This web only provides the extract of this article. If you want to read the figures and tables, please reference the PDF full text on Blackwell Synergy. Thank you.

- Original Article -

The expression and significance of CATSPER1 in human testis and ejaculated spermatozoa

Hong-Gang Li, Ai-Hua Liao, Xiao-Fang Ding, Hui Zhou, Cheng-Liang Xiong

Centre of Reproductive Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China

Abstract

Aim: To investigate the distribution of cation channel of sperm 1 (CATSPER1) protein and the presence of CATSPER1 mRNA in human testis and ejaculated spermatozoa. The influence of anti-human CATSPER1 antibody upon human sperm motility was used to evaluate the function of human CATSPER1 and to estimate its possible use as a target for immunocontraception. Methods: Human ejaculated sperm from normozoospermic donors (n=12) and liquid nitrogen frozen human testis were used for the study of mRNA and protein expression of CATSPER1 by reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry, respectively. Spermatozoa from normozoospermic donors (n=12) were individually processed using a swim-up procedure and were then incubated with CATSPER1 antibody at final concentrations of 20, 4 and 0.8mg/mL. After 1, 2 and 6 h incubation, progressive motility and fast progressive motility were measured by means of computer-assisted semen analysis. Results: CATSPER1 transcript was detected in both human testis and each human ejaculated semen sample. CATSPER1 protein expressed in the membrane of spermatid and was localized in the principal piece of the sperm tail. The application of CATSPER1 antibody at all concentrations significantly inhibited both progressive motility and fast progressive motility after 1, 2 and 6 h incubation, and significant dose-dependent changes were observed. Conclusion: CATSPER1 is meiotically and post-meiotically expressed in human testis tissue. CATSPER1 mRNA in human ejaculated spermatozoa could be a more feasible target for study and infertility screening than testis biopsy. In addition, our results suggest that human CATSPER1 could be a possible target for immunocontraception. (Asian J Androl 2006 May; 8: 301-306)

Keywords: cation channel of sperm 1; testis; spermatozoa; motility; immunocontraception; human

Correspondence to: Prof. Cheng-Liang Xiong, Centre of Reproductive Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China.
Tel: +86-27-8369-2651, Fax: +86-27-8363-4374
E-mail: clxiong@mails.tjmu.edu.cn
Received 2005-08-20 Accepted 2005-12-23

1 Introduction

Calcium channel activities are involved in the process of sperm maturation, motility, capacitation and sperm-egg interaction. Several calcium channels have been found to reside in mammalian sperm, including the T-type voltage operated Ca²⁺ channels alpha 1G and 1H, the cyclic nucleotide gated channels and the transient receptor potential (TRP) channel TRP2, the N-type, R-type, and L-type voltage operated Ca²⁺ channels, and the pkD2 cation channel. Recently, four members of a novel channel-like protein family, cation channel of sperm 1(CATSPER1), CATSPER2, CATSPER3 and CATSPER4, unlike other calcium channels, were identified to be exclusively expressed in mice testes and to be linked to mice sperm mobility and male fertility [1-4].

As the first member of the family, mice CATSPER1 was cloned in 2001 [2]. Recently, its functional characterization was further described [5]. In mice, CATSPER1 protein expressed exclusively in the testis and not in other tissues. In mice sperm, CATSPER1 is localized primarily in the tail’s principal piece and is directly associated with sperm mobility [2]. Moreover, CATSPER1 is required for sperm hyperactivation and penetrating the zona pellucida [5]. Gene-targeted elimination of the male mouse CATSPER1 results in poor sperm motility and infertility [2].

Based on its restricted expression pattern and important role in sperm mobility and male fertility, CATSPER1 is predicted to be a potential target for male infertility screening and an ideal target for contraception [1, 2, 5]. However, little is known about the expression and function of human CATSPER1. Here, we evaluate the distribution of CATSPER1 protein and the presence of CATSPER1 mRNA in human testis and human ejaculated spermatozoa, and the influence of CATSPER1 antibody upon human sperm progressive motility.

2 Materials and methods

2.1 Materials

Human testis was obtained from Tongji Hospital (Wuhan, China) after obtaining a signed informing consent and the approval of the Ethical Committee of this University. The tissue was immediately cryostored in liquid nitrogen after surgery. Human semen samples were obtained from 12 consenting donors who met all the World Health Organization (WHO) criteria [6] for normozoospermia by masturbation after 3-5 d of abstinence. Samples with leukocytes and/or immature germ cell concentration greater than 10⁶/mL were excluded.

Goat polyclonal antibody against human CATSPER1 (clone: H-20, 0.2mg/mL, in 0.01mol/L phosphate-buffered saline [PBS] containing 0.1% sodium azide and 0.2% gelatin) was from Santa Cruz Biotechnology incorporation (California, USA). All reagents for immunohistochemistry were obtained from ZhongShan Golden Bridge Biotechnology Company (Beijing, China). Percoll was purchased from Sigma Chemical Company (St. Louis, USA). TRI Reageant was from the Molecular Research Center (Cincinnati, USA). All reagents for reverse transcription polymerase chain reaction (RT-PCR) were obtained from Toyobo (Osaka, Japan).

2.2 Sperm preparation

1×10⁷ spermatozoa of each sample were used for RNA extraction immediately after liquefaction (30-60min at room temperature). The remaining spermatozoa were processed using the swim-up procedure [6, 7] and used to study of influence of CATSPER1 antibody upon sperm motility. For the swim-up procedure, semen samples were individually fractionated by two-layer (40-80%) Percoll gradient buffered in HEPES-balanced saline (115mmol/L NaCl, 4mmol/L KCl, 0.5mmol/L MgCl₂, 14mmol/L fructose, 25mmol/L HEPES, pH 8.0). After centrifugation at 800×g for 20min, the 80% Percoll fraction was pooled and examined under an optical microscope to verify the efficacy of the regimen.

2.3 RNA extraction

Total RNA from liquid nitrogen frozen human testis and ejaculated spermatozoa were extracted with TRI Reagent according to the manufacturer’s instruction. Briefly, approximately 0.1g human testis tissue and pellets containing approximately 1×10⁷ spermatozoa were repetitively individually pipetted in 1mL TRI Reagent. RNA was separated by chloroform and precipitated with isopropanol, and then washed with 75% ethanol. After briefly air-drying, RNA pellets were dissolved in diethyl pyrocarbonate treated water and then stored at -70°C. The purity of RNA samples was checked spectrophotometrically at 260 nm and 280mm.

2.4 RT-PCR

RT-PCR was performed as described in Sambrook and Russel [8]. Briefly, Total RNA (2mg) was reverse-transcribed to cDNA as follows: 1 h at 42°C with 100 IU MMLV reverse transcriptase, 500mmol/L of each deoxy-nucleotide-triphosphate, 1mg oligo(dT)₁₈ and 50 IU RNasin in a final volume of 25mL, then 5min at 95°C. The cDNA were further amplified by PCR using selected primers. PCR primers for human CATSPER1 (GenBank accession number AF407333) were designed using Primer 5 software by professional staff of AuGCT Company (Beijing, China). To eliminate possible contamination by genomic DNA, primers were chosen in different exons of CATSPER1 and were as follows: forward 5’-TTTACCTGCCTCTTCCTCTTCT-3’ (1905-1926nt), located in exon 5 and exon 6; reverse, 5’-ACCAGGTTGA

GGAAGATGAAGT-3’ (2110-2131nt), located in exon 7 and exon 8. PCR primer pairs amplified a 227-bp segment and the PCR amplification was performed on a Perkin Elmer DNA thermal cycler 480 (Wellesley, USA) in a final volume of 25mL PCR mixture consisting of 10mmol/L Tris-HCl (pH 8.3), 50mmol/L KCl, 2mmol/L MgCl₂, 200mmol/L of each deoxy-nucleotide-triphos- phate, 1.5IU Taq DNA polymerase and 50 pmol/L of each primer. 0.2mg cDNA reverse-transcribed from human testis or sperm RNA was used as template, and negative control (human sperm RNA reverse-transcribed without MMLV reverse transcriptase) was included. β-actin was used in parallel for each run as internal control. The forward primer (5’-GGGAAATCGTGCGTGACAT-3’) and reverse primer (5’-TCAGGAGGAGCAATGATCTTG-3’) for β-actin were designed to produce a 385 bp amplicon. PCR products were run on a 1.5% agarose gel stained with ethidium bromide and visualized under ultraviolet transillumination.

2.5 Immunolocalization of CATSPER1 protein in human testis and sperm

Smears of human ejaculated spermatozoa and 10mm thin frozen sections of human testis were used to study the immunolocalization of CATSPER1. Immunohistochemistry was performed as previously described [9]. Briefly, Goat anti-human CATSPER1 polyclonal antibody at 1: 50 dilution was used as the primary antibody. Fluorescein-isothiocyanate-labeled rabbit anti-goat antibody was used as the secondary antibody at a 1: 100 dilution. 0.01mol/L phorsphoric acid buffer solution (PBS, pH7.4) instead of primary antibodiy was used as the negative control. The human testis was stained by Hoechest (Beyotime Biotechnology, China) to discriminate nucleus of the cells in the seminiferous tubules.

2.6 Determination of CATSPER1 antibody influence upon sperm motility

Spermatozoa pooled in 80% Percoll layer described above were diluted to 50×10⁶ cells/mL in Biggers-Whitten-Whittingham medium devoid of bicarbonate and BSA and containing 1mmol/L CaCl₂ and 25mmol/L HEPES (pH8.0) [10]. Aliquots of 90mL were incubated with 10mL CATSPER1 antibodies (200mg/mL, 40mg/mL, 8mg/mL, diluted in 0.01mol/L PBS, pH7.4, containing 0.1% sodium azide and 0.2% gelatin) at final concentrations of 20, 4 and 0.8mg/mL. 10mL 0.01mol/L PBS (pH7.4, containing 0.1% sodium azide and 0.2% gelatin) instead of antibody was used as the negative control. After 1, 2 and 6 h at 37°C with 5% CO₂, progressive motility (WHO motility class a+b) and fast progressive motility (WHO motility class a) was measured using a computer-assisted motion analyzer (Beijing Weili, China) at 37°C. At least 200 spermatozoa in randomly chosen fields of vision were analyzed.

2.7 Statistical analysis

The data are presented as mean±SD. Statistical analyses were performed using the SPSS software (version 11.5) by paired sample t-tests after checking for normal distribution by means of the Kolmogorov-Smirnov test. All statistical tests were two-tailed and P <0.05 was considered as statistically significant.

3 Results

3.1 CATSPER1 expression

3.1.1 mRNA expression

In RNA isolated from human testis and 12 cases of human spermatozoa, robust PCR products of the expected 227 bp for CATSPER1 and 385 bp for β-actin were identified following analysis on agarose gels (Figure1). There was no detectable signal in samples without reverse transcriptase. The primers were designed to amplify nucleotides 1905-2131nt. Comparison with the genomic sequence of the human CATSPER1 indicated that this region encompasses 496 bp of DNA, including exons 5-8 and the intronic sequences. Therefore, it is highly unlike that the CATSPER1 RT-PCR products in the human testis and in ejaculated spermatozoa were derived from genomic DNA.

3.1.2 Protein expression

In human testis, abundant CATSPER1 protein was detected in the membrane of spermatid (Figure2). In human ejaculated spermatozoa, CATSPER1 protein was localized in the principal piece of the sperm tail (Figure3).

3.2 Influence of CATSPER1 antibody upon motility of human sperm

As shown in Table1, significant and dose-dependent changes in the percentage of progressively motile sperm were observed after 1, 2 and 6 h incubation with CATSPER1 antibody at all concentrations used in the present study. Moreover, under the influence of CATSPER1 antibody, similar changes of the percentage of fast progressively motile sperm were observed (Table2). The percentage of slow progressively motile sperm (WHO motility class b) was not affected by this treatment (data not show). Therefore, the decline of progressive motility caused by CATSPER1 antibody was mainly ascribed to the changes of fast progressive motility.

4 Discussion

The recent cloning and characterization of CATSPER1 is a matter of significance to the study of male reproduction and infertility [1, 5]: 1) CATSPER1 is the first calcium ion channel required for sperm mobility and hyperactivation. CATSPER1-deficient mice are infertile as a result of an impairment of sperm mobility and an inability to fertilize intact oocytes; 2) The vital role of mice CATSPER1 in male fertility and the restricted loca-lization of CATSPER1 to the mice testis and mature sperm suggest that CATSPER1 gene could be a potential target for male infertility screening and treatment, and it might be an excellent target for contraception. The study of the evolution of CATSPER1 in primates and rodents also suggests its possibly important physiological role in sperm competition [11, 12]. Frequent incidences of indel substitutions were discovered in the evolution of the first exon of CATSPER1 gene. Because exon 1 is supposed to be an important functional part of this gene, it is reasonable to conclude that these indel substitutions, particularly larger indels which are significantly more prevalent in exon 1 than in the neutral genomic regions, are positively selected for the evolution of CATSPER1, and positive selection on this gene suggests its important physiological role.

To further explore the role and significance of CATSPER1, the expression and function of human CATSPER1 need to be addressed. In the present study, the expression profiles of CATSPER1 in human testis and ejaculated spermatozoa were investigated for the first time. Consistent with the meiotic and postmeiotic expression in mice testis [2, 13], CATSPER1 protein expressed in the membrane of spermatid. In ejaculated spermatozoa, CATSPER1 protein was highly localized to the principal piece of the sperm tail. The same expre-ssion and localization of CATSPER1 in humans as in mice indicates the important role of CATSPER1 in human male fertility.

To further elucidate the function of human CATSPER1 and to estimate its possibility as a target for potential contraception, we studied the influence of CATSPER1 antibody upon human sperm motility in vitro. Significant and dose-dependent changes in progressive motility and fast progressive motility after 1, 2 and 6 h incubation with CATSPER1 antibody suggested that, consistent with the function of its mice counterpart, human CATSPER1, which was highly localized to the principal piece of the sperm tail, play an important role in the progressive motility of human spermatozoa. The inhibition effect of CATSPER1 antibody upon human sperm also implies that CATSPER1 could be a possible target for immunocontraception.

CATSPER1 was implicated as a potential target for male infertility screening and treatment. Recently, the profiles of CATSPER1 mRNA expression in testis biopsy of subfertile patients were investigated [13]. Compared with patients whose infertility cannot be ascribed to a deficiency in motility, a significant reduction in the level of CATSPER1 gene expression among patients who lack sperm motility was observed. However, testicular puncture is invasive and inconvenient and might not be accepted by patients because of ethical considerations. The presence of CATSPER1 mRNA in human testis and ejaculated spermatozoa were involved in the present study, and we found that CATSPER1 mRNA was not only detected in human testis, but also, as a post-meiotically active gene, CATSPER1 mRNA existed in human ejaculated spermatozoa. In fact, mRNA of some other CatSper family members were detected in human ejaculated spermatozoa by our group (unpublished data). During the last decade, findings from several studies support the conclusion that spermatozoa contain a complex repertoire of mRNA, including mRNA of some ion channels [7, 14-17]. Their putative roles are unknown, but the most common idea is to consider that these transcripts represent remnants of stored mRNA from post-meiotically active genes [15-17]. The study of mRNA in sperm could reflect past events of spermatogenesis and/or spermiogenesis, and could be used as a clinical assay to provide a panoramic view of testis gene expression that can be difficult to achieve from a testicular biopsy [15, 17]. Therefore, if CATSPER1 were to be evaluated as a target for male infertility screening and treatment, it is apparently more feasible to study its mRNA in ejaculated spermatozoa than in testicular biopsy.

Taken together, the work here provides insights into expression and function of CATSPER1 in human testis and ejaculated spermatozoa. Abundant CATSPER1 mRNA in human ejaculated spermatozoa might be a more feasible target than testis biopsy for male infertility scree-ning and study on human CATSPER1.

Acknowledgment

We are grateful to Prof. Ming-Da Zuo, Ms Xue-Bing Pang and Ms Shuang Li for their excellent technical assistances and advice. The investigation was partly supported by grants from the National Key Technologies R&D Program for the Tenth Five-year plan, China (No. 2004BA720A33-01) and the Hubei province health department project (No. JX2B03).

References

1 Garbers DL. Ion channels swimming with sperm. Nature 2001; 413: 579, 581-2.

2 Ren D, Navarro B, Perez G, Jackson AC, Hsu S, Shi Q, et al. A perm ion channel required for sperm motility and male fertility. Nature 2001; 413: 603-9.

3 Quill TA, Ren D, Clapham DE, Garbers DL. A voltage-gated ion expressed specifically in spermatozoa. Proc Natl Acad Sci U S A 2001; 98: 12527-31.

4 Lobley A, Pierron V, Reynolds L, Allen L, Michalovich D. Identification of human and mouse CatSper3 and CatSper4 genes: Characterisation of a common interaction domain and evidence for expression in testis. Reprod Biol Endocrinol 2003; 1: 53-67.

5 Carlson AE, Westenbroek RE, Quill T, Ren D, Clapham DE, Hille B, et al. CATSPER1 required for evoked Ca²⁺ entry and control of flagellar function in sperm. Proc Natl Acad Sci USA 2003; 100: 14864-8.

6 WHO (World Health Organization). WHO Laboratory Manual for the Examination of Human Semen and Sperm-Cervical Mucus Interactions, 4th edn. Cambridge: Cambridge University Press; 1999.

7 Aquila S, Sisci D, Gentile M, Middea E, Siciliano L, Ando S. Human ejaculated spermatozoa contain active P450 aromatase. J Clin Endocrinol Metab 2002; 87: 3385-90.

8 Sambrook J, Russel DW. Molecular Cloning: A Laboratory Manual, 3rd edn. New York: Cold Spring Harbor Laboratory Press; 2001.

9 Zhang YQ, He XZ, Zhang JS, Wang RA, Zhou J, Xu RJ. Stage-specific localization of transforming growth factor beta1 and beta3 and their receptors during spermatogenesis in men. Asian J Androl 2004; 6: 105-9.

10 O'Flaherty CO, de Lamirende ED, Gagnon C. Phosphorylation of the Arginine-X-X (Serine/Threonine) motif in human sperm proteins during capacitation: modulation and protein kinase A dependency. Mol Hum Reprod 2004; 10: 355-63.

11 Podlaha O, Zhang J. Positive selection on protein-length in the evolution of a primate sperm ion channel. Proc Natl Acad Sci U S A 2003; 100: 12241-6.

12 Podlaha O, Webb DM, Tucker PK, Zhang J. Positive selection for the rodent sperm protein CATSPER1. Mol Biol Evol 2005; 22: 1845-52.

13 Nikpoor P, Mowla SJ, Movahedin M, Ziaee SA, Tiraihi T. CatSper gene expression in postnatal development of mouse testis and in subfertile men with deficient sperm motility. Hum Reprod 2004; 19: 124-8.

14 Goodwin LO, Karabinus DS, Pergolizzi RG, Benoff S. L-type voltage-dependent calcium channel b-1C subunit mRNA is present in ejaculated human spermatozoa. Mol Hum Reprod 2000; 6: 127-36.

15 Ostermeier GC, Dix DJ, Miller D, Kathri P, Krametz SA. Spermtozoal RNA profiles of normal fertile men. Lancet 2002; 360: 772-7.

16 Lambard S, Galeraud-Denis I, Martin G, Levy R, Chocat A, Carreau S. Analysis and significance of mRNA in human ejaculated sperm from normozoospermic donors: Relationship to sperm motility and capacitation. Mol Hum Reprod 2004; 10:535-41.

17 Martins RP, Krawetz SA. RNA in human sperm. Asian J Androl 2005; 7: 115-20.