Inflammatory Stress on Autophagy in Peripheral Blood Mononuclear Cells from Patients with Alzheimer's Disease during 24 Months of Follow-Up

Abstract

Recent findings indicate that microglia in Alzheimer’s disease (AD) is senescent whereas peripheral blood mononuclear cells (PBMCs) could infiltrate the brain to phagocyte amyloid deposits. However, the molecular mechanisms involved in the amyloid peptide clearance remain unknown. Autophagy is a physiological degradation of proteins and organelles and can be controlled by pro-inflammatory cytokines. The purpose of this study was to evaluate the impact of inflammation on autophagy in PBMCs from AD patients at baseline, 12 and 24 months of follow-up. Furthermore, PBMCs from healthy patients were also included and treated with 20 μM amyloid peptide 1–42 to mimic AD environment. For each patient, PBMCs were stimulated with the mitogenic factor, phytohaemagglutin (PHA), and treated with either 1 μM C16 as an anti-inflammatory drug or its vehicle. Autophagic markers (Beclin-1, p62/sequestosome 1 and microtubule-associated protein-light chain 3: LC3) were quantified by western blot and cytokines (Interleukin (IL)-1β, Tumor necrosis Factor (TNF)-α and IL-6) by Luminex X-MAP® technology. Beclin-1 and TNF-α levels were inversely correlated in AD PBMCs at 12 months post-inclusion. In addition, Beclin-1 and p62 increased in the low inflammatory environment induced by C16. Only LC3-I levels were inversely correlated with cognitive decline at baseline. For the first time, this study describes longitudinal changes in autophagic markers in PBMCs of AD patients under an inflammatory environment. Inflammation would induce autophagy in the PBMCs of AD patients while an anti-inflammatory environment could inhibit their autophagic response. However, this positive response could be altered in a highly aggressive environment.

Amyloid Beta Peptide (Aβ1-42) Reverses the Cholinergic Control of Monocytic IL-1β Release

“…Numerous studies have shown pro-inflammatory functions of Aβ. Treatment of PBMCs with Aβ 1-42 leads to the secretion of pro-inflammatory cytokines like IL-1β, IL-6, IL-18, monocyte chemotactic protein-1 (MCP-1), and TNF-α [ 37 , 39 , 40 , 42 , 81 , 82 ]. Fibrillar Aβ 1-42 is supposed to directly interact with TLR2 and TLR4 to trigger TNF-α secretion in a monocytic cell line [ 83 ].…”

“…In addition, multiple non-neuronal immunological effects on leukocytes have been described. Both fibrillary and monomeric Aβ 1-42 can trigger inflammasome activation in mononuclear leukocytes and induce the secretion of the pro-inflammatory cytokines IL-1β and IL-18 [ 29 , 37 , 38 , 39 , 40 ]. In addition, inflammasome-independent cytokines IL-6, tumor necrosis factor-α (TNF-α), and monocyte chemotactic protein-1 (MCP-1) are released [ 29 , 37 , 39 , 40 , 41 , 42 ].…”

Metabolic effects of fasting on human and mouse blood in vivo

“…54,55 In addition, it has been previously demonstrated that detection of autophagy in neutrophils can be used to monitor autophagic flux at the whole body level in the context of pathological settings. 56 At present, the reasons for this discrepancy between mice and humans with respect to autophagy induction in all leukocyte subpopulation and neutrophils only, respectively, are elusive. This difference may be related to the intensity of the autophagy-inducing protocol between the 2 species, as well as to the fact that leupeptin was injected in vivo into mice but only used in vitro in the human context.…”

Longitudinal chemokine profile expression in a blood-brain barrier model from Alzheimer transgenic versus wild-type mice

“…Blood collection from deep anesthetized mice with 80 mg/kg IP pentobarbital (MSD, Santé Animale, Beaucouze, France) was performed by cardiac puncture and transferred into 10 mL BD Vacutainer® tube. Then, PBMCs were isolated using a Ficoll® Histopaque-1077 density gradient and cultured as previously described for human PBMCs [ 47 – 49 ]. PBMCs collected from blood samples of four mice were seeded in 500 μL of complete culture medium (RPMI 1640 medium completed with 10% of newborn calf serum, 1% of PS, and 20 μg/mL PHA) in 12-well plates during 24 h and then transferred into the upper side of transwell insert of the BBB model for 48 h. The most common agents used to stimulate PBMCs are either PHA, lipopolysaccharide (LPS), or β-amyloid peptide (Aβ).…”