Biallelic Mutations in PDE10A Lead to Loss of Striatal PDE10A and a Hyperkinetic Movement Disorder with Onset in Infancy.

Deficits in the basal ganglia pathways modulating cortical motor activity underlie both Parkinson disease (PD) and Huntington disease (HD). Phosphodiesterase 10A (PDE10A) is enriched in the striatum, and animal data suggest that it is a key regulator of this circuitry. Here, we report on germline PDE10A mutations in eight individuals from two families affected by a hyperkinetic movement disorder due to homozygous mutations c.320A>G (p.Tyr107Cys) and c.346G>C (p.Ala116Pro). Both mutations lead to a reduction in PDE10A levels in recombinant cellular systems, and critically, positron-emission-tomography (PET) studies with a specific PDE10A ligand confirmed that the p.Tyr107Cys variant also reduced striatal PDE10A levels in one of the affected individuals. A knock-in mouse model carrying the homologous p.Tyr97Cys variant had decreased striatal PDE10A and also displayed motor abnormalities. Striatal preparations from this animal had an impaired capacity to degrade cyclic adenosine monophosphate (cAMP) and a blunted pharmacological response to PDE10A inhibitors. These observations highlight the critical role of PDE10A in motor control across species.

The Stress-Inducible Protein DRR1 Exerts Distinct Effects on Actin Dynamics.

Cytoskeletal dynamics are pivotal to memory, learning, and stress physiology, and thus psychiatric diseases. Downregulated in renal cell carcinoma 1 (DRR1) protein was characterized as the link between stress, actin dynamics, neuronal function, and cognition. To elucidate the underlying molecular mechanisms, we undertook a domain analysis of DRR1 and probed the effects on actin binding, polymerization, and bundling, as well as on actin-dependent cellular processes. METHODS: DRR1 domains were cloned and expressed as recombinant proteins to perform in vitro analysis of actin dynamics (binding, bundling, polymerization, and nucleation). Cellular actin-dependent processes were analyzed in transfected HeLa cells with fluorescence recovery after photobleaching (FRAP) and confocal microscopy. RESULTS: DRR1 features an actin binding site at each terminus, separated by a coiled coil domain. DRR1 enhances actin bundling, the cellular F-actin content, and serum response factor (SRF)-dependent transcription, while it diminishes actin filament elongation, cell spreading, and actin treadmilling. We also provide evidence for a nucleation effect of DRR1. Blocking of pointed end elongation by addition of profilin indicates DRR1 as a novel barbed end capping factor. CONCLUSIONS: DRR1 impacts actin dynamics in several ways with implications for cytoskeletal dynamics in stress physiology and pathophysiology.

Tumor suppressor down-regulated in renal cell carcinoma 1 (DRR1) is a stress-induced actin bundling factor that modulates synaptic efficacy and cognition.

Stress has been identified as a major causal factor for many mental disorders. However, our knowledge about the chain of molecular and cellular events translating stress experience into altered behavior is still rather scant. Here, we have characterized a murine ortholog of the putative tumor suppressor gene DRR1 as a unique stress-induced protein in brain. It binds to actin, promotes bundling and stabilization of actin filaments, and impacts on actin-dependent neurite outgrowth. Endogenous DRR1 localizes to some, but not all, synapses, with preference for the presynaptic region. Hippocampal virus-mediated enhancement of DRR1 expression reduced spine density, diminished the probability of synaptic glutamate release, and altered cognitive performance. DRR1 emerges as a protein to link stress with actin dynamics, which in addition is able to act on synaptic function and cognition.

Current Understanding of PDE10A in the Modulation of Basal Ganglia Circuitry.

The basal ganglia are a forebrain network of interconnected nuclei that are involved in action selection, reward circuits and coordinating movement. PDE10A inhibition has been proposed as a novel way to modulate basal ganglia circuitry and to ameliorate symptoms in Huntington's disease, Parkinson's disease and Schizophrenia. However, despite encouraging results from pre-clinical models, PDE10A inhibitors failed to show efficacy as an antipsychotic in several clinical trials. PDE10A is expressed in the medium spiny neurons of the striatum and works to limit cyclic nucleotide signaling in response to modulatory neurotransmitters like dopamine. In this chapter, we will review the current literature on PDE10A and discuss how inhibition of PDE10A will result in alterations of the basal ganglia circuitry at the biochemical, physiological and behavioral level.

Chemoproteomics demonstrates target engagement and exquisite selectivity of the clinical phosphodiesterase 10A inhibitor MP-10 in its native environment.

Phosphodiesterases (PDEs) regulate the levels of the second messengers cAMP and cGMP and are important drug targets. PDE10A is highly enriched in medium spiny neurons of the striatum and is an attractive drug target for the treatment of basal ganglia diseases like schizophrenia, Parkinson's disease, or Huntington's disease. Here we describe the design, synthesis, and application of a variety of chemical biology probes, based on the first clinically tested PDE10A inhibitor MP-10, which were used to characterize the chemoproteomic profile of the clinical candidate in its native environment. A clickable photoaffinity probe was used to measure target engagement of MP-10 and revealed differences between whole cell and membrane preparations. Moreover, our results illustrate the importance of the linker design in the creation of functional probes. Biotinylated affinity probes allowed identification of drug-interaction partners in rodent and human tissue and quantitative mass spectrometry analysis revealed highly specific binding of MP-10 to PDE10A with virtually no off-target binding. The profiling of PDE10A chemical biology probes described herein illustrates a strategy by which high affinity inhibitors can be converted into probes for determining selectivity and target engagement of drug candidates in complex biological matrices from native sources.

Differential impact of tetratricopeptide repeat proteins on the steroid hormone receptors.

BACKGROUND: Tetratricopeptide repeat (TPR) motif containing co-chaperones of the chaperone Hsp90 are considered control modules that govern activity and specificity of this central folding platform. Steroid receptors are paradigm clients of Hsp90. The influence of some TPR proteins on selected receptors has been described, but a comprehensive analysis of the effects of TPR proteins on all steroid receptors has not been accomplished yet. METHODOLOGY AND PRINCIPAL FINDINGS: We compared the influence of the TPR proteins FK506 binding proteins 51 and 52, protein phosphatase-5, C-terminus of Hsp70 interacting protein, cyclophillin 40, hepatitis-virus-B X-associated protein-2, and tetratricopeptide repeat protein-2 on all six steroid hormone receptors in a homogeneous mammalian cell system. To be able to assess each cofactor's effect on the transcriptional activity of on each steroid receptor we employed transient transfection in a reporter gene assay. In addition, we evaluated the interactions of the TPR proteins with the receptors and components of the Hsp90 chaperone heterocomplex by coimmunoprecipitation. In the functional assays, corticosteroid and progesterone receptors displayed the most sensitive and distinct reaction to the TPR proteins. Androgen receptor's activity was moderately impaired by most cofactors, whereas the Estrogen receptors' activity was impaired by most cofactors only to a minor degree. Second, interaction studies revealed that the strongly receptor-interacting co-chaperones were all among the inhibitory proteins. Intriguingly, the TPR-proteins also differentially co-precipitated the heterochaperone complex components Hsp90, Hsp70, and p23, pointing to differences in their modes of action. CONCLUSION AND SIGNIFICANCE: The results of this comprehensive study provide important insight into chaperoning of diverse client proteins via the combinatorial action of (co)-chaperones. The differential effects of the TPR proteins on steroid receptors bear on all physiological processes related to steroid hormone activity.