Subcellular localization of branched-chain amino acid aminotransferase and lactate dehydrogenase C4 in rat and mouse spermatozoa

Bioenergetic changes in response to sperm capacitation and two-way metabolic compensation in a new murine model

The acquisition of fertilizing ability by mammalian spermatozoa, known as "capacitation," includes processes that depend on particular metabolic pathways. This has led to the hypothesis that ATP demands might differ between capacitated and non-capacitated cells. Mouse sperm can produce ATP via OXPHOS and aerobic glycolysis, an advantageous characteristic considering that these cells have to function in the complex and variable environment of the female reproductive tract. Nonetheless, despite evidence showing that both metabolic pathways play a role in events associated with mouse sperm capacitation, there is contradictory evidence regarding changes promoted by capacitation in this species. In addition, the vast majority of studies regarding murine sperm metabolism use Mus musculus laboratory strains as model, thus neglecting the wide diversity of sperm traits of other species of Mus. Focus on closely related species with distinct evolutionary histories, which may be the result of different selective pressures, could shed light on diversity of metabolic processes. Here, we analyzed variations in sperm bioenergetics associated with capacitation in spermatozoa of the steppe mouse, Mus spicilegus, a species with high sperm performance. Furthermore, we compared sperm metabolic traits of this species with similar traits previously characterized in M. musculus. We found that the metabolism of M. spicilegus sperm responded to capacitation in a manner similar to that of M. musculus sperm. However, M. spicilegus sperm showed distinct metabolic features, including the ability to perform cross-pathway metabolic compensation in response to either respiratory or glycolytic inhibition, thus revealing a delicate fine-tuning of its metabolic capacities.

Differences in ATP Generation Via Glycolysis and Oxidative Phosphorylation and Relationships with Sperm Motility in Mouse Species

Mouse sperm produce enough ATP to sustain motility by anaerobic glycolysis and respiration. However, previous studies indicated that an active glycolytic pathway is required to achieve normal sperm function and identified glycolysis as the main source of ATP to fuel the motility of mouse sperm. All the available evidence has been gathered from the studies performed using the laboratory mouse. However, comparative studies of closely related mouse species have revealed a wide range of variation in sperm motility and ATP production and that the laboratory mouse has comparatively low values in these traits. In this study, we compared the relative reliance on the usage of glycolysis or oxidative phosphorylation as ATP sources for sperm motility between mouse species that exhibit significantly different sperm performance parameters. We found that the sperm of species with higher oxygen consumption/lactate excretion rate ratios were able to produce higher amounts of ATP, achieving higher swimming velocities. Additionally, we show that the species with higher respiration/glycolysis ratios have a higher degree of dependence upon active oxidative phosphorylation. Moreover, we characterize for the first time two mouse species in which sperm depend on functional oxidative phosphorylation to achieve normal performance. Finally, we discuss that sexual selection could promote adaptations in sperm energetic metabolism tending to increase the usage of a more efficient pathway for the generation of ATP (and faster sperm).

Nanoparticle Delivery Systems Reduce the Reproductive Toxicity of Docetaxel in Rodents

Various docetaxel (DTX)-loaded nanoparticle delivery systems have been designed to enhance the solubility and pharmacological effects of DTX. However, the toxicity changes of these nano-modified DTX (nano-DTX) are not yet clear enough. Herein, to compare the reproductive toxicity between conventional DTX and nano-DTX, we performed sperm toxicity test in mice, and fertility and early embryo-fetal developmental toxicity test in rats. It was found that DTX severely repressed spermatogenesis and sperm motility, and dramatically increased sperm abnormality in mice and rats. Moreover, DTX significantly decreased copulation, conception and fertility indexes in rats, and no positive pregnant female rat was obtained after treatment with DTX. However, nano-DTX significantly reduced DTX-induced toxicity to sperm. Most importantly, nano-DTX obviously converted DTX-induced fertility and early embryo-fetal developmental toxicity. Furthermore, organ weights and histopathology examination revealed DTX, but not nano-DTX, significantly decreased testis and epididymis weights, and induced obvious histopathological atrophy of testes and epididymides in rats. Further studies indicated that changed activity of lactate dehydrogenase C4 (LDH-C4) in rodents testes was mainly responsible for the above observations. These results strongly support the idea that DTX-loaded nanoformulations have the potential to overcome the reproductive toxicity of DTX.

Glycolysis and mitochondrial respiration in mouse LDHC-null sperm

We demonstrated previously that a knockout (KO) of the lactate dehydrogenase type C (Ldhc) gene disrupted male fertility and caused a considerable reduction in sperm glucose consumption, ATP production, and motility. While that study used mice with a mixed genetic background, the present study used C57BL/6 (B6) and 129S6 (129) Ldhc KO mice. We found that B6 KO males were subfertile and 129 KO males were infertile. Sperm from 129 wild-type (WT) mice have a lower glycolytic rate than sperm from B6 WT mice, resulting in a greater reduction in ATP production in 129 KO sperm than in B6 KO sperm. The lower glycolytic rate in 129 sperm offered a novel opportunity to examine the role of mitochondrial respiration in sperm ATP production and motility. We observed that in media containing a mitochondrial substrate (pyruvate or lactate) as the sole energy source, ATP levels and progressive motility in 129 KO sperm were similar to those in 129 WT sperm. However, when glucose was added, lactate was unable to maintain ATP levels or progressive motility in 129 KO sperm. The rate of respiration (ZO2) was high when 129 KO or WT sperm were incubated with lactate alone, but addition of glucose caused a reduction in ZO2. These results indicate that in the absence of glucose, 129 sperm can produce ATP via oxidative phosphorylation, but in the presence of glucose, oxidative phosphorylation is suppressed and the sperm utilize aerobic glycolysis, a phenomenon known as the Crabtree effect.

Glucose is a pH-dependent motor for sperm beat frequency during early activation

To reach the egg in the ampulla, sperm have to travel along the female genital tract, thereby being dependent on external energy sources and substances to maintain and raise the flagellar beat. The vaginal fluid is rich in lactate, whereas in the uterine fluid glucose is the predominant substrate. This evokes changes in the lactate content of sperm as well as in the intracellular pH (pH(i)) since sperm possess lactate/proton co-transporters. It is well documented that glycolysis yields ATP and that HCO(3)- is a potent factor in the increase of beat frequency. We here show for the first time a pathway that connects both parts. We demonstrate a doubling of beat frequency in the mere presence of glucose. This effect can reversibly be blocked by 2-deoxy-D-glucose, dichloroacetate and aminooxyacetate, strongly suggesting that it requires both glycolysis and mitochondrial oxidation of glycolytic end products. We show that the glucose-mediated acceleration of flagellar beat and ATP production are hastened by a pH(i) ≥7.1, whereas a pH(i) ≤7.1 leaves both parameters unchanged. Since we observed a diminished rise in beat frequency in the presence of specific inhibitors against carbonic anhydrases, soluble adenylyl cyclase and protein kinase, we suggest that the glucose-mediated effect is linked to CO(2) hydration and thus the production of HCO(3)- by intracellular CA isoforms. In summary, we propose that, in sperm, glycolysis is an additional pH(i)-dependent way to produce HCO(3)-, thus enhancing sperm beat frequency and contributing to fertility.

Basigin interacts with both MCT1 and MCT2 in murine spermatozoa

Lactate is provided to spermatogenic cells by Sertoli cells as an energy substrate and its transport is regulated by H(+)-monocarboxylate co-transporters (MCTs). In the case of several cell types it is known that MCT1 is associated with basigin and MCT2 with embigin. Here we demonstrate co-localization and co-immunoprecipitation of basigin with both MCT1 and MCT2 in sperm, whereas no interaction with embigin was detectable. An investigation of the functional activity of MCT proteins revealed that it was mainly the application of L-lactate which resulted in a decrease in pH(i) . The pH(i) changes were blocked with α-cyano-4-OH cinnamate and the preference for L-lactate-as opposed to D-Lactate-was demonstrated by the determination of ATP after exposure to both lactate isomers. We propose that basigin interacts with MCT1 and MCT2 to locate them properly in the membrane of spermatogenic cells and that this may enable sperm to utilize lactate as an energy substrate contributing to cell survival.

Lactate and adenosine triphosphate in the extender enhance the cryosurvival of rat epididymal sperm

We evaluated the cryosurvival of rat epididymal sperm preserved in raffinose-modified Krebs-Ringer bicarbonate-egg yolk extender supplemented with various energy-yielding substrates (glucose, pyruvate, lactate, and ATP) and assessed the effect on sperm oxygen consumption. The incubation of sperm at 37 degrees C for 10 min in lactate-free extender decreased sperm motility and oxygen consumption before and after thawing compared with those of sperm in glucose- and pyruvate-free mediums. We then focused on the effect of supplementing the extender with lactate (0, 10.79, 21.58, 32.37, and 43.16 mM) and found that sperm frozen and thawed in extender supplemented with 32.37 mM lactate exhibited the highest motility. When we supplemented extender containing 32.37 mM lactate with ATP (0, 0.92, 1.85, 3.70, and 5.55 mM), sperm frozen and thawed in the extender supplemented with 1.85 mM ATP exhibited considerably higher motility and viability than those of sperm frozen and thawed in ATP-free extender. These results provide the first evidence that supplementation of the raffinose-modified Krebs-Ringer bicarbonate-egg yolk extender with 32.37 mM lactate and 1.85 mM ATP increases of number of motile sperm before freezing and enhances the cryosurvival of rat sperm. These supplements to the extender may enhance sperm cryosurvival by improving the metabolic capacity of sperm before freezing.

LDHC: the ultimate testis-specific gene

Lactate dehydrogenase C (LDHC) was, to the best of our knowledge, the first testis-specific isozyme discovered in male germ cells. In fact, this was accomplished shortly before "isozymes or isoenzymes" became a field of study. LDHC was detected initially in human spermatozoa and spermatogenic cells of the testes by gel electrophoresis. Immunohistochemistry was used to localize LDHC first in early-pachytene primary spermatocytes, with an apparent increase in quantity after meiosis, to its final localization in and on the principal piece of the sperm tail. After several decades of biologic, biochemical, and genetic investigations, we now know that the lactate dehydrogenase isozymes are ubiquitous in vertebrates, developmentally regulated, tissue and cell specific, and multifunctional. Here, we will review the history of LDHC and the work that demonstrates clearly that it is required for sperm to accomplish their ultimate goal, fertilization.

Trypanosoma cruzi: inhibition of alpha-hydroxyacid dehydrogenase isozyme II by N-allyl and N-propyl oxamates and their effects on intact epimastigotes

N-allyl (NAOx) and N-propyl (NPOx) oxamates were designed as inhibitors of alpha-hydroxyacid dehydrogenase (HADH) isozyme II from Trypanosoma cruzi. The kinetic studies showed that NAOx and NPOx were competitive inhibitors of HADH-isozyme II (Ki = 72 microM, IC50 = 0.33 mM and 70 microM, IC50 = 0.32 mM, respectively). The attachment of the allylic and propylic chains to nitrogen of the competitive inhibitor oxamate (Ki = 0.91 mM, IC50 = 4.25 mM), increased 12.6 and 13-folds respectively, the affinity for T. cruzi HADH-isozyme II. NAOx and NPOx were selective inhibitors of HADH-isozyme II, because other T. cruzi dehydrogenases were not inhibited by these substances. Since HADH-isozyme II participates in the energy metabolism of T. cruzi, a trypanocidal effect can be expected with these inhibitors. However, we were not able to detect any trypanocidal activity with these oxamates. When the corresponding ethyl esters of N-allyl (Et-NAOx) and N-propyl (Et-NPOx) oxamates were tested as a possible trypanocidal prodrugs, in comparison with nifurtimox and benznidazole, the expected trypanocidal effects were obtained.