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Selective Effects of PDE10A Inhibitors on Striatopallidal Neurons Require Phosphatase Inhibition by DARPP-32(1,2,3).

Polito M, Guiot E, Gangarossa G, Longueville S, Doulazmi M, Valjent E, Hervé D, Girault JA, Paupardin-Tritsch D, Castro LR, Vincent P - eNeuro (2015)

Bottom Line: PDE10A inhibitors have pharmacological and behavioral effects suggesting an antipsychotic profile, but the cellular bases of these effects are unclear.The PKA-dependent effects in D2 MSNs were prevented in brain slices and in vivo by mutation of the PKA-regulated phosphorylation site of 32 kDa dopamine- and cAMP-regulated phosphoprotein (DARPP-32), which is required for protein phosphatase-1 inhibition.These data highlight differences in the integration of the cAMP signal in D1 and D2 MSNs, resulting from stronger inhibition of protein phosphatase-1 by DARPP-32 in D2 MSNs than in D1 MSNs.

View Article: PubMed Central - HTML - PubMed

Affiliation: CNRS, UMR8256 "Biological Adaptation and Ageing", Institut de Biologie Paris-Seine (IBPS) , F-75005 Paris, France ; Université Pierre et Marie Curie (UPMC, Paris 6), Sorbonne Universités , Paris, F-75005, France.

ABSTRACT
Type 10A phosphodiesterase (PDE10A) is highly expressed in the striatum, in striatonigral and striatopallidal medium-sized spiny neurons (MSNs), which express D1 and D2 dopamine receptors, respectively. PDE10A inhibitors have pharmacological and behavioral effects suggesting an antipsychotic profile, but the cellular bases of these effects are unclear. We analyzed the effects of PDE10A inhibition in vivo by immunohistochemistry, and imaged cAMP, cAMP-dependent protein kinase A (PKA), and cGMP signals with biosensors in mouse brain slices. PDE10A inhibition in mouse striatal slices produced a steady-state increase in intracellular cAMP concentration in D1 and D2 MSNs, demonstrating that PDE10A regulates basal cAMP levels. Surprisingly, the PKA-dependent AKAR3 phosphorylation signal was strong in D2 MSNs, whereas D1 MSNs remained unresponsive. This effect was also observed in adult mice in vivo since PDE10A inhibition increased phospho-histone H3 immunoreactivity selectively in D2 MSNs in the dorsomedial striatum. The PKA-dependent effects in D2 MSNs were prevented in brain slices and in vivo by mutation of the PKA-regulated phosphorylation site of 32 kDa dopamine- and cAMP-regulated phosphoprotein (DARPP-32), which is required for protein phosphatase-1 inhibition. These data highlight differences in the integration of the cAMP signal in D1 and D2 MSNs, resulting from stronger inhibition of protein phosphatase-1 by DARPP-32 in D2 MSNs than in D1 MSNs. This study shows that PDE10A inhibitors share with antipsychotic medications the property of activating preferentially PKA-dependent signaling in D2 MSNs.

No MeSH data available.


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Diagram depicting the D1/D2 differential response to PDE10A inhibition. PDE10A inhibition increases cAMP and activates PKA to similar levels in D1 and D2 MSNs. In D2 MSNs, DARPP-32 is phosphorylated and inhibits PP-1: PKA substrates thus remain in the phosphorylated state, both in the cytosol and in the nucleus. In D1 MSNs, DARPP-32 is in a dephosphorylated state: PP-1 is fully active and dephosphorylates PKA substrates. Differences in PP2A/B activities between D1 and D2 MSNs may explain this imbalance.
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Figure 7: Diagram depicting the D1/D2 differential response to PDE10A inhibition. PDE10A inhibition increases cAMP and activates PKA to similar levels in D1 and D2 MSNs. In D2 MSNs, DARPP-32 is phosphorylated and inhibits PP-1: PKA substrates thus remain in the phosphorylated state, both in the cytosol and in the nucleus. In D1 MSNs, DARPP-32 is in a dephosphorylated state: PP-1 is fully active and dephosphorylates PKA substrates. Differences in PP2A/B activities between D1 and D2 MSNs may explain this imbalance.

Mentions: While D1 and D2 MSNs share a number of cellular features, more detailed studies revealed subtle differences (Valjent et al., 2009), such as different excitability profiles (Gertler et al., 2008; Threlfell et al., 2009). Differences were also reported at the level of PKA-dependent phosphorylation of GABAA receptors and DARPP-32, which were higher in D2 MSNs than in D1 MSNs (Janssen et al., 2009; Nishi et al., 2008). Our work reveals a possible basis for these D1/D2 differences, which lies at the level of DARPP-32-mediated PP-1 regulation. In D1 MSNs, the Thr34 of DARPP-32 is in a lower phosphorylation state than in D2 MSNs and, thus, the PP-1 activity reverts PKA target sites to the dephophorylated state (Fig. 7). This hypothesis implies that a powerful mechanism prevents DARPP-32 from remaining phosphorylated on the Thr34 position selectively in D1 MSNs. Thr34 residue is efficiently dephosphorylated by both PP-2A and PP-2B (but not by PP-1; Nishi et al., 1999), and further work is needed to analyze the possible differences in PP2A and PP2B activities between D1 and D2 MSNs. In contrast to tonic cAMP levels induced by PDE10A inhibition, cAMP signals elicited by D1 receptor stimulation lead to a phosphorylation of T34 and inhibition of PP-1 (Bateup et al., 2008), an effect that is also clearly visible on transient responses to dopamine stimulations (Castro et al., 2013). This is consistent with the observation that, in D1 MSNs, PDE10A inhibition only affects PKA-dependent modulation of synaptic transmission when cAMP production is stimulated (Mango et al., 2014). This nonlinearity in D1 MSNs may improve the detection of powerful but brief events such as the phasic dopamine signal associated with reward and novelty (Schultz, 2010), while filtering out smaller fluctuations in basal cAMP level.


Selective Effects of PDE10A Inhibitors on Striatopallidal Neurons Require Phosphatase Inhibition by DARPP-32(1,2,3).

Polito M, Guiot E, Gangarossa G, Longueville S, Doulazmi M, Valjent E, Hervé D, Girault JA, Paupardin-Tritsch D, Castro LR, Vincent P - eNeuro (2015)

Diagram depicting the D1/D2 differential response to PDE10A inhibition. PDE10A inhibition increases cAMP and activates PKA to similar levels in D1 and D2 MSNs. In D2 MSNs, DARPP-32 is phosphorylated and inhibits PP-1: PKA substrates thus remain in the phosphorylated state, both in the cytosol and in the nucleus. In D1 MSNs, DARPP-32 is in a dephosphorylated state: PP-1 is fully active and dephosphorylates PKA substrates. Differences in PP2A/B activities between D1 and D2 MSNs may explain this imbalance.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4596023&req=5

Figure 7: Diagram depicting the D1/D2 differential response to PDE10A inhibition. PDE10A inhibition increases cAMP and activates PKA to similar levels in D1 and D2 MSNs. In D2 MSNs, DARPP-32 is phosphorylated and inhibits PP-1: PKA substrates thus remain in the phosphorylated state, both in the cytosol and in the nucleus. In D1 MSNs, DARPP-32 is in a dephosphorylated state: PP-1 is fully active and dephosphorylates PKA substrates. Differences in PP2A/B activities between D1 and D2 MSNs may explain this imbalance.
Mentions: While D1 and D2 MSNs share a number of cellular features, more detailed studies revealed subtle differences (Valjent et al., 2009), such as different excitability profiles (Gertler et al., 2008; Threlfell et al., 2009). Differences were also reported at the level of PKA-dependent phosphorylation of GABAA receptors and DARPP-32, which were higher in D2 MSNs than in D1 MSNs (Janssen et al., 2009; Nishi et al., 2008). Our work reveals a possible basis for these D1/D2 differences, which lies at the level of DARPP-32-mediated PP-1 regulation. In D1 MSNs, the Thr34 of DARPP-32 is in a lower phosphorylation state than in D2 MSNs and, thus, the PP-1 activity reverts PKA target sites to the dephophorylated state (Fig. 7). This hypothesis implies that a powerful mechanism prevents DARPP-32 from remaining phosphorylated on the Thr34 position selectively in D1 MSNs. Thr34 residue is efficiently dephosphorylated by both PP-2A and PP-2B (but not by PP-1; Nishi et al., 1999), and further work is needed to analyze the possible differences in PP2A and PP2B activities between D1 and D2 MSNs. In contrast to tonic cAMP levels induced by PDE10A inhibition, cAMP signals elicited by D1 receptor stimulation lead to a phosphorylation of T34 and inhibition of PP-1 (Bateup et al., 2008), an effect that is also clearly visible on transient responses to dopamine stimulations (Castro et al., 2013). This is consistent with the observation that, in D1 MSNs, PDE10A inhibition only affects PKA-dependent modulation of synaptic transmission when cAMP production is stimulated (Mango et al., 2014). This nonlinearity in D1 MSNs may improve the detection of powerful but brief events such as the phasic dopamine signal associated with reward and novelty (Schultz, 2010), while filtering out smaller fluctuations in basal cAMP level.

Bottom Line: PDE10A inhibitors have pharmacological and behavioral effects suggesting an antipsychotic profile, but the cellular bases of these effects are unclear.The PKA-dependent effects in D2 MSNs were prevented in brain slices and in vivo by mutation of the PKA-regulated phosphorylation site of 32 kDa dopamine- and cAMP-regulated phosphoprotein (DARPP-32), which is required for protein phosphatase-1 inhibition.These data highlight differences in the integration of the cAMP signal in D1 and D2 MSNs, resulting from stronger inhibition of protein phosphatase-1 by DARPP-32 in D2 MSNs than in D1 MSNs.

View Article: PubMed Central - HTML - PubMed

Affiliation: CNRS, UMR8256 "Biological Adaptation and Ageing", Institut de Biologie Paris-Seine (IBPS) , F-75005 Paris, France ; Université Pierre et Marie Curie (UPMC, Paris 6), Sorbonne Universités , Paris, F-75005, France.

ABSTRACT
Type 10A phosphodiesterase (PDE10A) is highly expressed in the striatum, in striatonigral and striatopallidal medium-sized spiny neurons (MSNs), which express D1 and D2 dopamine receptors, respectively. PDE10A inhibitors have pharmacological and behavioral effects suggesting an antipsychotic profile, but the cellular bases of these effects are unclear. We analyzed the effects of PDE10A inhibition in vivo by immunohistochemistry, and imaged cAMP, cAMP-dependent protein kinase A (PKA), and cGMP signals with biosensors in mouse brain slices. PDE10A inhibition in mouse striatal slices produced a steady-state increase in intracellular cAMP concentration in D1 and D2 MSNs, demonstrating that PDE10A regulates basal cAMP levels. Surprisingly, the PKA-dependent AKAR3 phosphorylation signal was strong in D2 MSNs, whereas D1 MSNs remained unresponsive. This effect was also observed in adult mice in vivo since PDE10A inhibition increased phospho-histone H3 immunoreactivity selectively in D2 MSNs in the dorsomedial striatum. The PKA-dependent effects in D2 MSNs were prevented in brain slices and in vivo by mutation of the PKA-regulated phosphorylation site of 32 kDa dopamine- and cAMP-regulated phosphoprotein (DARPP-32), which is required for protein phosphatase-1 inhibition. These data highlight differences in the integration of the cAMP signal in D1 and D2 MSNs, resulting from stronger inhibition of protein phosphatase-1 by DARPP-32 in D2 MSNs than in D1 MSNs. This study shows that PDE10A inhibitors share with antipsychotic medications the property of activating preferentially PKA-dependent signaling in D2 MSNs.

No MeSH data available.


Related in: MedlinePlus