The cerebral hemorrhage-producing cystatin C variant (L68Q) in extracellular fluids.
A variant of the normal extracellular cysteine protease inhibitor cystatin C (L68Q-cystatin C), is the amyloid precursor in hereditary cystatin C amyloid angiopathy (HCCAA). It has been suggested that the mutation causes cellular entrapment of L68Q-cystatin C in vivo and that the variant protein is not secreted to extracellular fluids. In order to test this hypothesis, we used matrix-assisted laser desorption ionization time-of-flight mass spectrometry in an effort to demonstrate the presence of L68Q- along with wildtype cystatin C in plasma and cerebrospinal fluid (CSF) of HCCAA-patients. Plasma from all five investigated HCCAA-patients contained both L68Q- and wildtype cystatin C. The presence of approximately equal amounts of cystatin C dimers and monomers was demonstrated in plasma from HCCAA-patients, whereas only monomers could be found in normal plasma. L68Q-wildtype-cystatin C heterodimers seem to be present in the dimeric cystatin C population. CSF from six HCCAA-patients also contained cystatin C-dimers and monomers, but the dimeric fraction was minute. CSF from control patients did not contain dimeric cystatin C. These results suggest that the milieu of L68Q-cystatin C is important for its stability and dimerization status and that certain milieus might hinder its further development into oligomers, amyloid fibrils and other precipitating aggregates.
Bjarnadottir
M
M
Department of Clinical Chemistry, Institute of Laboratory Medicine, University of Lund, University Hospital, Sweden.
Nilsson
C
C
Lindström
V
V
Westman
A
A
Davidsson
P
P
Thormodsson
F
F
Blöndal
H
H
Gudmundsson
G
G
Grubb
A
A
D000328:Adult; D019943:Amino Acid Substitution; D016657:Cerebral Amyloid Angiopathy / Q000097:blood / Q000134:cerebrospinal fluid / Q000235:genetics*; D002543:Cerebral Hemorrhage / Q000097:blood / Q000134:cerebrospinal fluid / Q000235:genetics*; D002556:Cerebrospinal Fluid Proteins / Q000032:analysis / Q000737:chemistry / Q000235:genetics; D055316:Cystatin C; D015891:Cystatins / Q000032:analysis / Q000737:chemistry / Q000235:genetics*; D004797:Enzyme-Linked Immunosorbent Assay; D005110:Extracellular Space / Q000737:chemistry; D006580:Genetic Carrier Screening; D014644:Genetic Variation; D006801:Humans; D008875:Middle Aged; D012016:Reference Values; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
C525030:CST3 protein, human; D002556:Cerebrospinal Fluid Proteins; D055316:Cystatin C; D015891:Cystatins