Anchor Side Chains of Short Peptide Fragments Trigger Ligand-Exchange of Class II MHC Molecules

Class II MHC molecules display peptides on the cell surface for the surveillance by CD4+ T cells. To ensure that these ligands accurately reflect the content of the intracellular MHC loading compartment, a complex processing pathway has evolved that delivers only stable peptide/MHC complexes to the surface. As additional safeguard, MHC molecules quickly acquire a ‘non-receptive’ state once they have lost their ligand. Here we show now that amino acid side chains of short peptides can bypass these safety mechanisms by triggering the reversible ligand-exchange. The catalytic activity of dipeptides such as Tyr-Arg was stereo-specific and could be enhanced by modifications addressing the conserved H-bond network near the P1 pocket of the MHC molecule. It affected both antigen-loading and ligand-release and strictly correlated with reported anchor preferences of P1, the specific target site for the catalytic side chain of the dipeptide. The effect was evident also in CD4+ T cell assays, where the allele-selective influence of the dipeptides translated into increased sensitivities of the antigen-specific immune response. Molecular dynamic calculations support the hypothesis that occupation of P1 prevents the ‘closure’ of the empty peptide binding site into the non-receptive state. During antigen-processing and -presentation P1 may therefore function as important “sensor” for peptide-load. While it regulates maturation and trafficking of the complex, on the cell surface, short protein fragments present in blood or lymph could utilize this mechanism to alter the ligand composition on antigen presenting cells in a catalytic way

A rare case of schwannoma of the nasal vestibule

Abstract Background Schwannomas of the nose and paranasal are extremely rare. Few schwannomas arising from within the lateral wall of the nose have been reported to date. Case presentation A 32-year-old male presented to us with complaints of left-sided nasal obstruction and a mass in his nasal cavity. The evaluation revealed a benign spindle cell lesion arising from within the lateral wall nose which was excised. The final histopathology report revealed a nasal schwannoma. Discussion Schwannomas are benign tumors arising from Schwann cells. Schwann cells are responsible for the formation of the myelin sheath. They are rare, slow-growing tumors. Twenty-five to 45% tumors arise in the head and neck, of which only 4% were arising from nasal cavity and paranasal sinuses. Conclusion To generate awareness about the varying clinical presentations of Schwannomas in the nose and paranasal sinuses and their management

MeCP2 interacts with HP1 and modulates its heterochromatin association during myogenic differentiation.

There is increasing evidence of crosstalk between epigenetic modifications such as histone and DNA methylation, recognized by HP1 and methyl CpG-binding proteins, respectively. We have previously shown that the level of methyl CpG-binding proteins increased dramatically during myogenesis leading to large-scale heterochromatin reorganization. In this work, we show that the level of HP1 isoforms did not change significantly throughout myogenic differentiation but their localization did. In particular, HP1gamma relocalization to heterochromatin correlated with MeCP2 presence. Using co-immunoprecipitation assays, we found that these heterochromatic factors interact in vivo via the chromo shadow domain of HP1 and the first 55 amino acids of MeCP2. We propose that this dynamic interaction of HP1 and MeCP2 increases their concentration at heterochromatin linking two major gene silencing pathways to stabilize transcriptional repression during differentiation

MeCP2 Rett mutations affect large scale chromatin organization

Rett syndrome is a neurological, X chromosomal-linked disorder associated with mutations in the MECP2 gene. MeCP2 protein has been proposed to play a role in transcriptional regulation as well as in chromatin architecture. Since MeCP2 mutant cells exhibit surprisingly mild changes in gene expression, we have now explored the possibility that Rett mutations may affect the ability of MeCP2 to bind and organize chromatin. We found that all but one of the 21 missense MeCP2 mutants analyzed accumulated at heterochromatin and about half of them were significantly affected. Furthermore, two thirds of all mutants showed a significantly decreased ability to cluster heterochromatin. Three mutants containing different proline substitutions (P101H, P101R and P152R) were severely affected only in heterochromatin clustering and located far away from the DNA interface in the MeCP2 methyl binding domain structure. MeCP2 mutants affected in heterochromatin accumulation further exhibited the shortest residence time on heterochromatin, followed by intermediate binding kinetics for clustering impaired mutants. We propose that different interactions of MeCP2 with methyl cytosines, DNA and likely other heterochromatin proteins are required for MeCP2 function and their dysfunction lead to Rett syndrome

Global and 3D spatial assessment of neuroinflammation in rodent models of Multiple Sclerosis.

Multiple Sclerosis (MS) is a progressive autoimmune inflammatory and demyelinating disease of the central nervous system (CNS). T cells play a key role in the progression of neuroinflammation in MS and also in the experimental autoimmune encephalomyelitis (EAE) animal models for the disease. A technology for quantitative and 3 dimensional (3D) spatial assessment of inflammation in this and other CNS inflammatory conditions is much needed. Here we present a procedure for 3D spatial assessment and global quantification of the development of neuroinflammation based on Optical Projection Tomography (OPT). Applying this approach to the analysis of rodent models of MS, we provide global quantitative data of the major inflammatory component as a function of the clinical course. Our data demonstrates a strong correlation between the development and progression of neuroinflammation and clinical disease in several mouse and a rat model of MS refining the information regarding the spatial dynamics of the inflammatory component in EAE. This method provides a powerful tool to investigate the effect of environmental and genetic forces and for assessing the therapeutic effects of drug therapy in animal models of MS and other neuroinflammatory/neurodegenerative disorders

Global and 3D imaging of intact mouse CNS.

<p>(A). Spinal cords from C57BL/6 mice were stained with ASMA (red) and were further imaged by OPT. OPT scanned spinal cords were cryosectioned and imaged under a fluorescence microscope with 4× zoom (white frames). Selected regions were also imaged under a confocal microscope with 40× zoom (inlets). Nucleated cells were stained with 4,6-diamidino-2-phenylindole (DAPI). Spinal cord (B) and optic nerve (C) from B10RII mice were stained with MBP (red), and imaged by OPT. Cryosectioning was performed after OPT imaging and images were captured using a fluorescence microscope at 4× zoom. Spinal cords (D) and optic nerves (E) from C57BL/6 mice with a clinical score of 3.0 were stained with CD3 specific antibodies. OPT scanned tissues were cryosectioned and subsequently imaged under a fluorescence microscope at 4× zoom (white frames) or selected regions displaying evidence of CD3⁺ T cell infiltration were imaged using a confocal microscope at 63× zoom (inlets). CD3⁺ T cell staining is shown in red and the anatomy reconstructed from the CNS outline on the basis of the autofluorescence signal is shown in green. Scale bar: (A) Whole organ: 2 mm, 4× zoom images: 100 µm; 40× zoom image: 50 µm; (B, C) 4× zoom image: 100 µm; (D) whole organ: 2 mm, 4× zoom image: 100 µm, 40× zoom images: 50 µm, 63× zoom image: 50 µm; (E) whole organ: 2 mm, 4× zoom image: 100 µm, 63× zoom image: 50 µm.</p

Spatial assessment of neuroinflammation in B6 EAE.

<p>C57BL/6 mice were immunized with MOG_35-55/complete Freunds adjuvants (CFA)/pertussis toxin (PTX) and were observed for EAE. CNS tissue was obtained at different clinical scores and was stained for CD3⁺ T cells and imaged using OPT. The iso-surface rendered OPT images of spinal cord and optic nerve sections at different clinical scores during the progression of EAE were obtained. Infiltrating CD3⁺ T cells (red) due to the signal from the CD3 specific antibody. The reconstruction of the CNS outline is based on the autofluorescence signal (green), where the upper part of spinal cord is the cervical and thoracic region while the bottom parts are the lumbar and sacral regions. Images were generated for score 1 (n = 2), score 2 (n = 3), score 3 (n = 2). Scale bar = 2 mm.</p