PTEN Regulates Microtubule Polymerization via mTORC2, But Not mTORC1, in Peripheral Sensory Neurons.

Peripheral neuropathy affects over 18 million adults in the United States ( Hicks et al., 2021), but therapeutic outcomes are poor due to a lack of regenerative treatments. Development of novel, disease-modifying therapies is hindered by poor understanding of the mechanisms promoting axonal regeneration in peripheral neurons. Pten is a strong negative regulator of cell growth, and Pten-KO drives axonal regeneration in various neuronal subtypes potentially via downstream regulation of stability of the microtubule (MT) cytoskeleton, a vital component of axonal growth. While Pten-KO accelerates MT polymerization rates in the axonal growth cone, it remains unknown whether this action is dependent on mTORC1 or mTORC2 signaling and regeneration under Pten-KO is dependent on MT activation. Here, we perform in vitro codeletions of either Raptor (mTORC1) or Rictor (mTORC2) alongside Pten-KO in mouse peripheral sensory neuron cultures of either sex to isolate the effects of each pathway on the MT cytoskeleton. We use Pten-KO to increase MT polymerization and neuronal outgrowth and then show that suppression of mTORC2, but not mTORC1, is sufficient to reduce the accelerated MT polymerization and neuronal hypertrophy to wild-type levels. These results are specific to the axonal growth cone, and MT dynamics in the proximal axon shaft are not impacted by Pten-KO, mTORC1 suppression, or mTORC2 suppression. Our results help elucidate the mechanism by which Pten regulates the MT cytoskeleton and axonal outgrowth in peripheral sensory neurons, localize where this occurs in the axon, and highlight the MT cytoskeleton as a potential molecular target for regenerative therapies.