Tissue-Specific Upregulation of Drosophila Insulin Receptor (InR) Mitigates Poly(Q)-Mediated Neurotoxicity by Restoration of Cellular Transcription Machinery

Abstract

Polyglutamine [poly(Q)] disorders are a class of trinucleotide repeat expansion neurodegenerative disorders which are dominantly inherited and progressively acquired with age. This group of disorders entail the characteristic formation of protein aggregates leading to widespread loss of neurons in different regions of the brain. SCA3 and HD, the two most commonly occurring types of poly(Q) disorders were examined in the present study. With the aim of elucidating novel genetic modifiers of poly(Q) disorders, the Drosophila insulin receptor (InR) was identified as a potential suppressor of poly(Q)-induced neurotoxicity and degeneration. We demonstrate for the first time that targeted upregulation of InR could effectively mitigate poly(Q)-mediated neurodegeneration in fly models. A significant reduction in poly(Q)-mediated cellular stress and apoptosis was noted upon InR overexpression in poly(Q) background. We further reveal that targeted upregulation of InR causes a substantial reduction in poly(Q) aggregate formation with the residual inclusion bodies localised to the cytoplasm. We also demonstrate that InR achieves suppression of poly(Q) toxicity by replenishing the cellular pool of CREB binding protein and improving the histone acetylation status of the cell. This leads to restoration of the cellular transcriptional machinery which is otherwise severely compromised in poly(Q) disease conditions. Interestingly, there also appeared a possibility of autophagy-mediated rescue of poly(Q) phenotype due to upregulation of InR. Therefore, our study strongly suggests that modulation of the insulin signalling pathway could be an effective therapeutic intervention against poly(Q) disorders.

Keywords: Drosophila; InR; Neurodegeneration; Poly(Q).