Activation of Autophagy by Low-Dose Silica Nanoparticles Enhances Testosterone Secretion in Leydig Cells

Functional role of autophagy in testicular and ovarian steroidogenesis

Autophagy is an evolutionarily conserved cellular recycling process that maintains cellular homeostasis. Despite extensive research in endocrine contexts, the role of autophagy in ovarian and testicular steroidogenesis remains elusive. The significant role of autophagy in testosterone production suggests potential treatments for conditions like oligospermia and azoospermia. Further, influence of autophagy in folliculogenesis, ovulation, and luteal development emphasizes its importance for improved fertility and reproductive health. Thus, investigating autophagy in gonadal cells is clinically significant. Understanding these processes could transform treatments for endocrine disorders, enhancing reproductive health and longevity. Herein, we provide the functional role of autophagy in testicular and ovarian steroidogenesis to date, highlighting its modulation in testicular steroidogenesis and its impact on hormone synthesis, follicle development, and fertility therapies.

Melatonin counteracts cadmium-induced rat testicular toxicity via the mechanistic target rapamycin (mTOR) pathway

The protective action of melatonin (MLT) against the harmful effects of cadmium (Cd) on testicular activity in rats has been documented previously; however, the involved molecular mechanisms have yet to be elucidated. Herein, we investigate the involvement of the mammalian target of rapamycin (mTOR) on the ability of MLT to counteract the damage induced by Cd on the rat testicular activity. Our study confirmed that Cd has harmful effects on the testes of rats and the protective action exerted by MLT. We reported, for the first time, that the addition of rapamycin (Rapa), a specific mTOR inhibitor, to animals co-treated with Cd and MLT completely abolished the beneficial effects exerted by MLT, indicating that the mTOR pathway partially modulates its helpful effects on Cd testicular toxicity. Interestingly, Rapa-alone treatment, provoking mTOR inhibition, produced altered morphological parameters, increased autophagy of germ and somatic cells, and reduced serum testosterone concentration. In addition, mTOR inhibition also reduced protein levels of markers of steroidogenesis (3β-Hydroxysteroid dehydrogenase) and blood-testis barrier integrity (occludin and connexin 43). Finally, Rapa altered sperm parameters as well as the ability of mature spermatozoa to perform a proper acrosome reaction. Although further investigation is needed to better clarify the molecular pathway involved in MLT action, we confirm that MLT alleviating Cd effects can be used as a supplement to enhance testicular function and improve male gamete quality.

METTL3-m6A-SIRT1 axis affects autophagic flux contributing to PM2.5-induced inhibition of testosterone production in Leydig cells

Epidemiological studies have found that long-term inhalation of PM2.5 is closely related to spermatogenesis disorders and infertility, but the underlying molecular mechanism is still unidentified. Testosterone, an essential reproductive hormone produced by Leydig cells, whose synthesis is disrupted by multiple environmental pollutants. In the current study, we explored the role of METTL3-m6A-SIRT1 axis-mediated abnormal autophagy in PM2.5-induced inhibition of testosterone production in in vivo and in vitro models. Our in vivo findings shown that long-term inhalation of PM2.5 decreased sperm count, increased sperm deformity rates, and altered testicular interstitial morphology accompanied by reduced testosterone in serum and testes. Further, data from the in vitro model displayed that exposure to PM2.5 caused an increase in m6A modification and METTL3 levels, followed by a decrease in testosterone levels and autophagy dysfunction in Leydig cells. The knockdown of METTL3 promotes autophagy flux and testosterone production in Leydig cells. Mechanistically, PM2.5 increased METTL3-induced m6A modification of SIRT1 mRNA in Leydig cells, bringing about abnormal autophagy. Subsequently, administration of SRT1720 (a SIRT1 activator) enhanced autophagy and further promoted testosterone biosynthesis. Collectively, our discoveries indicate that METTL3-m6A-SIRT1 axis-mediated autophagic flux contributes to PM2.5-induced inhibition of testosterone biosynthesis. This research offers a novel viewpoint on the mechanism of male reproductive injury following PM2.5 exposure.

Autophagy regulation by inorganic, organic, and organic/inorganic hybrid nanoparticles: Organelle damage, regulation factors, and potential pathways

The rapid development of nanotechnology requires a more thorough understanding of the potential health effects caused by nanoparticles (NPs). As a programmed cell death, autophagy is one of the biological effects induced by NPs, which maintain intracellular homeostasis by degrading damaged organelles and removing aggregates of defective proteins through lysosomes. Currently, autophagy has been shown to be associated with the development of several diseases. A significant number of research have demonstrated that most NPs can regulate autophagy, and their regulation of autophagy is divided into induction and blockade. Studying the autophagy regulation by NPs will facilitate a more comprehensive understanding of the toxicity of NPs. In this review, we will illustrate the effects of different types of NPs on autophagy, including inorganic NPs, organic NPs, and organic/inorganic hybrid NPs. The potential mechanisms by which NPs regulate autophagy are highlighted, including organelle damage, oxidative stress, inducible factors, and multiple signaling pathways. In addition, we list the factors influencing NPs-regulated autophagy. This review may provide basic information for the safety assessment of NPs.

Impacts and potential mechanisms of fine particulate matter (PM2.5) on male testosterone biosynthesis disruption

Exposure to PM2.5 is the most significant air pollutant for health risk. The testosterone level in male is vulnerable to environmental toxicants. In the past, researchers focused more attention on the impacts of PM2.5 on respiratory system, cardiovascular system, and nervous system, and few researchers focused attention on the reproductive system. Recent studies have reported that PM2.5 involved in male testosterone biosynthesis disruption, which is closely associated with male reproductive health. However, the underlying mechanisms by which PM2.5 causes testosterone biosynthesis disruption are still not clear. To better understand its potential mechanisms, we based on the existing scientific publications to critically and comprehensively reviewed the role and potential mechanisms of PM2.5 that are participated in testosterone biosynthesis in male. In this review, we summarized the potential mechanisms of PM2.5 triggering the change of testosterone level in male, which involve in oxidative stress, inflammatory response, ferroptosis, pyroptosis, autophagy and mitophagy, microRNAs (miRNAs), endoplasmic reticulum (ER) stress, and N6-methyladenosine (m6A) modification. It will provide new suggestions and ideas for prevention and treatment of testosterone biosynthesis disruption caused by PM2.5 for future research.

Silica nanoparticles induce ovarian granulosa cell apoptosis via activation of the PERK-ATF4-CHOP-ERO1α pathway-mediated IP3R1-dependent calcium mobilization

Ambient particulate matters (PMs) have adverse effects in human and animal female reproductive health. Silica nanoparticles (SNPs), as a major component of PMs, can induce follicular atresia via the promotion of ovarian granulosa cell apoptosis. However, the molecular mechanisms of apoptosis induced by SNPs are not very clear. This work focuses on revealing the mechanisms of ER stress on SNP-induced apoptosis. Our results showed that spherical Stöber SNPs (110 nm, 25.0 mg/kg b.w.) induced follicular atresia via the promotion of granulosa cell apoptosis by intratracheal instillation in vivo; meanwhile, SNPs decreased the viability and increase apoptosis in granulosa cells in vitro. SNPs were taken up and accumulated in the vesicles of granulosa cells. Additionally, our results found that SNPs increased calcium ion (Ca2+) concentration in granulosa cell cytoplasm. Furthermore, SNPs activated ER stress via an increase in the PERK and ATF6 pathway-related protein levels and IP3R1-dependent calcium mobilization via an increase in IP3R1 level. In addition, 4-PBA restored IP3R1-dependent calcium mobilization and decreased apoptosis via the inhibition of ER stress. The ATF4-C/EBP homologous protein (CHOP)-ER oxidoreductase 1 alpha (ERO1α) pathway regulated SNP-induced IP3R1-dependent calcium mobilization and cell apoptosis via ATF4, CHOP, and ERO1α depletion in ovarian granulosa cells. Herein, we demonstrate that ER stress cooperated in SNP-induced ovarian toxicity via activation of IP3R1-mediated calcium mobilization, leading to apoptosis, in which the PERK-ATF4-CHOP-ERO1α pathway plays an essential role in ovarian granulosa cells.

Silica Nanoparticles Promote Apoptosis in Ovarian Granulosa Cells via Autophagy Dysfunction

Although silica nanoparticles (SNPs) are generally thought to be biocompatible and safe, the adverse effects of SNPs were also reported in previous studies. SNPs cause follicular atresia via the induction of ovarian granulosa cell apoptosis. However, the mechanisms for this phenomenon are not well understood. This study focuses on exploring the relationship between autophagy and apoptosis induced by SNPs in ovarian granulosa cells. Our results showed that 25.0 mg/kg body weight (b.w.)/intratracheal instillation of 110 nm in diameter spherical Stöber SNPs caused ovarian granulosa cell apoptosis in follicles in vivo. We also found that SNPs mainly internalized into the lumens of the lysosomes in primary cultured ovarian granulosa cells in vitro. SNPs induced cytotoxicity via a decrease in viability and an increase in apoptosis in a dose-dependent manner. SNPs increased BECLIN-1 and LC3-II levels, leading to the activation of autophagy and increased P62 level, resulting in the blockage of autophagic flux. SNPs increased the BAX/BCL-2 ratio and cleaved the caspase-3 level, resulting in the activation of the mitochondrial-mediated caspase-dependent apoptotic signaling pathway. SNPs enlarged the LysoTracker Red-positive compartments, decreased the CTSD level, and increased the acidity of lysosomes, leading to lysosomal impairment. Our results reveal that SNPs cause autophagy dysfunction via lysosomal impairment, resulting in follicular atresia via the enhancement of apoptosis in ovarian granulosa cells.

Hydroxysafflor Yellow A (HSYA) Protects Endplate Chondrocytes Against IL-1β-Induced Injury Through Promoting Autophagy

Background

Intervertebral disc degeneration (IDD) refers to intractable pain in patients' waist and legs, which is caused by internal structural disorder and degeneration of intervertebral. This disease severely affects the quality-of-life of people. It has been reported that hydroxysafflor yellow A (HSYA), the active ingredient in safflower extract, could inhibit IL-1β-induced apoptosis of endplate chondrocytes. However, the mechanism by which HSYA regulates the occurrence and progression of IDD remains unclear.

Methods

Rat endplate chondrocytes were isolated from the intervertebral disc. Next, toluidine blue staining and collagen II immunofluorescence staining were used to identify endplate chondrocytes. Then, MDC staining was used to detect the autophagy of endplate chondrocytes. In addition, Western blot was used to measure the expression of cleaved caspase 3, LC-3I/II and ATG7 in endplate chondrocytes.

Results

IL-1β obviously inhibited the viability and proliferation of endplate chondrocytes, while these phenomena were notably reversed by HSYA. Additionally, HSYA was able to inhibit IL-1β-induced apoptosis of endplate chondrocytes. Moreover, HSYA protected endplate chondrocytes against IL-1β-induced inflammation via inducing autophagy.

Conclusion

HSYA protected rat endplate chondrocytes against IL-1β-induced injury via promoting autophagy. Therefore, the present study might provide some theoretical basis for exploring novel and effective methods for patients with IDD.

BECLIN-1-Mediated Autophagy Suppresses Silica Nanoparticle-Induced Testicular Toxicity via the Inhibition of Caspase 8-Mediated Cell Apoptosis in Leydig Cells

Accumulation of silica nanoparticles (SNPs) in the testes leads to male reproductive toxicity. However, little is known about the effect and mechanistic insights of SNP-induced autophagy on apoptosis in Leydig cells. In this study, we aimed to verify the role of SNP-induced autophagy in apoptosis and explore the possible underlying mechanism in mouse primary Leydig cells (PLCs). H&E staining showed that SNPs changed the histological structures of the testes, including a reduction in the Leydig cell populations in vivo. CCK-8 assay showed that SNPs decreased cell viability, and flow cytometry showed that SNPs increased cell apoptosis, both in a dose-dependent manner in vitro. Additionally, Western blotting further found that SNPs activated autophagy by an increase in BECLIN-1, ATG16L, and LC3-II levels and promoted the intrinsic pathway of apoptosis by an increase in the BAX/BCL-2 ratio, cleaved the caspase 8 and caspase 3 levels. Furthermore, autophagy decreased SNP-induced apoptosis via regulation of the caspase 8 level combined with rapamycin, 3-methyladenine, and chloroquine. BECLIN-1 depletion increased the caspase 8 level, leading to an increase in SNP-induced cell apoptosis. Collectively, this evidence demonstrates that SNPs activated BECLIN-1-mediated autophagy, which prevented SNP-induced testicular toxicity via the inhibition of caspase 8-mediated cell apoptosis in Leydig cells.