Cellular Toxicity of Polyglutamine Proteins in Neurodegenerative Disease

<p>Cytotoxicity of polyQ expansions proteins<br>Schaffar et al, 2004, Mol. Cell 15, 95-105</p> Zoom Image

Cytotoxicity of polyQ expansions proteins
Schaffar et al, 2004, Mol. Cell 15, 95-105

We are using a combined biochemical and cell biological approach to gain insight into the molecular basis of polyglutamine expansion diseases and other neurodegenerative disorders associated with aberrant protein folding.. Our long-term goal is to understand the mechanisms by which protein misfolding and aggregation causes cellular toxicity and how molecular chaperones are involved in this process. This question is of general relevance in understanding neurodegenerative misfolding diseases and can be adequeately addressed in cellular model systems, including S. cerevisiae and mammalian cells in culture. In addition, we have begun to use C. elegans as a model to study the relationship between aberrant folding and aging.

The expansion of a polymorphic CAG tract encoding polyglutamine (polyQ) has been found to be the cause of nine human neurodegenerative diseases, including Huntington’s disease (HD), dentatorubral-pallidoluysian atrophy (DRPLA), spinobulbar muscular atrophy (SBMA), and spinocerebellar ataxia (SCA) types 1, 2, 3, 6 and 7. The mutant genes responsible for these diseases have no sequence similarity except for the CAG tract. Typically, normal individuals have between 6 to 39Q repeats, while affected individuals have repeats in the range of 36 to 180Q. The length of the CAG reiteration correlates inversely with the age of onset and disease severity. The mechanism by which the presence of these repeats leads to neurodegeneration is not yet well understood. Several recent reports have described intracellular aggregates or inclusions containing the expanded polyQ proteins. Evidence from patient samples, transgenic mice and cell culture models suggest that the aggregates (or the process of their formation) are associated with the pathology of CAG expansion diseases. Proteasome components as well as chaperone proteins have also been detected in the aggregates. HD is caused by mutation of the gene encoding the ubiquitously expressed protein huntingtin (htt), a 350 KDa protein of unknown but essential function.

We have established a simple and robust model system to characterize the effects of molecular chaperones on polyQ protein aggregation in vitro and in cells. Hsp70 was found to be most efficient in modulating the aggregation properties of polyQ expanded htt and in suppressing its cytotoxicity. Interestingly, the chaperones do not prevent aggregation of the polyQ protein per se but rather modulate the aggregation process such that amorphous aggregates may form instead of the typical amyloid fibrils.

We are using methods from cell biolog, genetics and proteomics in order to understand how aberrant protein folding causes cytotoxicity. We hope that our work will help in defining new strategies in the therapy of polyQ diseases and similar neurodegenerative disorders



Sakahira, H., Breuer, P., Hayer-Hartl, M.K. and Hartl, F.U. (2002). Molecular chaperones as modulators of polyglutamine protein aggregation and toxicity. Proc Natl Acad Sci U S A. 99, 16412-16418.

Barral, J.M., Broadley, S.A., Schaffar, G., and Hartl, F.U. (2004). Roles of molecular chaperones in protein misfolding diseases. Semin Cell Dev Biol. 15, 17-29.

Hipp, M.S., Park, S.H. and Hartl, F.U. (2014). Proteostasis impairment in protein-misfolding and -aggregation diseases. Trends Cell Biol. 24, 506-514.

Research papers

Muchowski, P.J., Schaffar, G., Sittler, A., Wanker, E., Hayer-Hartl, M. and Hartl, F.U. (2000). Hsp70 and Hsp40 inhibit self-assembly of polyglutamine proteins into amyloid-like fibrils. Proc Natl Acad Sci U S A. 97, 7841-7846.

Sittler, A., Lurz, R., Lüder, G., Priller, J., Hayer-Hartl, M.K., Lehrach, H., Hartl, F.U. and Wanker, E. (2001). Geldanamycin activates a heat shock response and inhibits Huntingtin aggregation in a cell culture model of Huntington’s disease. Hum Mol Genet. 10, 1307-1315.

Schaffar, G., Breuer, P., Boteva, R., Behrends, C., Tzvetkov, N., Strippel, N., Sakahira, H., Siegers, K., Hayer-Hartl, M., and Hartl, F.U. (2004). Cellular toxicity of polyglutamine expansion proteins: Mechanism of transcription factor deactivation. Mol Cell. 15, 95-105.

Haacke, A., Broadley, S., Boteva, R., Tzvetkov, N., Hartl, F.U. and Breuer, P. (2006). Proteolytic cleavage of polyglutamine-expanded Ataxin-3 is critical for aggregation and sequestration of non-expanded Ataxin-3. Hum Mol Genet. 15, 555-568.

Boeddrich, A., Gaumer. S., Haacke, A., Tzvetkov, N., Albrecht, M., Evert, B.O., Müller, E.C., Lurz, R., Breuer, P., Schugardt, N., Plassmann, S., Xu, K., Warrick, J.M., Suopanki, J., Wüllner, U., Frank, R., Hartl, F.U., Bonini, N.M. and Wanker, E.E. (2006). An arginine/lysine-rich motif is crucial for VCP/p97-mediated modulation of ataxin-3 fibrillogenesis. EMBO J. 25, 1547-1558.

Behrends, C., Langer, C.A., Boteva, R., Böttcher, U., Stemp, M.J., Schaffar, G., Vasudeva Rao, B., Giese, A., Kretzschmar, H., Siegers, K. and Hartl, F.U. (2006). Chaperonin TRiC promotes the assembly of polyQ expansion proteins into non-toxic oligomers. Mol Cell 23, 887-897.

Schiffer, N. W., Broadley, S.A., Hirschberger, T., Tavan, Pl, Kretzschmar, H.A., Giese, A., Haass, C., Hartl, F.U. and Schmid, B. (2007). Identification of anti-prion compounds as efficient inhibitors of polyglutamine protein aggregation in a zebrafish model. J Biol Chem. 282, 9195-9203.

Haacke, A., Hartl, F.U. and Breuer, P. (2007). Calpain inhibition is sufficient to suppress aggregation of polyglutamine-expanded Ataxin-3. J Biol Chem. 282, 18851-18856.

Schiffer, N. W., Céraline, J., Hartl, F. U., and Broadley, S. A. (2008). N-terminal polyglutamine-containing fragments inhibit androgen receptor transactivation function. Biol. Chem. 389,261-271.

Gamerdinger, M.,Hajieva, P., Kaya, A.M., Hartl, F.U. and Behl, C. (2009). Protein quality control during aging involves recruitment of the macroautophagy pathway by BAG3. EMBO J. 28, 889-991.

Broadley, S.A. and Hartl, F.U. (2009). The role of molecular chaperones in human misfolding diseases. FEBS Lett. 583, 2647-2653.

Olzscha, H., Schermann, S.M., Woerner, A.C., Pinkert, S., Hecht, M.H., Tartaglia, G.G.,  Vendruscolo, M., Hayer-Hartl, M., Hartl, F.U.*, and Vabulas, R.M.* (2011). Amyloid-like aggregates sequester numerous metastable proteins with essential cellular functions. Cell 144, 67-78.

Resenberger, U., Harmeier, A., Woerner, A.C., Goodman, J.L., Müller, V., Krishnan, R., Vabulas, R.M., Lindquist, S., Hartl, F.U., Multhaup, G., Winklhofer, K.F., and Tatzelt, J. (2010). The cellular prion protein mediates neurotoxic signaling of β-sheet-rich conformers independent of prion replication.  EMBO J 30, 2057-2070.

Gupta, R., Kasturi, P., Bracher, A., Loew, Ch., Zheng, M., Villella, A., Garza, D., Hartl, F.U.*, and Raychaudhuri, S.* (2011). Firefly luciferase mutants as sensors of proteome stress. Nature Methods 8, 879-884.

Kim, Y.E., Hipp, M., Bracher, A., Hayer-Hartl, M., and Hartl, F.U. (2013). Molecular chaperone functions in protein folding and proteostasis. Annual Rev Biochem 82, 323-355.

Park, S.-H., Kukushkin, Y., Chen, T., Gupta, R., Konagai, A., Hipp, M.S., Hayer Hartl, M., and Hartl, F.U. (2013). PolyQ Proteins Interfere with Nuclear Degradation of Cytosolic Proteins by Sequestering the Sis1p Chaperone. Cell 154, 134-145.

Leitman, J., Barak, B., Benyair, R., Shenkman, M., Ashery, U., Hartl F.U., and Lederkremer, G.Z. (2014). ER stress-induced eIF2-alpha phosphorylation underlies sensitivity of striatal neurons to pathogenic huntingtin. PLoS One 3;9(3):e90803. doi: 10.1371/journal.pone.0090803.

Raychaudhuri, S., Löw, C., Körner, R., Pinkert, S., Theis, M., Hayer-Hartl, M., Buchholz, F. and Hartl, F.U. (2013).  Interplay of acetyltransferase EP300 and the proteasome system in regulating heat shock transcription factor1. Cell 156, 975-985.

Leitman, J., Hartl, F.U, and Lederkremer, G.Z. (2013). Soluble forms of polyQ-expanded huntingtin rather than large aggregates cause endoplasmic reticulum stress. Nature Communications, doi:10.1038/ncomms3753. 

Ripaud, L., Chumakova, V., Antonin, M., Hastie, A., Pinkert, S., Körner, R., Ruff, K., Pappu, R., Hornburg, D., Mann, M., Hartl, F.U. and Hipp, M. (2014). Overexpression of Q-rich prion-like proteins suppresses polyQ cytotoxicity and alters the polyQ interactome. PNAS

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