Koh Ono

The p38 signal transduction pathway - Activation and function

The p38 signalling transduction pathway, a Mitogen-activated protein (MAP) kinase pathway, plays an essential role in regulating many cellular processes including inflammation, cell differentiation, cell growth and death. Activation of p38 often through extracellular stimuli such as bacterial pathogens and cytokines, mediates signal transduction into the nucleus to turn on the responsive genes. p38 also transduces signals to other cellular components to execute different cellular responses. In this review, we summarize the characteristics of the major components of the p38 signalling transduction pathway and highlight the targets of this pathway and the physiological function of the p38 activation.

Cytokine Gene Expression After Myocardial Infarction in Rat Hearts Possible Implication in Left Ventricular Remodeling

BACKGROUND A large transmural myocardial infarction may initiate structural and geometric changes in the left ventricle that are commonly referred to as remodeling. Progressive, adverse remodeling of the myocardium may lead to ventricular dilatation and congestive heart failure. Recent studies have highlighted the effects of some cytokines on immune-mediated myocyte injury, postischemic myocardial inflammation, and cardiac function. However, studies of the involvement of cytokines in remodeling of the heart are few. METHODS AND RESULTS In a rat model of myocardial infarction, progressive dilatation of the left ventricular cavity and lack of appropriate hypertrophy of the surviving myocardium were confirmed by transthoracic echocardiography. The relative expression of mRNA for tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-6 in the infarcted and noninfarcted myocardium of these rats, as well as in a group of sham-operated animals, was assessed by the technique of quantitative polymerase chain reaction amplification. In the infarcted region, TNF-alpha, IL-1beta, and IL-6 gene expression peaked at 1 week after infarction and decreased rapidly thereafter. In contrast, at 20 weeks after infarction, the gene expression levels of these cytokines remained significantly higher in the noninfarcted than in the infarcted zone or in the myocardium of sham-operated animals. Furthermore, the levels of these cytokines in the noninfarcted region correlated with the left ventricular end-diastolic diameter measured at 8 and 20 weeks after infarction. Among these cytokines, IL-1beta expression was highest, and its level correlated well with collagen deposition in the noninfarcted myocardium at 8 and 20 weeks after surgery. At 20 weeks after infarction, immunohistochemical analysis revealed the presence of IL-1beta in macrophages, endothelial cells, and vascular smooth muscle cells in the noninfarcted region, whereas no such immunoreactivity was found in the myocardium of sham-operated animals. CONCLUSIONS These findings suggest the possible involvement of cytokines during the remodeling process of the noninfarcted left ventricular myocardium.

MicroRNA-33 encoded by an intron of sterol regulatory element-binding protein 2 (Srebp2) regulates HDL in vivo

Sterol regulatory element-binding protein 2 (SREBP-2) transcription factor has been identified as a key protein in cholesterol metabolism through the transactivation of the LDL receptor and cholesterol biosynthesis genes. Here, we generated mice lacking microRNA (miR)-33, encoded by an intron of the Srebp2, and showed that miR-33 repressed the expression of ATP-binding cassette transporter A1 (ABCA1) protein, a key regulator of HDL synthesis by mediating cholesterol efflux from cells to apolipoprotein A (apoA)-I. In fact, peritoneal macrophages derived from miR-33–deficient mice showed a marked increase in ABCA1 levels and higher apoA-I–dependent cholesterol efflux than those from WT mice. ABCA1 protein levels in liver were also higher in miR-33–deficient mice than in WT mice. Moreover, miR-33–deficient mice had significantly higher serum HDL cholesterol levels than WT mice. These data establish a critical role for miR-33 in the regulation of ABCA1 expression and HDL biogenesis in vivo.

Evidence for a Role of Mast Cells in the Evolution to Congestive Heart Failure

Mast cells are believed to be involved in the pathophysiology of heart failure, but their precise role in the process is unknown. This study examined the role of mast cells in the progression of heart failure, using mast cell-deficient (WBB6F1-W/Wv) mice and their congenic controls (wild-type [WT] mice). Systolic pressure overload was produced by banding of the abdominal aorta, and cardiac function was monitored over 15 wk. At 4 wk after aortic constriction, cardiac hypertrophy with preserved left ventricular performance (compensated hypertrophy) was observed in both W/Wv and WT mice. Thereafter, left ventricular performance gradually decreased in WT mice, and pulmonary congestion became apparent at 15 wk (decompensated hypertrophy). In contrast, decompensation of cardiac function did not occur in W/Wv mice; left ventricular performance was preserved throughout, and pulmonary congestion was not observed. Perivascular fibrosis and upregulation of mast cell chymase were all less apparent in W/Wv mice. Treatment with tranilast, a mast cell–stabilizing agent, also prevented the evolution from compensated hypertrophy to heart failure. These observations suggest that mast cells play a critical role in the progression of heart failure. Stabilization of mast cells may represent a new approach in the management of heart failure.

Enhanced Expression of Hepatocyte Growth Factor/c-Met by Myocardial Ischemia and Reperfusion in a Rat Model

Background Hepatocyte growth factor (HGF) is a multifunctional factor implicated in tissue regeneration, wound healing, and angiogenesis. Circulating HGF is reportedly elevated during the early stage of myocardial infarction. However, its precise effect on the heart is unknown. To evaluate the regulation of HGF in ischemically damaged myocardium, the production of HGF and its high-affinity receptor, c-Met, was studied in a rat model of myocardial ischemia and reperfusion. Methods and Results The plasma concentration of HGF began to increase within 1 hour of reperfusion after 1 hour of ischemia. The peak level was reached at 3 hours after reperfusion. Northern blotting revealed that HGF mRNA expression in the heart was augmented threefold at 24 and 48 hours and remained elevated by twofold at 120 hours after the myocardium was reperfused. The signal for c-met , high-affinity HGF receptor mRNA, was also upregulated parallel to upregulation for HGF. In the kidney, liver, lung, and spleen, HGF mRNA was also m...

Increased Expression of Interleukin-1β and Monocyte Chemotactic and Activating Factor/Monocyte Chemoattractant Protein-1 in the Hypertrophied and Failing Heart With Pressure Overload

Studies on the effects of proinflammatory cytokines on the heart suggest that they play some roles in the pathogenesis of congestive heart failure (CHF). To determine the involvement of proinflammatory cytokine in cardiac hypertrophy and CHF induced by mechanical overload, we investigated the expression of interleukin (IL)-1 beta and monocyte chemotactic and activating factor (MCAF)/monocyte chemoattractant protein-1 (MCP-1) in the left ventricle (LV) of Dahl salt-sensitive (DS) rats that showed hypertrophy of the LV induced by hypertension and subsequently developed CHF. The IL-1 beta mRNA content in the LV of DS rats increased 3.9-fold when LV hypertrophy developed, and the increase reached 6.2-fold at the CHF stage compared with that of age-matched Dahl salt-resistant (DR) rats. The amount of IL-1 beta in the LV was positively correlated with the LV weight/body weight ratio. Most of the IL-1 beta immunoreactivity was localized in the endothelial cells and interstitial macrophages. The mRNA levels of MCAF in the LV increased 3.6-fold at 11 weeks and reached 4.8-fold at the CHF stage relative to the age-matched DR rats. MCAF protein was localized to the endothelial cells and interstitial macrophages. In DS rats, the number of interstitial macrophages increased diffusely throughout the LV. We suggest that increased chemokine expression, macrophage infiltration, and proinflammatory cytokine expression play some role in the pathogenesis of cardiac hypertrophy and failure induced by chronic mechanical overload.

Up-regulated expression of microRNA-143 in association with obesity in adipose tissue of mice fed high-fat diet

MicroRNAs (miRNAs) are short non-coding RNA that post-transcriptionally regulates gene expression. miR-143 has been proposed to play a role in the differentiation of adipocytes in culture. However, the mechanism regulating the expression of miR-143 in adult adipose tissue during the development of obesity in vivo is unknown. Here in, we showed that the expression of miR-143 in the mesenteric fat was up-regulated in mice fed a high-fat diet. Increased miR-143 expression was associated with an elevated body weight and mesenteric fat weight. Furthermore, miR-143 levels were closely correlated with expression levels of adipocyte differentiation markers such as PPARgamma and aP2 as well as plasma levels of leptin, one of the important adipocytokines involved in insulin resistance. These findings provide the first evidence for the up-regulated expression of miR-143 in the mesenteric fat of high-fat diet-induced obese mice, which might contribute to the regulated expression of adipocyte genes involved in the pathophysiology of obesity.

Cyclic Stretch Upregulates Production of Interleukin-8 and Monocyte Chemotactic and Activating Factor/Monocyte Chemoattractant Protein-1 in Human Endothelial Cells

In vivo, vascular walls are exposed to mechanical stretch, which may promote atherogenesis. This study was designed to investigate the effect of mechanical stretch on the production and gene expression of cytokines in endothelial cells (ECs) of human umbilical veins. ECs were cultured on flexible silicone membranes and exposed to cyclic mechanical stretch. Although the secretion levels of interleukin (IL)-1beta, tumor necrosis factor-alpha, IL-6, granulocyte (G) -colony stimulating factor (CSF), G and macrophage (M) -CSF, and M-CSF were not affected by cyclic stretch over 24 hours, the levels of IL-8 and monocyte chemotactic and activating factor (MCAF)/monocyte chemoattractant protein-1 (MCP-1) were significantly increased by cyclic stretch. Northern blot analysis indicated that the mRNA levels of IL-8 and MCAF/MCP-1 were upregulated by cyclic stretch as a function of its intensity. Cytochalasin D, which disrupts the actin cytoskeleton, abolished the stretch-induced gene expression of IL-8 and MCAF/MCP-1. In contrast, neither inhibition of stretch-activated ion channels nor disruption of microtubules affected the induction of these chemokines by cyclic stretch. Northern blot analysis using enzyme inhibitors showed that phospholipase C, protein kinase C, and tyrosine kinase were involved in the stretch-induced gene expression of IL-8 and MCAF/MCP-1, whereas cAMP- or cGMP-dependent protein kinase was not. In conclusion, cyclic stretch enhanced the secretion and gene expression of IL-8 and MCAF/MCP-1 in a stretch-dependent fashion, and the integrity of the actin cytoskeleton and activities of phospholipase C, protein kinase C, and tyrosine kinase may be essential in the process of stretch-induced gene induction of IL-8 and MCAF/MCP-1.

MicroRNA-33 Deficiency Reduces the Progression of Atherosclerotic Plaque in ApoE−/− Mice

Background Cholesterol efflux from cells to apolipoprotein A-I (apoA-I) acceptors via the ATP-binding cassette transporters ABCA1 and ABCG1 is thought to be central in the antiatherogenic mechanism. MicroRNA (miR)-33 is known to target ABCA1 and ABCG1 in vivo. Methods and Results We assessed the impact of the genetic loss of miR-33 in a mouse model of atherosclerosis. MiR-33 and apoE double-knockout mice (miR-33−/−Apoe−/−) showed an increase in circulating HDL-C levels with enhanced cholesterol efflux capacity compared with miR-33+/+Apoe−/− mice. Peritoneal macrophages from miR-33−/−Apoe−/− mice showed enhanced cholesterol efflux to apoA-I and HDL-C compared with miR-33+/+Apoe−/− macrophages. Consistent with these results, miR-33−/−Apoe−/− mice showed reductions in plaque size and lipid content. To elucidate the roles of miR-33 in blood cells, bone marrow transplantation was performed in these mice. Mice transplanted with miR-33−/−Apoe−/− bone marrow showed a significant reduction in lipid content in atherosclerotic plaque compared with mice transplanted with miR-33+/+Apoe−/− bone marrow, without an elevation of HDL-C. Some of the validated targets of miR-33 such as RIP140 (NRIP1) and CROT were upregulated in miR-33−/−Apoe−/− mice compared with miR-33+/+Apoe−/− mice, whereas CPT1a and AMPKα were not. Conclusions These data demonstrate that miR-33 deficiency serves to raise HDL-C, increase cholesterol efflux from macrophages via ABCA1 and ABCG1, and prevent the progression of atherosclerosis. Many genes are altered in miR-33-deficient mice, and detailed experiments are required to establish miR-33 targeting therapy in humans.

Acute doxorubicin cardiotoxicity is associated with miR-146a-induced inhibition of the neuregulin-ErbB pathway

Aims A significant increase in congestive heart failure (CHF) was reported when the anti-ErbB2 antibody trastuzumab was used in combination with the chemotherapy drug doxorubicin (Dox). The aim of the present study was to investigate the role(s) of miRNAs in acute Dox-induced cardiotoxicity. Methods and results Neuregulin-1-ErbB signalling is essential for maintaining adult cardiac function. We found a significant reduction in ErbB4 expression in the hearts of mice after Dox treatment. Because the proteasome pathway was only partially involved in the reduction of ErbB4 expression, we examined the involvement of microRNAs (miRs) in the reduction of ErbB4 expression. miR-146a was shown to be up-regulated by Dox in neonatal rat cardiac myocytes. Using a luciferase reporter assay and overexpression of miR-146a, we confirmed that miR-146a targets the ErbB4 3′UTR. After Dox treatment, overexpression of miR-146a, as well as that of siRNA against ErbB4, induced cell death in cardiomyocytes. Re-expression of ErbB4 in miR-146a-overexpressing cardiomyocytes ameliorated Dox-induced cell death. To examine the loss of miR-146a function, we constructed ‘decoy’ genes that had tandem complementary sequences for miR-146a in the 3′UTR of a luciferase gene. When miR-146a ‘decoy’ genes were introduced into cardiomyocytes, ErbB4 expression was up-regulated and Dox-induced cell death was reduced. Conclusion These findings suggested that the up-regulation of miR-146a after Dox treatment is involved in acute Dox-induced cardiotoxicity by targeting ErbB4. Inhibition of both ErbB2 and ErbB4 signalling may be one of the reasons why those patients who receive concurrent therapy with Dox and trastuzumab suffer from CHF.