Inhibition of the progesterone nuclear receptor during the bone linear growth phase increases peak bone mass in female mice

Hormonal Control of Bone Architecture Throughout the Lifespan: Implications for Fracture Prediction and Prevention

BACKGROUND

Skeletal modeling in childhood and adolescence and continuous remodeling throughout the lifespan are designed to adapt to a changing environment and resist external forces and fractures. The flux of sex steroids in men and women, beginning from fetal development and evolving through infancy, childhood, puberty, young adulthood, peri/menopause transition, and postmenopause, is critical for bone size, peak bone mass, and fracture resistance.

OBJECTIVE

This review will highlight how changes in sex steroids throughout the lifespan affect bone cells and the consequence of these changes on bone architecture and strength.

METHODS

Literature review and discussion.

RESULTS

The contributions of estrogen and testosterone on skeletal development have been difficult to study due to the reciprocal and intertwining contributions of one on the other. Although orchiectomy in men renders circulating testosterone absent, circulating estrogen also declines due to testosterone being the substrate for estradiol. The discovery of men with absent estradiol or resistance to estrogen and the study of mouse models led to the understanding that estrogen has a larger direct role in skeletal development and maintenance in men and women. The mechanistic reason for larger bone size in men is incompletely understood but related to indirect effects of testosterone on the skeleton, such as higher muscle mass leading to larger mechanical loading. Declines in sex steroids during menopause in women and androgen deprivation therapies in men have profound and negative effects on the skeleton. Therapies to prevent such bone loss are available, but how such therapies can be tailored based on bone size and architecture remains an area of investigation.

CONCLUSION

In this review, the elegant interplay and contribution of sex steroids on bone architecture in men and women throughout the lifespan is described.

Comparative- and network-based proteomic analysis of bacterial chondronecrosis with osteomyelitis lesions in broiler's proximal tibiae identifies new molecular signatures of lameness

Bacterial Chondronecrosis with Osteomyelitis (BCO) is a specific cause of lameness in commercial fast-growing broiler (meat-type) chickens and represents significant economic, health, and wellbeing burdens. However, the molecular mechanisms underlying the pathogenesis remain poorly understood. This study represents the first comprehensive characterization of the proximal tibia proteome from healthy and BCO chickens. Among a total of 547 proteins identified, 222 were differentially expressed (DE) with 158 up- and 64 down-regulated proteins in tibia of BCO vs. normal chickens. Biological function analysis using Ingenuity Pathways showed that the DE proteins were associated with a variety of diseases including cell death, organismal injury, skeletal and muscular disorder, immunological and inflammatory diseases. Canonical pathway and protein-protein interaction network analysis indicated that these DE proteins were involved in stress response, unfolded protein response, ribosomal protein dysfunction, and actin cytoskeleton signaling. Further, we identified proteins involved in bone resorption (osteoclast-stimulating factor 1, OSFT1) and bone structural integrity (collagen alpha-2 (I) chain, COL2A1), as potential key proteins involved in bone attrition. These results provide new insights by identifying key protein candidates involved in BCO and will have significant impact in understanding BCO pathogenesis.

Progesterone Inhibitory Role on Gastrointestinal Motility

Progesterone is a steroidal hormone that is produced from the corpus luteum of the ovaries and from the placenta. The main function of progesterone is to promote the secretory differentiation in the endometrium of the uterus and to maintain pregnancy by inhibiting uterine contractions throughout pregnancy. Progesterone performs its actions by activating the classical progesterone nuclear receptors that affect gene transcription and by the non-classical activation of cell surface membrane receptors that accounts for the rapid actions of progesterone. Besides the reproductive roles of progesterone, it exerts functions in many tissues and systems such as the nervous system, the bone, the vascular system, and the gastrointestinal (GI) tract. This review will summarize the recent literature that investigated the role of progesterone in GI tract motility. Most literature indicates that progesterone exerts an inhibitory role on gut smooth muscle cells in part by elevating nitric oxide synthesis, which induces relaxation in smooth muscle. Moreover, progesterone inhibits the signaling pathways that lead to contraction such as Rho kinase inhibition. These data serve as a quick resource for the future directions of progesterone research that could lead to better understanding and more effective treatment of gender-related GI tract motility disorders.

The Relationship Between Bone and Reproductive Hormones Beyond Estrogens and Androgens

Reproductive hormones play a crucial role in the growth and maintenance of the mammalian skeleton. Indeed, the biological significance for this hormonal regulation of skeletal homeostasis is best illustrated by common clinical reproductive disorders, such as primary ovarian insufficiency, hypothalamic amenorrhea, congenital hypogonadotropic hypogonadism, and early menopause, which contribute to the clinical burden of low bone mineral density and increased risk for fragility fracture. Emerging evidence relating to traditional reproductive hormones and the recent discovery of newer reproductive neuropeptides and hormones has deepened our understanding of the interaction between bone and the reproductive system. In this review, we provide a contemporary summary of the literature examining the relationship between bone biology and reproductive signals that extend beyond estrogens and androgens, and include kisspeptin, gonadotropin-releasing hormone, follicle-stimulating hormone, luteinizing hormone, prolactin, progesterone, inhibin, activin, and relaxin. A comprehensive and up-to-date review of the recent basic and clinical research advances is essential given the prevalence of clinical reproductive disorders, the emerging roles of upstream reproductive hormones in bone physiology, as well as the urgent need to develop novel safe and effective therapies for bone fragility in a rapidly aging population.

New insights into the functions of progesterone receptor (PR) isoforms and progesterone signaling

Progesterone, the ovarian steroid hormone, regulates a plentitude of biological processes in tissues ranging from the brain to bones. Recognizing the role of progesterone and its receptors in physiological processes and maladies can prevent and treat various diseases. Apart from its physiological functions, its role in developing diseases, especially breast cancer, is a recent topic of deliberation. There exists conflicting experimental and epidemiological evidence linking progesterone to breast cancer. This review tries to describe the physiological functions of progesterone and its receptors, genomic and non-genomic signaling, splice variants, and a different aspect of progesterone signaling. Furthermore, we seek to address or attempt to discuss the following pertinent questions on steroid hormone signaling; How does progesterone influence breast cancer progression? How does it change the molecular pathways in breast cancer with different receptor statuses, the specific role of each isoform, and how does the ER/and PR ratio affect progesterone signaling?

Aldo-keto reductase family 1 member C1 regulates the osteogenic differentiation of human ASCs by targeting the progesterone receptor

BACKGROUND

As a promising way to repair bone defect, bone tissue engineering has attracted a lot of attentions from researchers in recent years. Searching for new molecular target to modify the seed cells and enhance their osteogenesis capacity is one of the hot topics in this field. As a member of aldo-keto reductase family, aldo-keto reductase family 1 member C1 (AKR1C1) is reported to associate with various tumors. However, whether AKR1C1 takes part in regulating differentiation of adipose-derived mesenchymal stromal/stem cells (ASCs) and its relationship with progesterone receptor (PGR) remain unclear.

METHODS

Lost-and-gain-of-function experiments were performed using knockdown and overexpression of AKR1C1 to identify its role in regulating osteogenic and adipogenic differentiation of hASCs in vitro. Heterotypic bone and adipose tissue formation assay in nude mice were used to conduct the in vivo experiment. Plasmid and siRNA of PGR, as well as western blot, were used to clarify the mechanism AKR1C1 regulating osteogenesis.

RESULTS

Our results demonstrated that AKR1C1 acted as a negative regulator of osteogenesis and a positive regulator of adipogenesis of hASCs via its enzyme activity both in vitro and in vivo. Mechanistically, PGR mediated the regulation of AKR1C1 on osteogenesis.

CONCLUSIONS

Collectively, our study suggested that AKR1C1 could serve as a regulator of osteogenic differentiation via targeting PGR and be used as a new molecular target for ASCs modification in bone tissue engineering.

Estrogens and Progestogens in Triple Negative Breast Cancer: Do They Harm?

Triple-negative breast cancers (TNBC) occur more frequently in younger women and do not express estrogen receptor (ER) nor progesterone receptor (PR), and are therefore often considered hormone-insensitive. Treatment of premenopausal TNBC patients almost always includes chemotherapy, which may lead to premature ovarian insufficiency (POI) and can severely impact quality of life. Hormone replacement therapy (HRT) is contraindicated for patients with a history of hormone-sensitive breast cancer, but the data on safety for TNBC patients is inconclusive, with a few randomized trials showing increased risk-ratios with wide confidence intervals for recurrence after HRT. Here, we review the literature on alternative pathways from the classical ER/PR. We find that for both estrogens and progestogens, potential alternatives exist for exerting their effects on TNBC, ranging from receptor conversion, to alternative receptors capable of binding estrogens, as well as paracrine pathways, such as RANK/RANKL, which can cause progestogens to indirectly stimulate growth and metastasis of TNBC. Finally, HRT may also influence other hormones, such as androgens, and their effects on TNBCs expressing androgen receptors (AR). Concluding, the assumption that TNBC is completely hormone-insensitive is incorrect. However, the direction of the effects of the alternative pathways is not always clear, and will need to be investigated further.

The apoptotic effects of progesterone on breast cancer (MCF-7) and human osteosarcoma (MG-636) cells

Purpose

Progesterone has been reported to inhibit the proliferation of breast cancer and osteosarcoma cells; however, its inhibitory mechanism has not yet been clarified. The aim of the present study was to clarify the effects of progesterone on apoptosis in breast cancer (MCF-7) and human osteosarcoma (MG-63) cells.

Materials and methods

In this experimental study the cytotoxic effect of progesterone was measured in MCF-7 and MG-63 cells exposed to different concentrations of progesterone using MTT assay, and effective concentrations were identified. The expression levels of the Bax, P53 and Bcl-2 genes were evaluated by real-time PCR, and caspase-3, 8 and 9 activity levels were determined using a colorimetric method. Hoechst staining and flow cytometry were used to confirm apoptosis. The data were statistically analyzed using one-way analysis of variance (ANOVA) and independent-samples t-test.

Results

Compared to the control group, we observed a significant increase in the expression levels of the Bax and P53 genes and the activity levels of caspase-3 and 9, and a significant decrease in the expression level of the Bcl-2 gene in MCF-7 and MG-63 treated with effective concentration of progesterone. The caspase-8 activity level did not change significantly in treated MG-63 but increased in treated MCF-7 cells. Hoechst staining and flow cytometry results confirmed apoptosis in the cells exposed to effective concentration of progesterone.

Conclusions

The cytotoxic effect of progesterone on breast cancer and osteosarcoma cells was mediated by apoptotic pathways. In this context, progesterone triggers the extrinsic and intrinsic apoptotic pathways in MCF-7 cells and induces the intrinsic apoptotic pathway in MG-63 cells.

High susceptibility to collagen-induced arthritis in mice with progesterone receptors selectively inhibited in osteoprogenitor cells

Background

Progesterone receptor (PR) affects immunomodulation, and lack of PR in osteoprogenitor cells primarily affects pathways associated with immunomodulation, especially in males. In this study, we selectively deleted PR from osteoprogenitor cells using Prx1-Cre to evaluate the tissue-specific effects of PR on the pathegenesis of inflammatary arthritis (IA).

Methods

Collagen-induced arthritis (CIA) was used as an IA animal model. Both male and female PR^ΔPrx1 mice and their wild-type (WT) littermates were immunized with collagen II (CII) emulsified complete Freund’s adjuvant (CFA). Joint erosion, inflammation, and cartilage damage were assessed using a semiquantitative histologic scoring system. Bone volume and erosions in knee and ankle joints were quantitated using microCT and histology.

Results

Bone erosions developed in both paw joints in 37.5% and 41.7% of the WT and PR^ΔPrx1 female mice and in 45.4 and 83.3% of the WT and PR^ΔPrx1 male mice, respectively. Also, both joint damage and subchondral bone erosions were significantly more severe in male PRcKO-CIA mice than in male WT-CIA mice. Female PR^ΔPrx1 mice also developed higher bone loss in the knee joints than the KO-normal or WT-CIA females although with less severity compared to the male mice.

Conclusions

The presence of PR in osteoprogenitor cells decreased the development of collagen-induced arthritis and might help to explain the sex differences observed in human inflammatory arthritis.

A comparative study of hBM-MSCs' differentiation toward osteogenic lineage in the presence of progesterone and estrogen hormones separately and concurrently in vitro

Promising cell sources for tissue engineering comprise bone marrow derived-mesenchymal stem cells (BM-MSCs) that have multiple differentiation potentials. Also, sex hormones act as important elements in bone development and maintenance, and the roles of two female sex steroid hormones known as estrogen (17-β estradiol) and progesterone in osteogenic differentiation of human BM-MSCs (hBM-MSCs) are studied. For this purpose, hBM-MSCs were treated with a 1 × 10^-6  M concentration of 17-β estradiol and progesterone separately and simultaneously while the optimum concentrations were obtained by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Osteogenic differentiation tests including measurement of alkaline phosphatase (ALP) enzyme activity, the content of total mineral calcium, mineralized matrix staining by Alizarin Red and Von Kossa solutions, real-time reverse transcription polymerase chain reaction (RT-PCR), and immunofluorescence staining were carried out on Days 7 and 14 of differentiation. To exhibit the morphology of the cells, the BM-MSCs were stained with acridine orange (AO) solution. In this study, the results of ALP activity assay, calcium content and real-time RT-PCR assay and also all tests of differentiation staining have shown that 17-β estradiol has been recognized as an enhancing factor of osteogenic differentiation. Furthermore, MTT assay and AO staining revealed progesterone as a factor that seriously improved the proliferation of hBM-MSCs. Generally, the 17-β estradiol individually or in the presence of progesterone has more effects on BM-MSCs' osteogenic differentiation compared to progesterone alone. In this study, it is indicated that the effect of the 17-β estradiol and progesterone concurrently was the same as individual 17-β estradiol on the differentiation of hBM-MSCs.

The effect of female sex steroid hormones on osteogenic differentiation of endometrial stem cells

Bone regeneration is a significant and crucial health issue worldwide. Tissue bioengineering has shown itself to be the best substitute for common clinical treatment of bone loss. The suitable cell source is human endometrial stem cells (hEnSCs) which have several suitable characteristics for this approach. Since sex steroid hormones are involved in expansion and conservation of the skeleton, the effect of two sex steroid hormones known as estrogen (17-β estradiol) and progesterone on osteogenic differentiation of hEnSCs were examined. For this purpose, hEnSCs were treated with 17-β estradiol and progesterone separately (1 × 10^-6 M) and simultaneously (1 × 10^-7 M). Osteogenic differentiation tests including measurement of total mineral calcium content, Alizarin Red staining, the quantitative expression levels of some osteogenic markers by Real-time RT-PCR, and immunofluorescence staining were performed at 7 and 14 days of differentiation. To exhibit the morphology of the cells in osteogenic and culture medium, the hEnSCs were stained with Acridine Orange (AO) solution. In this research, MTT assay and AO staining revealed progesterone and 17-β estradiol increase the proliferation of hEnSCs in a dose-dependent manner. Furthermore, the results of calcium content analysis, Real-time RT-PCR assay, and all tests of differentiation staining have shown that 17-β estradiol and progesterone cannot induce hEnSCs' osteogenic differentiation. In conclusion, it is indicated that 17-β estradiol and progesterone do not have positive effects on hEnSCs' osteogenic differentiation in vitro.

Selective inhibition of progesterone receptor in osteochondral progenitor cells, but not in mature chondrocytes, modulated subchondral bone structures

OBJECTIVE

The presence or relative proportion of progesterone nuclear receptors (PR) in different tissues may contribute to sexual dimorphism in these tissues. PR is expressed in chondrocytes, but its function is mostly unknown. We hypothesized that the PR may regulate chondrocyte metabolism and affect subchondral bone structure.

METHODS

We utilized genetic fate mapping and immunohistochemistry to elucidate PR expression in and effect on cartilage. To define sex-dependent and chondrocyte-specific effects of the PR on subchondral bone, we selectively deleted PR in osteochondrogenic progenitor cells marked by Prx1 (Prx1; PRcKO) and Collagen 2 (Col2; PRcKO), or in matured chondrocytes marked by aggrecan (Acan; PRcKO) and evaluated subchondral bone structure at 4 months of age. Chondrocyte aging was monitored by anti-senescence marker p16INK4a, and MMP13, one of the Senescence-Associated Secretary Phenotype (SASP) components.

RESULTS

Compared to wild-type (WT) mice, the female Prx1; PRcKO and the Col2; PRcKO mice had greater total subchondral bone volume and greater subchondral cortical bone thickness, with increased estimated subchondral bone stiffness and failure load in both female and male Col2; PRcKO mice. Moreover, Col2; PRcKO mice from both sexes had greater bone formation and bone strength at the femurs. In contrast, we did not observe any subchondral bone changes in Acan; PRcKO mice other than higher work-to-failure observed in the male Acan; PRcKO mice. Despite no detected difference in articular cartilage between the WT and the PR; chondrocyte conditional deletion mice, there were greater numbers of senescent chondrocytes and increased MMP13 expression, especially in the male mutant mice.

CONCLUSION

These findings suggest that selective inhibition of PR in osteoprogenitor cells, but not in terminally differentiated chondrocytes, induced an increased subchondral bone phenotype and high estimated subchondral bone strength, which might be associated with the development of osteoarthritis in older age.

Strain-specific differences in the development of bone loss and incidence of osteonecrosis following glucocorticoid treatment in two different mouse strains

Objective

Glucocorticoids (GCs) are commonly prescribed as treatment for chronic inflammatory diseases. Prolonged use of GCs is a common cause of atraumatic osteonecrosis (ON) and secondary osteoporosis. Currently, there is no effective treatment for this disease; therefore, a reliable animal model would be useful to study both the pathology and novel treatment strategies for patients with the disease. The aim of this study was to establish a validated, reproducible model of GC-induced ON and bone loss in two different mouse strains (BALB/c and C57BL/6).

Methods

Seven-week-old male BALB/c (n = 32) and male C57BL/6 mice (n = 32) were randomised into placebo or GC groups and treated with daily 4 mg/L oral dexamethasone in drinking water for 90 days. Study outcome measures included histologic assessment of ON of the distal femur, bone mass and mechanical strength of tibia and lumbar vertebral body, osteoclast number, biochemical measure of bone formation and bone marrow fat quantitation.

Results

GC-induced ON lesions were observed in the distal femur in 47% of the male BALB/c mice and 25% of the male C57BL/6 mice. GC treatment decreased the trabecular bone volume and serum pro-collagen type 1N-protease (P1NP) in BALB/c mice compared with the placebo (p < 0.05) and reduced tibial bone strength in both BALB/c and C57BL/6 mice. GC-treated BALB/c mice had significantly greater marrow fat levels compared to the placebo group.

Conclusion

GC-induced ON was more prevalent in the male BALB/c mice compared to the male C57BL/6 mice. GC treatment significantly reduced bone mass, bone formation measured by P1NP, bone strength and increased marrow fat levels in male BALB/c mice. Therefore, the use of male BALB/c mice strain is recommended for both diagnostic and therapeutic studies for the prevention and treatment of ON and bone loss following prolonged treatment with GCs.

The Translational Potential of this Article

GCs are commonly used to treat patients with various chronic inflammatory diseases, and this is associated with both the development of ON and bone loss. Our study confirmed that the BALB/c mouse strain treated for 90 days with GC may be useful for developing novel treatments for ON.

Sex dimorphic regulation of osteoprogenitor progesterone in bone stromal cells

Increasing peak bone mass is a promising strategy to prevent osteoporosis. A mouse model of global progesterone receptor (PR) ablation showed increased bone mass through a sex-dependent mechanism. Cre-Lox recombination was used to generate a mouse model of osteoprogenitor-specific PR inactivation, which recapitulated the high bone mass phenotype seen in the PR global knockout mouse mode. In this work, we employed RNA sequencing analysis to evaluate sex-independent and sex-dependent differences in gene transcription of osteoprogenitors of wild-type and PR conditional knockout mice. PR deletion caused marked sex hormone-dependent changes in gene transcription in male mice as compared to wild-type controls. These transcriptional differences revealed dysregulation in pathways involving immunomodulation, osteoclasts, bone anabolism, extracellular matrix interaction and matrix interaction. These results identified many potential mechanisms that may explain our observed high bone mass phenotype with sex differences when PR was selectively deleted in the MSCs.

Sex-Dependent, Osteoblast Stage-Specific Effects of Progesterone Receptor on Bone Acquisition

The role of the progesterone receptor (PR) in the regulation of sexual dimorphism in bone has yet to be determined. Here we utilized genetic fate mapping and Western blotting to demonstrate age-dependent PR expression in the mouse femoral metaphysis and diaphysis. To define sex-dependent and osteoblast stage-specific effects of PR on bone acquisition, we selectively deleted PR at different stages of osteoblast differentiation. We found that when Prx1-Cre mice were crossed with PR floxed mice to generate a mesenchymal stem cell (MSC) conditional KO model (Prx1; PRcKO), the mutant mice developed greater trabecular bone volume with higher mineral apposition rate and bone formation. This may be explained by increased number of MSCs and greater osteogenic potential, particularly in males. Age-related trabecular bone loss was similar between the Prx1; PRcKO mice and their WT littermates in both sexes. Hormone deficiency during the period of rapid bone growth induced rapid trabecular bone loss in both the WT and the Prx1; PRcKO mice in both sexes. No differences in trabecular bone mass was observed when PR was deleted in mature osteoblasts using osteocalcin-Cre (Bglap-Cre). Also, there were no differences in cortical bone mass in all three PRcKO mice. In conclusion, PR inactivation in early osteoprogenitor cells but not in mature osteoblasts influenced trabecular bone accrual in a sex-dependent manner. PR deletion in osteoblast lineage cells did not affect cortical bone mass. © 2017 American Society for Bone and Mineral Research.

Acceleration of Fracture Healing by Overexpression of Basic Fibroblast Growth Factor in the Mesenchymal Stromal Cells

In this study, we engineered mesenchymal stem cells (MSCs) to over‐express basic fibroblast growth factor (bFGF) and evaluated its effects on fracture healing. Adipose‐derived mouse MSCs were transduced to express bFGF and green fluorescence protein (ADSC^bFGF‐GFP). Closed‐femoral fractures were performed with osterix‐mCherry reporter mice of both sexes. The mice received 3 × 10⁵ ADSCs transfected with control vector or bFGF via intramuscular injection within or around the fracture sites. Mice were euthanized at days 7, 14, and 35 to monitor MSC engraftment, osteogenic differentiation, callus formation, and bone strength. Compared to ADSC culture alone, ADSC^bFGF increased bFGF expression and higher levels of bFGF and vascular endothelial growth factor (VEGF) in the culture supernatant for up to 14 days. ADSC^bFGF treatment increased GFP‐labeled MSCs at the fracture gaps and these cells were incorporated into the newly formed callus. quantitative reverse transcription polymerase chain reaction (qRT‐PCR) from the callus revealed a 2‐ to 12‐fold increase in the expression of genes associated with nervous system regeneration, angiogenesis, and matrix formation. Compared to the control, ADSC^bFGF treatment increased VEGF expression at the periosteal region of the callus, remodeling of collagen into mineralized callus and bone strength. In summary, MSC^bFGF accelerated fracture healing by increasing the production of growth factors that stimulated angiogenesis and differentiation of MSCs to osteoblasts that formed new bone and accelerated fracture repair. This novel treatment may reduce the time required for fracture healing. Stem Cells Translational Medicine2017;6:1880–1893

Progesterone inhibits proliferation and modulates expression of proliferation-Related genes in classical progesterone receptor-negative human BxPC3 pancreatic adenocarcinoma cells

Recent studies suggest that progesterone may possess anti-tumorigenic properties. However, a growth-modulatory role of progestins in human cancer cells remains obscure. With the discovery of a new class of membrane progesterone receptors (mPRs) belonging to the progestin and adipoQ receptor gene family, it becomes important to study the effect of this hormone on proliferation of tumor cells that do not express classical nuclear progesterone receptors (nPRs). To identify a cell line expressing high levels of mPRs and lacking nPRs, we examined mRNA levels of nPRs and three forms of mPRs in sixteen human tumor cell lines of different origin. High expression of mPR mRNA has been found in pancreatic adenocarcinoma BxPC3 cells, while nPR mRNA has not been detected in these cells. Western blot analysis confirmed these findings at the protein level. We revealed specific binding of labeled progesterone in these cells with affinity constant similar to that of human mPR expressed in yeast cells. Progesterone at high concentration of 20 μM significantly reduced the mRNA levels of proliferation markers Ki67 and PCNA, as well as of cyclin D1, and increased the mRNA levels of cyclin dependent kinase inhibitors p21 and p27. Progesterone (1 μM and 20 μM) significantly inhibited proliferative activity of BxPC3 cells. These results point to anti-proliferative effects of the progesterone high concentrations on BxPC3 cells and suggest that activation of mPRs may mediate this action. Our data are a starting point for further investigations regarding the application of progesterone in pancreatic cancer.

Improved Mobilization of Exogenous Mesenchymal Stem Cells to Bone for Fracture Healing and Sex Difference

Mesenchymal stem cell (MSC) transplantation has been tested in animal and clinical fracture studies. We have developed a bone-seeking compound, LLP2A-Alendronate (LLP2A-Ale) that augments MSC homing to bone. The purpose of this study was to determine whether treatment with LLP2A-Ale or a combination of LLP2A-Ale and MSCs would accelerate bone healing in a mouse closed fracture model and if the effects are sex dependent. A right mid-femur fracture was induced in two-month-old osterix-mCherry (Osx-mCherry) male and female reporter mice. The mice were subsequently treated with placebo, LLP2A-Ale (500 μg/kg, IV), MSCs derived from wild-type female Osx-mCherry adipose tissue (ADSC, 3 x 10⁵ , IV) or ADSC + LLP2A-Ale. In phosphate buffered saline-treated mice, females had higher systemic and surface-based bone formation than males. However, male mice formed a larger callus and had higher volumetric bone mineral density and bone strength than females. LLP2A-Ale treatment increased exogenous MSC homing to the fracture gaps, enhanced incorporation of these cells into callus formation, and stimulated endochondral bone formation. Additionally, higher engraftment of exogenous MSCs in fracture gaps seemed to contribute to overall fracture healing and improved bone strength. These effects were sex-independent. There was a sex-difference in the rate of fracture healing. ADSC and LLP2A-Ale combination treatment was superior to on callus formation, which was independent of sex. Increased mobilization of exogenous MSCs to fracture sites accelerated endochondral bone formation and enhanced bone tissue regeneration. Stem Cells 2016;34:2587-2600.

Physiology, production and action of progesterone

INTRODUCTION

The aim of this article is to review the physiology of progesterone and focus on its physiological actions on tissues such as endometrium, uterus, mammary gland, cardiovascular system, central nervous system and bones. In the last decades, the interest of researchers has focused on the role of progesterone in genomic and non-genomic receptor mechanisms.

MATERIALS AND METHODS

We searched PubMed up to December 2014 for publications on progesterone/steroidogenesis.

RESULTS AND CONCLUSIONS

A better understanding of the biological genomic and non-genomic receptor mechanisms could enable us in the near future to obtain a more comprehensive knowledge of the safety and efficacy of this agent during hormone replacement therapy (natural progesterone), in vitro fertilization (water-soluble subcutaneous progesterone), in traumatic brain injury, Alzheimer's disease and diabetic neuropathy, even though further clinical studies are needed to prove its usefulness.

Sclerostin-antibody treatment of glucocorticoid-induced osteoporosis maintained bone mass and strength

This study was to determine if antibody against sclerostin (Scl-Ab) could prevent glucocorticoid (GC)-induced osteoporosis in mice. We found that Scl-Ab prevented GC-induced reduction in bone mass and bone strength and that the anabolic effects of Scl-Ab might be partially achieved through the preservation of osteoblast activity through autophagy.

INTRODUCTION

Glucocorticoids (GCs) inhibit bone formation by altering osteoblast and osteocyte cell activity and lifespan. A monoclonal antibody against sclerostin, Scl-Ab, increased bone mass in both preclinical animal and clinical studies in subjects with low bone mass. The objectives of this study were to determine if treatment with the Scl-Ab could prevent loss of bone mass and strength in a mouse model of GC excess and to elucidate if Scl-Ab modulated bone cell activity through autophagy.

METHODS

We generated reporter mice that globally expressed dsRed fused to LC3, a protein marker for autophagosomes, and evaluated the dose-dependent effects of GCs (0, 0.8, 2.8, and 4 mg/kg/day) and Scl-Ab on autophagic osteoblasts, bone mass, and bone strength.

RESULTS

GC treatment at 2.8 and 4 mg/kg/day of methylprednisolone significantly lowered trabecular bone volume (Tb-BV/TV) at the lumbar vertebrae and distal femurs, cortical bone mass at the mid-shaft femur (FS), and cortical bone strength compared to placebo (PL). In mice treated with GC and Scl-Ab, Tb-BV/TV increased by 60-125 %, apparent bone strength of the lumbar vertebrae by 30-70 %, FS-BV by 10-18 %, and FS-apparent strength by 13-15 %, as compared to GC vehicle-treated mice. GC treatment at 4 mg/kg/day reduced the number of autophagic osteoblasts by 70 % on the vertebral trabecular bone surface compared to the placebo group (PL, GC 0 mg), and GC + Scl-Ab treatment.

CONCLUSIONS

Treatment with Scl-Ab prevented GC-induced reduction in both trabecular and cortical bone mass and strength and appeared to maintain osteoblast activity through autophagy.

Optimizing tamoxifen-inducible Cre/loxp system to reduce tamoxifen effect on bone turnover in long bones of young mice

For tamoxifen-dependent Cre recombinase, also known as CreER recombinase, tamoxifen (TAM) is used to activate the Cre to generate time- and tissue-specific mouse mutants. TAM is a potent CreER system inducer; however, TAM is also an active selective estrogen receptor modulator (SERM) that can influence bone homeostasis. The purpose of this study was to optimize the TAM dose for Cre recombinase activation while minimizing the effects of TAM on bone turnover in young growing mice.

METHODS

To evaluate the effects of TAM on bone turnover and bone mass, 1-month-old wild-type male and female mice were intraperitoneally injected with TAM at 0, 1, 10 or 100mg/kg/day for four consecutive days, or 100, 300 mg/kg/day for one day. The distal femurs were analyzed one month after the last TAM injection by microCT, mechanical test, and surface-based bone histomorphometry. Similar doses of TAM were used in Col1 (2.3 kb)-CreERT2; mT/mG reporter male mice to evaluate the dose-dependent efficacy of Cre-ER activation in bone tissue.

RESULTS

A TAM dose of 100 mg/kg × 4 days significantly increased trabecular bone volume/total volume (BV/TV) of the distal femur, femur length, bone strength, and serum bone turnover markers compared to the 0mg control group. In contrast, TAM doses ≤ 10 mg/kg did not significantly change any of these parameters compared to the 0mg group, although a higher bone strength was observed in the 10mg group. Surface-based histomorphometry revealed that the 100mg/kg dose of TAM dose significantly increased trabecular bone formation and decreased periosteal bone formation at 1-week post-TAM treatment. Using the reporter mouse model Col1-CreERT2; mT/mG, we found that 10mg/kg TAM induced Col1-CreERT2 activity in bone at a comparable level to the 100mg/kg dose.

CONCLUSIONS

TAM treatment at 100mg/kg/day × 4 days significantly affects bone homeostasis, resulting in an anabolic bone effect on trabecular bone in 1-month-old male mice. However, a lower dose of TAM at 10 mg/kg/day × 4 days can yield similar Col1-CreERT2 induction efficacy with minimum effects on bone turnover in young male mice.

Inactivation of the Progesterone Receptor in Mx1+ Cells Potentiates Osteogenesis in Calvaria but Not in Long Bone

The effect of progesterone on bone remains elusive. We previously reported that global progesterone receptor (PR) knockout mice displayed high bone mass phenotype, suggesting that PR influences bone growth and modeling. Recently, Mx1+ cells were characterized to be mesenchymal stem cell-like pluripotent Cells. The aim of this study was to evaluate whether the PR in Mx1+ cells regulates osteogenesis. Using the Mx1-Cre;mT/mG reporter mouse model, we found that the calvarial cells exhibited minimal background Mx1-Cre activity prior to Cre activation by IFNα treatment as compared to the bone marrow stromal cells. IFNα treatment significantly activated Mx1-Cre in the calvarial cells. When the PR gene was deleted in the Mx1-Cre;PR-flox calvarial cells in vitro, significantly higher levels of expression of osteoblast maturation marker genes (RUNX2, Osteocalcin, and Dmp1) and osteogenic potential were detected. The PR-deficient calvariae exhibited greater bone volume, especially in the males. Although Mx1-Cre activity could be induced on the bone surface in vivo, the Mx1+ cells did not differentiate into osteocytes in long bones. Bone volumes at the distal femurs and the bone turnover marker serum Osteocalcin were similar between the Mx1-Cre;PR-flox mutant mice and the corresponding wild types in both sexes. In conclusion, our data demonstrates that blocking progesterone signaling via PRs in calvarial Mx1+ cells promoted osteoblast differentiation in the calvaria. Mx1+ was expressed by heterogeneous cells in bone marrow and did not differentiate into osteocyte during long bone development in vivo. Selectively inactivating the PR gene in Mx1+ cells affected the membrane bone formation but did not affect peripheral skeletal homeostasis.

β-Ecdysone Augments Peak Bone Mass in Mice of Both Sexes

BACKGROUND

One of the strongest predictors for osteoporosis is peak bone mass. Interventions to augment peak bone mass have yet to be developed. β-Ecdysone (βEcd), a natural steroid-like compound produced by arthropods to initiate metamorphosis, is believed to have androgenic effects and so may be used to augment bone mass.

QUESTIONS/PURPOSES

The purpose of this study was to use both male and female (1) gonadal-sufficient; and (2) -insufficient mice to investigate sex differences in terms of bone development and structure after βEcd administration.

METHODS

Two-month-old male and female Swiss-Webster mice were randomized to receive either vehicle or βEcd (0.5 mg/kg) for 3 weeks. In a separate experiment to evaluate the effects of βEcd on sex hormone-deficient mice, gonadectomy was performed in male (orchiectomy [ORX]) and female mice (ovariectomy [OVX]). Sham-operated and the ORX/OVX mice were then treated for 3 weeks with βEcd. Primary endpoints for the study were trabecular bone structure and bone strength.

RESULTS

In male mice, the trabecular bone volume was 0.18±0.02 in the placebo-treated (PL) and 0.23±0.02 in the βEcd-treated group (p<0.05 versus PL); and 0.09±0.01 in the ORX group (p<0.05 versus PL) and 0.12±0.01 in the ORX+βEcd group. Vertebral bone strength (maximum load) was 43±2 in PL and 51±1 in the βEcd-treated group (p<0.05 versus PL); and 30±4 in the ORX group (p<0.05 versus PL) and 37±3 in the ORX+βEcd group. In female mice, trabecular bone volume was 0.23±0.02 in PL and 0.26±0.02 in the βEcd-treated group (p<0.05 versus PL); and 0.15±0.01 in the OVX group (p<0.05 versus PL) and 0.14±0.01 in the OVX+βEcd group. Maximum load of the vertebrae was 45±2 in PL and 48±4 in the βEcd-treated group; and 39±4 in the OVX group (p<0.05 versus PL) and 44±4 in the OVX+βEcd group.

CONCLUSIONS

These findings suggest the potential use of βEcd in the augmentation of bone mass in growing male and female mice. It may also partially prevent the detrimental effects of gonadectomy on trabecular bone.

CLINICAL RELEVANCE

Our results support the potential use of βEcd or nature products that are rich in βEcd to augment peak bone mass. βEcd may differ from the other anabolic hormone treatments that may have severe side effects such as serious cardiac complications. However, its effects on humans remain to be determined.

Prevention of glucocorticoid induced bone changes with beta-ecdysone

Beta-ecdysone (βEcd) is a phytoecdysteroid found in the dry roots and seeds of the asteraceae and achyranthes plants, and is reported to increase osteogenesis in vitro. Since glucocorticoid (GC) excess is associated with a decrease in bone formation, the purpose of this study was to determine if treatment with βEcd could prevent GC-induced osteoporosis. Two-month-old male Swiss-Webster mice (n=8-10/group) were randomized to either placebo or slow release prednisolone pellets (3.3mg/kg/day) and treated with vehicle control or βEcd (0.5mg/kg/day) for 21days. GC treatment inhibited age-dependent trabecular gain and cortical bone expansion and this was accompanied by a 30-50% lower bone formation rate (BFR) at both the endosteal and periosteal surfaces. Mice treated with only βEcd significantly increased bone formation on the endosteal and periosteal bone surfaces, and increased cortical bone mass were their controls to compare to GC alone. Concurrent treatment of βEcd and GC completely prevented the GC-induced reduction in BFR, trabecular bone volume and partially prevented cortical bone loss. In vitro studies determined that βEcd prevented the GC increase in autophagy of the bone marrow stromal cells as well as in whole bone. In summary, βEcd prevented GC induced changes in bone formation, bone cell viability and bone mass. Additional studies are warranted of βEcd for the treatment of GC induced bone loss.

Improved trabecular bone structure of 20-month-old male spontaneously hypertensive rats

A few clinical studies have reported that elderly male participants with hypertensive disease frequently have higher bone mineral density (BMD) than the normotensive participants at several skeletal sites. The detailed mechanism is still unknown; therefore, a study of bone structure and density using the hypertensive animal models could be informative. We used micro-computed tomography to quantitatively evaluate the tibial and 3rd lumbar vertebral bones in the 20-month-old male spontaneous hypertensive rat (SHR). The BMD, volume fraction, and the microarchitecture changes of the SHR were compared to those of same-age normotensive controls (Wistar-Kyoto rat, WKY). We found that in the very old (20 month) male rats, the trabecular bone fraction and microstructure were higher than those in the same-age normotensive controls. The observation of the association of hypertension with BMD and bone strength in hypertensive rats warrants further investigations of bone mass and strength in elderly males with hypertension.

Reversing bone loss by directing mesenchymal stem cells to bone

Bone regeneration by systemic transplantation of mesenchymal stem cells (MSCs) is problematic due to the inability to control the MSCs' commitment, growth, and differentiation into functional osteoblasts on the bone surface. Our research group has developed a method to direct the MSCs to the bone surface by conjugating a synthetic peptidomimetic ligand (LLP2A) that has high affinity for activated α4β1 integrin on the MSC surface, with a bisphosphonates (alendronate) that has high affinity for bone (LLP2A-Ale), to direct the transplanted MSCs to bone. Our in vitro experiments demonstrated that mobilization of LLP2A-Ale to hydroxyapatite accelerated MSC migration that was associated with an increase in the phosphorylation of Akt kinase and osteoblastogenesis. LLP2A-Ale increased the homing of the transplanted MSCs to bone as well as the osteoblast surface, significantly increased the rate of bone formation and restored both trabecular and cortical bone loss induced by estrogen deficiency or advanced age in mice. These results support LLP2A-Ale as a novel therapeutic option to direct the transplanted MSCs to bone for the treatment of established bone loss related to hormone deficiency and aging.

Nuclear receptors in bone physiology and diseases

During the last decade, our view on the skeleton as a mere solid physical support structure has been transformed, as bone emerged as a dynamic, constantly remodeling tissue with systemic regulatory functions including those of an endocrine organ. Reflecting this remarkable functional complexity, distinct classes of humoral and intracellular regulatory factors have been shown to control vital processes in the bone. Among these regulators, nuclear receptors (NRs) play fundamental roles in bone development, growth, and maintenance. NRs are DNA-binding transcription factors that act as intracellular transducers of the respective ligand signaling pathways through modulation of expression of specific sets of cognate target genes. Aberrant NR signaling caused by receptor or ligand deficiency may profoundly affect bone health and compromise skeletal functions. Ligand dependency of NR action underlies a major strategy of therapeutic intervention to correct aberrant NR signaling, and significant efforts have been made to design novel synthetic NR ligands with enhanced beneficial properties and reduced potential negative side effects. As an example, estrogen deficiency causes bone loss and leads to development of osteoporosis, the most prevalent skeletal disorder in postmenopausal women. Since administration of natural estrogens for the treatment of osteoporosis often associates with undesirable side effects, several synthetic estrogen receptor ligands have been developed with higher therapeutic efficacy and specificity. This review presents current progress in our understanding of the roles of various nuclear receptor-mediated signaling pathways in bone physiology and disease, and in development of advanced NR ligands for treatment of common skeletal disorders.

Endochondral bone growth, bone calcium accretion, and bone mineral density: how are they related?

Endochondral bone growth in young growing mammals or adult mammals with persistent growth plates progresses from proliferation, maturation and hypertrophy of growth plate chondrocytes to mineralization of cartilaginous matrix to form an osseous tissue. This complex process is tightly regulated by a number of factors with different impacts, such as genetics, endocrine/paracrine factors [e.g., PTHrP, 1,25(OH)(2)D(3), IGF-1, FGFs, and prolactin], and nutritional status (e.g., dietary calcium and vitamin D). Despite a strong link between growth plate function and elongation of the long bone, little is known whether endochondral bone growth indeed determines bone calcium accretion, bone mineral density (BMD), and/or peak bone mass. Since the process ends with cartilaginous matrix calcification, an increase in endochondral bone growth typically leads to more calcium accretion in the primary spongiosa and thus higher BMD. However, in lactating rats with enhanced trabecular bone resorption, bone elongation is inversely correlated with BMD. Although BMD can be increased by factors that enhance endochondral bone growth, the endochondral bone growth itself is unlikely to be an important determinant of peak bone mass since it is strongly determined by genetics. Therefore, endochondral bone growth and bone elongation are associated with calcium accretion only in a particular subregion of the long bone, but do not necessarily predict BMD and peak bone mass.

Paracrine signaling by progesterone

Steroid hormones coordinate and control the development and function of many organs and are implicated in many pathological processes. Progesterone signaling, in particular, is essential for several important female reproductive functions. Physiological effects of progesterone are mediated by its cognate receptor, expressed in a subset of cells in target tissues. Experimental evidence has accumulated that progesterone acts through both cell intrinsic as well as paracrine signaling mechanisms. By relegating the hormonal stimulus to paracrine signaling cascades the systemic signal gets amplified locally and signaling reaches different cell types that are devoid of hormone receptors. Interestingly, distinct biological responses to progesterone in different target tissues rely on several tissue-specific and some common paracrine factors that coordinate biological responses in different cell types. Evidence is forthcoming that the intercellular signaling pathways that control development and physiological functions are important in tumorigenesis.

Novel actions of progesterone: what we know today and what will be the scenario in the future?

Objectives

This article is aimed to review the novel actions of progesterone, which otherwise is considered as a female reproductive hormone. The article focuses on its important physiological actions in males too and gives an overview of its novel perspectives in disorders of central and peripheral nervous system.

Key findings

Progesterone may have a potential benefit in treatment of traumatic brain injury, various neurological disorders and male related diseases like benign prostatic hypertrophy (BPH), prostate cancer and osteoporosis. Norethisterone (NETA), a progesterone derivative, decreases bone mineral loss in male castrated mice suggesting its role in osteoporosis. In the future, progesterone may find use as a male contraceptive too, but still needs confirmatory trials for safety, tolerability and acceptability. Megestrol acetate, a progesterone derivative is preferred in prostatic cancer. Further, it may find utility in nicotine addiction, traumatic brain injury (recently entered Phase III trial) and Alzheimer's disease, diabetic neuropathy and crush injuries. Studies also suggest role of progesterone in stroke, for which further clinical trials are needed. The non genomic actions of progesterone may be in part responsible for these novel actions.

Summary

Although progesterone has shown promising role in various non-hormonal benefits, further clinical studies are needed to prove its usefulness in conditions like stroke, traumatic brain injury, neuropathy and crush injury. In male related illnesses like BPH and prostatic Ca, it may prove a boon in near future. New era of hormonal male contraception may be initiated by use of progesterone along with testosterone.

Directing mesenchymal stem cells to bone to augment bone formation and increase bone mass

Aging reduces the number of mesenchymal stem cells (MSCs) in the bone marrow which leads to impairment of osteogenesis. However, if MSCs could be directed toward osteogenic differentiation, they could be a viable therapeutic option for bone regeneration. We have developed a method to direct the MSCs to the bone surface by attaching a synthetic high affinity and specific peptidomimetic ligand (LLP2A) against integrin α4β1 on the MSC surface, to a bisphosphonate (alendronate, Ale) that has high affinity for bone. LLP2A-Ale increased MSCs migration and osteogenic differentiation in vitro. A single intravenous injection of LLP2A-Ale increased trabecular bone formation and bone mass in both xenotransplantation and immune competent mice. Additionally, LLP2A-Ale prevented trabecular bone loss after peak bone acquisition was achieved or following estrogen deficiency. These results provide a proof of principle that LLP2A-Ale can direct MSCs to the bone to form new bone and increase bone strength.