Abnormal Social Interaction In Gabrb3 shRNA Transgenic Mice

Background: Multiple lines of evidence support a link between GABRB3, a GABA_A receptor subunit, and autism spectrum disorders. This association is likely a consequence of alterations in gene dosage or expression of gene variants, as total or conditional loss of Gabrb3 results in post-natal lethality in mouse, with the few survivors exhibiting severe seizures and behavioral disorders. Little is known regarding whether GABRB3 variation contributes to specific autism-related phenotypes, although the general association with autism is enhanced in populations with elevated perseveration.  In mouse, haploinsufficiency results in variable gene expression and only mild phenotypes that are gender, age and deletion parent-of-origin dependent.

Objectives: To characterize ASD-related behaviors in Gabrb3 shRNA transgenic animals.

Methods: Gabrb3 shRNA transgenic animals were generated on a C57Bl/6 background. Behavioral phenotypes in male and female young adult transgenic and littermate control animals were assessed using standard protocols, including activity and anxiety (open field), exploratory (place preference & T maze), socialization (interest, preference & memory: odor, tethered & free interactions), aggression (tube test), and learning and perseveration (radial/T maze). shRNA and mRNA expression levels were quantified using a custom TaqMan small RNA assay (Applied Biosciences) or SYBR-Green qRT-PCR, respectively.

Results: Gabrb3 shRNA transgenic animals demonstrate abnormal social interactions that appear specific to live, ‘free-range’ animal encounters. Both females and males show an apparent increase in social interest, exhibiting high levels of interaction and minimal acclimatization to repeated exposures to a stranger mouse, and limited relative enhanced interaction time with a novel mouse. This is unlikely to be a pure social memory defect, as Gabrb3 shRNA animals show normal acclimatization and response to novelty using soiled bedding rather than live stranger animals, albeit conversely with a somewhat decreased total interaction time as compared with wildtype littermates.  Furthermore, for male Gabrb3 shRNA animals, live encounters often result in aggression, yet no enhanced aggression or passivity is detected using the tube test. Nor do these persistent social interactions reflect a generalized increase in perseveration, as both genders show normal reversal learning in the T maze. Female Gabrb3 shRNA transgenic animals, however, show enhanced learning acquisition in the T maze, which is currently under further investigation.

Conclusions: shRNA-mediated Gabrb3 variation in mouse leads to gender specific phenotypes including abnormal, persistent social interactions reminiscent of the ‘active but odd’ categorization in autism spectrum patients. The association of specific traits or phenotypes with altered Gabrb3 expression will facilitate the identification of patient populations in which targeted therapies for this pathway will be most effective.