Decreased sensitivity to the anorectic effects of leptin in mice that lack a Pomc-specific neural enhancer.

Elisa S Na,Daniel D Lam,Jessica M Adams,Eva Yokosawa,David P Olson,Malcolm J Low,Julie A Chowen

doi:10.1371/journal.pone.0244793

Abstract

Enhancer redundancy has been postulated to provide a buffer for gene expression against genetic and environmental perturbations. While work in Drosophila has identified functionally overlapping enhancers, work in mammalian models has been limited. Recently, we have identified two partially redundant enhancers, nPE1 and nPE2, that drive proopiomelanocortin gene expression in the hypothalamus. Here we demonstrate that deletion of nPE1 produces mild obesity while knockout of nPE2 has no discernible metabolic phenotypes. Additionally, we show that acute leptin administration has significant effects on nPE1 knockout mice, with food intake and body weight change significantly impacted by peripheral leptin treatment. nPE1 knockout mice became less responsive to leptin treatment over time as percent body weight change increased over 2 week exposure to peripheral leptin. Both Pomc and Agrp mRNA were not differentially affected by chronic leptin treatment however we did see a decrease in Pomc and Agrp mRNA in both nPE1 and nPE2 knockout calorie restricted mice as compared to calorie restricted PBS-treated WT mice. Collectively, these data suggest dynamic regulation of Pomc by nPE1 such that mice with nPE1 knockout become less responsive to the anorectic effects of leptin treatment over time. Our results also support our earlier findings in which nPE2 may only be critical in adult mice that lack nPE1, indicating that these neural enhancers work synergistically to influence metabolism.

Highlights

The arcuate nucleus of the hypothalamus plays a critical role in integrating neuroendocrine signals regarding nutritional status and serves as an important site for maintenance of body energy homeostasis [1]
We observed group differences in acute food intake after leptin/PBS treatment between nPE1 KO leptin-treated mice compared to all other groups with the exception of WT leptintreated mice (p = 0.054), indicating that food intake in nPE1 KO mice is significantly attenuated by leptin treatment (Fig 1B)
A one-way ANOVA did not reveal significant between group differences in Pomc mRNA expression (Fig 3A) we show that Agrp mRNA is significantly decreased in all groups as compared to the WT PBS-treated group as determined by a one-way ANOVA, F (5,30) = 13.2, p

Summary

Introduction

The arcuate nucleus of the hypothalamus plays a critical role in integrating neuroendocrine signals regarding nutritional status and serves as an important site for maintenance of body energy homeostasis [1]. Leptin and nPE1 deletion including first-order neurons co-expressing proopiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) anorexigeic neuropeptides as well as orexigenic co-expressing neuropeptides neuropeptide Y (NPY) and agouti-related peptide (AgRP) [2]. These neuropeptides work in an opposing fashion to maintain energy balance at optimal levels. Simultaneous deletion of nPE1 and nPE2 leads to near complete abolishment of arcuate Pomc expression and compromised metabolic function, increased adiposity, hyperphagia and reduced expression of the melanocortins, α-MSH and β-endorphin, as well as morbid obesity [13]. The partial redundancy of nPE1 and nPE2 suggests that these enhancers have overlapping functions and that dysfunction of one enhancer can be counteracted by the intact function of its paralogue [13]

Methods

Results

Conclusion