In the male genital tract, reactive oxygen species (ROS) are generated by spermatozoa and leukocytes including neutrophils and macrophages. ROS are involved in the regulation of sperm functions such as capacitation and the acrosome reaction. Infections lead to an excessive ROS production, resulting in an 'oxidative burst' from neutrophils/macrophages as a first-line defence mechanism. This is modulated by several cytokines and the pro-oxidant mechanisms of bacteria and viruses. At the site of an infection, the degree of activation of leukocytes, i.e. the amount of ROS produced, and the available antioxidative systems determine whether spermatozoa are damaged or not. During an infection, an imbalance of pro- and antioxidants favouring the former results in oxidative stress which impairs the sperm functions mentioned, as well as motility and fertilization. ROS produced during infections of the testis and epididymis are especially harmful to spermatozoa due to the longer contact time and the lack of antioxidant protection. In the final ejaculate, only very high numbers of ROS-producing leukocytes are detrimental to sperm functions. An infectious injury involving ROS in the prostate gland, seminal vesicles or epididymis could impair sperm functions indirectly. Pro- and antioxidative properties of therapeutics are currently receiving more attention as part of anti-infectious therapies. At present, there are many unresolved questions concerning the exact role of ROS during infections of the male genital tract because of the difficulty of specifically assessing the site of generation and the short-lived effects of ROS. New techniques may enable specific studies to fill this gap in the near future.

Infections in the male genital tract and reactive oxygen species

Neisseria gonorrhoeae is capable of iron utilization from human transferrin in a receptor-mediated event. Transferrin-binding protein 1 (Tbp1) and Tbp2 have been implicated in transferrin receptor function, but their specific roles in transferrin binding and transferrin iron utilization have not yet been defined. We utilized specific gonococcal mutants lacking Tbp1 or Tbp2 to assess the relative transferrin-binding properties of each protein independently of the other. The apparent affinities of the wild-type transferrin receptor and of Tbp1 and Tbp2 individually were much higher than previously estimated for the gonococcal receptor and similar to the estimates for the mammalian transferrin receptor. The binding parameters of both of the mutants were distinct from those of the parent, which expressed two transferrin-binding sites. Tbp2 discriminated between ferrated transferrin and apotransferrin, while Tbp1 did not. Results of transferrin-binding affinity purification, and protease accessibility experiments were consistent with the hypothesis that Tbp1 and Tbp2 interact in the wild-type strain, although both proteins were capable of binding to transferrin independently when separated in the mutants. The presence of Tbp1 partially protected Tbp2 from trypsin proteolysis, and Tbp2 also protected Tbp1 from trypsin exposure. Addition of transferrin to wild-type but not mutant cells protected Tbp1 from trypsin but increased the trypsin susceptibility of Tbp2. These observations indicate that Tbp1 and Tbp2 function together in the wild-type strain to evoke binding conformations that are distinct from those expressed by the mutants lacking either protein.

Binding and surface exposure characteristics of the gonococcal transferrin receptor are dependent on both transferrin-binding proteins.

Iron and copper are essential trace nutrients playing important roles in general health and fertility. However, both elements are highly toxic when accumulating in large quantities. Their direct or indirect impact on the structure and function of male gonads and gametes is not completely understood yet. Excess or deficiency of either element may lead to defective spermatogenesis, reduced libido, and oxidative damage to the testicular tissue and spermatozoa, ultimately leading to fertility impairment. This review will detail the complex information currently available on the dual roles iron and copper play in male reproduction.

Iron and copper in male reproduction: a double-edged sword.

Soluble transferrin receptor (sTfR), one of the main regulators of cellular iron homeostasis, is the truncated form of the tissue receptor that is encoded by the human TfR gene (chromosome 3). Serum sTfR levels are determined to detect iron deficiency (ID) in inflammatory states and in anemia of chronic disease (ACD) and to monitor the efficiency of erythropoietin (EPO) treatment. The levels of sTfR reflect the receptor density on cells (tissue iron status) and the number of cells with receptors (erythropoietic activity). Currently assays for the measurements of sTfR are standardized using different reference materials, give different results, and have different reference ranges. The recent development of a lyophilized preparation of recombinant soluble transferrin receptor (rsTfR) as a World Health Organization (WHO) reference reagent should help in the standardization of sTfR immunoassays. This article reviews the general characteristics of (s)TfR, the assays for sTfR, biological confounders in the assays, and the clinical applications for measuring sTfR

Biological and clinical aspects of soluble transferrin receptor

Mammals and Drosophila melanogaster share some striking similarities in spermatogenesis. Mitochondria in spermatids undergo dramatic morphological changes and syncytial spermatids are stripped from their cytoplasm and then individually wrapped by single membranes in an individualization process. In mammalian and fruit fly testis, components of the mitochondrial iron metabolism are expressed, but so far their function during spermatogenesis is unknown. Here we investigate the role of Drosophila mitoferrin (dmfrn), which is a mitochondrial carrier protein with an established role in the mitochondrial iron metabolism, during spermatogenesis. We found that P-element insertions into the 5'-untranslated region of the dmfrn gene cause recessive male sterility, which was rescued by a fluorescently tagged transgenic dmfrn genomic construct (dmfrn
 venus
 ). Testes of mutant homozygous dmfrn
 SH115
 flies were either small with unorganized content or contained some partially elongated spermatids, or testes were of normal size but lacked mature sperm. Testis squashes indicated that spermatid elongation was defective and electron micrographs showed mitochondrial defects in elongated spermatids and indicated failed individualization. Using a LacZ reporter and the dmfrn
 venus
 transgene, we found that dmfrn expression in testes was highest in spermatids, coinciding with the stages that showed defects in the mutants. Dmfrn-venus protein accumulated in mitochondrial derivatives of spermatids, where it remained until most of it was stripped off during individualization and disposed of in waste bags. Male sterility in flies with the hypomorph alleles dmfrn
 BG00456
 and dmfrn
 EY01302
 over the deletion Df(3R)ED6277 was increased by dietary iron chelation and suppressed by iron supplementation of the food, while male sterility of dmfrn
 SH115
 /Df(3R)ED6277 flies was not affected by food iron levels. In this work, we show that mutations in the Drosophila mitoferrin gene result in male sterility caused by developmental defects. From the sensitivity of the hypomorph mutants to low food iron levels we conclude that mitochondrial iron is essential for spermatogenesis. This is the first time that a link between the mitochondrial iron metabolism and spermatogenesis has been shown. Furthermore, due to the similar expression patterns of some mitochondrial iron metabolism genes in Drosophila and mammals, it is likely that our results are applicable for mammals as well.

/pdf/drosophila-mitoferrin-is-essential-for-male-fertility-30l101lx1d.pdf

William G. Wood

Papers

Ceruloplasmin and transferrin in human seminal plasma: are they an index of seminiferous tubular function?