Date of Award

2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Pharmacology and Experimental Therapeutics

Abstract

Cardiovascular disease is the leading cause of death worldwide. A myocardial infarction (MI), commonly known as a heart attack, is a major event in cardiovascular disease characterized by reduced blood flow to the heart. The ischemia and reperfusion (I/R) injury associated with an MI results in a region of dead tissue in the heart called an infarct, the size of which influences patient prognosis. In the 1980s, it was discovered that short, non-lethal episodes of I/R, termed ischemic preconditioning (IPC), can protect the heart against a subsequent MI. Ischemic preconditioning demonstrated the phenomenon of endogenous cardioprotection. Cardioprotection has great potential to reduce myocardial cell death and improve patient outcomes after MI, and yet most cardioprotective strategies have had limited success in clinical scenarios. Remote nociceptor-induced cardioprotection (NIC) elicits the most powerful reduction of cell death ever reported. Electrical stimulation (ES) administered via cutaneous patches offers a clinically feasible way to induce cardioprotection via NIC. Our previous work demonstrates that the transcription factor nuclear factor k-light- chain-enhancer of activated B cells (NF-kB) regulates many cardioprotective genes in the heart following IPC, including the heat shock proteins (HSPs), which act in concert with each other and their cofactors to assist in protein folding, repair, and degradation following myocardial injury. Little is known about the molecular mechanisms of electrically-induced cardioprotection, which is a barrier to the therapy's optimization and successful translation to the clinic. Based on our work in IPC, we hypothesized that electrical stimulation of the skin is cardioprotective and requires the synthesis of NF-kB-dependent distal mediators of cardioprotection. In the studies herein, a cutaneous, 5-volt electrical stimulus applied to the abdomen reduces infarct size in a mouse surgical model of MI. Genetic blockade of NF-kB activation demonstrates the requirement of NF-kB in electrically-induced cardioprotection, yet RT-qPCR revealed small, nonsignificant changes in HSP mRNA and protein. Next-generation sequencing on mRNA and microRNA identified a unique transcriptome associated with electrically-induced cardioprotection that includes both recognized mediators and novel transcripts. Confirmatory studies on select molecular candidates were performed by RT-qPCR and Western blotting, and the functional role of the NF-kB-dependent gene nitric oxide synthase 2 (NOS2) was demonstrated in vivo. Results support that an electrical stimulus is cardioprotective in multiple paradigms of cardioprotection. Cardioprotection occurs without a concurrent increase in HSPs, but NF-kB and the NF-kB-dependent gene nitric oxide synthase 2 (NOS2) are required for ES- induced cardioprotection. Electrical stimulation also reduced cardiac levels of miR-10b, a circulating microRNA with no previously known role in cardioprotection. These changes were validated by RT-qPCR. In conclusion, electrically-induced cardioprotection is a novel and translational strategy to reduce cell death following MI. The molecular mechanisms of ES are cardioprotective via unique transcriptomic changes involving NF-kB and the NF-kB-dependent gene NOS2. The effect might be regulated epigenetically by microRNA.

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This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

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