SummaryRetinal pigment epithelial (RPE) cells are central to retinal health and homoeostasis. Dysfunction or death of RPE cells underlies many age‐related retinal degenerative disorders particularly age‐related macular degeneration. During aging RPE cells decline in number, suggesting an age‐dependent cell loss. RPE cells are considered to be postmitotic, and how they repair damage during aging remains poorly defined. We show that RPE cells increase in size and become multinucleate during aging in C57BL/6J mice. Multinucleation appeared not to be due to cell fusion, but to incomplete cell division, that is failure of cytokinesis. Interestingly, the phagocytic activity of multinucleate RPE cells was not different from that of mononuclear RPE cells. Furthermore, exposure of RPE cells in vitro to photoreceptor outer segment (POS), particularly oxidized POS, dose‐dependently promoted multinucleation and suppressed cell proliferation. Both failure of cytokinesis and suppression of proliferation required contact with POS. Exposure to POS also induced reactive oxygen species and DNA oxidation in RPE cells. We propose that RPE cells have the potential to proliferate in vivo and to repair defects in the monolayer. We further propose that the conventionally accepted ‘postmitotic’ status of RPE cells is due to a modified form of contact inhibition mediated by POS and that RPE cells are released from this state when contact with POS is lost. This is seen in long‐standing rhegmatogenous retinal detachment as overtly proliferating RPE cells (proliferative vitreoretinopathy) and more subtly as multinucleation during normal aging. Age‐related oxidative stress may promote failure of cytokinesis and multinucleation in RPE cells.
Human semen contains spermatozoa as well as populations of round nonspermatozoal cells primarily consisting of leukocytes. Activation of white blood cells present in the seminal plasma during genital tract inflammation and cellular reactions against microbial agents may provoke a release of a variety of products such as cytokines and reactive oxygen species. The aim of this study was to evaluate whether a panel of selected cytokines (interleukin [IL]-1, IL-6, IL-8, and tumor necrosis factor-␣ [TNF␣]) detectable in seminal plasma during male genital tract inflammation could be considered as mediators between altered semen parameters and changed levels of pro-oxidant and antioxidant substances. Studies using chemiluminometric, spectrophotometric, and enzyme-linked immunosorbent assay methods indicate that proinflammatory cytokines such as IL-1, IL-6, IL-8, and TNF␣ may modulate pro-oxidant and antioxidant activities in the male genital tract. The data also suggest that the function of pro-oxidant and antioxidant systems in semen may directly influence basic semen parameters. The elevated numbers of leukocytes present in semen during male genital tract inflammation without an associated contribution of cytokines and semen antioxidant capacity appear to be of little prognostic value in evaluating male fertilization potential.
Epidemiological studies regarding male infertility have revealed that more and more infertile men suffer from acute or chronic inflammation of the genitourinary tract, which often occurs without any symptoms. The inflammatory reactions within the male genital tract are inevitably connected with oxidative stress. Growing evidence indicates that imbalance between prooxidative and antioxidative substances in semen leads to metabolic and functional disorders of male germ cells and may be a primary cause of some types of infertility. The infectious factor and local tissue damage can lead to the infiltration of leukocytes to the inflammatory site. This is in an obvious way connected to the production and release of large amounts of reactive oxygen species (ROS), which trigger immune responses directed against the infectious agent, and the simultaneous secretion of numerous biological substances, thereby escalating the inflammation. Some of these factors are proteases and proinflammatory cytokines. Extended exposure of spermatozoa to ROS may lead to the peroxidation of sperm membrane lipids. Many studies point to the combined activities of inflammatory mediators in exerting toxic effects on spermatozoa. The local influences of biologically active substances released by activated leukocytes in the course of the inflammatory response and the mutual interactions of various factors (bacteria, leukocytes, proinflammatory cytokines) at the site represent a complex puzzle.
The invasion of the male reproductive tract by microorganisms, and its subsequent consequences for sperm fertilizing potential, has been intensely discussed. The role of the bacteria that are responsible for the colonization and contamination of the male urogenital tract, rather than its infection, in diminished sperm parameters raises the most controversy. There are numerous premises suggesting that bacterial semen infection is associated with male infertility. However, the molecular mechanism by which the fertility is affected is complex and multifactorial, and still presents a puzzle. Some authors have suggested that direct interactions between bacteria and human spermatozoa facilitate sperm immobilization, affect sperm morphology, and thus weaken the ability of sperm to fertilize. On the other hand, the massive infiltration of activated leukocytes into the inflammatory site may be associated with impairment of sperm fertilizing potential, due to oxidative, apoptotic, and immune processes. This review presents current research trends and aims to summarize the present knowledge of semen inflammation and causative bacterial agents in the male urogenital tract, with its consequence on seminological parameters, and male fertility status.
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