Murine neuronatin deficiency is associated with a hypervariable food intake and bimodal obesity

Abstract

Neuronatin (Nnat) has previously been reported to be part of a network of imprinted genes downstream of the chromatin regulator Trim28. Disruption of Trim28 or of members of this network, including neuronatin, results in an unusual phenotype of a bimodal body weight. To better characterise this variability, we examined the key contributors to energy balance in Nnat+/−p mice that carry a paternal null allele and do not express Nnat. Consistent with our previous studies, Nnat deficient mice on chow diet displayed a bimodal body weight phenotype with more than 30% of Nnat+/−p mice developing obesity. In response to both a 45% high fat diet and exposure to thermoneutrality (30 °C) Nnat deficient mice maintained the hypervariable body weight phenotype. Within a calorimetry system, food intake in Nnat+/−p mice was hypervariable, with some mice consuming more than twice the intake seen in wild type littermates. A hyperphagic response was also seen in Nnat+/−p mice in a second, non-home cage environment. An expected correlation between body weight and energy expenditure was seen, but corrections for the effects of positive energy balance and body weight greatly diminished the effect of neuronatin deficiency on energy expenditure. Male and female Nnat+/−p mice displayed subtle distinctions in the degree of variance body weight phenotype and food intake and further sexual dimorphism was reflected in different patterns of hypothalamic gene expression in Nnat+/−p mice. Loss of the imprinted gene Nnat is associated with a highly variable food intake, with the impact of this phenotype varying between genetically identical individuals.

Independent phenotypic plasticity axes define distinct obesity sub-types

“…1a,b and Extended Data Fig. 1a), which is distinct from the previously reported Trim28-buffered polyphenism and from other reports of heterogeneity using the Nnat +/-p allele 36,[41][42][43] . Nnat +/-p -Heavy animals were ~50% heavier than both their WT and Nnat +/-p -Light littermates and had increased white adipose tissue, spleen, pancreas, kidney, liver and heart mass (Fig.…”

“…Nnat loss triggers bi-stable β-cell hyperplasia. Previous work suggested that Nnat deletion causes a stochastic obesity (B6 background; several groups/vivaria 42,43 ) and partially penetrant, early-life growth restriction that is alleviated in later life through increased food intake (129S2/Sv background; one group 41 ). To capture early growth kinetics of the Nnat +/-p -Light and Nnat +/-p -Heavy animals, we tattooed animals at birth and tracked body composition.…”

“…One key translational question raised by these data is whether NNAT-associated phenotypic variation and bi-stable effects are influenced by genetic or environmental interactions. Since our original description 43 , several groups 41,42 generated anecdotal evidence for the existence of genetic and environmental modifiers of NNAT-dependent buffering of UPV. We have directly tested and validated the idea.…”

“…It was first described as a developmentally regulated gene of the embryonic brain 31,32 , but is also widely expressed and associated with energy homeostasis across tissues 33 . Nnat expression is necessary for proper glucose-stimulated insulin secretion in differentiated pancreatic β-cells [34][35][36] , for adipogenesis and glucose disposal in adipocytes [37][38][39] , appetite in the hypothalamus 40 and for energy expenditure and food intake 41,42 . It remains unclear whether any of these functions play a causal role in the emergence of UPV or mammalian polyphenism.…”

Mechanisms Driving Palmitate-Mediated Neuronal Dysregulation in the Hypothalamus

“…This increase in Npy may be the result of miR-708-5p-mediated downregulation of its target neuronatin (NNAT), a putative sarco/endoplasmic reticulum Ca 2+ inhibitor [122]. This hypothesis is supported by the fact that knockout of NNAT resulted in increased Npy expression in the ARC and an increased propensity to develop obesity in mice [123]. Transcription factors involved in the regulation of Agrp include Kruppel-like factor 4 (KLF4), activating transcription factor 3 (ATF3), STAT3, and FOXO1 [90,[124][125][126].…”