Excessive dietary salt intake is a major life-style risk factor of hypertension and related diseases such as cardiovascular and renal morbidities. Maladaptation of renal sodium handling to high salt intake is critical in development and maintenance of salt-sensitive and volume-expansive hypertension. We recently demonstrated a novel regulatory mechanism of renal sodium handling mediated by Na/K-ATPase signaling in renal proximal tubule. In this model, cardiotonic steroids (also known as endogenous digitalis-like substances such as ouabain) and reactive oxygen species (ROS), signaling through Na/K-ATPase, stimulate redistribution of Na/K-ATPase and Na/H exchanger isoform 3, leading to stimulation of total and fractional sodium excretion. Impairment of this mechanism is strongly implicated as causative of experimental Dahl salt-sensitive hypertension. Our data further indicates that direct protein carbonylation of two amino acid residues in the actuator domain of the Na/K-ATPase ?1 subunit is responsible for the regulation of Na/K-ATPase signaling and sodium reabsorption. Our central hypothesis is that Oxidative modification (carbonylation) of Na/K-ATPase ?1 subunit regulates Na/K-ATPase signaling and sodium handling in renal proximal tubules. Specifically, carbonylation modification of Na/K-ATPase ?1 subunit has bi-phasic effects. (1) Physiological and controllable ?1 carbonylation stimulates Na/K-ATPase signaling and sodium excretion rendering salt resistance, and (2) Pathologically overstimulated ?1 carbonylation desensitizes Na/K- ATPase signaling rendering salt-sensitivity.
Aim 1 is to investigate the role of ?1 carbonylation in Na/K-ATPase signaling and function. We will define the functional role of Pro222 and/or Thr224 carbonylation in Na/K-ATPase signaling that leads to inhibition of transepithelial 22Na+ flux.
Aim 2 is to investigate the role of ?1 carbonylationon proximal tubular Na/K-ATPase signaling and salt sensitivity. We will test if the phenotype of salt sensitivity could be changed by alteration of basal ?1 carbonylation level. Since both ouabain and ROS stimulate heme oxygenase-1 (HO-1) expression, we will also use wild-type and proximal tubule-specific HO-1 knockout and HO-1 overexpression mice to determine the role of HO-1 in regulation of Na/K-ATPase signaling and sodium handling. Validation of our hypothesis would further explain the progressive impairment of renal sodium handling under excessive oxidative stress such as hypertension, aging, obesity and diabetes. A clearer understanding of the molecular mechanisms would have pathophysiological and therapeutic implications for salt-sensitive hypertension that results from impaired Na/K-ATPase signaling.
High dietary salt intake is an independent risk factor of hypertension and related cardiovascular and renal diseases. An increase in oxidative stress is both a cause and consequence of hypertension. We propose to test how oxidative modification regulates the signaling function of Na/K-ATPase and thereby alters renal sodium handling. We will further test whether the phenotype of salt sensitivity could be altered by manipulating oxidative modification of the Na/K-ATPase and its Na/K-ATPase signaling. Validation of our hypothesis might ultimately lead to possible new therapeutic strategies and personal management for patients with hypertension.
