Proteomic analysis of testis biopsies in men treated with transient scrotal hyperthermia reveals the potential targets for contraceptive development

The role of HnrnpF/H as a driver of oligoteratozoospermia

Male subfertility or infertility is a common condition often characterized by men producing a low number of sperm with poor quality. To gain insight into this condition, we performed a quantitative proteomic analysis of semen samples obtained from infertile and fertile men. At least 6 proteins showed significant differences in regulation of alternatively spliced isoforms. To investigate this link between aberrant alternative splicing and production of poor-quality spermatozoa, we overexpressed the hnrnpH/F-orthologue Glorund (Glo) in Drosophila, which was also found to be abundant in poor quality human sperm. Transgenic animals produced low numbers of morphologically defective spermatozoa and aberrant formation of the "dense body," an organelle akin to the mammalian manchette. Furthermore, fertility trials demonstrated that transgenic flies were either completely infertile or highly subfertile. These findings suggest that dysregulation of hnrnpH/F is likely to result in the production of low-quality semen, leading to subfertility or infertility in men.

Stereological study of testes following experimentally-induced unilateral cryptorchidism in rats

OBJECTIVE

Cryptorchidism is one of the main causes of infertility and can result in testicular cancer. This study aimed to present quantitative data on the damage caused by cryptorchidism using stereological analysis.

METHODS

Thirty newborn rats were randomly divided into control and experimental groups. The experimental group underwent surgery to induce unilateral cryptorchidism in the left testis, whereas the control group underwent a sham surgical procedure 18 days after birth. The testes were removed at designated time points (40, 63, and 90 days after birth) for stereological evaluation and sperm analysis. Total testicular volume, interstitial tissue volume, seminiferous tubule volume and length, and seminiferous epithelium volume and surface area were measured. Other parameters, such as sperm count, sperm morphology, and sperm tail length, were also examined.

RESULTS

Statistically significant differences (p<0.05) were observed between the experimental and the control groups at different ages regarding the volumes of various parameters, including the surface area of the germinal layer, the length of the seminiferous tubules, sperm count, and sperm morphology. However, no significant differences were observed in the epithelial volume and the sperm tail length of the groups.

CONCLUSION

Given the substantial effect of cryptorchidism on different testicular parameters, as well as the irreversible damage it causes in the testes, it is important to take this abnormality seriously to prevent these consequences.

Testicular heat stress, a historical perspective and two postulates for why male germ cells are heat sensitive

Herein, we compare the different experimental regimes used to induce testicular heat stress and summarise their impact on sperm production and male fertility. Irrespective of the protocol used, scrotal heat stress causes loss of sperm production. This is first seen 1-2 weeks post heat stress, peaking 4-5 weeks thereafter. The higher the temperature, or the longer the duration of heat, the more pronounced germ cell loss becomes, within extreme cases this leads to azoospermia. The second, and often underappreciated impact of testicular hyperthermia is the production of poor-quality spermatozoa. Typically, those cells that survive hyperthermia develop into morphologically abnormal and poorly motile spermatozoa. While both apoptotic and non-apoptotic pathways are known to contribute to hyperthermic germ cell loss, the mechanisms leading to formation of poor-quality sperm remain unclear. Mechanistically, it is unlikely that testicular hyperthermia affects messenger RNA (mRNA) abundance, as a comparison of four different mammalian studies shows no consistent single gene changes. Using available evidence, we propose two novel models to explain how testicular hyperthermia impairs sperm formation. Our first model suggests aberrant alternative splicing, while the second model proposes a loss of RNA repression. Importantly, neither model requires consistent changes in RNA species.

Heat stress response of somatic cells in the testis

The testis is a temperature-sensitive organ that needs to be maintained 2-7 °C below core body temperature to ensure the production of normal sperm. Failure to maintain testicular temperature in mammals impairs spermatogenesis and leads to low sperm counts, poor sperm motility and abnormal sperm morphology in the ejaculate. This review discusses the recent knowledge on the response of testicular somatic cells to heat stress and, specifically, regarding the relevant contributions of heat, germ cell depletion and inflammatory reactions on the functions of Sertoli and Leydig cells. It also outlines mechanisms of testicular thermoregulation, as well as the thermogenic factors that impact testicular function.

TULP2, a New RNA-Binding Protein, Is Required for Mouse Spermatid Differentiation and Male Fertility

Spermatogenesis requires a large number of proteins to be properly expressed at certain stages, during which post-transcriptional regulation plays an important role. RNA-binding proteins (RBPs) are key players in post-transcriptional regulation, but only a few RBPs have been recognized and preliminary explored their function in spermatogenesis at present. Here we identified a new RBP tubby-like protein 2 (TULP2) and found three potential deleterious missense mutations of Tulp2 gene in dyszoospermia patients. Therefore, we explored the function and mechanism of TULP2 in male reproduction. TULP2 was specifically expressed in the testis and localized to spermatids. Studies on Tulp2 knockout mice demonstrated that the loss of TULP2 led to male sterility; on the one hand, increases in elongated spermatid apoptosis and restricted spermatid release resulted in a decreased sperm count; on the other hand, the abnormal differentiation of spermatids induced defective sperm tail structures and reduced ATP contents, influencing sperm motility. Transcriptome sequencing of mouse testis revealed the potential target molecular network of TULP2, which played its role in spermatogenesis by regulating specific transcripts related to the cytoskeleton, apoptosis, RNA metabolism and biosynthesis, and energy metabolism. We also explored the potential regulator of TULP2 protein function by using immunoprecipitation and mass spectrometry analysis, indicating that TUPL2 might be recognized by CCT8 and correctly folded by the CCT complex to play a role in spermiogenesis. Our results demonstrated the important role of TULP2 in spermatid differentiation and male fertility, which could provide an effective target for the clinical diagnosis and treatment of patients with oligo-astheno-teratozoospermia, and enrich the biological theory of the role of RBPs in male reproduction.

Effect of transient scrotal hyperthermia on human sperm: an iTRAQ-based proteomic analysis

BACKGROUND

Through this prospective study, we aimed to explore the change of molecular modification after the transient scrotal hyperthermia on human sperm.

METHODS

Ten healthy subjects selected with strict screening criteria underwent testicular warming in a 43 °C water bath for 30 min a day for 10 consecutive days. Semen samples were collected 2 weeks before the first heat treatment and 6 weeks after the first heat treatment. Proteins from the samples were labeled with isobaric tags for relative and absolute quantitation and analyzed by two-dimensional liquid chromatography-tandem mass spectrometry.

RESULTS

In contrast to the control, of the 3446 proteins identified, 61 proteins were deregulated: 28 were up-regulated and 33 were down-regulated. Approximately 95% of the differentially expressed proteins were found to participate in spermatogenesis, fertilization, or other aspects of reproduction. In particular, the expression of sperm motility and energy metabolism-related proteins AKAP4, SPESP1, ODF1, ODF2, GAPDHS, and ACTRT2, validated by western blotting of the proteins obtained from human and mouse samples, tended to be reduced under scrotal hyperthermia.

CONCLUSIONS

The results indicated that the proteins AKAP4, ODF1, ODF2, GAPDHS, SPESP1, and ACTRT2, play an important role in the heat-induced reversible reduction in sperm concentration and motility and have the potential to be the biomarkers and clinical targets for scrotal heat treatment induced male infertility.

Cold-induced RNA-binding protein (CIRBP) regulates the expression of Src-associated during mitosis of 68 kDa (Sam68) and extracellular signal-regulated kinases (ERK) during heat stress-induced testicular injury

In this study, the ability of cold-induced RNA-binding protein (CIRBP) to regulate the expression of Src-associated during mitosis of 68 kDa (Sam68) and extracellular signal-regulated kinases (ERK) in the mouse testis and mouse primary spermatocytes (GC-2spd cell line) before and after heat stress was examined to explore the molecular mechanism by which CIRBP decreases testicular injury. A mouse testicular hyperthermia model, a mouse primary spermatocyte hyperthermia model and a low CIRBP gene-expression cell model were constructed and their relevant parameters were analysed. The mRNA and protein levels of CIRBP and Sam68 were significantly decreased in the 3-h and 12-h testicular heat-stress groups, extracellular signal-regulated kinase 1/2 (ERK1/2) protein expression was not significantly affected but phospho-ERK1/2 protein levels were significantly decreased. GC-2spd cellular heat-stress results showed that the mRNA and protein concentrations of CIRBP and Sam68 were reduced 48h after heat stress. In the low CIRBP gene-expression cell model, CIRBP protein expression was significantly decreased. Sam68 mRNA expression was significantly decreased only at the maximum transfection concentration of 50nM and Sam68 protein expression was not significantly affected. These findings suggest that CIRBP may regulate the expression of Sam68 at the transcriptional level and the expression of phospho-ERK1/2 protein, both of which protect against heat-stress-induced testicular injury in mice.

14-3-3 epsilon plays an important role in testicular germ cell apoptosis: A functional proteomic study of experimental varicocele

The latest perspective indicates that apoptotic dysregulation is an important mechanism in male infertility induced by varicocele. To elucidate the molecular mechanism of apoptosis caused by varicocele, we used proteomics (2D-MALDI-TOF MS) to identify the altered proteins in the testes of experimental varicocele rats compared with the control. Here, 21 significantly different protein spots were detected by proteomics technology. 14-3-3 epsilon (14-3-3ε) was our subsequent research target because of its function in apoptosis. The expression of 14-3-3ε in rat testes was confirmed by Western blot and immunohistochemistry, and the terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) method was used to analyse the apoptosis of germ cells. GC-1 spg cells transfected with small interfering RNA were used to confirm the function of 14-3-3ε in vitro. 14-3-3ε protein expression decreased, accompanied by a higher apoptosis index in rat testes of the varicocele group. Furthermore, 14-3-3ε siRNA-treated GC-1 spg cells caused the upregulation of the apoptotic rate detected by flow cytometry. The expression of Bax and Bcl-2 was found to be regulated by 14-3-3ε in vitro. Our investigation demonstrated the pro-apoptotic function of the downregulation of 14-3-3ε, which may play an important role in germ cell apoptosis induced by varicocele.

Effects of cold-inducible RNA-binding protein on the proliferation and apoptosis of spermatogenic cells in vitro following heat stress

Cold-inducible RNA-binding protein (CIRBP) is reduced by scrotal hyperthermia in cryptorchidism, varicocoele and heat treatment, but there is no direct evidence clarifying the relationship between CIRBP and spermatogenesis. The aim of this study was to investigate the expression of CIRBP in GC2-spd cells (a mouse spermatocyte cell line) before and after heat treatment, and to determine the effects of the downregulation or overexpression of CIRBP on spermatocyte cell proliferation and apoptosis. GC2-spd cells overexpressing CIRBP and GC2-spd cells in CIRBP was knocked down were constructed to investigate the function of CIRBP in cell proliferation and apoptosis using a cell counting kit-8 and flow cytometry respectively. In addition, proliferation and apoptosis were evaluated in GC2-spd cells that had been heated for 30 or 60min, and were analysed 12, 24, and 48h after heat treatment. Heat treatment clearly suppressed the proliferation of GC2-spd cells, and upregulation of CIRBP expression in GC2-spd cells promoted cell proliferation and decreased apoptosis before and after heat stress; in contrast, downregulation of CIRBP expression inhibited cell proliferation and increased apoptosis. These findings suggest that CIRBP exerts a protective effect against spermatogenic injury caused by heat stress.

The regulation of CIRBP by transforming growth factor beta during heat shock-induced testicular injury

BACKGROUND

Cold-inducible RNA-binding protein (CIRBP) is associated with cell stress. However, its upstream regulatory factors are still largely unknown.

OBJECTIVES

This study investigated whether CIRBP expression was regulated by transforming growth factor beta (TGF-β) during the process of heat-induced testicular damage.

MATERIALS AND METHODS

Ten male adult ICR mice were allocated to heat treatment (scrotal hyperthermia at 43 °C for 30 min, n = 5) and control group (n = 5); CIRBP and TGF-β1, TGF-β2, and TGF-β3 expression levels in the testis in mRNA and protein were analyzed. Then, we conducted in vivo and in vitro studies to investigate the regulatory effects of TGF-β on CIRBP. In the in vivo study, male adult ICR mice were subjected to testicular hyperthermia followed by a local testicular injection of TGF-β antagonist (non-selective TGF-β I/II receptor inhibitor, 5 μg or 10 μg). In the in vitro study, GC2-spd cells were cultured under 43 °C for 30 min or with different TGF-β isoforms (10 ng/mL), and CIRBP expression levels in the testis and GC2-spd cells were analyzed 24 and 48 h, respectively, after treatment.

RESULTS

As a result, heat treatment significantly downregulated the relative CIRBP mRNA and protein expression (p = 0.006 and 0.011), and significantly upregulated TGF-β2 and TGF-β3 expression levels (p = 0.022 and 0.04, for mRNA, and p = 0.001 for both protein levels). Local testicular injection of 10 μg TGF-β antagonist significantly attenuated heat-induced histological damage to the testes and CIRBP downregulation (p = 0.038). Furthermore, TGF-β2 and TGF-β3 significantly downregulated CIRBP mRNA and protein expression in GC2-spd cells (all p < 0.01), exerting a similar effect to heat treatment.

DISCUSSION AND CONCLUSION

Our in vivo and in vitro experiments demonstrated that heat-induced CIRBP downregulation in the testes was mediated by the upregulation of TGF-β. Further studies are needed to clarify the molecular mechanisms underlying these processes.

Acute Heat Stress Changes Protein Expression in the Testes of a Broiler-Type Strain of Taiwan Country Chickens

Heat stress leads to decreased fertility in roosters. This study investigated the global protein expression in response to acute heat stress in the testes of a broiler-type strain of Taiwan country chickens (TCCs). Twelve 45-week-old roosters were randomly allocated to the control group maintained at 25°C, and three groups subjected to acute heat stress at 38°C for 4 h, with 0, 2, and 6 h of recovery, respectively. Testis samples were collected for hematoxylin and eosin staining, apoptosis assay, and protein analysis. The results revealed 101 protein spots that differed significantly from the control following exposure to acute heat stress. The proteins that were differentially expressed participated mainly in protein metabolism and other metabolic processes, responses to stimuli, apoptosis, cellular organization, and spermatogenesis. Proteins that negatively regulate apoptosis were downregulated and proteins involved in autophagy and major heat shock proteins (HSP90α, HSPA5, and HSPA8) were upregulated in the testes of heat-stressed chickens. In conclusion, acute heat stress causes a change in protein expression in the testes of broiler-type B strain TCCs and may thus impair cell morphology, spermatogenesis, and apoptosis. The expression of heat shock proteins increased to attenuate the testicular injury induced by acute heat stress.

Protective effect of calretinin on testicular Leydig cells via the inhibition of apoptosis

The core mechanism of Late-onset hypogonadism (LOH) is the deficiency of androgen due to the functional and quantitative decline of testicular Leydig cells. Here we explored the protective effect of calretinin, a Ca²⁺-binding protein, on Leydig cells. We found in MLTC-1 cells transfected with LV-calb2, the cell viability and optical density (OD) were higher (p<0.05), cells in the S phase of the cell cycle were increased (p<0.01) and p-ERK1/2 and p-AKT levels were significantly higher (p<0.01 and p<0.05), while in R2C cells transfected with LV-siRNA-calb2, all of the results mentioned above were adverse (p<0.05). The cell apoptotic index after calretinin over-expressed was significantly lower (p<0.001), while the expression levels of mitochondria-related apoptotic factors such as cleaved caspase-9 and cytochrome C (cyto C) were lower and ratio of Bcl2/Bax was higher (p<0.05). After calretinin down-regulated, the apoptotic index was higher (p<0.05), while the expression levels of mitochondria-related apoptotic factors were higher and the ratio of Bcl2/Bax was lower (p<0.05). Therefore, calretinin increases Leydig cell viability and proliferation, possibly via ERK1/2 and AKT pathways, and suppresses apoptosis possibly via the mitochondria-related apoptotic pathway, which could be beneficial in understanding the pathophysiology of LOH and could lead to the study of new treatments.

Effect of Seasonal Change on Testicular Protein Expression in White Roman Geese

The purpose of this study was to investigate the change in protein expression in the testes of ganders at various breeding stages. A total of nine 3-year-old male White Roman ganders were used. The blood and testis samples were collected at the nonbreeding, sexual reactivation, and breeding stages for sex hormone analysis and proteomic analysis, respectively. The testicular weight and serum testosterone observed for ganders at the breeding stage were higher than those for ganders at nonbreeding and sexual reactivation stages (P < 0.05). There were 124 protein spots differentially expressed in the testes of ganders at various reproductive stages. A total of 107 protein spots of 74 proteins was identified through mass spectrometry. Most of the differentially expressed proteins were responsible for the molecular functions of protein binding (24%) and catalytic activity (16%). A functional pathway analysis suggested that proteins involved in steroidogenesis, metabolism, and spermatogenesis pathways changed in the White Roman geese at various reproductive stages. In conclusion, ganders at various reproductive stages exhibited different levels of testosterone and protein expression in the testes. The varied levels of the proteins might be essential and unique key factors in seasonal reproduction in ganders.

Isobaric tags for relative and absolute quantification-based proteomic analysis of testis biopsies in rhesus monkeys treated with transient scrotal hyperthermia

This study aimed to examine the cellular and molecular events that occur in rhesus monkey testes after scrotal hyperthermia. Eight male adult rhesus monkeys were subjected to scrotal hyperthermia at 43°C for 30 min daily for 6 consecutive days. Sperm concentration, reproductive hormones, and testis histology were examined before hyperthermia (day 0), and at 8, 15, 30, 45, 60, 75, and 90 days after the initiation of hyperthermia. iTRAQ-based proteomic analysis was conducted on testicular tissues collected on days 0, 8, and 60 to identify differentially expressed proteins at the early and recovery stages of testicular damage. The sperm concentration was significantly decreased at days 30 and 45 after treatment (p < 0.01) and recovered to baseline at day 60. When compared with day 0, 101 and 24 differentially expressed proteins were identified at days 8 and 60 after heat treatment, respectively. The molecular functions of the differentially expressed proteins at day 8 were mainly nucleic acid binding, unfolded protein binding, nucleotide binding, and nucleoside phosphate binding. Spliceosome was enriched as the most significant pathway at day 8. CIRBP, PSIP1, Sam68, and Decorin were validated and found to be consistent with the proteomic data, indicating the reliability of the proteomic profiles identified in this study. In summary, we suggest that the proteins identified in this study may play important roles in heat-induced spermatogenic impairment. Some of these proteins, such as CIRBP, PSIP1, Sam68, and Decorin, may be early molecular targets responsible for spermatogenesis suppression induced by heat treatment.

Hormonal, chemical and thermal inhibition of spermatogenesis: contribution of French teams to international data with the aim of developing male contraception in France

Since the 1970s, international research on male contraception has been actively pursued. Hormonal and non-hormonal methods (thermal, chemical) have been tested, leading to clinical trials of interest to thousands of men and couples. The results showed that it was possible to develop methods of male contraception that inhibited spermatogenesis with good contraceptive efficacy. However, their side effects (mainly loss of libido), poorly accepted modes of administration, and the high frequency of poor responders prevented their widespread use. Based on earlier initiatives, new avenues were explored and significant progress was achieved, allowing the reasoned use of male contraception. For 40 years, several French teams have played an important role in this research. The aim of this paper is to outline the history and the progress of the experimental and clinical works of these teams who addressed hormonal, chemical and thermal approaches to male contraception. These approaches have led to a better comprehension of spermatogenesis that could be useful in fields other than male contraception: effects of toxic compounds, fertility preservation.

Specific autoantigens identified by sera obtained from mice that are immunized with testicular germ cells alone

There are various autoimmunogenic antigens (AIs) in testicular germ cells (TGCs) recognized as foreign by the body's immune system. However, there is little information of TGC-specific AIs being available. The aim of this study is to identify TGC-specific AIs. We have previously established that immunization using viable syngeneic TGC can also induce murine experimental autoimmune orchitis (EAO) without using any adjuvant. This study is to identify TGC-specific AIs by TGC liquid chromatography-tandem mass spectrometry analysis, followed by two-dimensional gel electrophoresis that reacted with serum IgG from EAO mice. In this study, we identified 11 TGC-specific AIs that reacted with serum from EAO mice. Real-time RT-PCR analysis showed that the mRNA expressions of seven TGC-specific AIs were significantly higher in only mature testis compared to other organs. Moreover, the recombinant proteins of identified 10 (except unnamed protein) TGC-specific AIs were created by using human embryonic kidney 293 (HEK293) cells and these antigencities were reconfirmed by Western blot using EAO serum reaction. These results indicated Atp6v1a, Hsc70t, Fbp1 and Dazap1 were candidates for TGC-specific AIs. Identification of these AIs will facilitate new approaches for understanding infertility and cancer pathogenesis and may provide a basis for the development of novel therapies.

Changes in Levels of Seminal Nitric Oxide Synthase, Macrophage Migration Inhibitory Factor, Sperm DNA Integrity and Caspase-3 in Fertile Men after Scrotal Heat Stress

Background

This study observes changes in levels of seminal nitric oxide (NO), nitric oxide synthase (NOS), macrophage migration inhibitory factor (MIF), sperm DNA integrity, chromatin condensation and Caspase-3in adult healthy men after scrotal heat stress (SHS).

Methods

Exposure of the scrotum of 25 healthy male volunteers locally at 40–43°C SHS belt warming 40 min each day for successive 2 d per week. The course of SHS was continuously 3 months. Routine semen analysis, hypo-osmotic swelling (HOS) test, Aniline blue (AB) staining, HOS/AB and terminal deoxynucleotidyl transferase-mediated d UDP nick-end labeling (TUNEL) were carried out before, during and after SHS. Seminal NO and NOS contents were determined by nitrate reduction method. The activated Caspase-3 levels of spermatozoa and MIF in seminal plasma were measured by the enzyme-linked immunosorbent assay (ELISA) method. Statistical significance between mean values was determined using statistical ANOVA tests.

Results

The mean parameters of sperm concentration, motile and progressive motile sperm and normal morphological sperm were significantly decreased in groups during SHS 1, 2 and 3 months compared with those in groups of pre-SHS (P<0.001). Statistically significant differences of sperm DNA fragmentation, normal sperm membrane, and Caspase-3 activity as well as the level of NO, NOS and MIF in semen were observed between the groups before SHS and after SHS 3 months and the groups during SHS 1, 2 and 3 months (P<0.001). After three months of the SHS, various parameters recovered to the level before SHS. WBC in semen showed a positively significant correlation with the levels of NO, NOS, MIF and Caspase-3 activity. The percentage of abnormal sperm by using the test of HOS showed a positively significant correlation with that of HOS/AB.

Conclusions

The continuously constant SHS can impact the semen quality and sperm DNA and chromatin, which may be contributed to the high level of NO, NOS, MIF and Caspase-3 by SHS.

SHCBP1L, a conserved protein in mammals, is predominantly expressed in male germ cells and maintains spindle stability during meiosis in testis

Male subfertility due to falling sperm counts has become an increasing problem over a short timescale (50-70 years). Recently, bioinformatics analysis of the human testis proteome has revealed the existence of human-testicular-predominantly-expressed-proteins, which are highly associated with spermatogenesis, although the functions of many of these proteins are still unknown. To understand the function of one of these proteins, SHCBP1L (1700012A16RIKEN), a knockout mouse was produced in which this gene was removed. Using this model, we showed that SHCBP1L binds to another protein, HSPA2, and maintains stability of the spindle. We showed that this complex was not present in knockout mice and that an abnormal number of spermatocytes were held in the early stages of meiosis. Many of these cells were undergoing programmed cell-death, or apoptosis, which is highly unusual for cells during the early stages of meiosis. We also found that proteins very similar to SHCBP1L exist in many other mammals. This led us to propose that SHCBP1L plays an important role in spermatogenesis in mammals.

Heat stress response of male germ cells

The vast majority of mammalian testes are located outside the body cavity for proper thermoregulation. Heat has an adverse effect on mammalian spermatogenesis and eventually leads to sub- or infertility. Recent studies have provided insights into the molecular response of male germ cells to high temperatures. Here, we review the effects of heat on male germ cells and discuss the mechanisms underlying germ cell loss and impairment. We also discuss the role of translational control in male germ cells as a potential protective mechanism against heat-induced germ cell apoptosis.

Transient scrotal hyperthermia induces lipid droplet accumulation and reveals a different ADFP expression pattern between the testes and liver in mice

BACKGROUND

In most mammals, the testes provide a stable environment for spermatogenesis, which depends on a lower temperature than the core body temperature. It has been reported that mild testicular heating safely and reversibly suppresses spermatogenesis, and is under consideration for its potential application as a male contraceptive. Previously, we focused on the molecular mechanism of germ cell apoptosis and anti-apoptotic factors induced by heat treatment in humans and mice. However, the recovery process remains under investigation.

RESULTS

In this study, we found that lipid droplets in mouse testes are dramatically increased after a brief period of scrotal hyperthermia, and gradually dissipate following temperature normalization. Analysis of the human testis proteome revealed nine proteins associated with lipid droplets. Two of them, ADFP (also known as ADRP and PLIN2) and TIP47 (also known as PLIN3) may participate in acute lipid droplet formation in mammalian testes. We show that Adfp expression is upregulated after scrotal heat treatment in mice. Surprisingly, we find Adfp lacking its 5'-UTR is observed in Adfp(Δ1/Δ1) mouse testes, but is not detectable in liver.

CONCLUSIONS

These results reveal testis Adfp transcriptional regulation is tissue-specific, and is associated with lipid droplet accumulation induced by heat. The results also indicate that the testes could retain functional proteins through testes-specific transcriptional regulation.

The hypoxic testicle: physiology and pathophysiology

Mammalian spermatogenesis is a complex biological process occurring in the seminiferous tubules in the testis. This process represents a delicate balance between cell proliferation, differentiation, and apoptosis. In most mammals, the testicles are kept in the scrotum 2 to 7°C below body core temperature, and the spermatogenic process proceeds with a blood and oxygen supply that is fairly independent of changes in other vascular beds in the body. Despite this apparently well-controlled local environment, pathologies such as varicocele or testicular torsion and environmental exposure to low oxygen (hypoxia) can result in changes in blood flow, nutrients, and oxygen supply along with an increased local temperature that may induce adverse effects on Leydig cell function and spermatogenesis. These conditions may lead to male subfertility or infertility. Our literature analyses and our own results suggest that conditions such as germ cell apoptosis and DNA damage are common features in hypoxia and varicocele and testicular torsion. Furthermore, oxidative damage seems to be present in these conditions during the initiation stages of germ cell damage and apoptosis. Other mechanisms like membrane-bound metalloproteinases and phospholipase A2 activation could also be part of the pathophysiological consequences of testicular hypoxia.

Autophagy and apoptosis act as partners to induce germ cell death after heat stress in mice

Testicular heating suppresses spermatogenesis which is marked by germ cell loss via apoptotic pathways. Recently, it is reported that autophagy also can be induced by heat treatment in somatic cells. In this study, the status of autophagy in germ cells after heat treatment, as well as the partnership between autophagy and apoptosis in these cells was investigated. The results demonstrated that besides initiating apoptotic pathways, heat also induced autophagic pathways in germ cells. Exposure of germ cells to hyperthermia resulted in several specific features of the autophagic process, including autophagosome formation and the conversion of LC3-I to LC3-II. Furthermore, the ubiquitin-like protein conjugation system was implicated as being likely responsible for heat-induced autophagy in germ cells since all genes involving this system were found to be expressed in the testes. In addition, the upstream protein in this system, Atg7 (Autophagy-related gene 7), was found to be expressed in all types of spermatogenic cells, and its expression level was positively correlated with the level of autophagy in germ cells. As a result, Atg7 was selected as the investigative target to further analyze the role of autophagy in heat-induced germ cell death. It was shown that down expression of Atg7 protein resulted in the notable decrease in the level of autophagy in heat-treated germ cells, and this down-regulation of autophagy caused by Atg7 knockdown further reduced the apoptotic rate of germ cells. These results suggest that autophagy plays a positive role in the process of germ cell apoptosis after heat treatment. In conclusion, this study demonstrates that heat triggers autophagy and apoptosis in germ cells. These two mechanisms might act as partners, not antagonist, to induce cell death and lead to eventual destruction of spermatogenesis.