Biomechanical forces in atherosclerosis-resistant vascular regions regulate endothelial redox balance via phosphoinositol 3-kinase/Akt-dependent activation of Nrf2

Harvard University, Cambridge, Massachusetts, United States
Circulation Research (Impact Factor: 11.02). 10/2007; 101(7):723-33. DOI: 10.1161/CIRCRESAHA.107.152942
Source: PubMed


Local patterns of biomechanical forces experienced by endothelial cells (ECs) in different vascular geometries appear to play an essential role in regulating EC function and determining the regional susceptibility to atherosclerosis, even in the face of systemic risk factors. To study how biomechanical forces regulate EC redox homeostasis, an important pathogenic factor in atherogenesis, we have cultured human ECs under 2 prototypic arterial shear stress waveforms, "atheroprone" and "atheroprotective," which were derived from 2 distinct vascular regions in vivo that are typically "susceptible" or "resistant" to atherosclerosis. We demonstrate that atheroprotective flow decreases EC intracellular redox level and protects ECs against oxidative stress-induced injury. To identify the molecular mechanisms that control this cellular response, we examined several major oxidative/antioxidative pathways and found that atheroprotective flow upregulated certain antioxidant genes and strongly activated the transcription factor Nrf2. Using a strategy of small interfering RNA inhibition of Nrf2 expression combined with genome-wide transcriptional profiling, we determined the downstream targets of Nrf2 activation and identified Nrf2 as a critical determinant for the changes in endothelial redox balance exerted by atheroprotective flow. In addition, we showed that atheroprotective flow activates Nrf2 via the phosphoinositol 3-kinase/Akt pathway, and this activation occurs differentially in atherosclerosis-resistant and atherosclerosis-susceptible regions of the mouse aorta. Taken together, our data demonstrate that hemodynamic forces present in atherosclerosis-resistant and -susceptible regions of the vasculature differentially regulate EC redox state and antioxidant potential. These alterations in redox homeostasis are primarily the result of the phosphoinositol 3-kinase/Akt-dependent activation of Nrf2 and its downstream transcriptional targets.

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    • "In addition, miR-221 targets PI3KR1 that is involved in the regulation of PI3K/Akt-mediated signaling that was shown to stimulate the atheroprotective transcription factor Nrf2 (nuclear factor (erythroid-derived 2)-like 2) [120]. Notably, expression of Nrf2 in ECs is induced by mechanical forces (e.g., by shear stress) [123] and contributes to formation of the endothelial regional atherosclerosis-resistant phenotype in vessels [120]. In ECs, Nrf2 drives expression of several antioxidant genes and downregulates several inflammatory mediators such as monocyte chemoattractant protein(MCP- ) 1 and vascular cell adhesion molecule-1 (VCAM- 1) therefore enhancing antioxidant and anti-inflammatory properties of the arterial epithelium [124]. "
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    ABSTRACT: A cluster of miR-221/222 is a key player in vascular biology through exhibiting its effects on vascular smooth muscle cells (VSMCs) and endothelial cells (ECs). These miRNAs contribute to vascular remodeling, an adaptive process involving phenotypic and behavioral changes in vascular cells in response to vascular injury. In proliferative vascular diseases such as atherosclerosis, pathological vascular remodeling plays a prominent role. The miR-221/222 cluster controls development and differentiation of ECs but inhibits their proangiogenic activation, proliferation, and migration. miR-221/222 are primarily implicated in maintaining endothelial integrity and supporting quiescent EC phenotype. Vascular expression of miR-221/222 is upregulated in initial atherogenic stages causing inhibition of angiogenic recruitment of ECs and increasing endothelial dysfunction and EC apoptosis. In contrast, these miRNAs stimulate VSMCs and switching from the VSMC "contractile" phenotype to the "synthetic" phenotype associated with induction of proliferation and motility. In atherosclerotic vessels, miR-221/222 drive neointima formation. Both miRNAs contribute to atherogenic calcification of VSMCs. In advanced plaques, chronic inflammation downregulates miR-221/222 expression in ECs that in turn could activate intralesion neoangiogenesis. In addition, both miRNAs could contribute to cardiovascular pathology through their effects on fat and glucose metabolism in nonvascular tissues such as adipose tissue, liver, and skeletal muscles.
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    • "However, upon exposure to oxidative stress, Nrf2 is released from Keap1, tranlocates into the nucleus and stimulates antioxidant response element (ARE)-dependent phase II gene expression 7, 8. There is increasing evidence to suggest that the role of Nrf2 in cardio-protection, such as fighting against pathological cardiac remodeling by suppresses oxidative stress and cell death 9,10, protection myocardium from ischemia /reperfusion injury by upregulating of antioxidative enzymes 11, and delay atherosclerotic lesions 12. Moreover, the studies supporting a role for Nrf2 in angiogenesis have shown that Nrf2 may promote vascular development through protection of the retina from hyperoxia induced oxidative stress in vivo 13, and that Nrf2 knockdown inhibits colon tumor angiogenesis in vitro 14 and cervical cancer growth in vivo 15. "
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    ABSTRACT: Angiogenesis plays an important role in myocardial repair after myocardial infarction (MI). Cardiac micro-vascular endothelial cells (CMECs) are important participants in myocardial angiogenesis processes. Recent studies have revealed that Nuclear factor-erythroid 2-related factor 2 (Nrf2), a master transcription factor of endogenous anti-oxidative defense systems, exerts cardio-protection in the cardiovascular system. However, the role of Nrf2 in the process of myocardial angiogenesis and corresponding mechanisms are not fully understood. Thus, the present study investigated the role of Nrf2 in the angiogenesis of rat CMECs to hypoxia. Trans-well assay, three-dimensional Matrigel assay were used to determine cell migration and vascular tube formation. Real-time RT-PCR, ELISA and Western blot were measured mRNA and protein expression. Here, we report that the mRNA and protein expression of Nrf2 and heme oxygenase-1(HO-1) were temporarily upregulated under hypoxic condition. Furthermore, knock down of Nrf2 significantly suppressed the migration and vascular tube formation of rat CMECs to hypoxia, Nrf2 knockdown also significantly decreased HO-1 and vascular endothelial growth factor (VEGF) expression at 48 h after transfection under hypoxic condition. Finally, transfection of CMECs with the Nrf2 over-expressing lentiviral vector upregulated HO-1 expression with a concomitant increase in cell migration and vascular tube formation induced by hypoxia, and this effect was greatly attenuated in the presence of ZnPP (a HO-1 inhibitor). Taken together, these results suggest that Nrf2 may mediate the angiogenesis of CMECs under hypoxic condition, and HO-1 is involved in regulating the angiogenesis of CMECs through Nrf2. Therefore, Nrf2 is a potent regulator of hypoxia-condition mediated angiogenesis in CMECs, which may provide a therapeutic strategy for myocardial repair after MI.
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    • "Remarkably, there was no overlap in the predicted transcription factors between WKY and SHR (Table 7). Several of the identified binding sites in WKY collaterals were for transcription factors known to be sensitive to mechanical stimulation (shear stress and/or circumferential wall stress) or redox status, including at least three known to be influenced by both mechanical stimuli and reactive oxygen or nitrogen species (NFĸB [Allen and Tresini 2000; Davis et al. 2004; Lan et al. 1994], AP-1[activator protein 1] [Lan et al. 1994; Allen and Tresini 2000], and NF-E2 [nuclear factor, erythroid derived 2] [Dai et al. 2007; Warabi et al. 2007]). "
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    ABSTRACT: Analysis of global gene expression in mesenteric control and collateral arteries was used to investigate potential molecules, pathways, and mechanisms responsible for impaired collateral growth in the Spontaneously Hypertensive Rat (SHR). A fundamental difference was observed in overall gene expression pattern in SHR versus Wistar Kyoto (WKY) collaterals; only 6% of genes altered in collaterals were similar between rat strains. Ingenuity® Pathway Analysis (IPA) identified major differences between WKY and SHR in networks and biological functions related to cell growth and proliferation and gene expression. In SHR control arteries, several mechano-sensitive and redox-dependent transcription regulators were downregulated including JUN (-5.2×, P = 0.02), EGR1 (-4.1×, P = 0.01), and NFĸB1 (-1.95×, P = 0.04). Predicted binding sites for NFĸB and AP-1 were present in genes altered in WKY but not SHR collaterals. Immunostaining showed increased NFĸB nuclear translocation in collateral arteries of WKY and apocynin-treated SHR, but not in untreated SHR. siRNA for the p65 subunit suppressed collateral growth in WKY, confirming a functional role of NFkB. Canonical pathways identified by IPA in WKY but not SHR included nitric oxide and renin-angiotensin system signaling. The angiotensin type 1 receptor (AGTR1) exhibited upregulation in WKY collaterals, but downregulation in SHR; pharmacological blockade of AGTR1 with losartan prevented collateral luminal expansion in WKY. Together, these results suggest that collateral growth impairment results from an abnormality in a fundamental regulatory mechanism that occurs at a level between signal transduction and gene transcription and implicate redox-dependent modulation of mechano-sensitive transcription factors such as NFĸB as a potential mechanism.
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