Stromal derived growth factor alpha (SDF-1α) induces the differentiation of bone marrow progenitor cells (BMCs) into pericytes by regulating platelet derived growth factor B (PDGF-B) transcription

We previously demonstrated that bone marrow cells (BMCs) migrate to TC71 and A4573 Ewing’s sarcoma tumors where they can differentiate into endothelial cells (ECs) and pericytes and, participate in the tumor vascular development. This process of neo-vascularization, known as vasculogenesis, is essential for Ewing’s sarcoma growth with the soluble vascular endothelial growth factor, VEGF165, being the chemotactic factor for BMC migration to the tumor site. Inhibiting VEGF165 in TC71 tumors (TC/siVEGF7-1) inhibited BMC infiltration to the tumor site and tumor growth. Introducing the stromal-derived growth factor (SDF-1α) into the TC/siVEGF7-1 tumors partially restored vasculogenesis with infiltration of BMCs to a perivascular area where they differentiated into pericytes and rescued tumor growth. RNA collected from the SDF-1α-treated TC/siVEGF7-1 tumors also revealed an increase in platelet-derived growth factor B (PDGF-B) mRNA levels. PDGF-B expression is elevated in several cancer types and the role of PDGF-B and its receptor, PDGFR-β, has been extensively described in the process of pericyte maturation. However, the mechanisms by which PDGF-B expression is up-regulated during vascular remodeling and the process by which BMCs differentiate into pericytes during tumor vasculogenesis remain areas of investigation. In this study, we are the first to demonstrate that SDF-1α regulates the expression of PDGF-B via a transcriptional mechanism which involves binding of the ELK-1 transcription factor to the pdgf-b promoter. We are also first to validate the critical role of the SDF-1α/PDGF-B pathway in the differentiation of BMCs into pericytes both in vitro and in vivo. SDF-1α up-regulated PDGF-B expression in both TC/siVEGF7-1 and HEK293 cells. In contrast, down-regulating SDF-1α, down-regulated PDGF-B. We cloned the 2 kb pdgf-b promoter fragment into the pGL3 reporter vector and showed that SDF-1α induced pdgf-b promoter activity. We used chromatin immunoprecipitation (ChIP) and demonstrated that the ELK-1 transcription factor bound to the pdgf-b promoter in response to SDF-1α stimulation in both TC/siVEGF7-1 and HEK293 cells. We collected BMCs from the hind femurs of mice and cultured the cells in medium containing SDF-1α and PDGF-B and found that PDGFR-β+ BMCs differentiated into NG2 and desmin positive pericytes in vitro. In contrast, inhibiting SDF-1α and PDGF-B abolished this differentiation process. In vivo, we injected TC71 or A4573 tumor-bearing mice with the SDF-1α antagonist, AMD3100 and found that inhibiting SDF-1α signaling in the tumor microenvironment decreased the tumor microvessel density, decreased the tumor blood vessel perfusion and, increased tumor cell apoptosis. We then analyzed the effect of AMD3100 on vasculogenesis of Ewing’s sarcoma and found that BMCs migrated to the tumor site where they differentiated into ECs but, they did not form thick perivascular layers of NG2 and desmin positive pericytes. Finally, we stained the AMD3100-treated tumors for PDGF-B and showed that inhibiting SDF-1α signaling also inhibited PDGF-B expression. All together, these findings demonstrated that the SDF-1α/PDGF-B pathway plays a critical role in the formation of BM-derived pericytes during vasculogenesis of Ewing’s sarcoma tumors.

Circulating endothelial progenitor cells in periodontitis.

BACKGROUND Several biologically plausible mechanisms have been proposed to mediate the association between periodontitis and atherosclerotic vascular disease (AVD), including adverse effects on vascular endothelial function. Circulating endothelial progenitor cells (cEPCs) are known to contribute to vascular repair, but limited data are available regarding the relationship between cEPC levels and periodontitis. The aims of this cross-sectional study are to investigate the levels of hemangioblastic and monocytic cEPCs in patients with periodontitis and periodontally healthy controls and to associate cEPC levels with the extent and severity of periodontitis. METHODS A total of 112 individuals (56 patients with periodontitis and 56 periodontally healthy controls, aged 26 to 65 years; mean age: 43 years) were enrolled. All participants underwent a full-mouth periodontal examination and provided a blood sample. Hemangioblastic cEPCs were assessed using flow cytometry, and monocytic cEPCs were identified using immunohistochemistry in cultured peripheral blood mononuclear cells. cEPC levels were analyzed in the entire sample, as well as in a subset of 50 pairs of patients with periodontitis/periodontally healthy controls, matched with respect to age, sex, and menstrual cycle. RESULTS Levels of hemangioblastic cEPCs were approximately 2.3-fold higher in patients with periodontitis than periodontally healthy controls, after adjustments for age, sex, physical activity, systolic blood pressure, and body mass index (P = 0.001). A non-significant trend for higher levels of monocytic cEPCs in periodontitis was also observed. The levels of hemangioblastic cEPCs were positively associated with the extent of bleeding on probing, probing depth, and clinical attachment loss. Hemangioblastic and monocytic cEPC levels were not correlated (Spearman correlation coefficient 0.03, P = 0.77), suggesting that they represent independent populations of progenitor cells. CONCLUSION These findings further support the notion that oral infections have extraoral effects and document that periodontitis is associated with a mobilization of EPCs from the bone marrow, apparently in response to systemic inflammation and endothelial injury.

Overexpression of EphB4 in the mammary epithelium shifts the differentiation pathway of progenitor cells and promotes branching activity and vascularization

Postnatally, the mammary gland undergoes continuous morphogenesis and thereby is especially prone to malignant transformation. Thus, the maintenance of the epithelium depends on a tight control of stem cell recruitment. We have previously shown that epithelial overexpression of the EphB4 receptor results in defective mammary epithelial development and conferred a metastasizing tumor phenotype on experimental mouse mammary tumors accompanied by a preponderance of progenitor cells. To analyze the effect of EphB4 overexpression on mammary epithelial cell fate, we have used Fluorescence Activated Cell Sorting (FACS) analyses to quantify epithelial sub-populations and repopulation assays of cleared fat pads to investigate their regenerative potential. These experiments revealed that deregulated EphB4 expression leads to an augmentation of bi-potent progenitor cells and to a shift of the differentiation pathway towards the luminal lineage. The analyses of the ductal outgrowths indicated that EphB4 overexpression leads to enforced branching activity, impedes ductal differentiation and stimulates angiogenesis. To elucidate the mechanisms forwarding EphB4 signals, we have compared the expression profile of defined cell populations between EphB4 transgene and wild type mammary glands concentrating on the wnt signaling pathway and on genes implicated in cell migration. With respect to wnt signaling, the progenitor cell population was the most affected, whereas the stem cell-enriched population showed the most pronounced deregulation of migration-associated genes. Thus, the luminal epithelial EphB4 signaling contributes, most likely via wnt signaling, to the regulation of migration and cell fate of early progenitors and is involved in the determination of branching points along the ductal tree.

The secretome of endothelial progenitor cells promotes brain endothelial cell activity through PI3-kinase and MAP-kinase

BACKGROUND Angiogenesis and vascular remodelling are crucial events in tissue repair mechanisms promoted by cell transplantation. Current evidence underscores the importance of the soluble factors secreted by stem cells in tissue regeneration. In the present study we investigated the effects of paracrine factors derived from cultured endothelial progenitor cells (EPC) on rat brain endothelial cell properties and addressed the signaling pathways involved. METHODS Endothelial cells derived from rat brain (rBCEC4) were incubated with EPC-derived conditioned medium (EPC-CM). The angiogenic response of rBCEC4 to EPC-CM was assessed as effect on cell number, migration and tubular network formation. In addition, we have compared the outcome of the in vitro experiments with the effects on capillary sprouting from rat aortic rings. The specific PI3K/AKT inhibitor LY294002 and the MEK/ERK inhibitor PD98059 were used to study the involvement of these two signaling pathways in the transduction of the angiogenic effects of EPC-CM. RESULTS Viable cell number, migration and tubule network formation were significantly augmented upon incubation with EPC-CM. Similar findings were observed for aortic ring outgrowth with significantly longer sprouts. The EPC-CM-induced activities were significantly reduced by the blockage of the PI3K/AKT and MEK/ERK signaling pathways. Similarly to the outcome of the rBCEC4 experiments, inhibition of the PI3K/AKT and MEK/ERK pathways significantly interfered with capillary sprouting induced by EPC-CM. CONCLUSION The present study demonstrates that EPC-derived paracrine factors substantially promote the angiogenic response of brain microvascular endothelial cells. In addition, our findings identified the PI3K/AKT and MEK/ERK pathways to play a central role in mediating these effects.

Successful transnasal delivery of stem cells in a rat model of perinatal hypoxic-ischemic brain injury

OBJECTIVE: New routes for cell transplantation into the brain need to be explored as intracerebral or intrathecal applications have a high risk to cause damage to the central nervous system. It has been hypothesized that transnasally administrated cells bypass the blood-brain barrier and migrate along the olfactory neural route into the brain and cerebrospinal fluid. Our goal is to confirm this hypothesis by transnasally administrating Wharton’s Jelly mesenchymal stem cells (WJ-MSC) and neural progenitor cells (NPC) to perinatal rats in a model of hypoxic-ischemic brain injury. STUDY DESIGN: Four-day-old Wistar rat pups, previously brain-damaged by combined hypoxic-ischemic and inflammatory insult, either received WJ-MSC or green fluorescent protein-expressing NPC: The heads of the rat pups were immobilized and 3 ml drops containing the cells (50’000 cells/ml) were placed on one nostril allowing it to be snorted. This procedure was repeated twice, alternating right to left nostril with an interval of one minute between administrations. The rat pups received a total of 600’000 cells. Animals were sacrificed 24h, 48h or 7 days after the application of the cells. Fixed brains were collected, embedded in paraffin and sectioned. RESULTS: Transplanted cells were found in the layers of the olfactory bulb (OB), the cerebral cortex, thalamus and the hippocampus. The amount of cells was highest in the OB. Animals treated with transnasally delivered stem cells showed significantly decreased gliosis compared to untreated animals. CONCLUSION: Our data show that transnasal delivery of WJ-MSC and NPC to the newborn brain after perinatal brain damage is successful. The cells not only migrate the brain, but also decrease scar formation and improve neurogenesis. Therefore, the non-invasive intranasal delivery of stem cells to the brain may be the preferred method for stem cell treatment of perinatal brain damage and should be preferred in future clinical trials.

Cell cycle reactivation of cochlear progenitor cells in neonatal FUCCI mice by a GSK3 small molecule inhibitor.

Due to the lack of regenerative capacity of the mammalian auditory epithelium, sensory hair cell loss results in permanent hearing deficit. Nevertheless, a population of tissue resident stem/progenitor cells has been recently described. Identification of methods to trigger their activity could lead to exploitation of their potential therapeutically. Here we validate the use of transgenic mice reporting cell cycle progression (FUCCI), and stemness (Lgr5-GFP), as a valuable tool to identify regulators of cell cycle re-entry of supporting cells within the auditory epithelium. The small molecule compound CHIR99021 was used to inhibit GSK3 activity. This led to a significant increase in the fraction of proliferating sphere-forming cells, labeled by the FUCCI markers and in the percentage of Lgr5-GFP + cells, as well as a selective increase in the fraction of S-G2-M cells in the Lgr5 + population. Using whole mount cultures of the organ of Corti we detected a statistically significant increment in the fraction of proliferating Sox2 supporting cells after CHIR99021 treatment, but only rarely appearance of novel MyoVIIa+/Edu + hair cells. In conclusion, these tools provide a robust mean to identify novel regulators of auditory organ regeneration and to clarify the contribution of stem cell activity.