Mitochondria Content and Activity Are Crucial Parameters for Bull Sperm Quality Evaluation

Abstract

Standard sperm evaluation parameters do not enable predicting their ability to survive cryopreservation. Mitochondria are highly prone to suffer injuries during freezing, and any abnormalities in their morphology or function are reflected by a decline of sperm quality. Our work focused on describing a link between the number and the activity of mitochondria, with an aim to validate its applicability as a biomarker of bovine sperm quality. Cryopreserved sperm collected from bulls with high (group 1) and low (group 2) semen quality was separated by swim up. The spermatozoa of group 1 overall retained more mitochondria (MitoTrackerGreen) and mtDNA copies, irrespective of the fraction. Regardless of the initial ejaculate quality, the motile sperm contained significantly more mitochondria and mtDNA copies. The same trend was observed for mitochondrial membrane potential (ΔΨm, JC-1), where motile sperm displayed high ΔΨm. These results stay in agreement with transcript-level evaluation (real-time polymerase chain reaction, PCR) of antioxidant enzymes (PRDX1, SOD1, GSS), which protect cells from the reactive oxygen species. An overall higher level of glutathione synthetase (GSS) mRNA was noted in group 1 bulls, suggesting higher ability to counteract free radicals. No differences were noted between basal oxygen consumption rate (OCR) (Seahorse XF Agilent) and ATP-linked respiration for group 1 and 2 bulls. In conclusion, mitochondrial content and activity may be used as reliable markers for bovine sperm quality evaluation.

Molecular and physiochemical evaluation of buck semen cryopreserved with antioxidants

“…The up‐regulation of these intracellular defence genes was coupled with reduced incidence of DNA fragmentation. In accordance with our results, two recent investigations have confirmed up‐regulation of genes regulating antioxidant enzymes (GPX7, PRDX1, SOD1, PRDX6, TXN2 and GSS) in high‐quality bull spermatozoa (Madeja et al, 2021; Saraf et al, 2021). Enhancing the antioxidant system at enzymatic and transcriptional levels is the key trigger for improvement in semen physiochemical quality traits which might enhance fertilizing potential of spermatozoa as reported by Zhu et al (2017).…”

“…These data are consistent with data reported earlier in rabbit (Zhu et al, 2017). Additionally, the improvement of physiochemical parameters was associated with up‐regulation of antioxidant and metabolic regulating genes which pointed to importance of sperm molecular profile during development processes (Steger et al, 2001), following cryopreservation (Chen et al, 2014; Dessouki et al, 2020), during embryonic development (Boerke et al, 2007; Guo et al, 2017; Yuan et al, 2016) and in relation to pregnancy rate following A.I (Madeja et al, 2021; Saraf et al, 2021).…”

“…Antioxidant capacity and metabolic activity are correlated when taken into account that some genes encoding for antioxidant enzymes (such as SOD1, SOD2 and PRDX1) are transcribed from mitochondria (Madeja et al, 2021; Saraf et al, 2021; Thomas et al, 2021). Mitochondria metabolic activity is crucial for sperm motion and fertilizing ability (Thomas et al, 2021).…”

“…However, freezing cause physiochemical changes, structural damages and molecular alterations of semen (Zhu et al, 2019). Moreover, freezing of semen causes structural damage to mitochondria which ultimately compromise sperm viability and fertilizing ability (Madeja et al, 2021).Sperm cryopreservation is a valuable method for conserving rabbit genetic strains and accelerating genetic improvement. However, the sperm of rabbits have a large head, which makes them susceptible to freezing and all steps of semen cryopreservation induce oxidative stress that reduced their viability (Zhu et al, 2017).…”

Mitochondria Biology in Reproductive Function

“…By using high-precision new generation flow cytometry, Kern and colleagues [ 7 ] proposed that the length of boar sperm mitochondrial sheath, measured by using an aggresome marker, may represent a measurable sperm phenotype correlated with fertility. In the bovine model, Madeja et al [ 8 ] discovered a correlation between the number and the activity of mitochondria and global sperm quality, by comparing sperm samples from bulls with high reproductive performance with samples from bulls temporarily disqualified from semen production. In this paper many mitochondrial parameters, including mtDNA copies, mitochondrial membrane potential, transcript-level of antioxidant enzymes, were correlated with sperm quality, although no differences were noted when samples were tested for oxygen consumption rate [ 8 ].…”