Autophagy is essential for mouse sense of balance
Guillermo Mariño, … , José M.P. Freije, Carlos López-Otín
Guillermo Mariño, … , José M.P. Freije, Carlos López-Otín
Published June 23, 2010
Citation Information: J Clin Invest. 2010;120(7):2331-2344. https://doi.org/10.1172/JCI42601.
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Research Article

Autophagy is essential for mouse sense of balance

Abstract

Autophagy is an evolutionarily conserved process that is essential for cellular homeostasis and organismal viability in eukaryotes. However, the extent of its functions in higher-order processes of organismal physiology and behavior is still unknown. Here, we report that autophagy is essential for the maintenance of balance in mice and that its deficiency leads to severe balance disorders. We generated mice deficient in autophagin-1 protease (Atg4b) and showed that they had substantial systemic reduction of autophagic activity. Autophagy reduction occurred through defective proteolytic processing of the autophagosome component LC3 and its paralogs, which compromised the rate of autophagosome maturation. Despite their viability, Atg4b-null mice showed unusual patterns of behavior that are common features of inner ear pathologies. Consistent with this, Atg4b-null mice showed defects in the development of otoconia, organic calcium carbonate crystals essential for sense of balance (equilibrioception). Furthermore, these abnormalities were exacerbated in Atg5–/– mice, which completely lack the ability to perform autophagy, confirming that autophagic activity is necessary for otoconial biogenesis. Autophagy deficiency also led to impaired secretion and assembly of otoconial core proteins, thus hampering otoconial development. Taken together, these results describe an essential role for autophagy in inner ear development and equilibrioception and open new possibilities for understanding and treating human balance disorders, which are of growing relevance among the elderly population.

Authors

Guillermo Mariño, Alvaro F. Fernández, Sandra Cabrera, Yunxia W. Lundberg, Rubén Cabanillas, Francisco Rodríguez, Natalia Salvador-Montoliu, José A. Vega, Antonino Germanà, Antonio Fueyo, José M.P. Freije, Carlos López-Otín

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Figure 5

Balance dysfunction in Atg4b–/– mice reveals a new physiological role for autophagy in otoconial development.

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Balance dysfunction in Atg4b–/– mice reveals a new physiological role fo...
(A) Rotarod analysis of Atg4b–/– and WT mice. **P < 0.01; ***P < 0.005. (B) Representative image of an Atg4b–/– mouse affected by head tilting (top right) and a WT mouse (top left). Insets show the angle of the head. As compared with WT mice (bottom left), Atg4b–/– mice were unable to swim or float in the forced swim test (bottom right). (C) Light (top) and scanning (bottom) electron microscopy analyses of WT and Atg4b–/– inner ears. Representative images show either the absence of otoconial crystals in the utricle of Atg4b–/– mice (right) or the presence of abnormal otoconia that are oversized, less numerous, loose, and occasionally fused (middle), as compared with WT otoconia (left). The blur in the image is due to electrical interference. Scale bars: 50 μm (top), 10 μm (bottom). (D) Fluorescent microphotographs of E15.5 GFP-LC3 transgenic mice utricles indicating the presence of numerous autophagosomal structures (green puncta) in macular and “roof” utricle epithelial cells. The insets show higher magnification of the macular epithelium. Scale bars: 15 μm. (E) Light (top) and scanning electron (bottom) microphotographs of WT and Atg5–/– inner ears. Representative images showing the absence of otoconia (right) or the presence of giant and abnormally shaped otoconial crystals (middle) in the utricle of Atg5–/– mice. Scale bars: 50 μm (top), 10 μm (bottom). (F) Graph showing the relative number of otoconial abnormalities observed in WT (n = 5), Atg4b–/– mice (n = 10 for unaffected mice; n = 12 for affected mice), and Atg5–/– mice (n = 5).