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Summary Intermittent administration of parathyroid hormone (iPTH) is used to treat osteoporosis as it improves bone architecture and strength, but the underlying cellular and molecular mechanisms are unclear. Here we show that iPTH increases the production of Wnt10b by bone marrow CD8+ T cells, and induces these lymphocytes to activate canonical Wnt-signaling in pre-osteoblasts. Accordingly, in responses to iPTH, T cell null mice display diminished Wnt signaling in pre-osteoblasts and blunted osteoblastic commitment, proliferation, differentiation and lifespan which result in decreased trabecular bone anabolism and no increase in strength. Demonstrating the specific role of lymphocytic Wnt10b, iPTH has no anabolic activity in mice lacking T cell produced Wnt10b. Therefore, T cell mediated activation of Wnt signaling in osteoblastic cells plays a key permissive role in the mechanism by which iPTH increases bone strength, suggesting that T cell osteoblast cross-talk pathways may provide pharmacological targets for bone anabolism.

NGAL is rapidly and massively induced in renal epithelial injury and NGAL: siderophore: iron complexes may comprise a physiological renoprotective mechanism. The data have implications for the diagnosis and treatment of acute renal injury.

The bone loss induced by ovariectomy (ovx) has been linked to increased production of osteoclastogenic cytokines by bone marrow cells, including T cells and stromal cells (SCs). It is presently unknown whether regulatory interactions between these lineages contribute to the effects of ovx in bone, however. Here, we show that the T-cell costimulatory molecule CD40 ligand (CD40L) is required for ovx to expand SCs; promote osteoblast proliferation and differentiation; regulate the SC production of the osteoclastogenic factors macrophage colony-stimulating factor, receptor activator of nuclear factor-κB ligand, and osteoprotegerin; and upregulate osteoclast formation. CD40L is also required for ovx to activate T cells and stimulate their production of TNF. Accordingly, ovx fails to promote bone loss and increase bone resorption in mice depleted of T cells or lacking CD40L. Therefore, cross-talk between T cells and SCs mediated by CD40L plays a pivotal role in the disregulation of osteoblastogenesis and osteoclastogenesis induced by ovx.estrogen | osteoporosis M enopause results in decreased production of estrogen (E) and a parallel increase in FSH levels, which together stimulate bone resorption (1) and cause a period of rapid bone loss that is central for the onset of postmenopausal osteoporosis (2). The acute effects of menopause are modeled by ovariectomy (ovx) which, like natural menopause, stimulates bone resorption by increasing osteoclast (OC) formation (3, 4) and lifespan (5, 6). The net bone loss caused by ovx is limited by an increase in bone formation resulting from stimulated osteoblast (OB) formation (7). This compensation is fueled by an expansion of the pool of bone marrow (BM) stromal cells (SCs), increased commitment of SCs to the osteoblastic lineage (7), and enhanced proliferation of early OB precursors (8). The stimulatory effect of ovx on SCs is equally relevant for osteoclastogenesis because one of the consequences of E deprivation is the formation of osteoblastic cells with increased osteoclastogenic activity (9), that is, the capacity to support OC formation.OC formation occurs when bone marrow macrophages (BMMs) are stimulated by the osteoclastogenic factors receptor activator of nuclear factor-κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF) (10, 11); however, in conditions of E deficiency, the secretion of the RANKL decoy receptor osteoprotegerin (OPG) decreased (12

Intermittent parathyroid hormone (iPTH) treatment stimulates Tcell production of the osteogenic Wnt ligand Wnt10b, a factor required for iPTH to activate Wnt signaling in osteoblasts and stimulate bone formation. However, it is unknown whether iPTH induces Wnt10b production and bone anabolism through direct activation of the parathyroid hormone (PTH)/PTH-related protein receptor (PPR) in T cells. Here, we show that conditional silencing of PPR in T cells blunts the capacity of iPTH to induce T-cell production of Wnt10b; activate Wnt signaling in osteoblasts; expand the osteoblastic pool; and increase bone turnover, bone mineral density, and trabecular bone volume. These findings demonstrate that direct PPR signaling in T cells plays an important role in PTH-induced bone anabolism by promoting T-cell production of Wnt10b and suggest that T cells may provide pharmacological targets for bone anabolism.bone mass | T lymphocytes | bone cells P arathyroid hormone (PTH) is a major regulator of calcium metabolism and defends against hypocalcemia, in part, by stimulating bone resorption, and thereby the release of calcium from the skeleton. However, when injected daily, a regimen known as intermittent parathyroid hormone (iPTH) treatment, the hormone markedly stimulates trabecular and cortical bone formation. Although this bone-forming activity is antagonized by a stimulation of bone resorption, the net effect of iPTH treatment is an improvement in bone microarchitecture and increased strength (1, 2). As a result, intermittent treatment with the 1-34 fragment of PTH is a Food and Drug Administration-approved treatment modality for postmenopausal osteoporosis (3).The effects of PTH on bone result from its binding to the PTH/PTH-related protein receptor (PPR or PTHR1) expressed on bone marrow (BM), stromal cells (SCs), osteoblasts (OBs), and osteocytes (1, 4, 5). iPTH stimulates bone formation by increasing the number of OBs (6-8), a phenomenon achieved through activation of quiescent lining cells (9), increased OB proliferation (10, 11) and differentiation (10, 12, 13), attenuation of OB apoptosis (14-17), and signaling in osteocytes (18). However, the specific contribution of each of these effects of iPTH remains controversial. The expansion of the osteoblastic pool induced by iPTH is initiated by the release from the matrix undergoing resorption of TGF-β, insulin-like growth factor 1, and other growth factors that recruit SCs to remodeling areas (19)(20)(21)(22). Subsequent events are driven primarily by the activation of Wnt signaling in osteoblastic cells (23). Activation of Wnt signaling induces OB proliferation (24) and differentiation (23, 25), prevents OB apoptosis (16,17,26), and augments OB production of osteoprotegerin (OPG) (27).iPTH activates Wnt signaling in OBs through multiple mechanisms that include Wnt ligand-independent activation of the Wnt coreceptor LRP6 (28), increased production of Wnt ligands by bone and BM cells (29,30), and suppression of sclerostin production (31-33). Additional effects on the ...

Mammalian nephrogenesis depends on the interaction between the ureteric bud and the metanephric mesenchyme. As the ureteric bud undergoes branching and segmentation, the stalks differentiate into the collecting system of the mature kidney, while the tip cells interact with the adjacent cells of the metanephric mesenchyme, inducing their conversion into nephrons. This induction is mediated by secreted factors. For identifying novel mediators, the tips of the ureteric tree were isolated and microarray analyses were performed using manually refined, multistep gene ontology annotations. For identifying conserved factors, two databases were developed, one from mouse E 12.5 and one from rat E 13.5 ureteric buds. The overlap of mouse and rat data sets yielded 20 different transcripts that were enriched in the ureteric bud compared with metanephric mesenchyme and predicted to code for secreted proteins. Real-time reverse transcriptase-PCR and in situ hybridization confirmed these identifications. One of the genes that was highly specific to the ureteric bud tip was cytokine-like factor 1 (CLF-1). Recombinant CLF-1 in complex with its physiologic ligand, cardiotrophin-like cytokine (CLC), triggered phosphorylation of signal transducer and activator of transcription 3 in mesenchyme, a pathway characteristic of mesenchymal-to-epithelial conversion. Indeed, when applied to isolated rat metanephric mesenchyme, CLF-1/CLC (3 nM) induced mature nephron structures expressing glomerular and tubular markers. These results underline the power of this first comprehensive gene expression analysis of the ureteric bud tip to identify bioactive molecules.

BackgroundHyperparathyroidism in humans and continuous parathyroid hormone (cPTH) treatment in mice cause bone loss by regulating the production of RANKL and OPG by stromal cells (SCs) and osteoblasts (OBs). Recently, it has been reported that T cells are required for cPTH to induce bone loss as the binding of the T cell costimulatory molecule CD40L to SC receptor CD40 augments SC sensitivity to cPTH. However it is unknown whether direct PTH stimulation of T cells is required for cPTH to induce bone loss, and whether T cells contribute to the bone catabolic activity of PTH with mechanisms other than induction of CD40 signaling in SCs.Methodology/Principal FindingsHere we show that silencing of PTH receptor 1 (PPR) in T cells blocks the bone loss and the osteoclastic expansion induced by cPTH, thus demonstrating that PPR signaling in T cells is central for PTH-induced reduction of bone mass. Mechanistic studies revealed that PTH activation of the T cell PPR stimulates T cell production of the osteoclastogenic cytokine tumor necrosis factor α (TNF). Attesting to the relevance of this effect, disruption of T cell TNF production prevents PTH-induced bone loss. We also show that a novel mechanism by which TNF mediates PTH induced osteoclast formation is upregulation of CD40 expression in SCs, which increases their RANKL/OPG production ratio.Conclusions/SignificanceThese findings demonstrate that PPR signaling in T cells plays an essential role in PTH induced bone loss by promoting T cell production of TNF. A previously unknown effect of TNF is to increase SC expression of CD40, which in turn increases SC osteoclastogenic activity by upregulating their RANKL/OPG production ratio. PPR-dependent stimulation of TNF production by T cells and the resulting TNF regulation of CD40 signaling in SCs are potential new therapeutic targets for the bone loss of hyperparathyroidism.

SUMMARY Primary hyperparathyroidism (PHPT) is a common cause of bone loss that is modeled by continuous PTH (cPTH) infusion. Here we show that the inflammatory cytokine IL-17A is upregulated by PHPT in humans and cPTH in mice. In humans IL-17A is normalized by parathyroidectomy. In mice treatment with anti-IL-17A antibody and silencing of IL-17A receptor IL-17RA prevent cPTH induced osteocytic and osteoblastic RANKL production and bone loss. Mechanistically, cPTH stimulates conventional T cell production of TNFα (TNF), which increases the differentiation of IL-17A producing Th17 cells via TNF receptor 1 (TNFR1) signaling in CD4+ cells. Moreover, cPTH enhances the sensitivity of naïve CD4+ cells to TNF via GαS/cAMP/Ca++ signaling. Accordingly, conditional deletion of GαS in CD4+ cells and treatment with the calcium channel blocker diltiazem prevents Th17 cell expansion and blocks cPTH induced bone loss. Neutralization of IL-17A and calcium channel blockers may thus represent novel therapeutic strategies for hyperparathyroidism.