Interaction of Double-stranded RNA-dependent Protein Kinase (PKR) with the Death Receptor Signaling Pathway in Amyloid β (Aβ)-treated Cells and in APPSLPS1 Knock-in Mice

Abstract

Alzheimer Disease (AD)2 is the leading cause of dementia in the elderly, affecting 25 million people in the world with about 5% of genetic origin. The biological features of AD are neuronal loss, senile plaques predominantly composed of amyloid ␤ peptide (A␤), and the presence of neurofibrillary tangles, leading to a progressive deterioration of cognitive function with loss of memory. Unfortunately, no definitive therapy for AD exists.The involvement of A␤ is clearly established, but mechanisms that underlie neuronal death are currently under investigation. For 10 years, research has focused on pathways controlling translation (1-5). They revealed that activated double-stranded RNA-dependent protein kinase (PKR), which phosphorylates the ␣-subunit of eIF2, was associated with degenerating neurons in AD brains (6 -8). Furthermore, the levels of phosphorylated forms of PKR and eIF2␣ were significantly increased in AD cellular models exposed to A␤42 (2, 5) in the brain of AD transgenic mice (1, 9) and in lymphocytes of AD patients (10). These modifications were negatively correlated with cognitive and memory test scores performed in AD patients (3, 10, 11). Besides its important role as a translational regulator, PKR is a key mediator in different signaling pathways. Indeed, among its downstream targets, the Fas-associated protein with a death domain (FADD) and subsequent caspase-8 are responsible for PKR-induced apoptosis in virus-infected cells (12). Furthermore, the overexpression of a dominant-negative FADD construct rescued SH-SY5Y cells from either tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) or A␤-induced neurotoxicity (13). FADD could be involved in apoptosis through its nuclear localization by interacting with the methylCpG binding domain protein 4 (MDB4), a protein known to be implicated in DNA repair, but that could promote apoptosis when associated with FADD (14). Furthermore, many postmortem studies have reported the role of the FADD-linked death receptor signaling pathway in the pathobiology of AD (15-17).However, control of FADD under the PKR activation in AD remains unknown. The present study performed a detailed analysis of PKR and FADD interaction in A␤-treated cells and in APP SL PS1 KI transgenic mice. The purpose is to determine if inhibition of PKR could reduce apoptosis through the decrease in this death adaptor activation. Here, we showed a physical interaction between PKR and FADD in nuclei of A␤42-treated SH-SY5Y and in APP SL PS1 KI mice. Furthermore, PKR inhibitory treatments prevented not only the nuclear translocation of FADD but also significantly decreased caspase-3 and -8 activities induced by A␤ neurotoxicity. EXPERIMENTAL PROCEDURES

Pharmacological Inhibition of PKR in APPswePS1dE9 Mice Transiently Prevents Inflammation at 12 Months of Age but Increases Aβ42 Levels in the Late Stages of the Alzheimer’s Disease

“…Our previous studies demonstrated that an inhibitor of PKR, the compound C16, prevented the A 42-induced toxicity in human SH-SY5Y neuroblastoma cell line and rat primary neuronal culture, indicating the role of PKR signaling pathway in apoptosis [26][27][28]. Recently, we showed that C16 prevented not only the inflammatory responses in A 42-treated mixed mouse primary co-cultures of neurons, astrocytes and microglia (data submitted) but also in PBMCs of patients with AD [36].…”

“…Furthermore, many papers described the role of PKR in Alzheimer's disease (AD) from in vitro to in vivo animal studies and in brain of patients with AD. Indeed, it is well-known that PKR negatively controls the translation [22,23], is associated with apoptotic neurons and dystrophic neurites around amyloid deposits [24][25][26], physically interacts with p53 [27] and Fasassociated protein with a death domain (FADD) [28] under amyloid stress. To date, the involvement of PKR in the control of inflammatory response in AD is not elucidated.…”

The Small Molecule Indirubin-3'-Oxime Inhibits Protein Kinase R: Antiapoptotic and Antioxidant Effect in Rat Cardiac Myocytes

“…Caspase-3 activation may be a part of high glucose-induced apoptosis. PKR is reported to mediate apoptosis through multiple mechanisms, including interaction with Fas-associated death domain protein upregulation of the proapoptotic factor Bax and downregulation of Bcl-2 and activation of the caspase-8/caspase-3 pathway [24,25,26,27,28,29,30]. PKR activation abolished the pro-proliferative effects of IGF-I by activating JNK and disrupting the IRS1/PI3K/Akt signaling pathway [6].…”

Neuroinflammation and β Amyloid Deposition in Alzheimer's Disease: In vivo Quantification with Molecular Imaging

“…Microglial cells may amplify several steps of the amyloid cascade [24,29]. Some studies have shown that this inflammatory response was also present at the periphery with increased levels of circulating cytokines and chemokines in plasma [30,31,32] and in peripheral blood mononuclear cells (PBMCs) [32,33,34] of patients with AD compared to age-matched controls. Furthermore, in patients with AD, both activated T cells and monocytes are present peripherally [35] and infiltrate around amyloid deposits in the brain [36,37].…”