Big mitogen-activated protein kinase 1 (BMK1), also known as extracellular signal-regulated kinase 5 (ERK5), is a newly identified member of the mitogen-activated protein (MAP) kinase family. BMK1 has been reported to be sensitive to various neuro-humoral factors and oxidative stress in various cells. In this review, we focused on the role of BMK1 in atherosclerosis in a cultured rat aortic smooth muscle cell model. Treatment with platelet-derived growth factor caused vascular smooth muscle cell (VSMC) migration in a BMK1 activation–dependent manner. H2O2 caused BMK1 activation and VSMC death, including apoptosis of VSMCs. An inhibitory function for BMK1 against cell death from oxidative stress was discovered using siRNA techniques to downregulate the expression of BMK1. These findings suggest a role for BMK1 in the pathogenesis and/or progression of atherosclerosis.
Understanding the regulation of cardiac ion channels is critical for the prevention of arrhythmia caused by abnormal excitability. Ion channels can be regulated by a change in function (qualitative) and a change in number (quantitative). Functional changes have been extensively investigated for many ion channels including cardiac voltage-dependent potassium channels. By contrast, the regulation of ion channel numbers has not been widely examined, particularly with respect to acute modulation of ion channels. This article briefly summarizes stimulus-induced endocytic regulation of major voltage-dependent potassium channels in the heart. The stimuli known to cause their endocytosis include receptor activation, drugs, and low extracellular [K+], following which the potassium channels undergo either clathrin-mediated or caveolin-mediated endocytosis. Receptor-mediated endocytic regulation has been demonstrated for Kv1.2, Kv1.5, KCNQ1 (Kv7.1), and Kv4.3, while drug-induced endocytosis has been demonstrated for Kv1.5 and hERG. Low [K+]o–induced endocytosis might be unique for hERG channels, whose electrophysiological characteristics are known to be under strong influence of [K+]o. Although the precise mechanisms have not been elucidated, it is obvious that major cardiac voltage-dependent potassium channels are modulated by endocytosis, which leads to changes in cardiac excitability.
Studies with knockout mice have indicated that the only isoform of phosphoinositide 3-kinase (PI3K) functioning in the oxidative burst of mouse neutrophils in response to heterotrimeric guanine nucleotide-binding protein–coupled receptor (GPCR) agonists is a class-IB PI3K, p110γ. In the present study, we observed that the cells from p110γ−/− mice gain a response to N-formyl-Met-Leu-Phe (fMLP) after priming with cytochalasin E. Even the unprimed cells, which show no response to fMLP, produce a significant amount of superoxide, when an effective agonist of the mouse-type fMLP receptors, Trp-Lys-Tyr-Met-Val-D-Met, is used to stimulate the cells. These results suggested that the class-IA isoforms (p110α, p110β, and p110δ) of PI3K are sufficient to trigger and maintain superoxide production. Examination of the effects of isoform-specific inhibitors suggested that the p110β isoform is the primary PI3K triggering the response to GPCR agonists when p110γ is absent.
Recent studies in vivo and vitro have shown that Fuzi polysaccharide has an antidepressant-like effect. Polysaccharide and total alkaloid are the two most important components of Fuzi. However, little is known about the antidepressant-like effect of Fuzi total alkaloid. To investigate the antidepressant-like effect of Fuzi total alkaloid, behavioral studies were performed in the open field test and forced swimming test. Repeated intragastric administration of Fuzi total alkaloid for 7 days (10 mg/kg) to normal mice decreased immobility time compared to the vehicle group. Furthermore, repeated administration of Fuzi total alkaloid (10 or 30 mg/kg) to ovariectomized mice also decreased immobility time in a dose-dependent manner. However, these antidepressant-like behavioral effects were not simply due to locomotor hyperactivity. Further experiments showed that Fuzi total alkaloid enhanced the ratio of phospho-CREB/CREB (cAMP response element-binding) and BDNF (brain-derived neurotrophic factor) protein level in the frontal cortex and hippocampus in ovariectomized mice but not in normal mice. These results indicate that the CREB-BDNF pathway may be involved in the antidepressant-like effect of Fuzi total alkaloid in ovariectomized mice.
ATP and hydrolysis products of ATP like adenosine regulate the chemotaxis of neutrophils by activating purinoceptors and adenosine receptors. The present study was designed to examine exogenous ATP, activation of purinoceptors, and activation of A3 adenosine receptor as key steps in the signal cascades that control cell orientation and migration of rat neutrophils. One or more of those steps might be potential therapeutic targets for treatment of inflammatory diseases. The chemotaxis of rat neutrophils was stimulated with N-formyl-methionyl-leucyl-phenylalanine (fMLP) and measured with an EZ-TAXIScan apparatus. The effects of apyrase, exogenous ATP, suramin (P2X and P2Y blocker), PPADS (a P2X blocker), TNP-ATP (P2X1 and P2X3 antagonist), and Reactive Blue 2 (a P2Y blocker) on the chemotactic response were also investigated. Rat neutrophil chemotaxis was significantly suppressed by apyrase. fMLP induced rat neutrophil chemotaxis was potentiated by ATP, blocked by suramin, not affected by PPADS or TNP-ATP, and significantly inhibited by RB-2. Western blotting showed that A3, P2Y2, and P2Y11 were expressed in rat neutrophils. The chemotactic response of rat neutrophils to fMLP stimulation is potentiated by ATP via P2Y11 purinoceptors but not P2X purinoceptors or A3 adenosine receptor, and that the response plays a critical role in host defense and pathogenicity.
Atrial inflammation is critical to atrial fibrillation initiation and progression. Although left atrial dilatation is a risk factor for atrial fibrillation, the mechanism linking atrial dilatation and inflammation is unclear. We evaluated the mechanisms underlying infiltration of macrophages induced by stretch of atrial myocytes. Murine macrophages were co-cultured with HL-1 murine atrial myocyte–derived cells. Mechanical stretch applied to atrial myocytes induced transwell macrophage migration. The gap junction–channel blocker carbenoxolone and the non-specific ATP-signaling modifiers apyrase and pyridoxal-phosphate-6-azophenyl-2′,4′-disulfonate inhibited the enhanced migration. Mechanical stretch of atrial myocytes induced transient increase in extracellular ATP concentration, which was inhibited by carbenoxolone. siRNA knockdown of pannexin-2 inhibited ATP release and macrophage migration. Mice underwent transverse aortic constriction or sham procedure. Transverse aortic constriction procedure induced macrophage infiltration. Daily carbenoxolone administration significantly inhibited macrophage infiltration in the atrium. Thus, mechanical stretch of atrial myocytes induces macrophage migration by ATP released through gap-junction channels, at least in part, in vitro. Administering a gap junction family–channel blocker inhibited this inflammatory change in vivo.
We investigated a possible drug efficacy enhancement obtained by combining inactive doses of galantamine and memantine in the scopolamine-induced amnesia model in mice. We evaluated the effects of the two drugs, either alone or in combination, using the spontaneous alternation and object recognition tasks. In both tests, combination of low doses of galantamine (0.1 mg/kg, s.c.) and memantine (0.5 mg/kg, i.p.), which were sub-active per se, rescued the memory impairment induced by scopolamine (1 mg/kg, i.p.). The results suggest that combinations of galantamine and memantine might provide a more effective treatment of memory impairments in cognitive disorders than either drug used alone.
Nicotine- and tar-free cigarette smoke extract (CSE) is reported to induce cell damage via activation of protein kinase C (PKC) and NADPH oxidase (NOX) in rat C6 glioma cells. Here we determined PKC isozyme(s) activated by CSE and their activation mechanism. In C6 glioma cells, mRNAs for PKCα, PKCδ, PKCε, and PKCι were expressed. CSE triggered translocation of PKCα and PKCε to plasma membrane. CSE-induced cell damage and PKC translocation were inhibited by chelating intracellular Ca2+ but not extracellular Ca2+. These results suggest that CSE induces cell damage through intracellular Ca2+-dependent activation of PKCα and PKCε and subsequent NOX activation.