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Linn E, Ghanem L, Bhakta H, Greer C, Avella M. Genes Regulating Spermatogenesis and Sperm Function Associated With Rare Disorders. Front Cell Dev Biol 2021; 9:634536. [PMID: 33665191 PMCID: PMC7921155 DOI: 10.3389/fcell.2021.634536] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2020] [Accepted: 01/20/2021] [Indexed: 12/26/2022] Open
Abstract
Spermatogenesis is a cell differentiation process that ensures the production of fertilizing sperm, which ultimately fuse with an egg to form a zygote. Normal spermatogenesis relies on Sertoli cells, which preserve cell junctions while providing nutrients for mitosis and meiosis of male germ cells. Several genes regulate normal spermatogenesis, some of which are not exclusively expressed in the testis and control multiple physiological processes in an organism. Loss-of-function mutations in some of these genes result in spermatogenesis and sperm functionality defects, potentially leading to the insurgence of rare genetic disorders. To identify genetic intersections between spermatogenesis and rare diseases, we screened public archives of human genetic conditions available on the Genetic and Rare Diseases Information Center (GARD), the Online Mendelian Inheritance in Man (OMIM), and the Clinical Variant (ClinVar), and after an extensive literature search, we identified 22 distinct genes associated with 21 rare genetic conditions and defective spermatogenesis or sperm function. These protein-coding genes regulate Sertoli cell development and function during spermatogenesis, checkpoint signaling pathways at meiosis, cellular organization and shape definition during spermiogenesis, sperm motility, and capacitation at fertilization. A number of these genes regulate folliculogenesis and oogenesis as well. For each gene, we review the genotype–phenotype association together with associative or causative polymorphisms in humans, and provide a description of the shared molecular mechanisms that regulate gametogenesis and fertilization obtained in transgenic animal models.
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Affiliation(s)
- Emma Linn
- Department of Biological Science, College of Engineering and Natural Sciences, University of Tulsa, Tulsa, OK, United States
| | - Lillian Ghanem
- Department of Biological Science, College of Engineering and Natural Sciences, University of Tulsa, Tulsa, OK, United States
| | - Hanisha Bhakta
- Department of Biological Science, College of Engineering and Natural Sciences, University of Tulsa, Tulsa, OK, United States
| | - Cory Greer
- Department of Biological Science, College of Engineering and Natural Sciences, University of Tulsa, Tulsa, OK, United States
| | - Matteo Avella
- Department of Biological Science, College of Engineering and Natural Sciences, University of Tulsa, Tulsa, OK, United States
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Carnitine/organic cation transporter 2 (OCTN2) contributes to rat epididymal epithelial cell growth and proliferation. Biomed Pharmacother 2017; 93:444-450. [DOI: 10.1016/j.biopha.2017.06.057] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Revised: 06/12/2017] [Accepted: 06/19/2017] [Indexed: 01/14/2023] Open
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Tamai I. Pharmacological and pathophysiological roles of carnitine/organic cation transporters (OCTNs: SLC22A4, SLC22A5 and Slc22a21). Biopharm Drug Dispos 2012; 34:29-44. [PMID: 22952014 DOI: 10.1002/bdd.1816] [Citation(s) in RCA: 99] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2012] [Revised: 08/27/2012] [Accepted: 08/30/2012] [Indexed: 02/06/2023]
Abstract
The carnitine/organic cation transporter (OCTN) family consists of three transporter isoforms, i.e. OCTN1 (SLC22A4) and OCTN2 (SLC22A5) in humans and animals and Octn3 (Slc22a21) in mice. These transporters are physiologically essential to maintain appropriate systemic and tissue concentrations of carnitine by regulating its membrane transport during intestinal absorption, tissue distribution and renal reabsorption. Among them, OCTN2 is a sodium-dependent, high-affinity transporter of carnitine, and a functional defect of OCTN2 due to genetic mutation causes primary systemic carnitine deficiency (SCD). Since carnitine is essential for beta-oxidation of long-chain fatty acids to produce ATP, OCTN2 gene mutation causes a range of symptoms, including cardiomyopathy, skeletal muscle weakness, fatty liver and male infertility. These functional consequences of Octn2 gene mutation can be seen clearly in an animal model, jvs mouse, which exhibits the SCD phenotype. In addition, although the mechanism is not clear, single nucleotide polymorphisms of OCTN1 and OCTN2 genes are associated with increased incidences of rheumatoid arthritis, Crohn's disease and asthma. OCTN1 and OCTN2 accept cationic drugs as substrates and contribute to intestinal and pulmonary absorption, tissue distribution (including to tumour cells), and renal excretion of these drugs. Modulation of the transport activity of OCTN2 by externally administered drugs may cause drug-induced secondary carnitine deficiency. Rodent Octn3 transports carnitine specifically, particularly in male reproductive tissues. Thus, the OCTNs are physiologically, pathologically and pharmacologically important. Detailed characterization of these transporters will greatly improve our understanding of the pathology associated with common diseases caused by functional deficiency of OCTNs.
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Affiliation(s)
- Ikumi Tamai
- Faculty of Pharmaceutical Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, 920-1192, Japan.
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Abstract
The epididymis is an excellent target for the development of a male contraceptive. This is because the process of sperm maturation occurs in this organ; spermatozoa become motile and are able to recognise and fertilise an egg once they have traversed the epididymal duct. However, a number of attempts to interfere in sperm maturation and epididymal function or both have not been successful. The use of transgenic animals has proved useful in identifying a few epididymal targets but has yet to open the doors for drug development. Continuous focus on identifying additional epididymal targets and sperm-specific and epididymal-specific drugs is key to bringing a male contraceptive acting on the epididymis to the public.
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Affiliation(s)
- B T Hinton
- Department of Cell Biology, University of Virginia School of Medicine, Charlottesville, VA, USA.
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Cotton LM, Rodriguez CM, Suzuki K, Orgebin-Crist MC, Hinton BT. Organic cation/carnitine transporter, OCTN2, transcriptional activity is regulated by osmotic stress in epididymal cells. Mol Reprod Dev 2009; 77:114-25. [DOI: 10.1002/mrd.21122] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Zhang KX, Yu L, Sun QW, Zhu TF, Saiyin H, Zhou GJ, Wu CQ, Zhao SY. Expression ofCDV-1RGene in Mouse Epididymis as Revealed byin SituHybridization. ACTA ACUST UNITED AC 2009; 51:7-13. [PMID: 15764413 DOI: 10.1080/014850190512914] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
We have previously studied mouse Cdv (carnitine deficiency-associated gene expressed in ventricle)-1 related gene Cdv-1IR and its human counterpart CDV-1R, and revealed that mouse Cdv-1R was predominantly expressed in testis by multiple tissue northern analysis. To further localize the Cdv-1R mRNA in mouse testis and epididymis tissue, in situ hybridization study was reported in this article. In the adult mice, the Cdv-1R expression was intensively found in the epithelial cells of the caput and corpus epididymis, whereas it was moderately detected in the initial segment, and weakly in the cauda epididymis. In the seminiferous tubles of the testis, no obvious hybridization signals were observed above the background level. This Cdv-1R region-specific expression pattern in the epididimis suggests Cdv-1R may play an important role in sperm maturation. Moreover, considering the Cdv-1R has a similar expression distribution in epididymis to the OCTN2, it would appear that Cdv-1R might be involved in the carnitine pathway in the epididimis.
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Affiliation(s)
- K X Zhang
- State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Sciences, Fudan University, Shanghai, People's Republic of China
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Kobayashi D, Tamai I, Sai Y, Yoshida K, Wakayama T, Kido Y, Nezu JI, Iseki S, Tsuji A. Transport of carnitine and acetylcarnitine by carnitine/organic cation transporter (OCTN) 2 and OCTN3 into epididymal spermatozoa. Reproduction 2007; 134:651-8. [DOI: 10.1530/rep-06-0173] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Carnitine and acetylcarnitine are important for the acquisition of motility and maturation of spermatozoa in the epididymis. In this study, we examined the involvement of carnitine/organic cation transporter (OCTN) in carnitine and acetylcarnitine transport in epididymal spermatozoa of mice. Uptake of both compounds by epididymal spermatozoa was time-dependent and partially Na+-dependent. Kinetic analyses revealed the presence of a high-affinity transport system in the spermatozoa, withKmvalues of 23.6 and 6.57 μM for carnitine and acetylcarnitine respectively in the presence of Na+. Expression of OCTN2 and OCTN3 in epididymal spermatozoa was confirmed by immunofluorescence analysis. The involvement of these two transporters in carnitine and acetylcarnitine transport was supported by a selective inhibition study. We conclude that both Na+-dependent and -independent carnitine transporters, OCTN2 and OCTN3, mediate the supply of carnitine and acetylcarnitine to epididymal spermatozoa in mice.
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Koepsell H, Lips K, Volk C. Polyspecific organic cation transporters: structure, function, physiological roles, and biopharmaceutical implications. Pharm Res 2007. [PMID: 17473959 DOI: 10.1007/s11095‐007‐9254‐z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The body is equipped with broad-specificity transporters for the excretion and distribution of endogeneous organic cations and for the uptake, elimination and distribution of cationic drugs, toxins and environmental waste products. This group of transporters consists of the electrogenic cation transporters OCT1-3 (SLC22A1-3), the cation and carnitine transporters OCTN1 (SLC22A4), OCTN2 (SLC22A5) and OCT6 (SLC22A16), and the proton/cation antiporters MATE1, MATE2-K and MATE2-B. The transporters show broadly overlapping sites of expression in many tissues such as small intestine, liver, kidney, heart, skeletal muscle, placenta, lung, brain, cells of the immune system, and tumors. In epithelial cells they may be located in the basolateral or luminal membranes. Transcellular cation movement in small intestine, kidney and liver is mediated by the combined action of electrogenic OCT-type uptake systems and MATE-type efflux transporters that operate as cation/proton antiporters. Recent data showed that OCT-type transporters participate in the regulation of extracellular concentrations of neurotransmitters in brain, mediate the release of acetylcholine in non-neuronal cholinergic reactions, and are critically involved in the regulation of histamine release from basophils. The recent identification of polymorphisms in human OCTs and OCTNs allows the identification of patients with an increased risk for adverse drug reactions. Transport studies with expressed OCTs will help to optimize pharmacokinetics during development of new drugs.
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Affiliation(s)
- Hermann Koepsell
- Institute of Anatomy and Cell Biology, Julius-Maximilians-University, Würzburg, Germany.
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Koepsell H, Lips K, Volk C. Polyspecific organic cation transporters: structure, function, physiological roles, and biopharmaceutical implications. Pharm Res 2007; 24:1227-51. [PMID: 17473959 DOI: 10.1007/s11095-007-9254-z] [Citation(s) in RCA: 745] [Impact Index Per Article: 43.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2006] [Accepted: 01/26/2007] [Indexed: 12/11/2022]
Abstract
The body is equipped with broad-specificity transporters for the excretion and distribution of endogeneous organic cations and for the uptake, elimination and distribution of cationic drugs, toxins and environmental waste products. This group of transporters consists of the electrogenic cation transporters OCT1-3 (SLC22A1-3), the cation and carnitine transporters OCTN1 (SLC22A4), OCTN2 (SLC22A5) and OCT6 (SLC22A16), and the proton/cation antiporters MATE1, MATE2-K and MATE2-B. The transporters show broadly overlapping sites of expression in many tissues such as small intestine, liver, kidney, heart, skeletal muscle, placenta, lung, brain, cells of the immune system, and tumors. In epithelial cells they may be located in the basolateral or luminal membranes. Transcellular cation movement in small intestine, kidney and liver is mediated by the combined action of electrogenic OCT-type uptake systems and MATE-type efflux transporters that operate as cation/proton antiporters. Recent data showed that OCT-type transporters participate in the regulation of extracellular concentrations of neurotransmitters in brain, mediate the release of acetylcholine in non-neuronal cholinergic reactions, and are critically involved in the regulation of histamine release from basophils. The recent identification of polymorphisms in human OCTs and OCTNs allows the identification of patients with an increased risk for adverse drug reactions. Transport studies with expressed OCTs will help to optimize pharmacokinetics during development of new drugs.
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Affiliation(s)
- Hermann Koepsell
- Institute of Anatomy and Cell Biology, Julius-Maximilians-University, Würzburg, Germany.
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Yakushiji K, Kai S, Yamauchi M, Kuwajima M, Osada Y, Toshimori K. Expression and distribution of OCTN2 in mouse epididymis and its association with obstructive azoospermia in juvenile visceral steatosis mice. Int J Urol 2006; 13:420-6. [PMID: 16734862 DOI: 10.1111/j.1442-2042.2006.01303.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
AIM L-carnitine, an essential cofactor for mitochondrial, beta-oxidation of long-chain fatty acids, is known to play important roles in sperm maturation and metabolism when spermatozoa pass and acquire motility in the epididymis. We reported that obstructive azoospermia occurred in the epididymis in the juvenile visceral steatosis (JVS) mice, which are OCTN2 dysfunction mice caused by mutations in the gene encoding OCTN2, have been used for animal models of primary systemic carnitine deficiency. The aim of present study is to investigate the expression of OCTN2 protein in the mouse epididymis and its relation between the localization of OCTN2 and obstructive azoospermia in JVS mice as animal models for human male infertility. METHODS Animals used in this study were wild-type (C57BL/6 J) mice (n = 4) and JVS mice (n = 4). We made a specific polyclonal antibody against OCTN2 and examined immunohistochemically the localization of OCTN2 in the mouse epididymis. RESULTS OCTN2 was localized on the apical membrane of the principal cells of distal corpus and cauda epididymides. Immunocytochemistry demonstrated that OCTN2 was localized on the surface of microvillus upon the principal cells. In JVS mice, immunoreactivity started in a region immediately distal to where the sperm obstruction occurred. CONCLUSIONS Our results suggest that OCTN2 functions as a carnitine transporter between the epithelium and the lumen in distal corpus and cauda epididymides and provides a clue as to why obstructive azoospermia is induced in distal parts of epididymis.
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Affiliation(s)
- Kazumichi Yakushiji
- Department of Urology, Miyazaki Medical College, University of Miyazaki, Miyazaki, Japan.
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Derks TGJ, Duran M, Waterham HR, Reijngoud DJ, Ten Kate LP, Smit GPA. The difference between observed and expected prevalence of MCAD deficiency in The Netherlands: a genetic epidemiological study. Eur J Hum Genet 2005; 13:947-52. [PMID: 15870827 DOI: 10.1038/sj.ejhg.5201428] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Medium chain acyl coenzyme A dehydrogenase (MCAD) deficiency is assumed to be the most common inherited disorder of mitochondrial fatty acid oxidation. Few reports mention the difference between the expected and observed prevalence of MCAD deficiency on the basis of the carrier frequency in the population. We performed a population-wide retrospective analysis of all known MCAD-deficient patients in The Netherlands. In this study, the observed prevalence of MCAD deficiency in The Netherlands was 1/27 400 (95% confidence interval (CI) 1/23 000-1/33 900), significantly different from the expected prevalence of 1/12 100 (95% CI 1/8450-1/18 500). The observed prevalence of MCAD deficiency showed a remarkable north-south trend within the country. From the patients in this cohort, it can be observed that underdiagnosis contributes to a larger extent to the difference between the expected and observed prevalences of MCAD deficiency in our country, than reduced penetrance. We determined estimates of the segregation proportion in a cohort of 73 families under the assumption of complete ascertainment (p(LM) = 0.41, 95% CI 0.31-0.51) and single ascertainment (p(D) = 0.28, 95% CI 0.19-0.37). With the expectation-maximization algorithm, a third estimate was obtained (p(EM) = 0.28, 95% CI 0.20-0.37). The agreement between the latter two estimates supports incomplete selection and the segregation proportions were in agreement with normal mendelian autosomal recessive inheritance.
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Affiliation(s)
- Terry G J Derks
- Department of Metabolic Diseases, Beatrix Children's Hospital, University Medical Centre, Groningen, The Netherlands.
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Kobayashi D, Irokawa M, Maeda T, Tsuji A, Tamai I. Carnitine/organic cation transporter OCTN2-mediated transport of carnitine in primary-cultured epididymal epithelial cells. Reproduction 2005; 130:931-7. [PMID: 16322553 DOI: 10.1530/rep.1.00737] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Carnitine is essential for the acquisition of motility and maturation of spermatozoa in the epididymis, and is accumulated in epididymal fluid. In this study, carnitine transport into primary-cultured rat epididymal epithelial cells was characterized to clarify the nature of the transporter molecules involved. Uptake of carnitine by primary-cultured epididymal epithelial cells was time, Na+and concentration dependent. Kinetic analysis of carnitine uptake by the cells revealed the involvement of high- and low-affinity transport systems withKm values of 21 μM and 2.2 mM respectively. The uptake of carnitine by the cells was significantly reduced by inhibitors of carnitine/organic cation transporter (OCTN2), such as carnitine analogues and cationic compounds. In RT-PCR analysis, OCTN2 expression was detected. These results demonstrated that the high-affinity carnitine transporter OCTN2, which is localized at the basolateral membrane of epididymal epithelial cells, mediates carnitine supply into those cells from the systemic circulation as the first step of permeation from blood to spermatozoa.
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Affiliation(s)
- Daisuke Kobayashi
- Faculty of Pharmaceutical Sciences, Tokyo University of Science, 2641 Yamasaki, Noda, Chiba 278-8510, Japan
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Maeda T, Hirayama M, Kobayashi D, Tamai I. Regulation of testis-specific carnitine transporter (octn3) gene by proximal cis-acting elements Sp1 in mice. Biochem Pharmacol 2005; 70:858-68. [PMID: 16051193 DOI: 10.1016/j.bcp.2005.06.014] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2005] [Revised: 06/14/2005] [Accepted: 06/16/2005] [Indexed: 11/27/2022]
Abstract
The mouse octn transporter family consists of three genes, octn1, octn2 and octn3. The gene products octn2 and octn3, which transport carnitine with high affinity, are both expressed in testis, where carnitine is required to maintain sperm cell motility. Here, we focused on the regulatory mechanism of the expression of octn3 in an attempt to determine whether the differential tissue expression profiles of the octn2 and octn3 genes reflect distinct physiological roles of octn2 and octn3. The promoter activity of the octn3 gene was examined by luciferase assay and gel mobility shift assay using the mouse Sertoli cell line TM4 as host cells. Deletion-mutant assay demonstrated that a gene segment of the 5'-untranslated region located at about -500 bp relative to the transcription start site is required for constitutive octn3 transcription. Deletion of the Sp1-binding site within the region resulted in loss of transcriptional activity. In addition, overexpression of Sp1 in TM4 cells led to a further increase of transcription of octn3. These results demonstrated that Sp1-binding sites are necessary and sufficient for constitutive octn3 gene transcription. Furthermore, the expressions of both of octn2 and octn3 genes in TM4 cells were up-regulated by palmitic acid, whereas carnitine increased only the expression of octn2 without any change in octn3 expression. Accordingly, the expressions of octn2 and 3 are regulated by distinct mechanisms, suggesting distinct roles of octn2 and octn3 in carnitine transport.
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Affiliation(s)
- Tomoji Maeda
- Department of Molecular Biopharmaceutics, Faculty of Pharmaceutical Sciences, Tokyo University of Science, 2641 Yamasaki, Noda, Chiba 278-8510, Japan
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Xuan W, Lamhonwah AM, Librach C, Jarvi K, Tein I. Characterization of organic cation/carnitine transporter family in human sperm. Biochem Biophys Res Commun 2003; 306:121-8. [PMID: 12788076 DOI: 10.1016/s0006-291x(03)00930-6] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Spermatozoan maturation, motility, and fertility are, in part, dependent upon the progressive increase in epididymal and spermatozoal carnitine, critical for mitochondrial fatty acid oxidation, as sperm pass from the caput to the cauda of the epididymis. We demonstrate that the organic cation/carnitine transporters, OCTN1, OCTN2, and OCTN3, are expressed in sperm as three distinct proteins with an expected molecular mass of 63 kDa, using Western blot analysis and our transporter-specific antibodies. Carnitine uptake studies in normal control human sperm samples further support the presence of high-affinity (OCTN2) carnitine uptake (K(m) of 3.39+/-1.16 microM; V(max) of 0.23+/-0.14 pmol/min/mg sperm protein; and mean+/-SD; n=12), intermediate-affinity (OCTN3) carnitine uptake (K(m) of 25.9+/-14.7 microM; V(max) of 1.49+/-1.03 pmol/min/mg protein; n=26), and low-affinity (OCTN1) carnitine uptake (K(m) of 412.6+/-191 microM; V(max) of 32.7+/-20.5 pmol/min/mg protein; n=18). Identification of individuals with defective sperm carnitine transport may provide potentially treatable etiologies of male infertility, responsive to L-carnitine supplementation.
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Affiliation(s)
- Wanli Xuan
- Division of Neurology, Department of Pediatrics, The Hospital for Sick Children, Ont., M5G 1X8, Toronto, Canada
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Abstract
Early-onset dilatative and/or hypertrophic cardiomyopathy with episodic hypoglycaemic coma and very low serum and tissue concentrations of carnitine should alert the clinician to the probability of the plasmalemmal high-affinity carnitine transporter defect. The diagnosis can be established by demonstration of impaired carnitine uptake in cultured skin fibroblasts or lymphoblasts and confirmed by mutation analysis of the human OCTN2 gene in the affected child and obligate heterozygote parents. The institution of high-dose oral carnitine supplementation reverses the pathology in this otherwise lethal autosomal recessive disease of childhood, and carnitine therapy from birth in prospectively screened siblings may altogether prevent the development of the clinical phenotype. Heterozygotes may be at risk for cardiomyopathy in later adult life, particularly in the presence of additional risk factors such as hypertension and competitive pharmacological agents. OCTN2 belongs to a family of organic cation/carnitine transporters that function primarily in the elimination of cationic drugs and other xenobiotics in kidney, intestine, liver and placenta. The high- and low-affinity human carnitine transporters, OCTN2 and OCTN1, are multifunctional polyspecific organic cation transporters; therefore, defects in these transporters may have widespread implications for the absorption and/or elimination of a number of key pharmacological agents such as cephalosporins, verapamil, quinidine and valproic acid. A third organic/cation carnitine transporter with high specificity for carnitine, Octn3, has been cloned in mice. The juvenile visceral steatosis (jvs) mouse serves as an excellent clinical, biochemical and molecular model for the high-affinity carnitine transporter OCTN2 defect and is due to a spontaneous point mutation in the murine Octn2 gene on mouse chromosome 11, which is syntenic to the human locus at 5q31 that harbours the human OCTN2 gene.
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Affiliation(s)
- I Tein
- Division of Neurology, Department of Pediatrics, The Hospital for Sick Children, Toronto, Canada.
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Peng J, Yu L, Horiuchi M, Zhang P, Huang X, Zhang Y, Li D, Jalil MA, Zhao S. Identification of human CDV-1R and mouse Cdv-1R, two novel proteins with putative signal peptides, especially highly expressed in testis and increased with the male sex maturation. Mol Biol Rep 2002; 29:353-62. [PMID: 12549821 DOI: 10.1023/a:1021232518628] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Human systemic carnitine deficiency (SCD) is a hereditary disease caused by the mutation of OCTN2 and has the characteristics of cardiac hypertrophy. Previous studies based on JVS mouse, an animal model of this disease, showed that Cdv-1 was highly expressed in ventricles of normal mouse, but was remarkably down-regulated in JVS mouse and can be up-regulated to normal level by breeding carnitine, which suggested Cdv-1 was possibly involved in cardiac hypertrophy caused by carnitine deficiency. In this study, the expression of human CDV-1, a homolog of mouse Cdv-1, was undetectable in heart by northern hybridization. The inconsistent expression levels of human CDV-1 and mouse Cdv-1 in heart implied that cardiac hypertrophy in human SCD might not be associated with the abnormal expression of CDV-1. Interestingly, another long transcripts of the gene, Cdv-1R/CDV-1R, were cloned in the present study, in mouse and human, respectively. This long transcript predominantly expressed in both human and mouse testis and its expression level was increased with testis development. Furthermore, we proved that the open reading frame of Cdv-1R/CDV-1R spans the exons 2 approximately 19 instead of exons 9 approximately 19; and the peptide encoded by CDV-1R was composed of 676 amino acids containing a putative signal peptide instead of 414 amino acids described previously. In addition, it was proved that the expression level of Cdv-1R in JVS mouse testis was as high as that in normal mouse testis, and both were not regulated by carnitine.
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Affiliation(s)
- Jisong Peng
- State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Science, Fudan University, Shanghai 200433, People's Republic of China
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Rodríguez CM, Labus JC, Hinton BT. Organic cation/carnitine transporter, OCTN2, is differentially expressed in the adult rat epididymis. Biol Reprod 2002; 67:314-9. [PMID: 12080034 DOI: 10.1095/biolreprod67.1.314] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
L-Carnitine must be transported against a substantial concentration gradient across the epididymal epithelium to achieve high intraluminal levels, approximately 50 mM in the cauda. Recently, an organic cation transporter, OCTN2, was cloned from rat intestinal epithelium and shown to transport L-carnitine in a sodium-dependent manner. To test the hypothesis that OCTN2 was present in the epididymis, primers were designed based on the published OCTN2 mRNA sequence. A 1.9-kilobase OCTN2 cDNA from rat epididymis was amplified by reverse transcription polymerase chain reaction (RT-PCR) and cloned. Northern analysis demonstrated the presence of OCTN2 transcripts in the epididymis, with highest expression in the distal caput and corpus. To localize the protein, an antibody raised against a carboxy-terminal peptide of OCTN2 was produced in rabbits and used for Western blot analysis and immunohistochemistry. The antibody recognized a band of approximately 65 kDa in Western blots using epididymal lysates. Immunohistochemical studies demonstrate that OCTN2 is present in the basolateral membrane of epithelial cells in the distal caput, corpus, and proximal cauda epididymides. In conclusion, OCTN2 is present in the rat epididymis in a region-dependent manner and is likely to be responsible for the transport of L-carnitine into the cells of the epididymal epithelium.
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Affiliation(s)
- Carmen M Rodríguez
- Department of Cell Biology, University of Virginia Health System, Charlottesville, VA 22908, USA
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