Cardiovascular disease (CVD) remains the leading cause of death in the United States and in the developing world, with ischemic heart disease the second most common form of CVD. Experimental and clinical studies have demonstrated that a number of interventions, including brief periods of ischemia or hypoxia and certain endogenous molecules such as growth factors, opioids, adenosine or pharmacological agents are capable of protecting the heart against post-ischemic cardiac dysfunction, arrhythmias and myocardial infarction. One of these growth factors, fibroblast growth factor-2 (FGF2), has been implicated to be a cardioprotective molecule. FGF2 consists of multiple protein isoforms (low molecular weight, LMW, and high molecular weight, HMW) produced by alternative translation from the Fgf2 gene and these protein isoforms are localized to different cellular compartments indicating unique biological activity. Currently, the roles of the FGF2 isoforms in ischemia-reperfusion injury and cardioprotection remain to be elucidated. Understanding the biological function(s) of the FGF2 isoforms in cardioprotection is of a great clinical importance and may lead to the development of novel pharmacological or gene therapy strategies for ischemic heart disease.
This dissertation research utilized mice with a targeted ablation of a specific FGF2 isoform (FGF2 LMWKO or FGF2 HMWKO) or mice in which all FGF2 isoforms (Fgf2 KO) were absent, and mice with a ubiquitous overexpression of the human FGF2 HMW 24 kD isoform (24 kD Tg) to evaluate the role(s) of the FGF2 protein isoforms in ischemia-reperfusion (I/R) injury. Cardioprotection in mice subjected to an isolated work-performing heart model of global, low-flow ischemia-reperfusion injury was indicated as an improvement in post-ischemic recovery of cardiac function and/or a reduction in creatine kinase release into coronary effluent or a reduction in myocardial infarct size. FGF2 LMWKO hearts had a significant decrease in post-ischemic cardiac function compared to wildtype hearts (p < 0.05). FGF2 HMWKO hearts, however, had a significantly enhanced post-ischemic recovery of cardiac function (p < 0.05). Furthermore, in human FGF2 HMW 24 kD Tg hearts, the post-ischemic recovery of cardiac function was significantly decreased compared to non-transgenic hearts (p < 0.05). Myocardial cell injury was not different between either Wt, Fgf2 KO, FGF2 HMWKO and FGF2 LMWKO or 24 kD Tg and NTg hearts after I/R injury indicating that all the isoforms were necessary to protect the heart from myocardial cell injury. The effect of FGF2 isoforms on I/R injury was independent of changes in coronary flow or blood vessel density. The cardioprotective effect mediated by the FGF2 LMW isoform was abolished when the mixed lineage kinase (MLK)/mitogen kinase kinase (MKK)/c-Jun N-terminal kinase (JNK) signaling pathway or FGF receptor (FGFR) was inhibited. The LMW isoform significantly inhibited MKK7, JNK, and c-Jun activation as well as apoptotic processes prior to and during ischemia-reperfusion injury (p < 0.05). The cardioprotective effect of FGF2 LMW isoform occurred through modulating apoptosis via inhibition of c-Jun and JNK activation. The cardioprotective effect of the LMW isoform also required the involvement of FGF receptor (FGFR), most likely the murine FGFR1. Another potential mechanism involved in the LMW isoform-mediated cardioprotection may be due to its actions on cardiac gene expression as preliminary results indicated that the LMW isoform decreased cardiotoxic gene expression and increased cardioprotective gene expression. The FGF2 HMW isoforms significantly decreased the activation of PKC α and increased the activation of PI3-kinase and NFκB signaling pathways that are involved in cardioprotection (p < 0.05). In addition, the FGF2 HMW isoforms regulated expression of genes involved in ischemia-reperfusion injury, gene transcription, and apoptosis. These genes could be potential targets regulated by FGF2 HMW isoforms during I/R injury. Together, these data show that the FGF2 LMW isoform had a beneficial role in protecting the heart from myocardial dysfunction while FGF2 HMW isoforms had a deleterious role in I/R injury. This dissertation provided a novel signaling mechanism of the LMW FGF2 isoform which could contribute to the cardioprotective effect. Though the mechanisms of the FGF2 HMW isoforms remain to be thoroughly characterized, this dissertation provides critical evidence for the role of the FGF2 HMW isoforms in ischemia-reperfusion injury including up-regulation of cardiotoxic gene expression and modulating transcription factor NF-κB. Together, these data show that the FGF2 LMW isoform has a beneficial effect, while FGF2 HMW isoforms have a detrimental effect in ischemia-reperfusion injury and the modulation of signals including FGFR, MAPK, NF-κB, c-JUN, and calcium leads to the differential outcomes on post-ischemic recovery of cardiac function and myocardial infarction.
|Commitee:||Doetschman, Thomas, Jones, W. Keith, Kranias, Evangelia G, Olah, Mark, Schultz, Jo El, Wang, Hong-Sheng|
|School:||University of Cincinnati|
|Department:||Molecular, Cellular and Biochemical Pharmacology|
|School Location:||United States -- Ohio|
|Source:||DAI-B 78/11(E), Dissertation Abstracts International|
|Keywords:||Fgfr, Fibroblast growth factor 2, Hmw, Ischemia reperfusion injury, Isoform, Lmw|
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