P-054 Paternal age and cryopreservation impact sperm chromatin status as indicated by changes in protamine and histone levels
Authors: Turchi D , Franchi V , Marchiani S , Traini G , Novara P , Mario M  R , Dal Canto M , Buratini J 
Published: July 2024

Abstract

Study question
Do paternal age and cryopreservation alter sperm chromatin status in normospermic men?

Summary answer
Paternal age and cryopreservation appear to impact sperm chromatin condensation by altering protamine and histone DNA levels.

What is known already
Semen parameters do not accurately reflect male fertility and thus are not adequate to assess the impact of patient profile and semen manipulation/conservation on sperm functional quality. DNA protamination leads to sperm chromatin condensation, which is associated with sperm maturity but also appears to function as a defence mechanism against oxidative attack. In the face of contrasting/insufficient previous data, the impact of advanced paternal age (APA) and cryopreservation on sperm chromatin condensation and histone/protamine balance remains unclear.

Study design, size, duration
Twenty-two normospermic men, 11 of which with advanced paternal age (APA; ≥42) and 11 pre-APA (≤35), provided semen samples by masturbation (1-5 days abstinence). Fresh and cryopreserved/thawed samples from all patients were assessed for chromatin histone staining, while samples from a subgroup of 10 patients (5 pre-APA and 5 APA) were assessed for protamine presence. The effects of age and cryopreservation on the percentage of stained cells were assessed with the Fisher’s exact test.

Participants/materials, setting, methods
Semen samples were provided by male partners of couples treated at our fertility centre. Sample aliquots were cryopreserved and analyzed after thawing (CryoSperm & Sperm Preparation Medium, Origio). Histone presence was assessed through aniline blue staining and protamine presence was indirectly assessed through staining with the protamine competitor Chromomycin A3 (CMA3); stained cells were visualized by bright field and fluorescence microscopy, respectively. Two hundred sperm cells were evaluated in each sample by the same embryologist.

Main results and the role of chance
Mean paternal age was 31.5±3.9 and 44.4±2.1 years for pre-APA and APA patient-groups, respectively. Major parameters observed in fresh semen samples were: 2.3±0.7 vs. 3.6±1.6mL (volume); 39±28 vs. 38±12 x10ˆ6/mL (concentration); 7±12 vs. 6±5% (rapid progressive motility); 41±12 vs. 38±13% (slow progressive motility); 12±5 vs. 11±4% (non-progressive motility); 40±17 vs. 45±16% (immotile) and 5±1 vs. 6±2% (normal morphology), for pre-APA and APA, respectively. The percentage of aniline blue (histone marker) positive cells was less than half in fresh samples from APA as compared to pre-APA patients (10.2% and 23.4%, respectively, p &lt; 0.0001). Consistently, the percentage of CMA3 (protamine absence marker) positive cells was less than half in APA as compared to pre-APA patients (6.4% and 16.4%, respectively, p &lt; 0.0001). In both age groups, the percentages of aniline blue and CMA3 positive cells were higher in cryopreserved/thawed samples as compared to their fresh counterparts (aniline blue positive: 35.2% vs. 23.4% and 22.0% vs. 10.2%; CMA3 positive: 27.2% vs. 16.4% and 18.8% vs. 6.4%, in cryopreserved vs. fresh in pre-APA and APA, respectively, p &lt; 0.0001).

Limitations, reasons for caution
Our study is limited by the potential interference of confounding factors not equally distributed in age groups. The conclusions from this study must be confirmed in other patient populations with different race/genetics and habits.

Wider implications of the findings
Our findings suggest that APA increases, while cryopreservation decreases, sperm chromatin condensation, as indicated by changes in DNA histone and protamine abundance. Our study thus sheds light on the impact of paternal age and cryopreservation on sperm quality, providing new valuable parameters for reproductive medicine practice and research.

Trial registration number
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