Constitutive overactivation of protein kinase C in guinea pig brain increases alpha-secretory APP processing without decreasing beta-amyloid generation.
Whilst it is generally accepted that the activation of protein kinase C (PKC) increases amyloid precursor protein (APP) secretion in vitro, the role of PKC in the regulation of APP processing and beta-amyloid generation in vivo is still not well understood. In order to address this question, we established the animal model of neocortical microencephalopathy in guinea pigs caused by in utero treatment with methylazoxymethanol acetate, a DNA-methylating substance that eliminates proliferating cells of neuroepithelial origin. The induction of this neocortical malformation is accompanied by constitutive overactivation of PKC in the neocortex of the offspring. In the cortical and hippocampal tissues of juvenile microencephalic guinea pigs (postnatal day 30), we observed significant increases in basal (by 58% and 74%, respectively,) and phorbol ester-stimulated PKC enzyme activity (by 47% and 71%) as compared to age-matched control animals. In the same cortical/hippocampal preparations of methylazoxymethanol-treated animals, there was increased alpha-secretion of APP by 35% and 30% as measured by Western blot analysis using the antibody 6E10, whilst total APP secretion as well as APP mRNA expression remained unaltered. This upregulation of APP alpha-secretion was limited to brain areas that displayed elevated PKC activity. However, constitutive overactivation of neocortical PKC did not affect the generation of beta-amyloid peptides 1-40 or 1-42 as measured by ELISA, suggesting that only the alpha-secretase pathway of APP processing is affected by chronic PKC overactivation in vivo.
Rossner
S
S
Department of Neurochemistry, Paul Flechsig Institute for Brain Research, Jahnallee 59, 04109 Leipzig, Germany. rossn@medizin.uni-leipzig.de
Beck
M
M
Stahl
T
T
Mendla
K
K
Schliebs
R
R
Bigl
V
V
D053829:Amyloid Precursor Protein Secretases; D016229:Amyloid beta-Peptides / Q000096:biosynthesis*; D016564:Amyloid beta-Protein Precursor / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002273:Carcinogens / Q000494:pharmacology; D010450:Endopeptidases / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D006168:Guinea Pigs; D006624:Hippocampus / Q000002:abnormalities / Q000196:embryology / Q000201:enzymology; D008746:Methylazoxymethanol Acetate / Q000494:pharmacology; D008831:Microcephaly / Q000201:enzymology; D023421:Models, Animal; D019579:Neocortex / Q000002:abnormalities / Q000196:embryology / Q000201:enzymology*; D010446:Peptide Fragments / Q000096:biosynthesis*; D010703:Phorbol Esters / Q000494:pharmacology; D011247:Pregnancy; D011493:Protein Kinase C / Q000032:analysis / Q000378:metabolism*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis
D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D002273:Carcinogens; D010446:Peptide Fragments; D010703:Phorbol Esters; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; C078592:amyloid beta-protein (1-40); D008746:Methylazoxymethanol Acetate; D011493:Protein Kinase C; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases