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.     

Rac1 drives intestinal stem cell proliferation and regeneration

Adult stem cells are responsible for maintaining the balance between cell proliferation and differentiation within self-renewing tissues. The molecular and cellular mechanisms mediating such balance are poorly understood. The production of reactive oxygen species (ROS) has emerged as an important mediator of stem cell homeostasis in various systems. Our recent work demonstrates that Rac1-dependent ROS production mediates intestinal stem cell (ISC) proliferation in mouse models of colorectal cancer (CRC). Here, we use the adult Drosophila midgut and the mouse small intestine to directly address the role of Rac1 in ISC proliferation and tissue regeneration in response to damage. Our results demonstrate that Rac1 is necessary and sufficient to drive ISC proliferation and regeneration in an ROS-dependent manner. Our data point to an evolutionarily conserved role of Rac1 in intestinal homeostasis and highlight the value of combining work in the mammalian and Drosophila intestine as paradigms to study stem cell biology.     

Thyroid hormone drives fetal cardiomyocyte maturation

Tri-iodo-l-thyronine (T(3)) suppresses the proliferation of near-term serum-stimulated fetal ovine cardiomyocytes in vitro. Thus, we hypothesized that T(3) is a major stimulant of cardiomyocyte maturation in vivo. We studied 3 groups of sheep fetuses on gestational days 125-130 (term ～145 d): a T(3)-infusion group, to mimic fetal term levels (plasma T(3) levels increased from ～0.1 to ～1.0 ng/ml; t(1/2)～24 h); a thyroidectomized group, to produce low thyroid hormone levels; and a vehicle-infusion group, to serve as intact controls. At 130 d of gestation, sections of left ventricular freewall were harvested, and the remaining myocardium was enzymatically dissociated. Proteins involved in cell cycle regulation (p21, cyclin D1), proliferation (ERK), and hypertrophy (mTOR) were measured in left ventricular tissue. Evidence that elevated T(3) augmented the maturation rate of cardiomyocytes included 14% increased width, 31% increase in binucleation, 39% reduction in proliferation, 150% reduction in cyclin D1 protein, and 500% increase in p21 protein. Increased expression of phospho-mTOR, ANP, and SERCA2a also suggests that T(3) promotes maturation and hypertrophy of fetal cardiomyocytes. Thyroidectomized fetuses had reduced cell cycle activity and binucleation. These findings support the hypothesis that T(3) is a prime driver of prenatal cardiomyocyte maturation.     

Sex hormone modulation of human uterine epithelial cell immune responses

Sexually transmitted infections are a major worldwide publichealth problem affecting millions of people. A number of bacteria,fungi, viruses, and protozoa can infect reproductive tissues,resulting in varying degrees of pathology ranging from littlediscomfort to death. The female reproductive tract has evolvedinnate and adaptive immune mechanisms that protect from microbialinfection, thereby reducing infection and disease. Central tothis protection are the epithelial cells that line the femalereproductive tract. In the uterus, columnar epithelial cellsprovide a physical barrier to microbial infection, possess toll-likereceptors that detect pathogens and secrete a number of constitutiveand induced factors that directly or indirectly hinder infection.For example, uterine epithelial cells secrete peptides thatdestroy pathogenic microbes. In addition, epithelial cells producechemokines and cytokines that attract and activate innate immunecells and serve as a link to the adaptive immune system. Further,uterine epithelial cells serve as a conduit for secretory antibodiesto enter the lumen and can present antigen to T cells. Theseprotective mechanisms contribute to an environment in the uterusthat is generally considered sterile, unlike the environmentin the lower female reproductive tract. The uterine environmentis in constant flux due to the concentration changes in sexhormones that occur in preparation for reproduction. The sexhormones estrogen and progesterone alter the local immune systemto prepare for conception, influence how well the immune systemwill tolerate antigenic sperm and a semi-allogeneic fetus andyet provide a network of protective immune mechanisms againstmicrobial pathogens. Understanding how sex hormones influenceuterine epithelial cell function will provide a basis for immuneprotection in the uterus.     

Thyroid hormone signaling controls hair follicle stem cell function

Observations in thyroid patients and experimental animals show that the skin is an important target for the thyroid hormones. We previously showed that deletion in mice of the thyroid hormone nuclear receptors TRα1 and TRβ (the main thyroid hormone–binding isoforms) results in impaired epidermal proliferation, hair growth, and wound healing. Stem cells located at the bulges of the hair follicles are responsible for hair cycling and contribute to the regeneration of the new epidermis after wounding. Therefore a reduction in the number or function of the bulge stem cells could be responsible for this phenotype. Bulge cells show increased levels of epigenetic repressive marks, can retain bromodeoxyuridine labeling for a long time, and have colony-forming efficiency (CFE) in vitro. Here we demonstrate that mice lacking TRs do not have a decrease of the bulge stem cell population. Instead, they show an increase of label-retaining cells (LRCs) in the bulges and enhanced CFE in vitro. Reduced activation of stem cells leading to their accumulation in the bulges is indicated by a strongly reduced response to mobilization by 12-O-tetradecanolyphorbol-13-acetate. Altered function of the bulge stem cells is associated with aberrant activation of Smad signaling, leading to reduced nuclear accumulation of β-catenin, which is crucial for stem cell proliferation and mobilization. LRCs of TR-deficient mice also show increased levels of epigenetic repressive marks. We conclude that thyroid hormone signaling is an important determinant of the mobilization of stem cells out of their niche in the hair bulge. These findings correlate with skin defects observed in mice and alterations found in human thyroid disorders.     

脐血干细胞与创面修复

脐血干细胞是一类具有多向分化潜能的原始祖细胞,具备自我更新和增殖的能力,在特定条件诱导下可以分化为不同细胞,逐渐作为临床组织工程的来源细胞。近年来随着对脐血干细胞的不断研究,发现其在创面修复中具有明显的优势,成为创面临床治疗的一条新途径。本文从脐血干细胞的生物学特性、采集与冻存、体外扩增等方面对创面修复的研究进行综述。     

Luteinizing hormone signaling restricts hematopoietic stem cell expansion during puberty

The number and self‐renewal capacity of hematopoietic stem cells (HSCs) are tightly regulated at different developmental stages. Many pathways have been implicated in regulating HSC development in cell autonomous manners; however, it remains unclear how HSCs sense and integrate developmental cues. In this study, we identified an extrinsic mechanism by which HSC number and functions are regulated during mouse puberty. We found that the HSC number in postnatal bone marrow reached homeostasis at 4 weeks after birth. Luteinizing hormone, but not downstream sex hormones, was involved in regulating HSC homeostasis during this period. Expression of luteinizing hormone receptor (Lhcgr) is highly restricted in HSCs and multipotent progenitor cells in the hematopoietic hierarchy. When Lhcgr was deleted, HSCs continued to expand even after 4 weeks after birth, leading to abnormally elevated hematopoiesis and leukocytosis. In a murine acute myeloid leukemia model, leukemia development was significantly accelerated upon Lhcgr deletion. Together, our work reveals an extrinsic counting mechanism that restricts HSC expansion during development and is physiologically important for maintaining normal hematopoiesis and inhibiting leukemogenesis.     

A specific endoplasmic reticulum export signal drives transport of stem cell factor (Kitl) to the cell surface

Stem cell factor, also known as Kit ligand (Kitl), belongs to the family of dimeric transmembrane growth factors. Efficient cell surface presentation of Kitl is essential for the migration, proliferation, and survival of melanocytes, germ cells, hemopoietic stem cells, and mastocytes. Here we demonstrate that intracellular transport of Kitl to the cell surface is driven by a motif in the cytoplasmic tail that acts independently of the previously described basolateral sorting signal. Transport of Kitl to the cell surface is controlled at the level of the endoplasmic reticulum (ER) and requires a C-terminal valine residue positioned at a distance of 19-36 amino acids from the border between the transmembrane and cytoplasmic domains. Deletion or substitution of the valine with other hydrophobic amino acids results in ER accumulation and reduced cell surface transport of Kitl at physiological expression levels. When these mutant proteins are overexpressed in the ER, they are transported by bulk flow to the cell surface albeit at lower efficiency. A fusion construct between Kitl and the green fluorescent protein-labeled extracellular domain of a temperature-sensitive mutant of vesicular stomatitis virus G protein revealed the valine-dependent recruitment into coat protein complex II-coated ER exit sites and vesicular ER to Golgi transport in living cells. Thus the C-terminal valine defines a specific ER export signal in Kitl. It is responsible for the capture of Kitl at coat protein complex II-coated ER exit sites, leading to subsequent cell surface transport under physiological conditions.     

Sex hormone modulation of cell growth and apoptosis of the human monocytic/macrophage cell line

Sex hormones seem to modulate the immune/inflammatory responses by different mechanisms in female and male rheumatoid arthritis patients. The effects of 17β-oestradiol and of testosterone were tested on the cultured human monocytic/macrophage cell line (THP-1) activated with IFN-γ in order to investigate their role in cell proliferation and apoptosis. Activated human THP-1 cells were cultured in the presence of 17β-oestradiol and testosterone (final concentration, 10 nM). The evaluation of markers of cell proliferation included the NF-κB DNA-binding assay, the NF-κB inhibition complex, the proliferating cell nuclear antigen expression and the methyl-tetrazolium salt test. Apoptosis was detected by the annexin V-propidium assay and by the cleaved poly-ADP ribose polymerase expression. Specific methods included flow analysis cytometry scatter analysis, immunocytochemistry and western blot analysis. Cell growth inhibition and increased apoptosis were observed in testosterone-treated THP-1 cells. Increased poly-ADP ribose polymerase-cleaved expression and decreased proliferating cell nuclear antigen expression, as well as an increase of IκB-α and a decrease of the IκB-α phosphorylated form (ser 32), were found in testosterone-treated THP-1 cells. However, the NF-κB DNA binding was found increased in 17β-oestradiol-treated THP-1 cells. The treatment with staurosporine (enhancer of apoptosis) induced decreased NF-κB DNA binding in all conditions, but particularly in testosterone-treated THP-1 cells. Treatment of THP-1 by sex hormones was found to influence cell proliferation and apoptosis. Androgens were found to increase the apoptosis, and oestrogens showed a protective trend on cell death – both acting as modulators of the NF-κB complex.     

Sex hormone profiles of premenarcheal athletes

Female gymnasts have a delayed onset and probably retarded progression of puberty. The aim of this study was to test the hypothesis that the delay in onset of puberty in gymnasts as compared to girl swimmers is modulated by a lower estrone level due to a smaller amount of body fat. The sex-hormone and gonadotropin levels of 46 gymnasts and 37 girl swimmers of the same biological maturation (breast development: M = 1 or M = 2) were studied. In each subject the following hormones were measured in plasma: estrone, 17-beta-estradiol, DHEAS, testosterone, androstenedione, LH, and FSH. In prepubertal children (M = 1) the levels of estrone, testosterone, and androstenedione were lower in the gymnastic group as compared to the swimming group. In the early pubertal (M = 2) gymnastic and swimming groups these hormone levels were no longer different. The other hormone levels were not significantly different in either the prepubertal groups or the early pubertal ones. Within the total prepubertal group there is a clear relationship between the estrone levels and the levels of testosterone and androstenedione, but not between estrone and 17-beta-estradiol, nor between the calculated fat mass and any of the hormone levels. It appears that the androstenedione and testosterone levels are responsible for the difference in estrone level, rather than the amount of body fat.     

Rho-GTPase signaling drives melanoma cell plasticity

To investigate mechanisms that underlie different modes of tumor cell movement we have studied how regulation of the activity of the Rho family GTPases determines the mode of tumor cell movement. Guanine nucleotide exchange factors (GEFs) and GTPase accelerating proteins (GAPs) are key regulators of the activity of small GTPases with GEFs promoting activation to the GTP bound state and GAPs promoting inactivation by stimulating GTP hydrolysis. We identified two important signaling pathways regulating amoeboid and mesenchymal types of motility in melanoma. Here, we discuss our findings in the context of how specificity of Rho signaling is achieved by GEFs and GAPs.     

A novel monoclonal antibody of human stem cell factor inhibits umbilical cord blood stem cell ex vivo expansion

Autologous stem cell transplantation (ASCT) is the gold standard therapy for suitable multiple myeloma (MM) patients after induction with high dose therapy. To date, the evidence of a reliable marker of prognosis in these cases remains scarce. Our aim was to evaluate appearance of unrelated atypical serum immunofixation patterns (ASIPs) as a marker of prognosis in MM patients submitted to ASCT. We retrospectively analysed data from 65 patients. Interestingly, we observed that presence of ASIPs was associated with longer progression-free survival and longer overall survival. Our results suggested that presence of ASIPs could be a novel marker of good prognosis in MM patients submitted to ASCT.     

Results of unrelated umbilical cord blood hematopoietic stem cell transplantation

The number of umbilical cord blood transplants is increasing worldwide. The purpose of Eurocord is to evaluate the results and to compare the outcome of umbilical cord blood transplants with allogeneic bone marrow transplants. Data have been reported to Eurocord by multiple transplant centers. Close links have been established with the cord blood banks through Netcord. Bone marrow transplant data have been provided by transplant centers and also through the European Group for Blood and Marrow Transplantation (EBMT) and International Bone Marrow Transplant Registries (IBMTR). Eurocord has analyzed the outcome of unrelated umbilical cord blood transplants from 121 transplant centers and 29 countries. The results showed that survival with unrelated mismatched umbilical cord blood transplants was comparable to that with unrelated bone marrow transplants. Engraftment with cord blood was delayed, resulting in an increased incidence of early transplant complications. The incidence of acute and chronic graft-vs.-host disease was reduced with cord blood grafts even in human leukocyte antigen (HLA)-mismatched transplants and in adults. In patients with leukemia, the rate of relapse was similar to the rate of relapse after bone marrow transplant. The overall event-free survival with umbilical cord blood transplantation was not statistically different when compared to bone marrow transplants. This large registry study confirms the potential benefit of using umbilical cord blood hematopoietic stem cells for allogeneic transplants.     

Cell–cell interaction networks regulate blood stem and progenitor cell fate

Communication networks between cells and tissues are necessary for homeostasis in multicellular organisms. Intercellular (between cell) communication networks are particularly relevant in stem cell biology, as stem cell fate decisions (self‐renewal, proliferation, lineage specification) are tightly regulated based on physiological demand. We have developed a novel mathematical model of blood stem cell development incorporating cell‐level kinetic parameters as functions of secreted molecule‐mediated intercellular networks. By relation to quantitative cellular assays, our model is capable of predictively simulating many disparate features of both normal and malignant hematopoiesis, relating internal parameters and microenvironmental variables to measurable cell fate outcomes. Through integrated in silico and experimental analyses, we show that blood stem and progenitor cell fate is regulated by cell–cell feedback, and can be controlled non‐cell autonomously by dynamically perturbing intercellular signalling. We extend this concept by demonstrating that variability in the secretion rates of the intercellular regulators is sufficient to explain heterogeneity in culture outputs, and that loss of responsiveness to cell–cell feedback signalling is both necessary and sufficient to induce leukemic transformation in silico.