Surface clustering of metabotropic glutamate receptor 1 induced by long Homer proteins.
Animals; Carrier Proteins/genetics/*metabolism; Cell Membrane/metabolism; Confocal; Gene Expression; Green Fluorescent Proteins/genetics; Homer Scaffolding Proteins; In Vitro Techniques; Metabotropic Glutamate/genetics/*metabolism; Microscopy; Neurons/*metabolism; Rats; Receptor Aggregation/*physiology; Receptors; Superior Cervical Ganglion/cytology; Sympathetic Nervous System/cytology; Transfection; Wistar
BACKGROUND: Metabotropic glutamate receptors (mGluRs) regulate neuronal excitability and synaptic strength. The group I mGluRs, mGluR1 and 5, are widespread in the brain and localize to post-synaptic sites. The Homer protein family regulates group I mGluR function and distribution. Constitutively expressed 'long' Homer proteins (Homer 1b, 1c, 2 and 3) induce dendritic localization of group I mGluRs and receptor clustering, either internally or on the plasma membrane. Short Homer proteins (Homer 1a, Ania-3) exhibit regulated expression and act as dominant negatives, producing effects on mGluR distribution and function that oppose those of the long Homer proteins. There remains some controversy over whether long Homer proteins induce receptor internalization by inducing retention in the endoplasmic reticulum, or induce mGluR clustering on the plasma membrane. Further, an exhaustive study of the effects of each long Homer isoform on mGluR distribution has not been published. RESULTS: The distribution of a GFP-tagged group I mGluR, mGluR1-GFP, was examined in the absence of Homer proteins and in the presence of several Homer isoforms expressed in sympathetic neurons from the rat superior cervical ganglion (SCG) using total internal reflection fluorescence (TIRF-M) and confocal microscopy. Quantitative analysis of mGluR1-GFP fluorescence using TIRF-M revealed that expression of each long Homer isoform tested (Homer 1b, 1c, 2b and 3) induced a significant degree of surface clustering. Using confocal imaging, Homer-induced mGluR clusters were observed intra-cellularly as well as on the plasma membrane. Further, in approximately 40% of neurons co-expressing mGluR1-GFP and Homer 1b, intracellular inclusions were observed, but plasma membrane clusters were also documented in some Homer 1b coexpressing cells. CONCLUSION: All long Homer proteins examined (Homer 1b, 1c, 2b and 3) induced a significant degree of mGluR1-GFP clustering on the plasma membrane compared to cells expressing mGluR1-GFP alone. Clusters induced by long Homers appeared on the plasma membrane and intracellularly, suggesting that clusters form prior to plasma membrane insertion and/or persist after internalization. Finally, while Homer 1b induced surface clustering of mGluR1 in some cells, under some conditions intracellular retention may occur.
Kammermeier Paul J
BMC neuroscience
2006
2006-01
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1186/1471-2202-7-1" target="_blank" rel="noreferrer noopener">10.1186/1471-2202-7-1</a>
Myocardial CXCR4 expression is required for mesenchymal stem cell mediated repair following acute myocardial infarction.
Animals; Apoptosis/physiology; Cardiac/cytology/physiology; Cell Movement/physiology; Chemokine CXCL12/*metabolism; Coronary Circulation/physiology; CXCR4/*genetics/metabolism; Gene Expression/physiology; Green Fluorescent Proteins/genetics; Inbred C57BL; Knockout; Mesenchymal Stem Cell Transplantation/*methods; Mesenchymal Stem Cells/*metabolism; Mice; Myocardial Infarction/genetics/pathology/*therapy; Myocardium/cytology; Myocytes; Paracrine Communication/physiology; Receptors; Ventricular Remodeling/physiology
BACKGROUND: Overexpression of stromal cell-derived factor-1 in injured tissue leads to improved end-organ function. In this study, we quantify the local trophic effects of mesenchymal stem cell (MSC) stromal cell-derived factor-1 release on the effects of MSC engraftment in the myocardium after acute myocardial infarction. METHODS AND RESULTS: Conditional cardiac myocyte CXCR4 (CM-CXCR4) null mice were generated by use of tamoxifen-inducible cardiac-specific cre by crossing CXCR4 floxed with MCM-cre mouse. Studies were performed in littermates with (CM-CXCR4 null) or without (control) tamoxifen injection 3 weeks before acute myocardial infarction. One day after acute myocardial infarction, mice received 100,000 MSC or saline via tail vein. We show alpha-myosin heavy chain MerCreMer and the MLC-2v promoters are active in cardiac progenitor cells. MSC engraftment in wild-type mice decreased terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling positive CM (-44%, P\textless0.01), increased cardiac progenitor cell recruitment (100.9%, P\textless0.01), and increased cardiac myosin-positive area (39%, P\textless0.05) at 4, 7, and 21 days after acute myocardial infarction, respectively. MSC in wild-type mice resulted in 107.4% (P\textless0.05) increase in ejection fraction in comparison with 25.9% (P=NS) increase in CM-CXCR4 null mice. These differences occurred despite equivalent increases (16%) in vascular density in response to MSC infusion in wild-type and
Dong Feng; Harvey James; Finan Amanda; Weber Kristal; Agarwal Udit; Penn Marc S
Circulation
2012
2012-07
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1161/CIRCULATIONAHA.111.082453" target="_blank" rel="noreferrer noopener">10.1161/CIRCULATIONAHA.111.082453</a>