Role of HIF-1alpha and VEGF in human mesenchymal stem cell proliferation by 17beta-estradiol: involvement of PKC, PI3K/Akt, and MAPKs

Treatment with a novel hypoxia-inducible factor hydroxylase inhibitor (TRC160334) ameliorates ischemic acute kidney injury

BACKGROUND

Hypoxia-inducible factor (HIF) transcriptional system plays a central role in cellular adaptation to low oxygen levels. Preconditional activation of HIF and/or expression of its individual target gene products leading to cytoprotection have been well established in hypoxic/ischemic renal injury. Increasing evidence indicate HIF activation is involved in hypoxic/ischemic postconditioning of heart, brain and kidney. Very few studies evaluated the potential benefits of postischemia HIF activation in renal injury employing a pharmacological agent. We hypothesized that postischemia augmentation of HIF activation with a pharmacological agent would protect renal ischemia/reperfusion injury. For this, TRC160334, a novel HIF hydroxylase inhibitor, was used.

METHODS

TRC160334, a novel HIF hydroxylase inhibitor, was synthesized. Ability of TRC160334 for stabilization of HIF-α and consequent HIF activation was evaluated in Hep3B cells. Efficacy of TRC160334 was evaluated in a rat model of ischemia/reperfusion-induced AKI. Two different treatment protocols were employed, one involved treatment with TRC160334 before onset of ischemia, the other involved treatment after the reperfusion of kidneys.

RESULTS

TRC160334 treatment results in stabilization of HIF-α leading to HIF activation in Hep3B cells. Significant reduction in renal injury was observed by both treatment protocols and remarkable reduction in serum creatinine (23 and 71% at 24 and 48 h, respectively, p < 0.01) was observed with TRC160334 treatment applied after reperfusion. Urine output was significantly improved up to 24 h by both treatment protocols.

CONCLUSION

The data presented here provide pharmacologic evidence for postischemia augmentation of HIF activation by TRC160334 as a promising and clinically feasible strategy for the treatment of renal ischemia/reperfusion injury.

Rapid actions of plasma membrane estrogen receptors regulate motility of mouse embryonic stem cells through a profilin-1/cofilin-1-directed kinase signaling pathway

Long-term estrogen actions are vital for driving cell growth, but more recent evidence suggests that estrogen mediates more rapid cellular effects. However, the function of estradiol-17β (E(2))-BSA in mouse embryonic stem cells has not been reported. Therefore, we examined the role of E(2)-BSA in mouse embryonic stem cell motility and its related signal pathways. E(2)-BSA (10(-8) m) significantly increased motility after 24 h incubation and increased filamentous (F)-actin expression; these effects were inhibited by the estrogen receptor antagonist ICI 182,780, indicating that E(2)-BSA bound membrane estrogen receptors and initiated a signal. E(2)-BSA increased c-Src and focal adhesion kinase (FAK) phosphorylation, which was attenuated by ICI 182,780. The E(2)-BSA-induced increase in epidermal growth factor receptor (EGFR) phosphorylation was inhibited by Src inhibitor PP2. As a downstream signal molecule, E(2)-BSA activated cdc42 and increased formation of a complex with the neural Wiskott-Aldrich syndrome protein (N-WASP)/cdc42/transducer of cdc42-dependent actin assembly-1 (TOCA-1), which was inhibited by FAK small interfering RNA (siRNA) and EGFR inhibitor AG 1478. In addition, E(2)-BSA increased profilin-1 expression and cofilin-1 phosphorylation, which was blocked by cdc42 siRNA. Subsequently, E(2)-BSA induced an increase in F-actin expression, and cell motility was inhibited by each signal pathway-related siRNA molecule or inhibitors but not by cofilin-1 siRNA. A combined treatment of cofilin-1 siRNA and E(2)-BSA increased F-actin expression and cell motility more than that of E(2)-BSA alone. These data demonstrate that E(2)-BSA stimulated motility by interacting with profilin-1/cofilin-1 and F-actin through FAK- and c-Src/EGFR transactivation-dependent N-WASP/cdc42/TOCA-1 complex.

Induction of inducible nitric oxide synthase by isoflurane post-conditioning via hypoxia inducible factor-1α during tolerance against ischemic neuronal injury

Recent studies have shown that isoflurane protects against ischemic injury via inducible nitric oxide synthase (iNOS). Hypoxia inducible factor (HIF)-1α is a transcriptional factor that activates after cerebral ischemia. However, whether iNOS gene containing the sequence of the hypoxia response element (HRE) is a HIF-1α target during tolerance against ischemic neuronal injury induced by isoflurane post-conditioning remains unknown. In this study, we report that HIF-1α and iNOS gene expression were augmented after cerebral ischemia in rats. Furthermore, isoflurane post-conditioning resulted in greater accumulation of HIF-1α and iNOS gene expression, following by HIF-1α transcriptional activity enhancement and co-localization of HIF-1α and iNOS. Accordingly, in the primary cortical neuron cultures, silencing of HIF-1α attenuated the accumulation of iNOS and the protective effects of isoflurane post-conditioning. Our results suggest the involvement of HIF-1α in the regulation of iNOS during tolerance against cerebral ischemia induced by isoflurane post-conditioning, which provide a mechanistic basis of novel therapeutic strategies for ischemic stroke.

Phosphatidylinositol 3′-kinase signaling pathway is essential for Rac1-induced hypoxia-inducible factor-1α and vascular endothelial growth factor expression

We have previously demonstrated the roles of RhoA, Rac1, and Cdc42 in hypoxia-driven angiogenesis. However, the role of oncogenes in hypoxia signaling is poorly understood. Given the importance of Rho proteins in the hypoxic response, we hypothesized that Rho family members could act as mediators of hypoxic signal transduction. We investigated the cross-talk between hypoxia and oncogene-driven signal transduction pathways and explored the role of Rac1 on hypoxia-induced hypoxia-inducible factor (HIF)-1α and VEGF expression. Since the phosphatidylinositol 3′-kinase (PI3K) pathway is involved in signal transduction of many oncogenes, we explored the role of PI3K on Rac1-mediated expression of HIF-1α and VEGF in hypoxia. We showed that LY-294002, a PI3K inhibitor, suppressed HIF-1α and VEGF induction under hypoxic conditions by up to 50%. Activation of Rac1 resulted in an upregulation of hypoxia-induced HIF-1α expression, which was blocked by LY-294002. These data suggested that Rac1 is an intermediate in the PI3K-mediated induction of HIF-1α. Interestingly, there was a significant downregulation of the tumor suppressor genes p53 and von Hippel-Lindau tumor suppressor (VHL) in cells expressing a constitutively active form of Rac1. Rac1-mediated inhibition of p53 and VHL could therefore be implicated in the upregulation of HIF-1α expression.

Intracoronary mesenchymal stem cells promote postischemic myocardial functional recovery, decrease inflammation, and reduce apoptosis via a signal transducer and activator of transcription 3 mechanism

BACKGROUND

Signal transducer and activator of transcription 3 (STAT3) regulates myocardial apoptosis, cellular proliferation, and the immune response after ischemia/reperfusion (I/R). STAT3 is also necessary for the production of vascular endothelial growth factor (VEGF) by mesenchymal stem cells (MSCs), which are known to reduce myocardial injury after I/R. However, it remains unknown whether STAT3 is an important mediator of MSC-based cardioprotection. We hypothesized that knockout of stem cell STAT3 would reduce MSC-derived myocardial functional recovery and increase myocardial inflammatory and apoptotic signaling.

STUDY DESIGN

With a Langendorff apparatus, male rat hearts were subjected to 15 minutes of equilibration and 25 minutes of ischemia, followed by 40 minutes of reperfusion. Immediately before ischemia, hearts received intracoronary infusions of vehicle, wild-type MSCs (WT MSCs) or STAT3 knockout MSCs (STAT3KO MSCs). Heart function was measured continuously. Myocardial homogenates were analyzed for production of interleukin (IL)-1, IL-6, and tumor necrosis factor-α (TNF-α). Additionally, MSC production of hepatocyte growth factor (HGF) and insulin-like growth factor-1 (IGF-1) were measured in vitro.

RESULTS

Hearts treated with WT MSCs exhibited the greatest functional recovery, and those treated with STAT3KO MSCs had equivalent recovery to vehicle. The highest proinflammatory cytokine levels were seen in vehicle-treated hearts, and the lowest in the WT MSC group. STAT3KO MSCs produced less IGF-1, but more HGF than WT MSCs. Finally, hearts treated with STAT3KO MSCs or vehicle had significantly higher caspase-3 levels than those treated with WT MSCs.

CONCLUSIONS

Intracoronary infusions of MSCs improve postischemic left ventricular function and reduce proapoptotic and proinflammatory signaling via a STAT3-dependent mechanism.

Hypoxia inducible factor-1α expression in areca quid chewing-associated oral squamous cell carcinomas

OBJECTIVES

Hypoxia inducible factor (HIF)-1α gene expression is mainly induced by tissue hypoxia. Overexpression of HIF-1α has been demonstrated in a variety of cancers. The aim of this study was to compare HIF-1α expression in normal human oral epithelium and areca quid chewing-associated oral squamous cell carcinoma (OSCC) and further to explore the potential mechanisms that may lead to induce HIF-1α expression.

METHODS

Twenty-five OSCC from areca quid chewing-associated OSCC and 10 normal oral tissue biopsy samples without areca quid chewing were analyzed by immunohistochemistry. The oral epithelial cell line GNM cells were challenged with arecoline, a major areca nut alkaloid, by using Western blot analysis. Furthermore, glutathione precursor N-acetyl-l-cysteine (NAC), AP-1 inhibitor curcumin, extracellular signal-regulated protein kinase inhibitor PD98059, and protein kinase C inhibitor staurosporine were added to find the possible regulatory mechanisms.

RESULTS

Hypoxia inducible factor-1α expression was significantly higher in OSCC specimens than normal specimen (P<0.05). Arecoline was found to elevate HIF-1α expression in a dose- and time-dependent manner (P<0.05). The addition of NAC, curcumin, PD98059, and staurosporine markedly inhibited the arecoline-induced HIF-1α expression (P<0.05).

CONCLUSIONS

Hypoxia inducible factor-1α expression is significantly upregulated in areca quid chewing-associated OSCC and HIF-1α expression induced by arecoline is downregulated by NAC, curcumin, PD98059, and staurosporine.

Supraphysiological estrogen levels adversely impact proliferation and histone modification in human embryonic stem cells: possible implications for controlled ovarian hyperstimulation assisted pregnancy

OBJECTIVE

Controlled ovarian hyperstimulation (COH) results in supraphysiologic levels of maternal serum estradiol (E(2)) during the luteal phase, thus promoting oocyte production at unknown risk to the subsequently developing embryo. Human embryonic stem cells (hESCs) have been identified as a model system to assess the impact of COH on early embryonic development, specifically 17β-estradiol mediated effects on proliferation, gene expression, and histone modification.

STUDY DESIGN

Cell proliferation and associated factors, such as HDAC1, as well as histone modification patterns were evaluated in ERα and β expressing hESCs after exposure to 17β-estradiol (1×10(-10) M to 1×10(-7) M), as well as in an untreated control.

RESULTS

Resultant data revealed that while physiologically relevant E(2) levels (1×10(-9)M E(2)) induced cell cycle progression from G1 to the proliferation phase, supraphysiologic levels akin to those observed after COH (1×10(-7) M E(2)) adversely affected hESCs proliferation via down regulation of HDAC1. Modification of H3K9me2, PhH3S10, H4K5ac, and H2A.Z histone patterns were also dependent on 17β-estradiol concentration.

CONCLUSION

While physiologic levels of 17β-estradiol induced cell proliferation, possibly via HDAC1 involvement in histone modification, cell proliferation in hESCs was suppressed at supraphysiologic levels.

Timing of the vascular actions of estrogens in experimental and human studies: why protective early, and not when delayed?

Estrogens, and in particular 17β-estradiol (E2), play a pivotal role in sexual development and reproduction and are also implicated in a large number of physiological processes including the cardiovascular system. Although epidemiological studies and Nurses' Health Study suggested, and all animal models of early atheroma clearly demonstrated a vasculoprotective action of both endogenous and exogenous estrogens, the Women's Health Initiative did not confirm the preventive action of estrogens against coronary heart disease (CHD). However, women who initiated hormone therapy closer to menopause tended to have reduced CHD risk compared with increased CHD risk among women more distant from menopause. Thus, it is now mandatory to try to understand the mechanisms that could have influenced the actions of estrogens at various stages of atherosclerosis and/or of life. In this current review, we will summarize our understanding of the potential cellular targets and mechanisms of the vasculoprotective actions of estrogens, as well as of the lack of action of estrogens when administered after a period of hormonal deprivation. The mechanisms of the aggravating role of progestogens such as medroxyprogesterone acetate will be considered. Finally, we will analyze the possibilities to uncouple some beneficial from other undesirable actions following the partial/selective activation of estrogen receptors.

Gender dimorphisms in progenitor and stem cell function in cardiovascular disease

Differences in cardiovascular disease outcomes between men and women have long been recognized and attributed, in part, to gender and sex steroids. Gender dimorphisms also exist with respect to the roles of progenitor and stem cells in post-ischemic myocardial and endothelial repair and regeneration. Understanding how these cells are influenced by donor gender and the recipient hormonal milieu may enable researchers to further account for the gender-related disparities in clinical outcomes as well as utilize the beneficial effects of these hormones to optimize transplanted cell function and survival. This review discusses (1) the cardiovascular effects of sex steroids (specifically estradiol and testosterone); (2) the therapeutic potentials of endothelial progenitor cells, mesenchymal stem cells, and embryonic stem cells; and (3) the direct effect of sex steroids on these cell types.

The role of hypoxia in bone marrow-derived mesenchymal stem cells: considerations for regenerative medicine approaches

Bone marrow-derived mesenchymal stem cells (MSCs) have demonstrated potential for regenerative medicine strategies. Knowledge of the way these cells respond to their environment in in vitro culture and after implantation in vivo is crucial for successful therapy. Oxygen tension plays a pivotal role in both situations. In vivo, a hypoxic environment can lead to apoptosis, but hypoxic preconditioning of MSCs and overexpression of prosurvival genes like Akt can reduce hypoxia-induced cell death. In cell culture, hypoxia can increase proliferation rates and enhance differentiation along the different mesenchymal lineages. Hypoxia also modulates the paracrine activity of MSCs, causing upregulation of various secretable factors, among which are important angiogenic factors such as vascular endothelial growth factor and interleukin-6 (IL6). Finally, hypoxia plays an important role in mobilization and homing of MSCs, primarily by its ability to induce stromal cell-derived factor-1 expression along with its receptor CXCR4. This article reviews the current literature on the effects of hypoxia on MSCs and aims to elucidate its potential role in regenerative medicine strategies.

Role of FAK phosphorylation in hypoxia-induced hMSCS migration: involvement of VEGF as well as MAPKS and eNOS pathways

Here we show that the effect of hypoxia on human umbilical cord blood mesenchymal stem cell (hMSC) migration is via the modulation of focal adhesion kinase (FAK) and its related signaling pathways. Hypoxia increased hMSC migration and cell viability, whereas lactate dehydrogenase (LDH) release was not affected for up to 48 h (data not shown). In addition, hypoxia increased the level of reactive oxygen species (ROS) generation in a time-dependent manner. Hypoxia-induced phosphorylation of p38 mitogen-activated protein kinase (MAPK) and stress-activated protein kinase/c-Jun NH(2)-terminal kinase (SAPK/JNK) were inhibited by the antioxidant (N-acetylcysteine, NAC, 10(-6) M) and (taurine, 4x10(-6) M). Hypoxia-induced endothelial nitric oxide synthase (eNOS) phosphorylation was regulated by p38 MAPK and SAPK/JNK activation. In addition, hypoxia increased the level of hypoxia inducible factor (HIF)-1alpha expression, which was blocked by inhibition of eNOS. Also, hypoxia-induced expression of Flk-1, vascular endothelial growth factor (VEGF), and its secreted form were inhibited by HIF-1alpha small interfering RNA (siRNA). In this hypoxic condition, FAK and Src phosphorylation were increased in a time-dependent manner. Inhibition of Src with specific inhibitor (PP2, 10(-8) M) blocked hypoxia-induced FAK activation. Subsequently, hypoxia-induced FAK phosphorylation was blocked by VEGF siRNA. Finally, hypoxia-induced increase of hMSC migration was inhibited by FAK siRNA. The results indicate that hypoxia increases migration of hMSCs via VEGF-mediated FAK phospholylation and involves the cooperative activity of the ROS, MAPK, eNOS and HIF-1alpha pathways.

Prolyl hydroxylase 2 deficiency limits proliferation of vascular smooth muscle cells by hypoxia-inducible factor-1{alpha}-dependent mechanisms

Arterial O(2) levels are thought to modulate vascular smooth muscle cell (VSMC) proliferation and vascular remodeling, but the mechanisms involved are poorly understood. Here, we tested the hypothesis that PHD2, a prolyl hydroxylase domain (PHD)-containing O(2) sensor, modulates growth factor-induced proliferative responses of human pulmonary artery SMC (HPASMC). We found that both PHD1 and PHD2 were robustly expressed by HPASMC, and inhibiting prolyl hydroxylase activity pharmacologically by using the nonselective dioxygenase inhibitor dimethyloxalylglycine (DMOG) inhibited proliferation and cyclin A expression induced by PDGF-AB or FGF-2. Specific knockdown of PHD2 using small interfering RNAs had similar effects. The inhibitory effects of DMOG and PHD2 knockdown on proliferation and cyclin A expression were seen under both normoxic (20% O(2)) and moderately hypoxic (5% O(2)) conditions, and PHD2 expression was not affected by O(2) level nor by stimulation with PDGF or FGF-2, indicating that the proproliferative influence of PHD2 does not involve alterations of its expression. Knockdown of PHD2 increased hypoxia-inducible factor (HIF)-1alpha expression, as expected, but we also found that HIF-1alpha knockdown abolished the inhibitory effect of PHD2 knockdown on PDGF-induced cyclin A expression. Therefore, we conclude that PHD2 promotes growth factor-induced responses of human VSMC, acting by HIF-1alpha-dependent mechanisms. Given the role of PHD2 as an oxygen sensor in mammalian cells, these results raise the possibility that PHD2 links VSMC proliferation to O(2) availability.