Kinetic theory of fibrillogenesis of amyloid β-protein

Abstract

Prior quasielastic light scattering (QLS) studies of fibrillogenesis of synthetic amyloid ␤-protein (A␤)-(1-40) at low pH have suggested a kinetic model in which: (i) fibrillogenesis requires a nucleation step; (ii) nuclei are produced by A␤ micelles in addition to seeds initially present; and (iii) fibril elongation occurs by irreversible binding of A␤ monomers to the fibril ends. Here we present the full mathematical formulation of this model. We describe the temporal evolution of the concentrations of A␤ monomers and micelles as well as the concentration and size distribution of fibrils. This formulation enables deduction of the fundamental parameters of the model-e.g., the nucleation and elongation rate constants k n and k e -from the time dependency of the apparent diffusion coefficient measured by QLS. The theory accurately represents the experimental observations for A␤ concentrations both below and above c*, the critical concentration for A␤ micelle formation. We suggest that the method of QLS in combination with this theory can serve as a powerful tool for understanding the molecular factors that control A␤ plaque formation.A seminal pathogenetic event in Alzheimer disease (AD) is the formation of fibrous amyloid plaques in the brain parenchyma and vasculature (1). The primary protein component of plaques is the amyloid ␤-protein (A␤) (2). In the plasma and cerebrospinal fluid, amyloid ␤-protein exists primarily as a soluble peptide 40 or 42 residues long (3). However, in the senile plaque, A␤ exists in the form of amyloid fibers (4). The conversion of soluble A␤ into insoluble fibers produces structures with neurotoxic activity (5). This observation, coupled with accumulating genetic evidence which links increased production of fibrillogenic forms of A␤ with familial AD (6), makes inhibiting fibrillogenesis an attractive therapeutic strategy.To properly target inhibitors, the structural stages and the kinetics of A␤ fibrillogenesis must be determined. In the past, turbidity and thioflavin T binding have been used to quantify levels of A␤ aggregation and amyloidogenesis, respectively (7-9). However, both methods detect only large polymeric structures and provide no information on either nucleation or elongation rate, the two key parameters controlling the kinetics of A␤ fibrillogenesis. Recently, however, static and dynamic light scattering, sophisticated optical methods capable of monitoring fibril length and structure, have been applied to the A␤ fibrillogenesis problem (10-12).In a previous communication (12) we reported an experimental study of the temporal evolution of A␤ fibrils using quasielastic light scattering (QLS). That study introduced an in vitro model system which permits quantitative monitoring of the kinetics of A␤ fibrillogenesis and enables the determination of the numerical values of the nucleation rate and elongation rate of the fibrils. Knowledge of these rate constants is vital in the effort to understand the molecular factors that control fibril creation and growth. This ...

Simulations of nucleation and elongation of amyloid fibrils

“…In contrast to the view that the elongation of amyloid fibrils is irreversible, 60,61 we note that adsorbed peptides can reversibly desorb into free space during the elongation process, i.e., a protofibril may undergo 120 adsorption and 100 desorption events in order to grow 20 cuboids longer. In conformity with the prevalent view in the literature, it appears that all fibrils are in fast, dynamic exchange with the peptide solution ͑free diffusing peptides dissolved in free space͒.…”

Amyloid Beta monomers regulate cyclic adenosine monophosphate response element binding protein functions by activating type‐1 insulin‐like growth factor receptors in neuronal cells

“…To answer this question, we used the H4‐APPswe cell line, engineered to over‐produce Aβ1–40 (Aβ40) and Aβ1–42 (Aβ42) by the introduction of the double Swedish mutation (K595N/M596L) in the amyloid precursor protein (APP) gene. Aβ levels reached in the conditioned medium (CM) of this stable transfected neuroglioma are low, likely insufficient to induce significant aggregation of the peptide (Lomakin et al ., 1997; Harper et al ., 1999). We collected a 6h and 24h conditioned medium from H4‐APPswe cultures, incubated in presence or absence of β‐ or γ‐secretase inhibitors, and Aβ levels were measured by ELISA (Fig.…”

Nucleation of amyloid fibrils

“…These energies affect also the fibril nucleus size n* and nucleation work w* whose CNT dependences on the supersaturation s are given by Eqs. (16) and (17). The corresponding CCNT dependences are given by Eqs.…”

“…[9][10][11][12][13][14][16][17][18]29,30,33,36,38,44,[52][53][54]68,70) or by the temperature at a fixed protein concentration (e.g., Refs. 9,10,14,19,25,26,70,74,76).…”