Decline in testicular function in ageing rats: Changes in the unfolded protein response and mitochondrial apoptotic pathway

Age-dependent variations in proteomic characteristics of spermatozoa in Simmental bull

Increasing the age of bulls results in a decrease in reproductive function, including a reduction in sperm quality, which plays a vital role in determining the fertility of bulls. Through a proteomic approach, this research aims to analyze the influence of age factors on various proteomes contained in bull sperm. Frozen semen samples from Simmental Bulls were categorized into three age groups: two, four, and ≥10 years old. Subsequently, the post-thaw sperm cells obtained were separated based on molecular weight using 1D-SDS-PAGE. Peptides extracted from the bands produced in each age group were subjected to LC-MS/MS analysis. A total of 72 protein types were identified, with 45 being detected in the 4-year-old group and 41 expressed in both the 2 and ≥10-year-old groups. The results provided insights into proteins' role in sperm metabolism across all age groups. Specifically, the 2-year-old group exhibited the expression of proteins associated with acrosome assembly and spermatid development (SPACA1). In contrast, those in the 4-year-old group were linked to motility (PEBP4) and sperm decapacitation factor (PEBP1). Proteins expressed in the 2 and -year-old groups were discovered to be involved in fertilization processes (TEX101). In contrast, the ≥10-year-old age group was associated with hyperactive movement related to capacitation (Tubulin). In conclusion, age influenced the differences observed in the proteomic profile of post-thaw Simmental bull sperm using the 1D-SDS-PAGE tandem LC-MS/MS approach.

X-box binding protein 1 caused an imbalance in pyroptosis and mitophagy in immature rats with di-(2-ethylhexyl) phthalate-induced testis toxicity

As a widely used plasticizer, di-(2-ethylhexyl) phthalate (DEHP) is known to induce significant testicular injury. However, the potential mechanism and effects of pubertal exposure to DEHP on testis development remain unclear. In vivo, postnatal day (PND) 21 male rats were gavaged with 0, 250, and 500 mg/kg DEHP for ten days. Damage to the seminiferous epithelium and disturbed spermatogenesis were observed after DEHP exposure. Meanwhile, oxidative stress-induced injury and pyroptosis were activated. Both endoplasmic reticulum (ER) stress and mitophagy were involved in this process. Monoethylhexyl phthalate (MEHP) was used as the biometabolite of DEHP in vitro. The GC-1 and GC-2 cell lines were exposed to 0, 100 μM, 200 μM, and 400 μM MEHP for 24 h. Reactive oxygen species (ROS) generation, oxidative stress damage, ER stress, mitophagy, and pyroptosis were significantly increased after MEHP exposure. The ultrastructure of the ER and mitochondria was destroyed. X-box binding protein 1 (XBP1) was observed to be activated and translocated into the nucleus. ROS generation was inhibited by acetylcysteine. The levels of antioxidative stress, ER stress, mitophagy, and pyroptosis were decreased as well. After the administration of the ER stress inhibitor 4-phenyl-butyric acid, both mitophagy and pyroptosis were inhibited. Toyocamycin-induced XBP1 down-regulation decreased the levels of mitophagy and pyroptosis. The equilibrium between pyroptosis and mitophagy was disturbed by XBP1 accumulation. In summary, our findings confirmed that DEHP induced a ROS-mediated imbalance in pyroptosis and mitophagy in immature rat testes via XBP1. Moreover, XBP1 might be the key target in DEHP-related testis dysfunction.

MAPKs signaling is obligatory for male reproductive function in a development-specific manner

Mitogen-activated protein kinases (MAPKs) represent widely expressed and evolutionarily conserved proteins crucial for governing signaling pathways and playing essential roles in mammalian male reproductive processes. These proteins facilitate the transmission of signals through phosphorylation cascades, regulating diverse intracellular functions encompassing germ cell development in testis, physiological maturation of spermatozoa within the epididymis, and motility regulation at ejaculation in the female reproductive tract. The conservation of these mechanisms appears prevalent across species, including humans, mice, and, to a limited extent, livestock species such as bovines. In Sertoli cells (SCs), MAPK signaling not only regulates the proliferation of immature SCs but also determines the appropriate number of SCs in the testes at puberty, thereby maintaining male fertility by ensuring the capacity for sperm cell production. In germ cells, MAPKs play a crucial role in dynamically regulating testicular cell-cell junctions, supporting germ cell proliferation and differentiation. Throughout spermatogenesis, MAPK signaling ensures the appropriate Sertoli-to-germ cell ratio by regulating apoptosis, controlling the metabolism of developing germ cells, and facilitating the maturation of spermatozoa within the cauda epididymis. During ejaculation in the female reproductive tract, MAPKs regulate two pivotal events-capacitation and the acrosome reaction essential for maintaining the fertility potential of sperm cells. Any disruptions in MAPK pathway signaling possibly may disturb the testicular microenvironment homeostasis, sperm physiology in the male body before ejaculation and in the female reproductive tract during fertilization, ultimately compromising male fertility. Despite decades of research, the physiological function of MAPK pathways in male reproductive health remains inadequately understood. The current review attempts to combine recent findings to elucidate the impact of MAPK signaling on male fertility and proposes future directions to enhance our understanding of male reproductive functions.

The landscape of aging

Aging is characterized by a progressive deterioration of physiological integrity, leading to impaired functional ability and ultimately increased susceptibility to death. It is a major risk factor for chronic human diseases, including cardiovascular disease, diabetes, neurological degeneration, and cancer. Therefore, the growing emphasis on "healthy aging" raises a series of important questions in life and social sciences. In recent years, there has been unprecedented progress in aging research, particularly the discovery that the rate of aging is at least partly controlled by evolutionarily conserved genetic pathways and biological processes. In an attempt to bring full-fledged understanding to both the aging process and age-associated diseases, we review the descriptive, conceptual, and interventive aspects of the landscape of aging composed of a number of layers at the cellular, tissue, organ, organ system, and organismal levels.

Icariin attenuates perfluorooctane sulfonate-induced testicular toxicity by alleviating Sertoli cell injury and downregulating the p38MAPK/MMP9 pathway

Perfluorooctane sulfonate (PFOS) is widely recognized as causing Sertoli cell injury and testicular toxicity in males. Icariin is a flavonoid from Epimedium, which effectively improves spermatogenesis disturbance induced by several factors in clinic. However, it is unclear whether icariin improves PFOS-induced testicular toxicity. In vivo, fifty-two male mice were randomly separated into four groups: normal control group, model group, and low and high doses of icariin-treated groups, with 13 mice in each group. Except for the normal control group, the mice in the model group and icariin-treated groups were administered PFOS (10 mg kg-1) by gavage daily for 28 consecutive days, and concurrently treated with a diet containing different doses of icariin (0, 5 or 20 mg kg-1). In vitro, TM4 cells were treated with 150 μM PFOS to induce Sertoli cell injury, and were then utilized for icariin treatment. Our results demonstrated that icariin attenuated PFOS-induced testicular toxicity by increasing the testicular, epididymal and seminal vesicle weights, epididymal and seminal vesicle indices, sperm parameters, and seminiferous epithelium height. In addition, icariin improved the PFOS-induced blood-testis barrier (BTB) disruption by alleviating the Sertoli cell junctional injury, but without affecting Sertoli cell numbers in the testis of mice. Moreover, icariin increased the expression levels of tight junction proteins (ZO-1, Occludin and Claudin-11) and gap junction proteins (CX43 and p-CX43), and decreased the expression levels of p-p38MAPK and matrix metalloproteinase 9 (MMP9) both in vivo and in vitro. Furthermore, alleviation of the Sertoli cell injury by icariin exerted similar effects as SB203580 (an inhibitor of p38MAPK) in TM4 cells. This study revealed that icariin effectively reduces PFOS-induced testicular toxicity by alleviating the Sertoli cell injury and downregulating the p38MAPK/MMP9 pathway, indicating that icariin may be an attractive dietary supplement for the intervention of PFOS-induced testicular dysfunction.

Multifaceted epigenetic regulation of porcine testicular aromatase

Testicular aromatase catalyzes the synthesis of estradiol, which contributes to regulation of porcine Sertoli cell proliferation and postpubertal maintenance of Sertoli cell numbers. Although aromatase enzymatic activity decreases with age and is persistently reprogrammed by prepubertal treatment with the aromatase inhibitor letrozole, the molecular bases for regulation have not been identified. DNA methylation was examined as a potential regulatory mechanism using DNA from Leydig cells isolated from 16-, 40-, and 68-week-old boars and from 68- week-old littermates treated with the aromatase inhibitor, letrozole. Methylation levels of individual CpG dinucleotides located in the distal untranslated exon 1 of the relevant aromatase encoding gene, CYP19A3, were quite high in Leydig cell DNA, and increased further with maturity of boar (P < 0.05), while aromatase activity and transcript abundance decreased more than two-fold. However, reduced aromatase activity following letrozole treatment was not accompanied by altered DNA methylation. Testicular expression of miR378 was altered by prepubertal treatment with letrozole. The data provide evidence for two different epigenetic mechanisms that regulate aromatase expression and enzymatic activity in the boar testis.

Extracellular and Intracellular Skeletons: How Do They Involve in Apoptosis

Apoptosis plays a key role in removing abnormal or senescent cells, maintaining the overall health of the tissue, and coordinating individual development. Recently, it has been discovered that the intracellular cytoskeleton plays a role in the apoptotic process. In addition, the regulatory role of extracellular matrix (ECM) fibrous proteins, which can be considered as the extracellular skeleton, in the process of apoptosis is rarely summarized. In this review, we collect the latest knowledge about how fibrous proteins inside and outside cells regulate apoptosis. We describe how ECM fibrous proteins participate in the regulation of death receptor and mitochondrial pathways through various signaling cascades mediated by integrins. We then explore the molecular mechanisms by which intracellular intermediate filaments regulate cell apoptosis by regulating death receptors on the cell membrane surface. Similarly, we report on novel supporting functions of microtubules in the execution phase of apoptosis and discuss their formation mechanisms. Finally, we discuss that the polypeptide fragments formed by caspase degradation of ECM fibrous proteins and intracellular intermediate filament act as local regulatory signals to play different regulatory roles in apoptosis.

SIRT 3 was involved in Lycium barbarum seed oil protection testis from oxidative stress: in vitro and in vivo analyses

CONTEXT

Lycium barbarum L. (Solanaceae) seed oil (LBSO) exerts LBSO exerts protective effects in the testis in vivo and in vitro via upregulating SIRT3.

OBJECTIVE

This study evaluates the effects and mechanism of LBSO in the d-galactose (d-gal)-induced ageing testis.

MATERIALS AND METHODS

Male Sprague Dawley (SD) rats (n = 30, 8-week-old) were randomly divided into three groups: LBSO group (n = 10) where rats received subcutaneous injection of d-gal at 125 mg/kg/day for 8 weeks and intragastric administration of LBSO at 1000 mg/kg/day for 4 weeks, ageing model group (n = 10) received 8-week-sunbcutaneous injection of d-gal, and control group (n = 10) with same administration of normal saline. Lentivirus had established TM4 cells with SIRT3 overexpression or silencing before LBSO intervened in vitro.

RESULTS

Treatment with LBSO, the levels of INHB and testosterone both increased, compared to ageing model. In vitro, we found the ED₅₀ of LBSO was 86.72 ± 1.49 and when the concentration of LBSO at 100 μg/mL to intervene TM4 cells, the number of cells increased from 8120 ± 676.2 to 15251 ± 1119, and the expression of SIRT3, HO-1, and SOD upregulated. However, HO-1 and SOD were dysregulated by silencing SIRT3. On the other hand, the expression of AMPK and PGC-1α upregulated as an effect of SIRT3 overexpression by lentivirus, meanwhile the same increasing trend of that being found in cells treated with LBSO, compared to control group.

DISCUSSION AND CONCLUSIONS

LBSO alleviated oxidative stress in d-gal-induced sub-acutely ageing testis and TM4 cells by suppressing the oxidative stress to mitochondria via SIRT3/AMPK/PGC-1α.

The dynamic changes of Nrf2 mediated oxidative stress, DNA damage and base excision repair in testis of rats during aging

Accumulation of oxidative stress, DNA damage and impaired DNA repair appear to play critical roles in the decline of testicular function with aging. However, when those factors begin to lose control in testis during aging has not yet been well understood. This study was designed to assess the changes of oxidative stress and DNA damage status, and DNA repair capacity in testis during aging. Thus, male Sprague-Dawley rats at 3, 9, 15 and 24 months of age were used to delineate the dynamic changes in testicular weight and index, testosterone concentration, testicular histology, Nrf2-mediated oxidative stress, DNA damage, DNA repair and apoptosis. Results showed that testicular weight and index, testosterone concentration and spermatid number progressively declined from 9 to 24 months of age. Similarly, seminiferous tubule diameters and seminiferous epithelium heights gradually diminished with aging. Nrf2-mediated antioxidant defense ability was significantly impaired in testis with increasing age including decreased the activity of SOD and the expression levels of Nrf2, HO-1 and NQO-1, and increased the contents of MDA. In addition, DNA damage including DNA single-strand breaks (SSBs) and DNA double-strand breaks (DSBs) also progressively increased accompanied by increased levels of 8-hydroxydeoxyguanosine (8-OHdG) and γ-H2AX, and activated ATM/Chk2 and ATR/Chk1 pathway. Consistent with the results of Nrf2 pathway, the expression levels of APE1, OGG1 and XRCC1 involved in base excision DNA repair (BER) pathway increased from 3 to 9 months of age, and then gradually decreased after 9 months of age. Finally, TUNEL and Western blot results further confirmed germ cell apoptosis progressively increased from 3 to 24 months of age as evidenced by decreased ratio of Bcl-2/Bax and levels of Bcl-2 expression, and increased Bax expression levels. Taken together, our results suggest that downregulation of antioxidant ability mediated by Nrf2 pathway and impairment of BER capacity might correlate with increased DNA damage, and then induce declining testicular function during aging after adult.

Male and female gonadal ageing: its impact on health span and life span

Ageing is linked to changes in the hypothalamic-pituitary-gonadal axis and a progressive decline in gonadal function. While women become infertile when they enter menopause, fertility decline in ageing men does not necessarily involve a complete cessation of spermatogenesis. Gonadal dysfunction in elderly people is characterized by morphological, endocrine and metabolic alterations affecting the reproductive function and quality of life. With advancing age, sexuality turns into a critical emotional and physical factor actually defining the number of years that ageing people live a healthy life. Gonadal ageing correlates with comorbidities and an increased risk of age-related diseases including diabetes, kidney problems, cardiovascular failures and cancer. This article briefly summarizes the current state of knowledge on ovarian and testicular senescence, explores the experimental models used in the study of gonadal ageing, and describes the local pro-inflammatory, oxidative and apoptotic events and the associated signalling pathways that take place in the gonads while people get older. Overall, literature reports that ageing exacerbates a mutual crosstalk among oxidative stress, apoptosis and the inflammatory response in the gonads leading to detrimental effects on fertility. Data also highlight the clinical implications of novel therapeutic interventions using antioxidant, anti-apoptotic and anti-inflammatory drugs on health span and life span.

Baking of methionine-choline deficient diet aggravates testis injury in mice

Dietary pattern and cooking methods are important factors to determine the nutrients supplementation for male reproduction. Methionine and choline are two methyl donors in daily diet, which could mediate the lipid metabolism, but their effects on the sperms are not clear. In this study, we fed the mice with methionine-choline deficient (MCD) diet or the baked MCD diet for 6 weeks to evaluate this dietary pattern and the appended high temperature cooking on the spermatogenesis. The results have shown that MCD diet induced testis degradation and the damage of spermatocytes, reduced sperm vitality, motility, but elevated sperm deformity. Additionally, baking of MCD diet aggravated the testis injury, further reduced sperm density, sperm motility, and decreased normal sperm morphology dramatically. These changes were not related to the blood-testis barrier nor the Leydig cells dysfunction, but related to spermatocytes lost and apoptosis. The spermatocyte apoptosis was mediated by reticulum stress, including GRP78, XBP-1 and CHOP gene expression. Our study has shown the importance of methionine and choline in diet, and emphasized the crucial role of cooking condition, which are dietary factors to influence the quality of sperms.

X-box binding protein 1 (XBP1) function in diseases

The accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER) causes endoplasmic reticulum stress (ERS), which is characteristic of cells with high levels of secretory activity and is involved in a variety of diseases. In response to ERS, cells initiate an adaptive process named the unfolding protein response (UPR) to maintain intracellular homeostasis and survival. However, long term and unresolved ERS can also induce apoptosis. As the most conserved signaling branch of UPR, the IRE1-XBP1 pathway plays an important role in both physiological and pathological states, and its activity has a profound impact on disease progression and prognosis. Here, the latest research progress of IRE1-XBP1 pathway in cancer, metabolic diseases, and other diseases was briefly introduced, and the relationship between several diseases and this pathway was analyzed. Besides, the new understanding and prospect of IRE1-XBP1 pathway regulating male reproduction were reviewed.

Comparative Study of the Steroidogenic Effects of Human Chorionic Gonadotropin and Thieno[2,3-D]pyrimidine-Based Allosteric Agonist of Luteinizing Hormone Receptor in Young Adult, Aging and Diabetic Male Rats

Low-molecular-weight agonists of luteinizing hormone (LH)/human chorionic gonadotropin (hCG) receptor (LHCGR), which interact with LHCGR transmembrane allosteric site and, in comparison with gonadotropins, more selectively activate intracellular effectors, are currently being developed. Meanwhile, their effects on testicular steroidogenesis have not been studied. The purpose of this work is to perform a comparative study of the effects of 5-amino-N-tert-butyl-4-(3-(1-methylpyrazole-4-carboxamido)phenyl)-2-(methylthio)thieno[2,3-d] pyrimidine-6-carboxamide (TP4/2), a LHCGR allosteric agonist developed by us, and hCG on adenylyl cyclase activity in rat testicular membranes, testosterone levels, testicular steroidogenesis and spermatogenesis in young (four-month-old), aging (18-month-old) and diabetic male Wistar rats. Type 1 diabetes was caused by a single streptozotocin (50 mg/kg) injection. TP4/2 (20 mg/kg/day) and hCG (20 IU/rat/day) were administered for 5 days. TP4/2 was less effective in adenylyl cyclase stimulation and ability to activate steroidogenesis when administered once into rats. On the 3rd–5th day, TP4/2 and hCG steroidogenic effects in young adult, aging and diabetic rats were comparable. Unlike hCG, TP4/2 did not inhibit LHCGR gene expression and did not hyperstimulate the testicular steroidogenesis system, moderately increasing steroidogenic proteins gene expression and testosterone production. In aging and diabetic testes, TP4/2 improved spermatogenesis. Thus, during five-day administration, TP4/2 steadily stimulates testicular steroidogenesis, and can be used to prevent androgen deficiency in aging and diabetes.

The Attenuating Effect of the Intraovarian Bone Morphogenetic Protein 4 on Age-Related Endoplasmic Reticulum Stress in Chicken Follicular Cells

In the poultry, only less than 5% primordial follicles in the ovary can develop into the prehierarchical follicles (PHFs) leading to progressive development, ovulation, and egg formation. This low rate of recruitment indicates a huge potential for improvement of the laying performance. A great reduction in egg production is caused by aging with extensive follicular atresia. In this study, age-related changes in the laying performance and ovarian status were compared between the peak-lay (D280) and aged (D580) chickens. Subsequently, a cross coculture of PHFs and granulosa cells (GCs) from D280 or D580 hens was adopted to reveal the mechanism of declined follicle development. Results showed that persistent endoplasmic reticulum (ER) stress in GCs of the aged hens was accompanied with intensified apoptosis. Bone morphogenetic protein 4 (BMP4) secreted by GCs of PHFs in D280 hens was capable of relieving ER stress and improving follicular dominance for selection in D580 hens. During this action, BMP4 reduced free calreticulin (CALR, an ER marker) content and attenuated cell apoptosis in PHFs of D580 hens via the PERK-CHOP-BCL2/caspase3 or CALR-Ca²⁺-BCL2-caspase12 pathway. Furthermore, BMP4 prevented follicular atresia by promoting production of steroid hormones to improve survival of GCs in PHFs from the aged hens. In conclusion, intensified ER stress and apoptosis occurred in GCs of PHFs in aged chickens, while BMP4 secreted by GCs was capable of improving follicular viability by alleviating ER stress to promote follicular development.