Intracerebral hemorrhage accounts for approximately 13 percent of all strokes and has a mortality of up to 44 percent, making it one of the most deadly types of strokes. Sporadic cerebral amyloid angiopathy is responsible for 15 percent of intracerebral hemorrhages in patients older than 60 years. It has been demonstrated that the prevalence of cerebral amyloid angiopathy found at autopsy increases significantly with advancing age. As the population continues to age, its prevalence will likewise increase, making intracerebral hemorrhage due to cerebral amyloid angiopathy increasingly common. Thus, cerebral amyloid angiopathy is a significant cause of morbidity and mortality in elderly humans. Cerebral amyloid angiopathy is an age-associated biochemically heterogeneous lesion in which amyloid is deposited primarily in the vascular wall. It can occur as a sporadic disorder in aged individuals, as a frequent component of Alzheimer's disease and Down's syndrome or in hereditary cerebral hemorrhage with amyloidosis. In these patients the amyloid in the cerebral vessel walls is composed mainly of amyloid beta-protein, cystatin C or both. The cystatin C deposited in cerebral vessel walls of Icelandic patients with hereditary cerebral hemorrhage with amyloidosis is an N-terminal truncated variant with an amino acid substitution Leu68Gln. We hypothesize that the amino acid substitution renders cystatin C susceptible to fibrillogenesis resulting in deposition of the N-terminal truncated form. This form has reduced inhibitory activity, resulting in increased cysteine protease mediated damage to the vessel walls. Furthermore, the association between cystatin C and A-beta and their colocalization in vessel walls attenuates the inhibitory activity of cystatin C, resulting in stroke. The applicant proposes to study the specific primary deposition of the amyloid in cerebral vessel walls as well as the role of cystatin C in stroke when secondarily deposited with A-beta. Specifically they propose to examine: 1. The tissue specific expression, secretion, and processing of the normal and variant cystatin C, using transfected tissue culture cell lines; 2. The effect of the amino acid substitution found in hereditary cerebral hemorrhage with amyloidosis, Icelandic type, on cystatin C aggregation, fibril formation and cleavage by elastase, as well as the association of the normal and variant cystatin C with A-beta, resulting in the secondary deposition of cystatin C in A-beta laden vessels; 3. The specific primary deposition of amyloid in cerebral vessel walls by analysis of the specific binding of normal and variant cystatin C to proteins in different tissues and body fluids; & 4. The effect of squirrel monkey cystatin C sequence on its aggregation and associ-ation with tissue specific proteins in order to develop the squirrel monkey as a model for cerebral amyloid angiopathy with deposition of both A-beta and cystatin C. The studies proposed in this grant application will not only unveil the pathogenesis of hereditary cerebral hemorrhage with amyloidosis, Icelandic type but also serve as a model for understanding the pathogenesis of amyloidoses formed by other amyloid proteins.
