Effects of Phosphodiesterase Inhibitor BAY 73-6691 on Expression/Phosphorylation of CREB and Expression of Amyloid Precursor Protein (APP)

Abstract

The presence of amyloid-beta (Aβ) plaques, resulting from abnormal processing of the amyloid precursor protein (APP), is thought to play a prominent role in the development and pathophysiological effects observed in people that suffer from Alzheimer’s disease. Nitric oxide (NO), a messenger found in the Central Nervous System, has been found to be neurologically beneficial at low physiological concentrations (10 pM – 10 nM) and one possible mechanism in the activation of cyclic guanosine monophosphate (cGMP)-dependent protein kinase pathways, specifically an isoform of protein kinase G (PKG) called PKG-I alpha (PKG-Iα). The neuroprotective PKG-Iα pathway has been shown to cause the phosphorylation of cAMP-response-element-binding protein (CREB) which in turn may play a role in increasing the expression of other proteins within neuronal cells. This study explored if a PDE9 inhibitor, BAY 73-6691, would have an increased effect on the activation of the cGMP/PKG-Iα signaling pathway in neuronal cells thereby increasing the expression/phosphorylation of CREB and the expression of APP. Confocal microscopy and Western blotting were utilized to examine NG108-15 cholinergic neuron-like cells, a cell culture model expressing both APP and CREB, as these proteins are potentially related to the pathological progression of Alzheimer’s disease. Experimental qualitative data gathered from confocal microscopy suggests that PKG-Iα and APP/Aβ are located within the cytosol of the NG108-15 cells. Western blot semi-quantitative data indicates that a 3 µM treatment with a PDE9 inhibitor, BAY 73-6691, caused the greatest ratio of phosphorylation of CREB as compared to total CREB, as well as the greatest increase in expression of APP.