(From the application abstract:) The goals of the current project are to investigate the structure, function, and regulation of plasma membrane transporters responsible for carnitine homeostasis and to understand the relevance of these transporters to the genetic disorders ofcarnitine metabolism. Carnitine is obligatory for fatty acid oxidation and hence for the maintenance of the energy status in tissues such as heart and skeletal muscle. Primary systemic carnitine deficiency is a genetic disorder associated with defectsin the Na+ dependent high-affinity carnitine transporter. Clinical symptoms of the disease consist primarily of cardiac and skeletal myopathy resulting from decreased intracellular carnitine levels. The octn2 gene codes for the high-affinity carnitine transporter. Loss-of-function mutations in this gene have been identified in patients with primary systemic carnitine deficiency. Interestingly, OCTN2 is also a drug transporter with affinity for a variety of pharmacologically active drugs. While the physiological relevance of the carnitine transport function of OCTN2 is understandable, the drug transport function of OCTN2 remains an enigma. OCTN2 may play a significant role in the bioavailability and pharmacokinetics of a number of therapeutic agents. Furthermore, OCTN2 expression is down-regulated by activators of peroxisome proliferator-activated receptors (PPARs). This suggests that chronic use of PPAR ligands may interfere with OCTN2 expression and decrease intracellular carnitine levels. This is clinically relevant because several PPAR ligands are currently in use as therapeutic agents (e.g., Rezulin, clofibrate). In addition, carnitine possesses anti-apoptotic activity and there are reasons to believe that OCTN2 is obligatory for this function. Studies are proposed in this project (a) to delineate the functional characteristics of OCTN2 with emphasis on the differential aspects of its drug transport function and the carnitine transport function, (b) to investigate the regulatory aspects of OCTN2 in the heart, skeletal muscle, kidney, intestine, liver, and placenta particularly with respect to the role of PPARs and substrate-dependent modulation of OCTN2 expression, (c) to delineate the molecular mechanism of the anti-apoptotic function of carnitine and its acyl esters and to analyze the role of OCTN2 in this process, (d) to identify the transporters responsible for vectorial transfer of carnitine in polarized tissues, and (e) to determine the functional identity of the closely related transport protein OCTN3. The transport function of the cloned transporters will be measured following heterologous expression in mammalian cells and in X. laevis oocytes. The regulation studies will be carried out in intact animals using the rat as a model and also in cultured cells of human origin.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL064196-02
Application #
6402792
Study Section
Medical Biochemistry Study Section (MEDB)
Program Officer
Liang, Isabella Y
Project Start
2000-09-15
Project End
2004-07-31
Budget Start
2001-08-01
Budget End
2002-07-31
Support Year
2
Fiscal Year
2001
Total Cost
$255,500
Indirect Cost
Name
Medical College of Georgia (MCG)
Department
Biochemistry
Type
Schools of Medicine
DUNS #
City
Augusta
State
GA
Country
United States
Zip Code
30912
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Miyauchi, Seiji; Abbot, Emily L; Zhuang, Lina et al. (2005) Isolation and function of the amino acid transporter PAT1 (slc36a1) from rabbit and discrimination between transport via PAT1 and system IMINO in renal brush-border membrane vesicles. Mol Membr Biol 22:549-59
Jiang, Guoliang; Zhuang, Lina; Miyauchi, Seiji et al. (2005) A Na+/Cl- -coupled GABA transporter, GAT-1, from Caenorhabditis elegans: structural and functional features, specific expression in GABA-ergic neurons, and involvement in muscle function. J Biol Chem 280:2065-77
Gopal, Elangovan; Fei, You-Jun; Sugawara, Mitsuru et al. (2004) Expression of slc5a8 in kidney and its role in Na(+)-coupled transport of lactate. J Biol Chem 279:44522-32
Fei, You-Jun; Liu, Jin-Cai; Inoue, Katsuhisa et al. (2004) Relevance of NAC-2, an Na+-coupled citrate transporter, to life span, body size and fat content in Caenorhabditis elegans. Biochem J 379:191-8
Miyauchi, Seiji; Gopal, Elangovan; Fei, You-Jun et al. (2004) Functional identification of SLC5A8, a tumor suppressor down-regulated in colon cancer, as a Na(+)-coupled transporter for short-chain fatty acids. J Biol Chem 279:13293-6
Shekhawat, Prem S; Yang, Han-Soo; Bennett, Michael J et al. (2004) Carnitine content and expression of mitochondrial beta-oxidation enzymes in placentas of wild-type (OCTN2(+/+)) and OCTN2 Null (OCTN2(-/-)) Mice. Pediatr Res 56:323-8
Bridges, Christy C; Hu, Huankai; Miyauchi, Seiji et al. (2004) Induction of cystine-glutamate transporter xc- by human immunodeficiency virus type 1 transactivator protein tat in retinal pigment epithelium. Invest Ophthalmol Vis Sci 45:2906-14
Chen, Zhong; Kennedy, David J; Wake, Katherine A et al. (2003) Structure, tissue expression pattern, and function of the amino acid transporter rat PAT2. Biochem Biophys Res Commun 304:747-54
Chen, Zhong; Fei, You-Jun; Anderson, Catriona M H et al. (2003) Structure, function and immunolocalization of a proton-coupled amino acid transporter (hPAT1) in the human intestinal cell line Caco-2. J Physiol 546:349-61

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