ALG-2 interacting protein AIP1: a novel link between D1 and D3 signalling

Electroacupuncture-Regulated miR-34a-3p/PDCD6 Axis Promotes Post-Spinal Cord Injury Recovery in Both In Vitro and In Vivo Settings

Electroacupuncture (EA) could enhance neuroregeneration and posttraumatic conditions; however, the underlying regulatory mechanisms remain ambiguous. PDCD6 (programmed cell death 6) is an established proapoptotic regulator which is responsible for motoneuronal death. However, its potential regulatory role in post-spinal cord injury (SCI) regeneration has remained largely unknown. Further investigations are warranted to clarify the involvement of PDCD6 post-SCI recovery and the underlying mechanisms. In our study, based on bioinformatics prediction, we found that miR-34a-3p might be an upstream regulator miRNA for PDCD6, which was subsequently validated through combined utilization of the qRT-PCR, western blot, and dual-luciferase reporter system. Our in vitro results showed that miR-34a-3p might promote the in vitro differentiation of neural stem cell (NSC) through suppressing PDCD6 and regulating other important neural markers such as fibroblast growth factor receptor 1 (FGFR1), MAP1/2 (MAP kinase kinases 1/2), myelin basic protein (MBP), βIII-tubulin Class III β-tubulin (βIII tubulin), and glial fibrillary acidic protein (GFAP). Notably, in the post-SCI rat model, exogenous miR-34a-3p agomir obviously inhibited the expression of PDCD6 at the protein level and promoted neuronal proliferation, motoneurons regeneration, and axonal myelination. The restorations at cellular level might contribute to the improved hindlimbs functions of post-SCI rats, which was manifested by the Basso-Beattie-Bresnahan (BBB) locomotor test. The impact of miR-34a-3p was further promoted by EA treatment in vivo. Conclusively, this paper argues that a miR-34a-3p/PDCD6 axis might be a candidate therapeutic target for treating SCI and that the therapeutic effect of EA is driven through this pathway.

Alix: A Candidate Serum Biomarker of Alzheimer's Disease

Alzheimer’s disease (AD) is the most common fatal neurodegenerative disease of the elderly worldwide. The identification of AD biomarkers will allow for earlier diagnosis and thus earlier intervention. The aim of this study was to find such biomarkers. It was observed that the expression of Alix was significantly decreased in brain tissues and serum samples from AD patients compared to the controls. A significant correlation between Alix levels and cognitive decline was observed (r = 0.80; p < 0.001) as well as a significant negative correlation between Alix and Aβ₄₀ in serum levels (r =−0.60, p < 0.001). The receiver operating characteristic curve (ROC) analysis showed the area under the curve (AUC) of Alix was 0.80, and the optimal cut-off point of 199.5 pg/ml was selected with the highest sum of sensitivity and specificity. The diagnostic accuracy for serum Alix was 74%, with 76% sensitivity and 71% specificity respectively, which could differentiate AD from controls. In addition, the expression of Alix was found to be significantly decreased in AD compared to vascular dementia (VaD). ROC analysis between AD and VaD showed that the AUC was 0.777, which could be indicative of the role of serum Alix as a biomarker in the differential diagnosis between AD and VaD. Most surprisingly, the decreased expression of Alix was attenuated after the treatment of Memantine in different AD animal models. In conclusion, our results indicate the possibility of serum Alix as a novel and non-invasive biomarker for AD for the first time.

Exome Sequencing Reveals Signal Transduction Genes Involved in Impulse Control Disorders in Parkinson's Disease

Introduction: Impulse control disorders (ICDs) frequently complicate dopamine agonist (DA) therapy in Parkinson's disease (PD). There is growing evidence of a high heritability for ICDs in the general population and in PD. Variants on genes belonging to the reward pathway have been shown to account for part of this heritability. We aimed to identify new pathways associated with ICDs in PD.

Methods: Thirty-six Parkinsonian patients on DA therapy with (n = 18) and without ICDs (n = 18) matched on age at PD's onset, and gender was selected to represent the most extreme phenotypes of their category. Exome sequencing was performed, and variants with a strong functional impact in brain-expressed genes were selected. Allele frequencies and their distribution in genes and pathways were analyzed with single variant and SKAT-O tests. The 10 most associated variants, genes, and pathways were retained for replication in the Parkinson's progression markers initiative (PPMI) cohort.

Results: None of markers tested passed the significance threshold adjusted for multiple comparisons. However, the “Adenylate cyclase activating” pathway, one of the top associated pathways in the discovery data set (p = 1.6 × 10⁻³) was replicated in the PPMI cohort and was significantly associated with ICDs in a post hoc pooled analysis (combined p-value 3.3 × 10⁻⁵). Two of the 10 most associated variants belonged to genes implicated in cAMP and ERK signaling (rs34193571 in RasGRF2, p = 5 × 10⁻⁴; rs1877652 in PDE2A, p = 8 × 10⁻⁴) although non-significant after Bonferroni correction.

Conclusion: Our results suggest that genes implicated in the signaling pathways linked to G protein-coupled receptors participate to genetic susceptibility to ICDs in PD.

Overexpression of the dopamine receptor-interacting protein Alix/AIP1 modulates NMDA receptor-triggered cell death

Alix/AIP1 is an adaptor protein involved in apoptosis, endocytic membrane trafficking and brain development. Alix has been found within the human postsynaptic density (PSD) and, since NMDA receptors (NMDARs) are central components of the PSD, we hypothesized that the close proximity of both proteins may allow Alix to influence the downstream pathways following NMDAR activation. NMDARs play important roles in excitotoxicity and we evaluated the effects of recombinant Alix in an NMDAR cell death assay. Overexpression of Alix with NMDARs increases the potency of NMDAR- induced cell death compared to cells expressing only NMDARs, and this requires expression of the Alix C-terminal region. Therefore, we demonstrate a previously unreported role for Alix as a potential modulator of NMDAR function.

Endo-lysosomal sorting of G-protein-coupled receptors by ubiquitin: Diverse pathways for G-protein-coupled receptor destruction and beyond

Ubiquitin is covalently attached to substrate proteins in the form of a single ubiquitin moiety or polyubiquitin chains and has been generally linked to protein degradation, however, distinct types of ubiquitin linkages are also used to control other critical cellular processes like cell signaling. Over forty mammalian G protein-coupled receptors (GPCRs) have been reported to be ubiquitinated, but despite the diverse and rich complexity of GPCR signaling, ubiquitin has been largely ascribed to receptor degradation. Indeed, GPCR ubiquitination targets the receptors for degradation by lysosome, which is mediated by the Endosomal Sorting Complexes Required for Transport (ESCRT) machinery, and the proteasome. This has led to the view that ubiquitin and ESCRTs primarily function as the signal to target GPCRs for destruction. Contrary to this conventional view, studies indicate that ubiquitination of certain GPCRs and canonical ubiquitin-binding ESCRTs are not required for receptor degradation and revealed that diverse and complex pathways exist to regulate endo-lysosomal sorting of GPCRs. In other studies, GPCR ubiquitination has been shown to drive signaling and not receptor degradation and further revealed novel insight into the mechanisms by which GPCRs trigger the activity of the ubiquitination machinery. Here, we discuss the diverse pathways by which ubiquitin controls GPCR endo-lysosomal sorting and beyond.

GPCRs in Cancer: Protease-Activated Receptors, Endocytic Adaptors and Signaling

G protein-coupled receptors (GPCRs) are a large diverse family of cell surface signaling receptors implicated in various types of cancers. Several studies indicate that GPCRs control many aspects of cancer progression including tumor growth, invasion, migration, survival and metastasis. While it is known that GPCR activity can be altered in cancer through aberrant overexpression, gain-of-function activating mutations, and increased production and secretion of agonists, the precise mechanisms of how GPCRs contribute to cancer progression remains elusive. Protease-activated receptors (PARs) are a unique class of GPCRs implicated in cancer. PARs are a subfamily of GPCRs comprised of four members that are irreversibly activated by proteolytic cleavage induced by various proteases generated in the tumor microenvironment. Given the unusual proteolytic irreversible activation of PARs, expression of receptors at the cell surface is a key feature that influences signaling responses and is exquisitely controlled by endocytic adaptor proteins. Here, we discuss new survey data from the Cancer Genome Atlas and the Genotype-Tissue Expression projects analysis of expression of all PAR family member expression in human tumor samples as well as the role and function of the endocytic sorting machinery that controls PAR expression and signaling of PARs in normal cells and in cancer.

Abnormalities of Dopamine D3 Receptor Signaling in the Diseased Brain

Dopamine D₃ receptors (D₃R) modulate neuronal activity in several brain regions including cortex, striatum, cerebellum, and hippocampus. A growing body of evidence suggests that aberrant D₃R signaling contributes to multiple brain diseases, such as Parkinson’s disease, essential tremor, schizophrenia, and addiction. In line with these findings, D₃R has emerged as a potential target in the treatment of neurological disorders. However, the mechanisms underlying neuronal D₃R signaling are poorly understood, either in healthy or diseased brain. Here, I review the molecular mechanisms involved in D₃R signaling via monomeric D₃R and heteromeric receptor complexes (e.g., D₃R-D₁R, D₃R-D₂R, D₃R-A_2aR, and D₃R-D₃nf). I focus on D₃R signaling pathways that, according to recent reports, contribute to pathological brain states. In particular, I describe evidence on both quantitative (e.g., increased number or affinity) and qualitative (e.g., switched signaling) changes in D₃R that has been associated with brain dysfunction. I conclude with a description of basic mechanisms that modulate D₃R signaling such as desensitization, as disruption of these mechanisms may underlie pathological changes in D₃R signaling. Because several lines of evidence support the idea that imbalances in D₃R signaling alter neural function, a better understanding of downstream D₃R pathways is likely to reveal novel therapeutic strategies toward dopamine-related brain disorders.

Striatal dopamine D1-like receptor binding is unchanged in primary focal dystonia

BACKGROUND

Multiple studies have demonstrated decreases in striatal D2-like (D2, D3) radioligand binding in primary focal dystonias. Although most investigations have focused on D2-specific receptors (D2R), a recent study suggests that the decreased D2-like binding may be due to a D3-specific (D3R) abnormality. However, only limited data exist on the role of D1-specific receptors (D1R) and the D1R-mediated pathways within basal ganglia in dystonia. Metabolic positron emission tomography (PET) data in primary generalized dystonia suggest resting state over activity in the D1R-mediated direct pathway, leading to excessive disinhibition of motor cortical areas. This work investigated whether striatal D1-like receptors are affected in primary focal dystonias.

METHODS

Striatal-specific (caudate and putamen) binding of the D1-like radioligand [(11)C]NNC 112 was measured using PET in 19 patients with primary focal dystonia (cranial, cervical, or arm) and 18 controls.

RESULTS

No statistically significant difference was detected in striatal D1-like binding between the two groups. The study had 91% power to detect a 20% difference, indicating that false-negative results were unlikely.

CONCLUSIONS

Because [(11)C]NNC 112 has high affinity for D1-like receptors, very low affinity for D2-like receptors, and minimal sensitivity to endogenous dopamine levels, we conclude that D1-like receptor binding is not impaired in these primary focal dystonias.

ALIX binds a YPX(3)L motif of the GPCR PAR1 and mediates ubiquitin-independent ESCRT-III/MVB sorting

The sorting of signaling receptors to lysosomes is an essential regulatory process in mammalian cells. During degradation, receptors are modified with ubiquitin and sorted by endosomal sorting complex required for transport (ESCRT)-0, -I, -II, and -III complexes into intraluminal vesicles (ILVs) of multivesicular bodies (MVBs). However, it remains unclear whether a single universal mechanism mediates MVB sorting of all receptors. We previously showed that protease-activated receptor 1 (PAR1), a G protein-coupled receptor (GPCR) for thrombin, is internalized after activation and sorted to lysosomes independent of ubiquitination and the ubiquitin-binding ESCRT components hepatocyte growth factor-regulated tyrosine kinase substrate and Tsg101. In this paper, we report that PAR1 sorted to ILVs of MVBs through an ESCRT-III-dependent pathway independent of ubiquitination. We further demonstrate that ALIX, a charged MVB protein 4-ESCRT-III interacting protein, bound to a YPX(3)L motif of PAR1 via its central V domain to mediate lysosomal degradation. This study reveals a novel MVB/lysosomal sorting pathway for signaling receptors that bypasses the requirement for ubiquitination and ubiquitin-binding ESCRTs and may be applicable to a subset of GPCRs containing YPX(n)L motifs.

Dopamine and renal function and blood pressure regulation

Dopamine is an important regulator of systemic blood pressure via multiple mechanisms. It affects fluid and electrolyte balance by its actions on renal hemodynamics and epithelial ion and water transport and by regulation of hormones and humoral agents. The kidney synthesizes dopamine from circulating or filtered L-DOPA independently from innervation. The major determinants of the renal tubular synthesis/release of dopamine are probably sodium intake and intracellular sodium. Dopamine exerts its actions via two families of cell surface receptors, D1-like receptors comprising D1R and D5R, and D2-like receptors comprising D2R, D3R, and D4R, and by interactions with other G protein-coupled receptors. D1-like receptors are linked to vasodilation, while the effect of D2-like receptors on the vasculature is variable and probably dependent upon the state of nerve activity. Dopamine secreted into the tubular lumen acts mainly via D1-like receptors in an autocrine/paracrine manner to regulate ion transport in the proximal and distal nephron. These effects are mediated mainly by tubular mechanisms and augmented by hemodynamic mechanisms. The natriuretic effect of D1-like receptors is caused by inhibition of ion transport in the apical and basolateral membranes. D2-like receptors participate in the inhibition of ion transport during conditions of euvolemia and moderate volume expansion. Dopamine also controls ion transport and blood pressure by regulating the production of reactive oxygen species and the inflammatory response. Essential hypertension is associated with abnormalities in dopamine production, receptor number, and/or posttranslational modification.

Altered expression and coregulation of dopamine signalling genes in schizophrenia and bipolar disorder

INTRODUCTION

signalling through dopamine receptors is of critical importance in the brain and is implicated in schizophrenia and bipolar disorder, but its underlying molecular mechanisms remain poorly understood.

MATERIALS AND METHODS

using a yeast two-hybrid approach, we previously identified 11 novel dopamine receptor-interacting proteins. Here we compare gene expression levels for 17 genes [including all 11 dopamine receptor interacting proteins, all 5 dopamine receptors (DRD1-DRD5) and DARPP-32] by real-time polymerase chain reaction, using prefrontal cortex post mortem brain samples from 33 schizophrenic, 32 bipolar disorder and 34 control subjects.

RESULTS

the expression of C14ORF28, GNB2L1, MLLT3, DRD2 and DARPP-32 genes was altered in schizophrenia and/or bipolar disorder samples relative to controls (P < 0.05). Hierarchical clustering analysis revealed the expression of these five genes (C14ORF28, GNB2L1, MLLT3, DARPP-32, DRD2) is closely correlated in patients. However, in controls, DRD2 expression in relation to the other genes appears to be very different, suggesting abnormal DRD2 activity is an important trigger in the pathophysiology of schizophrenia and bipolar disorder.

CONCLUSIONS

our data suggest: (i) C14ORF28, GNB2L1, MLLT3, DRD2 and DARPP-32 are important in the pathogenesis of schizophrenia and bipolar disorder; (ii) these two disorders share common disease-related mechanisms linked to dopamine signalling; (iii) the expression of these genes is closely correlated; and (iv) DRD2 provides the initial trigger in the pathogenesis of these disorders.

Modulation of monoamine receptors by adaptor proteins and lipid rafts: role in some effects of centrally acting drugs and therapeutic agents

The monoamines and their cognate receptors are widespread in the central nervous system and are vital for normal brain function. Dysfunction in these systems underlies several psychiatric and neurological disease states, and consequently monoamines are targets of a host of pharmacotherapies. This review provides an overview on how monoamine receptors are regulated by adaptor proteins and lipid rafts with emphasis on interactions in nerve cells. Monoamine receptors have prominent intracellular loops that provide binding sites for adaptor proteins. Receptor function is further modulated by cholesterol and submembranous microdomains termed lipid rafts. These interactions determine several facets of G protein-coupled receptor (GPCR) function including trafficking, localization, and signaling. Possible roles of adaptor proteins and lipid rafts in disease states and in mediating actions of drugs and therapeutic agents are also discussed.