Visualization of autophagic structures near solid polyQ aggregates reveals how they undermine autophagy

Aggregates of polyglutamine (polyQ) repeat extensions are known markers of several, predominantly inherited, neurodegenerative diseases. Removal of polyQ is essential for cellular proteostasis and macroautophagy/autophagy has been proposed to be an important tool in the clearance of polyQ aggregates. The mechanism of recognition and encapsulation of these aggregates within autophagosomes is largely unknown. A study described in this article employed in situ correlative cryo-electron tomography to visualize polyQ aggregates interacting with autophagic compartments. The tomograms revealed that only amorphous polyQ, but not fibrils, are engulfed by double-membrane structures and that SQSTM1/p62 is the receptor involved in recognition of polyQ during autophagy. Solidified amorphous polyQ and subsequent fibrils arrest the normal formation of autophagosomes and impair autophagy. Findings of the study described here have implications for therapies that rely on autophagy in targeting polyQ neurodegeneration.Abbreviation: cryo-CLEM, cryo-correlative light and electron microscopy; cryo-ET, cryo-electron tomography; ER, endoplasmic reticulum; HD, Huntington disease; HTT, huntingtin; polyQ, polyglutamine repeats.