Effects of Leptin, Growth Hormone and Photoperiod on Pituitary SOCS-3 Expression in Sheep.

Dorota Anna Zieba,Malgorzata Szczesna,Weronika Biernat,Katarzyna Kirsz

doi:10.3390/ani12030403

Dorota Anna Zieba, Malgorzata Szczesna + Show 2 more

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https://doi.org/10.3390/ani12030403

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Abstract

Simple SummaryMaintaining energy homeostasis requires numerous processes and interactions between many systems. This study investigated the relationships between leptin, growth hormone (GH), and factors involved in cell signaling, such as suppressors of cytokine signaling-3 (SOCS-3). Exogenous or endogenous factors affecting these relationships may have different origins, and their interactions are determined in this study. The finding that the length of day significantly influenced the concentrations of growth hormone as well as pituitary leptin- and GH-dependent SOCS-3 expressions suggests that photoperiod plays an important role in regulating the physiological processes underlying adaptive phenomena in response to changing seasons in sheep, which facilitates energy homeostasis despite changing external and internal conditions.This study examined how leptin affects growth hormone (GH) release and investigated the effects of leptin, GH, and day length on the suppressor of cytokine signaling-3 (SOCS-3) mRNA levels in the adenohypophyses of sheep. The study consisted of two experiments. The first experiment was conducted during long (LD) and short (SD) days. Within-season and replicate sheep were centrally infused with Ringer-Locke buffer or leptin three times at 60-min intervals at the beginning of experiments. The second experiment involved adenohypophyses collected from sheep that were euthanized in May or November. Pituitary explants were treated with medium alone (Control) or medium with leptin or GH at different concentrations and incubated for various times. The results of the first experiment indicated GH concentrations were seasonally dependent and that leptin had no effect on GH secretion. The results of the second experiment indicated a stronger influence of leptin on the expression of SOCS-3 during the SD season than the LD season. During SDs, significant effects of both GH doses on SOCS-3 expression were observed. These results indicate a strong association between leptin, GH, and SOCS-3, which may explain the disruption of SOCS-3 leptin and GH signaling and the dominant effect of photoperiod on the above relationships.

Highlights

Leptin is produced by many cells and in highest amounts by white adipose tissue cells
Depending on the day-length, plasma growth hormone (GH) concentration was enhanced in the control group (p < 0.01) in the long days (LDs) season compared with the short days (SDs) season (Figure 2)
The observed increase in GH secretion from the pituitary explants from fasted cows and the decreased secretion of GH from the tissues of normal-fed cows observed in that study could have resulted from differences in leptin receptor expression and a down-regulation of its expression in explants from well-fed cows or disturbance of the signaling pathway caused by higher expression of suppressor of cytokine signaling-3 (SOCS-3) in somatotrophs

Summary

Introduction

Leptin is produced by many cells and in highest amounts by white adipose tissue cells. An intracerebroventricular (icv) infusion of leptin demonstrated that this hormone decreased the expression of somatostatin and increased the expression levels of growth hormone releasing hormone (GHRH), which corresponded to an increase in the levels of GH mRNA [3]. This result suggests that leptin can directly stimulate GH secretion from pituitary explants [4,5,6]

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