Date of Award

2021

Degree Name

Biomedical Sciences

College

Joan C. Edwards School of Medicine

Type of Degree

Ph.D.

Document Type

Dissertation

First Advisor

Dr. Sandrine Pierre, Committee Chairperson

Second Advisor

Dr. Liquan Cai

Third Advisor

Dr. Joseph Shapiro

Fourth Advisor

Dr. Nalini Santanam

Fifth Advisor

Dr. Gustavo Blanco

Abstract

The Na/K-ATPase (NKA) was identified in 1957 by Dr. Jens C. Skou. It belongs to the P-type ATPase family, which can actively transport ions across cell membranes by using the energy from adenosine triphosphate (ATP) hydrolysis. During the second half of the 20th century, the molecular mechanism of the NKA catalytic cycle was clarified, and the isoform diversity of NKA in different species and organs was identified. The active ion transport through NKA generates cell membrane ion gradients and the electric potential. Hence, the enzymatic function of NKA is critical for cell viability as well as multiple physiological processes including muscle contraction, renal sodium reabsorption, and nerve impulse transmission. Inhibition of NKA-mediated ion transport by cardiotonic steroids (CTS), which have long been used in the clinical treatment of heart failure, improves cardiac inotropy. Moreover, CTS at low concentrations were found to induce signal transduction through NKA, revealing its receptor signaling function. In addition to its role as an ion pump, the NKA α1 isoform forms a signal receptor complex with the non-receptor tyrosine kinase Src and the scaffolding protein caveolin1 (Cav1). The gain of the caveolin binding motif (CBM) in the α1 NKA is required for the nonion pumping function of NKA and the early stages of organogenesis in mice and C. elegans.

Considering the reported importance of NKA non-ion-pumping function in metabolic disorders, we further tested whether the loss of this CBM altered adiposity in mice and impaired adipogenesis in a human induced pluripotent stem cell (iPSC) model. At the age of 6-months, NKA CBM mutant (mCBM) heterozygous mice exhibit altered adiposity and reduced white adipose tissue (WAT) mass. The histology of mCBM WAT indicated tissue fibrosis and chronic inflammation, which may contribute to adipose tissue metabolic dysfunction. To further understand the molecular mechanism, we used an mCBM human iPSC model and a differentiation protocol to mimic the adipogenesis process in vitro. These studies indicated that the loss of CBM function in NKA α1 in human iPSC induces extracellular matrix (ECM) fibrotic remodeling. The ECM remodeling does not block the commitment of stem cells into adipocytes. However, it results in increased oxidative stress, insulin resistance, chronic inflammation, and eventually metabolic dysfunction during adipogenesis.

Thus, we characterized a novel role of the non-ion pumping NKA and its interaction with Cav1 in the regulation of stem cell differentiation and adipogenesis. This provides novel insight into the complex dynamic of regulation of caveolar structure and function in the adipocyte and could be of therapeutic relevance in the management of fat-related disorders ranging from genetic lipodystrophies to metabolic syndromes.

Subject(s)

Cell physiology -- Research.

Ions -- Migration and velocity -- Research.

Download

Share

COinS