Understanding the effects of sperm metabolism leading to improved fertilization and embryo development.

ANA ROMAROWSKI

Simposio; Frontiers in Reproduction. Virtual Symposium 2021; 2021

Introduction and objectives:Sperm capacitation involves a fine crosstalk between metabolic and signaling pathways.Recently, the Visconti group developed a technique where all nutrients were removedfrom the medium, sperm were incubated until become motionless, and nutrients wereadded back. This method, named Sperm Energy restriction plus Recovery (SER)significantly improved the percentage of hyperactive sperm, in vitro fertilization andembryo development rates. The aim of this work was to understand the effect of SERtreatment on sperm at the metabolomic and molecular level.Results:We found that recovering in a medium with only glucose as energy substrate wassufficient to produce the increased hyperactivation and IVF levels obtained after SERtreatment, while recovering with only pyruvate was not. In addition, SER with onlyglucose treated sperm showed an increase in energy production pathways. We found thehighest glycolysis, krebs cycle and oxidative phosphorylation levels by measuringglucose consumption rate, by using the Seahorse technology, and by metabolomicsusing high-resolution NMR and Mass Spectrometry. Following 13C-labeled glucosemetabolites, 2D 1H- 13C HSQC NMR experiments showed that citrate is significantlyhigher in CAP condition than in NC. Because all these experiments were conductedonly in the presence of glucose (13C-citrate is derived from 13C-glucose), they suggestthat pyruvate (or lactate) produced during glycolysis in the sperm principal piece is ableto migrate to the mitochondria mid-piece and enter the Krebs cycle. Moreover, wefound that sperm intracellular ATP levels were recovered after SER treatment. OurNMR data show that there is a distinct metabolite profile signature observed in 1H 1DNMR spectra for each treatment. The most significant differences are seen betweenstarved and rescued CAP condition.Conclusions:Glucose alone was sufficient to produce the increased hyperactivation and IVF levelsobtained after SER treatment, while pyruvate alone was not, suggesting that theglycolytic pathway is necessary to be active for the SER improvement on spermfunction. Moreover, by using NMR and the Seahorse technology, we demonstrated thatpyruvate (or lactate) produced during glycolysis in the sperm principal piece is able tomigrate to the mitochondria mid-piece and enter the Krebs cycle. In addition, SERtreated sperm showed the highest glycolysis and oxidative phosphorylation levels.These results show that this treatment up-regulates energy production metabolicpathways and could explain why these sperm have improved functionality. However,we found that ATP levels were similar to non SER capacitated sperm. This could bebecause in the SER treated sperm even though there is more ATP production, there isalso more ATP consumption. Altogether, these results indicate that manipulation ofsperm metabolism can affect sperm function improving the outcome of embryodevelopment and suggest that changes occurring during sperm capacitation continue tobe relevant after fertilization has occurred.