Fig. 3: Estimation of the kinetic rate parameters from bulk aggregation kinetics and comparison with the single fibril data.

A, B, C represents bulk aggregation kinetics of 2 µM Aβ42, in 1x PBS pH 7.4 buffer in the presence of 1 nM monomer equivalent seeds at 25 °C. The symbols represent normalized ThT fluorescence from Aβ42 only (gray), and Aβ42 + 150 nM apoE4 (Blue), or apoE3 (Green), or apoE2 (Cyan) (data represents: mean ± SD, n = 3). In (A) and (B), the solid line represents the best global fit to the integrated rate law when we varied the \({k}_{+}\) keeping k₂ fixed and varied \({k}_{2}\) keeping k₊ fixed, respectively. Primary nucleation rate constant (\({k}_{n}\)) is set to zero. The best fit is achieved in (A). C We fixed the \({k}_{+}\) to the values obtained from the single fibril measurements in Fig. 2C with \({k}_{2}\) as free. All four curves yielded similar \({k}_{2}\) values varying between 0.8–0.4 × 10⁴ M⁻²s⁻¹. Panels(D),(E), (F), and (G) show examples of time traces of oligomer detection above a threshold (green dotted line) in the absence and presence of 150 nM apoE4, apoE3, and apoE2, respectively. Samples were taken at respective \({t}_{1/2}^{\prime} s\) of each samples, centrifuged to pellet down insoluble aggregates, and the supernatant was measured to assess the soluble oligomer population. Panel(H) shows the absence of oligomers in the lag phase, both in the absence (red, t = 40 min) and presence of apoE4 (Blue, t = 1.5 h), apoE3 (green, t = 2 h) and apoE2 (gray, t = 2 h). Panel(I) represents quantification of oligomer population in the presence and absence of 150 nM apoE isoforms at \({t}_{1/2}\). Each dot represents number of oligomers in a 30-s trace. Data represents mean ± SD,* indicates P < 0.05, ** indicates P < 0.01, and *** indicates P < 0.001 (using two-sample Student’s t test).