Involvement of dopaminergic neuronal cystatin C in neuronal injury-induced microglial activation and neurotoxicity

J. Neurochem. (2012) 122, 752–763. Factors released from injured dopaminergic (DA) neurons may trigger microglial activation and set in motion a vicious cycle of neuronal injury and inflammation that fuels progressive DA neurodegeneration in Parkinson’s disease. In this study, using proteomic and immunoblotting analysis, we detected elevated levels of cystatin C in conditioned media (CM) from 1‐methyl‐4‐phenylpyridinium and dieldrin‐injured rat DA neuronal cells. Immunodepletion of cystatin C significantly reduced the ability of DA neuronal CM to induce activation of rat microglial cells as determined by up‐regulation of inducible nitric oxide synthase, production of free radicals and release of proinflammatory cytokines as well as activated microglia‐mediated DA neurotoxicity. Treatment of the cystatin C‐containing CM with enzymes that remove O‐ and sialic acid‐, but not N‐linked carbohydrate moieties markedly reduced the ability of the DA neuronal CM to activate microglia. Taken together, these results suggest that DA neuronal cystatin C plays a role in the neuronal injury‐induced microglial activation and neurotoxicity. These findings from the rat DA neuron‐microglia in vitro model may help guide continued investigation to define the precise role of cystatin C in the complex interplay among neurons and glia in the pathogenesis of Parkinson’s disease. Cystatin C and the vicious cycle of neuronal injury and microglial activation The impact of factors released from neurons under stress on brain immune cells may be relevant to neuropathogenesis. In a rat cell‐based model, among proteomically identified secretome proteins from toxicant‐injured dopamine neurons, cystatin C was found to facilitate microglial activation and neurotoxicity. Dopamine neuronal cystatin C and/or related proteins may be key mediators of neuroinflammation and neurodegeneration.