Abstract
BackgroundIncreasing evidence suggests that inflammation associated with microglial cell activation in the substantia nigra (SN) of patients with Parkinson disease (PD) is not only a consequence of neuronal degeneration, but may actively sustain dopaminergic (DA) cell loss over time. We aimed to study whether the intracellular chaperone heat shock protein 60 (Hsp60) could serve as a signal of CNS injury for activation of microglial cells.MethodsHsp60 mRNA expression in the mesencephalon and the striatum of C57/BL6 mice treated with MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and the Hsp60/TH mRNA ratios in the SN of PD patients and aged-matched subjects were measured. To further investigate a possible link between the neuronal Hsp60 response and PD-related cellular stress, Hsp60 immunoblot analysis and quantification in cell lysates from SH-SY5Y after treatment with 100 μM MPP+ (1-methyl-4-phenylpyridinium) at different time points (6, 12, 24 and 48 hours) compared to control cells were performed. Additional MTT and LDH assay were used. We next addressed the question as to whether Hsp60 influences the survival of TH+ neurons in mesencephalic neuron-glia cultures treated either with MPP+ (1 μM), hHsp60 (10 μg/ml) or a combination of both. Finally, we measured IL-1β, IL-6, TNF-α and NO-release by ELISA in primary microglial cell cultures following treatment with different hHsp60 preparations. Control cultures were exposed to LPS.ResultsIn the mesencephalon and striatum of mice treated with MPTP and also in the SN of PD patients, we found that Hsp60 mRNA was up-regulated. MPP+, the active metabolite of MPTP, also caused an increased expression and release of Hsp60 in the human dopaminergic cell line SH-SY5Y. Interestingly, in addition to being toxic to DA neurons in primary mesencephalic cultures, exogenous Hsp60 aggravated the effects of MPP+. Yet, although we demonstrated that Hsp60 specifically binds to microglial cells, it failed to stimulate the production of pro-inflammatory cytokines or NO by these cells.ConclusionsOverall, our data suggest that Hsp60 is likely to participate in DA cell death in PD but via a mechanism unrelated to cytokine release.
Highlights
Increasing evidence suggests that inflammation associated with microglial cell activation in the substantia nigra (SN) of patients with Parkinson disease (PD) is a consequence of neuronal degeneration, but may actively sustain dopaminergic (DA) cell loss over time
heat shock protein 60 (Hsp60) mRNA up-regulation is observed in MPTP-treated mice and in PD patients We postulated that injury of DA neurons could result in the release of Hsp60, causing activation of microglia cells
We first examined the dynamic changes of Hsp60 mRNA expression in the mesencephalon and the striatum of C57/Bl6 mice intoxicated with MPTP
Summary
Increasing evidence suggests that inflammation associated with microglial cell activation in the substantia nigra (SN) of patients with Parkinson disease (PD) is a consequence of neuronal degeneration, but may actively sustain dopaminergic (DA) cell loss over time. The cardinal neuroanatomical feature of PD is a massive and preferential loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) of patients, resulting in a drastic decline in striatal dopamine concentrations. Another histopathologic hallmark of PD is microglial activation in the SNpc [2,3]. Several observations suggest that an ongoing stimulus could lead to disease progression long after the initial toxic insult [4,5,6], thereby amplifying and sustaining neuroinflammation and, leading to destruction of nigral DA neurons These processes are generally considered to be a non-specific consequence of neuronal death. The possibility that suffering/damaged DA neurons might participate in the activation of microglia and in sustaining neuroinflammation deserves consideration
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