Cardiovascular disease is the number one killer in the United States. Toll-like receptor (TLR)-mediated innate immune and inflammatory responses play a central role in the pathophysiologic mechanisms of myocardial ischemia/reperfusion (I/R) injury. It is well known that activation of TLR4-mediated NF-kB signaling plays a deleterious role in myocardial I/R injury, while activation of the PI3K/Akt signaling pathway protects against myocardial I/R injury. We have reported that either TLR4 deficiency or TLR2 modulation protects the myocardium from I/R injury via a PI3K/Akt dependent mechanism. We have discovered that TLR4 deficiency increases the expression of microRNA-146a (miR-146a) and miR-486 in the myocardium. We have also found that TLR2 modulation increases the amount of miR-146a and miR-486 in the myocardium, in circulating exosomes, and in exosomes secreted by bone marrow mesenchymal stem cells. We have demonstrated that increased expression of miR-146a in the myocardium decreases myocardial infarct size and improves cardiac function following myocardial I/R. MiR-146a targets IRAK1 and TRAF6 which are the important intermediates in TLR-mediated NF-kB activation, thus, attenuating I/R-induced NF-kB activation. In addition, we have found that miR-486 inhibits PTEN expression, leading to activation of PI3K/Akt signaling. Our findings suggest that either TLR4 deficiency or TLR2 modulation induce cardioprotection via up-regulation of microRNA expression that inhibits NF-kB activation and activates PI3K/Akt signaling. When considered together, our data and the literature clearly show that TLR4-mediated NF-kB activation is closely linked to disease progression in myocardial I/R injury, while activation of PI3K/Akt signaling pathways is closely associated with attenuation of myocardial injury. At present, we do not fully understand the mechanisms of differential regulation of NF-kB and PI3K/Akt in I/R injury. This application is directed at deciphering the cellular and molecular mechanisms that differentially regulate these signaling pathways in I/R induced myocardial injury. We will then apply that mechanistic knowledge in a practical fashion to develop new and novel therapies for heart attack. Specifically, we will define the role of microRNA in differential regulation of NF-kB and PI3K/Akt in myocardial I/R injury. We will also attempt to apply this knowledge for the development of new and novel miR based therapies for heart attack. We hypothesize that i) miRNAs differentially activate PI3K/Akt signaling and inhibit NF-kB activation in myocardial I/R injury and ii) miRNAs are carried in exosomes which are efficiently uptaken by cardiac myocytes, resulting in cardioprotection via differential activation f protective versus deleterious intracellular signaling.
Specific Aim 1 will elucidate the mechanisms by which modulation of NF-kB and PI3K/Akt regulates the expression of miR-146a and miR-486 in cardiac myocytes.
Specific Aim 2 will define the effect of miR-146a and miR-486 on myocardial injury and functional recovery.
Specific Aim 3 will investigate the role of synthetic exosomes carrying miR-146a and miR-486 as therapeutics in myocardial I/R injury.
Cardiovascular disease (CVD) is the number one killer in the United States. Each year, an estimated 785,000 Americans will have a new coronary attack and 470,000 will have a recurrent attack. In addition, each year 195,000 Americans will have so called 'silent' myocardial infarctions. Despite years of intensive research, there is still much tht we do not know about the mechanisms of the disease. Recent evidence suggests that innate immune and inflammatory responses mediated by Toll-like receptors (TLRs) play a pathogenic role in myocardial ischemic injury (heart attack) and heart failure. We have made the novel observation that modulation of TLR2 significantly increases the expression of microRNA-146a and microRNA-486 in the myocardium, in circulating exosomes, and in exosomes secreted by bone marrow mesenchymal stem cells (BM-MSCs). Transfection of miR-146a into the myocardium significantly decreased myocardial injury following ischemia/reperfusion. To the best of our knowledge, this is a new and novel role for microRNA-146a in protection against myocardial ischemic injury. More significantly, our studies will have practical significance in tha they may lead to the development of novel treatments that could decrease morbidity and mortality in heart attack patients.
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