Endothelial progenitor cells as a possible component of stem cell niche to promote self-renewal of mesenchymal stem cells

Bone Marrow-Derived Vasculogenic Mesenchymal Stem Cells Enhance In Vitro Angiogenic Sprouting of Human Umbilical Vein Endothelial Cells

Vasculogenic properties of bone marrow-derived mesenchymal stem cells (MSCs) have been reported, but it is still unclear whether the vasculogenic properties are restricted to some populations of MSCs or whether the entire population of MSCs has these properties. We cultured two different populations of MSCs in different culture media and their vasculogenic properties were evaluated using In vitro spheroid sprouting assay. Neither population of MSCs expressed markers of endothelial progenitor cells (EPCs), but they were different in the profiling of angiogenic factor expression as well as vasculogenic properties. One population of MSCs expressed basic fibroblast growth factor (bFGF) and another expressed hepatocyte growth factor (HGF). MSCs expressing HGF exhibited In vitro angiogenic sprouting capacity in response to bFGF derived from other MSCs as well as to their autocrine HGF. The vasculogenic mesenchymal stem cells (vMSCs) derived from the bone marrow also enhanced In vitro angiogenic sprouting capacity of human umbilical vein endothelial cells (HUVECs) in an HGF-dependent manner. These results suggest that MSCs exhibit different vasculogenic properties, and vMSCs that are different from EPCs may contribute to neovascularization and could be a promising cellular therapy for cardiovascular diseases.

Adipose-derived stem cells promote diabetic wound healing via the recruitment and differentiation of endothelial progenitor cells into endothelial cells mediated by the VEGF-PLCγ-ERK pathway

Adipose-derived stem cell (ADSC) therapy is a promising treatment strategy for wound healing; however, the mechanism underlying this effect remains unclear. In the present study, we aimed to explore the influence of ADSC-derived VEGF on diabetic wounds and its role in modulating endothelial progenitor cells. The effect of ADSCs and ADSC-derived VEGF in vivo was investigated using a diabetic wound healing model, and inflammatory factors, such as IL-6, IL-10, and TNF-α, were detected. RT-qPCR and western blot analysis were used to detect the expression of downstream targets. In addition, the role of ADSC-derived VEGF in modulating endothelial progenitor cells (EPCs) was investigated using EdU assay, CD-31 immunofluorescence, and Transwell assay in vitro. The results show that ADSCs accelerated diabetic wound tissue closure and decreased the expression of inflammatory factors, such as IL-6, IL-10, and TNF-α. Further molecular mechanism studies indicated that coculturing EPCs with ADSC--conditioned medium enhanced the proliferation, mobilization and differentiation of EPCs into endothelial cells. This enhancement was inhibited when the expression of the VEGF downstream signal molecules VEGFR2, PLCγ, and ERK1/ERK2 was blocked, indicating that ADSCs might accelerate diabetic wound healing through the recruitment and differentiation of EPCs mediated by VEGF. Overall, the results of the study revealed that ADSCs could promote diabetic wound healing through the recruitment and differentiation of EPCs via angiogenesis effects regulated by the VEGF-PLCγ-ERK1/ERK2 pathway and suppression of the inflammatory response. In addition, it will be helpful to establish further understanding of ADSC therapy for clinical application.

Simultaneous isolation of mesenchymal stem cells and endothelial progenitor cells derived from murine bone marrow

Mesenchymal stem or stromal cells (MSCs) are identified as sources of pluripotent stem cells with varying degrees of plasticity. Endothelial progenitor cells (EPCs) originate from either bone marrow (BM) or peripheral blood and can mature into cells that line the lumen of blood vessels. MSC and EPC therapies exhibit promising results in a variety of diseases. The current study described the simultaneous isolation of EPCs and MSCs from murine BM using a straightforward approach. The method is based on differences in attachment time and trypsin sensitivity of MSCs and EPCs. The proposed method revealed characteristics of isolated cells. Isolated MSCs were positive for cell surface markers, cluster of differentiation (CD)29, CD44 and stem cell antigen-1 (Sca-1), and negative for hematopoietic surface markers, CD45 and CD11b. Isolated EPCs were positive for Sca-1 and vascular endothelial growth factor receptor 2 and CD133. The results indicate that the proposed method ensured simultaneous isolation of homogenous populations of MSCs and EPCs from murine BM.

Interleukin-1β induces intercellular adhesion molecule-1 expression, thus enhancing the adhesion between mesenchymal stem cells and endothelial progenitor cells via the p38 MAPK signaling pathway

Endothelial progenitor cells (EPCs) are an important component of stem-cell niches, which are able to promote the self-renewal and pluripotency of mesenchymal stem cells (MSCs). The biological functions of these two cell types is dependent on adhesion, and the adhesion between MSCs and EPCs is important due to their critical role in neovascularization and bone regeneration in tissue engineering. Intercellular adhesion molecule-1 (ICAM-1, also known as cluster of differentiation 54), is a member of the immunoglobulin supergene family, which functions in cell-cell and cell-matrix adhesive interactions. Compared with other adhesion molecules, ICAM-1 is expressed in hematopoietic and nonhematopoietic cells, and can mediate adhesive interactions. The present study aimed to investigate the importance of ICAM-1 in the adhesion of MSCs and EPCs, and demonstrated that adhesion between these cells could be regulated by interleukin (IL)-1β via the p38 mitogen-activated protein kinase pathway. In addition, the results confirmed that ICAM-1 served a critical role in regulation of adhesion between MSCs and EPCs. ELISA, cell immunofluorescence, western blot analysis and adhesion assay were used to confirm our theory from phenomenon to essence. The present study provided evidence to support and explain the adhesion between MSCs and EPCs. Furthermore, the present findings provide a theoretical basis for further stem-cell niche transplantation to increase understanding of the function of MSCs and the crosstalk between MSCs and EPCs in the stem-cell niche.

Endogenous Stem Cells in Homeostasis and Aging

In almost all human tissues and organs, adult stem cells or tissue stem cells are present in a unique location, the so-called stem cell niche or its equivalent, continuously replenishing functional differentiated cells. Those endogenous stem cells can be expanded for cell therapeutics using ex vivo cell culture or recalled for tissue repair in situ through cell trafficking and homing. In the aging process, inefficiency in the endogenous stem cell-mediated healing mechanism can emerge from a variety of impairments that accumulate in the processes of stem cell self-renewal, function, differentiation capacity, and trafficking through cell autonomous intrinsic pathways (such as epigenetic alterations) or systemic extrinsic pathways. This review examines the homeostasis of endogenous stem cells, particularly bone marrow stem cells, and their dysregulation in disease and aging and discusses possible intervention strategies. Several systemic pro-aging and rejuvenating factors, recognized in heterochronic parabiosis or premature aging progeroid animal models, are reviewed as possible anti-aging pharmaceutical targets from the perspective of a healthy environment for endogenous stem cells. A variety of epigenetic modifications and chromosome architectures are reviewed as an intrinsic cellular pathway for aging and senescence. A gradual increase in inflammatory burden during aging is also reviewed. Finally, the tissue repair and anti-aging effects of Substance-P, a peptide stimulating stem cell trafficking from the bone marrow and modifying the inflammatory response, are discussed as a future anti-aging target.

VEGF secreted by mesenchymal stem cells mediates the differentiation of endothelial progenitor cells into endothelial cells via paracrine mechanisms

Stem cell therapy is a promising treatment strategy for ischemic diseases. Mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) adhere to each other in the bone marrow cavity and in in vitro cultures. We have previously demonstrated that the adhesion between MSCs and EPCs is critical for MSC self-renewal and their multi-differentiation into osteoblasts and chondrocytes. In the present study, the influence of the indirect communication between EPCs and MSCs on the endothelial differentiation potential of EPCs was investigated, and the molecular mechanisms underlying MSC-mediated EPC differentiation were explored. The effects of vascular endothelial growth factor (VEGF), which is secreted by MSCs, on EPC differentiation via paracrine mechanisms were examined via co-culturing MSCs and EPCs. Reverse transcription-quantitative polymerase chain reaction and western blot analysis were used to detect the expression of genes and proteins of interest. The present results demonstrated that co-culturing EPCs with MSCs enhanced the expression of cluster of differentiation 31 and von Willebrand factor, which are specific markers of an endothelial phenotype, thus indicating that MSCs may influence the endothelial differentiation of EPCs in vitro. VEGF appeared to be critical to this process. These findings are important for the understanding of the biological interactions between MSCs and EPCs, and for the development of applications of stem cell-based therapy in the treatment of ischemic diseases.

Suppressing angiogenesis regulates the irradiation-induced stimulation on osteoclastogenesis in vitro

Ionizing radiation-induced bone loss is a potential health concern in radiotherapy, occupational exposure, and astronauts. Although impaired bone vasculature and reduced proliferation of bone-forming osteoblasts has been implicated in this process, it has not been clearly characterized that whether radiation affects the growth of bone-resorbing osteoclasts. The molecular crosstalk between different cell populations in the skeletal system has not yet been elucidated in detail, especially between the increased bone resorption at early stage of post-irradiation and bone marrow-derived endothelial progenitor cells (BM-EPCs). In order to further understand the mechanisms involved in radiation-induced bone loss at the cellular level, we assessed the effects of irradiation on angiogenesis of BM-EPCs and osteoclastogenesis of receptor activator for nuclear factor-κB ligand (RANKL)-stimulated RAW 264.7 cells and crosstalk between these cell populations. We herein found significantly dysfunction of BM-EPCs in response to irradiation at a dose of 2 Gy, including inhibited proliferation, migration, tube-forming abilities, and downregulated expression of pro-angiogenesis vascular endothelial growth factors A (VEGF A). Meanwhile, we observed that irradiation promoted osteoclastogenesis of RANKL-stimulated RAW 264.7 cells directly or indirectly. These results provide quantitative evidences of irradiation induced osteoclastogenesis at a cellular level, and strongly suggest the involvement of osteoclastogenesis, angiogenesis and crosstalk between bone marrow cells in the radiation-induced bone loss. This study may provide new insights for the early diagnosis and intervention of bone loss post-irradiation.

Mesenchymal stem cells promote endothelial progenitor cell proliferation by secreting insulin‑like growth factor‑1

Bone marrow mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) interact with each other. EPCs are able to promote the self‑renewal of MSCs as niche cells in murine bone marrow, and MSCs are able to promote EPC proliferation in vitro in a co‑culture system. It has previously been reported that MSCs can secrete insulin‑like growth factor‑1 (IGF‑1), which serves critical functions in EPC proliferation. However, the mechanism underlying the IGF‑1‑mediated proliferation of EPCs remains unclear. The aim of the present study was to reveal the molecular mechanisms regulating this process. The effects of IGF‑1, which is secreted by MSCs, on EPC proliferation via the PI3K/Akt signaling pathway were examined by MTT assay, reverse transcription‑quantitative polymerase chain reaction and western blot analysis. The present study treated EPCs with various concentrations of IGF‑1. The results demonstrated that IGF‑1 significantly induced the proliferation of cultured EPCs. However, this effect was offset by treatment with the phosphatidylinositol 3‑kinase (PI3K) inhibitor LY294002. These results indicated that the pro‑proliferative effects of IGF‑1 are mediated in response to the PI3K/protein kinase B signaling pathway.

Combination of low-energy shock-wave therapy and bone marrow mesenchymal stem cell transplantation to improve the erectile function of diabetic rats

Stem cell transplantation and low-energy shock-wave therapy (LESWT) have emerged as potential and effective treatment protocols for diabetic erectile dysfunction. During the tracking of transplanted stem cells in diabetic erectile dysfunction models, the number of visible stem cells was rather low and decreased quickly. LESWT could recruit endogenous stem cells to the cavernous body and improve the microenvironment in diabetic cavernous tissue. Thus, we deduced that LESWT might benefit transplanted stem cell survival and improve the effects of stem cell transplantation. In this research, 42 streptozotocin-induced diabetic rats were randomized into four groups: the diabetic group (n = 6), the LESWT group (n = 6), the bone marrow-derived mesenchymal stem cell (BMSC) transplantation group (n = 15), and the combination of LESWT and BMSC transplantation group (n = 15). One and three days after BMSC transplantation, three rats were randomly chosen to observe the survival numbers of BMSCs in the cavernous body. Four weeks after BMSC transplantation, the following parameters were assessed: the surviving number of transplanted BMSCs in the cavernous tissue, erectile function, real-time polymerase chain reaction, and penile immunohistochemical assessment. Our research found that LESWT favored the survival of transplanted BMSCs in the cavernous body, which might be related to increased stromal cell-derived factor-1 expression and the enhancement of angiogenesis in the diabetic cavernous tissue. The combination of LESWT and BMSC transplantation could improve the erectile function of diabetic erectile function rats more effectively than LESWT or BMSC transplantation performed alone.

E-cadherin-mediated contact of endothelial progenitor cells with mesenchymal stem cells through β-catenin signaling

Mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) are attached to each other in the bone marrow (BM) cavity and in in vitro cultures, and this adhesion has important physiological significance. We demonstrated that cell proliferation could be promoted when MSCs were co-cultured with EPCs, which was beneficial to angiogenesis, tissue repair, and regeneration. The adhesion of MSCs and EPCs could promote the pluripotency of MSCs, particularly self-renewal and multi-differentiation to osteoblasts, chondrocytes, and adipocytes. This study focused on the mechanism of adhesion between EPCs and MSCs. The results showed that E-cadherin (E-cad) mediated the adhesion of MSCs and EPCs through the E-cad/beta-catenin signaling pathway. The E-cad of EPCs occupied a dominant position during this process, which activated and up-regulated the beta-catenin (β-catenin) of MSCs to improve cohesion and exert their biological function.