Modulation of Human Cardiac Progenitors via Hypoxia-ERK Circuit Improves their Functional Bioactivities

Aβ1-40-Induced Platelet Adhesion Is Ameliorated by Rosmarinic Acid through Inhibition of NADPH Oxidase/PKC-δ/Integrin αIIbβ3 Signaling

In platelets, oxidative stress reportedly increases platelet adhesion to vessels, thus promoting the vascular pathology of various neurodegenerative diseases, including Alzheimer’s disease (AD). Recently, it has been shown that β-amyloid (Aβ) can increase oxidative stress in platelets; however, the underlying mechanism remains elusive. In the present study, we aimed to elucidate the signaling pathway of platelet adhesion induced by Aβ_1–40, the major form of circulating Aβ, through Western blotting, immunofluorescence confocal microscopy, and fluorescence-activated cell sorting analysis. Additionally, we examined whether rosmarinic acid (RA), a natural polyphenol antioxidant, can modulate these processes. Our results show that Aβ_1–40-induced platelet adhesion is mediated through NADPH oxidase/ROS/PKC-δ/integrin α_IIbβ₃ signaling, and these signaling pathways are significantly inhibited by RA. Collectively, these results suggest that RA may have beneficial effects on platelet-associated vascular pathology in AD.

Yuzu and Hesperidin Ameliorate Blood-Brain Barrier Disruption during Hypoxia via Antioxidant Activity

Yuzu and its main component, hesperidin (HSP), have several health benefits owing to their anti-inflammatory and antioxidant properties. We examined the effects of yuzu and HSP on blood-brain barrier (BBB) dysfunction during ischemia/hypoxia in an in vivo animal model and an in vitro BBB endothelial cell model, and also investigated the underlying mechanisms. In an in vitro BBB endothelial cell model, BBB permeability was determined by measurement of Evans blue extravasation in vivo and in vitro. The expression of tight junction proteins, such as claudin-5 and zonula occludens-1 (ZO-1), was detected by immunochemistry and western blotting, and the reactive oxygen species (ROS) level was measured by 2'7'-dichlorofluorescein diacetate intensity. Yuzu and HSP significantly ameliorated the increase in BBB permeability and the disruption of claudin-5 and ZO-1 in both in vivo and in vitro models. In bEnd.3 cells, yuzu and HSP were shown to inhibit the disruption of claudin-5 and ZO-1 during hypoxia, and the protective effects of yuzu and HSP on claudin-5 degradation seemed to be mediated by Forkhead box O 3a (FoxO3a) and matrix metalloproteinase (MMP)-3/9. In addition, well-known antioxidants, trolox and N-acetyl cysteine, significantly attenuated the BBB permeability increase, disruption of claudin-5 and ZO-1, and FoxO3a activation during hypoxia, suggesting that ROS are important mediators of BBB dysfunction during hypoxia. Collectively, these results indicate that yuzu and HSP protect the BBB against dysfunction via maintaining integrity of claudin-5 and ZO-1, and these effects of yuzu and HSP appear to be a facet of their antioxidant properties. Our findings may contribute to therapeutic strategies for BBB-associated neurodegenerative diseases.

Pharmacological inhibition of mTOR attenuates replicative cell senescence and improves cellular function via regulating the STAT3-PIM1 axis in human cardiac progenitor cells

The mammalian target of rapamycin (mTOR) signaling pathway efficiently regulates the energy state of cells and maintains tissue homeostasis. Dysregulation of the mTOR pathway has been implicated in several human diseases. Rapamycin is a specific inhibitor of mTOR and pharmacological inhibition of mTOR with rapamycin promote cardiac cell generation from the differentiation of mouse and human embryonic stem cells. These studies strongly implicate a role of sustained mTOR activity in the differentiating functions of embryonic stem cells; however, they do not directly address the required effect for sustained mTOR activity in human cardiac progenitor cells. In the present study, we evaluated the effect of mTOR inhibition by rapamycin on the cellular function of human cardiac progenitor cells and discovered that treatment with rapamycin markedly attenuated replicative cell senescence in human cardiac progenitor cells (hCPCs) and promoted their cellular functions. Furthermore, rapamycin not only inhibited mTOR signaling but also influenced signaling pathways, including STAT3 and PIM1, in hCPCs. Therefore, these data reveal a crucial function for rapamycin in senescent hCPCs and provide clinical strategies based on chronic mTOR activity.

Hypoxic Stress Decreases c-Myc Protein Stability in Cardiac Progenitor Cells Inducing Quiescence and Compromising Their Proliferative and Vasculogenic Potential

Cardiac progenitor cells (CPCs) have been shown to promote cardiac regeneration and improve heart function. However, evidence suggests that their regenerative capacity may be limited in conditions of severe hypoxia. Elucidating the mechanisms involved in CPC protection against hypoxic stress is essential to maximize their cardioprotective and therapeutic potential. We investigated the effects of hypoxic stress on CPCs and found significant reduction in proliferation and impairment of vasculogenesis, which were associated with induction of quiescence, as indicated by accumulation of cells in the G0-phase of the cell cycle and growth recovery when cells were returned to normoxia. Induction of quiescence was associated with a decrease in the expression of c-Myc through mechanisms involving protein degradation and upregulation of p21. Inhibition of c-Myc mimicked the effects of severe hypoxia on CPC proliferation, also triggering quiescence. Surprisingly, these effects did not involve changes in p21 expression, indicating that other hypoxia-activated factors may induce p21 in CPCs. Our results suggest that hypoxic stress compromises CPC function by inducing quiescence in part through downregulation of c-Myc. In addition, we found that c-Myc is required to preserve CPC growth, suggesting that modulation of pathways downstream of it may re-activate CPC regenerative potential under ischemic conditions.

Hypoxic preconditioning of human cardiosphere-derived cell sheets enhances cellular functions via activation of the PI3K/Akt/mTOR/HIF-1α pathway

Cell sheet technology is a promising therapeutic strategy for the treatment of ischemic diseases such as myocardial infarction. We recently developed a novel protocol, termed "hypoxic preconditioning," capable of augmenting the therapeutic efficacy of cell sheets. Following this protocol, the pro-angiogenic and anti-fibrotic activity of cell sheets were enhanced by brief incubation of cell sheets under hypoxic culture conditions. However, the precise molecular mechanism underlying the hypoxic preconditioning of cell sheets is unclear. In the present study, we examined signal transducers in cell sheets to identify those responsive to hypoxic preconditioning, using cardiosphere-derived cell (CDC) sheets. We initially tested whether sheet-like structures were suitable for hypoxic preconditioning by comparing them with individual cells. Hypoxic preconditioning was more effective in sheeted cells than in individual cells. Expression of hypoxia inducible factor-1α (HIF-1α) and mammalian target of rapamycin (mTOR) were induced upon hypoxic preconditioning of cell sheets, as was the phosphoinositide 3-kinase (PI3K)/Akt pathway. In addition, hypoxic preconditioning increased phosphorylation of epidermal growth factor receptor (EGFR) and heat shock protein 60 (HSP60) in CDC sheets. Our findings provide novel insights into the utility of hypoxic preconditioning in cell sheet-based technologies for the treatment of ischemic diseases.

Oxygen cycling to improve survival of stem cells for myocardial repair: A review

Heart disease represents the leading cause of death among Americans. There is currently no clinical treatment to regenerate viable myocardium following myocardial infarction, and patients may suffer progressive deterioration and decreased myocardial function from the effects of remodeling of the necrotic myocardium. New therapeutic strategies hold promise for patients who suffer from ischemic heart disease by directly addressing the restoration of functional myocardium following death of cardiomyocytes. Therapeutic stem cell transplantation has shown modest benefit in clinical human trials with decreased fibrosis and increased functional myocardium. Moreover, autologous transplantation holds the potential to implement these therapies while avoiding the immunomodulation concerns of heart transplantation. Despite these benefits, stem cell therapy has been characterized by poor survival and low engraftment of injected stem cells. The hypoxic tissue environment of the ischemic/infracting myocardium impedes stem cell survival and engraftment in myocardial tissue. Hypoxic preconditioning has been suggested as a viable strategy to increase hypoxic tolerance of stem cells. A number of in vivo and in vitro studies have demonstrated improved stem cell viability by altering stem cell secretion of protein signals and up-regulation of numerous paracrine signaling pathways that affect inflammatory, survival, and angiogenic signaling pathways. This review will discuss both the mechanisms of hypoxic preconditioning as well as the effects of hypoxic preconditioning in different cell and animal models, examining the pitfalls in current research and the next steps into potentially implementing this methodology in clinical research trials.

Hypoxia induces FoxO3a-mediated dysfunction of blood-brain barrier

The Forkhead box O 3a (FoxO3a), a transcription factor, is known to be involve in change of endothelial permeability. During hypoxia, blood-brain barrier (BBB) permeability is increased through degradation of vascular endothelium cadherin (VE-cadherin) and clsudin-5. The hypoxia also increased mRNA levels of matrix metalloproteinase (MMP)-3/9 and promoted translocation of FoxO3a into nucleus in endothelial cells. However, little is known about the role of FoxO3a in hypoxia-induced BBB hyperpermeability. Here, we examined whether FoxO3a regulates hypoxia-induced BBB permeability through induction of MMPs. The transfection of siFoxO3a suppressed hypoxia-induced BBB hyperpermeability. The transfection of siFoxO3a also inhibited hypoxia-induced degradation of VE-cadherin and claudin-5. In addition, the transfection of siFoxO3a reduced hypoxia-induced increase of MMP-3 mRNA levels. However, transfection of siFoxO3a did not inhibits transcription of MMP-9 induced by hypoxia. Taken together, our findings suggest that FoxO3a is involved in hypoxia-induced degradation of VE-cadherin and claudin-5 through induction of MMPs indirectly.

Stem cell factor is a potent endothelial permeability factor

OBJECTIVE

Although stem cell factor (SCF) has been shown to play a critical role in hematopoiesis, gametogenesis, and melanogenesis, the function of SCF in the regulation of vascular integrity has not been studied.

APPROACH AND RESULTS

We demonstrated that SCF binds to and activates the cKit receptor in endothelial cells, thereby increasing the internalization of vascular endothelial-cadherin and enhancing extravasation of dyes to a similar extent as vascular endothelial growth factor. SCF-mediated cKit activation in endothelial cells enhanced the phosphorylation of endothelial nitric oxide (NO) synthase via the phosphoinositide 3-kinase/Akt signaling pathway and subsequently increased the production of NO. Inhibition of endothelial NO synthase expression and NO synthesis using small interfering RNA knockdown and chemical inhibitors substantially diminished the ability of SCF to increase the internalization of vascular endothelial-cadherin and in vitro endothelial permeability. SCF-induced increase in extravasation of the dyes was abrogated in endothelial NO synthase knockout mice, which indicates that endothelial NO synthase-mediated NO production was responsible for the SCF-induced vascular leakage. Furthermore, we demonstrated that the expression of SCF and cKit was significantly higher in the retina of streptozotocin-injected diabetic mice than in the nondiabetic control animals. Depletion of SCF by intravitreous injection of anti-SCF-neutralizing immunoglobulin G significantly prevented vascular hyperpermeability in the retinas of streptozotocin-injected diabetic mice.

CONCLUSIONS

Our data reveal that SCF disrupts the endothelial adherens junction and enhances vascular leakage, as well as suggest that anti-SCF/cKit therapy may hold promise as a potential therapy for the treatment of hyperpermeable vascular diseases.