Angiotensin AT2 receptor stimulates ERK1 and ERK2 in quiescent but inhibits ERK in NGF-stimulated PC12W cells
ABSTRACT To investigate the influence of AT2 receptor stimulation on the ERK pathway and elucidate potential mechanisms of angiotensin II (ANG II)-mediated neuronal differentiation, we analysed tyrosine phosphorylation and activity of ERK after ANG II treatment of both quiescent and NGF-treated PC12W cells. Tyrosine phosphorylation of ERK1 and ERK2 corresponded with the activity of ERK. While ANG II induced an initial activation of ERK in quiescent cells, the NGF-mediated plateau of ERK-stimulation was lowered by costimulation with ANG II. All effects of ANG II were sensitive to AT2 – but not AT1 receptor blockade. Ang II-mediated neurite outgrowth in PC12W cells was inhibited by co-treatment with the MEK inhibitor PD 098059. These findings demonstrate that the AT2 receptor modulates ERK activity depending on the overall cellular input. The distinct regulation of ERK by ANG II and NGF further indicates basic differences in AT2 receptor- and NGF-induced neuronal differentiation.
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ABSTRACT: Macrophages have an important role in the pathogenesis of hypertension and associated end-organ damage via the activation of the Toll-like receptors, such as Toll-like receptor-4 (TLR4). Accumulating evidence suggests that the angiotensin AT2 receptor (AT2R) has a protective role in pathological conditions involving inflammation and tissue injury. We have recently shown that AT2R stimulation is renoprotective, which occurs in part via increased levels of anti-inflammatory interleukin-10 (IL-10) production in renal epithelial cells; however, the role of AT2R in the inflammatory activity of macrophages is not known. The present study was designed to investigate whether AT2R activation stimulates an anti-inflammatory response in TLR4-induced inflammation. The effects of the anti-inflammatory mechanisms that occurred following pre-treatment with the AT2R agonist Compound 21 (C21) (1 μmol ml(-1)) on the cytokine profiles of THP-1 macrophages after activation by lipopolysaccharide (LPS) (1 μg ml(-1)) were studied. The AT2R agonist dose-dependently attenuated LPS-induced tumor necrosis factor-α (TNF-α) and IL-6 production but increased IL-10 production. IL-10 was critical for the anti-inflammatory effects of AT2R stimulation because the IL-10-neutralizing antibody dose-dependently abolished the AT2R-mediated decrease in TNF-α levels. Further, enhanced IL-10 levels were associated with a sustained, selective increase in the phosphorylation of extracellular signal-regulated kinase (ERK1/2) but not p38 mitogen-activated protein kinase (MAPK). Blocking the activation of ERK1/2 before C21 pre-treatment completely abrogated this increased IL-10 production in response to the AT2R agonist C21, while there was a partial reduction in IL-10 levels following the inhibition of p38. We conclude that AT2R stimulation exerts a novel anti-inflammatory response in THP-1 macrophages via enhanced IL-10 production as a result of sustained, selective ERK1/2 phosphorylation, which may have protective roles in hypertension and associated tissue injury.Hypertension Research advance online publication, 11 September 2014; doi:10.1038/hr.2014.132.Hypertension Research 09/2014; · 2.94 Impact Factor
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ABSTRACT: Angiotensin II receptor type 2 (AT2) agonists have been shown to limit brain ischemic insult and to improve its outcome. The activation of AT2 was also linked to induced neuronal proliferation and differentiation in vitro. In this study, we examined the therapeutic potential of AT2 activation following traumatic brain injury (TBI) in mice, a brain pathology that displays ischemia-like secondary damages. The AT2 agonist CGP42112A was continuously infused immediately after closed head injury (CHI) for 3 days. We have followed the functional recovery of the injured mice for 35 days post-CHI, and evaluated cognitive function, lesion volume, molecular signaling, and neurogenesis at different time points after the impact. We found dose-dependent improvement in functional recovery and cognitive performance after CGP42112A treatment that was accompanied by reduced lesion volume and induced neurogenesis in the neurogenic niches of the brain and also in the injury region. At the cellular/molecular level, CGP42112A induced early activation of neuroprotective kinases protein kinase B (Akt) and extracellular-regulated kinases ½ (ERK½), and the neurotrophins nerve growth factor and brain-derived neurotrophic factor; all were blocked by treatment with the AT2 antagonist PD123319. Our results suggest that AT2 activation after TBI promotes neuroprotection and neurogenesis, and may be a novel approach for the development of new drugs to treat victims of TBI.Journal of the American Society for Experimental NeuroTherapeutics 06/2014; · 3.88 Impact Factor
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ABSTRACT: Long-term exposure of mice to mild heat (34°C±1°C) confers neuroprotection against traumatic brain injury (TBI); however, the underling mechanisms are not fully understood. Heat acclimation (HA) increases hypothalamic angiotensin II receptor type 2 (AT2) expression and hypothalamic neurogenesis. Accumulating data suggest that activation of the brain AT2 receptor confers protection against several types of brain pathologies, including ischemia, a hallmark of the secondary injury occurring following TBI. As AT2 activates the same pro-survival pathways involved in HA-mediated neuroprotection (e.g., Akt phosphorylation, hypoxia-inducible factor 1α (HIF-1α), and brain-derived neurotrophic factor (BDNF)), we examined the role of AT2 in HA-mediated neuroprotection after TBI. Using an AT2-specific antagonist PD123319, we found that the improvements in motor and cognitive recovery as well as reduced lesion volume and neurogenesis seen in HA mice were all diminished by AT2 inhibition, whereas no significant alternations were observed in control mice. We also found that nerve growth factor/tropomyosin-related kinase receptor A (TrkA), BDNF/TrkB, and HIF-1α pathways are upregulated by HA and inhibited on PD123319 administration, suggesting that these pathways play a role in AT2 signaling in HA mice. In conclusion, AT2 is involved in HA-mediated neuroprotection, and AT2 activation may be protective and should be considered a novel drug target in the treatment of TBI patients.Journal of Cerebral Blood Flow & Metabolism (2014) 0, 000-000. doi:10.1038/jcbfm.2014.93.Journal of Cerebral Blood Flow & Metabolism 05/2014; 34(8). · 5.34 Impact Factor