Nicastrin, Presenilin, APH-1, and PEN-2 Form Active γ-Secretase Complexes in Mitochondria

Abstract

Mitochondria are central in the regulation of cell death. Apart from providing the cell with ATP, mitochondria also harbor several death factors that are released upon apoptotic stimuli. Alterations in mitochondrial functions, increased oxidative stress, and neurons dying by apoptosis have been detected in Alzheimer's disease patients. These findings suggest that mitochondria may trigger the abnormal onset of neuronal cell death in Alzheimer's disease. We previously reported that presenilin 1 (PS1), which is often mutated in familial forms of Alzheimer's disease, is located in mitochondria and hypothesized that presenilin mutations may sensitize cells to apoptotic stimuli at the mitochondrial level. Presenilin forms an active ␥-secretase complex together with Nicastrin (NCT), APH-1, and PEN-2, which among other substrates cleaves the ␤-amyloid precursor protein (␤-APP) generating the amyloid ␤-peptide and the ␤-APP intracellular domain. Here we have identified dual targeting sequences (for endoplasmic reticulum and mitochondria) in NCT and showed expression of NCT in mitochondria by immunoelectron microscopy. We also showed that NCT together with APH-1, PEN-2, and PS1 form a high molecular weight complex located in mitochondria. ␥-Secretase activity in isolated mitochondria was demonstrated using C83 (␣-secretasecleaved C-terminal 83-residue ␤-APP fragment from BD8 cells lacking presenilin and thus ␥-secretase activity) or recombinant C100-Flag (C-terminal 100-residue ␤-APP fragment) as substrates. Both systems generated an APP intracellular domain, and the activity was inhibited by the ␥-secretase inhibitors L-685,458 or Compound E. This novel localization of NCT, PS1, APH-1, and PEN-2 expands the role and importance of ␥-secretase activity to mitochondria.

Glucose and Endoplasmic Reticulum Calcium Channels Regulate HIF-1β via Presenilin in Pancreatic β-Cells

“…In the ␤-cell, presenilins appear to participate in a signaling network implicated in mitochondrial function and cell fate. Interestingly, presenilin-1 has been localized to the mitochondria in other cell types (62,63) and mitochondrial respiration was decreased in knock-in mice with a presenilin-1 gain-of-function mutation (64). Studies also point to the up-regulation of presenilins in hypoxic conditions (12,24,27,65), similar to our observation that hypoglycemia increases presenilin-1 expression.…”

Amyloid precursor protein and amyloid β-peptide bind to ATP synthase and regulate its activity at the surface of neural cells

“…58 New models of Alzheimer's disease also include negative effects of intracellular Ab in neurons, 59 and several findings have led to the hypothesis that an impairment of the electron transport chain in mitochondria is responsible for this pathology. 60 Recent publications and our findings describe a mitochondrial localization for APP 61 (Supplementary Figure 1), for a functional g-secretase complex 62 and for Ab. 63,64 Thus APP and Ab in mitochondria could inhibit the ATP synthase subunit a within the F 1 F 0 -ATP synthase complex of the electron transport chain, resulting in ATP depletion.…”

Prostaglandin I 2 upregulates the expression of anterior pharynx‐defective‐1α and anterior pharynx‐defective‐1β in amyloid precursor protein/presenilin 1 transgenic mice

“…Indeed, APH‐1 often combines with PEN‐2, nicastrin, and PS to generate an active form of γ‐secretase complex, which is responsible for the cleavage of β‐APP and for the deposition of Aβ (De Strooper, 2003). Once APH‐1 was found in C. elegans (Francis et al ., 2002), the APH‐1 complex was confirmed in several experimental models (Gu et al ., 2003; Luo et al ., 2003; Hansson et al ., 2004). Along these lines, APH‐1α/1β might also be involved in regulating the deposition of Aβ 1–42 in response to PGI 2 stimulation.…”