Autism-Associated 16p11.2 Microdeletion Impairs Prefrontal Functional Connectivity in Mouse and Human

Background: Abnormal brain connectivity has been repeatedly observed in autism spectrum disorder (ASD) patients. However great heterogeneity exists in the manifestation of these aberrancies, and little is known on the role of specific ASD-associated mutations in affecting brain functional coupling. Human chromosome 16p11.2 microdeletion, a trait associated to mild intellectual disability, is one of the most common gene copy number variation (CNV) in autism, accounting for approximately 0.5-1% of all ASD cases.

Objectives: Here we sought to causally probe a role of 16p11.2 CNV in affecting brain connectivity. To this purpose, we mapped resting-state connectivity in children with 16p11.2 deletion and in a mouse carrying an orthologous 16p11.2 deletion (Horev et al., 2011). To mechanistically probe the observed connectional impairments, we also performed electrophysiological and viral tracing mapping in 16p11.2 mouse mutants.

Methods: Human resting-state fMRI (rsfMRI) imaging was performed on 3T Siemens scanner on a previously characterized sample of 16p11.2 del carriers and control subjects from the Simons VIP consortium. Control of motion artefacts was achieved via data scrubbing at a FWD=0.5 mm, regression of motion traces, and by retaining subjects with > 80% of initial fMRI frames. All mouse fMRI images were acquired on adult male 16p11.2^+/- mutants and control littermates on a 7.0 Tesla MRI scanner (Bruker Biospin) under light halothane sedation, and images were analysed as described in Liska et al., 2017. In-vivo LFP were recorded by placing electrodes in anterior cingulate and retrosplenial regions. Quantification of retrogradely labelled cells was carried out with rabies virus injection as previously described (Liska et al., 2017).

Results: Inter-group connectivity mapping revealed reduced long-range prefrontal rsfMRI connectivity in human 16p11.2 del carriers (A-B), an effect robustly associated with increased social responsiveness scale (C-D). We also observed foci of reduced connectivity in temporal and parietal areas involved in sociocognitive functioning. To bolster a role of 16p11.2 CNV in affecting prefrontal connectivity, we used resting-state fMRI to map functional connectivity in a mouse line harbouring a deletion in orthologous regions to 16p11.2. In keeping with human findings, 16p11.2^+/- mice exhibited reduced long-range prefrontal connectivity (E-F). 16p11.2 mutants also presented impaired long-range neural synchronization in the delta frequency range, corroborating a neural origin for the observed connectivity impairment (G-H). Retrograde axonal labelling in 16p11.2^+/- mutants revealed altered neuronal density in prefrontal-projecting thalamic-nuclei, suggesting a possible contribution of thalamo-frontal miswiring to the observed connectivity impairment (I-L).

Conclusions: Our data document converging prefrontal connectivity impairments in human 16p11.2 del carriers and in a mouse with the same genetic deficit. We also show that 16p11.2 deletion in the mouse results in aberrant thalamo-frontal wiring and impaired long-range low-frequency neural synchronization. These findings establish a link between a common ASD-associated CNV and macroscale connectional aberrancies. They also suggest that 16p11.2 del can predispose to neurodevelopmental disorders and impaired socio-cognitive function via a dysregulation of long-range prefrontal connectivity.