Protein kinase N1 critically regulates cerebellar development and long-term function

J Clin Invest. 2018 May 1;128(5):2076-2088. doi: 10.1172/JCI96165. Epub 2018 Apr 16.


Increasing evidence suggests that synapse dysfunctions are a major determinant of several neurodevelopmental and neurodegenerative diseases. Here we identify protein kinase N1 (PKN1) as a novel key player in fine-tuning the balance between axonal outgrowth and presynaptic differentiation in the parallel fiber-forming (PF-forming) cerebellar granule cells (Cgcs). Postnatal Pkn1-/- animals showed a defective PF-Purkinje cell (PF-PC) synapse formation. In vitro, Pkn1-/- Cgcs exhibited deregulated axonal outgrowth, elevated AKT phosphorylation, and higher levels of neuronal differentiation-2 (NeuroD2), a transcription factor preventing presynaptic maturation. Concomitantly, Pkn1-/- Cgcs had a reduced density of presynaptic sites. By inhibiting AKT with MK-2206 and siRNA-mediated knockdown, we found that AKT hyperactivation is responsible for the elongated axons, higher NeuroD2 levels, and reduced density of presynaptic specifications in Pkn1-/- Cgcs. In line with our in vitro data, Pkn1-/- mice showed AKT hyperactivation, elevated NeuroD2 levels, and reduced expression of PF-PC synaptic markers during stages of PF maturation in vivo. The long-term effect of Pkn1 knockout was further seen in cerebellar atrophy and mild ataxia. In summary, our results demonstrate that PKN1 functions as a developmentally active gatekeeper of AKT activity, thereby fine-tuning axonal outgrowth and presynaptic differentiation of Cgcs and subsequently the correct PF-PC synapse formation.

Keywords: Neurodevelopment; Neuroscience; Protein kinases; Synapses.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Axons / enzymology*
  • Heterocyclic Compounds, 3-Ring / pharmacology
  • Mice
  • Mice, Knockout
  • Neuronal Outgrowth*
  • Protein Kinase C / genetics
  • Protein Kinase C / metabolism*
  • Proto-Oncogene Proteins c-akt / antagonists & inhibitors
  • Proto-Oncogene Proteins c-akt / genetics
  • Proto-Oncogene Proteins c-akt / metabolism
  • Purkinje Cells / cytology
  • Purkinje Cells / enzymology*
  • Synapses / genetics
  • Synapses / metabolism*


  • Heterocyclic Compounds, 3-Ring
  • MK 2206
  • protein kinase N
  • Proto-Oncogene Proteins c-akt
  • Protein Kinase C