Atg9a deficiency causes axon-specific lesions including neuronal circuit dysgenesis

Autophagy. 2018;14(5):764-777. doi: 10.1080/15548627.2017.1314897. Epub 2018 Mar 6.

Abstract

Conditional knockout mice for Atg9a, specifically in brain tissue, were generated to understand the roles of ATG9A in the neural tissue cells. The mice were born normally, but half of them died within one wk, and none lived beyond 4 wk of age. SQSTM1/p62 and NBR1, receptor proteins for selective autophagy, together with ubiquitin, accumulated in Atg9a-deficient neurosoma at postnatal d 15 (P15), indicating an inhibition of autophagy, whereas these proteins were significantly decreased at P28, as evidenced by immunohistochemistry, electron microscopy and western blot. Conversely, degenerative changes such as spongiosis of nerve fiber tracts proceeded in axons and their terminals that were occupied with aberrant membrane structures and amorphous materials at P28, although no clear-cut degenerative change was detected in neuronal cell bodies. Different from autophagy, diffusion tensor magnetic resonance imaging and histological observations revealed Atg9a-deficiency-induced dysgenesis of the corpus callosum and anterior commissure. As for the neurite extensions of primary cultured neurons, the neurite outgrowth after 3 d culturing was significantly impaired in primary neurons from atg9a-KO mouse brains, but not in those from atg7-KO and atg16l1-KO brains. Moreover, this tendency was also confirmed in Atg9a-knockdown neurons under an atg7-KO background, indicating the role of ATG9A in the regulation of neurite outgrowth that is independent of autophagy. These results suggest that Atg9a deficiency causes progressive degeneration in the axons and their terminals, but not in neuronal cell bodies, where the degradations of SQSTM1/p62 and NBR1 were insufficiently suppressed. Moreover, the deletion of Atg9a impaired nerve fiber tract formation.

Keywords: Atg9a; axon; conditional knockout mice; degeneration; diffusion tensor MRI; dysgenesis of commissure fibers; nonselective autophagy; selective autophagy; spongiosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Autophagy-Related Proteins / deficiency*
  • Autophagy-Related Proteins / metabolism
  • Axons / metabolism*
  • Axons / ultrastructure
  • Cells, Cultured
  • Corpus Callosum / metabolism
  • Corpus Callosum / pathology
  • Integrases / metabolism
  • Intracellular Signaling Peptides and Proteins
  • Membrane Proteins / deficiency*
  • Membrane Proteins / metabolism
  • Mice, Knockout
  • Nerve Net / metabolism*
  • Neurites / metabolism
  • Neurites / ultrastructure
  • Phenotype
  • Proteins / metabolism
  • Purkinje Cells / metabolism
  • Purkinje Cells / ultrastructure
  • Sequestosome-1 Protein / metabolism
  • Vesicular Transport Proteins / deficiency*
  • Vesicular Transport Proteins / metabolism

Substances

  • Atg9A protein, mouse
  • Autophagy-Related Proteins
  • Intracellular Signaling Peptides and Proteins
  • Membrane Proteins
  • Nbr1 protein, mouse
  • Proteins
  • Sequestosome-1 Protein
  • Sqstm1 protein, mouse
  • Vesicular Transport Proteins
  • Cre recombinase
  • Integrases

Grant support

This work was supported in part by Grants-in-Aids for Challenging Exploratory Research (Y.U.), Scientific Researches on Innovative Area, Grant-in-Aids for Scientific Research (B) (Y.U.), a Grant-in-Aid for challenging Exploratory Research (Y.U.), a Grant-in-Aid for the “High-Tech Research Center” Project for Private Universities, a matching fund subsidy (Y.U.), Program for the Strategic Research Foundation at Private Universities (Y.U.), and Program for the Private University Research Branding Project (Y.U.) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.