Mechanisms of ENaC Regulation by AMP-activated Kinase

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DESCRIPTION (provided by applicant): The goals of the parent K08 grant [DK59477] have been to discover the underlying mechanisms by which AMPK, a ubiquitous kinase whose activity is finely tuned to cellular metabolic status, modulates the function of the CFTR CI- channel in epithelial cells. This project has already yielded several important findings. The AMPK-CFTR interaction appears to be physiologically relevant in polarized lung and colonic epithelia and provides a new paradigm for the coupling of ion transport to cellular metabolism. AMPK regulates CFTR activity predominantly through an inhibition in the single-channel open probability of CFTR rather than through effects on CFTR plasma membrane expression. The molecular details underlying the AMPK-dependent inhibition of CFTR are also now becoming clearer. Because CFTR regulates other epithelial transport proteins and because the activity of other transport proteins are coupled to cellular metabolic status, AMPK may potentially regulate other important transport proteins, both through its regulation of CFTR and/or independently of CFTR. The epithelial Na+ channel (ENaC) plays a critical role in total-body Na+ and volume homeostasis by regulating renal Na+ reabsorption in the distal nephron. EnaC function is also modulated by CFTR in the lung and other tissues and may play an important rote in the pathogenesis of cystic fibrosis. Our preliminary data suggest that AMPK regulates ENaC function, potentially coupling ENaC function to metabolic status. This research program will expand the focus of the parent grant to include studies designed to elucidate the mechanisms for AMPK-dependent regulation of ENaC in Xenopus oocytes. Time-dependent differences in the effects of AMPK activation on ENaC activity will be closely examined. The effects of short- and long-term AMPK activity modulation on ENaC plasma membrane expression, trafficking, and channel properties will also be studied. Finally, the underlying signaling pathway(s) involved in AMPK-dependent regulation of ENaC will be sought. A better understanding of the mechanisms for AMPK-dependent regulation of ENaC in oocytes should provide the framework for future studies in polarized epithelial cells and in vivo and yield new insights into how salt and water transport by the kidney is coupled to metabolic state and into the pathogenesis of ischemic and hypoxic renal injury.