MicroRNA-34a-Mediated Down-Regulation of the Microglial-Enriched Triggering Receptor and Phagocytosis-Sensor TREM2 in Age-Related Macular Degeneration.

Surjyadipta Bhattacharjee,Evgeny I Rogaev,Prerna Dua,Walter J Lukiw,Yuhai Zhao,Michael E Boulton

doi:10.1371/journal.pone.0150211

Abstract

The aggregation of Aβ42-peptides and the formation of drusen in age-related macular degeneration (AMD) are due in part to the inability of homeostatic phagocytic mechanisms to clear self-aggregating Aβ42-peptides from the extracellular space. The triggering receptor expressed in myeloid/microglial cells-2 (TREM2), a trans-membrane-spanning, sensor-receptor of the immune-globulin/lectin-like gene superfamily is a critical component of Aβ42-peptide clearance. Here we report a significant deficit in TREM2 in AMD retina and in cytokine- or oxidatively-stressed microglial (MG) cells. RT-PCR, miRNA-array, LED-Northern and Western blot studies indicated up-regulation of a microglial-enriched NF-кB-sensitive miRNA-34a coupled to a down-regulation of TREM2 in the same samples. Bioinformatics/transfection-luciferase reporter assays indicated that miRNA-34a targets the 299 nucleotide TREM2-mRNA-3’UTR, resulting in TREM2 down-regulation. C8B4-microglial cells challenged with Aβ42 were able to phagocytose these peptides, while miRNA-34a down-regulated both TREM2 and the ability of microglial-cells to phagocytose. Treatment of TNFα-stressed MG cells with phenyl-butyl nitrone (PBN), caffeic-acid phenethyl ester (CAPE), the NF-B-inhibitor/resveratrol analog CAY10512 or curcumin abrogated these responses. Incubation of anti-miRNA-34a (AM-34a) normalized miRNA-34a abundance and restored TREM2 back to homeostatic levels. These data support five novel observations: (i) that a ROS- and NF-B-sensitive, miRNA-34a-mediated modulation of TREM2 may in part regulate the phagocytic response; (ii) that gene products encoded on two different chromosomes (miRNA-34a at chr1q36.22 and TREM2 at chr6p21.1) orchestrate a phagocytic-Aβ42-peptide clearance-system; (iii) that this NF-kB-mediated-miRNA-34a-TREM2 mechanism is inducible from outside of the cell; (iv) that when operating normally, this pathway can clear Aβ42 peptide monomers from the extracellular medium; and (v) that anti-NF-kB and/or anti-miRNA (AM)-based therapeutic strategies may be useful against deficits in TREM-2 receptor-based-sensing and -phagocytic signaling that promote pathogenic amyloidogenesis.

Highlights

Affecting about 150 million individuals worldwide, age-related macular degeneration (AMD) is a common, neurodegenerative disorder of the human retina characterized clinically by the progressive erosion of central vision [1,2]
post-mortem interval (PMI) for age-matched control or AMD human retinal tissues were all 2.5 hr; age-matched control or AMD sample tissues exhibited no significant differences in age, PMI, RNA A260/280 indices or RNA integrity numbers (RIN), age-matched control versus AMD
We noted no significant differences in total RNA purity or yields between the control and AMD groups for any tissues analyzed in this study

Summary

Introduction

Affecting about 150 million individuals worldwide, age-related macular degeneration (AMD) is a common, neurodegenerative disorder of the human retina characterized clinically by the progressive erosion of central vision [1,2]. The drusen of AMD typically develop with aging and contain a beta-amyloid precursor protein (βAPP)-derived 42 amino acid amyloid beta peptide (Aβ42) as a major component [3,4,5]. One prominent sensorreceptor for Aβ42-peptide clearance in the CNS is the triggering receptor expressed in myeloid/microglial cells-2 (TREM2; chr6p21.1), a ~230 amino acid, single pass type 1 transmembrane sensor-receptor protein enriched in the plasma membrane of microglial (MG) cells [6,7,8,9,10,11]. Mutations and loss-of-function for TREM2 have been associated with deficiencies in phagocytosis, the innate-immune system, axonal and synaptic abnormalities, amyloidogenesis and progressive dementia in progressive neurological diseases of the human CNS including polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy (PLOSL; known as Nasu-Hakola disease [6,7,8,9,10,11] as well as more recently in sporadic amyotrophic lateral sclerosis (ALS) [11] and in Alzheimer’s disease (AD) [6,7,8,9,10,11,12,13,14,15]

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