Encephalopathy due to elevated ammonia levels is a common and costly clinical condition associated either with congenital deficiency of hepatic urea cycle enzymes, with acquired liver disease and with a variety of other conditions. Despite a long recognition that elevated ammonia levels can lead to impaired neurologic functioning, the exact mechanism through which this occurs remains incompletely understood. Moreover, treatment of hyperammonemic encephalopathy has been limited by a lack of knowledge of the specific CNS protein(s) with which ammonia directly interacts. The broad, long-term objective of this project is to examine the hypothesis that Rh C Glycoprotein (RhCG) is a central nervous system (CNS) ammonia 'sensor.' We hypothesize that RhCG protein is expressed in specific CNS neuron populations, that ammonia-stimulation of RhCG is coupled to specific intracellular signaling pathways, most likely including MAP kinase, and that RhCG expression is regulated by specific physiology/pathophysiologic stimuli. We will examine this hypothesis with two specific aims. In the first, we will determine whether ammonia's stimulation of RhCG, or, possibly the related proteins, Rh A Glycoprotein (RhAG) or Rh B Glycoprotein (RhBG), activates specific intracellular signaling pathways in cultured neurons. We will use primary neuronal cultures, and will use RNA interference techniques to inhibit RhCG expression to show specificity of response. In parallel, we will determine whether RhCG can function as an ammonia sensor by determining whether it can complement the pseudohyphal transformation-defect of Amep2-Amep2 S. cerevisiae. To examine the second aim, we will determine whether cecal ligation and puncture-induced sepsis increases CNS expression of either RhCG, or of RhAG or RhBG. These studies will combine immunohistochemical analyses of cellular protein expression patterns with quantitative analyses of protein and mRNA expression with immunoblot and real-time RT-PCR, respectively. These studies fit the purpose of the R21 mechanism in two different manners. These studies will provide pilot data to assess the feasibility of a novel avenue of investigation into the role of RhCG, or related proteins, as CNS ammonia 'sensors.' Second, while these studies are admittedly high risk, their results could lead to a breakthrough in the field of hyperammonemic and hepatic encephalopathy.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Exploratory/Developmental Grants (R21)
Project #
1R21NS047624-01
Application #
6720095
Study Section
National Institute of Neurological Disorders and Stroke Initial Review Group (NSD)
Program Officer
Jacobs, Tom P
Project Start
2003-12-01
Project End
2005-11-30
Budget Start
2003-12-01
Budget End
2004-11-30
Support Year
1
Fiscal Year
2004
Total Cost
$153,275
Indirect Cost
Name
University of Florida
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
969663814
City
Gainesville
State
FL
Country
United States
Zip Code
32611
Han, Ki-Hwan; Mekala, Kavya; Babida, Venetia et al. (2009) Expression of the gas-transporting proteins, Rh B glycoprotein and Rh C glycoprotein, in the murine lung. Am J Physiol Lung Cell Mol Physiol 297:L153-63
Lim, Sun Woo; Ahn, Kyung Ohk; Kim, Wan Young et al. (2008) Expression of ammonia transporters, Rhbg and Rhcg, in chronic cyclosporine nephropathy in rats. Nephron Exp Nephrol 110:e49-58
Kim, Hye-Young; Baylis, Chris; Verlander, Jill W et al. (2007) Effect of reduced renal mass on renal ammonia transporter family, Rh C glycoprotein and Rh B glycoprotein, expression. Am J Physiol Renal Physiol 293:F1238-47
Han, Ki-Hwan; Kim, Hye-Young; Croker, Byron P et al. (2007) Effects of ischemia-reperfusion injury on renal ammonia metabolism and the collecting duct. Am J Physiol Renal Physiol 293:F1342-54
Weiner, I David; Hamm, L Lee (2007) Molecular mechanisms of renal ammonia transport. Annu Rev Physiol 69:317-40
Seshadri, Ramanathan M; Klein, Janet D; Smith, Tekla et al. (2006) Changes in subcellular distribution of the ammonia transporter, Rhcg, in response to chronic metabolic acidosis. Am J Physiol Renal Physiol 290:F1443-52
Seshadri, Ramanathan M; Klein, Janet D; Kozlowski, Shelley et al. (2006) Renal expression of the ammonia transporters, Rhbg and Rhcg, in response to chronic metabolic acidosis. Am J Physiol Renal Physiol 290:F397-408
Han, Ki-Hwan; Croker, Byron P; Clapp, William L et al. (2006) Expression of the ammonia transporter, rh C glycoprotein, in normal and neoplastic human kidney. J Am Soc Nephrol 17:2670-9
Weiner, I D (2006) Expression of the non-erythroid Rh glycoproteins in mammalian tissues. Transfus Clin Biol 13:159-63
Mak, Don-On Daniel; Dang, Binh; Weiner, I David et al. (2006) Characterization of ammonia transport by the kidney Rh glycoproteins RhBG and RhCG. Am J Physiol Renal Physiol 290:F297-305

Showing the most recent 10 out of 14 publications