Bone growth and turnover in progesterone receptor knockout mice.

The role of progesterone receptor (PR) signaling in skeletal metabolism is controversial. To address whether signaling through the PR is necessary for normal bone growth and turnover, we performed histomorphometric and microcomputed tomography analyses of bone from homozygous female PR knockout (PRKO) mice at 6, 12, and 26 wk of age. These mice possess a null mutation of the PR locus, which blocks the gene expression of A and B isoforms of PR. Body weight gain, uterine weight gain, and tibia longitudinal bone growth were normal in PRKO mice. In contrast, total, cancellous, and cortical bone mass were increased in the humerus of 12-wk-old PRKO mice, whereas cortical and cancellous bone mass in the tibia was normal. At 26 wk of age, cancellous bone area in the proximal tibia metaphysis of PRKO mice was 153% greater than age matched wild-type mice. The improved cancellous bone balance in 6-month-old PRKO mice was associated with elevated bone formation and a tendency toward reduced osteoclast perimeter. Taken together, these findings suggest that PR signaling in mice is not essential for bone growth and turnover. However, at some skeletal sites, PR signaling attenuates the accumulation of cortical and cancellous bone mass during adolescence.

TIEG1 null mouse-derived osteoblasts are defective in mineralization and in support of osteoclast differentiation in vitro.

Transforming growth factor beta-inducible early gene 1 (TIEG1) is a member of the Kruppel-like transcription factor family. To understand the physiological role of TIEG1, we generated TIEG(-/-) (null) mice and found that the TIEG(-/-) mice had increased osteoblast numbers with no increased bone formation parameters. However, when calvarial osteoblasts (OBs) were isolated from neonatal TIEG(-/-) and TIEG(+/+) mice and cultured in vitro, the TIEG(-/-) cells displayed reduced expression of important OB differentiation markers. When the OBs were differentiated in vitro by treatment with bone morphogenic protein 2, the OBs from TIEG(+/+) calvaria displayed several mineralized nodules in culture, whereas those from TIEG(-/-) mice showed no nodules. To characterize the OBs' ability to support osteoclast differentiation, the OBs from TIEG(+/+) and TIEG(-/-) mice were cultured with marrow and spleen cells from TIEG(+/+) mice. Significantly fewer osteoclasts developed when TIEG(-/-) OBs were used to support osteoclast differentiation than when TIEG(+/+) OBs were used. Examination of gene expression in the TIEG(-/-) OBs revealed decreased RANKL and increased OPG expression compared to TIEG(+/+) OBs. The addition of RANKL to these cocultures only partially restored the ability of TIEG(-/-) OBs to support osteoclast differentiation, whereas M-CSF alone or combined with RANKL had no additional effect on osteoclast differentiation. We conclude from these data that TIEG1 expression in OBs is critical for both osteoblast-mediated mineralization and osteoblast support of osteoclast differentiation.

Tapinarof Is a Natural AhR Agonist that Resolves Skin Inflammation in Mice and Humans.

Tapinarof (GSK2894512) is a naturally derived topical treatment with demonstrated efficacy for patients with psoriasis and atopic dermatitis, although the biologic target and mechanism of action had been unknown. We demonstrate that the anti-inflammatory properties of tapinarof are mediated through activation of the aryl hydrocarbon receptor (AhR). We show that tapinarof binds and activates AhR in multiple cell types, including cells of the target tissue-human skin. In addition, tapinarof moderates proinflammatory cytokine expression in stimulated peripheral blood CD4+ T cells and ex vivo human skin, and impacts barrier gene expression in primary human keratinocytes; both of these processes are likely to be downstream of AhR activation based on current evidence. That the anti-inflammatory properties of tapinarof derive from AhR agonism is conclusively demonstrated using the mouse model of imiquimod-induced psoriasiform skin lesions. Topical treatment of AhR-sufficient mice with tapinarof leads to compound-driven reductions in erythema, epidermal thickening, and tissue cytokine levels. In contrast, tapinarof has no impact on imiquimod-induced skin inflammation in AhR-deficient mice. In summary, these studies identify tapinarof as an AhR agonist and confirm that its efficacy is dependent on AhR.

Intermittent treatment with parathyroid hormone (PTH) as well as a non-peptide small molecule agonist of the PTH1 receptor inhibits adipocyte differentiation in human bone marrow stromal cells.

Whereas continuous PTH infusion increases bone resorption and bone loss, intermittent PTH treatment stimulates bone formation, in part, via reactivation of quiescent bone surfaces and reducing osteoblast apoptosis. We investigated the possibility that intermittent and continuous PTH treatment also differentially regulates osteogenic and adipocytic lineage commitment of bone marrow stromal progenitor/mesenchymal stem cells (MSC). The MSC were cultured under mildly adipogenic conditions in medium supplemented with dexamethasone, insulin, isobutyl-methylxanthine and troglitazone (DIIT), and treated with 50 nM human PTH(1-34) for either 1 h/day or continuously (PTH replenished every 48 h). After 6 days, cells treated with PTH for 1 h/day retained their normal fibroblastic appearance whereas those treated continuously adopted a polygonal, irregular morphology. After 12-18 days numerous lipid vacuole and oil red O-positive adipocytes had developed in cultures treated with DIIT alone, or with DIIT and continuous PTH. In contrast, adipocyte number was reduced and alkaline phosphatase staining increased in the cultures treated with DIIT and 1 h/day PTH, indicating suppression of adipogenesis and possible promotion of early osteoblastic differentiation. Furthermore, intermittent but not continuous PTH treatment suppressed markers of differentiated adipocytes such as mRNA expression of lipoprotein lipase and PPARgamma as well as glycerol 3-phosphate dehydrogenase activity. All of these effects of intermittent PTH were also produced by a 1 h/day treatment with AH3960 (30 microM), a small molecule, non-peptide agonist of the PTH1 receptor. AH3960, like PTH, activates both the cAMP and calcium signaling pathways. Treatment with the adenylyl cyclase activator forskolin for 1 h/day, mimicked the anti-adipogenic effect of intermittent PTH, whereas pretreatment with the protein kinase-A inhibitor H89 prior to intermittent PTH resulted in almost complete conversion to adipocytes. In contrast, the MAP kinase inhibitor PD 98059 failed to prevent the anti-adipocytic effect of intermittent PTH, suggesting that the inhibitory effect of PTH on adipocyte differentiation is predominantly cAMP-dependent. These results demonstrate a differential effect of PTH1 receptor agonists on the adipocytic commitment and differentiation of adult human bone marrow mesenchymal stem cells. This response may represent an additional mechanism that contributes to the overall bone anabolic action of intermittent PTH.

Estrogen receptor isoform-specific induction of progesterone receptors in human osteoblasts.

Estrogen induction of progesterone receptor (PR) expression may be important to bone physiology because progesterone has been implicated in the control of bone formation and resorption. Although PR gene expression can be induced in osteoblasts by estrogen signaling through the estrogen receptor (ER) a isoform, it is unknown whether the ER-beta isoform is involved in this regulation. The effect of estrogen on PR expression was examined in human fetal osteoblast (hFOB) cell lines stably transfected with either ER-alpha or ER-beta. Estrogen treatment of hFOB/ER-a cells induced PR messenger RNA (mRNA) steady-state levels after 24 h and protein levels after 48 h, as established by competitive reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting. Interestingly, no induction of PR expression was observed in the hFOB/ER-beta cells during this period. However, PR mRNA was induced progressively after 48 h of treatment with estrogen with maximum levels achieved at 12 days posttreatment. ER protein also was increased after 12 days of treatment. Both A and B isoforms of PR (PRA and PRB) were induced by estrogen in the hFOB/ER-a cells as well as much later in hFOB/ER-beta cells. The pure antiestrogen ICI 182,780 prevented PR induction by estrogen in both cell lines. An ER-beta-selective antagonist R, R-tetrahydrochrysene (THC) abolished the induction of PR mRNA in hFOB/ER-beta but not in hFOB/ER-a cells, verifying that the response in the former cell line was ER-beta-mediated. Transient cotransfection of hFOB cells with ER-a or ER-beta together with either a human PRA or PRB promoter linked to a reporter plasmid revealed that although the PRB promoter was stimulated equally by estrogen activation of either ER isoform, PRA was activated preferentially by ER-alpha. Together, these results show that although estrogen can up-regulate endogenous PR gene expression in osteoblasts via both ER isoforms, ER-alpha is the predominant inducer.

Identification of selective small molecule inhibitors of the nucleotide-binding oligomerization domain 1 (NOD1) signaling pathway.

NOD1 is an intracellular pattern recognition receptor that recognizes diaminopimelic acid (DAP), a peptidoglycan component in gram negative bacteria. Upon ligand binding, NOD1 assembles with receptor-interacting protein (RIP)-2 kinase and initiates a signaling cascade leading to the production of pro-inflammatory cytokines. Increased NOD1 signaling has been associated with a variety of inflammatory disorders suggesting that small-molecule inhibitors of this signaling complex may have therapeutic utility. We utilized a cell-based screening approach with extensive selectivity profiling to search for small molecule inhibitors of the NOD1 signaling pathway. Via this process we identified three distinct chemical series, xanthines (SB711), quinazolininones (GSK223) and aminobenzothiazoles (GSK966) that selectively inhibited iE-DAP-stimulated IL-8 release via the NOD1 signaling pathway. All three of the newly identified compound series failed to block IL-8 secretion in cells following stimulation with ligands for TNF receptor, TLR2 or NOD2 and, in addition, none of the compound series directly inhibited RIP2 kinase activity. Our initial exploration of the structure-activity relationship and physicochemical properties of the three series directed our focus to the quinazolininone biarylsulfonamides (GSK223). Further investigation allowed for the identification of significantly more potent analogs with the largest boost in activity achieved by fluoro to chloro replacement on the central aryl ring. These results indicate that the NOD1 signaling pathway, similarly to activation of NOD2, is amenable to modulation by small molecules that do not target RIP2 kinase. These compounds should prove useful tools to investigate the importance of NOD1 activation in various inflammatory processes and have potential clinical utility in diseases driven by hyperactive NOD1 signaling.

Identification of benzimidazole diamides as selective inhibitors of the nucleotide-binding oligomerization domain 2 (NOD2) signaling pathway.

NOD2 is an intracellular pattern recognition receptor that assembles with receptor-interacting protein (RIP)-2 kinase in response to the presence of bacterial muramyl dipeptide (MDP) in the host cell cytoplasm, thereby inducing signals leading to the production of pro-inflammatory cytokines. The dysregulation of NOD2 signaling has been associated with various inflammatory disorders suggesting that small-molecule inhibitors of this signaling complex may have therapeutic utility. To identify inhibitors of the NOD2 signaling pathway, we utilized a cell-based screening approach and identified a benzimidazole diamide compound designated GSK669 that selectively inhibited an MDP-stimulated, NOD2-mediated IL-8 response without directly inhibiting RIP2 kinase activity. Moreover, GSK669 failed to inhibit cytokine production in response to the activation of Toll-like receptor (TLR)-2, tumor necrosis factor receptor (TNFR)-1 and closely related NOD1, all of which share common downstream components with the NOD2 signaling pathway. While the inhibitors blocked MDP-induced NOD2 responses, they failed to block signaling induced by NOD2 over-expression or single stranded RNA, suggesting specificity for the MDP-induced signaling complex and activator-dependent differences in NOD2 signaling. Investigation of structure-activity relationship allowed the identification of more potent analogs that maintained NOD2 selectivity. The largest boost in activity was achieved by N-methylation of the C2-ethyl amide group. These findings demonstrate that the NOD2 signaling pathway is amenable to modulation by small molecules that do not target RIP2 kinase activity. The compounds we identified should prove useful tools to investigate the importance of NOD2 in various inflammatory processes and may have potential clinical utility.

A key role for the endothelium in NOD1 mediated vascular inflammation: comparison to TLR4 responses.

Understanding the mechanisms by which pathogens induce vascular inflammation and dysfunction may reveal novel therapeutic targets in sepsis and related conditions. The intracellular receptor NOD1 recognises peptidoglycan which features in the cell wall of gram negative and some gram positive bacteria. NOD1 engagement generates an inflammatory response via activation of NFκB and MAPK pathways. We have previously shown that stimulation of NOD1 directly activates blood vessels and causes experimental shock in vivo. In this study we have used an ex vivo vessel-organ culture model to characterise the relative contribution of the endothelium in the response of blood vessels to NOD1 agonists. In addition we present the novel finding that NOD1 directly activates human blood vessels. Using human cultured cells we confirm that endothelial cells respond more avidly to NOD1 agonists than vascular smooth muscle cells. Accordingly we have sought to pharmacologically differentiate NOD1 and TLR4 mediated signalling pathways in human endothelial cells, focussing on TAK1, NFκB and p38 MAPK. In addition we profile novel inhibitors of RIP2 and NOD1 itself, which specifically inhibit NOD1 ligand induced inflammatory signalling in the vasculature. This paper is the first to demonstrate activation of whole human artery by NOD1 stimulation and the relative importance of the endothelium in the sensing of NOD1 ligands by vessels. This data supports the potential utility of NOD1 and RIP2 as therapeutic targets in human disease where vascular inflammation is a clinical feature, such as in sepsis and septic shock.

Distribution of estrogen receptors alpha and beta mRNA in mouse urogenital tissues and their expression after oophorectomy and estrogen replacement.

Estrogen receptors are present in the urogenital tract. However, little is known about the quantitative distribution of the traditional estrogen receptor (ERalpha) mRNA and the recently identified ERbeta mRNA. By quantitative reverse transcription polymerase chain reaction analysis, the distributions of ERalpha and ERbeta mRNA in mouse urogenital tissues and their expression in selected urogenital tissues after oophorectomy, with or without estrogen replacement, were evaluated. ERalpha mRNA concentrations were higher in the ovary, oviduct, uterus and vagina than in the kidney, ureter or bladder ( P<0.05); ERbeta transcripts were highest in the ovary, oviduct and bladder ( P<0.05). After oophorectomy and estrogen replacement, significant changes were identified in ERalpha and ERbeta mRNA expression. ERalpha and ERbeta mRNA are differentially expressed in mouse urogenital tissues. Oophorectomy and estrogen replacement affect estrogen receptors differently in the bladder, vagina and uterus. These results may explain some tissue-specific responses to estrogen and selective estrogen receptor modulators. The mRNA distributions of estrogen receptors alpha and beta and their expression after oophorectomy, with or without estrogen replacement, differ in mouse urogenital tissues.

Further characterization of human fetal osteoblastic hFOB 1.19 and hFOB/ER alpha cells: bone formation in vivo and karyotype analysis using multicolor fluorescent in situ hybridization.

We have previously generated an immortalized human fetal osteoblastic cell line (hFOB) using stably transfected temperature sensitive SV40 T-antigen (Harris et al. [1995a] J. Bone. Miner. Res. 10:178-1860). To characterize these cells for phenotypic/genotypic attributes desired for a good cell model system, we performed karyotype analysis by multicolor fluorescent in situ hybridization (M-FISH), their ability to form bone in vivo without developing cell transformation, and finally their ability to form extracellular matrix formation in vitro. The karyotype analysis of hFOB cells revealed structural or numeric anomalies involving 1-2 chromosomes. In contrast, the human osteosarcoma MG63 cells displayed multiple, and often complex, numeric, and structural abnormalities. Subcutaneous injection of hFOB cells in the presence of Matrigel into nude mice resulted in bone formation after 2-3 weeks. Electron microscopic analysis of the extracellular matrix deposited by hFOB cells in culture revealed a parallel array of lightly banded fibrils typical of the fibrillar collagens such as type I and III. These results demonstrate that the hFOB cell line has minimal chromosome abnormalities, exhibit the matrix synthetic properties of differentiated osteoblasts, and are immortalized but non-transformed cell line. These hFOB cells thus appear to be an excellent model system for the study of osteoblast biology in vitro.