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Xiaoming Fan Dissertation Final.pdf (2.4 MB)

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Regulation of Na/K-ATPase and its Role in Cardiac Disease

Fan, Xiaoming
http://rave.ohiolink.edu/etdc/view?acc_num=mco1544722291840285

Abstract Details

2018, Doctor of Philosophy (PhD), University of Toledo, Biomedical Sciences (Molecular Medicine).
Heart failure is an important public health issue and a leading cause of mortality in the United States. Previous publications have shown that both protein amount and enzyme activity of cardiac Na/K-ATPase were reduced in heart failure patients. Analysis of gene expression database also demonstrated that expression of Na/K-ATPase α1 subunit in heart tissue from heart failure patients is lower compared to non-heart failure patients. However, it is not clear whether Na/K-ATPase reduction is causatively related with heart failure, and if so, how Na/K-ATPase expression is regulated. During the past twenty years tremendous work have been done to show that Na/K-ATPase, especially its signaling function, is associated with cardiac hypertrophy and cardiac fibrosis. Interestingly, data from our laboratory showed that reduction of Na/K-ATPase attenuates its signaling activation, which might be beneficial to reducing cardiac hypertrophy, but it also increases cardiac cell apoptosis. The aim of my project is to: 1) study how Na/K-ATPase is regulated during disease conditions; and 2) study the effect of Na/K-ATPase reduction on cardiac function and its mechanism. From these studies, we have identified a novel long-non-coding RNA, ATP1A1-AS1, as an endogenous Na/K-ATPase regulator that affect Na/K-ATPase expression and its signaling function (Chapter 3). We also demonstrated that reduction of Na/K-ATPase α1 had significant effect on cardiac function and remodeling due to the change in Na/K-ATPase signaling (Chapter 4). ATP1A1-AS1 gene is a natural antisense gene of Na/K-ATPase α1 (ATP1A1) which is located on the opposite strand of the Na/K-ATPase α1 gene. Our results showed that 4 splice variants expressed in human adult kidney cells (HK2 cells) and embryonic kidney cells (HEK293 cells). We found that inhibition of DNA methylation had a differential effect on the expression of ATP1A1-AS1 and its sense gene. To investigate the physiological role of this antisense gene, overexpression of ATP1A1-AS1 was performed and its effect on Na/K-ATPase expression was examined. The result showed that ATP1A1-AS1-203 overexpression reduced the Na/K-ATPase α1 (ATP1A1) gene expression in HK2 cells by about 20% (p<0.05), it also reduced the Na/K-ATPase α1 protein by about 22% (p<0.05). In addition, overexpression of ATP1A1-AS1-203 attenuated ouabain-induced Src activation in HK2 cells and subsequently inhibited the cell proliferation in the presence or absence of ouabain. These results demonstrate that ATP1A1-AS1 gene is a moderate negative regulator of Na/K-ATPase α1 and can modulate Na/K-ATPase-related signaling pathways. Importantly, these results suggest that a moderate reduction of Na/K-ATPase expression could disproportionally affect the signaling function of Na/K-ATPase, which is consistent to the previous findings in Na/K-ATPase knockdown cell lines. To study the effect of Na/K-ATPase on cardiac function in disease conditions, we used a mouse chronic kidney disease (CKD) model (5/6th partial nephrectomy or PNx) in Na/K-ATPase alpha 1 heterozygous (α1+/-) mice and their wild type (WT) littermates. The cardiac Na/K-ATPase alpha 1 expression in α1+/- mice is about 40% less than that of WT mice. The experimental results showed that reduction of Na/K-ATPase significantly reduced cardiac hypertrophy in the CKD animals. However, it showed no significant change in cardiac fibrosis between the two animal strains. To further study the role of Na/K-ATPase in cardiac fibrosis, we found that CKD induces activation of Src and NFB signaling in the heart tissue of WT mice, which subsequently causes reduction of microRNA-29b-3p (miR-29b), an antifibrotic microRNA. However, in α1+/- mice, Src and NFB activation was significantly attenuated. We further found that in WT mice, inhibition of Src signaling using pNaKtide blocked NFB activation and restored miR-29b expression to a level close to the controls. Whereas, the pNaKtide had no significant effect on Src/NFB activation or miR-29b expression in α1+/- mice. Injection of pNaKtide also significantly reduces cardiac fibrosis in WT mice. These results suggest that Na/K-ATPase reduction not only attenuates Na/K-ATPase signaling function, it may also adopt other pathological pathways, which can cause cardiac fibrosis independent of Na/K-ATPase-related Src and NFB signaling. The specific mechanisms are elusive and merit further investigations.
Jiang Tian (Committee Chair)
Andrew D. Beavis (Committee Member)
Kevin Z Pan (Committee Member)
David Giovannucci (Committee Member)
Lijun Liu (Committee Member)
Christopher J. Cooper (Committee Member)
Biomedical Research

Recommended Citations

Citations

  • Fan, X. (2018). Regulation of Na/K-ATPase and its Role in Cardiac Disease [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=mco1544722291840285

    APA Style (7th edition)

  • Fan, Xiaoming. Regulation of Na/K-ATPase and its Role in Cardiac Disease. 2018. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=mco1544722291840285.

    MLA Style (8th edition)

  • Fan, Xiaoming. "Regulation of Na/K-ATPase and its Role in Cardiac Disease." Doctoral dissertation, University of Toledo, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=mco1544722291840285

    Chicago Manual of Style (17th edition)

mco1544722291840285
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This open access ETD is published by University of Toledo Health Science Campus and OhioLINK.