The structure of neuronal circuits that subserve cognitive functions in the brain is shaped and refined throughout development and into adulthood. Evidence from human and animal studies suggests that the cellular and synaptic substrates of these circuits are atypical in neuropsychiatric disorders, indicating that altered structural plasticity may be an important part of the disease biology. Advances in genetics have redefined our understanding of neuropsychiatric disorders and have revealed a spectrum of risk factors that impact pathways known to influence structural plasticity. In this Review, we discuss the importance of recent genetic findings on the different mechanisms of structural plasticity and propose that these converge on shared pathways that can be targeted with novel therapeutics.

HighlightsAlthough tractable to drug development, targeting of cAMP signalling has side effects.Selectively targeting EPAC1 and EPAC2 cAMP sensor enzymes may limit some of these off-target effects.EPAC agonists could be used to treat vascular inflammation (EPAC1) or type 2 diabetes (EPAC2).EPAC1 and EPAC2 antagonists could be used to treat heart disease.

Screening of a carefully selected library of 5,195 small molecules identified 34 hit compounds that interact with the regulatory cyclic nucleotide-binding domain (CNB) of the cAMP sensor, EPAC1. Two of these hits (I942 and I178) were selected for their robust and reproducible inhibitory effects within the primary screening assay. Follow-up characterisation by ligand observed nuclear magnetic resonance (NMR) revealed direct interaction of I942 and I178 with EPAC1 and EPAC2-CNBs in vitro. Moreover, in vitro guanine nucleotide exchange factor (GEF) assays revealed that I942 and, to a lesser extent, I178 had partial agonist properties towards EPAC1, leading to activation of EPAC1, in the absence of cAMP, and inhibition of GEF activity in the presence of cAMP. In contrast, there was very little agonist action of I942 towards EPAC2 or protein kinase A (PKA). To our knowledge, this is the first observation of non-cyclic-nucleotide small molecules with agonist properties towards EPAC1. Furthermore, the isoform selective agonist nature of these compounds highlights the potential for the development of small molecule tools that selectively up-regulate EPAC1 activity.

Patient now 19 years old has intellectual disability, developmental delay, absent speech, seizures, hypotonia, severe motor disability (non-ambulatory), short stature, relative macrocephaly. Patient uses gastric tube for feeding and has gastroesophageal reflux. Facial dysmorphisms include short palpebral fissures, large incisors, full eyebrows. Fingers are short and trident-shaped.Brain MRI revealed progressive cerebral and cerebellar volume loss, hypodensity in the left basal ganglia, unchanged and consistent with a lacune infarct (remote). There is a less conspicuous area of hypodensity on the contralateral side. There are hypodense white matter changes along the periventricular white matter and bilateral centrum semiovale.

We have identified a conserved nuclear pore localisation signal (NPLS; amino acids 764–838 of EPAC1) in the catalytic domains of the cAMP-sensors, EPAC1 and EPAC2A. Consequently, EPAC1 is mainly localised to the nuclear pore complex in HEK293T cells where it becomes activated following stimulation with cAMP. In contrast, structural models indicate that the cAMP-binding domain of EPAC2A (CNBD1) blocks access to the conserved NPLS in EPAC2A, reducing its ability to interact with nuclear binding sites. Consequently, a naturally occurring EPAC2 isoform, EPAC2B, which lacks CNBD1 is enriched in nuclear fractions, similar to EPAC1. Structural differences in EPAC isoforms may therefore determine their intracellular location and their response to elevations in intracellular cAMP.

Life-threatening diseases of the cardiovascular system, like atherosclerosis, are exacerbated by unwanted inflammation within the structures of large blood vessels. This inflammation involves increased permeability of the vascular endothelial cells (VECs) that form the lining of blood vessels, leading to exaggerated extravasation of blood components and accumulation of fluid in the extravascular space. This results in tissue dysfunction and increased secretion of chemokines that attract leukocytes and monocytes to the inflamed endothelium. Cyclic AMP is synthesized in VECs in response to endogenous Gs-coupled receptors and is known to limit cytokine action and reduce endothelial hyperpermeability induced by multiple pro-inflammatory stimuli. The mechanisms underlying this anti-inflammatory action of cyclic AMP are now being elucidated and it is becoming clear that the cyclic AMP sensor, exchange protein activated by cyclic AMP (EPAC1), appears to play a key role in suppressing unwanted inflammation. EPAC1 mediates at least three anti-inflammatory pathways in VECs by down-regulating inflammatory signalling through the induction of the suppressors of cytokine signalling 3 (SOCS-3) gene, limiting integrin-dependent vascular permeability and enhancing endothelial barrier function through the stabilization of VE-cadherin junctions. Given that manipulation of cellular cyclic AMP levels currently forms the basis of many effective pharmaceuticals and that EPAC1 is involved in multiple anti-inflammatory protective processes in VECs, does this make EPAC1 an attractive target for the development of activators capable of eliciting a coordinated programme of 'protection' against the development of endothelial dysfunction? Here we discuss whether EPAC1 represents an attractive therapeutic target for limiting endothelial dysfunction associated with cardiovascular diseases like atherosclerosis. LINKED ARTICLESThis article is part of a themed section on Novel cAMP Signalling Paradigms. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.166.issue-2 Abbreviations 8-pCPT-2′OMe-cAMP, -(4-chlorophenylthio)-2′-O-methyladenosine-3′, 5′-cyclic monophosphate; AKAP, A-kinase anchoring protein; EPAC, exchange protein activated by cyclic AMP; MAP; microtubule-associated protein IntroductonInflammation is the normal body response to microbial, chemical, physical injury and aging, and is associated with increased levels of pro-inflammatory cytokines in the circulation, including IL-1, IL-6 and TNF-a (Hobbs and Ernst, 1997). Unresolved chronic pro-inflammatory signalling in vascular endothelial cells (VECs) is a common feature in the progression of cardiovascular diseases (CVDs) including atherosclerosis, hypertension, congestive heart failure, primary pulmonary hypertension and other inflammatory syndromes. Atherosclerosis arises from chronic localized inflammation at coronary and carotid arterial branch points, and remains the principle cause of death in the developed world despite changes in lifestyle and t...

Variants in the ANK3 gene encoding ankyrin-G are associated with neurodevelopmental disorders, including intellectual disability, autism, schizophrenia, and bipolar disorder. However, no upstream regulators of ankyrin-G at synapses are known. Here, we show that ankyrin-G interacts with Usp9X, a neurodevelopmental-disorder-associated deubiquitinase (DUB). Usp9X phosphorylation enhances their interaction, decreases ankyrin-G polyubiquitination, and stabilizes ankyrin-G to maintain dendritic spine development. In forebrain-specific Usp9X knockout mice (Usp9X -/Y ), ankyrin-G as well as multiple ankyrin-repeat domain (ANKRD)-containing proteins are transiently reduced at 2 but recovered at 12 weeks postnatally. However, reduced cortical spine density in knockouts persists into adulthood. Usp9X -/Y mice display increase of ankyrin-G ubiquitination and aggregation and hyperactivity. USP9X mutations in patients with intellectual disability and autism ablate its catalytic activity or ankyrin-G interaction. Our data reveal a DUB-dependent mechanism of ANKRD protein homeostasis, the impairment of which only transiently affects ANKRD protein levels but leads to persistent neuronal, behavioral, and clinical abnormalities.

The cyclic 3′,5′-adenosine monophosphate (cAMP) sensor enzyme, EPAC1, is a candidate drug target in vascular endothelial cells (VECs) due to its ability to attenuate proinflammatory cytokine signalling normally associated with cardiovascular diseases (CVDs), including atherosclerosis. This is through the EPAC1-dependent induction of the suppressor of cytokine signalling gene, SOCS3, which targets inflammatory signalling proteins for ubiquitinylation and destruction by the proteosome. Given this important role for the EPAC1/SOCS3 signalling axis, we have used high throughput screening (HTS) to identify small molecule EPAC1 regulators and have recently isolated the first known non-cyclic nucleotide (NCN) EPAC1 agonist, I942. I942 therefore represents the first in class, isoform selective EPAC1 activator, with the potential to suppress pro-inflammatory cytokine signalling with a reduced risk of side effects associated with general cAMP-elevating agents that activate multiple response pathways. The development of augmented I942 analogues may therefore provide improved research tools to validate EPAC1 as a potential therapeutic target for the treatment of chronic inflammation associated with deadly CVDs.