Estrogen receptor alpha genotype confers interindividual variability of response to estrogen and testosterone in mesenchymal-stem-cell-derived osteoblasts

Osteogenic differentiation of human induced pluripotent stem cell in the presence of testosterone and 17 β-estradiol in vitro

Recently, numerous scientific approaches have been explored to treat various diseases using stem cells. In 2006, induced pluripotent stem cell (iPSC) were introduced by Takahashi and Yamanaka and showed the potential of self-renewing and differentiation into all types of targeted cells in vitro. In this investigation, we studied the effect of testosterone (T) individually or in the presence of 17 β-estradiol (E2) on osteogenic differentiation of human iPSC (hiPSC) during 2 wk. The optimal concentrations of sex steroid hormones were examined by MTT assay and acridine orange (AO) staining. The impact of E2 and T either individually or together as a combination was examined by ALP activity; the content of total mineral calcium, by von Kossa and alizarin red staining. Additionally, the expression rate of osteogenic specific markers was studied via real-time RT-PCR and immunocytochemistry analyses at day 14 of differentiation. The obtained results illustrated that the differentiation medium supplemented with T-E2 increased not only the ALP enzyme activity and the content of calcium but also the osteogenic-related gene and protein expressions on the 14^th day. Furthermore, the results were confirmed by mineralized matrix staining. In conclusion, these data suggest that T could be used as an effective factor for osteogenic induction of hiPSCs combined with the E2 in bone regeneration.

Impacts of Angelica Polysaccharide on Proliferation and Differentiation of Mesenchymal Stem Cells of Rat Bone Marrow

In literature, antiosteoporotic effects of Angelica sinensis root have been confirmed, but the impact of Angelica sinensis polysaccharide (ASP) on osteoblastic or adipogenic distinction of BMSCs is limited. This paper aimed to explore the role of ASP on proliferation and differentiation of rat BMSCs. Rat BMSCs were subjected to isolation and identification through flow cytometry. The proliferation of rat BMSCs under ASP was performed by CCK-8 kit. Measures of osteogenesis under different concentrations of ASP were detected by using alizarin red staining for mesenchymal cells differentiation and ALP activity assay to identify ALP activity. Quantitative RT-PCR was selected to identify osteoblastic or adipogenic biomarkers from a genetic perspective. Likewise, we have evaluated measures of indicators of Wnt/β-catenin signal. ASP significantly promoted the proliferation, increased osteogenesis, and decreased adipogenesis of rat BMSCs within the limit of 20-60 mg/L in a dose-dependent manner but was suppressed at 80 mg/L. The expression of cyclin D1 and ß-catenin showed a considerable rise over the course of ASP induced osteogenesis. Dickkopf 1 (DKK1) suppressed the regulation of rat BMSCs differentiation through the mediation of ASP. We have observed that ASP upregulated the osteogenic but downregulated adipogenic differentiation of BMSCs, and our findings help to contribute to effective solutions for treating bone disorders.

Comparative characterization and osteogenic / adipogenic differentiation of mesenchymal stem cells derived from male rat hair follicles and bone marrow

Clinical applications of cell therapy and tissue regeneration under different conditions need a multiplicity of adult stem cell sources. Up to date, little is available on the comparative isolation, characterization, proliferation, rapid amplification, and osteogenic/adipogenic differentiation of rat mesenchymal stem cells (MSCs) isolated from living bulge cells of the hair follicle (HF) and bone marrow (BM) from the same animal. This work hopes to use HF-MSCs as an additional adult stem cell source for research and application. After reaching 80% confluence, the cell counting, viability %, and yields of HF-MSCs and BM-MSCs were nearly similar. The viability % was 91.41 ± 2.98 and 93.11 ± 3.06 while the cells yield of initial seeding was 33.15 ± 2.76 and 34.22 ± 3.99 and of second passage was 28.76 ± 1.01 and 29.56 ± 3.11 for HF-MSCs and BM-MSCs respectively. Clusters of differentiation (CDs) analysis revealed that HF-MSCs were positively expressed CD34, CD73 and CD200 and negatively expressed CD45. BM-MSCs were positively expressed CD73 and CD200 and negatively expressed of CD34 and CD45. The proliferation of HF-MSCs and BM-MSCs was determined by means of incorporation of Brd-U, population doubling time (PDT) assays and the quantity of formazan release. The percentage of Brd-U positive cells and PDT were relatively similar in both types of cells. The proliferation, as expressed by the quantity of formazan assay in confluent cells, revealed that the quantity of release by BM-MSCs was slightly higher than HF-MSCs. Adipogenic differentiated BM-MSCs showed moderate accumulation of oil red-O stained lipid droplets when compared to that of HF-MSCs which exhibited high stain. The total lipid concentration was significantly higher in adipogenic differentiated HF-MSCs than BM-MSCs (P < 0.05). It was found that activity of bone alkaline phosphatase and calcium concentration were significantly higher (P < 0.01 and P < 0.05 respectively) in osteogenic differentiated BM-MSCs than that of HF-MSCs. The present findings demonstrate that the HF-MSCs are very similar in most tested characteristics to BM-MSCs with the exception of differentiation. Additionally; no issues have been reported during the collection of HF-MSCs. Therefore, the HF may represent a suitable and accessible source for adult stem cells and can be considered an ideal cell source for adipogenesis research.

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.

Effects of testosterone and 17β-estradiol on osteogenic and adipogenic differentiation capacity of human bone-derived mesenchymal stromal cells of postmenopausal women

Progressive bone loss is a predominant symptom of aging and osteoporosis. Therefore, the effects of sex steroids (i.e. testosterone and 17β-estradiol) on the differentiation capacity of human bone-derived mesenchymal stromal cells (hMSCs), as progenitors of osteoblasts and adipocytes, are of particular interest. The objectives of the present study were, thus, to elucidate whether bone-derived hMSCs of postmenopausal women produce aromatase (CYP19A1) and, whether they modulate their differentiation behaviour in response to testosterone and 17β-estradiol (E2), in relation to their steroid receptor expression. Supplementation of testosterone resulted in a considerable formation of E2 under osteogenic and adipogenic culture conditions, whereas E2 synthesis remained minimal in the cells cultured in basal medium. Concomitant with high aromatase expression and 17β-estradiol formation of the cells cultured in osteogenic medium supplemented with testosterone, a distinct promotion of late-stage osteogenesis was found, as shown by significant matrix mineralization and a notable increase in osteogenic markers. These effects were abrogated by the aromatase inhibitor anastrozole. Under adipogenic conditions, testosterone reduced the occurrence of lipid droplets and led to a decrease in PPARγ and AR expression, independent of anastrozole. Regardless of the culture conditions, ERα was detectable whilst ERβ was not. In conclusion, aromatase activity is limited to differentiated hMSCs and the resulting 17β-estradiol enhances late osteogenic differentiation stages via ERα. Adipogenic differentiation, on the other hand, is reduced by both sex steroids: testosterone via AR and 17β-estradiol.

Stem cell-based bone and dental regeneration: a view of microenvironmental modulation

In modern medicine, bone and dental loss and defects are common and widespread morbidities, for which regenerative therapy has shown great promise. Mesenchymal stem cells, obtained from various sources and playing an essential role in organ development and postnatal repair, have exhibited enormous potential for regenerating bone and dental tissue. Currently, mesenchymal stem cells (MSCs)-based bone and dental regeneration mainly includes two strategies: the rescue or mobilization of endogenous MSCs and the application of exogenous MSCs in cytotherapy or tissue engineering. Nevertheless, the efficacy of MSC-based regeneration is not always fulfilled, especially in diseased microenvironments. Specifically, the diseased microenvironment not only impairs the regenerative potential of resident MSCs but also controls the therapeutic efficacy of exogenous MSCs, both as donors and recipients. Accordingly, approaches targeting a diseased microenvironment have been established, including improving the diseased niche to restore endogenous MSCs, enhancing MSC resistance to a diseased microenvironment and renormalizing the microenvironment to guarantee MSC-mediated therapies. Moreover, the application of extracellular vesicles (EVs) as cell-free therapy has emerged as a promising therapeutic strategy. In this review, we summarize current knowledge regarding the tactics of MSC-based bone and dental regeneration and the decisive role of the microenvironment, emphasizing the therapeutic potential of microenvironment-targeting strategies in bone and dental regenerative medicine.

Stem cell-based bone regeneration in diseased microenvironments: Challenges and solutions

Restoration of extensive bone loss and defects remain as an unfulfilled challenge in modern medicine. Given the critical contributions to bone homeostasis and diseases, mesenchymal stem cells (MSCs) have shown great promise to jumpstart and facilitate bone healing, with immense regenerative potential in both pharmacology-based endogenous MSC rescue/mobilization in skeletal diseases and emerging application of MSC transplantation in bone tissue engineering and cytotherapy. However, efficacy of MSC-based bone regeneration was not always achieved; particularly, fulfillment of MSC-mediated bone healing in diseased microenvironments of host comorbidities remains as a major challenge. Indeed, impacts of diseased microenvironments on MSC function rely not only on the dynamic regulation of resident MSCs by surrounding niche to convoy pathological signals of bone, but also on the profound interplay between transplanted MSCs and recipient components that mediates and modulates therapeutic effects on skeletal conditions. Accordingly, novel solutions have recently been developed, including improving resistance of MSCs to diseased microenvironments, recreating beneficial microenvironments to guarantee MSC-based regeneration, and usage of subcellular vesicles of MSCs in cell-free therapies. In this review, we summarize state-of-the-art knowledge regarding applications and challenges of MSC-mediated bone healing, further offering principles and effective strategies to optimize MSC-based bone regeneration in aging and diseases.

Mesenchymal progenitors in osteopenias of diverse pathologies: differential characteristics in the common shift from osteoblastogenesis to adipogenesis

Osteoporosis is caused by pathologic factors such as aging, hormone deficiency or excess, inflammation, and systemic diseases like diabetes. Bone marrow stromal cells (BMSCs), the mesenchymal progenitors for both osteoblasts and adipocytes, are modulated by niche signals. In differential pathologic states, the pathological characteristics of BMSCs to osteoporoses and functional differences are unknown. Here, we detected that trabecular bone loss co-existed with increased marrow adiposity in 6 osteoporotic models, respectively induced by natural aging, accelerated senescence (SAMP6), ovariectomy (OVX), type 1 diabetes (T1D), excessive glucocorticoids (GIOP) and orchidectomy (ORX). Of the ex vivo characteristics of BMSCs, the colony-forming efficiency and the proliferation rate in aging, SAMP6, OVX, GIOP and ORX models decreased. The apoptosis and cellular senescence increased except in T1D, with up-regulation of p53 and p16 expression. The osteogenesis declined except in GIOP, with corresponding down-regulation of Runt-related transcription factor 2 (RUNX2) expression. The adipogenesis increased in 6 osteoporotic models, with corresponding up-regulation of Peroxisome proliferator activated receptor gamma (PPARγ) expression. These findings revealed differential characteristics of BMSCs in a common shift from osteoblastogenesis to adipogenesis among different osteoporoses and between sexes, and provide theoretical basis for the functional modulation of resident BMSCs in the regenerative therapy for osteoporosis.

Microenvironmental Views on Mesenchymal Stem Cell Differentiation in Aging

Aging is characterized by common environmental changes, such as hormonal, immunologic, and metabolic disorders. These pathologic factors impair the capability of mesenchymal stem cells (MSCs) to generate and maintain functionalized tissue components, contributing to age-related tissue degeneration (e.g., osteoporosis). However, in organismal aging, whether the microenvironmental signals induce common or differential MSC compromise and how they interact at the molecular level in mediating the functional decline of MSCs are not fully understood. In this review, we discuss the respective contribution of microenvironmental pathologic factors to age-related MSC dysfunction-particularly, the shifted differentiation from osteoblasts to adipocytes of bone marrow-derived MSCs. The authors summarize recent works regarding mechanisms underlying MSC-biased differentiation under altered microenvironments, which involve the activation of key signaling pathways, intracellular oxidative stress, and posttranscriptional regulations. In addition, we compare the differential influences of systemic and local microenvironments on MSC differentiation based on our findings. The authors also propose strategies to rescue differentiation disorders of MSCs in aging via modulating microenvironments, by using signaling modulators, anti-inflammatory agents, antioxidants, and metabolic regulators and by promoting mobilization of systemic MSCs to local injury sites. The authors hope that these insights contribute to MSC-based organismal aging research and treatments.

Gender difference in the neuroprotective effect of rat bone marrow mesenchymal cells against hypoxia-induced apoptosis of retinal ganglion cells

Bone marrow mesenchymal stem cells can reduce retinal ganglion cell death and effectively prevent vision loss. Previously, we found that during differentiation, female rhesus monkey bone marrow mesenchymal stem cells acquire a higher neurogenic potential compared with male rhesus monkey bone marrow mesenchymal stem cells. This suggests that female bone marrow mesenchymal stem cells have a stronger neuroprotective effect than male bone marrow mesenchymal stem cells. Here, we first isolated and cultured bone marrow mesenchymal stem cells from female and male rats by density gradient centrifugation. Retinal tissue from newborn rats was prepared by enzymatic digestion to obtain primary retinal ganglion cells. Using the transwell system, retinal ganglion cells were co-cultured with bone marrow mesenchymal stem cells under hypoxia. Cell apoptosis was detected by flow cytometry and caspase-3 activity assay. We found a marked increase in apoptotic rate and caspase-3 activity of retinal ganglion cells after 24 hours of hypoxia compared with normoxia. Moreover, apoptotic rate and caspase-3 activity of retinal ganglion cells significantly decreased with both female and male bone marrow mesenchymal stem cell co-culture under hypoxia compared with culture alone, with more significant effects from female bone marrow mesenchymal stem cells. Our results indicate that bone marrow mesenchymal stem cells exert a neuroprotective effect against hypoxia-induced apoptosis of retinal ganglion cells, and also that female cells have greater neuroprotective ability compared with male cells.

Hepatitis C virus coinfection as a risk factor for osteoporosis and fracture

PURPOSE OF REVIEW

With increased survival of HIV-infected patients, osteoporotic fractures have developed as a major cause of morbidity in these patients, and chronic hepatitis C virus (HCV) coinfection has emerged as a significant contributor to this increased fracture risk. The present article reviews the epidemiologic and clinical evidence for osteoporosis and increased fracture risk among HIV/HCV coinfected patients, and potential mechanisms for these outcomes with HCV coinfection.

RECENT FINDINGS

Epidemiologic studies suggest that HIV/HCV coinfected patients exhibit a three-fold increased fracture incidence compared with uninfected controls, and 1.2-2.4-fold increased fracture risk compared with HIV monoinfected patients. Recent reports suggest that chronic HCV coinfection is independently associated with reduced bone mineral density in HIV, but that it is not associated with significantly increased bone turnover. The deleterious impact of chronic HCV on BMD and fracture risk occurs even in the absence of advanced liver fibrosis or cirrhosis. New tools to assess bone quality, including the trabecular bone score, high-resolution peripheral quantitative computed tomography, and in-vivo microindentation, may help improve understanding of the mechanisms of HCV-associated skeletal fragility. The impact of approved antiosteoporosis medications and direct-acting antivirals for the treatment of chronic HCV infection on patients' bone health remain to be studied.

SUMMARY

Chronic HCV infection is an independent risk factor for osteoporosis and fractures among HIV-infected patients, even before the development of cirrhosis. The underlying mechanisms are being unraveled, but major questions persist regarding the optimal evaluation and management of bone health in HIV/HCV coinfected patients.

17β-estradiol differently affects osteogenic differentiation of mesenchymal stem/stromal cells from adipose tissue and bone marrow

Adipose-derived and bone marrow stem/stromal cells (ASCs and BMSCs) have been often compared for their application in regenerative medicine, and several factors sustaining their differentiation and efficacy have been investigated. 17 β-estradiol (E2) has been reported to influence some functions of progenitor cells. Here we studied the effects of 10 and 100nM E2 on ASC and BMSC vitality, proliferation and differentiation towards osteogenic and adipogenic lineages. E2 did not modulate ASC and BMSC vitality and growth rate, while the hormone produced a pro-adipogenic effect on both mesenchymal stem/stromal cells (MSCs). In particular, the synergy between 7-day pre-treatment and 100nM E2 led to the most evident result, increasing lipid vacuoles formation in ASCs and BMSCs of +44% and +82%, respectively. Despite the fact that E2 did not alter collagen deposition of osteo-induced MSCs, we observed a different modulation of ASC and BMSC alkaline phosphatase (ALP) activity. Indeed, this osteogenic marker was always enhanced by 17 β-estradiol in BMSCs, and 7-day pre-treatment with 100nM E2 increased it of about 70%. In contrast, E2 weakened ASC osteogenic potential, reducing their ALP activity of about 20%, with the most evident effect on ASCs isolated from pre-menopausal women (-30%). Finally, we identified an estrogen receptor α (ERα) variant of about 37kDa expressed in both MSCs. Interestingly, adipogenic stimuli drastically reduced its expression, while osteogenic ones mildly increased this isoform in BMSCs only. In conclusion, E2 positively affected the adipogenic process of both MSCs while it favored osteogenic induction in BMSCs only, and both mesenchymal progenitors expressed a novel 37kDa ER-α variant whose expression was modulated during differentiation.

Mechanisms of bone disease in HIV and hepatitis C virus: impact of bone turnover, tenofovir exposure, sex steroids and severity of liver disease

OBJECTIVE

Both HIV and hepatitis C virus (HCV) infections are associated with higher osteoporotic fracture risk. Increased bone turnover, liver fibrosis, tenofovir (TDF) use or hormonal imbalances are possible underlying mechanisms.

DESIGN

This prospective, cross-sectional study assessed 298 male volunteers with either virologically suppressed HIV or untreated HCV mono-infections, HIV/HCV co-infection and noninfected controls.

METHODOLOGY

Study participants underwent bone mineral density (BMD) by dual-energy x-ray absorptiometry and measurement of bone turnover markers [BTM: C-telopeptide (CTX) and osteocalcin (OC)], insulin-like growth factor-1 (IGF-1), the sex steroids testosterone (T) and estradiol (E2), and the aspartate aminotransferase-to-platelet ratio index (APRI). Impact of HIV and HCV status on BMD was evaluated in multivariate models adjusting for APRI score, BTM, TDF exposure, IGF-1, and sex steroids.

RESULTS

HIV and HCV status independently predicted lower BMD, controlling for age, race, BMI, and smoking (P = 0.017 and P = 0.010, respectively), whereas APRI did not (P = 0.84). HIV was associated with increased bone resorption (CTX: P < 0.001) and formation (OC: P = 0.014), whereas HCV infection was not associated with CTX (P = 0.30) or OC (P = 0.36). TDF exposure was associated with lower BMD (P < 0.01). IGF-1 was significantly decreased in HCV and increased in HIV. Tumor necrosis factor-α (P = 0.98), IGF-1 (P = 0.80), bioavailable T (P = 0.45) and E2 (P = 0.27) were not associated with BMD and did not attenuate the impact of HIV or HCV on BMD.

CONCLUSION

HIV and TDF exposure decrease BMD through increased bone turnover, although the lower BMD in HCV is not explained by a high turnover state. Neither virus' effect on BMD is likely mediated through increased inflammation, liver fibrosis, IGF-1, or sex steroids.

In vitro proliferation and differentiation potential of bone marrow-derived mesenchymal stem cells from ovariectomized rats

Bone marrow-derived mesenchymal stem cells (BMMSCs) from the patients suffering from age-related osteoporosis were found to have numerous degeneration, such as decreased growth rate, impaired capacity of differentiating into local tissue, and repressed telomerase activity. However, it is not clear whether post-menopausal osteoporotic bone is either subject to such decline in cellular function. In the present study, bone marrow cells were harvested from ovariectomized (OVX) and Sham rats and cultured in vitro at 3 months post-surgery. MTT assay indicated that the proliferation potential of (OVX)BMMSCs was always higher than that of (Sham)BMMSCs, no matter cultured in basic, osteoblastic or adipogenic medium. Alkaline phosphatase activity assay, Alizarin red S staining, Oil red O staining and real-time RT-PCR analysis further demonstrated that bilateral ovariectomization positively influenced the osteoblastic and adipogenic differentiation potential of BMMSCs, this action may be partly mediated through up-regulation of osteoblastic special markers core binding factor a1, collagen type I and low-density lipoprotein receptor-related protein 5, as well as adipogenic special markers peroxisome proliferators activated receptor gamma, CCAAT/enhancer binding protein alpha and adipocyte lipid-binding protein 2. These results may hold great promise for using post-menopausal osteoporotic bone as an attractive autologous marrow source for tissue engineering and cell-based therapies.

Effects of total lignans from Eucommia ulmoides barks prevent bone loss in vivo and in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

The present study systematically investigate the in vivo and in vitro effect of total lignans (TL) extracted from Eucommia ulmoides Oliv. barks on bone formation using ovariectomy rat model and primary cultures of rat osteoblasts.

MATERIALS AND METHODS

Eighty 3-month-old female Sprague-Dawley rats were used and randomly assigned into sham-operated group (SHAM) and five ovariectomy (OVX) subgroups, i.e. OVX with vehicle (OVX); OVX with 17α-ethinylestradiol (E2, 25 μg/kg/day); OVX with TL of graded doses (20, 40, or 80 mg/kg/day). The treatment began 4 weeks after the surgery and lasted for 16 weeks. in vitro experiments were performed to determine the potential mechanisms of the anti-osteoporotic effect of TL.

RESULTS

Treatment with TL significantly prevent OVX-induced decrease in biomechanical quality of femur such as maximum stress and Young׳s modulus. The mechanical changes were associated with the prevention of a further BMD decrease or even with some improvements in microarchitecture. TL inhibited BMD decrease in the femur caused by OVX, which was accompanied by a significant decrease in skeletal remodeling, as was evidenced by the decreased levels of the bone turnover markers. μCT analysis of the femoral metaphysis showed how to prevent the deterioration of trabecular microarchitecture. TL induced primary osteoblastic cell proliferation and differentiation, inhibition of osteoclastogenesis through an increase in osteoprotegrin (OPG) and a decrease in NF-κB ligand (RANKL) expression in vitro.

CONCLUSIONS

We concluded that TL treatment can effectively suppress the loss of bone mass induced by OVX and in vitro evidence suggests this could be through actions on both osteoblasts and osteoclasts.

Nonviral Gene Delivery of Growth and Differentiation Factor 5 to Human Mesenchymal Stem Cells Injected into a 3D Bovine Intervertebral Disc Organ Culture System

Intervertebral disc (IVD) cell therapy with unconditioned 2D expanded mesenchymal stem cells (MSC) is a promising concept yet challenging to realize. Differentiation of MSCs by nonviral gene delivery of growth and differentiation factor 5 (GDF5) by electroporation mediated gene transfer could be an excellent source for cell transplantation. Human MSCs were harvested from bone marrow aspirate and GDF5 gene transfer was achieved by in vitro electroporation. Transfected cells were cultured as monolayers and as 3D cultures in 1.2% alginate bead culture. MSC expressed GDF5 efficiently for up to 21 days. The combination of GDF5 gene transfer and 3D culture in alginate showed an upregulation of aggrecan and SOX9, two markers for chondrogenesis, and KRT19 as a marker for discogenesis compared to untransfected cells. The cells encapsulated in alginate produced more proteoglycans expressed in GAG/DNA ratio. Furthermore, GDF5 transfected MCS injected into an IVD papain degeneration organ culture model showed a partial recovery of the GAG/DNA ratio after 7 days. In this study we demonstrate the potential of GDF5 transfected MSC as a promising approach for clinical translation for disc regeneration.

Gene silencing of chordin improves BMP-2 effects on osteogenic differentiation of human adipose tissue-derived stromal cells

Although bone morphogenic protein (BMP)-2 is known to potently induce osteogenic differentiation of human mesenchymal stem cells, strong individual differences have been reported. In part, this is due to internal antagonists of BMP-2 for example, noggin and chordin, secreted by differentiating cells. This enabling study was performed to prove the hypothesis that osteogenic effects of BMP-2 can be improved by transient nonviral gene silencing of chordin. We investigated the effect of siRNA against chordin on osteogenic differentiation in human adipose tissue-derived stromal cells (hASC). Cells of two different donors were isolated after liposuction and proliferated for passage 4 or 5. On seeding, hASCs were transfected with siRNA using a commercial liposomal transfection reagent. Subsequently, cells were differentiated in the presence or absence of BMP-2 (100 ng/mL). Noncoding siRNA as well as siRNA against noggin served as a control. Osteogenic differentiation of hASC was determined by alkaline phosphase (ALP) activity and matrix mineralization. ALP activity of hASC treated with siRNA against chordin was increased for cells of both donors. In contrast, silencing of noggin had no effect in any of the donors. In combination with BMP-2, silencing of either chordin or noggin showed strongly improved ALP activity compared with the control group that was also supplemented with BMP-2. Mineralization was observed to start earlier in groups that received siRNA against chordin or noggin and showed increased amounts of incorporated calcium on day 15 compared with the control groups. Silencing chordin in hASCs was successful to increase BMP-2 effects on osteogenic differentiation in both donors, while effects of noggin silencing were reliably observed only in one of the two investigated donors. In contrast to noggin silencing, chordin silencing also increased osteogenic differentiation without supplemented BMP-2.

Estrogen receptors' roles in the control of mechanically adaptive bone (re)modeling

The discovery that estrogen receptors (ERs) are involved in bone cells' responses to mechanical strain offered the prospect of establishing the link between declining levels of circulating estrogen and the progressive failure of the mechanically adaptive mechanisms that should maintain structurally appropriate levels of bone mass in age-related and post-menopausal osteoporosis. Such clarification remains elusive but studies have confirmed ligand-independent involvement of ERs as facilitators in a number of the pathways by which mechanical strain stimulates osteoblast proliferation and bone formation. The presence of α and β forms of ER that oppose, supplement or replace one another has complicated interpretation of studies to identify their individual roles when both are present in normal amounts. However, it appears that, in mice at least, ERα promotes cortical bone mass in both males and females through its effects in early members of the osteoblast lineage, but enhances loading-related cortical bone gain only in females. In addition to its role as a potential replacement for ERα, and modifier of ERα activity, the less well-studied ERβ appears to facilitate rapid early effects of strain including activation of extracellular signal-regulated kinase and downregulation of Sost in well-differentiated cells of the osteoblast lineage including osteocytes. If these different roles are substantiated by further studies, it would appear that under normal circumstances ERα contributes primarily to the size and extent of bones' osteogenic response to load bearing through facilitating anabolic influences in osteoblasts and osteoblast progenitors, whereas ERβ is more involved in the strain-related responses generated within resident cells including osteocytes.

Estrogen receptor α mediates proliferation of osteoblastic cells stimulated by estrogen and mechanical strain, but their acute down-regulation of the Wnt antagonist Sost is mediated by estrogen receptor β

Mechanical strain and estrogens both stimulate osteoblast proliferation through estrogen receptor (ER)-mediated effects, and both down-regulate the Wnt antagonist Sost/sclerostin. Here, we investigate the differential effects of ERα and -β in these processes in mouse long bone-derived osteoblastic cells and human Saos-2 cells. Recruitment to the cell cycle following strain or 17β-estradiol occurs within 30 min, as determined by Ki-67 staining, and is prevented by the ERα antagonist 1,3-bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1H-pyrazole dihydrochloride. ERβ inhibition with 4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-β]pyrimidin-3-yl] phenol (PTHPP) increases basal proliferation similarly to strain or estradiol. Both strain and estradiol down-regulate Sost expression, as does in vitro inhibition or in vivo deletion of ERα. The ERβ agonists 2,3-bis(4-hydroxyphenyl)-propionitrile and ERB041 also down-regulated Sost expression in vitro, whereas the ERα agonist 4,4′,4″-[4-propyl-(1H)-pyrazol-1,3,5-triyl]tris-phenol or the ERβ antagonist PTHPP has no effect. Tamoxifen, a nongenomic ERβ agonist, down-regulates Sost expression in vitro and in bones in vivo. Inhibition of both ERs with fulvestrant or selective antagonism of ERβ, but not ERα, prevents Sost down-regulation by strain or estradiol. Sost down-regulation by strain or ERβ activation is prevented by MEK/ERK blockade. Exogenous sclerostin has no effect on estradiol-induced proliferation but prevents that following strain. Thus, in osteoblastic cells the acute proliferative effects of both estradiol and strain are ERα-mediated. Basal Sost down-regulation follows decreased activity of ERα and increased activity of ERβ. Sost down-regulation by strain or increased estrogens is mediated by ERβ, not ERα. ER-targeting therapy may facilitate structurally appropriate bone formation by enhancing the distinct ligand-independent, strain-related contributions to proliferation of both ERα and ERβ.

Suppression of androgen receptor enhances the self-renewal of mesenchymal stem cells through elevated expression of EGFR

Bone marrow derived mesenchymal stem cells (BM-MSCs) have been widely applied in several clinical trials of diseases, such as myocardial infarction, liver cirrhosis, neurodegenerative disease, and osteogenesis imperfecta. Although most studies demonstrated that transplantation of BM-MSCs did exert a temporary relief and short-term therapeutic effects, eventually all symptoms recur, therefore it is essential to improve the therapeutic efficacy of transplantation by either elevating the self-renewal of BM-MSCs or enhancing their survival rate. Herein we demonstrated that the BM-MSCs and adipocyte derived mesenchymal stem cells (ADSCs) isolated from the androgen receptor (AR) knockout mice have higher self-renewal ability than those obtained from the wild-type mice. Knockdown of AR in MSC cell lines exhibited similar results. Mechanistic dissection studies showed that the depletion of AR resulted in activation of Erk and Akt signaling pathways through epidermal growth factor receptor (EGFR) activation or pathway to mediate higher self-renewal of BM-MSCs. Targeting AR signals using ASC-J9® (an AR degradation enhancer), hydroxyflutamide (antagonist of AR), and AR-siRNA all led to enhanced self-renewal of MSCs, suggesting the future possibility of using these anti-AR agents in therapeutic approaches.

Differential responsiveness to 17β-estradiol of mesenchymal stem cells from postmenopausal women between osteoporosis and osteoarthritis

Differential osteogenic potential and responsiveness to 17β-estradiol (E2) of mesenchymal stem cells (MSCs) were found between postmenopausal women with osteoporosis (OP) and osteoarthritis (OA). These results suggest differential biological mechanisms of estrogen deficiency in regulation of bone remodeling between OP and OA.

INTRODUCTION

OP and OA are two common disorders in postmenopausal women. The inverse relationship has been suggested between OP and OA, but their mechanisms that relate to estrogen deficiency are not fully understood. The aim of this study was to compare the differential responsiveness to E2 of MSCs from osteoporotic versus osteoarthritic donors.

METHODS

Twenty postmenopausal patients, ten with osteoporotic hip fractures and ten with hip osteoarthritis, were included into this study. MSCs were derived from cancellous bones of femoral heads from OA and OP donors and cultured in osteogenic and adipogenic medium with or without E2 added. The alkaline phosphatase (ALP) activity, calcium content, calcified nodules, lipid droplets, messenger RNA (mRNA) expression of ALP, osteocalcin (OC), collagen 1α (COL1α), peroxisome proliferators-activated receptor γ2 (PPARγ2) and lipoprotein lipase (LPL) were measured and compared between two groups with OP and OA.

RESULTS

In osteogenic medium, ALP activity, calcium content and mRNA expression of OC and COL1α in MSCs from OA were significantly higher than those from OP group. In adipogenic condition, there was no significant difference in lipid droplets formation and mRNA expression of PPARγ2 and LPL between OP and OA groups. With E2 added in osteogenic medium, ALP activity, calcium content and OC mRNA were significantly higher in OP group than in OA group, whereas E2 had no significant effect on lipid droplet formation and mRNA expression of PPARγ2 and LPL.

CONCLUSION

Differential osteogenic potential and responsiveness to E2 of MSCs were found between postmenopausal women with OP and OA. These results may provide information for clinical application of MSCs in the differential setting of estrogen deficiency.

Sp1 transcription factor interaction with accumulated prelamin a impairs adipose lineage differentiation in human mesenchymal stem cells: essential role of sp1 in the integrity of lipid vesicles

Lamin A (LMNA)-linked lipodystrophies may be either genetic (associated with LMNA mutations) or acquired (associated with the use of human immunodeficiency virus protease inhibitors [PIs]), and in both cases they share clinical features such as anomalous distribution of body fat or generalized loss of adipose tissue, metabolic alterations, and early cardiovascular complications. Both LMNA-linked lipodystrophies are characterized by the accumulation of the lamin A precursor prelamin A. The pathological mechanism by which prelamin A accumulation induces the lipodystrophy associated phenotypes remains unclear. Since the affected tissues in these disorders are of mesenchymal origin, we have generated an LMNA-linked experimental model using human mesenchymal stem cells treated with a PI, which recapitulates the phenotypes observed in patient biopsies. This model has been demonstrated to be a useful tool to unravel the pathological mechanism of the LMNA-linked lipodystrophies, providing an ideal system to identify potential targets to generate new therapies for drug discovery screening. We report for the first time that impaired adipogenesis is a consequence of the interaction between accumulated prelamin A and Sp1 transcription factor, sequestration of which results in altered extracellular matrix gene expression. In fact, our study shows a novel, essential, and finely tuned role for Sp1 in adipose lineage differentiation in human mesenchymal stem cells. These findings define a new physiological experimental model to elucidate the pathological mechanisms LMNA-linked lipodystrophies, creating new opportunities for research and treatment not only of LMNA-linked lipodystrophies but also of other adipogenesis-associated metabolic diseases.

Small molecule mesengenic induction of human induced pluripotent stem cells to generate mesenchymal stem/stromal cells

The translational potential of mesenchymal stem/stromal cells (MSCs) is limited by their rarity in somatic organs, heterogeneity, and need for harvest by invasive procedures. Induced pluripotent stem cells (iPSCs) could be an advantageous source of MSCs, but attempts to derive MSCs from pluripotent cells have required cumbersome or untranslatable techniques, such as coculture, physical manipulation, sorting, or viral transduction. We devised a single-step method to direct mesengenic differentiation of human embryonic stem cells (ESCs) and iPSCs using a small molecule inhibitor. First, epithelial-like monolayer cells were generated by culturing ESCs/iPSCs in serum-free medium containing the transforming growth factor-β pathway inhibitor SB431542. After 10 days, iPSCs showed upregulation of mesodermal genes (MSX2, NCAM, HOXA2) and downregulation of pluripotency genes (OCT4, LEFTY1/2). Differentiation was then completed by transferring cells into conventional MSC medium. The resultant development of MSC-like morphology was associated with increased expression of genes, reflecting epithelial-to-mesenchymal transition. Both ESC- and iPSC-derived MSCs exhibited a typical MSC immunophenotype, expressed high levels of vimentin and N-cadherin, and lacked expression of pluripotency markers at the protein level. Robust osteogenic and chondrogenic differentiation was induced in vitro in ES-MSCs and iPS-MSCs, whereas adipogenic differentiation was limited, as reported for primitive fetal MSCs and ES-MSCs derived by other methods. We conclude that treatment with SB431542 in two-dimensional cultures followed by culture-induced epithelial-to-mesenchymal transition leads to rapid and uniform MSC conversion of human pluripotent cells without the need for embryoid body formation or feeder cell coculture, providing a robust, clinically applicable, and efficient system for generating MSCs from human iPSCs.

Bone regeneration and stem cells

This invited review covers research areas of central importance for orthopaedic and maxillofacial bone tissue repair, including normal fracture healing and healing problems, biomaterial scaffolds for tissue engineering, mesenchymal and foetal stem cells, effects of sex steroids on mesenchymal stem cells, use of platelet-rich plasma for tissue repair, osteogenesis and its molecular markers. A variety of cells in addition to stem cells, as well as advances in materials science to meet specific requirements for bone and soft tissue regeneration by addition of bioactive molecules, are discussed.

A human iPSC model of Hutchinson Gilford Progeria reveals vascular smooth muscle and mesenchymal stem cell defects

The segmental premature aging disease Hutchinson-Gilford Progeria syndrome (HGPS) is caused by a truncated and farnesylated form of Lamin A called progerin. HGPS affects mesenchymal lineages, including the skeletal system, dermis, and vascular smooth muscle (VSMC). To understand the underlying molecular pathology of HGPS, we derived induced pluripotent stem cells (iPSCs) from HGPS dermal fibroblasts. The iPSCs were differentiated into neural progenitors, endothelial cells, fibroblasts, VSMCs, and mesenchymal stem cells (MSCs). Progerin levels were highest in MSCs, VSMCs, and fibroblasts, in that order, with these lineages displaying increased DNA damage, nuclear abnormalities, and HGPS-VSMC accumulating numerous calponin-staining inclusion bodies. Both HGPS-MSC and -VSMC viability was compromised by stress and hypoxia in vitro and in vivo (MSC). Because MSCs reside in low oxygen niches in vivo, we propose that, in HGPS, this causes additional depletion of the MSC pool responsible for replacing differentiated cells lost to progerin toxicity.

Common variations in estrogen-related genes are associated with severe large-joint osteoarthritis: a multicenter genetic and functional study

OBJECTIVE

Several lines of evidence suggest that estrogens influence the development of osteoarthritis (OA). The aim of this study was to explore the association of two common polymorphisms within the aromatase (CYP19A1) and estrogen receptor (ER) alpha (ESR1) genes with severe OA of the lower limbs.

METHODS

The rs1062033 (CYP19A1) and rs2234693 (ESR1) single nucleotide polymorphisms were genotyped in 5528 individuals (3147 patients with severe hip or knee OA, and 2381 controls) from four centres in Spain and the United Kingdom. Gene expression was measured in femoral bone samples from a group of patients.

RESULTS

In the global analysis, both polymorphisms were associated with OA, but there was a significant sex interaction. The GG genotype at rs1062033 was associated with an increased risk of knee OA in women [odds ratio (OR) 1.23; P=0.04]. The CC genotype at rs2234693 tended to be associated with reduced OA risk in women (OR 0.76, P=0.028, for knee OA; OR=0.84, P=0.076 for hip OA), but with increased risk of hip OA in men (OR 1.28; P=0.029). Women with unfavourable genotypes at both loci had an OR of 1.61 for knee OA (P=0.006). The rs1062033 genotype associated with higher OA risk was also associated with reduced expression of the aromatase gene in bone.

CONCLUSIONS

Common genetic variations of the aromatase and ER genes are associated with the risk of severe OA of the large joints of the lower limb in a sex-specific manner. These results are consistent with the hypothesis that estrogen activity may influence the development of large-joint OA.

The Src inhibitor dasatinib accelerates the differentiation of human bone marrow-derived mesenchymal stromal cells into osteoblasts

Background

The proto-oncogene Src is an important non-receptor protein tyrosine kinase involved in signaling pathways that control cell adhesion, growth, migration and differentiation. It negatively regulates osteoblast activity, and, as such, its inhibition is a potential means to prevent bone loss. Dasatinib is a new dual Src/Bcr-Abl tyrosine kinase inhibitor initially developed for the treatment of chronic myeloid leukemia. It has also shown promising results in preclinical studies in various solid tumors. However, its effects on the differentiation of human osteoblasts have never been examined.

Methods

We evaluated the effects of dasatinib on bone marrow-derived mesenchymal stromal cells (MSC) differentiation into osteoblasts, in the presence or absence of a mixture of dexamethasone, ascorbic acid and β-glycerophosphate (DAG) for up to 21 days. The differentiation kinetics was assessed by evaluating mineralization of the extracellular matrix, alkaline phosphatase (ALP) activity, and expression of osteoblastic markers (receptor activator of nuclear factor kappa B ligand [RANKL], bone sialoprotein [BSP], osteopontin [OPN]).

Results

Dasatinib significantly increased the activity of ALP and the level of calcium deposition in MSC cultured with DAG after, respectively, 7 and 14 days; it upregulated the expression of BSP and OPN genes independently of DAG; and it markedly downregulated the expression of RANKL gene and protein (decrease in RANKL/OPG ratio), the key factor that stimulates osteoclast differentiation and activity.

Conclusions

Our results suggest a dual role for dasatinib in both (i) stimulating osteoblast differentiation leading to a direct increase in bone formation, and (ii) downregulating RANKL synthesis by osteoblasts leading to an indirect inhibition of osteoclastogenesis. Thus, dasatinib is a potentially interesting candidate drug for the treatment of osteolysis through its dual effect on bone metabolism.

ERRalpha regulates osteoblastic and adipogenic differentiation of mouse bone marrow mesenchymal stem cells

The orphan nuclear receptor estrogen-related receptor-alpha (ERRalpha) has been reported to have both a positive and a negative regulatory role in osteoblastic and adipocytic differentiation. We have studied the role of ERRalpha in osteoblastic and adipogenic differentiation of mesenchymal stem cells. Bone marrow mesenchymal stem cells were isolated from ERRalpha deficient mice and their differentiation capacities were compared to that of the wild-type cells. ERRalpha deficient cultures displayed reduced cellular proliferation, osteoblastic differentiation, and mineralization. In the complementary experiment, overexpression of ERRalpha in MC3T3-E1 cells increased the expression of osteoblastic markers and mineralization. Alterations in the expression of bone sialoprotein (BSP) may at least partially explain the effects on mineralization as BSP expression was reduced in ERRalpha deficient MSCs and enhanced upon ERRalpha overexpression in MC3T3-E1 cells. Furthermore, a luciferase reporter construct driven by the BSP promoter was efficiently transactivated by ERRalpha. Under adipogenic conditions, ERRalpha deficient cultures displayed reduced adipocytic differentiation. Our data thus propose a positive role for ERRalpha in osteoblastic and adipocytic differentiation. The variability in the results yielded in the different studies implies that ERRalpha may play different roles in bone under different physiological conditions.

Sex differences of chondrogenic progenitor cells in late stages of osteoarthritis

OBJECTIVE

Osteoarthritis (OA), a mainly degenerative disease, is known to be multifactorial in origin. Gene expression patterns vary between populations and sexes. Sex hormone receptors have been described in the cartilage tissue of animals and humans. We undertook this study to determine whether the regenerative potential of chondrogenic progenitor cells (CPCs) present in the arthritic tissue during the late stages of human OA might also be subject to sex-specific differences and influenced by sex steroids.

METHODS

We analyzed sex-specific differences in the regenerative potential of CPCs and the involvement of sex hormones in vitro in cartilage samples from patients with late-stage knee OA, using electrochemiluminescence immunoassay, microarray analysis, real-time reverse transcription-polymerase chain reaction, immunohistochemistry, Western blot analysis, fluorescence-activated cell sorting, and cell culture.

RESULTS

We detected expression of estrogen and testosterone in the OA synovial fluid as well as CPCs positive for estrogen receptor alpha (ERalpha), ERbeta, and androgen receptor. Both hormones influenced the expression of all 3 receptor genes as well as the chondrogenic potential of CPCs by regulating gene expression of Sox9, Runx2, type II collagen, and type I collagen. We found regulatory effects on the collagens via Sox9 and Runx2 as well as regulatory effects independent of these transcription factors. These effects were sex-specific and relied on hormone concentrations.

CONCLUSION

Physiologic concentrations of testosterone in men and premenopausal concentrations of estrogen in women have a positive effect on the chondrogenic potential of CPCs in vitro. Therefore, strategies of hormone replacement in the synovial fluid of women and men might have beneficial effects on the regenerative potential of arthritic cartilage tissue in late stages of human OA.

Metformin regulates osteoblast and adipocyte differentiation of rat mesenchymal stem cells

Metformin is widely used for the treatment of type 2 diabetes mellitus. In this study, we evaluated the effects of metformin on the osteoblast and adipocyte differentiation of rat marrow mesenchymal stem cells (MSCs) in culture. Treatment of MSCs in osteoblastic or adipogenic medium with 100 μM metformin for 21 days led to an increased mRNA expression of the osteoblast markers but a decreased mRNA expression of the adipocyte markers in the MSCs. Metformin markedly stimulated deposition of mineralized nodules and blocked the formation of cytoplasmic lipid droplets. In addition, alkaline phosphate activity and Western blot analysis for core binding factor a1 (Cbfa 1) and peroxisome proliferator-activated receptor gamma 2 (PPARγ2) proteins also confirmed that metformin inhibited adipocyte differentiation and promoted osteoblast differentiation. The reciprocal relationship between osteoblastic and adipogenic differentiation suggests that metformin may regulate osteoblastic and adipogenic differentiation through inhibition of PPARγ.

Putative heterotopic ossification progenitor cells derived from traumatized muscle

Heterotopic ossification (HO) is a frequent complication following combat-related trauma, but the pathogenesis of traumatic HO is poorly understood. Building on our recent identification of mesenchymal progenitor cells (MPCs) in traumatically injured muscle, the goal of this study was to evaluate the osteogenic potential of the MPCs in order to assess the role of these cells in HO formation. Compared to bone marrow-derived mesenchymal stem cells (MSCs), a well-characterized population of osteoprogenitor cells, the MPCs exhibited several significant differences during osteogenic differentiation and in the expression of genes related to osteogenesis. Upon osteogenic induction, MPCs showed increased alkaline phosphatase activity, production of a mineralized matrix, and up-regulated expression of the osteoblast-associated genes CBFA1 and alkaline phosphatase. However, MPCs did not appear to reach terminal differentiation as the expression of osteocalcin was not substantially up-regulated. With the exception of a few genes, the osteogenic gene expression profile of traumatized muscle-derived MPCs was comparable to that of the MSCs after osteogenic induction. These findings indicate that traumatized muscle-derived MPCs have the potential to function as osteoprogenitor cells when exposed to the appropriate biochemical environment and are the putative osteoprogenitor cells that initiate ectopic bone formation in HO.

Signal transducer and activator of transcription 3-stimulated hypoxia inducible factor-1alpha mediates estrogen receptor-alpha-induced mesenchymal stem cell vascular endothelial growth factor production

OBJECTIVE

Vascular endothelial growth factor, a critical factor in angiogenesis, mediates stem cell paracrine protective effects on ischemic myocardium. Studies on the role of sex in stem cell function have demonstrated that female mesenchymal stem cells produce greater vascular endothelial growth factor and provide better cardiac protection compared with male mesenchymal stem cells. The purpose of this study was to determine the mechanisms by which estrogen affects mesenchymal stem cell function as a potential therapeutic measure during ex vivo expansion, before therapeutic use.

METHODS

A single-step purification method using adhesion to cell culture plastic was adopted to isolate mesenchymal stem cells from wild-type, estrogen receptor-alpha knockout, estrogen receptor-beta knockout, and signal transducer and activator of transcription 3 knockout mice. Mesenchymal stem cells were treated with or without 17beta-estradiol, estrogen receptor-alpha agonist (propyl pyrazoletriol), and estrogen receptor-beta agonist (diarylpropionitrile).

RESULTS

17beta-estradiol significantly increased mesenchymal stem cell vascular endothelial growth factor production in a dose-dependent manner. Both estrogen receptor-alpha and estrogen receptor-beta were expressed in mesenchymal stem cells. Administration of 17beta-estradiol or estrogen receptor-alpha agonist (not estrogen receptor-beta agonist) elevated mesenchymal stem cell vascular endothelial growth factor, hypoxia inducible factor-1alpha expression, and signal transducer and activator of transcription 3 activation. However, these effects were neutralized in estrogen receptor-alpha knockout mesenchymal stem cells, not estrogen receptor-beta knockout. Signal transducer and activator of transcription 3 knockout abolished estrogen receptor-alpha-induced hypoxia inducible factor-1alpha and subsequent vascular endothelial growth factor production.

CONCLUSION

17beta-estradiol-induced vascular endothelial growth factor production from mesenchymal stem cells appears to be mediated through estrogen receptor-alpha-activated signal transducer and activator of transcription 3-mediated hypoxia inducible factor-1alpha expression.

Intracrine androgenic apparatus in human bone marrow stromal cells

It was suggested that human mesenchymal stromal cells might contain an intracrine enzyme machinery potentially able to synthesize the cell’s own supply of dihydrotestosterone (DHT) from dehydroepiandrosterone (DHEA) pro-hormone produced in the adrenal cortex in the reticular zone, which is unique to primates. Indeed, 3β-hydroxysteroid dehydrogenase (3β-HSD) and 5α-reductase enzyme proteins were expressed in resting mesenchymal stromal cells (MSCs) in vitro. However, the ‘bridging’ enzymes 17β-HSDs, catalysing interconversion between 17β-ketosteroids and 17β-hydroxysteroids, were not found in resting MSCs, but 17β-HSD enzyme protein was induced in a dose-dependent manner by DHEA. Quantitative real-time polymerase chain reactions disclosed that this was mainly due to induction of the isoform 5 catalysing this reaction in ‘forward’, androgen-bound direction (P < 0.01). This work demonstrates that the MSCs have an intracrine machinery to convert DHEA to DHT if and when challenged by DHEA. DHEA as substrate exerts a positive, feed-forward up-regulation on the 17β-hydroxy steroid dehydrogenase-5, which may imply that DHEA-DHT tailor-making in MSCs is subjected to chronobiological regulation.

Sex steroids and stem cell function

Gender dimorphisms exist in the pathogenesis of a variety of cardiovascular, cardiopulmonary, neurodegenerative, and endocrine disorders. Estrogens exert immense influence on myocardial remodeling following ischemic insult, partially through paracrine growth hormone production by bone marrow mesenchymal stem cells (MSCs) and endothelial progenitor cells. Estrogens also facilitate the mobilization of endothelial progenitor cells to the ischemic myocardium and enhance neovascularization at the ischemic border zone. Moreover, estrogens limit pathological myocardial remodeling through the inhibitory effects on the proliferation of the cardiac fibroblasts. Androgens also may stimulate endothelial progenitor cell migration from the bone marrow, yet the larger role of androgens in disease pathogenesis is not well characterized. The beneficial effects of sex steroids include alteration of lipid metabolism in preadipocytes, modulation of bone metabolism and skeletal maturation, and prevention of osteoporosis through their effects on osteogenic precursors. In an example of sex steroid-specific effects, neural stem cells exhibit enhanced proliferation in response to estrogens, whereas androgens mediate inhibitory effects on their proliferation. Although stem cells can offer significant therapeutic benefits in various cardiovascular, neurodegenerative, endocrine disorders, and disorders of bone metabolism, a greater understanding of sex hormones on diverse stem cell populations is required to improve their ultimate clinical efficacy. In this review, we focus on the effects of estrogen and testosterone on various stem and progenitor cell types, and their relevant intracellular mechanisms.

Simvastatin induces estrogen receptor-alpha (ER-alpha) in murine bone marrow stromal cells

Simvastatin has been shown to stimulate osteogenesis both in vitro and in vivo. However, the mechanism by which simvastatin exerts its effects is still unclear. We previously reported that simvastatin promotes bone morphogenetic protein 2 (BMP-2) expression, induces osteoblastic differentiation, and inhibits adipocytic differentiation in mouse bone marrow stromal cells (BMSCs), and that this occurs, at least in part, via a BMP-2-dependent pathway. The aim of this study was to investigate further the mechanisms by which simvastatin stimulates osteogenesis in mouse BMSCs. To determine whether simvastatin-mediated osteogenesis was dependent on BMP-2, mouse BMSCs were treated with nonimmune normal mouse IgG or BMP-2 neutralizing antibodies combined with different concentrations of simvastatin. Surprisingly, the stimulatory effect of simvastatin on alkaline phosphatase (ALP) activity was not completely blocked by neutralizing BMP-2 monoclonal antibody treatment. Interestingly, we found that estrogen receptor-alpha (ER-alpha) protein levels increased after mouse BMSCs were treated with simvastatin for 72 h in a concentration-dependent manner. Moreover, the stimulatory effect of simvastatin on ALP activity in BMSCs was blocked by the estrogen receptor agonist ICI 182,780, and cotreatment with 17-beta-estradiol and simvastatin increased ALP activities by two-to threefold in the BMSCs compared with treatment with simvastatin alone. These results suggest that simvastatin-induced in vitro osteogenesis in mouse BMSCs is mediated, at least in part, by induction of ER-alpha and not by BMP-2 alone. These results provide new insight into the mechanisms of simvastatin-induced bone formation in BMSCs.

Undifferentiated human mesenchymal stem cells (hMSCs) are highly sensitive to mechanical strain: transcriptionally controlled early osteo-chondrogenic response in vitro

OBJECTIVE

Physical cues play a crucial role in skeletogenesis and osteochondral regeneration. Although human mesenchymal stem cells (hMSCs) offer considerable therapeutic potential, little is known about the molecular mechanisms that control their differentiation. We hypothesized that mechanical strain might be an inherent stimulus for chondrogenic and/or osteogenic differentiation in undifferentiated hMSCs, where c-Fos (FOS) might play a major role in mechanotransduction.

METHOD

hMSCs from 10 donors were intermittently stimulated by cyclic tensile strain (CTS) at 3000 mustrain for a period of 3 days. Differential gene expression of strained and unstrained hMSCs was analysed by real-time RT-PCR for several marker genes, including the transcription factors FOS, RUNX2, SOX9, and others. Additionally, alkaline phosphatase activity (ALP) was determined kinetically.

RESULTS

The application of CTS significantly stimulated the expression levels of the early chondrogenic and osteogenic marker genes (SOX9, LUM, DCN; RUNX2, SPARC, SPP1, ALPL); this was accompanied by stimulation of ALP activity (+38%+/-12 standard error of mean, P<0.05). Matrix analysis revealed that the osteo-chondrogenic response followed a coordinated expression pattern, in which FOS was attributed to early osteogenic but not chondrogenic differentiation.

CONCLUSION

Undifferentiated hMSCs are highly sensitive to mechanical strain with a transcriptionally controlled osteo-chondrogenic differentiation response in vitro.

In the adult mesenchymal stem cell population, source gender is a biologically relevant aspect of protective power

BACKGROUND

Acute treatment with bone marrow mesenchymal stem cells (MSC) reduces myocardial infarct size by multiple mechanisms, including the paracrine release of protective growth factors. Female MSCs produce more growth factor when stressed; therefore, we hypothesized that myocardial protection provoked by female MSCs would be greater than that elicited by male MSCs.

METHODS

Hearts were subjected to 25 min of warm global ischemia, 40 min of reperfusion, and randomly assigned into one of three groups: (1) vehicle treated; (2) male MSC treated; and (3) female MSC treated. Myocardial function was continuously recorded and in separate experiments, male and female MSC growth factor production was assessed by ELISA.

RESULTS

All indices of functional recovery were significantly higher in the stem cell infused rat heart compared with control hearts. Interestingly, female MSC treated rat hearts demonstrated significantly greater recovery of left ventricular developed pressure, +dP/dT, and -dP/dT than male MSC treated hearts at end reperfusion. In addition, male MSCs produced significantly greater tumor necrosis factor alpha, and significantly less vascular endothelial growth factor than female MSCs.

CONCLUSIONS

This study is the first to demonstrate that, in the adult mesenchymal population, source gender is a biologically relevant aspect of ultimate stem cell function in the heart.

Estrogen receptor alpha genotype is associated with a reduced prevalence of radiographic hip osteoarthritis in elderly Caucasian women

PURPOSE

This study evaluated the association between polymorphisms in the estrogen receptor (ER) alpha gene (ESR1) and prevalent and incident radiographic hip osteoarthritis (RHOA) in a large, well-defined prospective cohort of elderly Caucasian women.

METHODS

Prevalent and incident RHOA was evaluated from all available pelvis X-rays obtained from the Study of Osteoporotic Fractures at baseline and after a mean of 8.3 years. Evaluable DNA samples were available from 4746 of these subjects. RHOA cases were defined by published methods. The ESR1 polymorphisms at intron I (Pvu II for a T/C substitution and Xba I for an A/G substitution) were genotyped in the context of a multiplex polymerase chain reaction (PCR) amplification followed by allele-specific single nucleotide polymorphism (SNP) detection with immobilized oligonucleotide probes in linear arrays. Multiple logistic regression was performed to estimate odds ratios (ORs) and 95% confidence intervals (95% CI) associated with the T/C and A/G polymorphisms.

RESULTS

RHOA was present in 12.1% of subjects, of whom 325 had joint space narrowing (JSN) score > or =3 and 130 had an osteophyte score > or =2 and JSN score > or =2. There was a significant reduction in the odds of prevalent RHOA for individuals with the C/C compared to T/T genotype at the Pvu II site with an OR of 0.71 (95% CI: 0.55-0.92) (P=0.01). Adjustments for age, weight, height, hip Bone mineral density (BMD) and estrogen use did not alter the relationship between the C/C genotype and reduced risk of RHOA, with an OR of 0.71 (95% CI: 0.54-0.94) (P=0.01). The risk of incident RHOA was reduced for the Pvu II C/C compared to the T/T genotype (P=0.11). Also, the reduced risk of incident RHOA in C/C subjects varied by estrogen use. There was no association between the Xba I G/G or G/A genotypes and RHOA with OR of 0.82 (95% CI: 0.61-1.10) (P=0.19) compared to women with A/A genotype.

CONCLUSIONS

We conclude that the C/C genotype of the ER alpha Pvu II polymorphism was associated with a modestly reduced risk of prevalent and incident RHOA in elderly Caucasian women. Additional work is required to understand how the intron I ESR1 polymorphism may alter joint degeneration.

Gender differences in injury induced mesenchymal stem cell apoptosis and VEGF, TNF, IL-6 expression: role of the 55 kDa TNF receptor (TNFR1)

Concomitant pro- and anti-inflammatory properties of bone marrow stem cells (BMSC) may be an important aspect of their ability to heal injured tissue. However, very few studies have examined whether gender differences exist in BMSC function. Indeed, it remains unknown whether gender differences exist in BMSC function and ability to resist apoptosis, and if so, whether TNF receptor 1 (TNFR1) plays a role in these differences. We hypothesized that TNFR1 ablation equalizes gender differences in bone marrow mesenchymal stem cell (MSC) apoptosis, as well as expression of vascular endothelial growth factor (VEGF), TNF and interleukin (IL)-6. Mouse MSCs from male wild type (WT), female WT, male TNFR1 knockouts (TNFR1KO) and female TNFR1KO were stressed by endotoxin 200 ng/ml or 1 h hypoxia. MSC activation was determined by measuring VEGF, TNF and IL-6 production (ELISA). Differences considered significant if p<0.05. LPS and hypoxia resulted in significant activation in all experimental groups compared to controls. Male WT demonstrated significantly greater TNF and IL-6 and significantly less VEGF release than female WT MSCs. However, release of TNF, IL-6 and VEGF in male TNFR1 knockouts differed from male WT, but was not different from female WT MSCs. Similarly apoptosis in hypoxic male TNFRIKO differed from male WT, but it was not different from apoptosis from WT female. Female WT did not differ in TNF, IL-6 and VEGF release compared to female TNFR1KO. Gender differences exist in injury induced BMSC VEGF, TNF and IL-6 expression. TNFR1 may autoregulate VEGF, TNF and IL-6 expression in males more than females. MSCs are novel therapeutic agents for organ protection, but further study of the disparate expression of VEGF, TNF and IL-6 in males and females as well as the role of TNFR1 in these gender differences is necessary to maximize this protection.