a-Synuclein is a neuronally expressed protein which is mutated in familial Parkinson's disease. We have previously shown that disease-associated mutants of a-synuclein cause enhanced neuronal cell death in response to a variety of stimuli, whereas wild-type a-synuclein has a protective effect against some stimuli, whilst enhancing the death response to others. We demonstrate, for the first time, that over-expression of the heat shock protein HSP27 has a potent protective anti-apoptotic effect against the damaging effects of wild-type and particularly of mutant a-synuclein. In contrast, HSP70 has some protective effect against the damaging effect of the wild-type protein, but has no effect against the mutant proteins, whilst HSP56 has no protective effect in this system. Our results indicate that disease-associated mutants of a-synuclein enhance its death-inducing properties and lead to increased apoptosis, which can be mitigated by either the use of specific caspase inhibitors or HSP27 over-expression. This potent protective effect of HSP27 against the mutant and wild-type proteins may be of potential therapeutic importance.
Huntington's disease (HD) is caused by an expanded polyglutamine tract in the huntingtin protein. Mitochondrial dysfunction and free radical damage occur in both R6/2 mice and HD patient brains and might play a role in disease pathogenesis. In cell culture systems, heat-shock protein 27 (Hsp27), a small molecular chaperone, suppresses mutant huntingtin-induced reactive oxygen species formation and cell death. To investigate this in vivo, we conducted an extensive phenotypic characterization of mice arising from a cross between R6/2 mice and Hsp27 transgenic mice but did not observe an improvement of the R6/2 phenotype. Hsp27 overexpression had no effect in reducing oxidative stress in the R6/2 brain, assessed by measuring striatal aconitase activity and protein carbonylation levels. Native protein gel analysis revealed that transgenic Hsp27 forms active, large oligomeric species in heat-shocked brain lysates, demonstrating that it is efficiently activated upon stress. In contrast, Hsp27 in double transgenic brains exists predominantly as a low molecular weight, inactive species. This suggests that Hsp27, which is otherwise activatable upon heat shock, remains inactive in the R6/2 model of chronic neurodegeneration. Hsp27 transgenics had been previously shown to be protected from acute stresses such as kainate administration, ischemia/reperfusion heart injury and neonatal nerve injury. Our study is the first to suggest a differential modulation of Hsp27 activation in vivo and, importantly, it illustrates the diverse effect of Hsp27 on acute versus chronic models of disease.
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