TGF-alpha increases human mesenchymal stem cell-secreted VEGF by MEK- and PI3-K- but not JNK- or ERK-dependent mechanisms

MEK mediates the novel cross talk between TNFR2 and TGF-EGFR in enhancing vascular endothelial growth factor (VEGF) secretion from human mesenchymal stem cells

BACKGROUND

Bone marrow mesenchymal stem cells (MSCs) may mediate their beneficial effects by paracrine mechanisms. Recently, we reported that tumor necrosis factor-alpha (TNF-alpha) increased the release of vascular endothelial growth factor (VEGF) from human MSCs and augmented transforming growth factor-alpha (TGF-alpha)-stimulated VEGF secretion. However, it is unknown whether TNF-alpha stimulates VEGF production via TNF receptor 1 (TNFR1) or 2 (TNFR2) and the mechanism by which TNF-alpha augments TGF-alpha (a ligand of epidermal growth factor receptor, EGFR) stimulated VEGF production. We hypothesized that the ablation of TNFR2 would decrease TNF-alpha-stimulated and/or TGF-alpha- stimulated VEGF production via MEK-dependent mechanisms.

METHODS

MSCs transfected with TNFR1, TNFR2, or GAPDH siRNA were stimulated with TNF-alpha and/or TGF-alpha for 24 h. VEGF levels in the supernatant were determined by enzyme-linked immunosorbent assay (ELISA). A Western blot analysis was performed to measure the activation of MEK and ERK and the expression of TNFR1 and TNFR2.

RESULTS

TNF-alpha or TGF-alpha increased VEGF secretion in cells transfected with GAPDH or TNFR1 siRNA. The combination of TNF-alpha and TGF-alpha increased VEGF production. TNF-alpha and/or TGF-alpha stimulation increased phospho-MEK and phospho-ERK in cells transfected with TNFR1 siRNA. Conversely, the effects of TNF-alpha and/or TGF-alpha on MSC VEGF production were significantly decreased, and MEK/ERK activation was negated in cells transfected TNFR2 siRNA.

CONCLUSION

TNFR2 plays a vital role in the effects of TNF-alpha and TGF-alpha on MSC VEGF production. The activation of MEK was implicated in this novel cross talk between TNFR2 and TGF-alpha-EGFR in regulating the production of VEGF in human MSCs.

High glucose concentration in cell culture medium does not acutely affect human mesenchymal stem cell growth factor production or proliferation

Optimizing the function and proliferative capacity of stem cells is essential to maximize their therapeutic benefits. High glucose concentrations are known to have detrimental effects on many cell types. We hypothesized that human mesenchymal stem cells (hMSCs) cultured in high glucose-containing media would exhibit diminished proliferation and attenuated production of VEGF, hepatocyte growth factor (HGF), and FGF2 in response to treatment with TNF-alpha, LPS, or hypoxia. hMSCs were plated in medium containing low (5.5 mM) and high (20 mM or 30 mM) glucose concentrations and treated with TNF-alpha, LPS, or hypoxia. Supernatants were collected at 24 and 48 h and assayed via ELISA for VEGF, HGF, and FGF2. In addition, hMSCs were cultured on 96-well plates at the above glucose concentrations, and proliferation at 48 h was determined via bromo-2'-deoxy-uridine (BrdU) incorporation. At 24 and 48 h, TNF-alpha, LPS, and hypoxia-treated hMSCs produced significantly higher VEGF, HGF, and FGF2 compared with control. Hypoxia-induced VEGF production by hMSCs was the most pronounced change over baseline. At both 24 and 48 h, glucose concentration did not affect production of VEGF, HGF, or FGF2 by untreated hMSCs and those treated with TNF-alpha, LPS, or hypoxia. Proliferation of hMSCs as determined via BrdU incorporation was unaffected by glucose concentration of the media. Contrary to what has been observed with other cells, hMSCs may be resistant to the short-term effects of high glucose. Ongoing efforts to characterize and optimize ex vivo and in vivo conditions are critical if the therapeutic benefits of MSCs are to be maximized.

Role of tumor necrosis factor receptor 1 in sex differences of stem cell mediated cardioprotection

BACKGROUND

Mesenchymal stem cells (MSCs) hold great therapeutic potential for the repair and regeneration of ischemic tissue, possibly through the release of beneficial paracrine factors. Sex differences have been observed in the paracrine function of MSCs. Female stem cells produce lower proinflammatory cytokines and higher levels of growth factors compared with their male counterparts. Ablation of tumor necrosis factor receptor 1 (TNFR1) increases protective growth factor production by male, but not by female, MSCs. We therefore hypothesized the following: (1) that female MSCs would improve myocardial recovery compared with male MSCs after ischemia-reperfusion injury (I/R); and (2) that MSCs isolated from TNFR1 knock out male, but not female, mice, would improve postischemic myocardial recovery compared with their wild type (WT) counterparts.

METHODS

Male adult Sprague-Dawley rat hearts were subjected to I/R by Langendorff isolated heart preparation. The MSCs were harvested from adult mice and cultured under normal conditions. Immediately prior to ischemia, one million MSCs were infused into the coronary circulation. Cardiac functional parameters were recorded continuously.

RESULTS

Pretreatment with MSCs from either sex significantly increased postischemic myocardial recovery as evidenced by improved left ventricular developed pressure, contractility, and rate of relaxation. Infusion with female MSCs was associated with a greater degree of myocardial recovery after I/R compared with male MSCs. The TNFR1 deficiency increased the degree of myocardial recovery associated with male MSCs, but not with female MSCs. No additional cardioprotection was observed when TNFR1 was ablated in female MSCs.

CONCLUSION

Sex differences influence the cardioprotective effects of both WT and TNFR1 ablated MSCs.