Wortmannin Reduces Insulin Signaling and Death in Seizure-Prone Pcmt1−/− Mice

Kennen B. MacKay, Jonathan D. Lowenson, Steven G. Clarke

L-isoaspartyl (D-aspartyl) O-methyltransferase deficient mice (Pcmt1(-/-)) accumulate isomerized aspartyl residues in intracellular proteins until their death due to seizures at approximately 45 days. Previous studies have shown that these mice have constitutively activated insulin signaling in their brains, and that these brains are 20-30% larger than those from age-matched wild-type animals. To determine whether insulin pathway activation and brain enlargement is responsible for the fatal seizures, we administered wortmannin, an inhibitor of the phosphoinositide 3-kinase that catalyzes an early step in the insulin pathway. Oral wortmannin reduced the average brain size in the Pcmt1(-/-) animals to within 6% of the wild-type DMSO administered controls, and nearly doubled the lifespan of Pcmt1(-/-) at 60% survival of the original population. Immunoblotting revealed significant decreases in phosphorylation of Akt, PDK1, and mTOR in Pcmt1(-/-) mice and Akt and PDK1 in wild-type animals upon treatment with wortmannin. These data suggest activation of the insulin pathway and its resulting brain enlargement contributes to the early death of Pcmt1-/- mice, but is not solely responsible for the early death observed in these animals.