Involvement of cystatin C in pathophysiology of CNS diseases.

Cystatin C Leu68Gln variant is known to induce amyloid deposition in cerebral arterioles, resulting in Icelandic type cerebral amyloid angiopathy (CAA). Wild-type cystatin C is also observed in solitary CAA involving amyloid beta protein (Abeta), and accelerates the amyloidogenicity of Abeta in vitro. In neurological inflammatory diseases and leptomeningeal metastasis, low cystatin C levels are accompanied with high activities of cathepsins in the cerebrospinal fluid. Among the cells in CNS, astrocytes appear to secrete cystatin C in response to various proteases and cytokines. Co-localization of Abeta and cystatin C in the brains of Alzheimer's disease (AD) led to the hypothesis that cystatin C is involved in the disease process. We demonstrated that cystatin C microinjection into rat hippocampus induced neuronal cell death in dentate gyrus. Furthermore, apoptotic cell death was observed in neuronal cells treated with cystatin C in vitro. Up-regulation of cystatin C was observed in glial cells with neuronal cell death in vivo. These findings indicate the involvement of cystatin C in the process of neuronal cell death.