The novel long PDE4A10 cyclic AMP phosphodiesterase shows a pattern of expression within brain that is distinct from the long PDE4A5 and short PDE4A1 isoforms.

In situ hybridisation methods were used to map the distribution of the novel long PDE4A10 isoform in the brain. PDE4A10 distribution was compared to that of the long PDE4A5 isoform and the short PDE4A1 isoform using probes specific for unique sequences within each of these isoforms. Coronal sections of the brain, taken at the level of the olfactory bulb, prefrontal cortex, striatum, thalamus, hippocampus and cerebellum, were analysed. Strongest expression of PDE4A isoforms was found in the olfactory bulb granular layer with high signals also in the piriform cortex, the dentate gyrus and the CA1 and CA2 pyramidal cells. For the two long forms, level general staining was noted throughout the striatum, thalamus and hippocampus but no signal was evident in the cerebellum. The long PDE4A10 and PDE4A5 isoforms localised to essentially the same regions throughout the brain, although PDE4A10 was uniquely expressed in the major island of Calleja. A signal for the short PDE4A1 isoform was found in regions in which the two long isoforms were both expressed, with the exception of the medial nucleus of the amygdala where weak signals for PDE4A5 and PDE4A10 were detected but PDE4A1 was absent. Uniquely, strong signals for PDE4A1 were detected in the glomerular layer of the olfactory bulb, the CA3 pyramidal cell region and the cerebellum; areas where signals for the two long forms were not evident. PDE4A transcripts for both PDE4A5 and PDE4A10 were not apparent in the brain stem and those for PDE4A1 were low. PDE4A isoforms are present in several key areas of the brain and therefore present valid targets for therapeutic interventions. Whilst the two long PDE4A isoforms show a remarkably similar distribution, in at least three regions there is clear segregation between their pattern of expression and that of the PDE4A1 short form. This identifies differential regulation of the expression of PDE4A long and short isoforms. We suggest that specific PDE4A isoforms may have distinct functional roles in the brain, indicating that PDE4A isoform-selective inhibitors may have specific therapeutic and pharmacologic properties.