Adverse effects of leptin on histone-to-protamine transition during spermatogenesis are prevented by melatonin in Sprague-Dawley rats

Protective effects of melatonin against oxidative stress induced by metabolic disorders in the male reproductive system: a systematic review and meta-analysis of rodent models

Background

Male infertility is a multifaceted issue that has gained scientific interest due to its increasing rate. Studies have demonstrated that oxidative stress is involved in male infertility development. Furthermore, metabolic disorders, including obesity, diabetes, hypo- and hyperthyroidism, are risk factors for male infertility, and oxidative stress is believed to contribute to this association. Melatonin, functioning as an oxidative scavenger, may represent a promising therapeutic approach for the prevention and treatment of metabolic disorder-associated male infertility.

Material and methods

We systematically searched three online databases (PubMed, Scopus, and Web of Science) for studies that evaluated the effects of melatonin therapy on metabolic disorders-induce infertility in male rodents. The favorable outcomes were histopathological parameters of testicular tissue, reproductive hormones, and markers of oxidative stress. Then, meta-analyses were done for each outcome. The results are reported as standardized mean difference (Cohen's d) and 95% confidence interval.

Results

24 studies with 31 outcomes were included. Rats and mice were the subjects. Studies have employed obesity, diabetes, hypothyroidism, hyperthyroidism, hyperlipidemia, and food deprivation as metabolic disorders. To induce these disorders, a high-fat diet, high-fructose diet, leptin, streptozotocin, alloxan, carbimazole, and levothyroxine were used. The outcomes included histopathologic characteristics (abnormal sperm morphology, apoptotic cells, apoptotic index, Johnsen's testicular biopsy score, seminiferous epithelial height, tubular basement membrane thickness, tubular diameter, sperm count, and motility), weight-related measurements (absolute epididymis, testis, and body weight, body weight gain, epididymal adipose tissue weight, and relative testis to body weight), hormonal characteristics (androgen receptor expression, serum FSH, LH, and testosterone level), markers of oxidative stress (tissue and serum GPx and MDA activity, tissue CAT, GSH, and SOD activity), and exploratory outcomes (serum HDL, LDL, total cholesterol, triglyceride, and blood glucose level). The overall pooled effect sizes were statistically significant for all histopathological characteristics and some markers of oxidative stress.

Conclusions

Melatonin can reduce damage to male rodents' gonadal tissue and improve sperm count, motility, and morphology in metabolic diseases. Future clinical studies and randomized controlled trials are needed to evaluate the safety and effectiveness of melatonin for male infertility in patients with metabolic diseases.

Systematic Review of Literature Documenting the Link Between BMI, Sperm Parameters, and Leptin

Background: Leptin administration to rats causes adverse effects on sperm that resemble those reported in obese males. The purpose of this review is, therefore, to examine whether human and animal studies have taken this information on board and have attempted to link the poor sperm quality in obese or overweight individuals to leptin in their methodology, data analysis, and discussion. The review also documents the link between low sperm quality in the obese and leptin.

Method: A search was made for articles reporting body mass index (BMI), sperm parameters, and leptin, published until September 2020 in PubMed, Science Direct, Google Scholar, and Springer Link using a number of search terms.

Results: Forty-four of the 53 human and animal studies on BMI and sperm parameters reported abnormal sperm parameters in the obese but only 9 of those had measured serum leptin. None, however, attempted to link sperm abnormalities to leptin. Nine animal studies report of adverse effects of leptin on sperm in normal weight rats that were found to be similar to those reported in obese males.

Conclusion: Although none of the human studies had actually linked the raised leptin to sperm abnormalities in the obese, there is nevertheless, convincing evidence linking leptin to obesity-related poor sperm quality and male infertility. There is a need, therefore, to include measures that will help reduce the impact of raised leptin levels on male reproductive function, particularly, in obese infertile or subfertile males.

Synthetic leptin c-fragment peptide minimises heat-induced impairment of spermatogenesis in mice via Stat3 signalling

Mammalian spermatogenesis is a temperature-sensitive process, and an increase in testicular temperature impairs spermatogenesis. Leptin modulates testicular activity, but the effect of leptin or its synthetic analogue on heat-induced testicular impairment is unclear. We investigated the effects of synthetic leptin peptide (116-130 amides) on testicular activity in heat-stressed mice model. 15 adult mice (25.54 ± 1.43 g) were selected for the study. Ten mice were subjected to a single heat stress treatment (HS) at 43 °C for 15 min by submerging the lower half of the body in a thermostatic water bath. After heat treatment, mice were divided into two groups, the heat-stressed HS group (n = 5) and the second group as HSL, treated with leptin peptide (116-130 amide) for 14 days. The HS group showed a significant (p < 0.05) decline in the GSI (0.25 ± 0.018), Johnsenscore (4.5 ±.19), seminiferous tubule diameter (160.75 ± 10.18 μm), germinal epithelium height, (GEH) (37.5 ± 1.59 μm) compared to the CN (GSI-0.37 ± 0.015; Johnsen score-7.9 ± 0.20; GEH- 73.25 ± 1.29 μm; tubule diameter-230.25 ± 1.39 μm) and the HSL groups (GSI-0.38 ± 0.014; Johnsen' score-8.0 ± 0.32; GEH- 37.5 ± 1.59 μm; tubule diameter-160.75 ± 10.18 μm) groups. Heat treatment significantly (p < 0.05) increased the intra-testicular levels of leptin (HS-20.11 ± 2.1 pg/mg protein; CN-10.50 ± 0.17 pg/mg protein; HSL-12.99 ± 0.52 pg/mg protein) with a reduced level of pStat3, suggesting leptin resistance during testicular hyperthermia. Furthermore, heat treatment was associated with significantly (p < 0.05) decreased germ cell proliferation and reduced circulating testosterone levels (HS-2.69 ± 2.01 ng/mL; CN-7.69 ± 0.32 ng/mL; HSL-5.36 ± 0.73 ng/mL). However, the circulating androstenedione levels showed a significant (p < 0.05) increase in the HS group (0.75 ± 0.03 ng/mL) compared to the CN (0.51 ± 0.02 ng/mL) and HSL (0.57 ± 0.07 ng/mL) groups. Immunolocalisation of 3β-HSD showed moderate to faint staining in the Leydig cells in the HS group compared to the CN and HSL groups. Treatment with leptin peptide resulted in decrease in the intra-testicular leptin levels with increased phosphorylation of Stat3, suggesting improved leptin resistance, which was positively associated with increased germ cell proliferation, elevated testosterone levels, and improved testicular histoarchitecture. Testicular hyperthermia may cause leptin resistance and impaired leptin signalling, decreased testosterone biosynthesis and suppressed spermatogenesis, which could be a manifestation of leptin resistance. Treatment with leptin peptide improves leptin signalling and testicular activity in heat-stressed mice, but the underlying mechanism is still unclear.

Coding and Non-Coding RNAs, as Male Fertility and Infertility Biomarkers

Semen analysis is usually the first step in the assessment of male fertility. Although analyzes provide valuable information about male fertility, success of cytoplasmic sperm injection using this method is not predictable. In the recent years, studies have shown that sperm quality assessment helps clinicians predict male fertility status based on the expression of biomarkers. To write this article, a comprehensive study was conducted on several RNA transcripts by searching related words on medical information databases by 2018. According to the literature, spermatogenesis based disorders in male infertility have a significant relationship with the expression level of some RNA molecules (like DAZ and PRM1/PRM2 ratio) in semen and testicular tissue. Thus, they might be used as predictor biomarkersto evaluate success rate of testicular sperm extraction (TESE) procedure, but confirmation of this hypothesis requires more extensive research. By comparing the number of RNAs attributed to each fertility disorder in men, it is possible to trace the causes of disease or return fertility to some infertile patients by regulating the mentioned molecules. Further researches can provide a better understanding of the use of RNA expression profiles in the diagnosis and treatment of male infertility.

Insights into the Mechanism of Bovine Spermiogenesis Based on Comparative Transcriptomic Studies

Simple Summary

Any irregularity in spermiogenesis reduces the quality of semen and may lead to male sterility in cattle and humans. Thus, we investigated the differential transcriptomics of spermatids from round spermatid to epididymal sperm and compared them with the transcriptomics of mice in the same period. We found differentially expressed genes (DEGs) involved in sperm head and tail formation, and epigenetic regulatory networks which regulated genetic material condensation, the deformation of the spermatid, and the expression of genes in it. According to the sterility report on the ART3 protein and its possible epigenetic function, we detected that it was localised outside the spermatocyte, in round and elongated spermatids. Interestingly, we observed that the ART3 protein on round and elongated spermatids was localised approximately to the lumen of seminiferous tubule. It was also localised on the head and tail part near the head in epididymal sperm, suggesting its important role in the deformation from round spermatids to sperm. Our findings provide new insights into the molecular mechanism underlying bovine spermiogenesis, thereby contributing to the improved reproductive potential of cattle and the development of strategies for the diagnosis and treatment of male infertility.

Abstract

To reduce subfertility caused by low semen quality and provide theoretical guidance for the eradication of human male infertility, we sequenced the bovine transcriptomes of round, elongated spermatids and epididymal sperms. The differential analysis was carried out with the reference of the mouse transcriptome, and the homology trends of gene expression to the mouse were also analysed. First, to explore the physiological mechanism of spermiogenesis that profoundly affects semen quality, homological trends of differential genes were compared during spermiogenesis in dairy cattle and mice. Next, Gene Ontology (GO), Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway enrichment, protein–protein interaction network (PPI network), and bioinformatics analyses were performed to uncover the regulation network of acrosome formation during the transition from round to elongated spermatids. In addition, processes that regulate gene expression during spermiogenesis from elongated spermatid to epididymal sperm, such as ubiquitination, acetylation, deacetylation, and glycosylation, and the functional ART3 gene may play important roles during spermiogenesis. Therefore, its localisation in the seminiferous tubules and epididymal sperm were investigated using immunofluorescent analysis, and its structure and function were also predicted. Our findings provide a deeper understanding of the process of spermiogenesis, which involves acrosome formation, histone replacement, and the fine regulation of gene expression.

The protective role of l-carnitine on spermatogenesis after cisplatin treatment during prepubertal period in rats: A pathophysiological study

AIMS

As the spermatogenesis process is targeted by cisplatin (Cis) that changes testicular morphology, alters sperm quality, and hence causes male infertility. This study investigated the possible therapeutic effects of l-carnitine (LC) on Cis impaired spermatogenesis's establishment during the prepubertal phase.

MATERIALS AND METHODS

Ninety-six prepubertal Sprague Dawley male rats were divided into four groups.

CONTROL GROUP

rats were injected with 0.9% saline solution intraperitoneally (i.p.). LC group: animals were injected for eight weeks, with 250 mg/kg/wk. LC (i.p.). Cis group: animals were injected with a single dose of 5 mg/kg Cis (i.p.). LC + Cis group: animals were pre-injected with LC 250 mg/kg 2 h before Cis injection. The rats were sacrificed at 37, 60, and 90 days old, and their testes were taken for biochemical, molecular, and histopathological studies. The motility, viability, morphology, and DNA fragmentation of sperm in adult rats were also measured.

KEY FINDINGS

Group treated with LC and Cis showed an increase in antioxidant and hormonal activity compared to the Cis treated group in the pre and post-pubertal period. Moreover, there was an increase in sperm survival, motility, and DNA integrity. Furthermore, LC showed an increase in the anti-apoptotic and chromatin remodeling genes and a decrease in the pro-inflammatory genes.

SIGNIFICANCE

LC could enhance the spermatogenesis process after exposure to Cis during the prepubertal phase by restoring the balance between reactive oxygen species and antioxidant activity, improving hormonal activity, sperm quality and DNA integrity, promoting protamination and blood-testis barrier integrity, and maintaining the testicular architecture.

Association between leptin, obesity, hormonal interplay and male infertility

Male infertility is a major health problem worldwide. We investigated a possible association between leptin, obesity, hormonal interplay and male infertility. This cross-sectional study of 313 males (178 infertile and 135 fertile) was carried out in 2017. The subjects were categorised by body mass index (BMI) and body fat percentage (BF%) into normal weight, overweight and obese. Significantly higher levels of BMI and BF% (p-value < 0.001) and lower levels of FSH, LH, testosterone, and SHBG (p-value < 0.001) were found in infertile males. However, no significant difference was observed in leptin levels (p-value = 0.35). Leptin levels were significantly higher, and all the sex hormones were significantly lower (p-value < 0.001) in obese subjects, whereas according to BF% only leptin, FSH and SHBG were significantly different. Leptin showed a significant positive correlation with BMI and BF% (p < 0.001). A strong positive link to serum testosterone was found with age, FSH, and LH (p < 0.001) and a negative one with BMI and BF% (p < 0.001). In mutivariable anlaysis, after adjusting for the other covariates, a significant association between FSH and testosterone (p-value <0.001) was found. Serum leptin levels did not differ significantly in fertile and infertile groups, and no association was found with infertility. Furthermore, male obesity was found to be associated with infertility with the decrease in levels of sex hormones.

Exogenous leptin affects sperm parameters and impairs blood testis barrier integrity in adult male mice

BACKGROUND

Serum leptin levels are augmented in obese infertile men and in men with azoospermia. They also correlate inversely with sperm concentration, motility and normal forms. The mechanisms underlying the adverse effects of excess leptin on male reproductive function remain unclear. The present study aimed to evaluate the effects of exogenous leptin on sperm parameters in mice and to explore the underlying mechanisms.

METHODS

We treated normal adult male mice with saline, 0.1, 0.5 or 3 mg/kg leptin daily for 2 weeks. After treatment, serum leptin levels, serum testosterone levels, sperm parameters and testicular cell apoptosis were evaluated. Blood testis barrier integrity and the expression of tight junction-associated proteins in testes were also assessed. We further verified the direct effects of leptin on tight junction-associated proteins in Sertoli cells and the possible leptin signaling pathways involved in this process.

RESULTS

After treatment, there were no significant differences in body weights, reproductive organ weights, serum leptin levels and serum testosterone levels between leptin-treated mice and control mice. Administration of 3 mg/kg leptin reduced sperm concentration, motility and progressive motility while increasing the percentage of abnormal sperm and testicular cell apoptosis. Mice treated with 3 mg/kg leptin also had impaired blood testis barrier integrity, which was related to decreased tight junction-associated proteins in testes. Leptin directly reduced tight junction-associated proteins in Sertoli cells, JAK2/STAT, PI3K and ERK pathways were suggested to be involved in this process.

CONCLUSIONS

Exogenous leptin negatively affects sperm parameters and impairs blood testis barrier integrity in mice. Leptin reduced tight junction-associated proteins in Sertoli cells, indicating that leptin has a direct role in impairing blood testis barrier integrity. Given the function of blood testis barrier in maintaining normal spermatogenesis, leptin-induced blood testis barrier impairment may be one of the mechanisms contributing to male subfertility and infertility.

Review of the role of leptin in the regulation of male reproductive function

Since discovered in 1994, leptin has been thought to be a pleiotropic hormone that regulates food intake, controls energy balance in the body and influences multiple tissues in the body. Leptin plays an important mediating role in the regulation of neuroendocrine and can transmit the nutritional status signals to the reproductive-related central nervous system. Many studies have shown that leptin may play an important role in the control of reproductive function. Leptin can act on all levels of the hypothalamus-pituitary-gonadal (HPG) axis and may have local effects on the function of testis and spermatogenesis. Leptin is critical for puberty initiation and can also modulate testosterone synthesis by downregulating cAMP-dependent activation of steroidogenic genes expressions. Leptin is found to be higher in infertile men than in normal subjects. Yet, the exact role of leptin in the regulation of male reproductive function remains incomplete. The purpose of this review was to summarise the recent research about the biological effects of leptin on male reproductive system. In-depth study of leptin in reproductive system will help to reveal the pathogenesis of infertility and provide new treatment ideas for human assisted reproductive technology.