Abnormalities in BDNF/TrkB/PI3K signaling pathways in autism (728.3)

Cortical connectivity and spine abnormalities may account for clinical features of autism. BDNF, a key spine regulator, exhibits altered isoform balance in autism. Here, we investigated whether BDNF receptors and their signaling pathways are disrupted in post‐mortem fusiform gyrus from subjects with autism compared to controls and in the valproic acid (VPA)‐induced rat model of autism. Protein levels were examined by Western blot in 11 autism vs 13 control subjects and in lateral temporal neocortices of VPA rats vs controls. Reduced TrkB, PI3K, Akt, mTOR, phospho‐mTOR, p70S6K, eIF4B and PSD‐95 and a trend towards increased truncated TrkB and p75 NTR , but no changes in 4E‐BP1 or eIF4E, were found in autism subjects versus controls. Similar deficits were observed in VPA rats, although total and phospho‐4E‐BP1 were decreased in these rats. These findings suggest imbalances in BDNF/TrkB/PI3K and proBDNF/p75 NTR signaling in autism which could lead to spine defects. Reduced Akt‐mTOR protein and signaling, suggesting spine protein synthesis deficits, were observed in both autism and VPA rats, despite minor differences in down‐regulated signaling cascades. The resulting spine defects might lead to loss of excitatory synapses/decreased PSD‐95 in autism. Reduced excitatory synapses might perturb cortical circuitry, contributing to autism’s cognitive and behavioral deficits.