PTEN Regulates Dendritic Arborization by Decreasing Microtubule Polymerization Rate

Abstract

Phosphatase and tensin homolog (PTEN) is a major negative regulator of the phosphatidylinositol-3-kinase (PI3K)/Akt/mechanistic target of rapamycin (mTOR) pathway. Loss-of-function mutations inPTENhave been found in a subset of patients with macrocephaly and autism spectrum disorder (ASD). PTEN loss in neurons leads to somal hypertrophy, aberrant migration, dendritic overgrowth, increased spine density, and hyperactivity of neuronal circuits. These neuronal overgrowth phenotypes are present onPtenknock-out (KO) and reconstitution with autism-associated point mutations. The mechanism underlying dendritic overgrowth inPtendeficient neurons is unclear. In this study, we examined howPtenloss impacts microtubule (MT) dynamics in both sexes using retroviral infection and transfection strategies to manipulate PTEN expression and tag the plus-end MT binding protein, end-binding protein 3 (EB3). We foundPtenKO neurons sprout more new processes over time compared with wild-type (WT) neurons. We also found an increase in MT polymerization rate inPtenKO dendritic growth cones. Reducing MT polymerization rate to the WT level was sufficient to reduce dendritic overgrowth inPtenKO neuronsin vitroandin vivo. Finally, we found that rescue of dendritic overgrowth via inhibition of MT polymerization was sufficient to improve the performance ofPtenKO mice in a spatial memory task. Taken together, our data suggests that one factor underlying PTEN loss dependent dendritic overgrowth is increased MT polymerization. This opens the possibility for an intersectional approach targeting MT polymerization and mTOR with low doses of inhibitors to achieve therapeutic gains with minimal side effects in pathologies associated with loss of neuronal PTEN function.SIGNIFICANCE STATEMENTLoss ofPtenfunction because of genetic deletion or expression of mutations associated with autism spectrum disorder (ASD), results in overgrowth of neurons including increased total dendritic length and branching. We have discovered that this overgrowth is accompanied by increased rate of microtubule (MT) polymerization. The increased polymerization rate is insensitive to acute inhibition of mechanistic target of rapamycin (mTOR)C1 or protein synthesis. Direct pharmacological inhibition of MT polymerization can slow the polymerization rate inPtenknock-out (KO) neurons to rates seen in wild-type (WT) neurons. Correction of the MT polymerization rate rescues increased total dendritic arborization and spatial memory. Our studies suggest that phosphatase and tensin homolog (PTEN) inhibits dendritic growth through parallel regulation of protein synthesis and cytoskeletal polymerization.