Nitric Oxide SUPPRESSES THE SECRETION OF VASCULAR ENDOTHELIAL GROWTH FACTOR AND HEPATOCYTE GROWTH FACTOR FROM HUMAN MESENCHYMAL STEM CELLS

Vascular endothelial growth factor secretion and immunosuppression are distinct potency mechanisms of human bone marrow mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) are investigated as cellular therapeutics for inflammatory bowel diseases and associated perianal fistula, although consistent efficacy remains a concern. Determining host factors that modulate MSCs' potency including their secretion of angiogenic and wound-healing factors, immunosuppression, and anti-inflammatory properties are important determinants of their functionality. We investigated the mechanisms that regulate the secretion of angiogenic and wound-healing factors and immune suppression of human bone marrow MSCs. Secretory analysis of MSCs focusing on 18 angiogenic and wound-healing secretory molecules identified the most abundancy of vascular endothelial growth factor A (VEGF-A). MSC viability and secretion of other angiogenic factors are not dependent on VEGF-A secretion which exclude the autocrine role of VEGF-A on MSC's fitness. However, the combination of inflammatory cytokines IFNγ and TNFα reduces MSC's VEGF-A secretion. To identify the effect of intestinal microvasculature on MSCs' potency, coculture analysis was performed between human large intestine microvascular endothelial cells (HLMVECs) and human bone marrow-derived MSCs. HLMVECs do not attenuate MSCs' viability despite blocking their VEGF-A secretion. In addition, HLMVECs neither attenuate MSC's IFNγ mediated upregulation of immunosuppressive enzyme indoleamine 2,3-dioxygenase nor abrogate suppression of T-cell proliferation despite the attenuation of VEGF-A secretion. We found that HLMVECs express copious amounts of endothelial nitric oxide synthase and mechanistic analysis showed that pharmacological blocking reverses HLMVEC-mediated attenuation of MSC's VEGF-A secretion. Together these results suggest that secretion of VEGF-A and immunosuppression are separable functions of MSCs which are regulated by distinct mechanisms in the host.

Depletion of EREG enhances the osteo/dentinogenic differentiation ability of dental pulp stem cells via the p38 MAPK and Erk pathways in an inflammatory microenvironment

BACKGROUND

Epiregulin (EREG) is an important component of EGF and was demonstrated to promote the osteo/dentinogenic differentiation of stem cells from dental apical papilla (SCAPs). Whether EREG can stimulate the osteo/dentinogenic differentiation of dental pulp stem cells (DPSCs) in inflammatory environment is not clear. The purpose of the present study is to investigate the role of EREG on the osteo/dentinogenic differentiation ability of DPSCs in inflammatory environment.

METHODS

DPSCs were isolated from human third molars. Short hairpin RNAs (shRNAs) were used to knock down EREG expression in DPSCs. Recombinant human EREG (rhEREG) protein was used in the rescue experiment. TNF-α was employed to mimic the inflammatory environment in vitro. Alkaline phosphatase (ALP) staining, Alizarin red staining, quantitative calcium analysis, and real-time RT-PCR were performed to detect osteo/dentinogenic differentiation markers and related signalling pathways under normal and inflammatory conditions.

RESULTS

EREG depletion promoted the ALP activity and mineralization ability of DPSCs. The expression of BSP, DMP-1, and DSPP was also enhanced. Moreover, 50 ng/mL rhEREG treatment decreased the osteo/dentinogenic differentiation potential of DPSCs, while treatment with 10 ng/mL TNF-α for 4 h increased the expression of EREG in DPSCs. Conversely, EREG knockdown rescued the impaired osteo/dentinogenic differentiation ability caused by TNF-α treatment. Further mechanistic studies showed that EREG depletion activated the p38 MAPK and Erk signalling pathways in DPSCs under normal and inflammatory conditions.

CONCLUSIONS

Our results demonstrated that EREG could inhibit the osteo/dentinogenic differentiation potential of DPSCs via the p38 MAPK and Erk signalling pathways. Under inflammatory environment, EREG depletion enhanced osteo/dentinogenic differentiation potential of DPSCs by improving the expression of p-p38 MAPK and p-Erk.

Rebuilding the Damaged Heart: Mesenchymal Stem Cells, Cell-Based Therapy, and Engineered Heart Tissue

Mesenchymal stem cells (MSCs) are broadly distributed cells that retain postnatal capacity for self-renewal and multilineage differentiation. MSCs evade immune detection, secrete an array of anti-inflammatory and anti-fibrotic mediators, and very importantly activate resident precursors. These properties form the basis for the strategy of clinical application of cell-based therapeutics for inflammatory and fibrotic conditions. In cardiovascular medicine, administration of autologous or allogeneic MSCs in patients with ischemic and nonischemic cardiomyopathy holds significant promise. Numerous preclinical studies of ischemic and nonischemic cardiomyopathy employing MSC-based therapy have demonstrated that the properties of reducing fibrosis, stimulating angiogenesis, and cardiomyogenesis have led to improvements in the structure and function of remodeled ventricles. Further attempts have been made to augment MSCs' effects through genetic modification and cell preconditioning. Progression of MSC therapy to early clinical trials has supported their role in improving cardiac structure and function, functional capacity, and patient quality of life. Emerging data have supported larger clinical trials that have been either completed or are currently underway. Mechanistically, MSC therapy is thought to benefit the heart by stimulating innate anti-fibrotic and regenerative responses. The mechanisms of action involve paracrine signaling, cell-cell interactions, and fusion with resident cells. Trans-differentiation of MSCs to bona fide cardiomyocytes and coronary vessels is also thought to occur, although at a nonphysiological level. Recently, MSC-based tissue engineering for cardiovascular disease has been examined with quite encouraging results. This review discusses MSCs from their basic biological characteristics to their role as a promising therapeutic strategy for clinical cardiovascular disease.

Hepatocyte growth factor as a downstream mediator of vascular endothelial growth factor-dependent preservation of growth in the developing lung

Impaired vascular endothelial growth factor (VEGF) signaling contributes to the pathogenesis of bronchopulmonary dysplasia (BPD). We hypothesized that the effects of VEGF on lung structure during development may be mediated through its downstream effects on both endothelial nitric oxide synthase (eNOS) and hepatocyte growth factor (HGF) activity, and that, in the absence of eNOS, trophic effects of VEGF would be mediated through HGF signaling. To test this hypothesis, we performed an integrative series of in vitro (fetal rat lung explants and isolated fetal alveolar and endothelial cells) and in vivo studies with normal rat pups and eNOS(-/-) mice. Compared with controls, fetal lung explants from eNOS(-/-) mice had decreased terminal lung bud formation, which was restored with recombinant human VEGF (rhVEGF) treatment. Neonatal eNOS(-/-) mice were more susceptible to hyperoxia-induced inhibition of lung growth than controls, which was prevented with rhVEGF treatment. Fetal alveolar type II (AT2) cell proliferation was increased with rhVEGF treatment only with mesenchymal cell (MC) coculture, and these effects were attenuated with anti-HGF antibody treatment. Unlike VEGF, HGF directly stimulated isolated AT2 cells even without MC coculture. HGF directly stimulates fetal pulmonary artery endothelial cell growth and tube formation, which is attenuated by treatment with JNJ-38877605, a c-Met inhibitor. rHGF treatment preserves alveolar and vascular growth after postnatal exposure to SU-5416, a VEGF receptor inhibitor. We conclude that the effects of VEGF on AT2 and endothelial cells during lung development are partly mediated through HGF-c-Met signaling and speculate that reciprocal VEGF-HGF signaling between epithelia and endothelia is disrupted in infants who develop BPD.

Effects of nitric oxide on stem cell therapy

The use of stem cells as a research tool and a therapeutic vehicle has demonstrated their great potential in the treatment of various diseases. With unveiling of nitric oxide synthase (NOS) universally present at various levels in nearly all types of body tissues, the potential therapeutic implication of nitric oxide (NO) has been magnified, and thus scientists have explored new treatment strategies involved with stem cells and NO against various diseases. As the functionality of NO encompasses cardiovascular, neuronal and immune systems, NO is involved in stem cell differentiation, epigenetic regulation and immune suppression. Stem cells trigger cellular responses to external signals on the basis of both NO specific pathways and concerted action with endogenous compounds including stem cell regulators. As potency and interaction of NO with stem cells generally depend on the concentrations of NO and the presence of the cofactors at the active site, the suitable carriers for NO delivery is integral for exerting maximal efficacy of stem cells. The innovative utilization of NO functionality and involved mechanisms would invariably alter the paradigm of therapeutic application of stem cells. Future prospects in NO-involved stem cell research which promises to enhance drug discovery efforts by opening new era to improve drug efficacy, reduce drug toxicity and understand disease mechanisms and pathways, were also addressed.

S-nitrosoglutathione reductase (GSNOR) enhances vasculogenesis by mesenchymal stem cells

Although nitric oxide (NO) signaling promotes differentiation and maturation of endothelial progenitor cells, its role in the differentiation of mesenchymal stem cells (MSCs) into endothelial cells remains controversial. We tested the role of NO signaling in MSCs derived from WT mice and mice homozygous for a deletion of S-nitrosoglutathione reductase (GSNOR(-/-)), a denitrosylase that regulates S-nitrosylation. GSNOR(-/-) MSCs exhibited markedly diminished capacity for vasculogenesis in an in vitro Matrigel tube-forming assay and in vivo relative to WT MSCs. This decrease was associated with down-regulation of the PDGF receptorα (PDGFRα) in GSNOR(-/-) MSCs, a receptor essential for VEGF-A action in MSCs. Pharmacologic inhibition of NO synthase with L-N(G)-nitroarginine methyl ester (L-NAME) and stimulation of growth hormone-releasing hormone receptor (GHRHR) with GHRH agonists augmented VEGF-A production and normalized tube formation in GSNOR(-/-) MSCs, whereas NO donors or PDGFR antagonist reduced tube formation ∼50% by murine and human MSCs. The antagonist also blocked the rescue of tube formation in GSNOR(-/-) MSCs by L-NAME or the GHRH agonists JI-38, MR-409, and MR-356. Therefore, GSNOR(-/-) MSCs have a deficient capacity for endothelial differentiation due to downregulation of PDGFRα related to NO/GSNOR imbalance. These findings unravel important aspects of modulation of MSCs by VEGF-A activation of the PDGFR and illustrate a paradoxical inhibitory role of S-nitrosylation signaling in MSC vasculogenesis. Accordingly, disease states characterized by NO deficiency may trigger MSC-mediated vasculogenesis. These findings have important implications for therapeutic application of GHRH agonists to ischemic disorders.

Effect and mechanism of erythropoietin on mesenchymal stem cell proliferation in vitro under the acute kidney injury microenvironment

Erythropoietin (EPO) can stimulate the proliferation and protraction of endothelial progenitor cells, and plays an important role in the proliferation and differentiation of marrow-derived mesenchymal stem cells (mMSCs) under the acute kidney injury (AKI) microenvironment. In the present study, C57BL/6 mice mMSCs were isolated, and AKI mice models were prepared. The renal cortex was obtained to prepare the ischemia/reperfusion (I/R) kidney homogenate supernatant. P3-mMSCs were treated by different methods: one group was added only I/R kidney homogenate supernatant, and another contained different concentrations of EPO (1, 5, 10, 50 IU/mL) in I/R kidney homogenate supernatant. The proliferation and apoptosis of mMSCs were detected by CCK-8 and TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling), respectively. Expression of erythropoietin receptor (EPOR) and protein of the signal pathway related to proliferation/apoptosis were also examined. The results showed that the proliferation ability of mMSCs treated with I/R kidney homogenate supernatant decreased significantly, while the apoptosis percentage was significantly higher than that of the control. After intervention of EPO, their proliferation enhanced and the apoptosis percentage decreased. EPOR expression was positive in P3-mMSCs. EPO decreased the expression of caspase-3 of mMSCs under the AKI microenvironment in a dose- and time-dependent manner, but increased the Bcl-2 expression. The expression of phosphor-Janus kinase 2, phosphor-signal transducer and activator of transcription (pSTAT-5) increased significantly in 10 IU/mL EPO cultured for five days. Our results show that EPO can promote proliferation of mMSCs in vitro under the AKI microenvironment, which is mediated by EPOR and related with the proliferation/apoptosis signal pathway.

Mechanism of TNF-α-induced migration and hepatocyte growth factor production in human mesenchymal stem cells

Accumulating evidence suggests that mesenchymal stem cells (MSCs) may decrease destructive inflammation and reduce tissue loss. Tumor necrosis factor-α (TNF-α) plays a central role in induction of proinflammatory signaling and paradoxically activates intracellular anti-inflammatory survival pathways. In this study, we investigated whether TNF-α could induce a chemotactic effect on human MSCs and stimulate their production of anti-inflammatory factors in vitro, as well as determined mechanisms that mediated this effect. Migration assays demonstrated that TNF-α had a chemotactic effect on MSCs. TNF-α increased both hepatocyte growth factor (HGF) mRNA expression in MSCs and HGF secretion in conditioned medium. These effects were dependent on the p38 MAPK and PI3K/Akt, but not JNK and ERK signaling pathways. Furthermore, these effects were inhibited by a specific neutralizing antibody to TNF receptor II, but not TNF receptor I. We conclude that TNF-α can enhance human MSCs migration and stimulate their production of HGF. These effects are mediated via a specific TNF receptor and signaling pathways.

Stem cells as a potential future treatment of pediatric intestinal disorders

All surgical disciplines encounter planned and unplanned ischemic events that may ultimately lead to cellular dysfunction and death. Stem cell therapy has shown promise for the treatment of a variety of ischemic and inflammatory disorders where tissue damage has occurred. As stem cells have proven beneficial in many disease processes, important opportunities in the future treatment of gastrointestinal disorders may exist. Therefore, this article will serve to review the different types of stem cells that may be applicable to the treatment of gastrointestinal disorders, review the mechanisms suggesting that stem cells may work for these conditions, discuss current practices for harvesting and purifying stem cells, and provide a concise summary of a few of the pediatric intestinal disorders that could be treated with cellular therapy.