Genetic deficits and loss of function for the triggering receptor expressed in myeloid cells 2 (TREM2; encoded at chr6p21.1), a transmembrane spanning stimulatory receptor of the immunoglobulin/lectin-like gene superfamily, have been associated with deficiencies in phagocytosis and the innate immune system in Alzheimer’s disease. In this study, we provide evidence that TREM2 is downregulated in samples of sporadic Alzheimer hippocampal CA1 compared with age-matched controls. A nuclear factor-κB (NF-κB)-sensitive miRNA-34a (encoded at chr1p36.22), upregulated in Alzheimer’s disease, was found to target the 299 nucleotide human TREM2 mRNA 3′-untranslated region (3′-UTR) and downregulate the expression of a TREM2-3′-UTR reporter vector. A stabilized anti-miRNA-34a (AM-34a) quenched this pathogenic response. The results suggest that an epigenetic mechanism involving an NF-κB-mediated, miRNA-34a-regulated downregulation of TREM2 expression may shape innate immune and phagocytic responses that contribute to inflammatory neurodegeneration.

DEPDC5 is a newly identified epilepsy-related gene implicated in focal epilepsy, brain malformations, and Sudden Unexplained Death in Epilepsy (SUDEP). In vitro, DEPDC5 negatively regulates amino acid sensing by the mTOR complex 1 (mTORC1) pathway, but the role of DEPDC5 in neurodevelopment and epilepsy has not been described. No animal model of DEPDC5-related epilepsy has recapitulated the neurological phenotypes seen in patients, and germline knockout rodent models are embryonic lethal. Here, we establish a neuron-specific Depdc5 conditional knockout mouse by cre-recombination under the Synapsin1 promotor. Depdc5-Syn1 (Depdc5cc+) mice survive to adulthood with a progressive neurologic phenotype that includes motor abnormalities (i.e., hind limb clasping) and reduced survival compared to littermate control mice. Depdc5cc+ mice have larger brains with increased cortical neuron size and dysplastic neurons throughout the cortex, comparable to the abnormal neurons seen in human focal cortical dysplasia specimens. Depdc5 results in constitutive mTORC1 hyperactivation exclusively in neurons as measured by the increased phosphorylation of the downstream ribosomal protein S6. Despite a lack of increased mTORC1 signaling within astrocytes, Depdc5cc+ brains show reactive astrogliosis. We observed two Depdc5cc+ mice to have spontaneous seizures, including a terminal seizure. We demonstrate that as a group Depdc5cc+ mice have lowered seizure thresholds, as evidenced by decreased latency to seizures after chemoconvulsant injection and increased mortality from pentylenetetrazole-induced seizures. In summary, our neuron-specific Depdc5 knockout mouse model recapitulates clinical, pathological, and biochemical features of human DEPDC5-related epilepsy and brain malformations. We thereby present an important model in which to study targeted therapeutic strategies for DEPDC5-related conditions.

Inducible micro RNAs (miRNAs) perform critical regulatory roles in central nervous system (CNS) development, aging, health and disease. Using miRNA arrays, RNA-sequencing, enhanced Northern dot blot hybridization technologies, Western immunoblot and bioinformatics analysis we have studied miRNA abundance and complexity in Alzheimer’s disease (AD) brain tissues compared to age-matched controls. In both short post-mortem AD and in stressed primary human neuronal-glial (HNG) cells we observe a consistent up-regulation of several brain-enriched miRNAs that are under transcriptional control by the pro-inflammatory transcription factor NF-kB. These include miRNA-9, miRNA-34a, miRNA-125b, miRNA-146a and miRNA-155. Of the inducible miRNAs in this subfamily, miRNA-125b is amongst the most abundant and significantly induced miRNA species in human brain cells and tissues. Bioinformatics analysis indicates that up-regulated miRNA-125b targeted expression of (a) the 15-lipoxygenase (15-LOX; ALOX15; chr 17p13.3), utilized in the conversion of docosa-hexaneoic acid (DHA) into neuroprotectin D1 (NPD1), and (b) the vitamin D3 receptor (VDR; VD3R; chr12q13.11) of the nuclear hormone receptor superfamily. 15-LOX and VDR are key neuromolecular factors essential in lipid-mediated signaling, neurotrophic support, defense against reactive oxygen and nitrogen species (ROS, RNS) and neuroprotection in the CNS. Pathogenic effects appear to be mediated via specific interaction of miRNA-125b with the 3′-untranslated region (3′-UTR) of the 15-LOX and VDR messenger RNAs (mRNAs). In AD hippocampal CA1 and in stressed HNG cells, 15-LOX and VDR down-regulation and a deficiency in neurotrophic support, may therefore be explained by the actions of a single inducible, pro-inflammatory miRNA-125b. We will review recent data on the pathogenic actions of this up-regulated miRNA-125b in AD, and discuss potential therapeutic approaches using either anti-NF-kB or anti-miRNA-125b strategies. These may be of clinical relevance in the restoration of 15-LOX and VDR expression back to control levels and the re-establishment of homeostatic neurotrophic signaling in the CNS.

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One of the key classical pathological features of Alzheimer’s disease (AD) is the progressive accumulation of amyloid beta (Aβ42) peptides and their coalescence into highly insoluble senile plaque cores. A major factor driving Aβ42 peptide accumulation is the inability of brain cells to effectively clear excessive amounts of Aβ42 via phagocytosis. The trans-membrane spanning, sensor-receptor known as the ‘triggering receptor expressed in myeloid cells 2′ (TREM2; chr6p21) is essential in the sensing, recognition, phagocytosis and clearance of noxious cellular debris from brain cells, including neurotoxic Aβ42 peptides. Recently, mutations in the TREM2 gene have been associated with amyloidogenesis in neurodegenerative diseases including AD. In this report, we provide evidence that aluminum-sulfate, when incubated with microglial cells, induces the up-regulation of an NF-kB-sensitive micro RNA-34a (miRNA-34a; chr1p36) that is known to target the TREM2 mRNA 3′-untranslated region (3′-UTR), significantly down-regulating TREM2 expression. The aluminum-induced up-regulation of miRNA-34a and down-regulation of TREM2 expression was effectively quenched using the natural phenolic compound and NF-kB inhibitor CAPE [2-phenylethyl-(2E)-3-(3,4-dihydroxyphenyl) acrylate; caffeic-acid phenethyl ester]. These results suggest, for the first time, that an epigenetic mechanism involving an aluminum-triggered, NF-kB-sensitive, miRNA-34a-mediated down-regulation of TREM2 expression may impair phagocytic responses that ultimately contribute to Aβ42 peptide accumulation, aggregation, amyloidogenesis and inflammatory degeneration in the brain.