Leptin/leptin receptor system in the regulation of reproductive functions and stress response in the European beaver

Reproductive phase-dependent and sexually dimorphic expression of leptin and its receptor in different parts of brain of spotted snakehead Channa punctata

The reproductive phase-wise leptin (lep) and its receptor (lepr) expression in different parts of the brain of adult male and female spotted snakehead Channa punctata reveals sexual dimorphism in the brain leptin system. In anterior, middle and posterior parts of the brain of males, a maximum lep was observed in resting, spawning and postspawning reproductive phases, respectively. In females, a high level of lep was seen during the preparatory phase in the anterior brain, preparatory and postspawning phases in the middle brain and resting and postspawning phases in the posterior brain. Nonetheless, the transcript level of lepr was recorded highest during the spawning phase, irrespective of sex and region of the brain. Regardless of the reproductive state of fishes, lep and lepr were seen considerably high in middle and posterior parts of male brain than that of female, implying the involvement of factors other than sex steroids for sex-related variation in the leptin system in these regions of the brain. Nonetheless, no sex difference was evidenced in the expression of either ligand or its receptor in the anterior brain. In summary, the presence of lep and lepr in different regions of the brain and variation in their expression depending on sex and reproductive phases raise the possibility of pivotal actions of leptin in influencing neuronal circuitry and thereby reproductive functions.

Seasonal change of circulating leptin associated with testicular activities of the wild ground squirrels (Citellus dauricus)

The purpose of this study was to explore the variations in the circulating leptin concentrations of the wild ground squirrels in relation to seasonal changes in testicular activities. Hematoxylin-eosin staining showed all types of elongated spermatids and spermatogenic cells existed in the testis in April, while the primary spermatocytes and spermatogonia were most advanced stages of germ cells in June. In addition, the primary spermatocytes, secondary spermatocytes, and spermatogonia were most advanced stages of germ cells in September. The highest circulating leptin concentration was consistent with the maximum body weight results from accumulation of adipose tissue in September. The mRNA expression level of leptin receptor (Ob-R) and STAT3 was lowest in June, raised in September, and remained increased in April. Ob-R and STAT3 were stronger staining in the Leydig cells in July. Moreover, the concentrations of testosterone (T) showed the maximum values in April, the minimum values in June, and significant increases in September. Furthermore, it is worth noting that the levels of T increased with the mRNA levels of Ob-R, STAT3, StAR, and testicular steroidogenic enzymes (3β-HSD, P450c17, and P450scc). Moreover, RNA-seq analyses of testis during the different periods showed that a total of 4209 genes were differentially expressed genes (DEGs); further analysis revealed that DEGs related with the Jak/STAT pathways and reproduction were altered. Taken together, the results suggested that the leptin regulated testicular function through the Jak/STAT pathways and testicular steroidogenic factor expressions.

Seasonality, sex-specificity and transcriptional regulation of hepatic leptin system in spotted snakehead Channa punctata

The present study deals with sex-specific reproductive phase-dependent variation and sex steroids-induced transcriptional regulation of hepatic lep and lepr in nutritionally valuable spotted snakehead, Channa punctata. The data on seasonality reveals sex-specific variation in pattern of lep transcription where a high level was recorded during resting and postspawning quiescent phases in female while during resting and spawning phases in male. Unlike lep, lepr exhibited similar expression pattern along the reproductive phases in both the sexes. As compared to female, a three-fold higher expression of lep was detected in male during reproductively active phase only. However, no sexual dimorphism was evidenced in lepr either during active or quiescent phase. To explore the implication of sex steroids in regulation of leptin system, we correlated levels of plasma testosterone (T) and 17β-estradiol (E₂) with leptin system in males as well as females. Further, criss-cross in vivo and in vitro experiments with dihydrotestosterone (DHT) and E₂ were conducted in male and female spotted snakehead. The leptin system was downregulated after DHT administration in both the sexes. However, with E₂, a marked decrease was evidenced in male only. The sex-wise variable response of leptin system to sex steroids was validated by in vitro experiments wherein liver fragments from male and female fish were incubated individually with both the sex steroids. In conclusion, sex steroids modulate hepatic leptin system differentially depending on sex and reproductive state of spotted snakehead.

Sex- and season-dependent differences in the expression of adiponectin and adiponectin receptors (AdipoR1 and AdipoR2) in the hypothalamic-pituitary-adrenal axis of the Eurasian beaver (Castor fiber L.)

Adiponectin, a product of the Adipoq gene, is an adipocyte-derived protein hormone of the cytokine family and the most abundantly expressed adipokine. Adiponectin and its receptors AdipoR1 and AdipoR2 (collectively referred to as the adiponectin system) are widely expressed in the central nervous system and other tissues, which suggests that this hormone has pleiotropic effects. Adiponectin could also play a role in the modulation of the hypothalamic-pituitaryadrenal (HPA) hormonal regulatory axis. There is a general scarcity of data on the adiponectin system in wild animals where annual changes in reproductive activity are linked with fluctuations in the activity of the HPA axis. The Eurasian beaver (Castor fiber L.) could be an interesting and suitable model for investigating the above processes. We hypothesized that the expression of the adiponectin system in the tissues of the beaver HPA axis is sex- and season-dependent. The study was performed on adult animals harvested during three different stages of reproductive activity: April ('breeding'), July ('post-breeding') and November ('pre-breeding'). The expression of the adiponectin system was confirmed in all branches (mediobasal hypothalamus, pituitary, adrenal cortex) of the HPA axis in both sexes and during all periods of reproductive activity. The expression of Adipoq, AdipoR1 and AdipoR2 was generally dependent on sex and the period of the reproductive season. The expression of adiponectin system genes was particularly pronounced in the adrenal cortex. These findings suggest that the adiponectin system in the Eurasian beaver could link reproductive processes with stress responses and energy metabolism.