Alzheimer's disease-related presenilin 1 M146L mutation disrupts SERCA2a regulation and increases propensity of Ca waves in ventricular cardiomyocytes.

Abstract

Presenilin 1 (PS1) is a transmembrane protein expressed in the endoplasmic reticulum (ER) of different cell types. It has been shown that Ca mishandling due to PS1 mutations contributes to the Alzheimer's disease (AD)-related neurodegeneration. PS1 is also expressed in the heart. Several clinical studies revealed that PS1 mutations are associated with cardiomyopathies. We previously showed that PS1 interacts with the cardiac ER Ca ATPase (SERCA2a) and regulates its function. Here, we studied the role of AD-related PS1M146L mutation in regulation of intracellular Ca homeostasis. Fluorescent resonance energy transfer (FRET) experiments in HEK293 cells transfected with fluorescently labeled SERCA2a and PS1M146L revealed that the mutation does not disrupt the interaction between these two proteins. Measurements of SERCA2a-mediated Ca transport showed that at low ER Ca loads ([Ca]ER≤0.15 mM), both PS1WT and PS1M146L enhance ER Ca uptake by a similar level (∼40%) compared to control (no PS1 expression). At high ER Ca loads ([Ca]ER≥0.35 mM), however, PS1WT reduced ER Ca uptake and ER Ca load, whereas PS1M146L was less effective in regulating SERCA2a function. We used in vivo gene delivery in mouse cardiac wall to study the effect of PS1WT and PS1M146L overexpression on Ca regulation in ventricular myocytes. We found that both PS1WT and PS1M146L localized predominantly at the sarcoplasmic reticulum. Analysis of cytosolic Ca dynamics revealed that PS1WT overexpression in cardiomyocytes increases diastolic Ca and decreases Ca transient amplitudes. In contrast, PS1M146L expression increased propensity of spontaneous Ca waves. These results illustrate that the lack of SERCA2a regulation by PS1M146L at high ER Ca loads can lead to ER Ca overload and Ca waves. These defects in Ca regulation might contribute to the onset of cardiomyopathies in patients with PS1 mutations.