Distribution of filipin-sterol complexes in sperm membranes from hypercholesterolaemic rabbits

Extra-virgin olive oil ameliorates high-fat diet-induced seminal and testicular disorders by modulating the cholesterol pathway

BACKGROUND

Rabbits are sensitive to dietary cholesterol and rapidly develop hypercholesterolemia, leading to prominent subfertility. Sterol regulatory element-binding protein isoform 2 drives the intracellular cholesterol pathway in many tissues, including the testicles. Its abnormal regulation could be the mainly responsible for the failure of suppressing cholesterol synthesis in a cholesterol-enriched environment, ultimately leading to testicular and seminal alterations. However, extra-virgin olive oil consumption has beneficial properties that promote lowering of cholesterol levels, including the recovery of seminal parameters altered under a high-fat diet.

OBJECTIVES

Our goal was to investigate the effects of high-fat diet supplementation with extra-virgin olive oil at the molecular level on rabbit testes, by analyzing sterol regulatory element-binding protein isoform 2 protein and its corresponding downstream effectors.

MATERIALS AND METHODS

During 12 months, male rabbits were fed a control diet, high-fat diet, or 6-month high-fat diet followed by 6-month high-fat diet plus extra-virgin olive oil. Serum lipids, testosterone levels, bodyweight, and seminal parameters were tested. The mRNA and protein levels of sterol regulatory element-binding protein isoform 2, 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase, and low-density lipoprotein receptor were determined by semi-quantitative polymerase chain reaction and Western blotting techniques. The expression pattern of sterol regulatory element-binding protein isoform 2 protein in the rabbit testicles was studied by indirect immunofluorescence. In addition, testicular cholesterol was detected and quantified by filipin staining and gas chromatography.

RESULTS

The data showed that the addition of extra-virgin olive oil to high-fat diet reduced testicular cholesterol levels and recovered the expression of sterol regulatory element-binding protein isoform 2, 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase, and low-density lipoprotein receptor initially altered by the high-fat diet.

DISCUSSION AND CONCLUSIONS

The combination of high-fat diet with extra-virgin olive oil encourages testicular recovery by modifying the expression of the enzymes related to intracellular cholesterol management.

Cerebrotendinous xanthomatosis and infertility: A case report

Cerebrotendinous xanthomatosis (CTX) is a lipid storage disorder that causes neurological, ophthalmic, vascular, and musculoskeletal disorders due to the deposition of cholesterol in the tissues. Hence, we report clinical and imaging of a 31-year-old mentally retarded man with cerebellar ataxia, bilateral swelling of the posterior aspect of Achill, and infertility.

L-Carnitine effect on induced hyperlipidemia on premature rats: fertility profile

This study was designed to investigate the effect of hypercholesterolemia on the reproductive performance of premature male rats and to evaluate the influence of L-Carnitine (CAR) in maintaining their fertility. Sixty rats were divided randomly into three groups. Control group (CG n=20 rats), cholesterol feeding group 1 (CFG1 n=20 rats) fed 1.5% cholesterol with diet for one month, and cholesterol feeding group 2 (CFG2 n=20 rats) fed 1.5% cholesterol with diet + CAR 150 mg/kg body weight (B.W.) given by water for one month. Results showed a significant increase in body weight of CFG1 compared with CG and CFG2. The lipid profile of CFG1 after one month of feeding cholesterol showed a significant increase in serum cholesterol and triglyceride compared with CG and with the group that watered by CAR and CFG2. Results of sperms parameters in CGF2 showed a significant increase in sperms count with sperms live percentage and a significant decrease in sperms abnormalities percentage compared with CGF1 and CG. The hormonal profile showed a significant decrease in serum testosterone levels in rats from CFG1 compared with CFG2 and CG. In conclusion, CAR is a powerful antioxidant that can maintain the parameters of sperms of hypercholesterolemic premature rats, which may enhance the fertilizing ability of subfertile rats that may occur due to hyperlipidemia.

Semen quality and sperm function loss by hypercholesterolemic diet was recovered by addition of olive oil to diet in rabbit

Fat increment (0.05% cholesterol, chol) in standard diet promoted a significant increase in serum and sperm membrane chol, which ultimately altered membrane-coupled sperm specific functions: osmotic resistance, acrosomal reaction, and sperm capacitation in White New Zealand rabbits. These changes were also associated with a reduction in motility percentage and appearance of abnormal sperm morphology. The present study was carried out to evaluate the effect of dietary olive oil (OO, 7% v/w) administration to several male hypercholesterolemic rabbits (hypercholesterolemic rabbits, HCR) with altered fertility parameters. These HCR males were achieved by feeding normal rabbits with a high-fat diet (0.05% chol). HCR were associated with a modest non-significant increase in body weight (standard diet, 4.08±0.17 Kg, versus high-fat diet, 4.37±0.24 Kg). Hypercholesterolemic rabbits presented a marked decrease in semen volume, sperm cell count, and percentage of sperm motility, associated with a significant increase in sperm cell abnormalities. Moreover, sperm capacitation measured by the characteristic phosphorylated protein pattern in and induced acrosomal reaction were also altered suggesting sperm dysfunction. However, the administration of OO (for 16 weeks) to rabbits that were fed with 50% of the high-fat diet normalized serum chol. Curiously, OO supply succeeded to attenuate the seminal and sperm alterations observed in HCR group. Administration of OO alone did not cause any significant changes in above mentioned parameters. These data suggest that OO administration to HCR male rabbits recovers the loss of semen quality and sperm functionality.

Hypercholesterolemia impaired sperm functionality in rabbits

Hypercholesterolemia represents a high risk factor for frequent diseases and it has also been associated with poor semen quality that may lead to male infertility. The aim of this study was to analyze semen and sperm function in diet-induced hypercholesterolemic rabbits. Twelve adult White New Zealand male rabbits were fed ad libitum a control diet or a diet supplemented with 0.05% cholesterol. Rabbits under cholesterol-enriched diet significantly increased total cholesterol level in the serum. Semen examination revealed a significant reduction in semen volume and sperm motility in hypercholesterolemic rabbits (HCR). Sperm cell morphology was seriously affected, displaying primarily a "folded head"-head fold along the major axe-, and the presence of cytoplasmic droplet on sperm flagellum. Cholesterol was particularly increased in acrosomal region when detected by filipin probe. The rise in cholesterol concentration in sperm cells was determined quantitatively by Gas chromatographic-mass spectrometric analyses. We also found a reduction of protein tyrosine phosphorylation in sperm incubated under capacitating conditions from HCR. Interestingly, the addition of Protein Kinase A pathway activators -dibutyryl-cyclic AMP and iso-butylmethylxanthine- to the medium restored sperm capacitation. Finally, it was also reported a significant decrease in the percentage of reacted sperm in the presence of progesterone. In conclusion, our data showed that diet-induced hypercholesterolemia adversely affects semen quality and sperm motility, capacitation and acrosomal reaction in rabbits; probably due to an increase in cellular cholesterol content that alters membrane related events.

Cholesterol efflux-mediated signal transduction in mammalian sperm: cholesterol release signals an increase in protein tyrosine phosphorylation during mouse sperm capacitation

We previously demonstrated that mouse sperm capacitation is accompanied by a time-dependent increase in protein tyrosine phosphorylation that is dependent on the presence of BSA, Ca2+, and NaHCO(3), all three of which are also required for this maturational event. We also demonstrated that activation of protein kinase A (PK-A) is upstream of this capacitation-associated increase in protein tyrosine phosphorylation. BSA is hypothesized to modulate capacitation through the removal of cholesterol from the sperm plasma membrane. In this report, we demonstrate that incubation of mouse sperm medium containing BSA results in a release of cholesterol from the sperm plasma membrane to the medium; release of this sterol does not occur in medium devoid of BSA. We next determined whether cholesterol release leads to changes in protein tyrosine phosphorylation. Blocking the action of BSA by adding exogenous cholesterol-SO-(4) to the BSA-containing medium inhibits the increase in protein tyrosine phosphorylation as well as capacitation. This inhibitory effect is overcome by (1) the addition of increasing concentrations of BSA at a given concentration of cholesterol-SO-(4) and (2) the addition of dibutyryl cAMP plus IBMX. High-density lipoprotein (HDL), another cholesterol binding protein, also supports the capacitation-associated increase in protein tyrosine phosphorylation through a cAMP-dependent pathway, whereas proteins that do not interact with cholesterol have no effect. HDL also supports sperm capacitation, as assessed by fertilization in vitro. Finally, we previously demonstrated that HCO-(3) is necessary for the capacitation-associated increase in protein tyrosine phosphorylation and demonstrate here, by examining the effectiveness of HCO-(3) or BSA addition to sperm on protein tyrosine phosphorylation, that the HCO-(3) effect is downstream of the site of BSA action. Taken together, these data demonstrate that cholesterol release is associated with the activation of a transmembrane signal transduction pathway involving PK-A and protein tyrosine phosphorylation, leading to functional maturation of the sperm.

Effects of hypercholesterolaemia on Leydig and Sertoli cell secretory function and the overall sperm fertilizing capacity in the rabbit

The effects of hypercholesterolaemia on testicular endocrine and exocrine function were evaluated. The influence of hypercholesterolaemia on sperm quality, quantity, and fertilizing potential was also determined. Ten mature rabbits (group A) were fed chow containing 3% cholesterol for 12 weeks. Ten control rabbits (group B) were fed normal chow for the same period. At the end of the experimental period testosterone profiles and sperm parameters were evaluated and the sperm reproductive potential was assessed by in vitro fertilization (IVF) techniques. Peripheral serum testosterone responses to testicular stimulation with human chorionic gonadotrophin, androgen-binding protein activity in testicular cytosols, sperm concentration, sperm motility, length of sperm midpiece, and IVF outcome were all significantly lower in group A than in group B. In contrast, serum cholesterol concentrations were significantly higher in group A. There were no significant differences in either testicular versus intra-abdominal temperature differences or cholesterol concentrations in seminal plasma or testicular tissue between groups A and B. The results suggest that hypercholesterolaemia has a detrimental effect on Leydig and Sertoli cell secretory function, spermatogenesis, epididymal sperm maturation process, and the overall sperm fertilizing capacity.

Experimental hypercholesterolaemia in rabbits. Effect on lipid domains in homologous spermatozoa

The distribution of membrane filipin sterol complexes (FSC) in the plasma membrane of the acrosomal region (PMAR) of rabbit sperm from epididymis and testis, in normal and hypercholesterolaemic rabbits, was examined at ultrastructural level. Membrane FSG were quantitatively analysed on freeze fracture replicas of filipin-treated cells. Cauda epididymal sperm shows a significant increase in filipin sterol complexes concentration in PMAR of hypercholesterolaemic animals compared to normal rabbits. Hypercholesterolaemic animals had 0.53 +/- 0.08 FSC micron-2 in the marginal segment of PMAR and 0.26 +/- 0.03 FSC micron-2 for normal animals. In the principal piece we found 0.70 +/- 0.07 FSC micron-2 for hypercholesterolaemic and 0.43 +/- 0.03 FSC micron-2 for control animals. We also counted 0.58 +/- 0.04 FSC micron-2 in the equatorial segment of PMAR for hypercholesterolaemic and 0.38 +/- 0.03 FSC micron-2 for normal animals respectively. The FSC concentration of testicular sperm, like sperm from corpus and caput of epididymis in hypercholesterolaemic animals, did not differ from the controls. Cholesterol, phospholipids and cholesterol:phospholipid ratio in caudal epididymal sperm from treated males did not differ from controls. Only the sphingomyelin concentration decreases in cauda epididymal sperm from hypercholesterolaemic males compared to controls. The results presented in this paper suggest that the lipidic domains in PMAR of hypercholesterolaemic rabbits changes when the gametes go through the epididymis.

Antisperm antibody binding to human sperm inhibits capacitation induced changes in the levels of plasma membrane sterols

PROBLEM

Human spermatozoa express mannose ligand receptors (MLRs) over the entire head when incubated under conditions that promote loss of free cholesterol. Binding of IgA, IgG, and/or IgM head-directed anti-sperm antibodies (ASAs) to freshly isolated sperm blocks MLR expression in a dose dependent manner.

METHODS

Comparison of Western blots of immunoprecipitated glycoproteins from fresh sperm exposed to ASAs from women with those of sperm membrane proteins isolated from capacitated sperm probed with a goat anti-human macrophage MLR antiserum showed that ASAs do not react with human sperm MLRs of 48 and 61 kd apparent molecular weight.

RESULTS

The direct effect of ASA binding was to increase membrane free cholesterol content which remained greater than 0.005 mumol/10(9) sperm after 18 h incubations, whereas the sterol content of controls decreased to less than 0.001 mumol/10(9) sperm. Cholesterol addition to sperm inhibited MLR expression in a manner analogous to ASA binding, while increasing temperatures up to the crystalline/liquid-crystalline phase transition for sperm membranes; less than 45 degrees C failed to promote the appearance of MLRs on the surface of fresh sperm.

CONCLUSIONS

We conclude that ASA effects on membrane cholesterol content prevent the membrane fluidity changes needed for MLR expression.

Cholesterol and polyunsaturated acid enriched diet: effect on kinetics of the acrosome reaction in rabbit spermatozoa

In this study we examined the effect of cholesterol (Diet 2), cholesterol and fish oil (FO) polyunsaturated acid (Diet 3), and polyunsaturated acid (Diet 4) enriched diets upon the acrosome reaction (AR) of New Zealand White rabbit spermatozoa. Male rabbits fed with cholesterol alone or with FO increased their cholesterol and LDL-cholesterol serum levels after 15 days of diet. Ten semen samples were obtained after 2 months of diet. Our results suggest that hypercholesterolemia and hypertriglyceridemia in male rabbits could produce a decreased capacity of sperm AR after 4 h (0%, 0%, and 60% lower than the control), 6 h (0%, 68%, and 44%), or 8 h (58%, 52% and 32%) of incubation in capacitating medium. Another set of experiments were made with lysophosphatidylcholine (LPC), 80 micrograms/ml, and the same pattern of AR was seen. Nevertheless, the high cholesterol and total lipids (TL) levels in serum did not affect the cholesterol levels in seminal plasma (SP) but affect the SP total lipids. The diminished capacity of rabbit sperm to undergo the AR was not reverted by in vitro incubation with the Shinitsky medium for cholesterol depletion (MDC). These results indirectly suggest that the cholesterol/phospholipid ratio in hypercholesterolemic sperm is similar to that of controls and are in agreement with preliminary studies made in our laboratory that evidenced the same cholesterol/phospholipid ratio in rabbit sperm from hypercholesterolemic animals than from controls.(ABSTRACT TRUNCATED AT 250 WORDS)