A plant cell model of polyglutamine aggregation: Identification and characterisation of macromolecular and...

In vitro studies have shown that LEA proteins from plants and invertebrates protect and stabilise other proteins under conditions of water stress, suggesting a role in stress tolerance. However, there is little information on LEA protein function in whole plants or plant cells, particularly with respect to their anti-aggregation activity. To address this, we expressed in tobacco BY-2 suspension cells an aggregation-prone protein based on that responsible for Huntington's disease (HD). In HD, abnormally long stretches of polyglutamine (polyQ) in huntingtin (Htt) protein cause aggregation of Htt fragments within cells. We constructed stably transformed BY-2 cell lines expressing enhanced green fluorescent protein (EGFP)-HttQ23 or EGFP-HttQ52 fusion proteins (encoding 23 or 52 glutamine residues, pertaining to the normal and disease states, respectively), as well as an EGFP control. EGFP-HttQ52 protein aggregated in the cytoplasm of transformed tobacco cells, which showed slow growth kinetics; in contrast, EGFP-HttQ23 or EGFP did not form aggregates and cells expressing these constructs grew normally. To test the effect of LEA proteins on protein aggregation in plant cells, we constructed cell lines expressing both EGFP-HttQ52 and LEA proteins (PM1, PM18, ZLDE-2 or AavLEA1) or a sHSP (PM31). Of these, AavLEA1 and PM31 reduced intracellular EGFP-HttQ52 aggregation and alleviated the associated growth inhibition, while PM18 and ZLDE-2 partially restored growth rates. Treatment of EGFP-HttQ52-expressing BY2 cells with the polyphenol epigallocatechin-3-gallate (EGCG) also reduced EGFP-HttQ52 aggregation and improved cell growth rate. The EGFP-HttQ52 cell line therefore has potential for characterising both macromolecular and small molecule inhibitors of protein aggregation in plant cells.