CRISPR-Cas9 editing of the arginine-vasopressin V1a receptor produces paradoxical changes in social behavior in Syrian hamsters.

Studies from a variety of species indicate that arginine­vasopressin (AVP) and its V1a receptor (Avpr1a) play a critical role in the regulation of a range of social behaviors by their actions in the social behavior neural network. To further investigate the role of AVPRs in social behavior, we performed CRISPR-Cas9­mediated editing at the Avpr1a gene via pronuclear microinjections in Syrian hamsters (Mesocricetus auratus), a species used extensively in behavioral neuroendocrinology because they produce a rich suite of social behaviors. Using this germ-line gene-editing approach, we generated a stable line of hamsters with a frame-shift mutation in the Avpr1a gene resulting in the null expression of functional Avpr1as. Avpr1a knockout (KO) hamsters exhibited a complete lack of Avpr1a-specific autoradiographic binding throughout the brain, behavioral insensitivity to centrally administered AVP, and no pressor response to a peripherally injected Avpr1a-specific agonist, thus confirming the absence of functional Avpr1as in the brain and periphery. Contradictory to expectations, Avpr1a KO hamsters exhibited substantially higher levels of conspecific social communication (i.e., odor-stimulated flank marking) than their wild-type (WT) littermates. Furthermore, sex differences in aggression were absent, as both male and female KOs exhibited more aggression toward same-sex conspecifics than did their WT littermates. Taken together, these data emphasize the importance of comparative studies employing gene-editing approaches and suggest the startling possibility that Avpr1a-specific modulation of the social behavior neural network may be more inhibitory than permissive.

Prolonged diet-induced obesity modifies DNA methylation and gene expression in the hippocampus.

Obesity and age independently have negative effects on the brain, increasing the risk of neurodegenerative events. How these events synergize to increase disease susceptibility remains poorly understood. To better understand the epigenetic implications of poor diet with increased age, we sought to determine CpG methylation changes in the dorsal hippocampus attributable to age and/or diet-induced obesity. Male C57BL/6J mice were fed either normal chow or an obesogenic diet until six or 14 months of age. Hippocampus was analyzed by Reduced Representation Bisulfite Sequencing. In total, 107 differentially methylated regions (DMRs) were identified across all four conditions; older obese mice accounted for 63% of those DMRs. Gene ontology analysis showed two affected pathways, nervous system development and regulation of multicellular organismal process, in older obese mice only. From the RRBS results, five genes were selected for qPCR quantification: Bridging Integrator 1 (BIN1), Histone Deacetylase 5 (HDAC5), Folliculin Interacting Protein 2 (FNIP2), Proline, Glutamate and Leucine Rich Protein 1 (PELP1), and Protein Tyrosine Phosphatase Non-Receptor Type 1 (PTPN1). Generally, DMR changes aligned with mRNA expression changes in BIN1, HDAC5, FNIP2, PELP1, and PTPN1. Notably BIN1 decreased and HDAC5 increased due to obesity and age. In summary, obesity interacts with aging to significantly affect the hippocampal methylome, changing the expression of genes implicated in neurodegeneration and metabolism.

Obesity Prevents S-Adenosylmethionine-Mediated Improvements in Age-Related Peripheral and Hippocampal Outcomes.

BACKGROUND: Age predisposes individuals to a myriad of disorders involving inflammation; this includes stress-related neuropsychiatric disorders such as depression and anxiety, and neurodegenerative diseases. Obesity can further exacerbate these effects in the brain. We investigated whether an inexpensive dietary supplement, s-adenosylmethionine (SAMe), could improve age- and/or obesity-related inflammatory and affective measures in the hippocampus. METHODS: Mice were placed on their diets at six weeks of age and then aged to 14 months, receiving SAMe (0.1 g/kg of food) for the final six weeks of the experiment. Prior to tissue collection, mice were tested for anxiety-like behaviors in the open field test and for metabolic outcomes related to type 2 diabetes. RESULTS: SAMe treatment significantly improved outcomes in aged control mice, where fasting glucose decreased, liver glutathione levels increased, and hippocampal microglia morphology improved. SAMe increased transforming growth factor ß-1 mRNA in both control mice, potentially accounting for improved microglial outcomes. Obese mice demonstrated increased anxiety-like behavior, where SAMe improved some, but not all, open field measures. CONCLUSIONS: In summary, SAMe boosted antioxidant levels, improved diabetic measures, and hippocampal inflammatory and behavioral outcomes in aged mice. The effects of SAMe in obese mice were more subdued, but it could still provide some positive outcomes for obese individuals dealing with anxiety and having difficulty changing their behaviors to improve health outcomes.