P-106 The inhibition of sperm SIRT1 enhances fertilization and modifies subsequent embryonic epigenetic quality
Authors: Iniesta-Cuerda M , Řimnáčová H , Krapf D , Nevoral J 
Published: June 2023

Abstract

Study question
Is SIRT1 present in sperm and thus involved in fertilization and/or sperm epigenetic code? Do the SIRT1-driven epigenetic marks be transmitted to the progeny?

Summary answer
SIRT1 localized at the sperm head and influences fertilization and sperm epigenetic code via its deacetylation activity. SIRT1-modulated epigenome is transmitted to zygotes and blastocysts.

What is known already
The addition or removal of acetyl group from lysine residua (i.e. acetylation) post-translationally modulates proteins through the action of acetylases and deacetylases, respectively. SIRT1 (also Sirtuin 1) is capable to deacetylate a number of proteins, including histones, with roles in male reproduction. Testicular SIRT1 deficit leads to subfertility and increases number of abnormal and immotile spermatozoa that fail to fertilize. However, neither sperm SIRT1 presence nor its function has been investigated despite the significance of acetylation in the events around fertilization. Moreover, the epigenetic mode of action of sperm SIRT1 highlights its relevance for the success of the pre-implantation embryo.

Study design, size, duration
Mouse sperm of 14-18-weeks-old males of CD-1 x C57Bl6 hybrid strain were isolated from the epididymis. Sperm were incubated under capacitating conditions in presence of sirtinol (5 µM), a selective SIRT1 inhibitor, or the vehicle (0.1% v/v DMSO) for 1 h in 37 °C and 5% CO2.

Participants/materials, setting, methods
Motility and acrosome reaction was evaluated as previously stated (Ritagliati et al., 2018). Moreover, sperm proteins were extracted into RIPA-buffer and acetylated proteins were depicted by western blot. Finally, in vitro fertilization and embryo culture were performed. Above parameters defining IVF outcomes (i.e., fertilization, cleavage, and blastocyst rate), immunocytochemistry of acetylated histone 4 in the 16th residua of lysine (H4K16) in zygotes and blastocyst was quantified.

Main results and the role of chance
SIRT1 was localized in the sperm head, apparently at the perinuclear theca and perforatorium. Inhibition of SIRT1 leads to the increase of lysine acetylation (2.28 vs 1, fold change values) and hyperactivation (16.55 ± 0.79 vs 10.84 ± 0.79 %sperm), the enhanced motility that facilitates sperm to penetrate the oocyte, as well as the acrosome reaction (28.69 ± 0.41 vs 17.98 ± 0.41 %sperm). Subsequently, these spermatozoa were able to better fertilize oocytes in vitro (90.5 ± 7.21 vs 66.25 ± 7.21, %). Interestingly, zygotes derived from sirtinol-pre-treated spermatozoa developed to 2-cell embryos at a higher rate than those fertilized by untreated spermatozoa (79.33 ± 7.21 vs 67.00 ± 7.21, %). Moreover, we observed significant hyperacetylation of H4K16 in the male pronuclei of zygotes and embryos derived from sirtinol-treated sperm (8.19 ± 1.02 vs 6.10 ± 2.09 and 45.55 ± 13.96 vs 27.62 ± 13.96, integrated density of the signals, respectively).

Limitations, reasons for caution
Although acetylation of H4K16 was accumulated in male pronuclei, we do not know which subset of genes was affected. Therefore, we only can assure that SIRT1-driven epigenetic marks are transmitted to the offspring, but their consequences should be further elucidated. For knowledge transfer to humans, a verification study is required.

Wider implications of the findings
the reduction in testicular SIRT1 expression is an age-related phenomenon. Therefore, our results support SIRT1 as the basis for new interventions against age-related male infertility. Moreover, due to the high reactivity of SIRT1 to its inactivation, SIRT1 becomes a target to pharmacologically enhance sperm fertilization ability in assisted reproductive techniques.

Trial registration number
Animal procedures were conducted in accordance with Act No. 246/1992 Coll. on the Protection of Animals Against Cruelty under the supervision of the Animal Welfare Committee of the Ministry of Education, Youth and Sports of the Czech Republic, approval ID MSMT-11925/2016-3.