Testis-Specific Cytochrome c-Null Mice Produce Functional Sperm but Undergo Early Testicular Atrophy

Abstract

Differentiating male germ cells express a testis-specific form of cytochrome c (Cyt c T ) that is distinct from the cytochrome c expressed in somatic cells (Cyt c S ). To examine the role of Cyt c T in germ cells, we generated mice null for Cyt c T . Homozygous Cyt c T ؊/؊ pups were statistically underrepresented (21%) but developed normally and were fertile. However, spermatozoa isolated from the cauda epididymis of Cyt c T -null animals were less effective in fertilizing oocytes in vitro and contain reduced levels of ATP compared to wild-type sperm. Sperm from Cyt c T -null mice contained a greater number of immotile spermatozoa than did samples from control mice, i.e., 53.1% ؎ 13.7% versus 33.2% ؎ 10.3% (P < 0.0001) for vas deferens sperm and 40.1% ؎ 9.6% versus 33.2% ؎ 7.5% (P ‫؍‬ 0.0104) for epididymal sperm. Cyt c T -null mice often exhibit early atrophy of the testes after 4 months of age, losing germ cells as a result of increased apoptosis. However, no difference in the activation of caspase-3, -8, or -9 was detected between the Cyt c T ؊/؊ testes and controls. Our data indicate that the Cyt c T -null testes undergo early atrophy equivalent to that which occurs during aging as a consequence of a reduction in oxidative phosphorylation.

Moving to the beat: a review of mammalian sperm motility regulation

“…In addition, it has been shown, in mice, that if mitochondrial oxidative phosphorylation is defective, fertilisation can still occur, sperm still produce ATP (at lower levels than wild-type sperm) and sperm motility is still present, although reduced (Narisawa et al 2002). These data suggest that mitochondrial oxidative phosphorylation is not the main source of ATP that supports flagellar motility.…”

Caspase-independent death of meiotic and postmeiotic cells overexpressing p53: calpain involvement

“…In spermatogenesis, the shift in cytochrome c isoforms (somatic cytochrome c is replaced by testicular cytochrome c) in pachytene cells might explain the caspase failure in differentiating cells. 31 In addition, mitochondria release other molecules like AIF responsible for an 'apoptosis-like' phenotype without full nucleosomal DNA fragmentation (but TUNEL positivity) and which can be coupled to caspase-independent cell death. 32,33 Finally, by enhancing levels of caspase-2S antiapoptotic variant in transgenic cells, the caspase pathway could be blocked.…”

Mitochondria functionality and sperm quality

“…These include, for example, the need for glucose to maintain sperm function, a need that cannot be replaced with OXPHOS substrates (Peterson & Freund 1970, Williams & Ford 2001, Hereng et al 2011. Furthermore, male mouse knock-out models for the glycolysis-associated enzymes enolase 4 (Nakamura et al 2013), phosphoglycerate kinase 2 Testis-specific cytochrome c knock-out Homozygous males were fertile, but presented testicular atrophy and their sperm were less motile, had lower levels of ATP and had a lower fertilisation ability compared with wild-types Narisawa et al (2002) Mitochondrial DNA polymerase gamma (POLG) knock-in expressing a proofreading-deficient polymerase Increased levels of mtDNA point mutations and deletions, reduced lifespan and premature onset of age-related phenotypes, including reduced fertility Trifunovic et al (2004) Transmitochondrial (carrying mtDNA deletions)…”

“…In addition, the normalisation of other activities to citrate synthase (often used as a marker for mitochondrial content) suggested that the main explanation for these correlations might be mitochondrial volume, not distinct enzymatic activities in samples of varying quality (Ruiz-Pesini et al 1998). Additionally, mice lacking the testis-specific form of cytochrome c also have impaired sperm function (Narisawa et al 2002). Furthermore, oxygen consumption in sperm mitochondria and mitochondrial respiratory efficiency also correlate with motility (Stendardi et al 2011, Ferramosca et al 2012, and many different ETC inhibitors (Fig.…”