Insulin-degrading enzyme in brain microvessels: proteolysis of amyloid {beta} vasculotropic variants and reduced activity in cerebral amyloid angiopathy.
The accumulation of amyloid beta (Abeta) in the walls of small vessels in the cerebral cortex is associated with diseases characterized by dementia or stroke. These include Alzheimer's disease, Down syndrome, and sporadic and hereditary cerebral amyloid angiopathies (CAAs) related to mutations within the Abeta sequence. A higher tendency of Abeta to aggregate, a defective clearance to the systemic circulation, and insufficient proteolytic removal have been proposed as mechanisms that lead to Abeta accumulation in the brain. By using immunoprecipitation and mass spectrometry, we show that insulin-degrading enzyme (IDE) from isolated human brain microvessels was capable of degrading (125)I-insulin and cleaved Abeta-(1-40) wild type and the genetic variants Abeta A21G (Flemish), Abeta E22Q (Dutch), and Abeta E22K (Italian) at the predicted sites. In microvessels from Alzheimer's disease cases with CAA, IDE protein levels showed a 44% increase as determined by sandwich enzyme-linked immunosorbent assay and Western blot. However, the activity of IDE upon radiolabeled insulin was significantly reduced in CAA as compared with age-matched controls. These results support the notion that a defect in Abeta proteolysis by IDE contributes to the accumulation of this peptide in the cortical microvasculature. Moreover they raise the possibility that IDE inhibition or inactivation is a pathogenic mechanism that may open novel strategies for the treatment of cerebrovascular Abeta amyloidoses.
IQUIFIB/Consejo Nacional de Investigaciones Científicas y Técnicas, Cátedra de Química Biológica Patológica, Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junin 956, C1113AAD, Buenos Aires, Argentina.
Laura
L
Morelli
Ramiro E
RE
Llovera
Irina
I
Mathov
Lih-Fen
LF
Lue
Blas
B
Frangione
Jorge
J
Ghiso
Eduardo M
EM
Castaño
D000328:Adult; D016229:Amyloid beta-Peptides / Q000737:chemistry*; D000818:Animals; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism* / Q000473:pathology; D016657:Cerebral Amyloid Angiopathy / Q000235:genetics* / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D007328:Insulin / Q000378:metabolism; D007339:Insulysin / Q000737:chemistry / Q000502:physiology*; D007700:Kinetics; D013058:Mass Spectrometry; D008833:Microcirculation; D008856:Microscopy, Fluorescence; D008875:Middle Aged; D009154:Mutation; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors
D016229:Amyloid beta-Peptides; D018076:DNA, Complementary; D007328:Insulin; D010455:Peptides; D011994:Recombinant Proteins; D007339:Insulysin