The major focus of the Moe laboratory is to study the mechanisms of regulation of the principal sodium transporter in the kidney, Na/H exchanger type 3 (NHE3). Normal NHE3 function and regulation are essential for the maintenance of normal extracellular fluid volume, blood pressure and acid-base balance. All the following projects are currently involving or will involve trainees:
- Regulation of NHE3. Role of protein trafficking. NHE3 can be acutely regulated by alterations in endocytotic retrieval or exocytotic insertion into the membrane. We are currently studying the regulation of both of these trafficking events. We have recently uncovered a non-genomic mechanism of activation of NHE3 by glucocorticoid hormones through NHE3 exocytosis.
- Regulation of NHE3.Role of phosphorylation and binding proteins. Phosphorylation of NHE3 is necessary but insufficient to affect its regulation. We propose that regulatory cofactors are crucial to modulate the phosphorylated protein. We are using multiple approaches to isolate these protein factors. The figure shows one such interacting partner which is calcineurin homologous protein (CHP). CHP-1 interacts with NHE3 and is responsible for mediating the regulation of NHE3 by adenosine.
- Regulation of NHE3. Role of membrane lipids. In collaboration with the laboratory of Don Hilgemann, we have developed a novel electrophysiologic method to assay Na/H exchange. Using this method, we are examining the role of membrane lipids in the regulation of NHE3.
- Regulation of NHE3 translation. NHE3 is regulated at the translation level by a variety of agonists including dopamine and glucocorticoids. We will define cis-elements in the 5'-untranslated region of the NHE3 transcript that confer this type of regulation.
- Regulation of NHE3 degradation. NHE3 protein is degraded by both the lysosomal and proteasomal pathways. We are currently studying how NHE3 degradation via these pathways is regulated.
- Regulation of NHE3 in renal ischemia. Na/H exchanger NHE3 expression virtually disappears with ischemia-reperfusion injury and is increased during recovery. We are studying the mechanisms of suppression and activation of NHE3 expression in ischemia-reperfusion injury.
In addition to NHE3, the laboratory is also studying other areas that are complementary to some of the clinical projects that are under the same P.I.:
- Regulation of proximal tubule glycolysis in renal ischemia. The proximal tubule is normally an aerobic tissue with an enormous dormant glycolytic reserve. This reserve is rapidly activated upon ischemia. We are currently studying the role of the bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase in mediating the recruitment of glycolytic reserve.
- Insulin signaling in the kidney and regulation of remal ammoniagenesis and transport by insulin. The renal effects of insulin are not well defined. Our group recently identified impairment in renal ammonium and uric acid excretion as potential renal manifestations of insulin resistance. Complementary to the clinical efforts are laboratory studies designed to elucidate the mechanisms by which insulin regulates renal ammonium and uric acid excretion.
- Functional and structural characterization of the soluble adenylyl cyclase. The recently discovered soluble adenylyl cyclase is a bicarbonate sensor. We have identified that certain base changes of this gene are associated with disturbances in calcium metabolism . We are studying the function of the wild type and mutant soluble adenylyl cyclase to clarify its role in calcium metabolism in the bone, gut and kidney.
Bobulescu IA, Moe OW. Na+/H+ exchangers in renal regulation of Acid-base balance. Semin Nephrol. 2006 Sep;26(5):334-44.
Fuster DG, Bobulescu IA, Zhang J, Wade J, Moe OW. Characterization of the Regulation of Renal Na/H Exchanger NHE3 by Insulin. Am J Physiol Renal Physiol. 2006 Oct 3 (in press)
Bobulescu IA, Di Sole F, Moe OW.Na/H exchangers: physiology and link to hypertension and organ ischemia. Curr Opin Nephrol Hypertens. 2005 Sep;14(5):485-94.
Bobulescu IA, Dwarakanath V, Zou L, Zhang J, Baum M, Moe OW. Glucocorticoids acutely increase cell surface Na/H exchanger-3 (NHE3) by activation of NHE3 exocytosis. Am J Physiol Renal Physiol. 2005 Oct;289(4):F685-91.
Geng W, Wang Z, Zhang J, Reed BY, Pak CY, Moe OW. Cloning and characterization of the human soluble adenylyl cyclase. Am J Physiol Cell Physiol. 2005 Jun;288(6):C1305-16.
Moe OW, Bonny O. Genetic hypercalciuria. J Am Soc Nephrol. 2005 Mar;16(3):729-45.
Fuster D, Moe OW, Hilgemann DW.Lipid- and mechanosensitivities of sodium/hydrogen exchangers analyzed by electrical methods. Proc Natl Acad Sci U S A. 2004 Jul 13;101(28):10482-7.
Di Sole F, Cerull R, Babich V, Quinones H, Gisler SM, Biber J, Murer H, Burckhardt G, Helmle-Kolb C, Moe OW. Acute regulation of Na/H exchanger NHE3 by adenosine A1 receptors is mediated by calcineurin homologous protein (CHP). J Biol Chem. 2004 Jan 23;279(4):2962-74.
Bacic D, Kaissling B, McLeroy P, Zou L, Baum M, Moe OW. Dopamine acutely decreases apical membrane Na/H exchanger NHE3 protein in mouse renal proximal tubule. Kidney Int. 2003 Dec;64(6):2133-41.
Moe OW. Scaffolds: Orchestrating proteins to achieve concerted function. Kidney Int. 2003 Nov;64(5):1916-7.
Hu MC, Fan L, Crowder LA, Karim-Jimenez Z, Murer H, Moe OW. Dopamine acutely stimulates Na/H exchanger (NHE3) endocytosis via clathrin-coated vesicles: dependence on protein kinase A-mediated NHE3 phosphorylation. J Biol Chem. 2001 Jul 20;276(29):26906-15.
Collazo R, Fan L, Hu MC, Zhao H, Wiederkehr MR, Moe OW. Acute regulation of Na/H exchanger NHE3 by parathyroid hormone via NHE3 phosphorylation and dynamin-dependent endocytosis. J Biol Chem. 2000 Oct 13;275(41):31601-8.
Moe OW. Acute regulation of proximal tubule apical membrane Na/H exchanger NHE-3: role of phosphorylation, protein trafficking, and regulatory factors. J Am Soc Nephrol. 1999 Nov;10(11):2412-25.
Baum M, Amemiya M, Dwarakanath V, Alpern RJ, Moe OW. Glucocorticoids regulate NHE-3 transcription in OKP cells. Am J Physiol. 1996 Jan;270(1 Pt 2):F164-9.
Amemiya M, Loffing J, Lotscher M, Kaissling B, Alpern RJ, Moe OW. Expression of NHE-3 in the apical membrane of rat renal proximal tubule and thick ascending limb. Kidney Int. 1995 Oct;48(4):1206-15.