Effect of Vasectomy on Sperm Nuclear Chromatin Condensation in the Rabbit

Molecular morphology and function of bull spermatozoa linked to histones and associated with fertility

Sub-par fertility in bulls is influenced by alterations in sperm chromatin, and it might not be solved with increased sperm concentration in artificial insemination. Appropriate histone retention during sperm chromatin condensation plays critical roles in male fertility. The objective of this study was to determine failures of sperm chromatin condensation associated with abnormal persistence or accessibility of histones by aniline blue (ANBL) test, expression levels, and cellular localizations of one variant and two core histones (H3.3, H2B, and H4 respectively) in the spermatozoa of low-fertility (LF) vs high-fertility (HF) bulls. The expression levels and cellular localizations of histones in spermatozoa were studied using immunoblotting, immunocytochemistry, and staining methods. The bioinformatics focused on the sequence identity and evolutionary distance of these proteins among three mammalian species: bovine, mouse, and human. We demonstrated that ANBL staining was different within the LF (1.73 (0.55, 0.19)) and HF (0.67 (0.17, 0.06)) groups (P<0.0001), which was also negatively correlated within vivobull fertility (r=−0.90,P<0.0001). Although these histones were consistently detectable and specifically localized in bull sperm cells, they were not different between the two groups. Except H2B variants, H3.3 and H4 showed 100% identity and were evolutionarily conserved in bulls, mice and humans. The H2B variants were more conserved between bulls and humans, than in mice. In conclusion, we showed that H2B, H3.3, and H4 were detectable in bull spermatozoa and that sperm chromatin condensation status, changed by histone retention, is related to bull fertility.

Effect of vasectomy via inguinal canal on spermatogenesis in rabbits

AIM

To determine whether vasectomy away from the epididymal tail (via the inguinal canal) in rabbits can reduce the early postoperative effects on spermatogenesis.

METHODS

Twenty-nine normal male Japanese white rabbits (aged 4-6 months) were subjected to unilateral close-ended (conventional) or open-ended (the cut end of the juxta-epididymal vas deferens not ligated) vasectomy via the inguinal canal. Ten days and 3 months after operation, testes, epididymides and vasa deferentia were removed and methacrylate resin-embedded sections prepared. The histology of the testis, epididymis and vas deferens was examined under light microscope, and the volume and diameter of the seminiferous tubules were quantitatively studied using stereological methods.

RESULTS

Neither of the methods of vasectomy led to apparent damage to spermatogenesis on the vasectomized side in comparison with the contralateral sham-operated side, but the juxta-epididymal vas deferens on the vasectomized side was highly distended and contained numerous sperm 3 months after operation.

CONCLUSION

Vasectomy away from the cauda epididymis has no significant early postoperative effects on spermatogenesis in rabbits.

Reduced sperm yield from testicular biopsies of vasectomized men is due to increased apoptosis

OBJECTIVE

To compare sperm yields, apoptotic indices, and sperm DNA fragmentation from vasectomized men and fertile men undergoing vasectomy.

DESIGN

Testicular biopsies from vasectomized (n = 26) and fertile men (n = 46), were milked to calculate sperm/gram and also formalin-fixed to determine the numbers of developing sperm and incidence and intensities of testicular FasL, Fas, Bax, and Bcl-2. Testicular sperm DNA fragmentation was assessed using the alkaline Comet assay.

SETTING

An ART unit.

PATIENT(S)

Twenty-six men attending for intracytoplasmic sperm injection (ICSI) and 46 men attending for vasectomies.

MAIN OUTCOME MEASURE(S)

Spermatocyte, spermatid and sperm yields, Fas, FasL, and Bax staining.

RESULT(S)

Sperm yields from men vasectomized >5 years previously were markedly reduced compared to fertile men. Increased intensities of FasL and Bax staining were observed in the seminiferous tubules of vasectomy men. FasL positivity (percentage) also increased in Sertoli cells, and both FasL and Fas positivity (percentage) increased in primary spermatocytes and round spermatids of vasectomized men. Sperm DNA fragmentation, an end point marker of apoptosis, increased significantly in vasectomized men compared to fertile men.

CONCLUSION(S)

Reduced sperm yields after vasectomy are associated with increased apoptosis through the Fas-FasL and Bax pathways. Sperm after vasectomy displayed increased DNA fragmentation.

Protamines and male infertility

Protamines are the major nuclear sperm proteins. The human sperm nucleus contains two types of protamine: protamine 1 (P1) encoded by a single-copy gene and the family of protamine 2 (P2) proteins (P2, P3 and P4), all also encoded by a single gene that is transcribed and translated into a precursor protein. The protamines were discovered more than a century ago, but their function is not yet fully understood. In fact, different hypotheses have been proposed: condensation of the sperm nucleus into a compact hydrodynamic shape, protection of the genetic message delivered by the spermatozoa, involvement in the processes maintaining the integrity and repair of DNA during or after the nucleohistone-nucleoprotamine transition and involvement in the epigenetic imprinting of the spermatozoa. Protamines are also one of the most variable proteins found in nature, with data supporting a positive Darwinian selection. Changes in the expression of P1 and P2 protamines have been found to be associated with infertility in man. Mutations in the protamine genes have also been found in some infertile patients. Transgenic mice defective in the expression of protamines also present several structural defects in the sperm nucleus and have variable degrees of infertility. There is also evidence that altered levels of protamines may result in an increased susceptibility to injury in the spermatozoan DNA causing infertility or poor outcomes in assisted reproduction. The present work reviews the articles published to date on the relationship between protamines and infertility.

The treatment of obstructive azoospermia by intracytoplasmic sperm injection

Intracytoplasmic sperm injection (ICSI) allows the treatment of virtually every type of male infertility. Unlike in vitro fertilization (IVF), its success does not depend on sperm concentration, motility or morphology and most of the physical barriers to fertilisation are by-passes. Since ICSI does not require strongly motile sperm, its use has now been expanded to incorporate immature sperm from the testes and epididymides. Successful fertilisation, pregnancies and healthy babies have all been reported. However, concerns about the safety of ICSI remain due to its short clinical history and the lack of testing on animal models.

Male fertility potential for assisted reproduction by ICSI cannot be measured by conventional parameters. Sperm DNA integrity is increasingly recognised as a more useful indicator. Studies have shown that sperm with higher levels of DNA damage have lower fertilisation rates after IVF and ICSI. Sperm with DNA damage above a certain threshold are associated with a longer time to conceive in otherwise apparently fertile couples and a higher miscarriage rate. DNA damage has been shown to be associated with impaired embryo cleavage. Our group has shown that sperm DNA from testicular sperm is less fragmented than that from epididymal sperm and suggest its preferred use in ICSI.

In addition to nuclear (n) DNA we also assessed the quality of mitochondrial (mt) DNA from testicular sperm from men with obstructive azoospermia undergoing ICSI. We observed that couples achieving a pregnancy had both less mtDNA deletions and less nDNA fragmentation. We found inverse relationships between pregnancy and sperm mtDNA deletion numbers, size and nDNA fragmentation. No relationships were observed with fertilisation rates. With this knowledge, we designed an algorithm for the prediction of pregnancy based on the quality of sperm nDNA and mtDNA.

Each year 40,000 men have a vasectomy in the UK but every year 2500 request a reversal to begin a second family. For such men, vasectomy reversal has recently been replaced in part by testicular biopsy via fine-needle testicular sperm aspiration (TESA) or percutaneous epididymal sperm aspiration (PESA) performed at an outpatient clinic and subsequently used in ICSI. Since these were previously fertile men it has been assumed that they had ‘fertile’ sperm. However the assited conception success rates of these mens partners has not been assessed until recently. We have shown a significant reduction in the clinical pregnancy rates in the partners of men who had had a vasectomy ≥10yrs previously. There is also evidence to suggest that spermatogenesis is significantly impaired in vasectomised men. Marked decreases in spermatocytes, spermatids and spermatozoa have been observed. We have found this to be associated with concomitant increases in apoptotic markers, such as Fas, FasL and Bax. The quality of the remaining sperm is also compromised. Sperm DNA from vasectomized men shows substantial damage which increases with time after surgery. This new use of ICSI will be discussed.