Novel 5′ Untranslated Region Directed Blockers of Iron-Regulatory Protein-1 Dependent Amyloid Precursor Protein Translation: Implications for Down Syndrome and Alzheimer's Disease

Abstract

We reported that iron influx drives the translational expression of the neuronal amyloid precursor protein (APP), which has a role in iron efflux. This is via a classic release of repressor interaction of APP mRNA with iron-regulatory protein-1 (IRP1) whereas IRP2 controls the mRNAs encoding the L- and H-subunits of the iron storage protein, ferritin. Here, we identified thirteen potent APP translation blockers that acted selectively towards the uniquely configured iron-responsive element (IRE) RNA stem loop in the 5′ untranslated region (UTR) of APP mRNA. These agents were 10-fold less inhibitory of 5′UTR sequences of the related prion protein (PrP) mRNA. Western blotting confirmed that the ‘ninth’ small molecule in the series selectively reduced neural APP production in SH-SY5Y cells at picomolar concentrations without affecting viability or the expression of α-synuclein and ferritin. APP blocker-9 (JTR-009), a benzimidazole, reduced the production of toxic Aβ in SH-SY5Y neuronal cells to a greater extent than other well tolerated APP 5′UTR-directed translation blockers, including posiphen, that were shown to limit amyloid burden in mouse models of Alzheimer's disease (AD). RNA binding assays demonstrated that JTR-009 operated by preventing IRP1 from binding to the IRE in APP mRNA, while maintaining IRP1 interaction with the H-ferritin IRE RNA stem loop. Thus, JTR-009 constitutively repressed translation driven by APP 5′UTR sequences. Calcein staining showed that JTR-009 did not indirectly change iron uptake in neuronal cells suggesting a direct interaction with the APP 5′UTR. These studies provide key data to develop small molecules that selectively reduce neural APP and Aβ production at 10-fold lower concentrations than related previously characterized translation blockers. Our data evidenced a novel therapeutic strategy of potential impact for people with trisomy of the APP gene on chromosome 21, which is a phenotype long associated with Down syndrome (DS) that can also cause familial Alzheimer's disease.

Decrease in APP and CP mRNA expression supports impairment of iron export in Alzheimer's disease patients

“…Briefly, after translation and assembly to the cytoplasm membrane, APP is cleaved by β-secretase originating sAPP and a β-APP C-terminal fragment. The latter is then cleaved by other secretases originating the Aβ peptides [55,56]. Here, we show that APP mRNA expression is decreased in AD patients PBMCs.…”

The relationship between iron dyshomeostasis and amyloidogenesis in Alzheimer's disease: Two sides of the same coin

“…The depletion of NMDAR is subsequently followed by synaptic loss and cell death via the FYN pathway 121 . The misfolding of PrPc into PrP-scrapie in Cruetzfeldt-Jakob disease leads to iron dyshomeostasis and elevated PrP Sc has been found in the AD brain 122,172 .…”

Iron misregulation and neurodegenerative disease in mouse models that lack iron regulatory proteins

“…Kirsch and his collaborators reported decreased levels of copper and increased expression of amyloid β precursor protein (AβPP) in the hippocampus of Irp2 −/− mice suggesting that IRP2 may have a significant role in Alzheimer’s disease (Mueller et al, 2009). Recently, Rogers and his colleagues found that the amyloid precursor protein (APP) also has an IRE-like RNA stem loop in its 5′ untranslated region, and that IRP1 selectively binds to this APP IRE in human neural cells (Bandyopadhyay et al, 2013, 2014; Cho et al, 2010). High expression of Irp1 in the cortex suggests that Irp1 might play an important role in Alzheimer’s disease.…”