Leptin has a modulatory impact on the course of inflammation, affecting the expression of proinflammatory cytokines and their receptors. Pathophysiological leptin resistance identified in humans occurs typically in sheep during the long-day photoperiod. This study aimed to determine the effect of the photoperiod with relation to the leptin-modulating action on the expression of the proinflammatory cytokines and their receptors in the anterior pituitary under physiological or acute inflammation. Two in vivo experiments were conducted on 24 blackface sheep per experiment in different photoperiods. The real-time PCR analysis for the expression of the genes IL1B, IL1R1, IL1R2, IL6, IL6R, IL6ST, TNF, TNFR1, and TNFR2 was performed. Expression of all examined genes, except IL1β and IL1R2, was higher during short days. The leptin injection increased the expression of all examined genes during short days. In short days the synergistic effect of lipopolysaccharide and leptin increased the expression of IL1B, IL1R1, IL1R2, IL6, TNF, and TNFR2, and decreased expression of IL6ST. This mechanism was inhibited during long days for the expression of IL1R1, IL6, IL6ST, and TNFR1. The obtained results suggest the occurrence of leptin resistance during long days and suggest that leptin modulates the course of inflammation in a photoperiod-dependent manner in the anterior pituitary.

The modulation of leptin sensitivity in hypothalamic neurons plays a crucial role in metabolic regulation and the development of obesity. Three distinct approaches, exposure to leptin (LEPA), administration of leptin antagonist (LANTA), and treatment with palmitate (PA), were explored in this study to assess their effects on adult-derived mHypoA-2/12 neurons and the resulting transcriptomic signatures. To this end, 3’ mRNA-Seq transcriptome analysis was employed, unexpectedly revealing downregulation of key genes associated with the NOD-like receptor signaling pathway (Irf9, Mapk3, Stat2, Nfkbia, Ikbkg, Rela, Cxcl1, and Traf5), the C-type lectin receptor signaling pathway (Nfkb2, Irf9, Mapk3, Stat2, Nfkbia, Ikbkg, Rela, and Ptgs2), the NF kappa B signaling pathway (Nfkbia, Ikbkg, Nfkb2, Rela, Traf5, Cxcl1, and Ptgs2), and the IL 17 signaling pathway (Nfkbia, Ikbkg, Mapk3, Rela, Traf5, Cxcl1, and Ptgs2). These findings help elucidate the molecular mechanisms through which these factors influence leptin sensitivity and provide insights into the pathways implicated in the development of leptin resistance in hypothalamic neurons. The surprising downregulation of these pathways suggests a complex interplay between leptin signaling and the cellular stress response in hypothalamic neurons. This alteration may reflect adaptive mechanisms in response to prolonged leptin or fatty acid exposure. Understanding these dynamics is essential for elucidating the role of hypothalamic inflammation in the progression of leptin resistance and associated metabolic disorders.

The present study investigated the impact of microplastics, specifically polystyrene microparticles (PS-MP), on the hypothalamic-pituitary-gonadal (HPG) neurohormonal axis, which regulates reproductive functions in animals and humans. The primary objective was to examine the effects of PS-MP on the expression of key genes and hormone concentrations within the gonadotropic system of sheep. Two doses of PS-MP—the lower dose (LD; 0.015 mg/kg) and the higher dose (HD; 0.15 mg/kg)—were administered intravenously every three days over two estrous cycles (34 days). Both doses significantly decreased the relative abundance of gonadotropin-releasing hormone (GnRH) transcripts in the mediobasal hypothalamus (MBH), whereas only the HD reduced GnRH mRNA levels in the preoptic area (POA). These transcript-level changes were not accompanied by detectable alterations in GnRH protein concentration. In the MBH, the expression of kisspeptin (KISS-1) and neurokinin B (NKB) genes decreased following exposure to the HD, whereas in the POA, significant decrease in expression were observed only after the LD administration. Changes in prodynorphin (PDYN) gene expression were confined to the MBH and were dose-dependent: the LD increased transcript levels, whereas the HD caused a decrease. The HD of PS-MP also significantly downregulated GnRH receptor (GnRHR) expression in the anterior pituitary (AP). Both PS-MP doses resulted in marked reductions in luteinizing hormone beta (LHβ) and follicle-stimulating hormone beta (FSHβ) subunit gene expression in the AP, without significant changes in hormone protein concentrations. Exposure to PS-MP reduced plasma LH and FSH concentrations: the lower dose reduced both hormones, while the higher dose significantly reduced mainly FSH, showing statistical differences between doses. To summarize, the present study demonstrates that PS-MP exerts a modulatory effect on the secretory activity of the central reproductive system in sheep, at both the hypothalamic and pituitary levels. Consequently, PS-MP has the potential to induce significant disruptions to the reproductive processes of large farm animals.

Background: Circulating cell-free microRNAs (miRNAs) are emerging mediators of inter-organ communication and biomarkers of metabolic and inflammatory regulation; however, the relationship between circulating miRNA dynamics and inflammatory cytokine responses during the development of obesity-induced leptin resistance remains incompletely characterised. Thus, this study investigated the longitudinal interplay between circulating miRNAs and cytokine profiles in sheep with diet-induced leptin resistance. Results: Obese ewes developed persistent hyperleptinemia and progressive insulin resistance, consistent with leptin resistance. Cytokine profiling revealed a two-phase inflammatory response, with sustained TNF-α and IL-1α elevation from week seven and a transient acute episode at week ten marked by IL-1β and IL-6 peaks. IL-10 was consistently lower in obese ewes, and the rise in IL-36RA seen in controls by week fourteen was absent in obese animals. Plasma small RNA sequencing identified ten differentially expressed miRNAs with predicted origins in immune cells (oar-miR-150, oar-miR-17-5p), and adipose and metabolic organs (oar-miR-30b, oar-miR-29a), alongside 257 novel ovine miRNA candidates, of which 16 were differentially expressed at padj < 0.10, including a homolog of miR-342-3p linked to adipogenesis. Plasma miR-150 concentrations were highest at week ten, when they correlated positively with IL-1β and IL-6 in the validation cohort, though this increase was not significant relative to baseline after correction for multiple testing. Members of the miR-30 family declined progressively and correlated negatively with IL-6 and IL-8, a relationship that persisted after accounting for repeated animal sampling. Plasma and CSF concentrations of the four miRNAs were not significantly correlated, although with three animals per group this does not establish independent central and peripheral compartments. oar-let-7c concentrations were markedly higher in CSF of obese animals at week fourteen but were unchanged in plasma. Conclusions: Plasma miRNA and cytokine profiles undergo coordinated temporal changes during obesity-induced leptin resistance in sheep, with specific miRNA subsets tracking acute and chronic inflammatory phases. These findings position circulating miRNAs as candidate biomarkers of the inflammatory response accompanying obesity-induced leptin resistance, warranting future mechanistic investigation of their functional role. De novo discovery of differentially expressed novel ovine miRNA candidates broadens the annotated ovine miRNome and opens new lines of investigation.