In the large GWAS studies, NEGR1 gene has been one of the most significant gene loci for body mass phenotype. The purpose of the current study was to clarify the role of NEGR1 in the maintenance of systemic metabolism, including glucose homeostasis, by using both male and female Negr1^−/− mice receiving a standard or high fat diet (HFD). We found that 6 weeks of HFD leads to higher levels of blood glucose in Negr1^−/− mice. In the glucose tolerance test, HFD induced phenotype difference only in male mice; Negr1^−/− male mice displayed altered glucose tolerance, accompanied with upregulation of circulatory branched-chain amino acids (BCAA). The general metabolomic profile indicates that Negr1^−/− mice are biased towards glyconeogenesis, fatty acid synthesis, and higher protein catabolism, all of which are amplified by HFD. Negr1 deficiency appears to induce alterations in the efficiency of energy storage; reduced food intake could be an attempt to compensate for the metabolic challenge present in the Negr1^−/− males, particularly during the HFD exposure. Our results suggest that the presence of functional Negr1 allows male mice to consume more HFD and prevents the development of glucose intolerance, liver steatosis, and excessive weight gain.

In GWAS studies, the neural adhesion molecule encoding the neuronal growth regulator 1 (NEGR1) gene has been consistently linked with both depression and obesity. Although the linkage between NEGR1 and depression is the strongest, evidence also suggests the involvement of NEGR1 in a wide spectrum of psychiatric conditions. Here we show the expression of NEGR1 both in tyrosine- and tryptophan hydroxylase-positive cells. Negr1^−/− mice show a time-dependent increase in behavioral sensitization to amphetamine associated with increased dopamine release in both the dorsal and ventral striatum. Upregulation of transcripts encoding dopamine and serotonin transporters and higher levels of several monoamines and their metabolites was evident in distinct brain areas of Negr1^−/− mice. Chronic (23 days) escitalopram-induced reduction of serotonin and dopamine turnover is enhanced in Negr1^−/− mice, and escitalopram rescued reduced weight of hippocampi in Negr1^−/− mice. The current study is the first to show alterations in the brain monoaminergic systems in Negr1-deficient mice, suggesting that monoaminergic neural circuits contribute to both depressive and obesity-related phenotypes linked to the human NEGR1 gene.

Objective: Neuronal growth regulator 1 (Negr1) is a GPI-anchored neuronal cell adhesion molecule of the IgLON superfamily associated with multiple psychiatric disorders. This study aimed to investigate behavioral and molecular adaptations to social isolation (SI) stress in Negr1-deficient (Negr1^−/−) mice. Methods: Male and female Negr1^−/− and wild-type (Wt) mice (n = 10 per group) were exposed to two weeks of SI or group housing (Ctl). Behavioral assays assessed exploratory and anxiety-like behavior. Gene expression analyses in the prefrontal cortex and hippocampus were performed using RT-qPCR, focusing on GABAergic, neurotrophic, and IgLON family genes. Results: SI-induced weight loss in Negr1^−/− mice compared to Wt was evident in both sexes but more pronounced in males. Behaviorally, SI Wt males showed stress-induced hyperactivity compared to Ctl Wt, whereas SI Negr1^−/− males exhibited blunted exploratory behavior relative to SI Wt in the open field test (OFT). Negr1^−/− females showed reduced exploration in the elevated plus maze (EPM), suggesting increased anxiety. Hippocampal Pvalb was downregulated in SI Negr1^−/− mice of both sexes compared to Wts, with a stronger decrease in males, indicating heightened male vulnerability in GABAergic interneuron function. In males, SI reduced hippocampal Bdnf in both genotypes, whereas Ntrk2 (TrkB) upregulation occurred only in Negr1^−/− mice, suggesting a genotype-specific compensatory response. Hippocampal expression of Fgfr2 and IgLON members (Ntm1a/1b, Lsamp1a/1b) was increased in SI Negr1^−/− males compared to SI Wt, with minimal changes in females. Conclusions: Negr1 deficiency leads to sex-specific behavioral and molecular adaptations to social isolation stress, highlighting the role of Negr1 in modulating neurotrophic and GABAergic signaling pathways under adverse environmental conditions.