Effects of estrogen on diverse stem cells and relevant intracellular mechanisms

Estrogen Signaling Dictates Musculoskeletal Stem Cell Behavior: Sex Differences in Tissue Repair

Sexual dimorphisms in humans and other species exist in visually evident features such as body size and less apparent characteristics, including disease prevalence. Current research is adding to a growing understanding of sex differences in stem cell function and response to external stimuli, including sex hormones such as estrogens. These differences are proving significant and directly impact both the understanding of stem cell processes in tissue repair and the clinical implementation of stem cell therapies. Adult stem cells of the musculoskeletal system, including those used for development and repair of muscle, bone, cartilage, fibrocartilage, ligaments, and tendons, are no exception. Both in vitro and in vivo studies have found differences in stem cell number, proliferative and differentiation capabilities, and response to estrogen treatment between males and females of many species. Maintaining the stemness and reducing senescence of adult stem cells is an important topic with implications in regenerative therapy and aging. As such, this review discusses the effect of estrogens on musculoskeletal system stem cell response in multiple species and highlights the research gaps that still need to be addressed. The following evidence from investigations of sex-related phenotypes in adult progenitor and stem cells are pieces to the big puzzle of sex-related effects on aging and disease and critical information for both fundamental tissue repair and regeneration studies and safe and effective clinical use of stem cells. Impact Statement This review summarizes current knowledge of sex differences in and the effects of estrogen treatment on musculoskeletal stem cells in the context of tissue engineering. Specifically, it highlights the impact of sex on musculoskeletal stem cell function and ability to regenerate tissue. Furthermore, it discusses the varying effects of estrogen on stem cell properties, including proliferation and differentiation, important to tissue engineering. This review aims to highlight the potential impact of estrogens and the importance of performing sex comparative studies in the field of tissue engineering.

Sex-Related Effects on Cardiac Development and Disease

Cardiovascular diseases (CVD) are the leading cause of morbidity and mortality. Interestingly, male and female patients with CVD exhibit distinct epidemiological and pathophysiological characteristics, implying a potentially important role for primary and secondary sex determination factors in heart development, aging, disease and therapeutic responses. Here, we provide a concise review of the field and discuss current gaps in knowledge as a step towards elucidating the “sex determination–heart axis”. We specifically focus on cardiovascular manifestations of abnormal sex determination in humans, such as in Turner and Klinefelter syndromes, as well as on the differences in cardiac regenerative potential between species with plastic and non-plastic sexual phenotypes. Sex-biased cardiac repair mechanisms are also discussed with a focus on the role of the steroid hormone 17β-estradiol. Understanding the “sex determination–heart axis” may offer new therapeutic possibilities for enhanced cardiac regeneration and/or repair post-injury.

Estrogen is required for maintaining the quality of cardiac stem cells

Compared to the age-matched men, the incidence of cardiovascular diseases is lower in premenopausal but higher in postmenopausal women, suggesting the cardio-protective role of estrogen in females. Although cardiac stem cells (CSCs) express estrogen receptors, yet the effects of estrogen on CSCs remain unclear. In this study, we investigated the potential role of estrogen in maintaining the quality of CSCs by in vivo and in vitro experiments. For the in vivo study, estrogen deficiency was induced by ovariectomy in 6-weeks-old C57BL/6 female mice, and then randomly given 17β-estradiol (E₂) replacements at a low dose (0.01 mg/60 days) and high dose (0.18 mg/60 days), or vehicle treatment. All mice were killed 2 months after treatments, and heart tissues were collected for ex vivo expansion of CSCs. Compared to age-matched healthy controls, estrogen deficiency slightly decreased the yield of CSCs with significantly lower telomerase activity and more DNA damage. Interestingly, E₂ replacements at low and high doses significantly increased the yield of CSCs and reversed the quality impairment of CSCs following estrogen deficiency. For the in vitro study, twice-passaged CSCs from the hearts of adult healthy female mice were cultured with the supplement of 0.01, 0.1, and 1 μM E₂ in the medium for 3 days. We found that E₂ supplement increased c-kit expression, increased proliferative activity, improved telomerase activity, and reduced DNA damage of CSCs in a dose-dependent manner. Our data suggested the potential role of estrogen in maintaining the quality of CSCs, providing new insight into the cardio-protective effects of estrogen.

Protective Effects of Punicalagin on Osteoporosis by Inhibiting Osteoclastogenesis and Inflammation via the NF-κB and MAPK Pathways

Postmenopausal osteoporosis is a worldwide disease characterized by reduced bone mineral density and increased fracture risk. Inflammatory bone loss due to excessive osteoclast bone resorption is significant in the pathogenesis and development of osteoporosis. Punicalagin (PUN) is a pomegranate fruit derivative and has potential anti-inflammatory effects. However, the effect of PUN on osteoporotic bone loss has yet to be clarified. In this study, we investigated the effect of PUN on RANKL-induced osteoclast formation and bone resorption in vitro, as well as its potential therapeutic effect on ovariectomized-induced bone loss in vivo. PUN was demonstrated to suppress osteoclast formation and bone resorptive function dose-dependently, while osteoclast-specific genes were also downregulated by PUN. In vivo micro-CT and histopathological staining showed that the OVX procedure led to significant bone loss characterized by decreased bone parameters and increased osteoclast numbers, while PUN treatment dramatically prevented these changes. Furthermore, PUN treatment effectively inhibited proinflammatory cytokine expression in vitro. Mechanistically, PUN maintained bone mass via suppressing nuclear factor κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathway activation. Collectively, our observations provide evidence that PUN is a potential candidate for the treatment of osteoporosis.

Effects of estrogen on growth and smooth muscle differentiation of vascular wall-resident CD34(+) stem/progenitor cells

OBJECTIVES

To investigate the effects of estrogen on growth and smooth muscle cell (SMC)-differentiation of vascular wall-resident CD34(+) stem/progenitor cells (VRS/Pcs).

METHODS AND RESULTS

The existence of CD34(+) VRS/Pcs was confirmed by immunohistochemistry in the adventitia of arteries of young (2-month-old) and old (24-month-old) female SD rats with less CD34(+) adventitial cells detected in the old. The VRS/Pcs isolated from young animals were grown in Stem cell growth medium or induced to differentiate into SMC with PDGF-BB in the presence or absence of 17β-estrodiol (E2). Flow cytometry, RT-qPCR and Western blot showed that E2 promoted Brdu incorporation of the CD34(+) VRS/Pcs growing in Stem cell growth medium; but when the cells were incubated in PDGF-BB, the hormone enhanced their expression of SMC marker SM22. ChIP and IP assays showed that E2 significantly promoted the binding of pELK1-SRF complex to the promoter of c-fos gene in CD34(+) VRS/Pcs growing in the Stem cell growth medium; but when the cells were stimulated with PDGF-BB, an E2-enhanced binding of myocardin-SRF to the promoter of SM22 gene was found with enhanced expression of SRC3 and its binding to myocardin. The effects of E2 above could be blocked by the estrogen receptor antagonist ICI 182,780 or inhibited by SRF-siRNA.

CONCLUSION

Estrogen has dual effects on CD34(+) VRS/Pcs. For the undifferentiated VRS/Pcs, it accelerates their proliferation by enhancing binding of pELK1-SRF complex to c-fos gene; while for the differentiating VRS/Pcs, it promotes their differentiation to SMC through a mechanism of SRC3-mediated interaction of myocardin-SRF complex with SM22 gene.

Sex differences in estrogen receptor promoter expression in the area postrema

Estrogen receptor α is widely distributed in the rat brain, but the tissue- or target-specificity of the estrogen receptor α gene promoters remains unknown. In the present study, we used transgenic rats expressing enhanced green fluorescent protein under the control of the estrogen receptor α 0/B promoter to examine expression driven by this promoter in two significant nuclei that regulate cardiovascular activity, the area postrema and the nucleus tractus solitarius. Immunohistochemistry showed that enhanced green fluorescent protein-labeled cells were distributed in the area postrema and the nucleus tractus solitarius of both female and male transgenic rats, and a neural network of enhanced green fluorescent protein-positive fibers was seen between the area postrema and the nucleus tractus solitarius. The number of enhanced green fluorescent protein-labeled cells in the area postrema of female rats was significantly higher than in the males, but no significant difference was found in the number of enhanced green fluorescent protein-labeled cells in the nucleus tractus solitarius. The sex differences in the number of enhanced green fluorescent protein-labeled cells in the area postrema was not affected after ovariectomy or 17β-estradiol benzoate treatment in adult rats. Our results suggest that the effects of estrogen in the area postrema are related to the expression of estrogen receptor α under the control of the 0/B promoter, and changes in the sex hormone environment in the adult period do not affect estrogen receptor α expression in the area postrema or the nucleus tractus solitarius.

The effect of estrogen compounds on human embryoid bodies

Human embryonic stem cells are derived from the inner cell mass of preimplantation embryo at the blastocyst stage and their differentiation occurs through an intermediate step involving the formation of embryoid bodies (EBs), which are aggregates of embryonic stem cells. The EBs seem to be a powerful tool for investigating the development of embryos, as they can mimic the initial stages of embryonic development. In this study, we aimed to investigate the effect of estrogen compounds on the proliferation and differentiation of short-term and long-term cultured EBs in vitro. For this study, 10-day-old (short-term cultured) and 30-day-old (long-term cultured) EBs were subjected to estradiol (E2), estriol (E3), selective estrogen receptor modulator (raloxifene [RLX]), bisphenol A, and 1,3,5-tris(4-hydroxyphenyl)-4-propyl-1H-pyrazole for 7 days. To confirm the effects of estrogen treatment, ICI-182780 was added to the respective EBs for additional 7 days following estrogen treatment. Quantitative reverse transcription-polymerase chain reaction was performed to analyze the relative expression of differentiation marker genes representing the 3 germ layers. The expression of 7 marker genes, which included α-fetoprotein, hepatocyte nuclear factor (HNF)-3β, HNF-4α (endoderm), brachyury, cardiac actin ([cACT]; mesoderm), nestin (ectoderm), and Oct-4 (undifferentiated), was measured. Significantly, lower expression of HNF-4α in both short-term and long-term cultured EBs was observed after treatment of estrogen compounds compared to control. The expression of HNF-3β in short-term cultured EBs has been positively affected by E2, E3, and RLX. Regarding cACT, higher expression was observed after treatment of E2 (10(-7) mol/L) and E3 (10(-9) mol/L) in short-term cultured EBs, but opposite effects were demonstrated in long-term cultured EBs. The lower expressions of HNF-4α by E2 and RLX were negated by ICI-182780 treatment, although these findings were not statistically significant in E3-treated group. These findings suggest that estrogen compounds have effects on endodermal and mesodermal differentiation of human EBs.

Repair mechanisms of bone marrow mesenchymal stem cells in myocardial infarction

The prognosis of patients with myocardial infarction (MI) and resultant chronic heart failure remains extremely poor despite advances in optimal medical therapy and interventional procedures. Animal experiments and clinical trials using adult stem cell therapy following MI have shown a global improvement of myocardial function. Bone marrow-derived mesenchymal stem cells (MSCs) hold promise for cardiac repair following MI, due to their multilineage, self-renewal and proliferation potential. In addition, MSCs can be easily isolated, expanded in culture, and have immunoprivileged properties to the host tissue. Experimental studies and clinical trials have revealed that MSCs not only differentiate into cardiomyocytes and vascular cells, but also secrete amounts of growth factors and cytokines which may mediate endogenous regeneration via activation of resident cardiac stem cells and other stem cells, as well as induce neovascularization, anti-inflammation, anti-apoptosis, anti-remodelling and cardiac contractility in a paracrine manner. It has also been postulated that the anti-arrhythmic and cardiac nerve sprouting potential of MSCs may contribute to their beneficial effects in cardiac repair. Most molecular and cellular mechanisms involved in the MSC-based therapy after MI are still unclear at present. This article reviews the potential repair mechanisms of MSCs in the setting of MI.