HDAC Inhibitors as Epigenetic Regulators

1B) was observed in cells transfected with siRNA directed to Gq, and not in those that received G12or G13siRNA. lowered brain APP protein levels in aged 5XFAD mice. These results provide new insights into potential AD therapeutic strategies. A vital pathological feature of the Alzheimers disease (AD) brain is the presence of senile plaques comprised of A peptides, which are proteolytically-derived from the amyloid precursor protein (APP)1. These plaques are thought to contribute, either directly or indirectly, to the neuronal dysfunction and dementia associated with AD2. Other factors that are believed to contribute to AD pathogenesis include intracellular aggregates of hyperphosphorylated tau protein3, oxidative stress4, and neuroinflammation5. The inflammation observed in AD brain results mainly from increased microglial activation in the vicinity of senile plaques6, 7and a number of glial-derived inflammatory molecules, including cytokines, chemokines and eicosanoids, as well as oxidizing molecules, have been suggested to exacerbate AD neuropathology5, 8. For example , isoprostane F2III (iPF2III), a lipid oxidation product thought to be elevated in AD brain9, 10, can activate the thromboxane A2 (TXA2)-prostanoid (TP) receptor on neurons with a resulting increase of APP mRNA stability that leads to enhanced APP expression and A production11, 12. Similarly, TXA2 itself may also be increased in AD brain, because this eicosanoid is created by activated microglia13. The signaling pathways that underlie the conversion of TP receptor activation into increases of APP expression and A production have not been previously explored, and here we demonstrate the involvement of Gqand conventional PKC isoforms. Importantly, we have discovered that activation of additional eicosanoid receptors, including those that bind prostaglandin E2 (PGE2) and leukotriene D4 (LTD4), also leads to increased APP levels in receptor-transfected cells, as well as in primary rat or mouse neurons. As PGE2, TXA2, and LTD4 can be released from microglia5, 14, with the former shown to be raised in the cerebrospinal fluid of AD patients15, 16, these studies further implicate glial inflammation in the pathogenesis of AD. An assessment of 5XFAD transgenic mice that develop A plaques revealed an age-dependent elevation of PGE2 and TXA2, as well as APP. Importantly, inhibiting eicosanoid synthesis in old 5XFAD mice led to significant diminutions of total APP levels and of – and -secretase processed COOH-terminal fragments of APP. The results of these studies provide important new insights into the regulation of APP in the AD brain. == Results == == TP Receptor Regulation of APP and A Synthesis is Dependent on Gqand Conventional PKC Isoforms == To investigate the intracellular signaling molecules involved in the previously reported TP receptor-induced increases in APP expression and A production that result from APP mRNA stabilization11, 12, we utilized siRNA directed to Gq, G12, and G13, the G-protein -subunits most commonly implicated in TP receptor signal transduction17. QBI293 cells stably expressing both the human TP receptor (hTP) and human being APP695(hTP-hAPP cells) were transfected with control siRNA or siRNA directed Doxycycline HCl to each of the three G-proteins and incubated to get 24 h, Doxycycline HCl followed by 48 h treatment in the presence or absence of the TP receptor agonist, [1S-1, 2(5Z), 3(1E, 3R*), 4)]-7-[-3-(3-hydroxy-4-(4-iodophenoxy)-1-butenyl)-7-oxabicyclo-[2. 2 . 1]heptan-2-yl]-5-heptenoic acidity (IBOP). In agreement with prior studies11, 12, IBOP caused a 2-3-fold increase in APP mRNA and protein in cells receiving control MYL2 siRNA relative to non-IBOP treated cells (Fig. 1). A significant and nearly complete reduction of the IBOP-induced APP mRNA (Fig. 1A) and protein (Fig. 1B) was observed in cells transfected with siRNA directed to Gq, and not in those that received G12or G13siRNA. There was a substantial knockdown of each of the G mRNAs and corresponding proteins under these conditions Doxycycline HCl (Supplementary Table 1). == Physique 1 . Knockdown of Gqinhibits TP receptor-mediated increases in APP and A. == hTP-hAPP cells were transfected with 50 nM of control siRNA or siRNA directed to Gq, G12, or G13and cultured.