The Sertoli cell-germ cell interactions and the seminiferous tubule interleukin-1 and interleukin-6 system

MERTK-Mediated LC3-Associated Phagocytosis (LAP) of Apoptotic Substrates in Blood-Separated Tissues: Retina, Testis, Ovarian Follicles

Timely and efficient elimination of apoptotic substrates, continuously produced during one’s lifespan, is a vital need for all tissues of the body. This task is achieved by cells endowed with phagocytic activity. In blood-separated tissues such as the retina, the testis and the ovaries, the resident cells of epithelial origin as retinal pigmented epithelial cells (RPE), testis Sertoli cells and ovarian granulosa cells (GC) provide phagocytic cleaning of apoptotic cells and cell membranes. Disruption of this process leads to functional ablation as blindness in the retina and compromised fertility in males and females. To ensure the efficient elimination of apoptotic substrates, RPE, Sertoli cells and GC combine various mechanisms allowing maintenance of tissue homeostasis and avoiding acute inflammation, tissue disorganization and functional ablation. In tight cooperation with other phagocytosis receptors, MERTK—a member of the TAM family of receptor tyrosine kinases (RTK)—plays a pivotal role in apoptotic substrate cleaning from the retina, the testis and the ovaries through unconventional autophagy-assisted phagocytosis process LAP (LC3-associated phagocytosis). In this review, we focus on the interplay between TAM RTKs, autophagy-related proteins, LAP, and Toll-like receptors (TLR), as well as the regulatory mechanisms allowing these components to sustain tissue homeostasis and prevent functional ablation of the retina, the testis and the ovaries.

A Highly Selective MNK Inhibitor Rescues Deficits Associated with Fragile X Syndrome in Mice

Fragile X syndrome (FXS) is the most common inherited source of intellectual disability in humans. FXS is caused by mutations that trigger epigenetic silencing of the Fmr1 gene. Loss of Fmr1 results in increased activity of the mitogen-activated protein kinase (MAPK) pathway. An important downstream consequence is activation of the mitogen-activated protein kinase interacting protein kinase (MNK). MNK phosphorylates the mRNA cap-binding protein, eukaryotic initiation factor 4E (eIF4E). Excessive phosphorylation of eIF4E has been directly implicated in the cognitive and behavioral deficits associated with FXS. Pharmacological reduction of eIF4E phosphorylation is one potential strategy for FXS treatment. We demonstrate that systemic dosing of a highly specific, orally available MNK inhibitor, eFT508, attenuates numerous deficits associated with loss of Fmr1 in mice. eFT508 resolves a range of phenotypic abnormalities associated with FXS including macroorchidism, aberrant spinogenesis, and alterations in synaptic plasticity. Key behavioral deficits related to anxiety, social interaction, obsessive and repetitive activities, and object recognition are ameliorated by eFT508. Collectively, this work establishes eFT508 as a potential means to reverse deficits associated with FXS.

The Sertoli cell: one hundred fifty years of beauty and plasticity

It has been one and a half centuries since Enrico Sertoli published the seminal discovery of the testicular 'nurse cell', not only a key cell in the testis, but indeed one of the most amazing cells in the vertebrate body. In this review, we begin by examining the three phases of morphological research that have occurred in the study of Sertoli cells, because microscopic anatomy was essentially the only scientific discipline available for about the first 75 years after the discovery. Biochemistry and molecular biology then changed all of biological sciences, including our understanding of the functions of Sertoli cells. Immunology and stem cell biology were not even topics of science in 1865, but they have now become major issues in our appreciation of Sertoli cell's role in spermatogenesis. We end with the universal importance and plasticity of function by comparing Sertoli cells in fish, amphibians, and mammals. In these various classes of vertebrates, Sertoli cells have quite different modes of proliferation and epithelial maintenance, cystic vs. tubular formation, yet accomplish essentially the same function but in strikingly different ways.

Opposite regulation of connexin33 and connexin43 by LPS and IL-1α in spermatogenesis

The gap junction proteins, connexins (Cxs), are present in the testis, and among them, Cx43 play an essential role in spermatogenesis. In the present study, we investigated the testicular expression and regulation of another Cx, Cx33, previously described as a negative regulator of gap junction communication. Cx33 mRNA was present in testis and undetectable in heart, liver, ovary, and uterus. In the mature testis, Cx33 was specifically immunolocalized in the basal compartment of the seminiferous tubules, whereas Cx43 was present in both seminiferous tubule and interstitial compartments. During stages IX and X of spermatogenesis, characterized by Sertoli cell phagocytosis of residual bodies, Cx43 was poorly expressed within seminiferous tubules, while Cx33 signal was strong. To evaluate the role of phagocytosis in the control of Cx33 and Cx43 expression, the effect of LPS was analyzed in the Sertoli cell line 42GPA9. We show herein that phagocytosis activation by LPS concomitantly stimulated Cx33 and inhibited Cx43 mRNA levels. These effects appear to have been mediated through IL-1α, because the exposure of Sertoli cells to the IL-1 receptor antagonist partly reversed these effects. IL-1α enhanced and reduced, respectively, the levels of Cx33 and Cx43 mRNA in a time- and dose-dependent manner. These data reveal that Cx33 and Cx43 genes are controlled differently within the testis and suggest that these two Cxs may exert opposite and complementary effects on spermatogenesis.

Endotoxin and proinflammatory cytokines modulate Sertoli cell proliferation in vitro

Sertoli cells play a key role in testicular function and their final number in the adult testis determines the capacity of germ cell production. Sertoli cell proliferation, stimulated by FSH and paracrine factors, occurs only in fetal and prepubertal life and may be an important target of pathogenic influences affecting testis development. We used a Sertoli cell proliferation assay to address the question whether if bacterial endotoxin (lipopolysaccharide; LPS) and proinflammatory cytokines could influence early postnatal Sertoli cell development. LPS and tumor necrosis factor-alpha (TNF-alpha) dose-dependently stimulated proliferation of primary cultures of isolated Sertoli cells from 8- to 9-day-old rats, assessed by (3)H-thymidine and BrdU incorporation. LPS also significantly increased the number of living cells in culture, measured by supravital staining. Interleukin-6 (IL-6) and interferon-gamma (IFN-gamma) had no direct effect on Sertoli cell growth, but were found to modulate FSH action. IL-6 increased, while IFN-gamma inhibited, FSH-induced Sertoli cell DNA-synthesis. We conclude that endotoxin and TNF-alpha are potent direct stimulators of Sertoli cell proliferation in vitro, and that IL-6 and IFN-gamma can modulate the mitogenic action of FSH on immature Sertoli cells. This may contribute to the pathogenesis of testicular damage after infections and inflammatory diseases in fetal and early postnatal life, with subsequent disturbance of adult germ cell production.

Testicular macrophage modulation of Leydig cell steroidogenesis

This review will highlight recent advances in the study of the immuno-endocrinology of the testis, in particular how macrophage-derived inflammatory mediators affect Leydig cell functions. Both the beneficial and deleterious outcomes resulting from macrophage-Leydig cell interactions are discussed. A brief overview of testicular physiology is provided that discusses the functional and anatomical compartmentalization of the testis into the gamete and endocrine compartments where spermatogenesis and testosterone biosynthesis take place, respectively. The process of steroidogenesis including the activities of the steroidogenic enzymes and the role of steroidogenic acute regulatory protein (StAR) are described. The close physical association between Leydig cells and interstitial testicular macrophages suggests that these cells are functionally related. Under normal physiological and non-inflammatory conditions macrophages play an important role in Leydig cell development. If macrophages are absent from the testicular interstitium, Leydig cells fail to develop normally, which suggest that macrophages provide essential growth and differentiation factors for Leydig cells. In contrast, when macrophages are activated and elaborate inflammatory mediators, Leydig cell steroidogenesis is inhibited. Activated macrophages produce pro-inflammatory cytokines such as interleukin-1 (IL-1) and tumor necrosis factor (TNF) that are profoundly inhibitory to Leydig cells and appear to act as transcriptional repressors of steroidogenic enzyme gene expression. Macrophages also produce reactive oxygen species (ROS) such as hydrogen peroxide, which also inhibits Leydig cell functions. ROS appear to act acutely by perturbing Leydig cell mitochondria resulting in the inhibition of StAR protein expression. One important consequence of this immune modulation of Leydig cell function may be manifest behaviorally by switching the affected animal from 'testosterone' behavior, to 'sickness' behavior. Increased interest in immune-endocrine control of reproductive function over the past decade has stimulated research into the molecular and biochemical immunopathophysiology of the reproductive system. As investigations unravel mechanisms underlying reproductive dysfunction caused by inflammation and infection, an understanding of the role that immune-endocrine interactions play in the normal physiology of the reproductive system has emerged.