorptive agent osteoprotegerin produced a profound reduction in bone resorption and formation in male and oophorectomized female mice, accompanied by an increase in serum levels of fibroblast growth factor 23 (FGF23) and a reduction in circulating 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. In contrast, exogenous PTH(1-34) administration increased bone turnover and reduced circulating FGF23. In 1,25(OH)(2)D-deficient, 25-hydroxyvitamin D 1alpha-hydroxylase null mice on a high-calcium diet, endogenous PTH was elevated, bone formation but not resorption was increased, and serum FGF23 was virtually undetectable; on a rescue diet, serum calcium was normalized, PTH levels were reduced, bone formation was reduced, and serum FGF23 levels increased. After PTH treatment of wild-type mice, gene expression of dentin matrix protein 1 (DMP1) in bone was increased, whereas gene expression of FGF23 was reduced. In vitro studies in the osteoblastic cell line UMR-106 showed that externally added DMP1 could inhibit FGF23 gene expression and production stimulated by 1,25(OH)(2)D(3). The results show that osteoblastic bone formation is a potent modulator of FGF23 production and release into the circulation, suggest that the biological consequences on mineral homeostasis of circulating FGF23 may also be dependent on the prevailing rate of bone turnover, and provide evidence that DMP1 may be a direct negative regulator of FGF23 production in osteoblastic cells.

These results indicate that non-(1-84) PTH fragments are composed of a family of fragments which may be generated by specific or progressive cleavage at the N region. The longest fragment starts at position 4 and the shortest at position 15. A peptide starting at position 7 appears as the major component of non-(1-84) PTH fragments. The generation process is similar to the one described for smaller C-PTH fragments a number of years ago, suggesting a similar production mechanism and source for all C-PTH fragments.

Even if the carboxyl-terminal (C-) fragments/intact (I-) PTH ratio is tightly regulated by the ionized calcium (Ca(2+)) concentration in humans and animals, in health and in disease, the physiological roles of C-PTH fragments and of the C-PTH receptor remain elusive. To explore these issues, we studied the influence of synthetic C-PTH peptides of various lengths on Ca(2+) concentration and on the calcemic response to human (h) PTH-(1-34) and hPTH-(1-84) in anesthetized thyroparathyroidectomized (TPTX) rats. We also looked at the capacity of these PTH preparations to react with the PTH/PTHrP receptor and with a receptor for the carboxyl (C)-terminal portion of PTH (C-PTH receptor) in rat osteosarcoma cells, ROS 17/2.8. The Ca(2+) concentration was reduced by 0.19 +/- 0.03 mmol/liter over 2 h in all TPTX groups. Infusion of solvent over 2 more h had no further effect on the Ca(2+) concentration (-0.01 +/- 0.01 mmol/liter), whereas infusion of hPTH-(7-84) or a fragment mixture [10% hPTH-(7-84) and 45% each of hPTH-(39-84) and hPTH-(53-84)] 10 nmol/h further decreased the Ca(2+) concentration by 0.18 +/- 0.02 (P<0.001) and 0.07+/-0.04 mmol/liter (P< 0.001), respectively. Infusion of hPTH-(1-84) or hPTH-(1-34) (1 nmol/h) increased the Ca(2+) concentration by 0.16 +/- 0.03 (P < 0.001) and 0.19 +/- 0.03 mmol/liter (P < 0.001), respectively. Adding hPTH-(7-84) (10 nmol/h) to these preparations prevented the calcemic response and maintained Ca(2+) concentrations equal to or below levels observed in TPTX animals infused with solvent alone. Adding the fragment mixture (10 nmol/h) to hPTH-(1-84) did not prevent a normal calcemic response, but partially blocked the response to hPTH-(1-34), and more than 3 nmol/h hPTH-(7-84) prevented it. Both hPTH-(1-84) and hPTH-(1-34) stimulated cAMP production in ROS 17/2.8 clonal cells, whereas hPTH-(7-84) was ineffective in this respect. Both hPTH-(1-84) and hPTH-(1-34) displaced (125)I-[Nle(8,18),Tyr(34)]hPTH-(1-34) amide from the PTH/PTHrP receptor, whereas hPTH-(7-84) had no such influence. Both hPTH-(1-84) and hPTH-(7-84) displaced (125)I-[Tyr(34)]hPTH-(19-84) from the C-PTH receptor, the former preparation being more potent on a molar basis, whereas hPTH-(1-34) had no effect. These results suggest that C-PTH fragments, particularly hPTH-(7-84), can influence the Ca(2+) concentration negatively in vivo and limit in such a way the calcemic responses to hPTH-(1-84) and hPTH-(1-34) by interacting with a receptor different from the PTH/PTHrP receptor, possibly a C-PTH receptor.