Loss of stimulatory effect of guanosine triphosphate on [³⁵S]GTPγS binding correlates with Alzheimer's disease neurofibrillary pathology in entorhinal cortex and CA1 hippocampal subfield

Abstract

Heterotrimeric guanosine triphosphate (GTP)-binding proteins (G-proteins) couple many different cell surface receptor types to intracellular effector mechanisms. Uncoupling between receptors and G-proteins and between G-proteins and adenylyl cyclase (AC) and phospholipase C (PLC) has been described for Alzheimer's disease (AD) brain. However, there is little information on whether altered G-protein signaling in AD is just an end-stage phenomenon or is important for the progression of disease pathology. Here we used [(35)S]GTPgammaS autoradiography to study G-protein distribution in sections of entorhinal cortex and hippocampus from 23 cases staged for neurofibrillary changes and amyloid deposits according to Braak and Braak (Acta Neuropathol. [1991] 82:239-259). We also studied the effects of GTP, which has been found to increase [(35)S]GTPgammaS binding in an Mg(2+)-dependent manner. Results show that the ability of GTP (3 microM) to stimulate [(35)S]GTPgammaS binding declined significantly with staging for neurofibrillary changes in the entorhinal cortex (P < 0.05, ANOVA) and CA1 subfield of the hippocampus (P < 0.05, ANOVA). No significant changes were seen for [(35)S]GTPgammaS binding in the absence of GTP. Our results suggest a decrease in G-protein GTP hydrolysis, which correlates with the progression of AD neurofibrillary changes, in the regions most affected by this pathology. These alterations appear to occur prior to stages corresponding to clinical disease and could lead to an impaired regulation of several signaling systems in AD brain.

The [35S]GTPγS binding assay: approaches and applications in pharmacology

“…Canabinoid CB 1 receptor stimulated [ 35 S]GTPgS binding is increased in caudate nucleus, putamen, globus paladus and substantia nigra of post mortem human brain samples from patients affected with Parkinson's disease compared to controls (Lastres-Becker et al, 2001). GTP stimulates [ 35 S]GTPgS binding in post-mortem brain samples but this declines significantly in line with neuropathological changes in Alzheimer's disease (Garcia-Jimenez et al, 2002). In postmortem samples of human heroin addicts the concentration response curve for the mu-opioid agonist DAMGO to stimulate [ 35 S]GTPgS was unchanged compared with controls, but there was a rightward shift in the concentration response curve for the a 2 agonist UK14304, implying a decreased noradrenergic activity induced by chronic opioid exposure (Meana et al, 2000).…”

Quantitative Proteomic Analysis of Mitochondria from Primary Neuron Cultures Treated with Amyloid Beta Peptide

“…Several previous studies show that Aß can stimulate GTP binding (30,39,40) in neural tissues perhaps representing an early step in the mechanism of Aß toxicity (40). Studies of levels of G proteins in AD brain show that the proteins tend to be preserved (41)(42)(43) although function tends to be impaired with progression of the disease (43)(44)(45). Recent studies of Molna´r et al (46) show that Aß [25][26][27][28][29][30][31][32][33][34][35] and Aß 1-40 caused a concentration-dependent increase in GTP binding.…”

In Vitro Imaging Techniques in Neurodegenerative Diseases

“…Moreover, the same group reported a significant decrease in the ability of GTP to stimulate the binding of [ 35 ]SGTPgS to the G-protein. This indicates that there is a decreased response to G-protein stimulation in AD, which thus would interfere with the neuronal signaling [47]. Impaired coupling of muscarinic receptors to G-proteins has also been demonstrated (see below).…”