Serine/threonine phosphorylation associated with hamster sperm hyperactivation

Background and Aims: Mammalian sperm activation and hyperactivation is regulated by protein phosphorylation. Although tyrosine phosphorylation is considered very important, several studies have investigated whether serine and threonine phosphorylation are also associated with sperm activation and hyperactivation, and that was also the aim of the present study.
Methods: Protein phosphorylation of hamster spermatozoa was detected by Western blotting using antiphospho-amino acid monoclonal antibodies after tricine sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Amino acid sequences were analyzed using a peptide sequencer.
Results: Four proteins were phosphorylated at serine residues during hyperactivation via activation and their approximate molecular weights were 90, 38, 32 and 10 kDa, respectively. Five proteins were phosphorylated or dephosphorylated at threonine residues and their approximate molecular weights were 90, 70, 65, 35 and 10 kDa, respectively. The 10-kDa protein corresponded to a previously reported 10-kDa tyrosine phosphoprotein. N-terminal sequences of the 10-kDa protein were similar to carcinustatin, which is a neuropeptide.
Conclusions: During hyperactivation, four serine phosphorylation and five threonine phospho- or dephosphorylations occurred, which suggested that the 10-kDa protein was phosphorylated at tyrosine residues when spermatozoa were activated and then dual-phosphorylated at the serine and threonine residues during hyperactivation. (Reprod Med Biol 2004; 3 : 223–230)     

Identification of 66 kDa phosphoprotein associated with motility initiation of hamster spermatozoa

Background and Aims:  Sperm motility is regulated by protein phosphorylation. The 66 kDa protein obtained from hamster sperm flagella was phosphorylated at serine residues associated with the motility initiation. In order to understand the regulatory mechanism of sperm motility, the 66 kDa protein was identified in the present study.
Methods:  The 66 kDa protein was purified by 2-D gel electrophoresis and identified by matrix-assisted laser desorption ionization mass spectrometry, liquid chromatography-tandem mass spectrometry and peptide sequencer.
Results:  The 66 kDa protein was tubulin β chain.
Conclusion:  The 66 kDa protein is one of the tubulin β chain isoforms and phosphorylated in relation to the motility initiation. (Reprod Med Biol 2004; 3 : 133–139)     

Regulation of hyperactivation of hamster spermatozoa by progesterone

Aim:  Although it is accepted that progesterone (P) induces acrosome reaction through non-genomic regulation, it is not well known if P also affects hyperactivation of sperm.
Methods:  Hamster spermatozoa were hyperactivated by incubation for 4 h on modified Tyrode's albumin lactate pyruvate medium and recorded on a DVD via a charge-coupled device camera attached to a microscope with phase-contrast illumination and a small CO₂ incubator. Phosphorylation of proteins was detected by western blotting using antiphosphotyrosine antibodies.
Results:  Sperm hyperactivation was significantly increased and accelerated by a non-genomic signal of P. Although acceleration of motility of hyperactivated sperm occurred with 10, 20 and 40 ng/mL P, the most effective concentration was 20 ng/mL. Progesterone also significantly increased 80-kDa tyrosine phosphorylation of sperm proteins. Both extracellular Ca²⁺ and albumin were essential for sperm hyperactivation, and the former was also essential for maintaining sperm flagellar movement. Moreover, phospholipase C (PLC) was associated with the regulation of hyperactivation by P.
Conclusion:  It is likely that P regulates sperm hyperactivation by a non-genomic signal in relation to tyrosine phosphorylation and PLC. (Reprod Med Biol 2008; 7 : 63–74)     

Protein kinase C activity and protein phosphorylation in mouse eggs

The treatment of mouse eggs with phorbol esters and diacylglycerol inhibits sperm peretration and results in biochemical modification of the zona pellucida. In this report, we have demonstrated the presence of protein kinase C (PKC) activity in mouse eggs as determined by 12-O-tetradecanoyl phorbol-13-acetate (TPA) dependent in vivo and in vitro protein phosphorylation in mouse eggs. When mouse eggs were radiolabeled with [³²P]phosphate and treated with TPA, two specific proteins, 70 and 20 kDa, were phosphorylated. The 70-kDa protein was also phosphorylated in vitro by endogenous PKC. In addition, we have shown that exogenous PKC induced the in vitro phosphorylation of 70-, 55-, and 20-kDa proteins in egg extract. The 70-kDa protein was also phosphorylated in vitro after treatment of the cytosol fraction of mouse eggs with TPA, suggesting that this protein might be a specific substrate for PKC and that it is located in the cytosol. These results demonstrate that mouse eggs contain PKC activity and suggest that PKC-catalyzed protein phosphorylation of specific proteins might be involved in the regulation of egg-induced modification of the zona pellucida.     

Differential regulation of Akt phosphorylation in endometriosis

Protein kinase B (PKB/Akt), a serine/threonine kinase, regulates the function of many cellular proteins involved in apoptosis and proliferation. It was postulated that there is a higher Akt activity in endometriosis compared with normal endometrium, and that oestrogen may be one of the factors responsible for the high Akt activation in endometriotic cells. Phospho-Akt (pAkt) concentrations in normal, eutopic and ectopic endometrial tissues were compared by immunohistochemistry, and a higher pAkt immunoreactivity was revealed in eutopic and ectopic endometrium compared with normal endometrium, in vivo. Higher Akt phosphorylation in stromal cells from eutopic endometrium was observed, when compared with normal, in vitro (P < 0.05). Akt phosphorylation was rapidly (2–10 min) stimulated when endometrial stromal cells from normal and endometriosis patients were treated with 17β-oestradiol. In endometrial stromal cells from the endometriosis group, ICI 182,780 (ICI, a specific oestrogen receptor antagonist) failed to antagonize the effect of oestradiol when combined with oestradiol, and revealed a stimulatory effect on Akt phosphorylation when given alone (P < 0.05). In conclusion, since Akt affects cell survival, it is suggested that increased Akt phosphorylation may be related to the altered apoptosis/proliferation harmony in endometriosis, and therefore Akt may play a critical role in the pathogenesis of endometriosis.     

C-type natriuretic peptide regulates sperm capacitation by the cGMP/PKG signalling pathway via Ca2+ influx and tyrosine phosphorylation

Research question

What is the effect of C-type natriuretic peptide (CNP) on human sperm capacitation in vitro and what is the mechanism of this effect?

Protein kinase C activity and protein phosphorylation in mouse sperm

It has been suggested that the Ca2+ and phospholipid dependent protein kinase (protein kinase C; PKC) plays some intermediary roles in the regulation of the zona pellucida-induced acrosome reaction in mouse sperm. We here demonstrated that PKC activity is in the cytosol fraction of mouse sperm and that treatment of sperm with a PKC activator, 12-O-tetradecanoyl phorbol 13-acetate (TPA), induces translocation of PKC to the membrane fraction. Treatment of epididymal sperm with 20 ng/ml TPA or 20 microM of the Ca2+ ionophore A23187 did not induce any specific protein phosphorylation. However, two specific proteins, with molecular weights of 215 kDa and 35 kDa, were significantly phosphorylated when sperm were incubated with A23187 prior to TPA treatment. A similar synergistic effect of TPA and A23187 was observed in Ca2+ accumulation in sperm. We also demonstrated that exogenous PKC purified from human pancreatic cells catalyzes the phosphorylation of these two proteins in vitro as well. The present data support the idea that the activation of PKC and subsequent protein phosphorylation are involved in the regulation of the zona pellucida-induced acrosome reaction.     

血管内皮生长因子体外刺激卵巢癌细胞株信号转导及转录激活因子3磷酸化的研究

目的观察血管内皮生长因子(VEGF)刺激上皮性卵巢癌细胞株Caov-3(Caov-3细胞)后,信号转导及转录激活因子3(STAT3)磷酸化的变化,探讨磷酸化的STAT3是否参与Caov-3细胞VEGF的信号转导.方法采用免疫细胞化学和蛋白印迹的方法,测定体外不同浓度VEGF刺激Caov-3细胞STAT3磷酸化的水平;并观察能与VEGF受体2(VEGFR2)特异性结合的短肽,对VEGF刺激STAT3磷酸化的阻断作用.结果 VEGF能够刺激Caov-3细胞的STAT3磷酸化.采用免疫细胞化学和蛋白印迹方法,浓度为50 ng/ml的VEGF刺激Caov-3细胞30 min后,Caov-3细胞STAT3磷酸化水平均增高,分别为2.20±0.28和1.37±0.17,与VEGF浓度为0 ng/ml时Caov-3细胞STAT3磷酸化的水平(分别为0.56±0.15和0.47±0.19)比较,差异有极显著性(P<0.001);并且STAT3磷酸化蛋白发生向细胞核内移位.VEGF刺激Caov-3细胞60 min后,Caov-3细胞STAT3磷酸化的水平(分别为0.95±0.18和0.66±0.20),与刺激30 min时Caov-3细胞STAT3磷酸化的水平(分别为2.03±0.17和1.58±0.23)比较,差异有极显著性(P<0.001).与VEGFR2特异性结合的80 μmol/L的短肽能有效抑制VEGF诱导STAT3的磷酸化水平. 结论 VEGF在体外可诱导Caov-3细胞内STAT3发生磷酸化; STAT3的磷酸化参与了VEGF在Caov-3细胞内通过VEGFR2介导的信号转导过程.     

Influence of speed of sample processing on placental energetics and signalling pathways: Implications for tissue collection

Introduction

The placenta is metabolically highly active due to extensive endocrine and active transport functions. Hence, placental tissues soon become ischaemic after separation from the maternal blood supply. Ischaemia rapidly depletes intracellular ATP, and leads to activation of stress-response pathways aimed at reducing metabolic demands and conserving energy resources for vital functions. Therefore, this study aimed to elucidate the effects of ischaemia ex vivo as may occur during tissue collection on phosphorylation of placental proteins and kinases involved in growth and cell survival, and on mitochondrial complexes.

Methods

Eight term placentas obtained from normotensive non-laboured elective caesarean sections were kept at room-temperature and sampled at 10, 20, 30 and 45 min after delivery. Samples were analyzed by Western blotting.

Results

Between 10 and 45 min the survival signalling pathway intermediates, P-AKT, P-GSK3α and β, P-4E-BP1 and P-p70S6K were reduced by 30–65%. Stress signalling intermediates, P-eIF2α increased almost 3 fold after 45 min. However, other endoplasmic reticulum stress markers and the Heat Shock Proteins, HSP27, HSP70 and HSP90, did not change. Phosphorylation of AMPK, an energy sensor, was elevated 2 fold after 45 min. Contemporaneously, there was an ∼25% reduction in mitochondrial complex IV subunit I.

Discussion and conclusions

These results suggest that for placental signalling studies, samples should be taken and processed within 10 min of caesarean delivery to minimize the impact of ischaemia on protein phosphorylation.     

Non-genomic regulation of mammalian sperm hyperactivation

Although it has been suggested that the acrosome reaction is induced through non-genomic regulation in a ligand-dependent manner, it is not known whether hyperactivation is similarly regulated. Progesterone and melatonin have been identified as ligands that regulate hyperactivation, the former through non-genomic regulation with phospholipase C and the latter most likely through a reactive oxygen species-mitogen activated protein kinase cascade. Both may be involved in spontaneous regulation of hyperactivation via tyrosine phosphorylation. The concentration of many hormones changes according to environmental conditions and biological rhythms, which will modulate ligand-dependent regulation of hyperactivation.     

Membrane-associated serine/threonine protein phosphatase in endometrial cancer

OBJECTIVE: Reversible serine/threonine protein phosphorylation catalyzed by kinases and phosphatases plays a crucial role in cellular growth and differentiation. We attempted to determine the subcellular location of serine/threonine phosphatase (protein phosphatase type 2A [PP2A]) in endometrial cancer. STUDY DESIGN: Endometrial cancers surgically removed were examined. PP2A activity was assessed by measuring the dephosphorylation of phosphopeptide highly selective for the PP2A in cytosol and membranes fractionated on a continuous sucrose density gradient. Its protein level was detected by immunoblotting with a specific antibody. RESULTS: There were three peaks of PP2A enzyme activity and immunoreactivity corresponding by marker enzyme analysis to the cytoplasm, plasma membrane, and endoplasmic reticulum fractions. An enzyme kinetic analysis showed the different activity in cytosol and plasma membrane; K(m) values of 98+/-12 micromol/L for cytosol and 32+/-6.2 micromol/L for plasma membrane (P<.01), respectively. The membrane phosphatase was sensitive to inhibition by okadaic acid and sodium fluoride, characteristics suggestive of PP2A activity. CONCLUSION: PP2A activity in the plasma membrane of endometrial cancers might be distinct from that present in the cytosol. The plasma membrane PP2A may be responsible for a rapid and initial decrease in intracellular level of phosphoserine and phosphothreonine, interfering with serine/threonine protein phosphorylation-mediated growth of endometrial cancer.     

Effects of extracellular adenosine 5'-triphosphate on human sperm motility

Extracellular adenosine 5'-triphosphate (ATP) previously has been shown to increase the fertilization percentage in human in vitro fertilization (IVF) performed for male factor infertility. The objective of this study is to determine the effects of extracellular adenosine 5'-triphosphate (ATPe) on human sperm function by examining its effects on end points of sperm capacitation. Sperm obtained from healthy volunteers with normal semen parameters, asthenozoospermic men, and cryopreserved samples were incubated in medium with or without 2.5 mM ATPe. The effects of ATPe on acrosomal exocytosis, protein tyrosine phosphorylation, and sperm motility parameters were quantified. Although ATPe did not affect acrosomal exocytosis or protein tyrosine phosphorylation in sperm from healthy donors, it significantly altered several motility parameters, with the largest effects manifested in increased curvilinear velocity and percentage hyperactivation. ATPe similarly affected sperm selected for poor motility and thawed cryopreserved sperm but to a lesser extent than its effects on sperm with normal motility. ATPe increased straight-line velocity and linearity of sperm obtained from asthenozoospermic men. Human sperm motility characteristics are altered by ATPe; this finding may explain its previously reported beneficial effect on human IVF. These results suggest that ATPe could constitute a new therapeutic modality in the treatment of male infertility.     

Heat-Induced Hyperactivation

Purpose: The objectives of this study were (1) to determine the sperm hyperactivation and related kinematic parameters at 40°C after using four sperm wash procedures and (2) to correlate the heat-induced hyperactivation data with cases of clinical pregnancies from either artificial insemination or standard in vitro fertilization (IVF). Methods: Semen samples (n = 51) were collected by ejaculation, and semen analyses were carried out to determine the pretreatment data. Sperm kinematic measurements were performed using the Hamilton Thorn HTM-C computer-aided sperm analyzer. Hyperactivation was determined using the sort module on the HTM-C. Membrane integrity was assessed using the hypoosmotic sperm swelling procedure. Sperm morphology and acrosomal status were also determined using the Spermac stain. Each semen specimen was divided and processed through either the swim-up wash, the 1-h test-yolk buffer (TYB) wash, the 1 mg/ml pentoxifylline stimulant procedure, or the two-layer 90:47% gradient colloidal solution procedure. The washed sperm were incubated at 25 or at 40° C for 4 hr. After incubation, kinematic parameters were assessed for the posttreatment data. Semen specimens were obtained on different occasions for artificial insemination or standard IVF. Data from intracytoplasmic sperm injection cases were not included to avoid confounding factors. Live births and/or pregnancies with fetal heartbeat examined by ultrasound were considered clinical pregnancies. Results: Heat-induced hyperactive motility was significantly higher in sperm of the male partner of pregnant (n = 7) patients compared with nonpregnant (n = 44) patients (mean ± SE, 10.0 ± 3.3 versus 5.5 ± 0.8%) after TYB processing fallowed by 4 hr of incubation at 40°C. This was also observed after colloid (Percoll) processing (11.6 ± 4.6 versus 5.8 ± 0.8%). There were no differences in hyperactivation after 4 hr at 23°C between pregnant and nonpregnant cases. Parameters such as count, volume, motility, viability, and acrosomal status were not different for the groups. However, the percentage of sperm with normal morphology (WHO classification) was twice as high in the pregnant group versus the nonpregnant group. Conclusions: Heat-induced hyperactivation was associated with fertile sperm and was predictive of pregnancy obtained after artificial insemination or IVF. The association was evident only after TYB or Percoll sperm processing. The study could not confirm the finding of significant decreases in motility after heat treatment of sperm derived from infertile males. The mechanism for heat-induced hyperactivation did not involve membrane integrity or the sperm acrosome, although an involvement of heat shock proteins was postulated. Interestingly, there were no pregnancies when sperm did not exhibit heat-induced hyperactivation.     

Regulation of the metastasis suppressor gene MKK4 in ovarian cancer

OBJECTIVES: MKK4 is a metastasis suppressor that is downregulated in some ovarian cancers. We sought to investigate whether promoter methylation, loss of heterozygosity, or changes in phosphorylation are involved in MKK4 dysregulation during ovarian carcinogenesis. METHODS: Bisulfite sequencing was used to determine MKK4 promoter methylation. PCR analysis of tumor/normal DNA was performed to determine LOH at the MKK4 locus. Normal human ovarian surface epithelium (HOSE) and SKOV-3 cells were serum starved and treated with EGF, TGFbeta, or wortmannin. Western blotting was performed using antibodies that detect total and phosphorylated MKK4. RESULTS: No MKK4 promoter hypermethylation was detected in 21 ovarian cancers. LOH was detected at the MKK4 intragenic marker D17S969 in 35% of cases and at D17S1303 in 20%. MKK4 protein was detected in 97% of ovarian tumors. The inactivated phosphoserine 80 (ser-80) form comprised 62% of phosphorylated MKK4 protein in ovarian tumors. Treatment of HOSE or SKOV-3 cells with EGF induced a 1.7- to 4.2-fold increase in phosphorylation of ser-80 MKK4 without altering total MKK4 protein. TGFbeta increased MKK4 ser-80 phosphorylation by 5.4-fold above baseline. The PI3K/Akt pathway inhibitor wortmannin decreased the amount of ser-80 MKK4 by 50%, and inhibited EGF stimulation of MKK4 ser-80 phosphorylation by 60%. CONCLUSIONS: LOH of MKK4 occurs in some ovarian cancers, but without loss of MKK4 protein. MKK4 expression does not appear to be downregulated by promoter methylation. Peptide growth factors induce MKK4 ser-80 phosphorylation, which downregulates its activity. PI3K/Akt pathway inhibitors can partially block ser-80 phosphorylation and this may have therapeutic implications.     

Immunological response of female macaques to the PH-20 sperm protein following injection of recombinant proteins or synthesized peptides

Because of its location on the sperm surface and its multiple functions during fertilization, the PH-20 protein is a potential target for contraceptive vaccines. Cynomolgus macaques were immunized using four different adjuvants together with synthesized peptides or recombinant proteins representing selected regions of macaque PH-20. The synthesized peptide (amino acids 387-412, designated Peptide 4) was used as a linear molecule in a 1:1 ratio with a peptide sequence of tetanus toxoid, as well as a multiple antigenic peptide (MAP) matrix held together by scaffolding lysine residues. In the MAP construct, the ratio of Peptide 4 to tetanus peptide was 4:1. To circumvent the poor production of recombinant PH-20 in bacterial cells, two truncated forms of the molecule were expressed in Escherichia coli, G18 (encoding amino acids 143-510) and E10 (encoding amino acids 291-510). The adjuvants were Montanide ISA 51, Titermax Gold, Syntex adjuvant formulation (SAF), and QS-21. All of the antigen/adjuvant combinations produced significant immune responses as measured by ELISA. The circulating antibodies from immunized animals recognized macaque sperm surface PH-20 on Western blots and were shown by indirect immunofluorescence to bind to the surface of macaque sperm. Montanide and Titermax were associated with higher titers of anti-PH-20 antibodies than QS-21 and SAF adjuvants. Immunization with Titermax, however, resulted in sterile abscesses in 4 of 8 animals injected. We conclude that antigens derived from synthesized peptides and recombinant proteins representing selected regions of the PH-20 molecule can be used as vaccine components in combination with the adjuvant Montanide to elicit a significant sperm-directed antibody response in immunized macaques.     

Protein phosphorylation regulates the mouse sperm acrosome reaction induced by the zona pellucida

Recently, the ligand-receptor signal transduction mechanism has been implicated in mediating the zona pellucida (ZP)-induced acrosome reaction. Little is known about the role of protein phosphorylation in this specific event. We examine whether modification of protein phosphorylation and dephosphorylation affects the kinetics of the acid-solubilized ZP-induced acrosome reaction of mouse sperm. Mouse epididymal sperm were incubated in modified Krebs-Ringer bicarbonate medium for a period of 90 to 120 min and then treated with 2 acidsolubilized ZP/µl for an additional 60 min. The chlortetracycline fluorescence assay was used to monitor the acrosome reaction. Capacitated sperm were inhibited from undergoing acid-solubilized ZP-induced acrosome reaction in the presence of an inhibitor of cyclic nucleotide-dependent protein kinase, H8; activators of the Ca²⁺-and phospholipid-dependent protein kinase (protein kinase C); an inhibitor of phosphatases 1 and 2A, okadaic acid; or an inhibitor of protein tyrosine kinases, genistein. The addition of inhibitors of protein kinase C, such as staurosporine, H7, and protein kinase C [19–36] pseudosubstrate, inhibited the phorbol ester-dependent inhibition of the acid-solubilized ZP-induced acrosome reaction. The present study suggests that protein phosphorylation and dephosphorylation play a regulatory role in the process of the ZP-induced acrosome reaction.     

Sperm proteomic changes associated with early embryo quality after ICSI

Research questionDo alterations of human sperm protein profile affect embryo quality?DesignSperm proteins from 27 infertile couples undergoing intracytoplasmic sperm injection (ICSI) were extracted and digested. The resulting peptides were labelled using tandem mass tags, separated by two-dimensional liquid chromatography, and identified and quantified using tandem mass spectrometry. Subsequently, sperm protein and peptide abundance were statistically analysed for correlation with ICSI-derived embryo quality in the subset of idiopathic infertile couples. Detected correlations were further assessed in the subset of infertile patients with a known factor.ResultsThe abundance of 18 individual sperm proteins was found to correlate with embryo quality after ICSI. Of note, a high percentage of poor-quality ICSI-derived embryos was associated with alterations in several components of the eight-membered chaperonin-containing T-complex, which plays an important role in the folding of many essential proteins. Additionally, the abundance of sperm proteins with known functions in embryogenesis, such as RUBVL1, also correlated with early embryo quality (r = –0.547; P = 0.028). Some of the correlations found in this study were validated using either proteomic data from infertile patients with a known factor or data from similar published studies. Analysis at the peptide level revealed the association of some correlations with specific post-translational modifications or isoforms.ConclusionsOur results support the hypothesis that the sperm proteome plays a role in early embryogenesis. Moreover, several sperm proteins have emerged as potential biomarkers that could predict the outcome of in-vitro assisted reproductive technologies, leading to the possibility of improved diagnosis of couples with idiopathic infertility.     

Ultrastruktur des Myometriums

Even though the function of the myometrium is vital for the existence of all mammals, there is little knowledge about its ultrastructure. So far, only the contractile filaments actin and myosin have been identified. There is no evidence for the existence of other filament systems, either my means of electron microscopy or histochemically. Special low-percentage SDS gradient gel electrophoresis, which is capable of splitting proteins in the megadalton area, was used in myometrial biopsies. Proteins from these bands were injected into rabbits to stimulate antibodies. These antibodies were used to search a uterus cDNA gene expression library to isolate those cDNA clones which code for the uterine megadalton proteins. The extensions of various positive cDNA clones by RT-PCR technique allows the sequencing of the isolated proteins. More myofibril proteins could be isolated: Titin is a > 3.000 kDA filamentous protein, and single molecules extend the filament system. Determination of the cDNA sequence has shown that the titin filament is formed by a single giant 27,000-residue long polypeptide chain. The titin peptide is modular in structure and different module arrangements are expressed by differential splicing. The titin molecule contains a class of unique sequence insertions. Among these sequences are phosphorylation sites, a serine/threonine kinase domain, and binding sites for muscle-specific calpain proteases. It is thus likely that the titin filament also plays a role in myofibrillar signal transduction pathways to coordinate the contraction of labor. Overexpression of titin might be the cause of premature labor in some cases, and therefore antagonizing its expression might be largely more effective than the present tocolytic agents.     

The presence of bacteria species in semen and sperm quality

Purpose  To verify the prevalence of semen bacterial contamination and whether the contamination could decrease sperm quality. Methods  Spermiogram, semen culture, and sperm transmission electron microscopy (TEM) analysis were performed. TEM data were elaborated using a mathematical formula that calculates a fertility index (FI)—able to define patients as fertile or infertile—and the percentage of sperm apoptosis, immaturity and necrosis. We aligned the amino acid sequence of beta-tubulin with protein of the most frequent species isolated from semen. Results  Patients were divided according to the contaminating species; in each group, we observed fertile individuals, in whom the semen quality was similar to that of controls and infertile men whose sperm quality was significantly decreased, in terms of motility, FI, apoptosis and necrosis. Partial homology between β-tubulin and bacterial proteins was observed. Conclusion  Sperm bacterial contamination is quite frequent and could contribute to the deterioration of the sperm quality of infertile men. Capsule the presence of bacteria in semen may decrease sperm motility and increase apoptosis and necrosis particularly in infertile men.