Pivotal role of PDE10A in the integration of dopamine signals in mice striatal D1 and D2 medium-sized spiny neurones

Abstract

Dopamine in the striatum plays a crucial role in reward processes and action selection. Dopamine signals are transduced by D1 and D2 dopamine receptors which trigger mirror effects through the cAMP/PKA signalling cascade in D1 and D2 medium-sized spiny neurones (MSNs). Phosphodiesterases (PDEs), which determine the profile of cAMP signals, are highly expressed in MSNs, but their respective roles in dopamine signal integration remain poorly understood. We used genetically-encoded FRET biosensors to monitor at the single cell level the functional contribution of PDE2A, PDE4 and PDE10A in the changes of the cAMP/PKA response to transient and continuous dopamine in mouse striatal brain slices. We found that PDE2A, PDE4 and PDE10A operate on the moderate to high cAMP levels elicited by D1 or A2A receptor stimulation. In contrast, only PDE10A is able to reduce cAMP down to baseline in both type of neurones, leading to the dephosphorylation of PKA substrates. PDE10A is therefore critically required for dopamine signal integration in both D1 and D2 MSNs.

Cellular context shapes cyclic nucleotide signaling in neurons through multiple levels of integration

“…This D2/D1 imbalance was consistent with PDE10A inhibitors mimicking the D2 antagonistic action of antipsychotic agents, which had sparked considerable interest in PDE10A as a potential therapeutic target to treat schizophrenia (Kehler and Nielsen, 2011;Schülke and Brandon, 2017;Harada et al, 2020). So far, this hope has not met clinical success (Menniti et al, 2020), possibly because inhibiting such an essential signaling enzyme profoundly destabilizes signal integration in MSNs (Mota et al, 2021). Compared to PDE10A, PDE2A and PDE4 display much lower affinity for cAMP and therefore preferentially regulate high cAMP concentration.…”

“…In addition, PDE10A shows a prominent functional role in the regulation of the cAMP/PKA response in both D1 and D2 MSNs (Mota et al, 2021), as shown by cAMP measurements in striatal brain slices. This work showed that PDE10A is required to degrade cAMP to a sufficiently low level to allow for PKA de-activation: when PDE10A is blocked, dopamine signals can no longer be detected at the level of PKA.…”

“…It is more difficult to determine Rmin in every experiment and instead, the average basal cAMP level in a typical set of experiment should be determined: ACs can be inhibited with dideoxy-adenosine, SQ22536 or MDL-12,330A (Mironov et al, 2009;Börner et al, 2011;Castro et al, 2013;Polito et al, 2015), and the hypothesis is made that such inhibition is sufficient for the biosensor to reach Rmin. In striatal spiny neurons, SQ22536 (200 µM) slightly decreased the basal ratio of the Epac-S H150 biosensor, indicating a basal cAMP concentration in the range of 100 nM (Mota et al, 2021). Knowing Rmin, Rmax, EC50 and the Hill coefficient, the ratio value can be converted into an estimate of cAMP concentration (Russwurm and Koesling, 2018).…”

“…The conversion of ratio to concentration tends to artificially blow up the noise in traces showing calculated cAMP concentrations when the ratio gets close to Rmin and Rmax. Instead of showing traces converted in cAMP concentration on a log scale, which typically enhances these noises, we rather display and perform statistics on ratio values, and add an axis showing the estimated concentration besides the ratio trace (Mota et al, 2021).…”

“…Both dopamine and adenosine are present simultaneously in the striatum, with large variations of dopamine levels depending on the tonic or phasic activity of dopaminergic inputs. In the continuous presence of adenosine, biosensor imaging indeed shows that D2 receptors efficiently switches off cAMP production in spiny neurons, leading to PKA de-activation (Yapo et al, 2017;Mota et al, 2021).…”