Modulation of dopamine D1 receptors via histamine H3 receptors is a novel therapeutic target for Huntington's disease

Early Huntington's disease (HD) include over-activation of dopamine D₁ receptors (D₁R), producing an imbalance in dopaminergic neurotransmission and cell death. To reduce D₁R over-activation, we present a strategy based on targeting complexes of D₁R and histamine H₃ receptors (H₃R). Using an HD mouse striatal cell model and HD mouse organotypic brain slices we found that D₁R-induced cell death signaling and neuronal degeneration, are mitigated by an H₃R antagonist. We demonstrate that the D₁R-H₃R heteromer is expressed in HD mice at early but not late stages of HD, correlating with HD progression. In accordance, we found this target expressed in human control subjects and low-grade HD patients. Finally, treatment of HD mice with an H₃R antagonist prevented cognitive and motor learning deficits and the loss of heteromer expression. Taken together, our results indicate that D₁R - H₃R heteromers play a pivotal role in dopamine signaling and represent novel targets for treating HD.

Astrocytic BDNF and TrkB regulate severity and neuronal activity in mouse models of temporal lobe epilepsy

Astrocytes have emerged as crucial regulators of neuronal network activity, synapse formation, and underlying behavioral and cognitive processes. Despite some pathways have been identified, the communication between astrocytes and neurons remains to be completely elucidated. Unraveling this communication is crucial to design potential treatments for neurological disorders like temporal lobe epilepsy (TLE). The BDNF and TrkB molecules have emerged as very promising therapeutic targets. However, their modulation can be accompanied by several off-target effects such as excitotoxicity in case of uncontrolled upregulation or dementia, amnesia, and other memory disorders in case of downregulation. Here, we show that BDNF and TrkB from astrocytes modulate neuronal dysfunction in TLE models. First, conditional overexpression of BDNF from astrocytes worsened the phenotype in the lithium-pilocarpine mouse model. Our evidences pointed out to the astrocytic pro-BDNF isoform as a major player of this altered phenotype. Conversely, specific genetic deletion of BDNF in astrocytes prevented the increase in the number of firing neurons and the global firing rate in an in vitro model of TLE. Regarding to the TrkB, we generated mice with a genetic deletion of TrkB specifically in hippocampal neurons or astrocytes. Interestingly, both lines displayed neuroprotection in the lithium-pilocarpine model but only the mice with genetic deletion of TrkB in astrocytes showed significantly preserved spatial learning skills. These data identify the astrocytic BDNF and TrkB molecules as promising therapeutic targets for the treatment of TLE.

Deficits in coordinated neuronal activity and network topology are striatal hallmarks in Huntington's disease

Background

Network alterations underlying neurodegenerative diseases often precede symptoms and functional deficits. Thus, their early identification is central for improved prognosis. In Huntington’s disease (HD), the cortico-striatal networks, involved in motor function processing, are the most compromised neural substrate. However, whether the network alterations are intrinsic of the striatum or the cortex is not fully understood.

Results

In order to identify early HD neural deficits, we characterized neuronal ensemble calcium activity and network topology of HD striatal and cortical cultures. We used large-scale calcium imaging combined with activity-based network inference analysis. We extracted collective activity events and inferred the topology of the neuronal network in cortical and striatal primary cultures from wild-type and R6/1 mouse model of HD. Striatal, but not cortical, HD networks displayed lower activity and a lessened ability to integrate information. GABA_A receptor blockade in healthy and HD striatal cultures generated similar coordinated ensemble activity and network topology, highlighting that the excitatory component of striatal system is spared in HD. Conversely, NMDA receptor activation increased individual neuronal activity while coordinated activity became highly variable and undefined. Interestingly, by boosting NMDA activity, we rectified striatal HD network alterations.

Conclusions

Overall, our integrative approach highlights striatal defective network integration capacity as a major contributor of basal ganglia dysfunction in HD and suggests that increased excitatory drive may serve as a potential intervention. In addition, our work provides a valuable tool to evaluate in vitro network recovery after treatment intervention in basal ganglia disorders.

Lack of Helios During Neural Development Induces Adult Schizophrenia-Like Behaviors Associated With Aberrant Levels of the TRIF-Recruiter Protein WDFY1

The role of the WDFY1 protein has been studied as a TLR3/4 scaffold/recruiting protein in the immune system and in different oncogenic conditions. However, its function in brain remains poorly understood. We have found that in mice devoid of Helios (He^-/- mice), a transcription factor specifically expressed during the development of the immune cells and the central nervous system, there is a permanent and sustained increase of Wdfy1 gene expression in the striatum and hippocampus. Interestingly, we observed that WDFY1 protein levels were also increased in the hippocampus and dorsolateral prefrontal cortex of schizophrenic patients, but not in the hippocampus of Alzheimer's disease patients with an associated psychotic disorder. Accordingly, young He^-/- mice displayed several schizophrenic-like behaviors related to dysfunctions in the striatum and hippocampus. These changes were associated with an increase in spine density in medium spiny neurons (MSNs) and with a decrease in the number and size of PSD-95-positive clusters in the stratum radiatum of the CA1. Moreover, these alterations in structural synaptic plasticity were associated with a strong reduction of neuronal NF-κB in the pyramidal layer of the CA1 in He^-/- mice. Altogether, our data indicate that alterations involving the molecular axis Helios-WDFY1 in neurons during the development of core brain regions could be relevant for the pathophysiology of neuropsychiatric disorders such as schizophrenia.

Meridianins and Lignarenone B as Potential GSK3β Inhibitors and Inductors of Structural Neuronal Plasticity

Glycogen Synthase Kinase 3 (GSK3) is an essential protein, with a relevant role in many diseases such as diabetes, cancer and neurodegenerative disorders. Particularly, the isoform GSK3β is related to pathologies such as Alzheimer's disease (AD). This enzyme constitutes a very interesting target for the discovery and/or design of new therapeutic agents against AD due to its relation to the hyperphosphorylation of the microtubule-associated protein tau (MAPT), and therefore, its contribution to neurofibrillary tangles (NFT) formation. An in silico target profiling study identified two marine molecular families, the indole alkaloids meridianins from the tunicate genus Aplidium, and lignarenones, the secondary metabolites of the shelled cephalaspidean mollusc Scaphander lignarius, as possible GSK3β inhibitors. The analysis of the surface of GSK3β, aimed to find possible binding regions, and the subsequent in silico binding studies revealed that both marine molecular families can act over the ATP and/or substrate binding regions. The predicted inhibitory potential of the molecules from these two chemical families was experimentally validated in vitro by showing a ~50% of increased Ser9 phosphorylation levels of the GSK3β protein. Furthermore, we determined that molecules from both molecular families potentiate structural neuronal plasticity in vitro. These results allow us to suggest that meridianins and lignarenone B could be used as possible therapeutic candidates for the treatment of GSK3β involved pathologies, such as AD.

Cyclin-Dependent Kinase 5 Dysfunction Contributes to Depressive-like Behaviors in Huntington's Disease by Altering the DARPP-32 Phosphorylation Status in the Nucleus Accumbens

BACKGROUND

Depression is the most common psychiatric condition in Huntington's disease (HD), with rates more than twice those found in the general population. At the present time, there is no established molecular evidence to use as a basis for depression treatment in HD. Indeed, in some patients, classic antidepressant drugs exacerbate chorea or anxiety. Cyclin-dependent kinase 5 (Cdk5) has been involved in processes associated with anxiety and depression. This study evaluated the involvement of Cdk5 in the development and prevalence of depressive-like behaviors in HD and aimed to validate Cdk5 as a target for depression treatment.

METHODS

We evaluated the impact of pharmacological inhibition of Cdk5 in depressive-like and anxiety-like behaviors in Hdh^+/Q111 knock-in mutant mice by using a battery of behavioral tests. Biochemical and morphological studies were performed to define the molecular mechanisms acting downstream of Cdk5 activation. A double huntingtin/DARPP-32 (dopamine- and cAMP-regulated phosphoprotein 32) knock-in mutant mouse was generated to analyze the role of DARPP-32 in HD depression.

RESULTS

We found that Hdh^+/Q111 mutant mice exhibited depressive-like, but not anxiety-like, behaviors starting at 2 months of age. Cdk5 inhibition by roscovitine infusion prevented depressive-like behavior and reduced DARPP-32 phosphorylation at Thr75 in the nucleus accumbens. Hdh^+/Q111 mice heterozygous for DARPP-32 Thr75Ala point mutation were resistant to depressive-like behaviors. We identified β-adducin phosphorylation as a Cdk5 downstream mechanism potentially mediating structural spine plasticity changes in the nucleus accumbens and depressive-like behavior.

CONCLUSIONS

These results point to Cdk5 in the nucleus accumbens as a critical contributor to depressive-like behaviors in HD mice by altering DARPP-32/β-adducin signaling and disrupting the dendritic spine cytoskeleton.

Early Downregulation of p75NTR by Genetic and Pharmacological Approaches Delays the Onset of Motor Deficits and Striatal Dysfunction in Huntington's Disease Mice

Deficits in striatal brain-derived neurotrophic factor (BDNF) delivery and/or BDNF/tropomyosin receptor kinase B (TrkB) signaling may contribute to neurotrophic support reduction and selective early degeneration of striatal medium spiny neurons in Huntington's disease (HD). Furthermore, we and others have demonstrated that TrkB/p75NTR imbalance in vitro increases the vulnerability of striatal neurons to excitotoxic insults and induces corticostriatal synaptic alterations. We have now expanded these studies by analyzing the consequences of BDNF/TrkB/p75NTR imbalance in the onset of motor behavior and striatal neuropathology in HD mice. Our findings demonstrate for the first time that the onset of motor coordination abnormalities, in a full-length knock-in HD mouse model (KI), correlates with the reduction of BDNF and TrkB levels, along with an increase in p75NTR expression. Genetic normalization of p75NTR expression in KI mutant mice delayed the onset of motor deficits and striatal neuropathology, as shown by restored levels of striatal-enriched proteins and dendritic spine density and reduced huntingtin aggregation. We found that the BDNF/TrkB/p75NTR imbalance led to abnormal BDNF signaling, manifested as a diminished activation of TrkB-phospholipase C-gamma pathway but upregulation of c-Jun kinase pathway. Moreover, we confirmed the contribution of the proper balance of BDNF/TrkB/p75NTR on HD pathology by a pharmacological approach using fingolimod. We observed that chronic infusion of fingolimod normalizes p75NTR levels, which is likely to improve motor coordination and striatal neuropathology in HD transgenic mice. We conclude that downregulation of p75NTR expression can delay disease progression suggesting that therapeutic approaches aimed to restore the balance between BDNF, TrkB, and p75NTR could be promising to prevent motor deficits in HD.

Social Memory and Social Patterns Alterations in the Absence of STriatal-Enriched Protein Tyrosine Phosphatase

STriatal-Enriched protein tyrosine Phosphatase (STEP) is a neural-specific protein that opposes the development of synaptic strengthening and whose levels are altered in several neurodegenerative and psychiatric disorders. Since STEP is expressed in brain regions implicated in social behavior, namely the striatum, the CA2 region of the hippocampus, cortex and amygdala, here we investigated whether social memory and social patterns were altered in STEP knockout (KO) mice. Our data robustly demonstrated that STEP KO mice presented specific social memory impairment as indicated by the three-chamber sociability test, the social discrimination test, the 11-trial habituation/dishabituation social recognition test, and the novel object recognition test (NORT). This affectation was not related to deficiencies in the detection of social olfactory cues, altered sociability or anxiety levels. However, STEP KO mice showed lower exploratory activity, reduced interaction time with an intruder, less dominant behavior and higher immobility time in the tail suspension test than controls, suggesting alterations in motivation. Moreover, the extracellular levels of dopamine (DA), but not serotonin (5-HT), were increased in the dorsal striatum of STEP KO mice. Overall, our results indicate that STEP deficiency disrupts social memory and other social behaviors as well as DA homeostasis in the dorsal striatum.

Pharmacogenetic modulation of STEP improves motor and cognitive function in a mouse model of Huntington's disease

Huntington's disease (HD) is a hereditary neurodegenerative disorder caused by an expansion of a CAG repeat in the huntingtin (htt) gene, which results in an aberrant form of the protein (mhtt). This leads to motor and cognitive deficits associated with corticostriatal and hippocampal alterations. The levels of STriatal-Enriched protein tyrosine Phosphatase (STEP), a neural-specific tyrosine phosphatase that opposes the development of synaptic strengthening, are decreased in the striatum of HD patients and also in R6/1 mice, thereby contributing to the resistance to excitotoxicity described in this HD mouse model. Here, we aimed to analyze whether STEP inactivation plays a role in the pathophysiology of HD by investigating its effect on motor and cognitive impairment in the R6/1 mouse model of HD. We found that genetic deletion of STEP delayed the onset of motor dysfunction and prevented the appearance of cognitive deficits in R6/1 mice. This phenotype was accompanied by an increase in pERK1/2 levels, a delay in the decrease of striatal DARPP-32 levels and a reduction in the size of mhtt aggregates, both in the striatum and CA1 hippocampal region. We also found that acute pharmacological inhibition of STEP with TC-2153 improved cognitive function in R6/1 mice. In conclusion, our results show that deletion of STEP has a beneficial effect on motor coordination and cognition in a mouse model of HD suggesting that STEP inhibition could be a good therapeutic strategy in HD patients.

Proteolytic Degradation of Hippocampal STEP61 in LTP and Learning

Striatal-enriched protein tyrosine phosphatase (STEP) modulates key signaling molecules involved in synaptic plasticity and neuronal function. It is postulated that STEP opposes the development of long-term potentiation (LTP) and that it exerts a restraint on long-term memory (LTM). Here, we examined whether STEP₆₁ levels are regulated during hippocampal LTP and after training in hippocampal-dependent tasks. We found that after inducing LTP by high frequency stimulation or theta-burst stimulation STEP₆₁ levels were significantly reduced, with a concomitant increase of STEP₃₃ levels, a product of calpain cleavage. Importantly, inhibition of STEP with TC-2153 improved LTP in hippocampal slices. Moreover, we observed that after training in the passive avoidance and the T-maze spontaneous alternation task, hippocampal STEP₆₁ levels were significantly reduced, but STEP₃₃ levels were unchanged. Yet, hippocampal BDNF content and TrkB levels were increased in trained mice, and it is known that BDNF promotes STEP degradation through the proteasome. Accordingly, hippocampal pTrkB^Tyr816, pPLCγ^Tyr783, and protein ubiquitination levels were increased in T-SAT trained mice. Remarkably, injection of the TrkB antagonist ANA-12 (2 mg/Kg, but not 0.5 mg/Kg) elicited LTM deficits and promoted STEP₆₁ accumulation in the hippocampus. Also, STEP knockout mice outperformed wild-type animals in an age- and test-dependent manner. Summarizing, STEP₆₁ undergoes proteolytic degradation in conditions leading to synaptic strengthening and memory formation, thus highlighting its role as a molecular constrain, which is removed to enable the activation of pathways important for plasticity processes.

Human alpha 1-antitrypsin protects neurons and glial cells against oxygen and glucose deprivation through inhibition of interleukins expression

BACKGROUND

Death due to cerebral stroke afflicts a large number of neuronal populations, including glial cells depending on the brain region affected. Drugs with a wide cellular range of protection are needed to develop effective therapies for stroke. Human alpha 1-antitrypsin (hAAT) is a serine proteinase inhibitor with potent anti-inflammatory, anti-apoptotic and immunoregulatory activities. This study aimed to test whether hAAT can protect different kind of neurons and glial cells after the oxygen and glucose deprivation (OGD).

METHODS

Addition of hAAT to mouse neuronal cortical, hippocampal and striatal cultures, as well as glial cultures, was performed 30 min after OGD induction and cell viability was assessed 24 h later. The expression of different apoptotic markers and several inflammatory parameters were assessed by immunoblotting and RT-PCR.

RESULTS

hAAT had a concentration-dependent survival effect in all neuronal cultures exposed to OGD, with a maximal effect at 1-2 mg/mL. The addition of hAAT at 1 mg/mL reduced the OGD-mediated necrotic and apoptotic death in all neuronal cultures. This neuroprotective activity of hAAT was associated with a decrease of cleaved caspase-3 and an increase of MAP2 levels. It was also associated with a reduction of pro-inflammatory cytokines protein levels and expression, increase of IL-10 protein levels and decrease of nuclear localization of nuclear factor-kappaB. Similar to neurons, addition of hAAT protected astrocytes and oligodendrocytes against OGD-induced cell death.

CONCLUSIONS

Human AAT protects neuronal and glial cells against OGD through interaction with cytokines.

GENERAL SIGNIFICANCE

Human AAT could be a good therapeutic neuroprotective candidate to treat ischemic stroke.

Huntington's disease: novel therapeutic perspectives hanging in the balance

INTRODUCTION

Huntington's disease (HD), an autosomal dominant neurodegenerative disorder caused by an expansion of CAG repeats in the huntingtin gene, has long been characterized by the presence of motor symptoms due to the loss of striatal projection neurons. Cognitive dysfunction and neuropsychiatric symptoms are also present and they occur in the absence of cell death in most mouse models, pointing to neuronal dysfunction and abnormal synaptic plasticity as causative mechanisms. Areas covered: Here, we focus on those common mechanisms altered by the presence of mutant huntingtin affecting corticostriatal and hippocampal function as therapeutic targets that could prove beneficial to ameliorate both cognitive and motor function in HD. Specifically, we discuss the importance of reestablishing the balance in (1) synaptic/extrasynaptic N-methyl-D-aspartate receptor signaling, (2) mitochondrial dynamics/trafficking, (3) TrkB/p75^NTR signaling, and (4) transcriptional activity. Expert opinion: Mutant huntingtin has a broad impact on multiple cellular processes, which makes it very challenging to design a curative therapeutic strategy. As we point out here, novel therapeutic interventions should look for multi-purpose drugs targeting common and early affected processes leading to corticostriatal and hippocampal dysfunction that additionally operate in a feedforward vicious cycle downstream the activation of extrasynaptic N-methyl-D-aspartate receptor.

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Enhances Hippocampal Synaptic Plasticity and Improves Memory Performance in Huntington's Disease

Deficits in hippocampal synaptic plasticity result in cognitive impairment in Huntington's disease (HD). Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that exerts neuroprotective actions, mainly through the PAC1 receptor. However, the role of PACAP in cognition is poorly understood, and no data exists in the context of Huntington's disease (HD). Here, we investigated the ability of PACAP receptor stimulation to enhance memory development in HD. First, we observed a hippocampal decline of all three PACAP receptor expressions, i.e., PAC1, VPAC1, and VPAC2, in two different HD mouse models, R6/1 and HdhQ7/Q111, from the onset of cognitive dysfunction. In hippocampal post-mortem human samples, we found a specific decrease of PAC1, without changes in VPAC1 and VPAC2 receptors. To determine whether activation of PACAP receptors could contribute to improve memory performance, we conducted daily intranasal administration of PACAP38 to R6/1 mice at the onset of cognitive impairment for seven days. We found that PACAP treatment rescued PAC1 level in R6/1 mice, promoted expression of the hippocampal brain-derived neurotrophic factor, and reduced the formation of mutant huntingtin aggregates. Furthermore, PACAP administration counteracted R6/1 mice memory deficits as analyzed by the novel object recognition test and the T-maze spontaneous alternation task. Importantly, the effect of PACAP on cognitive performance was associated with an increase of VGlut-1 and PSD95 immunolabeling in hippocampus of R6/1 mice. Taken together, these results suggest that PACAP, acting through stimulation of PAC1 receptor, may have a therapeutic potential to counteract cognitive deficits induced in HD.

7,8-dihydroxyflavone ameliorates cognitive and motor deficits in a Huntington's disease mouse model through specific activation of the PLCγ1 pathway

Huntington's disease (HD) is a fatal neurodegenerative disease with motor, cognitive and psychiatric impairment. Dysfunctions in HD models have been related to reduced levels of striatal brain-derived neurotrophic factor (BDNF) and imbalance between its receptors TrkB and p75(NTR). Thus, molecules with activity on the BDNF/TrkB/p75 system can have therapeutic potential. 7,8-Dihydroxyflavone (7,8-DHF) was described as a TrkB agonist in several models of neuro-degenerative diseases, however, its TrkB activation profile needs further investigation due to its pleiotropic properties and divergence from BDNF effect. To investigate this, we used in vitro and in vivo models of HD to dissect TrkB activation upon 7,8-DHF treatment. 7,8-DHF treatment in primary cultures showed phosphorylation of TrkBY816 but not TrkBY515 with activation of the PLCγ1 pathway leading to morphological and functional improvements. Chronic administration of 7,8-DHF delayed motor deficits in R6/1 mice and reversed deficits on the Novel Object Recognition Test (NORT) at 17 weeks. Morphological and biochemical analyses revealed improved striatal levels of enkephalin, and prevention of striatal volume loss. We found a TrkBY816 but not TrkBY515 phosphorylation recovery in striatum concordant with in vitro results. Additionally, 7,8-DHF normalized striatal levels of induced and neuronal nitric oxide synthase (iNOS and nNOS, respectively) and ameliorated the imbalance of p75/TrkB. Our results provide new insights into the mechanism of action of 7,8-DHF suggesting that its effect through the TrkB receptor in striatum is via selective phosphorylation of its Y816 residue and activation of PLCγ1 pathway, but pleiotropic effects of the drug also contribute to its therapeutic potential.

Helios expression coordinates the development of a subset of striatopallidal medium spiny neurons

Here, we unravel the mechanism of action of the Ikaros family zinc finger protein Helios (He) during the development of striatal medium spiny neurons (MSNs). He regulates the second wave of striatal neurogenesis involved in the generation of striatopallidal neurons, which express dopamine 2 receptor and enkephalin. To exert this effect, He is expressed in neural progenitor cells (NPCs) keeping them in the G₁/G₀ phase of the cell cycle. Thus, a lack of He results in an increase of S-phase entry and S-phase length of NPCs, which in turn impairs striatal neurogenesis and produces an accumulation of the number of cycling NPCs in the germinal zone (GZ), which end up dying at postnatal stages. Therefore, He^−/− mice show a reduction in the number of dorso-medial striatal MSNs in the adult that produces deficits in motor skills acquisition. In addition, overexpression of He in NPCs induces misexpression of DARPP-32 when transplanted in mouse striatum. These findings demonstrate that He is involved in the correct development of a subset of striatopallidal MSNs and reveal new cellular mechanisms for neuronal development.

Summary: The transcription factor Helios regulates G1-S transition to promote neuronal differentiation of a striatopallidal neuronal subpopulation involved in motor skill acquisition.

Cognitive Dysfunction in Huntington's Disease: Humans, Mouse Models and Molecular Mechanisms

Huntington's disease (HD) is an autosomal dominant progressive neurodegenerative disorder due to an expanded CAG/polyglutamine repeat in the coding region of the huntingtin (htt) gene that causes the preferential degeneration of striatal neurons. Although HD is classically considered a motor disorder, cognitive decline manifests even before the appearance of motor symptoms, and reflects the impairment of additional neuronal populations, such as cortical and hippocampal neurons, in the presence of mutant htt (mhtt). Studies on cognitive dysfunction in HD patients have focused on the cortico-striatal pathway. Here we will describe that HD patients and mouse models share many cognitive defects. Alterations in hippocampal synaptic plasticity and function found in HD mouse models highlight that changes in the functioning of the hippocampal formation contribute to cognitive dysfunction in humans. The similarity between the cognitive dysfunction in HD patients and mouse models has helped to understand better how cognitive dysfunction takes place. Moreover, it validates the use of HD mice to study the molecular mechanisms involved in HD cognitive decline. Several studies in HD mouse models indicate that altered synaptic composition/function, deficient neurotrophic support, kinase/phosphatase imbalance, and transcription dysregulation play an important role in cognitive impairment. This knowledge opens the possibility of identifying relevant therapeutic targets to fight cognitive decline in HD. The finding that in HD many mechanisms are similarly altered in hippocampal and striatal neurons suggests the possibility of a common therapeutic strategy to ameliorate both cognitive and motor dysfunction.

Aberrant epigenome in iPSC-derived dopaminergic neurons from Parkinson's disease patients

The epigenomic landscape of Parkinson's disease (PD) remains unknown. We performed a genomewide DNA methylation and a transcriptome studies in induced pluripotent stem cell (iPSC)-derived dopaminergic neurons (DAn) generated by cell reprogramming of somatic skin cells from patients with monogenic LRRK2-associated PD (L2PD) or sporadic PD (sPD), and healthy subjects. We observed extensive DNA methylation changes in PD DAn, and of RNA expression, which were common in L2PD and sPD. No significant methylation differences were present in parental skin cells, undifferentiated iPSCs nor iPSC-derived neural cultures not-enriched-in-DAn. These findings suggest the presence of molecular defects in PD somatic cells which manifest only upon differentiation into the DAn cells targeted in PD. The methylation profile from PD DAn, but not from controls, resembled that of neural cultures not-enriched-in-DAn indicating a failure to fully acquire the epigenetic identity own to healthy DAn in PD. The PD-associated hypermethylation was prominent in gene regulatory regions such as enhancers and was related to the RNA and/or protein downregulation of a network of transcription factors relevant to PD (FOXA1, NR3C1, HNF4A, and FOSL2). Using a patient-specific iPSC-based DAn model, our study provides the first evidence that epigenetic deregulation is associated with monogenic and sporadic PD.

A role for Kalirin-7 in corticostriatal synaptic dysfunction in Huntington's disease

Cognitive dysfunction is an early clinical hallmark of Huntington's disease (HD) preceding the appearance of motor symptoms by several years. Neuronal dysfunction and altered corticostriatal connectivity have been postulated to be fundamental to explain these early disturbances. However, no treatments to attenuate cognitive changes have been successful: the reason may rely on the idea that the temporal sequence of pathological changes is as critical as the changes per se when new therapies are in development. To this aim, it becomes critical to use HD mouse models in which cognitive impairments appear prior to motor symptoms. In this study, we demonstrate procedural memory and motor learning deficits in two different HD mice and at ages preceding motor disturbances. These impairments are associated with altered corticostriatal long-term potentiation (LTP) and specific reduction of dendritic spine density and postsynaptic density (PSD)-95 and spinophilin-positive clusters in the cortex of HD mice. As a potential mechanism, we described an early decrease of Kalirin-7 (Kal7), a guanine-nucleotide exchange factor for Rho-like small GTPases critical to maintain excitatory synapse, in the cortex of HD mice. Supporting a role for Kal7 in HD synaptic deficits, exogenous expression of Kal7 restores the reduction of excitatory synapses in HD cortical cultures. Altogether, our results suggest that cortical dysfunction precedes striatal disturbances in HD and underlie early corticostriatal LTP and cognitive defects. Moreover, we identified diminished Kal7 as a key contributor to HD cortical alterations, placing Kal7 as a molecular target for future therapies aimed to restore corticostriatal function in HD.

Quantitative high-throughput gene expression profiling of human striatal development to screen stem cell-derived medium spiny neurons

A systematic characterization of the spatio-temporal gene expression during human neurodevelopment is essential to understand brain function in both physiological and pathological conditions. In recent years, stem cell technology has provided an in vitro tool to recapitulate human development, permitting also the generation of human models for many diseases. The correct differentiation of human pluripotent stem cell (hPSC) into specific cell types should be evaluated by comparison with specific cells/tissue profiles from the equivalent adult in vivo organ. Here, we define by a quantitative high-throughput gene expression analysis the subset of specific genes of the whole ganglionic eminence (WGE) and adult human striatum. Our results demonstrate that not only the number of specific genes is crucial but also their relative expression levels between brain areas. We next used these gene profiles to characterize the differentiation of hPSCs. Our findings demonstrate a temporal progression of gene expression during striatal differentiation of hPSCs from a WGE toward an adult striatum identity. Present results establish a gene expression profile to qualitatively and quantitatively evaluate the telencephalic hPSC-derived progenitors eventually used for transplantation and mature striatal neurons for disease modeling and drug-screening.

Prostaglandin E2 EP2 activation reduces memory decline in R6/1 mouse model of Huntington's disease by the induction of BDNF-dependent synaptic plasticity

Huntington's disease (HD) patients and mouse models show learning and memory impairment even before the onset of motor symptoms. Deficits in hippocampal synaptic plasticity have been involved in the HD memory impairment. Several studies show that prostaglandin E2 (PGE2) EP2 receptor stimulates synaptic plasticity and memory formation. However, this role was not explored in neurodegenerative diseases. Here, we investigated the capacity of PGE2 EP2 receptor to promote synaptic plasticity and memory improvements in a model of HD, the R6/1 mice, by administration of the agonist misoprostol. We found that misoprostol increases dendritic branching in cultured hippocampal neurons in a brain-derived neurotrophic factor (BDNF)-dependent manner. Then, we implanted an osmotic mini-pump system to chronically administrate misoprostol to R6/1 mice from 14 to 18weeks of age. We observed that misoprostol treatment ameliorates the R6/1 long-term memory deficits as analyzed by the T-maze spontaneous alternation task and the novel object recognition test. Importantly, administration of misoprostol promoted the expression of hippocampal BDNF. Moreover, the treatment with misoprostol in R6/1 mice blocked the reduction in the number of PSD-95 and VGluT-1 positive particles observed in hippocampus of vehicle-R6/1 mice. In addition, we observed an increase of cAMP levels in the dentate ` of WT and R6/1 mice treated with misoprostol. Accordingly, we showed a reduction in the number of mutant huntingtin nuclear inclusions in the dentate gyrus of R6/1 mice. Altogether, these results suggest a putative therapeutic effect of PGE2 EP2 receptor in reducing cognitive deficits in HD.