[Frontiers in Bioscience 13, 3470-3479, May 1, 2008] 3470 Involvement of cystatin C in pathophysiology of CNS diseases Atsushi Nagai 1 , Masaharu Terashima 2 , Abdullah Md Sheikh 1 , Yoshitomo Notsu 1 , Koichi Shimode 3 , Shuhei Yamaguchi 3 , Shotai Kobayashi 4 , Seung U. Kim 5 , Junichi Masuda 1 1 Department of Laboratory Medicine, 2 Department of Biochemistry and Molecular Medicine, 3 Department of Internal Medicine III, and 4 University Hospital, Shimane University Faculty of Medicine, Izumo, Japan, 5 Division of Neurology, UBC Hospital, University of British Columbia, Vancouver, Canada TABLE OF CONTENTS 1. Abstract 2. Cystatin C-type cerebral amyloid angiopathy 3. Amyloid fibril formation by cystatin C 4. Concentration in CSF 5. Involvement in AD 6. Involvement in neuronal cell death 7. Conclusions 8. Acknowledgments 9. References 1. ABSTRACT 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 β protein (Aβ), and accelerates the amyloidogenicity of Aβ 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 Aβ 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. 2. CYSTATIN C-TYPE CEREBRAL AMYLOID ANGIOPATHY The deposition of abnormal fibrillar protein aggregates (so-called amyloid) in the walls of arteries, arterioles, and sometimes capillaries and veins of the central nervous system (CNS) is known as cerebral amyloid angiopathy (CAA). The most prevalent form of CAA is the β-amyloid (Aβ) type that frequently accompanies Alzheimer’s disease (AD). In AD, both parenchymal amyloid and vascular deposition are seen. Mutated cystatin C deposition was also observed in hereditary CAA with amyloidosis, Icelandic type (HCHWA-I) (1). The common features in CAA are vasculopathies associated with amyloid infiltration, such as clusters of multiple arteriole lamina, glomerular formation, obliterative intimal changes and double-barreling, especially in cortical arterioles and leptomeningeal vessels (2). CAA often leads to recurrent brain hemorrhage or infarction in cortical and subcortical regions. Patients with HCHWA-I have been extensively studied by molecular biological methods, and the deposited