Amyloidosis induced by variants of Human Apolipoprotein A-I: effect of cellular microenvironment.

RAMELLA, N.; SCHINELLA, GUILLERMO; RIMOLDI. O. J.; PRIETO, E. D.; VELA, M E.; TRICERRI, M. A.

Groeningen

Simposio; XIII International Symposium on Amyloidosis; 2012

Universitair Medisch Centrum Groningen

Background Nonhereditary apolipoprotein A-I (apoA-I) amyloid is characterized by deposits of nonvariant protein in atherosclerotic arteries (1). In addition, mutant forms of apoA-I have been involved in familial amyloidosis (2). In order to understand the molecular events determining protein misfolding it is clue to study the complex scenario in which apoA-I circulates during its lifetime. Factors such as protein stability, chemical modifications pH or pro-inflammatory environment could be critical to shift protein structure into other conformation prone to aggregate or induce pathology (3). Objective We studied biophysical and biochemical events that could induce amyloidosis by Wild type apoA-I (Wt) and by two natural mutants detected in patients (Gly26Arg y Lys107-0). Methods Proteins were incubated under different conditions (low pH, in the presence of activated neutrofils, etc) and structural features associated to protein folding were analyzed by fluorescence spectroscopy and western blotting. Aggregates were characterized by Atomic Force Microscopy. Results Mildly acidic pH promoted misfolding, aggregation, and increased binding of apoA-I variants to extracellular matrix elements, thus favoring protein deposition as amyloid like-complexes. In addition, activated neutrophils and oxidative/proteolytic cleavage of the proteins gave rise to pro amyloidogenic products. Both pathological variants were less stable than Wt but only Lys107-0 showed higher tendency to aggregate. Discussion Drastic structural changes do not seem required in order to induce protein pro-amyloid processing, as weaker bonding at protein contacts could shift the equilibrium between native and pathological conformations. Conclusion Our results strongly suggest that different events taking place in chronic inflammatory hallmark, such as atherosclerosis conduct to a pro-amyloidogenic processing of apoA-I which in turn could impair vascular disease. References (1) Obici L. et al. (2006). Amyloid 13: 191-205. (2) Eriksson, M. et al. (2009). J Mol Diagn. 11:257?262 (3) Ramella, N. et al. (2011), PLoS ONE, 6(7):e22532. Epub 2011 Jul 19.