Understanding Huntingtin Exon 1 protein aggregation using the Cryptochrome 2 (Cry2) optogenetic system

Abstract

Studying neurodegenerative-related protein aggregation is a key field of research for understanding diseases such as Parkinson’s and Amyotrophic Lateral Sclerosis (ALS). However, the tools for studying protein aggregation in vivo are lacking, making it difficult to develop disease models. In this report, we present findings from using the Cryptochrome 2 (Cry2) optogenetic module to model Huntingtin Exon 1 (HttExon1) protein aggregation, a truncated version of the protein huntingtin which has widely been used to study Huntington’s disease. The Cry2 optogenetic module was recently used to spatiotemporally control aggregation of different intrinsically disordered proteins (IDPs) including FUS which has been linked to ALS. One of the defining characteristics of Huntington’s disease is that as the polyglutamine tract within the huntingtin protein is expanded past 37 repeats, the disease is prevalent at some time during a patient’s lifespan and with each additional repeat, the age of onset decreases. To study this phenomenon, two different polyglutamine lengths within the HttExon1 domain were inserted into mCherry-Cry2WT and mCherry-Cry2Olig vectors. Additionally, the HttExon1 domain was further truncated to study the roles that each of the flanking sequences within the HttExon1 domain play in light-induced clustering. With these various HttExon1 domains expressed into the Cry2 module, we were able to affirm the importance of the N-terminal N17 domain in accelerating HttExon1 aggregation in addition to controlling cytoplasmic localization and binding to the ER and late endosomes. However, usage of the Cry2 module failed to detect significant quantitative or qualitative differences between the different polyglutamine lengths. This result along with further exploration of the HttExon1 flanking sequences will be areas of future research.