Activation of the Fibrinolytic System by Amyloid Cross-b Structure Results In reply to: Cell Detachment AND Processing of Neuroendocrine Factors

Abstract number: OR327

Bouma¹ B, Kranenburg¹ O, Schiks¹ B, Romijn² EP, Posthuma¹ G, Kayed³ R, Heck² AJR, Aarsman¹ CJ, Gent¹ YJJ, Voest EE, de Groot¹ PhG, Gebbink¹ MFBG

¹¹Department of Hematology, Cell Biology or Medical Oncology, University Medical Center Utrecht, Utrecht, The Netherlands ¹¹Department of Hematology, Cell Biology or Medical Oncology, University Medical Center Utrecht, Utrecht, The Netherlands ²²The Department of Biomolecular Mass Spectrometry, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands ³³Department of Molecular Biology and Biochemistry, University of California, Irvine, CA, USA

Amyloid-b, a major constituent of plaques associated with Alzheimer's disease, activates tissue-type plasminogen activator (tPA). We found that tPA mediates cell detachment (Kranenburg, O., et al. Mol Cell Neurosci. 2005) and processing of 5 major neuronal cell-produced Ab-associated neuroendocrine endocrine factors (NEFs) (Kranenburg, O., et al. Neuroscience. 2005). Conversion of plasminogen into plasmin by tPA requires a cofactor. Fibrin is the classical cofactor, but denatured proteins, glycated proteins and amyloid-b can also function as cofactor for tPA-mediated plasmin formation. We previously showed that the common denominator in tPA-activating ligands is the amyloid cross-b structure, that classified tPA as a general amyloid cross-b structure binding protein (Kranenburg, O., et al. Curr Biol. 2002). We further studied the consequences of the interaction of tPA with amyloid. We found that Ab induces excessive cell associated plasmin generation that causes cell detachment. Cell detachment is inhibited by carboxypeptidase B (CPB), an enzyme that blocks plasmin formation by cleaving off C-terminal lysines. Plasmin and CPB control Ab-induced cell detachment independently of direct effects on cell viability. Ab40 and oligomeric and fibrillar forms of Ab42 stimulated tPA-mediated plasminogen activation and cell detachment. This suggests that plasmin-mediated cell detachment could contribute to pathological effects of Ab in diseased brain. We identified 5 NEFs: Chromogranins A, B and C, truncated chromogranin B, and VGF that are associated with amyloid and processed by plasmin. Plasmin caused processing of Ab-bound tPA, chromogranin B and VGF and the products were released. Processing of the NEFs was dependent on tPA as it was abrogated in tPA^-/- cells or in the presence of a tPA-inhibitor. Some of these peptides may have biological activity, for instance in regulating neurotransmitter release that may affect the pathology of Alzheimer's disease.