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. Joseph Shapiro

Third Advisor

Dr. Jiang Liu

Fourth Advisor

Dr. Gustavo Blanco

Fifth Advisor

Dr. Jiang Tian

Abstract

The renal proximal tubule (RPT) is the center stage for renal handling of Na+ , a potent determinant of systemic Na+ and volume homeostasis in health and disease. In the RPT, through its classic ion-pumping function, Na + /K+ -ATPase (NKA) generates the Na+ gradient that drives apical Na+ absorption, mostly through Na+ /H+ exchanger (NHE3). In contrast, pharmacological evidence suggests that the activation of the NKA non-enzymatic signaling function, through Src and other signaling partners, triggers a cellular redistribution of NKA and NHE3 that decreases transcellular Na+ flux in cultured RPT cells. However, the physiological relevance of the nonenzymatic function of NKA compared to its enzymatic function in the regulation of RPT Na+ transport has not been directly studied. Thus, to address this, we developed a genetic approach in RPT cells and mice. Loss of NKA α1 in RPT cells in vitro and in vivo resulted in a prominent increase in transepithelial Na+ transport coupled to an increased membrane abundance of apical NHE3 and basolateral Na/HCO3 - cotransporter-1A (NBCe1A). Consistently, the hyperabsorptive phenotype observed in RPT-specific hypomorphic NKA α1 mice was rescued upon crossing with RPT-specific hypomorphic NHE3 mice, confirming the importance of NKA/NHE3 coupling. Consistent with previous pharmacological studies reported a role for Src in the natriuretic regulation by NKA receptor, rescue of RPT cells with wild-type but not Src-binding null NKA α1 restored NHE3 and NBCe1A to basal levels, indicative of a role for NKA/Src receptor function in the tonic inhibition of Na+ transporters in vitro. In vivo, while female mice expressing Src-binding mutant NKA α1 in RPT exhibit increased NHE3 and RPT Na+ transport, male mice exhibit no change. These observations are compatible with a sexual dimorphism in the NKA/Src mechanism of regulation of NHE3 and Na+ transport in the RPT. Hence, NKA nonenzymatic signaling is a potent natriuretic mechanism of tonic inhibition of RPT Na+ transport by regulating key apical and basolateral Na+ transporters. Remarkably, the natriuretic NKA signaling is also functionally dominant over its classically recognized anti-natriuretic ion-pumping role. NKA signaling therefore provides a long sought-after mechanism for the natriuretic action of endogenous NKA ligands such as cardiotonic steroids.

Subject(s)

Cell physiology -- Research.

Kidneys -- Physiology -- Research.

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