The gain-of-function enhancement of IP3-receptor channel gating by familial Alzheimer's disease-linked presenilin mutants increases the open probability of mitochondrial permeability transition pore

摘要

Mutants in presenilins (PS1 or PS2) are the major cause of familial Alzheimer's disease (FAD). They affect intracellular Ca~(2+) homeostasis by increasing the open probability (P_o) of inositol 1,4,5-trisposphate (IP3) receptor (IP3R) Ca~(2+) release channel located on the endoplasmic reticulum (ER) leading to exaggerated Ca~(2+) release into a cytoplasmic microdomain formed by neighboring cluster of a few IP3R channels and mitochondrial Ca~(2+) uniporter (MCU). Ca~(2+) concentration in the microdomain ([Ca~(2+)]_(mic)) depends on the distance between the cluster and MCU (r); the number of IP3 R in the cluster releasing Ca~(2+) to the cytoplasm (n1p3R), and P_o of IP3R. Using experimental whole-cell IP3R-mediated cytosolic Ca~(2+) data, in conjunction with a computational model of cell bioenergetics, a data-driven Markov chain model for IP3R gating, and a model for the dynamics of the mitochondrial permeability transition pore (PTP), we explore differences in mitochondrial Ca~(2+) uptake in cells expressing wild type (PS1-WT) and FAD-causing mutant (PS1-M146L) PS. We find that increased mitochondrial [Ca~(2+)]_m due to the gain-of-function enhancement of IP3R channels in the cells expressing PS1-M146L leads to the opening of PTP in high conductance state (PTP_h), where the latency of opening is inversely correlated with r and proportional to Hip_3r. Furthermore, we observe diminished inner mitochondrial membrane potential (△ψ_m), (NADH], [Ca~(2+)]_m, and [ATP] when PTP opens. Additionally, we explore how parameters such as the pH gradient, inorganic phosphate concentration, and the rate of the Na+/Ca~(2+)-exchanger affect the latency of PTP to open in PTP_h.