Autophagy is a major regulator of beta cell insulin homeostasis

Yael Riahi, Jakob D. Wikstrom, Etty Bachar-Wikstrom, Nava Polin, Hava Zucker, Myung Shik Lee, Wenying Quan, Leena Haataja, Ming Liu, Peter Arvan, Erol Cerasi, Gil Leibowitz*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

115 Scopus citations

Abstract

Aims/hypothesis: We studied the role of protein degradation pathways in the regulation of insulin production and secretion and hypothesised that autophagy regulates proinsulin degradation, thereby modulating beta cell function. Methods: Proinsulin localisation in autophagosomes was demonstrated by confocal and electron microscopy. Autophagy was inhibited by knockdown of autophagy-related (ATG) proteins and using the H+-ATPase inhibitor bafilomycin-A1. Proinsulin and insulin content and secretion were assessed in static incubations by ELISA and RIA. Results: Confocal and electron microscopy showed proinsulin localised in autophagosomes and lysosomes. Beta-Atg7−/− mice had proinsulin-containing sequestosome 1 (p62 [also known as SQSTM1])+ aggregates in beta cells, indicating proinsulin is regulated by autophagy in vivo. Short-term bafilomycin-A1 treatment and ATG5/7 knockdown increased steady-state proinsulin and hormone precursor chromogranin A content. ATG5/7 knockdown also increased glucose- and non-fuel-stimulated insulin secretion. Finally, mutated forms of proinsulin that are irreparably misfolded and trapped in the endoplasmic reticulum are more resistant to degradation by autophagy. Conclusions/interpretation: In the beta cell, transport-competent secretory peptide precursors, including proinsulin, are regulated by autophagy, whereas efficient clearance of transport-incompetent mutated forms of proinsulin by alternative degradative pathways may be necessary to avoid beta cell proteotoxicity. Reduction of autophagic degradation of proinsulin increases its residency in the secretory pathway, followed by enhanced secretion in response to stimuli.

Original languageAmerican English
Pages (from-to)1480-1491
Number of pages12
JournalDiabetologia
Volume59
Issue number7
DOIs
StatePublished - 1 Jul 2016
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2016, Springer-Verlag Berlin Heidelberg.

Keywords

  • Autophagy
  • Beta cells
  • Insulin secretion
  • Lysosome
  • Proinsulin
  • Proteasome
  • Protein degradation

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