Corticosteroid-binding globulin, induced in testicular Leydig cells by perfluorooctanoic acid, promotes steroid hormone synthesis

Regulation of corticosteroid-binding globulin release in murine leydig tumor cell line mLTC-1 by luteinizing hormone and interleukin-6

Exogenous assaults interfere with homeostatic processes in the body by inducing stress responses. Corticosteroid-binding globulin (CBG) binds to stress hormone glucocorticoids to transport and dynamically control their availability to target tissues. In our previous study, we confirmed that CBG is locally produced by Leydig cells in the testes. Here, we explored the potential regulators of CBG using a murine Leydig tumor cell line (mLTC-1). Results indicated that luteinizing hormone (LH) and interleukin-6 (IL-6) were important factors stimulating the release of CBG from mLTC-1 cells. In addition, IL-6 stimulated mLTC-1 cells to release alpha-1 antitrypsin (AAT), a serine proteinase inhibitor (serpin) that affects CBG conformation. The results implied that any challenge that altered LH or IL-6 levels also changed the release and binding status of CBG with steroid hormones in the testicular microenvironment and modulated cellular responses to these stress hormones. In addition, secretory proteomic analysis indicated that the extracellular matrix (ECM), cytoskeleton, and proteasomes were essentially produced by the mLTC-1 cells, and LH evoked the secretion of proteins involved in binding and metabolism. These results emphasize that Leydig cells may undertake more functions than just steroidogenesis, and the regulation of Leydig cells by LH is versatile.

Comparative steroidogenic effects of hexafluoropropylene oxide trimer acid (HFPO-TA) and perfluorooctanoic acid (PFOA): Regulation of histone modifications

As a widely used alternative to perfluorooctanoic acid (PFOA), hexafluoropropylene oxide trimer acid (HFPO-TA) has been detected in the environment and humans; however, little is known regarding its male reproductive toxicity. To compare the effects of HFPO-TA on steroid hormone synthesis with PFOA, we exposed Leydig cells (MLTC-1) to non-lethal doses (0.1, 1, and 10 μM) of PFOA and HFPO-TA for 48 h. It was found that the levels of steroid hormones, 17α-hydroxyprogesterone (OHP), androstenedione (ASD), and testosterone (T) were significantly increased in 1 and 10 μM of PFOA and HFPO-TA groups, with greater elevation being observed in the HFPO-TA groups than in the PFOA groups at 10 μM. We further showed that the two rate-limiting steroidogenic genes (Star and Cyp11a1) were up-regulated, while Hsd3b, Cyp17a1, and Hsd17b were down-regulated or unchanged after PFOA/HFPO-TA exposure. Moreover, PFOA exposure significantly up-regulated histone H3K4me1/3 and H3K9me1, while down-regulated H3K4me2 and H3K9me2/3 levels. By contrast, H3K4me2/3 and H3K9me2/3 were enhanced, while H3K4me1 and H3K9me1 were repressed after HFPO-TA treatment. It was further confirmed that H3K4me1/3 were increased and H3K9me2 was decreased in Star and Cyp11a1 promoters by PFOA, while HFPO-TA increased H3K4me2/3 and decreased H3K9me1 in the two gene promoters. Therefore, we propose that low levels of PFOA/HFPO-TA enhance the expression of Star and Cyp11a1 by regulating H3K4 and H3K9 methylation, thus stimulating the production of steroid hormones in MLTC-1 cells. Collectively, HFPO-TA exhibits stronger effects on steroidogenesis compared to PFOA, which may be ascribed to the distinct regulation of histone modifications. These data suggest that HFPO-TA does not appear to be a safer alternative to PFOA on the aspect of male reproductive toxicity.

Endocrine Disruptors: Focus on the Adrenal Cortex

Endocrine-disrupting chemicals (EDCs) are exogenous substances known to interfere with endocrine homeostasis and promote adverse health outcomes. Their impact on the adrenal cortex, corticosteroids and their physiological role in the organism has not yet been sufficiently elucidated. In this review, we collect experimental and epidemiological evidence on adrenal disruption by relevant endocrine disruptors. In vitro data suggest significant alterations of gene expression, cell signalling, steroid production, steroid distribution, and action. Additionally, morphological studies revealed disturbances in tissue organization and development, local inflammation, and zone-specific hyperplasia. Finally, endocrine circuits, such as the hypothalamic-pituitary-adrenal axis, might be affected by EDCs. Many questions regarding the detection of steroidogenesis disruption and the effects of combined toxicity remain unanswered. Not only due to the diverse mode of action of adrenal steroids and their implication in many common diseases, there is no doubt that further research on endocrine disruption of the adrenocortical system is needed.

Fetal Glucocorticoid Mediates the Association between Prenatal Per- and Polyfluoroalkyl Substance Exposure and Neonatal Growth Index: Evidence from a Birth Cohort Study

Glucocorticoid plays a key role in the growth and organ maturation of fetus. However, the effect of glucocorticoid on the association between per- and polyfluoroalkyl substance (PFAS) exposure and fetal growth is still unknown. We detected cord cortisol (active glucocorticoid in human) and 34 PFAS concentrations in the maternal serum samples, which were collected from 202 mother-fetus pairs in the Maoming Birth Cohort from 2015 to 2018. The mediation effect of cord cortisol on the association between maternal PFAS and the neonatal growth index (NGI) was estimated. We found that higher PFAS concentrations were associated with lower NGI in terms of ponderal index, birth weight (BW), head circumference (HC), and its z-scores (BWZ and HCZ) (P < 0.05). Fetal cortisol could mediate 12.6-27.3% of the associations between PFAS and NGI. Specifically, cord cortisol mediated the association between branched perfluorooctane sulfonate (branched PFOS) and HCZ by 20.4% and between perfluorooctanoate (PFOA) and HCZ by 27.3%. Our findings provide the first epidemiological data evincing that fetal cortisol could mediate the association between prenatal PFAS exposure and fetal growth. Further investigations are recommended to elucidate the interactions among cord cortisol, PFAS, and fetal growth.

Low Levels of Perfluorooctanoic Acid Exposure Activates Steroid Hormone Biosynthesis through Repressing Histone Methylation in Rats

Perfluorooctanoic acid (PFOA) is a persistent organic pollutant, which has endocrine-disrupting properties and can interfere with the synthesis and secretion of testicular steroid hormones, but the underlying molecular mechanisms are still not fully understood. In this study, we investigated the effects of low doses of PFOA exposure on testicular steroidogenesis in rats and revealed the role of histone modifications. It was found that the serum levels of progesterone, testosterone, and estradiol were significantly increased after 0.015 and 0.15 mg/kg of PFOA exposure, and the expression of Star, a key rate-limiting gene, was up-regulated, while other steroidogenic genes Cyp11a1, Hsd3b, Cyp17a1, and Hsd17b were down-regulated. In addition, the levels of multiple histone modifications (H3K9me1/2/3 and H3K9/18/23ac) were all significantly reduced by PFOA in rat testis. Histone H3K9 methylation is associated with gene silencing, while histone acetylation leads to gene activation. ChIP analysis further showed that H3K9me1/3 was significantly decreased in the promoter region of Star, while H3K18ac levels were down-regulated in other gene promoters. Accordingly, we suggest that low-level PFOA enhances StAR expression through the repression of H3K9me1/3, which stimulates steroid hormone production in rat testis. These results are expected to shed new light on the molecular mechanisms by which low-dose PFOA disturbs male reproductive endocrine from an epigenetic aspect and may be useful for human health risk assessment regarding environmental PFOA exposure.

Low-dose perfluorooctanoic acid stimulates steroid hormone synthesis in Leydig cells: Integrated proteomics and metabolomics evidence

Perfluorooctanoic acid (PFOA), one of the well-known perfluoroalkyl substances (PFASs), has been widespread in the environment and associated with male reproductive toxicity. However, the molecular mechanism involved in low-level PFOA-induced male endocrine disruption remains to be elucidated. In this study, we performed a combined proteomics and metabolomics analysis to investigate the proteomic and metabolic alterations in MLTC-1 Leydig cells responsive to low levels of PFOA exposure. The results showed that PFOA significantly regulated the expressions of 67 proteins and 17 metabolites, among which 18 proteins and 7 metabolites were specifically tied to lipid and fatty acid metabolism as well as testicular steroidogenesis. It is further suggested that low-dose PFOA stimulates steroid hormone synthesis by accelerating fatty acid metabolism and steroidogenic process, which is involved in the repression of p38 and cAMP-dependent ERK signaling pathway. The animal studies also revealed that environmentally relevant levels of PFOA increased serum steroid hormone levels accompanied by the activated cAMP and inhibited p38/ERK pathway in testis, which confirmed our in vitro findings. Overall, the present study will provide novel insights into the toxicological mechanisms of low-level PFOA-mediated steroidogenic disturbance, and may implicate the reproductive health risk of humans with environmental PFOA exposure.

N-acetyl cysteine co-treatment abates perfluorooctanoic acid-induced reproductive toxicity in male rats

Perfluorooctanoic acid is a synthetic perfluoroalkyl-persistent in the environment and toxic to humans. N-acetylcysteine is a pro-drug of both amino acid l-cysteine and glutathione-a non-enzymatic antioxidant. N-acetylcysteine serves as an antidote for paracetamol poisoning and alleviates cellular oxidative and inflammatory stressors. We investigated N-acetylcysteine role against reproductive toxicity in male Wistar rats (weight: 140-220 g; 10 weeks old) posed by perfluorooctanoic acid exposure. Randomised rat cohorts were dosed both with perfluorooctanoic acid (5 mg/kg; p.o) or co-dosed with N-acetylcysteine (25 and 50 mg/kg p.o) for 28 days. Sperm physiognomies, biomarkers of testicular function and reproductive hormones, oxidative stress and inflammation were evaluated. Co-treatment with N-acetylcysteine significantly (p < .05) reversed perfluorooctanoic acid-mediated decreases in reproductive enzyme activities, and adverse effect on testosterone, luteinising and follicle-stimulating hormone concentrations. N-acetylcysteine treatment alone, improved sperm motility, count and viability, and reduced total sperm abnormalities. Co-treatment with N-acetylcysteine mitigated perfluorooctanoic acid-induced alterations in sperm function parameters. N-acetylcysteine abated (p < .05) perfluorooctanoic acid-induced oxidative stress in experimental rats testes and epididymis, and generally improved antioxidant enzyme activities and cellular thiol levels. Furthermore, N-acetylcysteine suppressed inflammatory responses and remedied perfluorooctanoic acid-mediated histological injuries in rat. Cooperatively, N-acetylcysteine enhanced reproductive function in perfluorooctanoic acid dosed rats, by lessening oxidative and nitrative stressors and mitigated inflammatory responses in the examined organ.

Perfluoroundecanoic acid inhibits Leydig cell development in pubertal male rats via inducing oxidative stress and autophagy

Perfluoroundecanoic acid (PFUnA) is one of long-chain perfluoroalkyl carboxylic acids. However, the effect of PFUnA on pubertal development of Leydig cells remains unclear. The goal of this study was to investigate the effect of PFUnA on Leydig cell development in pubertal male rats. We orally dosed male Sprague-Dawley rats (age 35 days) with PFUnA at doses of 0, 1, 5, and 10 mg/kg/day from postnatal day (PND) 35 to PND 56. Serum testosterone and luteinizing hormone levels were remarkably reduced by PFUnA at ≥1 mg/kg while serum follicle-stimulating hormone levels were lowered at 5 and 10 mg/kg. PFUnA down-regulated the expression of Lhcgr, Scarb1, Star, Cyp11a1, Hsd3b1, Cyp17a1, Hsd17b3, Hsd11b1, Insl3, Nr5a1, Fshr, Dhh, Sod1, and Sod2 and their proteins in the testis and the expression of Lhb and Fshb in the pituitary. PFUnA reduced Leydig cell number at 5 and 10 mg/kg. PFUnA induced oxidative stress and increased autophagy. These may result from the inhibition of phosphorylation of mTOR, AKT1, AKT2, and ERK1/2 in the testis. In conclusion, PFUnA exhibits inhibitory effects on pubertal Leydig cell development possibly via inducing oxidative stress and increasing autophagy.

Interleukin 17A deficiency alleviates fluoride-induced testicular injury by inhibiting the immune response and apoptosis

The reproductive toxicity of fluoride (F) has been verified by various epidemiological and experimental studies. Our previous work suggested that the interleukin 17A (IL-17A) is involved in the testicular damage induced by excessive F exposure. In this study, we further investigated the role of IL-17A in F-induced testicular injury. Wild type (WT) and IL-17A knockout (IL-17A^-/-) mice were exposed to 0, 25, 50, or 100 mg/L sodium fluoride (NaF) for 90 days. We found that exposure to excessive F levels caused testicular damage, decreased semen quality, negatively affected testicular morphology, and increased the inflammatory response. Specifically, excessive F intake increased the expression levels of IL-17A in the testis and increased the protein levels of Act1, NF-κB, IL-17R, C/EBP-α, and TRAF6 in the IL-17A signaling pathway. The increase in IL-17A expression corresponded to increases expression of IL-17R, IL-6, IL-23, IL-1β, TGF-β and TNF-α as assessed by RT-PCR and ELISA assays. Remarkably, IL-17A knockout in mice ameliorated the effects of F on testicular damage, semen quality, testicular morphology, and the immune response. Additionally, we found the in vitro exposure of Leydig cells to NaF and recombinant IL-17A led to abnormal apoptosis and a decrease in testosterone secretion. Our findings prove that IL-17A plays a key role in the exacerbation of testicular injuries in F-exposed mice, and that IL-17A deficiency can alleviate F-induced injury by inhibiting the immune response and apoptosis in the testis. These data suggest that targeting IL-17A may be a useful therapeutic strategy for treating F-mediated toxicity in the testis.

Heavy ion radiation-induced DNA damage mediates apoptosis via the Rpl27a-Rpl5-MDM2-p53/E2F1 signaling pathway in mouse spermatogonia

The risk of exposure to ionizing radiation (IR) environments has increased with the development of nuclear technology. IR exposure induces excessive apoptosis of the spermatogonia, which leads to male infertility. Spermatogonia apoptosis may be involved in ribosomal stress triggered by DNA damage following exposure to IR because ribosomal proteins (RPs) directly interact with mouse double minute 2 homolog (MDM2) to induce apoptosis. This study aimed to use comparative proteomics and transcriptomics approach to screen the differential RPs and ribosomal mRNAs in mouse testes following high linear energy transfer (LET) carbon ion radiation (CIR). The expression of ribosomal large subunit protein 27a (Rpl27a) decreased at both protein and mRNA levels in the spermatogonia in vivo. After 6 h of CIR, the immunofluorescence signal of 8-oxo-dG and phosphorylated ataxia-telangiectasia-mutated protein (ATM)/histone H2Ax increased, but that of Rpl27a decreased in the spermatogonia of p53 wild-type and knockout mouse testes. Moreover, the nucleolin was scattered throughout the nucleoplasm after CIR. These results suggested that CIR-induced DNA damage might trigger ribosomal stress, and the reduction in the expression of Rpl27a was associated with DNA damage in the spermatogonia. Similarly, in vitro, the immunofluorescence signal of 8-oxo-dG increased in the GC-1 cells after CIR. Moreover, the expression of Rpl27a was regulated by DNA damage because the co-transfection of ATM and Rpl27a or inhibition of ATM-treated CIR could restore the expression of Rpl27a. Furthermore, the reduction in the expression of Rpl27a led to weakened binding of E2F transcription factor 1 (E2F1) and p53 to MDM2, causing p53 activation and E2F1 degradation in p53 wild-type and knockdown GC-1 cells. This study proposed that heavy ion radiation-induced DNA damage mediated spermatogonia apoptosis via the Rpl27a-Rpl5-MDM2-p53/E2F1 signaling pathway. The results provided the underlying molecular mechanisms of spermatogonia apoptosis following exposure to high LET radiation.

Perfluoroalkyl substances cause Leydig cell dysfunction as endocrine disruptors

Perfluoroalkyl substances (PFASs) are a group of man-made organic substances. Some of PFASs have been classified as persistent organic pollutants and endocrine disruptors. They might interfere with the male sex endocrine system, causing the abnormal development of the male reproductive tract and failure of pubertal onset and infertility. The present review discusses the development and function of two generations of Leydig cells in rodents and the effects of PFASs on Leydig cell development after their exposure in gestational and postnatal periods. We also discuss human epidemiological data for the effects of PFASs on male sex hormone levels. The structure-activity relationship of PFASs on Leydig cell steroidogenesis and enzyme activities are also discussed.

Corticosteroid-Binding Globulin is expressed in the adrenal gland and its absence impairs corticosterone synthesis and secretion in a sex-dependent manner

Corticosteroid-binding globulin (CBG) is synthesized by the liver and secreted into the bloodstream where binds to glucocorticoids. Thus CBG has the role of glucocorticoid transport and free hormone control. In addition, CBG has been detected in some extrahepatic tissues without a known role. CBG-deficient mice show decreased total corticosterone levels with missing of classical sexual dimorphism, increased free corticosterone, higher adrenal gland size and altered HPA axis response to stress. Our aim was to ascertain whether CBG deficiency could affect the endocrine synthetic activity of adrenal gland and if the adrenal gland produces CBG. We determined the expression in adrenal gland of proteins involved in the cholesterol uptake and its transport to mitochondria and the main enzymes involved in the corticosterone, aldosterone and catecholamine synthesis. The results showed that CBG is synthesized in the adrenal gland. CBG-deficiency reduced the expression of ACTH receptor, SRB1 and the main genes involved in the adrenal hormones synthesis, stronger in females resulting in the loss of sexual dimorphism in corticosteroid adrenal synthesis, despite corticosterone content in adrenal glands from CBG-deficient females was similar to wildtype ones. In conclusion, these results point to an unexplored and relevant role of CBG in the adrenal gland functionality related to corticosterone production and release.