Leptin Modulates the mRNA Expression of Follicle Development Markers in Post-hatch Chicks in an Age-Dependent Manner

A Bird's-Eye Overview of Leptin and Female Reproduction -with Mammalian Comparisons

Leptin, a key regulator of reproductive physiology, influences various processes in vertebrates, including oocyte proliferation, embryogenesis, the onset of puberty, ovarian function, and follicle development. In mammals, leptin affects steroidogenesis, folliculogenesis, and hormonal regulation through the hypothalamic-pituitary-gonadal axis. Instead, in avian species, leptin-controlled mechanisms are poorly understood, because birds do not produce leptin in adipocytes. In birds, leptin is expressed in the brain, pituitary glands, and gonads, where it enhances ovarian function and egg-laying performance, particularly during feed deprivation. In this review, we discuss and summarize the recently discovered role of leptin in regulating ovarian function during different life stages in birds and compare it with its function in mammals.

Leptin- and cytokine-like unpaired signaling in Drosophila

Animals have evolved a multitude of signaling pathways that enable them to orchestrate diverse physiological processes to tightly regulate systemic homeostasis. This signaling is mediated by various families of peptide hormones and cytokines that are conserved across the animal kingdom. In this review, we primarily focus on the unpaired (Upd) family of proteins in Drosophila which are evolutionarily related to mammalian leptin and the cytokine interleukin 6. We summarize expression patterns of Upd in Drosophila and discuss the parallels in structure, signaling pathway, and functions between Upd and their mammalian counterparts. In particular, we focus on the roles of Upd in governing metabolic homeostasis, growth and development, and immune responses. We aim to stimulate future studies on leptin-like signaling in other phyla which can help bridge the evolutionary gap between insect Upd and vertebrate leptin and cytokines like interleukin 6.

Vitrified turkey ovarian tissue cultured and assessed through gene expression patterns: A potential screening tool

Biobanking of turkey ovarian tissue has the potential to play a crucial part in preserving female genetics. To date, ovarian tissue has only been vitrified using a standard protocol, with immediate analyses after warming, therefore, long-term cryoinjury is unknown. Long-term cryoinjury was investigated here by in-ovo culturing, fresh (non-vitrified), a purposefully suboptimal poor vitrification (PV), and the standard vitrified (StV) protocol. Assessments were performed via cellular morphological changes and mRNA gene expression differences, immediately (day 0) or after 2, 4, or 6 days of in-ovo culturing. On day 0, the mRNA levels of heat-shock protein A2 (HSPA2) were lowest in the fresh tissue, and increased 5-fold in the StV treatment, and 18-fold in the PV treatment. Whereas, by day 6, growth determining factor 9 (GDF9) mRNA levels within the fresh tissue were over 3-fold and 21-fold higher than StV and PV treatments, respectively. After 6 days of in-ovo culture the follicle density was highest in the fresh ovarian tissue (4701 ± 950 #/mm3), followed by the StV (1601 ± 300 #/mm3), with PV having the lowest density (172 ± 145 #/mm3). This shows that although the density of follicles was higher in StV versus PV, a considerable number (∼65 %) were lost compared to the fresh treatment. Additionally, the HSPA2 expression could be an early screening tool, whereas GDF9 expression could be a late screening tool, used to assess turkey ovarian tissue vitrification protocols. We conclude that the StV protocol should be further optimized to try and improve follicle numbers post-warming.

Impact of In Ovo Leptin Injection and Dietary Protein Levels on Ovarian Growth Markers and Early Folliculogenesis in Post-Hatch Chicks (Gallus gallus domesticus)

Genetically bred for rapid growth, broiler breeder hens develop obesity and ovarian dysfunction when fed ad libitum, resembling a condition that resembles human polycystic ovary syndrome (PCOS). Nutritional control applies to post-hatched chicks from one week onward to prevent the development of a PCOS-like phenotype in adult broilers. This study investigated the impact of a growth marker, leptin, and post-hatch nutritional intake on early-life ovarian function. Fertile broiler eggs were injected in ovo with physiological saline solution or 5 µg of leptin and then incubated. After hatching, female chicks were fed ad libitum a diet containing low protein (17% low crude protein (LP)) or standard protein (22% standard crude protein (SP)). Tissues were collected from 7- and 28-day-old chicks for RT-qPCR and histological analysis. In contrast to the LP diet, the SP diet suppressed the mRNA expression of ovarian growth markers essential for folliculogenesis in post-hatched chicks. Leptin injection did not influence ovarian growth markers but increased pituitary gonadotropin transcripts in 7-day-old chicks fed with LP diet. No treatment effects on follicle activation were noted on day 7, but by day 28, in ovo leptin-treated LP-fed chicks exhibited a higher percentage of primary follicles. These changes may have resulted from the early upregulation of genes by leptin during the first week, including pituitary gonadotropins and ovarian leptin receptors. The decline in ovarian growth markers with the SP diet highlights the importance of precise post-hatch protein calculation, which may influence future ovarian function in animals. These findings may contribute to future dietary strategies to enhance broiler reproduction.

Leptin alleviated ovarian ischemia-reperfusion injury in rats via modulation of Sirt-1/Nrf2 and TLR4/NF-kB/caspase-3 signaling pathways

Objective. Ovarian torsion is a gynecological emergency that occurs mostly during the female reproductive years due to ovarian masses or surgical manipulation. This work aims to explore the probable protective effect of leptin on rat ovaries due to ischemia-reperfusion (IR) injury. Methods. Wistar albino rats were divided into four groups: 1) control group; 2) ovarian IR group (OVIR); 3) leptin group I [OVIR + leptin (10 µg/kg body weight, b.w.)]; and 4) leptin group II (OVIR + leptin (100 µg/kg b.w.)]. Serum levels of estradiol and anti-Mullerian hormone (AMH) were measured. Levels of oxidative stress and inflammatory markers in ovarian tissue were determined along with the expression of sirtuin 1 (Sirt1), nuclear erythroid factor-2 (Nrf2), cyclooxygenase-2 (COX-2), nuclear factor kappa (NF-κB), toll like receptor-4 (TLR4), and caspase-3. Results. Serum estradiol and AMH levels were decreased with increased expression of COX-2, TLR4, caspase-3, and NF-κB and decreased expression of Sirt1and Nrf2 in ovary of the OVIR group, which were improved by exogenous administration of both leptin doses. Conclusion. Leptin administration dose-dependently reduced the severity of OVIR injury via modulation of Sirt-1/Nrf2 and TLR4/NF-kB/caspase-3 signaling pathways. Thus, leptin may be used as an adjuvant measure to prevent ovarian damage and improve the outcomes. However, clinical studies are needed to evaluate these results in humans.

Leptin Promotes Primordial Follicle Activation by Regulating Ovarian Insulin-like Growth Factor System in Chicken

Leptin and insulin-like growth factor 1 (IGF-1) regulate follicle development and reproduction in vertebrates. This study investigated the role played by leptin and IGF-1 in primordial follicle activation in the ovary of 7-day-old chicks. Different doses of leptin were intraperitoneally administrated to female layer chicks, and further analyses were performed. While leptin administration did not affect hepatic leptin receptor (LEPR), growth hormone receptor (GHR), or IGF-1, the lower dose of leptin significantly increased the messenger RNA (mRNA) expression of IGF-1, IGF-1 receptor, and IGF-binding protein (IGFBP)-2 and attenuated anti-Müllerian hormone (AMH) gene expression in the ovary. Furthermore, the ovaries of the same age chicks were challenged with leptin and/or IGF-1 in vitro. Leptin at a lower dose increased the mRNA expression of IGF-1, LEPR, and leptin; 100 ng/mL leptin and 10 ng/mL IGF-1 alone or combined with leptin reduced IGFBP-2 mRNA expression. AMH gene expression was also reduced by all doses except 10 ng/mL leptin. Histological studies showed that a lower dose of leptin injection induced the primordial follicle growth in the ovary in vivo, and the number of primordial follicles was higher in all leptin treatments over control in vitro. Moreover, the luciferase assay revealed that leptin enhanced IGF-1 promoter activity in LEPR-expressing CHO-K1 cells. Collectively, these results indicate that leptin directly affects the IGF-1/IGFBP system and promotes primordial follicular growth in the ovary of early posthatch chicks. In addition, the follicular development by leptin-induced IGF-1 is, at least in part, caused by the suppression of AMH in the ovary.