Antagonism of NF-κB-up-regulated micro RNAs (miRNAs) in sporadic Alzheimer's disease (AD)—anti-NF-κB vs. anti-miRNA strategies

Abstract

As research into micro RNA (miRNA) speciation, complexity, and biological activity progresses, it is becoming clear that a selective subset of all so far characterized miRNAs utilized by human cells and tissues is under the transcriptional control of the pro-inflammatory and immune system-linked transcription factor NF-κB (Sen and Baltimore, 1986; Lukiw and Bazan, 1998; Taganov et al., 2006; Lukiw, 2007, 2012a,b,c; Bazzoni et al., 2009; Ma et al., 2011; Boldin and Baltimore, 2012; Cremer et al., 2012; Li et al., 2012; Lukiw and Alexandrov, 2012; Zhao et al., 2013). The inducible up-regulation of NF-κ B-sensitive miRNAs is by virtue of single, and often multiple, NF-κB-DNA binding recognition sites in the regulatory regions of miRNA-containing genes that drive RNA polymerase II-mediated transcription of pre-miRNA species (Ambros, 2004; Taganov et al., 2006; Baltimore et al., 2008; Cui et al., 2010; Guo et al., 2010; Bredy et al., 2011; Lukiw, 2012a). In neurodegenerative disease research, stress-triggered up-regulation of these NF-κ B-induced miRNAs appear to be playing pathogenic roles in the down-regulation of brain-essential messenger RNAs (mRNA), and the initiation and propagation of pathological gene expression programs that are, for example, characteristic of the Alzheimer's disease (AD) process (Figure 1). NF-κB-mediated up-regulated miRNAs and down-regulated mRNA targets thereby form a highly integrated, pathogenic NF-κ B-miRNA-mRNA signaling network that can explain much of the observed neuropathology in AD, including deficits in phagocytosis (Niemitz, 2012; Zhao et al., 2013), NF-κ B-mediated innate-immune signaling and chronic inflammation (Cui et al., 2010; Heneka et al., 2010; Lukiw and Bazan, 2010; Lukiw et al., 2012), impairments in neurotransmitter packaging and release, neurotrophism and amyloidogenesis (Xu et al., 2009; Lukiw, 2012a,b,c). Under homeostatic conditions, NF-κ B activation involves a coordinated, sequential, and self-limiting sequence of events controlled by positive and negative regulatory mechanisms, however, this does not appear to be the case in early, moderate or especially advanced stages of sporadic AD. In sporadic AD, once initiated, NF-κ B-mediated disruption of homeostatic gene expression can be self-perpetuating due, in part, to the chronic re-activation of NF-κ B activities via up-regulation of interleukin-1β receptor associated kinase-2 (IRAK-2) signaling pathways (Cui et al., 2010). Selective inhibition of the actions of NF-κ B and specific NF-κ B-sensitive miRNAs therefore seems a plausible therapeutic strategy towards neutralizing their combined effects in sporadic AD, and related progressive, age-related neurological diseases with an innate-immune and inflammatory component. Figure 1. (A) In recent experiments human primary neuronal-glial (HNG) cells were treated with an AD-relevant, NF-κ B-inducing cocktail of amyloid beta 42 (Aβ 42) and interleukin-1beta (IL-1β), and inducible miRNAs were analyzed using miRNA arrays (Lukiw, 2012a). Confirmation of miRNA induction and NF-κ B sensitivity was obtained (1) using LED-Northern dot blot and/or RT-PCR analysis; (2) by inhibition of this induction using specific NF-κ B inhibitors CAPE, CAY10512, and PDTC and (3) by bioinformatics analysis of functional NF-κ B binding sites in the promoters of the genes that encode these inducible miRNAs (Lukiw et al., 2008; Cui et al., 2010; Lukiw, 2012a). A small family of 5 miRNAs—miRNA-9, miRNA-34a, miRNA-125b, miRNA-146a, and miRNA-155—appear to be up-regulated in high quality total RNA isolated from short post-mortem AD brains; note that hsa-miR-128 and miR-25 are variably up-regulated; N = 6; (B) These findings in part define a highly interactive network of NF-κ B-sensitive, up-regulated miRNAs in stressed human brain cells and AD hippocampus that can explain much of the observed neuropathology in AD including deficits in phagocytosis (TREM2), innate-immune signaling and chronic inflammation (IkBKG, CFH, IRAK-1, and IRAK-2), impairments in neurotransmitter packaging and release (SYN-2), neurotrophism (15-LOX), and amyloidogenesis (TSPAN12) (see references in text); these up-regulated miRNAs and down-regulated mRNAs form a highly integrated, pathogenic miRNA-mRNA signaling network resulting in gene expression deficits in sporadic AD that may be self-perpetuating due to chronic re-activation of NF-κB stimulation via IRAK-2 pathways (Cui et al., 2010; Lukiw, 2012a,b,c). Inhibition of the NF-κB initiator or individual blocking of the pathogenic induction of these five miRNAs may provide novel therapeutic approaches for the clinical management of AD, however, what NF-κ B or miRNA inhibition strategies, or whether they can be utilized either alone or in combination, remain open to question. Preliminary data has indicated that these approaches may neutralize this chronic, inducible, progressive pathogenic gene expression program to re-establish brain cell homeostasis, and ultimately be of novel pharmacological use in the clinical management of AD. The brain-ubiquitous transcription factor NF-κ B comprises a family of heterodimeric DNA-binding proteins, for example the relatively common p50–p65 complex, that normally reside in a “resting state” in the cytoplasm (Sen and Baltimore, 1986; Lukiw and Bazan, 1998; Mattson and Camandola, 2001; Yamamoto and Gaynor, 2001; Lukiw, 2012a,b). In general, cytoplasmic NF-κ B activation is stimulated via a wide array of physiological stressors including ionizing radiation, viral infection, neurotoxic metals, elevations in reactive oxygen species (ROS), inflammatory cytokines and chemokines, Aβ 42 peptides, hypoxia, and other forms of physiological stress (Baltimore et al., 2008; Pogue et al.,...