Aquaporin-2 (AQP2) expressed in kidney collecting duct epithelial principal cells is essential for the maintenance of total body volume homeostasis. The hormone arginine vasopressin (AVP;or antidiuretic hormone) is secreted from the hypothalamus/pituitary as a normal response to increased serum osmolality or decreased blood pressure. In principal cells, AVP acts via the vasopressin receptor type II (V2R), leading to a cascade involving cAMP/PKA, AQP2 phosphorylation, apical membrane insertion of AQP2-containing vesicles and water reabsorption from the urine into the interstitium. AQP2 trafficking and subcellular localization are mediated by the phosphorylation status of several Ser residues in the AQP2 C-terminus as well as by ubiquitination status. Indeed, research on AQP2 regulation has shed light on the pathogenesis of diseases such as nephrogenic diabetes insipidus (NDI), SIADH and heart failure. Our preliminary data show that the metabolic sensor AMP-activated kinase (AMPK), which is upregulated by metabolic stress (e.g., during ischemia), prevents acute PKA-mediated AQP2 apical accumulation ex vivo in kidney slices. In addition, dominant-negative AMPK accelerates AQP2-mediated oocyte swelling upon hypotonic shock, suggesting that inhibition of AMPK activity stimulates AQP2 function. We hypothesize that AMPK induces intracellular accumulation of AQP2, either via direct phosphorylation or by modulating PKA-mediated AQP2 phosphorylation, and promotes AQP2 ubiquitination and degradation during periods of metabolic stress.
Our aims are to examine the mechanisms by which AMPK-dependent phosphorylation regulates AQP2 trafficking and function and to examine the role of AMPK in enhancing the ubiquitination, cytoplasmic redistribution, and degradation of AQP2. We will determine which AQP2 residues are phosphorylated by AMPK by mass spectrometry and the role of those residues on the subcellular localization and activity of this water channel in oocytes and mpkCCDc14 cells. We will also determine whether AMPK increases AQP2 ubiquitination and degradation in kidney slices and in mpkCCDc14 cells. Finally, we will determine whether AMPK inhibition prevents AQP2 redistribution and/or degradation in kidney slices and mpkCCDc14 cells following chemical ischemia. This proposal addresses a novel potential mechanism by which metabolic stress, as occurs during ischemia, regulates AQP2. Our research will likely contribute to a better understanding of how body water homeostasis may be coupled to metabolism and pathology of vital organs such as heart and kidney.

Public Health Relevance

Aquaporin-2 (AQP2), a water channel expressed in kidney epithelium, is essential for the maintenance of total body volume homeostasis. Research on AQP2 has shed light on the pathogenesis of nephrogenic diabetes insipidus, the syndrome of inappropriate antidiuretic hormone release, and heart failure. We hypothesize that AMPK, which is activated by ischemia, regulates AQP2 abundance and function during acute kidney ischemia. Our research should contribute to a better understanding of how body water homeostasis may be coupled to metabolism and kidney pathology. In addition, it may provide insight into the treatment of important body water balance disorders like nephrogenic diabetes insipidus.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Postdoctoral Individual National Research Service Award (F32)
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Special Emphasis Panel (ZDK1-GRB-G (O1))
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Rankin, Tracy L
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University of Pittsburgh
Internal Medicine/Medicine
Schools of Medicine
United States
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Al-bataineh, Mohammad M; Gong, Fan; Marciszyn, Allison L et al. (2014) Regulation of proximal tubule vacuolar H(+)-ATPase by PKA and AMP-activated protein kinase. Am J Physiol Renal Physiol 306:F981-95
Gidon, Alexandre; Al-Bataineh, Mohammad M; Jean-Alphonse, Frederic G et al. (2014) Endosomal GPCR signaling turned off by negative feedback actions of PKA and v-ATPase. Nat Chem Biol 10:707-9