Effect of raloxifene-analog (LY 117018-Hcl) on the bone marrow of ovariectomized mice

Improving Combination Osteoporosis Therapy in a Preclinical Model of Heightened Osteoanabolism

Combining anticatabolic agents with parathyroid hormone (PTH) to enhance bone mass has yielded mixed results in osteoporosis patients. Toward the goal of enhancing the efficacy of these regimens, we tested their utility in combination with loss of the transcription factor Nmp4 because disabling this gene amplifies PTH-induced increases in trabecular bone in mice by boosting osteoblast secretory activity. We addressed whether combining a sustained anabolic response with an anticatabolic results in superior bone acquisition compared with PTH monotherapy. Additionally, we inquired whether Nmp4 interferes with anticatabolic efficacy. Wild-type and Nmp4-/- mice were ovariectomized at 12 weeks of age, followed by therapy regimens, administered from 16 to 24 weeks, and included individually or combined PTH, alendronate (ALN), zoledronate (ZOL), and raloxifene (RAL). Anabolic therapeutic efficacy generally corresponded with PTH + RAL = PTH + ZOL > PTH + ALN = PTH > vehicle control. Loss of Nmp4 enhanced femoral trabecular bone increases under PTH + RAL and PTH + ZOL. RAL and ZOL promoted bone restoration, but unexpectedly, loss of Nmp4 boosted RAL-induced increases in femoral trabecular bone. The combination of PTH, RAL, and loss of Nmp4 significantly increased bone marrow osteoprogenitor number, but did not affect adipogenesis or osteoclastogenesis. RAL, but not ZOL, increased osteoprogenitors in both genotypes. Nmp4 status did not influence bone serum marker responses to treatments, but Nmp4-/- mice as a group showed elevated levels of the bone formation marker osteocalcin. We conclude that the heightened osteoanabolism of the Nmp4-/- skeleton enhances the effectiveness of diverse osteoporosis treatments, in part by increasing hyperanabolic osteoprogenitors. Nmp4 provides a promising target pathway for identifying barriers to pharmacologically induced bone formation.

Muscle-bound primordial stem cells give rise to myofiber-associated myogenic and non-myogenic progenitors

Myofiber cultures give rise to myogenic as well as to non-myogenic cells. Whether these myofiber-associated non-myogenic cells develop from resident stem cells that possess mesenchymal plasticity or from other stem cells such as mesenchymal stem cells (MSCs) remain unsolved. To address this question, we applied a method for reconstructing cell lineage trees from somatic mutations to MSCs and myogenic and non-myogenic cells from individual myofibers that were cultured at clonal density.

Our analyses show that (i) in addition to myogenic progenitors, myofibers also harbor non-myogenic progenitors of a distinct, yet close, lineage; (ii) myofiber-associated non-myogenic and myogenic cells share the same muscle-bound primordial stem cells of a lineage distinct from bone marrow MSCs; (iii) these muscle-bound primordial stem-cells first part to individual muscles and then differentiate into myogenic and non-myogenic stem cells.

The regulation of MS-KIF18A expression and cross talk with estrogen receptor

This study provides a novel view on the interactions between the MS-KIF18A, a kinesin protein, and estrogen receptor alpha (ERα) which were studied in vivo and in vitro. Additionally, the regulation of MS-KIF18A expression by estrogen was investigated at the gene and protein levels. An association between recombinant proteins; ERα and MS-KIF18A was demonstrated in vitro in a pull down assay. Such interactions were proven also for endogenous proteins in MBA-15 cells were detected prominently in the cytoplasm and are up-regulated by estrogen. Additionally, an association between these proteins and the transcription factor NF-κB was identified. MS-KIF18A mRNA expression was measured in vivo in relation to age and estrogen level in mice and rats models. A decrease in MS-KIF18A mRNA level was measured in old and in OVX-estrogen depleted rats as compared to young animals. The low MS-KIF18A mRNA expression in OVX rats was restored by estrogen treatment. We studied the regulation of MS-KIF18A transcription by estrogen using the luciferase reporter gene and chromatin immuno-percipitation (ChIP) assays. The luciferase reporter gene assay demonstrated an increase in MS-KIF18A promoter activity in response to 10⁻⁸ M estrogen and 10⁻⁷M ICI-182,780. Complimentary, the ChIP assay quantified the binding of ERα and pcJun to the MS-KIF18A promoter that was enhanced in cells treated by estrogen and ICI-182,780. In addition, cells treated by estrogen expressed higher levels of MS-KIF18A mRNA and protein and the protein turnover in MBA-15 cells was accelerated. Presented data demonstrated that ERα is a defined cargo of MS-KIF18A and added novel insight on the role of estrogen in regulation of MS-KIF18A expression both in vivo and in vitro.

Reconstruction of cell lineage trees in mice

The cell lineage tree of a multicellular organism represents its history of cell divisions from the very first cell, the zygote. A new method for high-resolution reconstruction of parts of such cell lineage trees was recently developed based on phylogenetic analysis of somatic mutations accumulated during normal development of an organism. In this study we apply this method in mice to reconstruct the lineage trees of distinct cell types. We address for the first time basic questions in developmental biology of higher organisms, namely what is the correlation between the lineage relation among cells and their (1) function, (2) physical proximity and (3) anatomical proximity. We analyzed B-cells, kidney-, mesenchymal- and hematopoietic-stem cells, as well as satellite cells, which are adult skeletal muscle stem cells isolated from their niche on the muscle fibers (myofibers) from various skeletal muscles. Our results demonstrate that all analyzed cell types are intermingled in the lineage tree, indicating that none of these cell types are single exclusive clones. We also show a significant correlation between the physical proximity of satellite cells within muscles and their lineage. Furthermore, we show that satellite cells obtained from a single myofiber are significantly clustered in the lineage tree, reflecting their common developmental origin. Lineage analysis based on somatic mutations enables performing high resolution reconstruction of lineage trees in mice and humans, which can provide fundamental insights to many aspects of their development and tissue maintenance.

Ovariectomy of 12-month-old rats: effects on osteoprogenitor numbers in bone cell populations isolated from femur and on histomorphometric parameters of bone turnover in corresponding tibia

Ovariectomy (OVX) in rats results in increased bone turnover and decreased bone volume and bone mineral density when measured in the metaphyses of long bones. We have investigated the effects of OVX on changes in the number of progenitors in cell populations derived from the metaphyseal bone of femurs of ovariectomized rats at 12 months of age, by using colony assays, bone nodule assays, and limiting dilution analysis at 1.5 and 9 months post-OVX. We have also measured histomorphometric parameters of bone formation and resorption in the corresponding tibia at the same time-points. A significant increase, as shown by bone nodule assays and limiting dilution analysis, occurs in the number of progesterone- and dexamethasone-responsive osteoprogenitors in cell populations isolated from ovariectomized rats at the 9-month post-OVX time-point. Progesterone-responsive osteoprogenitors are also increased at 1.5 months post-OVX. The number of fibroblast colony-forming units does not change. Histomorphometry has shown that OVX causes an increase in osteoblast surfaces, mineralizing surfaces, and bone formation rate at both 1.5 and 9 months post-OVX. The mineral apposition rate is increased at 1.5 months post-OVX. OVX also increases parameters of bone resorption at both time-points, the net result being a decrease in bone mineral density and cancellous bone volume at 9 months post-OVX. Thus, OVX in rats at 12 months of age is associated with an increase in the number of both progesterone- and dexamethasone-responsive osteoprogenitors 9 months post-OVX; this corresponds with increases in the histomorphometric parameters of bone formation.

SVEP1 expression is regulated in estrogen-dependent manner

The SVEP1 protein comprises modules related to the selectin super family and other motifs found in cell surface molecules. Earlier, we demonstrated that SVEP1 is expressed in osteogenic cells both in vivo and in vitro; in the current study we elaborate on the regulation of SVEP1 by 17beta-Estradiol (17betaE2). SVEP1 message is expressed in vivo by bone marrow cells of sham-operated rats, but not in estrogen-depleted ovariectomized (OVX) rats. We demonstrated that 17betaE2 treatment increases the level of the SVEP1 expression in cultured osteoblasts. SVEP1 was identified also in breast carcinoma (BC) cells known to reside in bone when metastasized from the primary tumor. SVEP1 expression was demonstrated by immunohistochemistry and fluorescence-activated cell sorting (FACS) on various BC cell lines. The chromatin immunoprecipitation (ChIP) assay was applied to analyze the estrogen receptor (ER) binding to the putative SVEP1 promoter. We demonstrated that treatment with 17betaE2 or ICI 182,780 affects this binding and regulates the mRNA and protein levels of SVEP1 in BC cells. We propose that SVEP1 may serve as a useful biomarker for studying the mechanism of cells interactions within the local microenvironment affected by estrogen.

Expression and regulation of CReMM, a chromodomain helicase-DNA-binding (CHD), in marrow stroma derived osteoprogenitors

This study follows the expression of CReMM, a new CHD family member, in osteoprogenitors. CReMM expression was analyzed in primary cultured mesnchymal cells from rat and human. Analysis in ex vivo cultured marrow stromal cells (MSC) from rats revealed higher level of CReMM in cells from young (3 months), when compared to cells from old (15 months) rats. CReMM level was higher in human MSC then in mature trabecular bone cells (TBC). Within the MSC population, osteogenic clones showed higher levels of CReMM then non-osteogenic ones. We used bone marrow derived osteogenic cell line (MBA-15) to elaborate on the regulation of CReMM expression in correlation with cell proliferation and co-expression with alkaline phosphatase (ALK). CReMM is highly expressed in proliferating cells and is inversely related to expression of ALK. MBA-15 cells were challenged with dexamethasone (Dex) or 17beta-estradiol and quantification of CReMM at the protein (ELISA) and mRNA (RT-PCR) levels had shown that Dex upregulated CReMM levels. Since CReMM is regulated by Dex, we analyzed the interaction of CReMM with the glucocorticoid receptor (GR), which mediates Dex action. Co-immunopercipitation (Co-IP) demonstrated an association between CReMM and GR. In summary, CReMM is a CHD protein expressed by osteoprogenitors, and we suggest it plays a role in mediating transcriptional response to hormones that coordinate osteoblast function.

Expression and regulation of CReMM, a chromodomain helicase-DNA-binding (CHD), in marrow stroma derived osteoprogenitors

This study follows the expression of CReMM, a new CHD family member, in osteoprogenitors. CReMM expression was analyzed in primary cultured mesnchymal cells from rat and human. Analysis in ex vivo cultured marrow stromal cells (MSC) from rats revealed higher level of CReMM in cells from young (3 months), when compared to cells from old (15 months) rats. CReMM level was higher in human MSC then in mature trabecular bone cells (TBC). Within the MSC population, osteogenic clones showed higher levels of CReMM then non-osteogenic ones. We used bone marrow derived osteogenic cell line (MBA-15) to elaborate on the regulation of CReMM expression in correlation with cell proliferation and co-expression with alkaline phosphatase (ALK). CReMM is highly expressed in proliferating cells and is inversely related to expression of ALK. MBA-15 cells were challenged with dexamethasone (Dex) or 17beta-estradiol and quantification of CReMM at the protein (ELISA) and mRNA (RT-PCR) levels had shown that Dex upregulated CReMM levels. Since CReMM is regulated by Dex, we analyzed the interaction of CReMM with the glucocorticoid receptor (GR), which mediates Dex action. Co-immunopercipitation (Co-IP) demonstrated an association between CReMM and GR. In summary, CReMM is a CHD protein expressed by osteoprogenitors, and we suggest it plays a role in mediating transcriptional response to hormones that coordinate osteoblast function.

Transcriptional profiling of mesenchymal stromal cells from young and old rats in response to Dexamethasone

Background

Marrow-derived stromal cells (MSCs) maintain the capability of self-renewal and differentiation into multiple lineages in adult life. Age-related changes are recognized by a decline in the stemness potential that result in reduced regeneration potential of the skeleton. To explore the molecular events that underline skeletal physiology during aging we catalogued the profile of gene expression in ex vivo cultured MSCs derived from 3 and 15 month old rats. The ex vivo cultured cells were analyzed following challenge with or without Dexamethasone (Dex). RNA retrieved from these cells was analyzed using Affymetrix Gene Chips to compare the effect of Dex on gene expression in both age groups.

Results

The molecular mechanisms that underline skeletal senescence were studied by gene expression analysis of RNA harvested from MSCs. The analysis resulted in complex profiles of gene expression of various differentiation pathways. We revealed changes of lineage-specific gene expression; in general the pattern of expression included repression of proliferation and induction of differentiation. The functional analysis of genes clustered were related to major pathways; an increase in bone remodeling, osteogenesis and muscle formation, coupled with a decrease in adipogenesis. We demonstrated a Dex-related decrease in immune response and in genes that regulate bone resorption and an increase in osteoblastic differentiation. Myogenic-related genes and genes that regulate cell cycle were induced by Dex. While Dex repressed genes related to adipogenesis and catabolism, this decrease was complementary to an increase in expression of genes related to osteogenesis.

Conclusion

This study summarizes the genes expressed in the ex vivo cultured mesenchymal cells and their response to Dex. Functional clustering highlights the complexity of gene expression in MSCs and will advance the understanding of major pathways that trigger the natural changes underlining physiological aging. The high throughput analysis shed light on the anabolic effect of Dex and the relationship between osteogenesis, myogenesis and adipogenesis in the bone marrow cells.

Effect of ovariectomy on dexamethasone- and progesterone-dependent osteoprogenitors in vertebral and femoral rat bone cell populations

We have found previously that the skeleton of adult female rats contains dexamethasone (Dex)- and progesterone (Prog)-dependent osteoprogenitors, and that estrogen treatment in vitro upregulates proliferation and differentiation of the Prog-dependent but not of the Dex-dependent osteoprogenitors (Bone 1997;20:17-25). The purpose of the present study was to determine whether ovariectomy (OVX) would have different effects on these two classes of osteoprogenitors. Six-month-old Sprague-Dawley rats underwent OVX and the lumbar vertebrae and proximal femurs were collected 1.5, 3, and 6 months after OVX. Cells were obtained from outgrowths of explant cultures and grown in alpha-MEM with 10% FBS, 50 microg/ml ascorbic acid, and 5 mM beta-glycerophosphate. Osteoprogenitors were identified by their ability to generate a colony of osteoblastic cells forming bone (bone nodule). We also evaluated the number of colony-forming units-fibroblast (CFU-F) and of alkaline phosphatase (AP)-positive CFU-F. In cell populations obtained from vertebrae of rats ovariectomized for 1.5, 3, and 6 months and their corresponding control rats, both Dex (1-100 nM) and Prog (1-10 microM) dose-dependently stimulated nodule formation. Both Dex- and Prog-induced nodule formation were higher in cell populations from control rats than in those from ovariectomized rats (P < 0.001). Numbers of CFU-F and AP-positive CFU-F were also higher in cell populations from control rats compared with those from ovariectomized rats. Estrogen (10 nM) enhanced Prog-dependent bone nodule formation but decreased Dex-dependent bone nodule formation in populations from both control and ovariectomized rats. In femoral populations, the responses to Dex (10 nM), Prog (3 microM), and estrogen (10 nM) were similar to those of the vertebral populations in both control and ovariectomized rats. Our results demonstrate that ovariectomy in rats results in a dramatic decrease in the number of both Dex- and Prog-dependent osteoprogenitors in cell populations from vertebrae and proximal femurs. In addition, we confirmed our previous observation that estrogen upregulated proliferation and differentiation of Prog-dependent progenitors, but found here that estrogen clearly downregulated proliferation and differentiation of the Dex-dependent progenitors.

Hormonal changes affect the bone and bone marrow cells in a rat model

In this study, we used a rat model to investigate the effects of gonad hormones and replacement therapy on bone structure and the immune system. In the first phase of the study, 3- and 11-month-old F344 rats underwent ovariectomy (OVX) or were sham operated. Three months later, severe osteopenia was histologically observed in OVX rats of both age groups. The changes in the bone marrow structure of OVX rats included deterioration of cancellous bone that was associated with a remarkable increase of adipocyte cells. Furthermore, differential analyses for the expression of cell surface antigens by lymph-myeloid cells was studied using flow cytometry (FACS). The number of myeloid cells expressing ED-9(+) or CD-44(+) was similar in both age groups, and unaffected by OVX. However, an augmentation of T-lymphoid cells expressing CD4(+), CD5(+), or both, were observed with age, as well as after OVX. In the second phase of the study, 11-month-old rats were divided into five experimental groups: sham-operated, OVX, and OVX treated with sustained-release pellets of 17beta-estradiol (OVX-E), progesterone (OVX-P), or both (OVX-E/P). Hormone replacement therapy maintained low physiological levels, and rats were tested 12 weeks after treatment initiation. Administration of 17beta-E, with or without the addition of progesterone, prevented the rise of T lymphoid cells observed in OVX rats, whereas progesterone alone had no effect. In agreement with findings from the first phase, neither OVX nor replacement therapy affected the myeloid cells expression of ED-9 or CD-44. In summary, the cellular changes in the bone marrow of OVX rats were associated with an increase in adipocytes that was correlated with bone atrophy. An augmentation of T-lymphopoiesis was noted with increase in age or after OVX. This increase was reversed to baseline levels by 17beta-E treatment.