Ataxin-3 and huntingtin induced endoplasmic reticulum stress and cell death are ameliorated by overexpression of stanniocalcin 2

Abstract

Spinocerebellar ataxia type 3 (SCA3) and Huntington's disease (HD) are polyglutamine (polyQ) disorders associated with progressive neurodegeneration in aftlicted persons. At the molecular level, these diseases are characterized by mutated proteins containing expanded glutamine tracts that ultimately confer endoplasmic reticulum (ER) stress and inclusion body formation. In eukaryotic cells,enduring ER stress, induction of a conserved pathway deemed the unfolded protein response) (UPR) ensues. This pathway leads to upregulated expression of stanniocalcin 2 (STC2), a protein shown to possess cytoprotective properties and to play a role in maintaining intracellular calcium homeostasis. Interestingly, recent research has shown that calcium-dependent autophagy may confer beneficial protective properties on cells experiencing ER stress, possibly through degradation of misfolded proteins that aggregate in inclusion bodies. In the present study, we aimed to determine if co-expression of the SCA3 and HD proteins, ataxin-3 (AT3) and huntingtin (Htt), respectively, with STC2 would ameliorate inclusion body formation and cell death in a cytoprotective manner dependent on calcium- induced autophagy. In initial experiements, to elucidate the cytoprotective properties of STC2 in cells expressing polyQ proteins, CV-l originating cells carrying simian virus 40 (COS) and HeLa Tet-Off cells transfected with pCMV-LacI-NLS construct (HeTOFLI) expressing AT3 and Htt, respectively, were transfected with exogenous STC2. Cells were examined via fluorescence microscopy and flow cytometry analysis. Results showed transfected COS and HeTOFLI cells did not generate any detectable inclusion bodies. Consequently, the cytoprotective property of STC2 was undeterminable in this approach. However, flow cytometry analysis showed decreased cellular death in COS cells co-transfected with AT3 Q80 and STC2. In combination, these results suggested STC2 is cytoprotective in polyQ-expressing cells, possibly conferring protection via induction of autophagy. Nevertheless, the method by which STC2 extends cytoprotection in these cells is only postulated at this stage and further research to validate this mechanism is needed.