Up-regulation of adenosine A 1 receptors in frontal cortex from Pick’s disease cases Jose ´ Luis Albasanz 1 , Agustı ´n Rodrı ´guez, 2 Isidro Ferrer 2,3 and Mairena Martı ´n 1 1 Departamento de Quı ´mica Inorga ´ nica, Orga ´nica y Bioquı ´mica, Facultad de Quı ´micas, Centro Regional de Investigaciones Biome ´ dicas, Universidad de Castilla-La Mancha, Ciudad Real, Spain 2 Departamento de Biologı ´a Celular y Anatomı ´a Patolo ´ gica, Facultad de Medicina, Universidad de Barcelona, campus de Bellvitge, Hospitalet de Llobregat, Spain 3 Instituto de Neuropatologı ´a, Servicio de Anatomı ´a Patolo ´ gica, IDIBELL-Hospital Universitario de Bellvitge, Hospitalet de Llobregat, Spain Keywords: adenylyl cyclase, dementia, human, PiD, post-mortem Abstract The adenosine A 1 receptor (A 1 R)–adenylyl cyclase (AC) pathway was studied in post-mortem human frontal and occipital cortex from Pick’s disease (PiD) cases and age-matched nondemented controls. In frontal cortex, the main brain area affected in PiD, A 1 Rs, determined by radioligand binding, Western blotting and real-time PCR assays, were significantly increased in PiD samples, suggesting up-regulation of this receptor. AC activity was determined in basal and stimulated conditions via stimulatory guanine nucleotide binding proteins (Gs) using GTP, or directly with forskolin. Basal AC activity was reduced in brains from PiD cases. This agrees with the decrease in AC type I (AC I) level detected by Western blotting. However, inhibition of forskolin-stimulated AC activity by a selective A 1 R agonist was significantly increased in brains from PiD. In occipital cortex, adenosine A 1 R numbers were similar in control and PiD cases, and no significant differences were found in A 1 R-mediated AC inhibition. These results show that the adenosine A 1 R–AC transduction pathway is specifically up-regulated and sensitized in frontal cortex brain in PiD. Introduction Adenosine is a nucleoside widely distributed in both the central and the peripheral nervous systems. It is now widely accepted to be the major inhibitory neuromodulator in the central nervous system where, it has been suggested, it may be an endogenous neuroprotective metabolite (Deckert & Gleiter, 1994). Multiple adenosine actions are mediated through specific receptors which belong to the G-protein- coupled receptor family with topography of seven transmembrane domains. Adenosine receptors have been classified into four types: A 1 , A 2A ,A 2B and A 3 receptors. A 1 and A 3 receptors inhibit adenylyl cyclase (AC) through Gi ⁄ o proteins, while A 2A and A 2B receptors stimulate AC through Gs proteins (Ralevic & Burnstock, 1998; Fredholm et al., 2001a). It is generally believed that adenosine is a much more potent agonist at A 1 and A 2A receptors than at A 2B and A 3 receptors (Dunwiddie & Masino, 2001). However, data using human adenosine receptors transfected onto CHO cells indicate that adeno- sine is as potent on human A 3 as on A 1 and A 2A receptors (Schulte & Fredholm, 2000; Fredholm et al., 2001b). Adenosine A 1 receptors (A 1 Rs) are widely expressed in the brain and bind adenosine at physiological concentrations. These receptors are involved in the modulation of physiological actions of the nucleoside, including modulation of neurotransmitter release, mainly glutamate, and in protective effects against ischemic and hypoxic damage (Dunwiddie & Masino, 2001; Reppert et al., 1991). Therefore, most of the neuroprotective effects of adenosine in the adult brain are thought to be mediated by neuronal A 1 Rs (Fredholm et al., 2005). Accordingly, the acute administration of A 1 R agonists affords brain neuroprotection and, conversely, A 1 R antagonists exacerbate brain damage in adult animals (de Mendonca et al., 2000). However, the role of A 2A receptors in neuroprotection is different. Despite their low levels in brain regions other than the striatum, the blocking of A 2A receptor function using antagonists or by deleting the A 2A receptor gene results in a decrease in the extent of neuronal damage in adult animals. However, the mechanisms of this neuroprotection remain unknown (Cunha, 2005). Pick’s disease (PiD) is a frontotemporal dementia characterized by severe atrophy of the frontal and temporal lobes that spares the precentral gyrus and the posterior two-thirds of the superior temporal gyrus. This is accompanied by marked neuron loss, mainly in the upper cortical layers, and the appearance of typical phospho-tau- immunoreactive intraneuronal inclusions called Pick bodies, princi- pally in the dentate gyrus of the hippocampus, CA1 region of the hippocampus, amygdala, septal nuclei and upper layers of the entorhinal cortex and isocortex. These are found together with phospho-tau-immunoreactive thorn-shaped and ramified astrocytes, and tau-positive bodies in oligodendroglia (Dickson, 1998; Markes- bery, 1998). Immunoelectrophoresis and Western blotting of fractions enriched with abnormal filaments have shown two main bands of 55 and 64 kDa, mostly consisting of 3-repeat tau but also of 4-repeat tau in significant amounts (Delacourte et al., 1996; Zhukareva et al., 2002; Arai et al., 2003). Correspondence: Dr Mairena Martı ´n, A ´ rea de Bioquı ´mica, Facultad de Ciencias Quı ´micas, Avenida Camilo Jose ´ Cela, 10, 13071 Ciudad Real, Spain. E-mail: Mairena.Martin@uclm.es Received 29 March 2007, revised 24 October 2007, accepted 28 October 2007 European Journal of Neuroscience, Vol. 26, pp. 3501–3508, 2007 doi:10.1111/j.1460-9568.2007.05965.x ª The Authors (2007). Journal Compilation ª Federation of European Neuroscience Societies and Blackwell Publishing Ltd