Lipid Rafts and Dopamine Receptor Signaling

Glycoprotein-glycoprotein Receptor Binding Detection Using Bioluminescence Resonance Energy Transfer

The glycoprotein receptors, members of the large G protein-coupled receptor family, are characterized by a large extracellular domains responsible for binding their glycoprotein hormones. Hormone-receptor interactions are traditionally analyzed by ligand-binding assays, most often using radiolabeling but also by thermal shift assays. Despite their high sensitivity, these assays require appropriate laboratory conditions and, often, purified plasma cell membranes, which do not provide information on receptor localization or activity because the assays typically focus on measuring binding only. Here, we apply bioluminescence resonance energy transfer in living cells to determine hormone-receptor interactions between a Gaussia luciferase (Gluc)-luteinizing hormone/chorionic gonadotropin receptor (LHCGR) fusion and its ligands (human chorionic gonadotropin or LH) fused to the enhanced green fluorescent protein. The Gluc-LHCGR, as well as other Gluc-G protein-coupled receptors such as the somatostatin and the C-X-C motif chemokine receptors, is expressed on the plasma membrane, where luminescence activity is equal to membrane receptor expression, and is fully functional. The chimeric enhanced green fluorescent protein-ligands are properly secreted from cells and able to bind and activate the wild-type LHCGR as well as the Gluc-LHCGR. Finally, bioluminescence resonance energy transfer was used to determine the interactions between clinically relevant mutations of the hormones and the LHCGR that show that this bioassay provides a fast and effective, safe, and cost-efficient tool to assist the molecular characterization of mutations in either the receptor or ligand and that it is compatible with downstream cellular assays to determine receptor activation/function.

The delayed effect of rotenone on the relative content of brain isatin-binding proteins of rats with experimental parkinsonism

Isatin (indoldione-2,3) is an endogenous biological regulator found in the brain, peripheral tissues, and biological fluids of humans and animals. Its biological activity is realized via isatin-binding proteins, many of which were identified during proteomic profiling of the brain of mice and rats. A number of these proteins are related to the development of neurodegenerative diseases. Previously, using a model of experimental Parkinsonism induced by a seven-day course of rotenone injections, we have observed behavioral disturbances, as well as changes in the profile and relative content of brain isatin-binding proteins. In this study, we have investigated behavioral responses and the relative content of brain isatin-binding proteins in rats with rotenone-induced Parkinsonism 5 days after the last administration of this neurotoxin. Despite the elimination of rotenone, animals exhibited motor and coordination impairments. Proteomic profiling of isatin-binding proteins revealed changes in the relative content of 120 proteins (the relative content of 83 proteins increased and that of 37 proteins decreased). Comparison of isatin-binding proteins characterized by the changes in the relative content observed in the brain right after the last injection of rotenone (n=16) and 5 days later (n=11) revealed only two common proteins (glyceraldehyde-3-phosphate dehydrogenase and subunit B of V-type proton ATPase). However, most of these proteins are associated with neurodegeneration, including Parkinson's and Alzheimer's diseases.

Aminopeptidase N/CD13 Crosslinking Promotes the Activation and Membrane Expression of Integrin CD11b/CD18

The β2 integrin CD11b/CD18, also known as complement receptor 3 (CR3), and the moonlighting protein aminopeptidase N (CD13), are two myeloid immune receptors with overlapping activities: adhesion, migration, phagocytosis of opsonized particles, and respiratory burst induction. Given their common functions, shared physical location, and the fact that some receptors can activate a selection of integrins, we hypothesized that CD13 could induce CR3 activation through an inside-out signaling mechanism and possibly have an influence on its membrane expression. We revealed that crosslinking CD13 on the surface of human macrophages not only activates CR3 but also influences its membrane expression. Both phenomena are affected by inhibitors of Src, PLCγ, Syk, and actin polymerization. Additionally, after only 10 min at 37 °C, cells with crosslinked CD13 start secreting pro-inflammatory cytokines like interferons type 1 and 2, IL-12p70, and IL-17a. We integrated our data with a bioinformatic analysis to confirm the connection between these receptors and to suggest the signaling cascade linking them. Our findings expand the list of features of CD13 by adding the activation of a different receptor via inside-out signaling. This opens the possibility of studying the joint contribution of CD13 and CR3 in contexts where either receptor has a recognized role, such as the progression of some leukemias.

Effect of oxyresveratrol on the quality and membrane lipid metabolism of shiitake mushroom (Lentinus edodes) during storage

The effect of oxyresveratrol on postharvest quality and membrane lipid metabolism of shiitake mushroom was investigated. The result exhibited that oxyresveratrol retarded browning, maintained firmness and alleviated occurrence of decay of shiitake mushroom. The oxidation and hydrolysis of membrane phospholipids were suppressed by oxyresveratrol treatment, which was associated with reduced LOX and PLD activities and increased SOD and CAT activities. The membrane lipidomics of shiitake mushroom was determined by LC-MS. 385 lipid species and 13 fatty acids in membrane lipids were identified by multiple reaction monitoring method. Compared with control group, the phospholipic acid and lysophospholipid reduced by 29.24% and 21.29% in oxyresveratrol-treated group, respectively, which alleviated hydrolysis of phospholipid. Meanwhile, oxyresveratrol maintained the unsaturation of fatty acids and alleviated oxidation of phospholipid. These results demonstrated that oxyresveratrol could play a dual role of inhibiting the oxidation and hydrolysis of phospholipids to mitigate cellular damage of shiitake mushroom.

Untargeted Metabolomics Analysis Using UHPLC-Q-TOF/MS Reveals Metabolic Changes Associated with Hypertension in Children

The mechanism of hypertension in children remains elusive. The objective of this study was to analyze plasma metabolomics characteristics to explore the potential mechanism of hypertension in children. Serum samples from 29 control children, 38 children with normal body mass index and simple hypertension (NBp), 8 children overweight with simple hypertension (OBp), 37 children with normal body mass index and H-type hypertension (NH) and 19 children overweight with H-type hypertension (OH) were analyzed by non-targeted metabolomics. A total of 1235 differential metabolites were identified between children with hypertension and normal controls, of which 193 metabolites including various lipids were significantly expressed. Compared with the control group, 3-dehydroepiandrosterone sulfate, oleic acid and linoleic acid were up-regulated, and gamma-muricholic acid was down-regulated in the NBp group; 3-dehydroepiandrosterone sulfate, 4-acetamidobutanoate and 1-hexadecanoyl-2-octadecadienoyl-sn-glyero-3-phosphocholine were up-regulated in the OBp group, whereas adenosine and 1-myristoyl-sn-glyero-3-phosphocholine were down-regulated; in the NH group, 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphocholine, phenol and 3-methoxytyramine were up-regulated, while pentadecanoic acid was down-regulated; in the OH group, NG,NG-dimethyl-L-arginine, 1-palmitoyl-sn-glycero-3-phosphocholine and monoethyl phthalate were up-regulated, while phloretin and glycine were down-regulated. The results showed that the children with hypertension had obvious disorders of lipid metabolism (especially in the overweight hypertension group), which led to the occurrence of hypertension. Additionally, the concentration of NO production-related NG, NG-dimethyl-L-arginine, was significantly increased, which may play an important role in H-type hypertension in children.

Sorting nexins: role in the regulation of blood pressure

Sorting nexins (SNXs) are a family of proteins that regulate cellular cargo sorting and trafficking, maintain intracellular protein homeostasis, and participate in intracellular signaling. SNXs are also important in the regulation of blood pressure via several mechanisms. Aberrant expression and dysfunction of SNXs participate in the dysregulation of blood pressure. Genetic studies show a correlation between SNX gene variants and the response to antihypertensive drugs. In this review, we summarize the progress in SNX-mediated regulation of blood pressure, discuss the potential role of SNXs in the pathophysiology and treatment of hypertension, and propose novel strategies for the medical therapy of hypertension.

Association of cholesterol level with dopamine loss and motor deficits in Parkinson disease: A cross-sectional study

BACKGROUND AND PURPOSE

Cholesterol is vital in neuronal function; however, the influence of cholesterol levels on parkinsonism is unclear. This study investigated the relationship between baseline total cholesterol (TC) levels, dopamine loss, and motor symptoms in drug-naïve Parkinson disease (PD).

METHODS

This cross-sectional study enrolled 447 drug-naïve patients with PD who underwent dopamine transporter (DAT) imaging. Multivariate linear regression was used to investigate the effect of cholesterol levels on Unified Parkinson's Disease Rating Scale Part III (UPDRS-III) total score and each subscore after adjusting for the covariates. An interaction analysis was performed to examine the interaction between TC levels and statin use on the UPDRS-III scores.

RESULTS

No significant correlation was found between TC levels and DAT availability after adjusting for potential confounders. Multivariate linear regression showed that TC levels were significantly and negatively associated with the UPDRS-III total score (β = -0.116, p = 0.013) and bradykinesia subscore (β = -0.145, p = 0.011). Dichotomized analysis according to TC levels showed that TC levels were significantly associated with UPDRS-III total score, and rigidity, bradykinesia, and axial subscores only in the low TC group. There was an interaction effect between TC levels and statin use for the axial subscores (β = -0.523, p = 0.025). Subgroup analysis showed that TC levels were significantly and negatively associated with the axial subscore in statin users; however, no association was found in statin nonusers.

CONCLUSIONS

This study suggests that TC levels affect parkinsonian motor symptoms, especially in subjects with low cholesterol status, whereas the severity of axial motor symptoms is negatively associated with TC levels only in statin users.

Lipid Raft Facilitated Receptor Organization and Signaling: A Functional Rheostat in Embryonic Development, Stem Cell Biology and Cancer

Molecular views of plasma membrane organization and dynamics are gradually changing over the past fifty years. Dynamics of plasma membrane instigate several signaling nexuses in eukaryotic cells. The striking feature of plasma membrane dynamics is that, it is internally transfigured into various subdomains of clustered macromolecules. Lipid rafts are nanoscale subdomains, enriched with cholesterol and sphingolipids, reside as floating entity mostly on the exoplasmic leaflet of the lipid bilayer. In terms of functionality, lipid rafts are unique among other membrane subdomains. Herein, advances on the roles of lipid rafts in cellular physiology and homeostasis are discussed, precisely, on how rafts dynamically harbor signaling proteins, including GPCRs, catalytic receptors, and ionotropic receptors within it and orchestrate multiple signaling pathways. In the developmental proceedings signaling are designed for patterning of overall organism and they differ from the somatic cell physiology and signaling of fully developed organisms. Some of the developmental signals are characteristic in maintenance of stemness and activated during several types of tumor development and cancer progression. The harmony between extracellular signaling and lineage specific transcriptional programs are extremely important for embryonic development. The roles of plasma membrane lipid rafts mediated signaling in lineage specificity, early embryonic development, stem cell maintenance are emerging. In view of this, we have highlighted and analyzed the roles of lipid rafts in receptor organization, cell signaling, and gene expression during embryonic development; from pre-implantation through the post-implantation phase, in stem cell and cancer biology.

Dopamine, Immunity, and Disease

The neurotransmitter dopamine is a key factor in central nervous system (CNS) function, regulating many processes including reward, movement, and cognition. Dopamine also regulates critical functions in peripheral organs, such as blood pressure, renal activity, and intestinal motility. Beyond these functions, a growing body of evidence indicates that dopamine is an important immunoregulatory factor. Most types of immune cells express dopamine receptors and other dopaminergic proteins, and many immune cells take up, produce, store, and/or release dopamine, suggesting that dopaminergic immunomodulation is important for immune function. Targeting these pathways could be a promising avenue for the treatment of inflammation and disease, but despite increasing research in this area, data on the specific effects of dopamine on many immune cells and disease processes remain inconsistent and poorly understood. Therefore, this review integrates the current knowledge of the role of dopamine in immune cell function and inflammatory signaling across systems. We also discuss the current understanding of dopaminergic regulation of immune signaling in the CNS and peripheral tissues, highlighting the role of dopaminergic immunomodulation in diseases such as Parkinson's disease, several neuropsychiatric conditions, neurologic human immunodeficiency virus, inflammatory bowel disease, rheumatoid arthritis, and others. Careful consideration is given to the influence of experimental design on results, and we note a number of areas in need of further research. Overall, this review integrates our knowledge of dopaminergic immunology at the cellular, tissue, and disease level and prompts the development of therapeutics and strategies targeted toward ameliorating disease through dopaminergic regulation of immunity. SIGNIFICANCE STATEMENT: Canonically, dopamine is recognized as a neurotransmitter involved in the regulation of movement, cognition, and reward. However, dopamine also acts as an immune modulator in the central nervous system and periphery. This review comprehensively assesses the current knowledge of dopaminergic immunomodulation and the role of dopamine in disease pathogenesis at the cellular and tissue level. This will provide broad access to this information across fields, identify areas in need of further investigation, and drive the development of dopaminergic therapeutic strategies.

DRD1 and DRD4 are differentially expressed in breast tumors and breast cancer stem cells: pharmacological implications

BACKGROUND

Abnormal expression of dopamine receptors (DRs) has been described in multiple tumors, but their roles in breast cancer are inconclusive or contradictory since evidence of pro- and anti-tumoral effects have been reported. Herein, we analyzed the expression of DRs in breast cancer, especially in the subpopulation of cancer stem cells (CSCs), and evaluated the functional role of the receptors by pharmacological targeting.

METHODS

Expression of DRD1, DRD2, DRD3, DRD4 and DRD5 was investigated in human breast tumors and cancer cell lines using public databases. Correlation between gene expression and clinical outcome was studied by Kaplan-Mayer analyses. By flow cytometry, we assessed DRD1, DRD2, and DRD4 expression in cultures of MCF-7 (luminal) and MDA-MB-231 (triple-negative) cells. Using the previously reported SORE6 reporter system we examined the differential expression of DRD1, DRD2, and DRD4 in CSCs and tumor-bulk cells. The effect of pharmacological modulation of DRs on stemness and cell migration was studied by quantification of the reporter-positive fraction and wound healing assays, respectively.

RESULTS

DRD1, DRD2 and DRD4 transcripts were expressed in breast tumors. DRD4 was overexpressed compared to normal tissue and showed prognostic value. DRD1, DRD2 and DRD4 transcripts were also found in MCF-7 and MDA-MB-231 cells, but only DRD1 and DRD4 proteins were detected. DRD4 was underexpressed in CSCs compared to tumor-bulk cells, whereas DRD1 was found only in the CSCs fraction, suggesting that those receptors may have relevance in stemness control. Subtoxic concentrations of DRD1-targeting compounds did not induced significant changes in the CSCs pool. On the other hand, DRD4 inhibition by Haloperidol slightly increased the CSCs content but also reduced cell migration.

CONCLUSIONS

Pharmacological modulation of DRD1 in MCF-7 or MDA-MB-231 cells seems to be irrelevant for stemness maintenance. DRD4 reduced expression in breast CSCs or its inhibition by Haloperidol favors CSCs-pool expansion. DRD4 inhibition can also reduce cell migration, indicating that DRD4 plays different roles in stem and non-stem breast cancer cells.

The Role of Lipids in Allosteric Modulation of Dopamine D2 Receptor-In Silico Study

The dopamine D₂ receptor, belonging to the class A G protein-coupled receptors (GPCRs), is an important drug target for several diseases, including schizophrenia and Parkinson’s disease. The D₂ receptor can be activated by the natural neurotransmitter dopamine or by synthetic ligands, which in both cases leads to the receptor coupling with a G protein. In addition to receptor modulation by orthosteric or allosteric ligands, it has been shown that lipids may affect the behaviour of membrane proteins. We constructed a model of a D₂ receptor with a long intracellular loop (ICL3) coupled with G_iα1 or G_iα2 proteins, embedded in a complex asymmetric membrane, and simulated it in complex with positive, negative or neutral allosteric ligands. In this study, we focused on the influence of ligand binding and G protein coupling on the membrane–receptor interactions. We show that there is a noticeable interplay between the cell membrane, G proteins, D₂ receptor and its modulators.

Recent advances in microscale separation techniques for lipidome analysis

This review paper highlights the recent research on liquid-phase microscale separation techniques for lipidome analysis over the last 10 years, mainly focusing on capillary liquid chromatography (LC) and capillary electrophoresis (CE) coupled with mass spectrometry (MS). Lipids are one of the most important classes of biomolecules which are involved in the cell membrane, energy storage, signal transduction, and so on. Since lipids include a variety of hydrophobic compounds including numerous structural isomers, lipidomes are a challenging target in bioanalytical chemistry. MS is the key technology that comprehensively identifies lipids; however, separation techniques like LC and CE are necessary prior to MS detection in order to avoid ionization suppression and resolve structural isomers. Separation techniques using μm-scale columns, such as a fused silica capillary and microfluidic device, are effective at realizing high-resolution separation. Microscale separation usually employs a nL-scale flow, which is also compatible with nanoelectrospray ionization-MS that achieves high sensitivity. Owing to such analytical advantages, microscale separation techniques like capillary/microchip LC and CE have been employed for more than 100 lipidome studies. Such techniques are still being evolved and achieving further higher resolution and wider coverage of lipidomes. Therefore, microscale separation techniques are promising as the fundamental technology in next-generation lipidome analysis.

Dopamine D1 receptor alleviates doxorubicin-induced cardiac injury by inhibiting NLRP3 inflammasome

Doxorubicin (DOX) is a broad-spectrum antineoplastic drug; however, its serious cardiotoxic side effects in inflammatory responses limit its use in clinical applications. Dopamine D1 receptor (DRD1), a G protein-coupled receptor, is crucial for the development and function of the nervous system; additionally, it also play a role in immune regulation. However, the specific role of DRD1 in DOX-induced cardiac inflammation has not yet been clarified. Here, we discovered that DRD1 expression was induced by DOX treatment in H9C2 cardiomyocytes. DRD1 activation by A-68930, a DRD1-specific agonist, decreased DOX-induced nucleotide-binding domain-like receptor protein 3 (NLRP3) expression, caspase-1 activation, and IL-1β maturation in H9C2 cells. Expression of the cytokines IL-1β and IL-18 in the supernatants was also inhibited by A-68930 treatment. DRD1 knockdown, using siRNA, abolished the effects of A-68930 on the DOX-induced NLRP3 inflammasome. Furthermore, we found that DRD1 signaling downregulated the NLRP3 inflammasome in H9C2 cells through cyclic adenosine monophosphate (cAMP). Moreover, application of A-68930 to activate DRD1 reduced cardiac injury and fibrosis in a DOX-treated mouse model by suppressing the NLRP3 inflammasome in the heart. These findings indicate that DRD1 signaling may protect against DOX-induced cardiac injury by inhibiting the NLRP3 inflammasome-mediated inflammation.