The Human AVPR1A BAC Transgenic Mouse: A Preclinical Model for Elucidating the Role of AVPR1A in Autism Spectrum Disorders

Background: Genetic studies have demonstrated an association between arginine vasopressin receptor 1A (AVPR1A) and ASDs. Furthermore, knockout mouse models and vole studies have demonstrated the importance of the AVPR1A receptor in mediating behaviors associated with ASDs. Thus, the AVPR1A receptor has been highlighted as a key player in ASDs. Central vasopressin signaling is regulated by AVP release and AVPR1A receptor binding and expression. In particular, the brain AVPR1A expression pattern differs across species and this is thought to be a critical determinant of behavior, as evidenced by rodent and primate studies. Interspecies differences in AVPR1A thus limit the potential clinical translation of any rodent studies. We propose that generating a mouse expressing the human form of AVPR1A will provide a more relevant in vivo system in which we can better understand the human AVPR1A receptor, its role in modulating behaviors associated with ASDs, while providing a preclinical model for the evaluation of treatments targeting the receptor.

Objectives: The purpose of this study is to generate transgenic mice expressing only human AVPR1A and to validate these animals via biochemical and behavioral analyses.

Methods: To generate fully humanized transgenic animals expressing only the human AVPR1A, we performed BAC transgenesis followed by an extensive series of selective breeding. Integration of the BAC was tested by PCR genotyping using primers directed at the non-conserved 5’ flanking region of gene and mRNA expression was measured using UPL-based quantitative PCR. The AVPR1A protein expression pattern was mapped and quantified in transgenics by performing autoradiographic ligand binding using AVPR1A selective I-125 ligands. Preliminary behavioral tests have been performed, including measures of anxiety, social behavior and sensorimotor gating.

Results: In transgenic animals, the AVPR1A ligand binding was more intense and widely distributed than the expression pattern observed in wildtype controls. The human AVPR1A protein expression pattern showed some overlap with documented expression in humans and primates, including expression in regions distinct from the endogenous murine receptor. Given previous animal model studies as well as our data showing changes in expression in the lateral septum, ventral pallidum and amygdala among other regions in the transgenic animals, we expect behavioral alterations, particularly in social interaction and anxiety, to be demonstrated. Studies are ongoing but, preliminary results suggest that there may be changes in these behaviors in the humanized mouse as compared to wildtype and knockout animals.

Conclusions: Our findings demonstrate that transgenic animals robustly express human AVPR1A and the expression pattern is different from that of the wildtype animal, with similarities to the expression of humans and primates. These results suggest that the human and mouse forms of the AVPR1A gene are differentially regulated by cis-acting elements.  Given that differential expression patterns of AVPR1A have been suggested as important determinants of behavioral differences between species, mice expressing the human receptor may be informative of human AVPR1A signaling and circuitry with possible therapeutic relevance to ASDs.