EXPLORING THE CONTRIBUTION OF HOMEOSTATIC PLASTICITY IN THE PATHOGENESIS OF AUTISM SPECTRUM DISORDER

Rare and common variants of the CNTNAP2 gene, which encodes cell-adhesion molecule Contactin-associated protein 2 (CASPR2), have been identified in autism spectrum disorder (ASD) patients, flagging CNTNAP2 as a major risk gene for ASD. However, it is not clear how mutated CASPR2 results in pathogenesis. Our group previously established a role for CASPR2 in mediating excitatory transmission and homeostatic synaptic plasticity. We hypothesize that ASD associated CNTNAP2 mutations disrupt CASPR2 function in the regulation of homeostatic plasticity, ultimately driving pathogenesis. We generated human induced pluripotent stem cell (hiPSC) lines harbouring either a complete loss of CASPR2 (CASPR2 knockout) or an ASD-associated truncating mutation (I1253X). We examined the morphological and functional consequences of CASPR2 loss or mutation in a co-culture system of human excitatory and inhibitory neurons. Network activity was assessed using multielectrode arrays (MEAs) during development and following induction of homeostatic synaptic plasticity via prolonged activity blockade (tetrodotoxin, TTX) or enhanced activity (picrotoxin, PTX) to drive synaptic upscaling or downscaling, respectively. Both CASPR2 loss and expression of the I1253X mutation altered developmental activity trajectories and impaired homeostatic compensatory responses. Additionally, excitatory neurons in both conditions exhibited reduced dendritic length and altered dendritic complexity. The activity profiles of CASPR2 knockout and CASPR2 I1253X-expressing neurons were not fully overlapping, suggesting that the ASD-associated I1253X mutation may produce a distinct phenotype than complete loss of CASPR2. These findings indicate that CASPR2 mutations disrupt neuronal development and homeostatic plasticity through partially divergent mechanisms, providing insight into how CNTNAP2 variants may contribute to ASD pathogenesis.