Dicarbonyl L-xylulose reductase (DCXR), a "moonlighting protein" in the bovine epididymis

Molecular Markers: A New Paradigm in the Prediction of Sperm Freezability

For decades now, sperm cryopreservation has been a pillar of assisted reproduction in animals as well as humans. Nevertheless, the success of cryopreservation varies across species, seasons, and latitudes and even within the same individual. With the dawn of progressive analytical techniques in the field of genomics, proteomics, and metabolomics, new options for a more accurate semen quality assessment have become available. This review summarizes currently available information on specific molecular characteristics of spermatozoa that could predict their cryotolerance before the freezing process. Understanding the changes in sperm biology as a result of their exposure to low temperatures may contribute to the development and implementation of appropriate measures to assure high post-thaw sperm quality. Furthermore, an early prediction of cryotolerance or cryosensitivity may lead to the establishment of customized protocols interconnecting adequate sperm processing procedures, freezing techniques, and cryosupplements that are most feasible for the individual needs of the ejaculate.

Moonlighting in drug metabolism

Drug metabolizing enzymes catalyze the biotransformation of many of drugs and chemicals. The drug metabolizing enzymes are distributed among several evolutionary families and catalyze a range of detoxication reactions, including oxidation/reduction, conjugative, and hydrolytic reactions that serve to detoxify potentially toxic compounds. This detoxication function requires that drug metabolizing enzymes exhibit substrate promiscuity. In addition to their catalytic functions, many drug metabolizing enzymes possess functions unrelated to or in addition to catalysis. Such proteins are termed 'moonlighting proteins' and are defined as proteins with multiple biochemical or biophysical functions that reside in a single protein. This review discusses the diverse moonlighting functions of drug metabolizing enzymes and the roles they play in physiological functions relating to reproduction, vision, cell signaling, cancer, and transport. Further research will likely reveal new examples of moonlighting functions of drug metabolizing enzymes.

Fluoride Interferes with the Sperm Fertilizing Ability via Downregulated SPAM1, ACR, and PRSS21 Expression in Rat Epididymis

Fluoride is a widespread environmental pollutant that can induce low sperm quality and fertilizing ability; however, the underlying mechanism still remains unclear. Hence, we aimed to investigate the influence of fluoride on the sperm fertilizing ability via some key proteins in the epididymis. For this, 40 adult rats were assigned randomly into four groups. The control group was given distilled water, while the other three groups were given 25, 50, and 100 mg of NaF/L via drinking water for 56 days, respectively. After 1 day, epididymides were processed for sperm-egg binding, RNA extraction, western blot, and immunofluorescence analysis. Fluoride exposure reduced the ability of sperm to break down the egg cumulus cell layer. A further study revealed that fluoride altered the expression levels of genes and proteins related to acrosome reaction in vivo, including SPAM1, ACR, and PRSS21. However, fluoride only affected the expression of the ACR protein only in the epididymis but not in the testis. Fluoride also affected the expression levels of the membrane proteins CD9 and CD81 of epididymosomes in the epididymis. From the results, it can be concluded that fluoride exposure reduced the ability of sperm to break down the egg cumulus cell layer, which could be one of the reasons for decreased fertility ability in males treated with fluoride. These results provide some theoretical guidance and new ideas for treatments of low fertility, infertility, and other reproductive diseases.

Proteins from male and female reproductive tracts involved in sperm function regulation

Spermatogenesis is a dynamic process that culminates in the production of mature spermatozoa in the seminiferous tubules of sexually mature animals. Although sperm leaving the testis are fully differentiated, they must further undergo two additional maturation steps before acquiring the capability to fertilize the egg. Such processes take place during the epididymal residency and transport in the seminal fluid during ejaculation and, after delivery into the female reproductive tract, during the journey aiming the encountering the egg in the oviduct. Throughout this trip, spermatozoa are exposed to different reproductive fluids whose molecular compositions regulate the progress towards obtaining a fertilized competent cell. This review summarizes the evidence obtained so far supporting the participation of male and female reproductive tract-derived proteins in the modulation of sperm fertilizing ability and discusses the mechanisms by which such regulation may be accomplished.

Changes in Protein O-GlcNAcylation During Mouse Epididymal Sperm Maturation

After leaving the testis, sperm undergo two sequential maturational processes before acquiring fertilizing capacity: sperm maturation in the male epididymis, and sperm capacitation in the female reproductive tract. During their transit through the epididymis, sperm experience several maturational changes; the acquisition of motility is one of them. The molecular basis of the regulation of this process is still not fully understood. Sperm are both transcriptionally and translationally silent, therefore post-translational modifications are essential to regulate their function. The post-translational modification by the addition of O-linked β-N-acetylglucosamine (O-GlcNAc) can act as a counterpart of phosphorylation in different cellular processes. Therefore, our work was aimed to characterize the O-GlcNAcylation system in the male reproductive tract and the occurrence of this phenomenon during sperm maturation. Our results indicate that O-GlcNAc transferase (OGT), the enzyme responsible for O-GlcNAcylation, is present in the testis, epididymis and immature caput sperm. Its presence is significantly reduced in mature cauda sperm. Consistently, caput sperm display high levels of O-GlcNAcylation when compared to mature cauda sperm, where it is mostly absent. Our results indicate that the modulation of O-GlcNAcylation takes place during sperm maturation and suggest a role for this post-translational modification in this process.

Molecular changes and signaling events occurring in spermatozoa during epididymal maturation

After leaving the testis, spermatozoa have not yet acquired the ability to move progressively and are unable to fertilize oocytes. To become fertilization competent, they must go through an epididymal maturation process in the male, and capacitation in the female tract. Epididymal maturation can be defined as those changes occurring to spermatozoa in the epididymis that render the spermatozoa the ability to capacitate in the female tract. As part of this process, sperm cells undergo a series of biochemical and physiological changes that require incorporation of new molecules derived from the epididymal epithelium, as well as post-translational modifications of endogenous proteins synthesized during spermiogenesis in the testis. This review will focus on epididymal maturation events, with emphasis in recent advances in the understanding of the molecular basis of this process.

Luminal fluid of epididymis and vas deferens contributes to sperm chromatin fragmentation

STUDY QUESTION

Do the luminal fluids of the epididymis and the vas deferens contribute to sperm chromatin fragmentation (SCF) in mice?

SUMMARY ANSWER

The luminal fluids of both organs are required for activating SCF in mice, but the vas deferens luminal fluid does this more efficiently than that of the epididymis.

WHAT IS KNOWN ALREADY

Mice sperm have the ability to degrade their DNA in an apoptotic-like fashion when treated with divalent cations in a process termed SCF. SCF has two steps: the induction of reversible double-strand DNA breaks at the nuclear matrix attachment sites, followed by the irreversible degradation of DNA by nuclease. Single stranded DNA breaks accompany SCF.

STUDY DESIGN, SIZE, DURATION

Luminal fluids from two reproductive organs of the mouse (B6D2F1 strain), the epididymis and vas deferens, were extracted and tested for SCF activation with divalent cations using four different combinations of the sperm and the surrounding luminal fluids: (i) in situ--sperm were kept in their luminal fluid and activated directly; (ii) reconstituted--sperm were centrifuged and resuspended in their luminal fluid before SCF activation; (iii) mixed--sperm were centrifuged and resuspended in the luminal fluid of the other organ; (iv) no luminal fluid--sperm were centrifuged and reconstituted in buffer. All four experiments were performed without (controls) and with divalent cations (resulting in SCF). For each experimental condition, two different mice were used and the analyses averaged.

PARTICIPANTS/MATERIALS, SETTING, METHODS

DNA damage by SCF was analyzed by three different methods, the sperm chromatin structure assay (SCSA), terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling (TUNEL) analysis and field inversion gel electrophoresis.

MAIN RESULTS AND THE ROLE OF CHANCE

In all three assays that we used, the vas deferens luminal fluid was much more efficient in stimulating SCF in the sperm from either source than that of the epididymis (P < 0.0001). Vas deferens sperm were capable of initiating lower levels of SCF in the absence of luminal fluid (P < 0.0001).

LIMITATIONS, REASONS FOR CAUTION

Analyses were performed in only one species, the mouse, but we used three separate assays in our analysis.

WIDER IMPLICATIONS OF THE FINDINGS

The data suggest that the luminal fluid of the male reproductive tract interacts with sperm during their transit providing a mechanism to degrade the DNA. We hypothesize that this is part of an apoptotic-like mechanism that allows the reproductive tract to eliminate defective sperm. The SCF model also allowed us to identify differences in the types of DNA lesions that the three tests can identify, providing important background information for the use of these tests clinically.