Evaluation of the leptin receptor in human spermatozoa

Insights into leptin signaling and male reproductive health: the missing link between overweight and subfertility?

Obesity stands as one of the greatest healthcare challenges of the 21st century. Obesity in reproductive-age men is ever more frequent and is reaching upsetting levels. At the same time, fertility has taken an inverse direction and is decreasing, leading to an increased demand for fertility treatments. In half of infertile couples, there is a male factor alone or combined with a female factor. Furthermore, male fertility parameters such as sperm count and concentration went on a downward spiral during the last few decades and are now approaching the minimum levels established to achieve successful fertilization. Hence, the hypothesis that obesity and deleterious effects in male reproductive health, as reflected in deterioration of sperm parameters, are somehow related is tempting. Most often, overweight and obese individuals present leptin levels directly proportional to the increased fat mass. Leptin, besides the well-described central hypothalamic effects, also acts in several peripheral organs, including the testes, thus highlighting a possible regulatory role in male reproductive function. In the last years, research focusing on leptin effects in male reproductive function has unveiled additional roles and molecular mechanisms of action for this hormone at the testicular level. Herein, we summarize the novel molecular signals linking metabolism and male reproductive function with a focus on leptin signaling, mitochondria and relevant pathways for the nutritional support of spermatogenesis.

Adipokines in Semen: Physiopathology and Effects on Spermatozoas

Adipokines are secreted by adipose tissue and could be the link between obesity and infertility. Different studies investigated the involvement of adipokines in reproductive functions but only a few have looked into the male part. This review assesses adipokine functions on male reproductive parameters. Adiponectin seems to have a positive effect on sperm parameters, whereas other adipokines such as resistin or chemerin would have a rather deleterious effect on spermatogenesis. Semen parameters seem to be impacted when resistin and chemerin are increased: indeed, there is a decrease of sperm motility. Sperm morphology is improved when adiponectin is increased. The most studied adipokine, leptin, has a dual effect with a positive effect on sperm at physiological levels and a negative one for high seminal concentrations. Many semen parameters and fertility itself are disturbed according to semen adipokine levels, even if it is not the only interfering element. Taken together, adipokines are found in human and animal semen and most of them or their receptors are expressed in male genital tract. Although the pathophysiological role of adipokines in semen is not clearly elucidated, the adipokines could influence sperm functionality and could be potential biomarkers of male fertility.

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.

Effect of brain-derived neurotrophic factor (BDNF) on sperm quality of normozoospermic men

The neurotrophin family of proteins and their receptors act as important proliferative and pro-survival factors in differentiation of nerve cells and are thought to play key roles in the development of reproductive tissues and normal function of spermatozoa. The objective of the present study was to evaluate the effect of Brain-Derived Neurotrophic Factor (BDNF) on the sperm viability and motility, lipid peroxidation (LPO), mitochondrial activity and concentration of leptin, nitric oxide (NO) and insulin in normozoospermic men. Semen samples from 20 normozoospermic men were divided into three groups: (i) control, (ii) BDNF and (iii) BDNF + K252a. BDNF and K252a were added in the dose of 0.133 and 0.1 nM, respectively. Viability was assessed by eosin-nigrosin staining technique, and motility was observed by microscopy. NO concentration and mitochondrial activity were measured with flow cytometry, and LPO was analyzed using enzyme-linked immunosorbent assay (ELISA) kits. Results showed that exogenous BDNF at 0.133 nM could significantly (p < 0.05) influence viability, motility, NO concentration, mitochondrial activity and LPO content. Secretions of insulin and leptin by human sperm were increased in cells exposed to the exogenous BDNF, whereas viability, mitochondrial activity and insulin and leptin secretions were decreased in cells exposed to the K252.

Impaired steroidogenesis in the testis of leptin-deficient mice (ob/ob -/-)

The obesity and its comorbidities, including resistance to leptin, impacts the reproductive function. Testes express leptin receptors in the germ cells and Leydig cells. Then, leptin-deficient animals are obese and infertile. We aimed to evaluate the structure and steroidogenic pathway of the testis of deficient leptin mice. Three months old male C57BL/6 mice (wild-type, WT) and deficient leptin (ob/ob) mice had their testes dissected and prepared for analyses. Compared to the WT group, the ob/ob group showed a greater body mass with smaller testes, and alterations in the germinative epithelium: fewer spermatogonia, spermatocytes, and spermatids. The Sertoli cells and the germ cells showed condensed nuclei and nuclear fragmentation indicating cell death, in agreement with a low expression of the proliferating cell nuclear antigen and a high expression of Caspase3. In the ob/ob group, the sperm was absent in the seminiferous tubules, and the steroidogenic pathway was compromised (low 3Beta hydroxysteroid dehydrogenase and steroidogenic acute regulatory protein). Further, all hormone receptors involved in the testicular function were down expressed (androgen, estrogen, follicle-stimulating, luteinizing, aromatase, and nicotinamide adenine dinucleotide phosphate). In conclusion, the findings indicate significant morphological, hormonal and enzymatic changes in the testis of the ob/ob mice. The shifts in the enzymatic steroidogenic pathway and the enzymes related to spermatic activity support the insights about the failures in the fertility of these animals. The study provides new evidence and contributes to the understanding of how the lack of leptin and obesity might negatively modulate the testicular function leading to infertility.

The effects of long-term leptin administration on morphometrical changes of mice testicular tissue

OBJECTIVES

Leptin is a novel and interesting hormone for anyone trying to lose weight, but its effects on male gonad structure in longitudinal study is unknown. The present study was designed to explore morphometrical changes of mouse testicular tissue after long-term administration of leptin.

MATERIALS AND METHODS

Thirty healthy mature male mice were randomly assigned to either control (n=15) or treatment (n=15) groups. Leptin was intraperitoneally injected to the treatment group (0.1 µg/100 µl of physiological saline) once a day for 30 consecutive days, and control animals received normal saline with the same volume and route. Five mice from each experimental group were sacrificed at 15, 30 and 60 days after the beginning of treatments. Left testes were removed, weighted and then fixed in 10% buffered formalin, and stained with hematoxylin and eosine for morphometrical assays.

RESULTS

Except for sertoli cell nucleus diameter, which was affected from 30(th) day, evaluation of other morphometrical parameters such as Johnsen's score, meiotic index, spermatogenesis, epithelial height, seminiferous tubules diameter and spermatogonial nucleus diameter revealed significant decrease from 15(th) day after leptin administration compare to those of the control group (P<0.05). Thus, meiotic index and spermatogonial cell nucleus diameter were two parameters that were further disturbed on 30(th) day compare to the day 15 (3.09±0.03 vs. 3.23±0.03, P=0.006 and 5.50±0.09 vs. 6.08±0.14, P=0.007, respectively).

CONCLUSION

Our results showed that long-term administration of leptin could disturb testicular tissue structure and delay spermatogenesis process.

The in vitro effect of leptin on semen quality of water buffalo (Bubalus bubalis) bulls

The purpose of this study was to evaluate the probable effects of leptin addition in different levels to the semen extender on sperm quality (motility and motility parameters, viability, sperm membrane integrity, and DNA damage). Semen specimens were evaluated immediately after leptin addition, equilibration time and after thawing the frozen semen. Five healthy buffalo bulls (5 ejaculates from each bull) were used. Each ejaculate was diluted at 37 ˚C with tris-based extender containing 0 (control), 10, 20, 50, 100, and 200 ng mL(-1) leptin. The diluted semen was kept 4 hr in refrigerator to reach to the equilibration time and then packed in 0.5 mL French straws and frozen in liquid nitrogen. Our results showed that, in the fresh semen, no significant difference was observed in all sperm quality parameters evaluated among all of the examined leptin concentrations. Addition of 10 ng mL(-1) leptin into semen extender significantly preserved sperm motility, all of the motility parameters, and viability in equilibrated semen compared to that of control group. However, in vitro addition of 200 ng mL(-1) leptin, significantly decreased theses parameters. In the frozen thawed semen, all leptin concentrations decreased sperm motility and viability, but significant decrease was observed in concentrations of 100 and 200 ng mL(-1). Adding leptin to semen extender did not have any significant influence on sperm DNA damage and sperm membrane integrity in all examined groups. These findings suggest that in vitro addition of 10 ng mL(-1) leptin could preserve sperm motility and viability in cooled semen of buffaloes.