Showing papers by "Dick Hoekstra published in 2011"

Organellar Na+/H+ exchangers: novel players in organelle pH regulation and their emerging functions.

Abstract: Mammalian Na+/H+ exchangers (NHEs) play a fundamental role in cellular ion homeostasis. NHEs exhibit an appreciable variation in expression, regulation, and physiological function, dictated by their dynamics in subcellular localization and/or interaction with regulatory proteins. In recent years, a subgroup of NHEs consisting of four isoforms has been identified, and its members predominantly localize to the membranes of the Golgi apparatus and endosomes. These organellar NHEs constitute a family of transporters with an emerging function in the regulation of luminal pH and in intracellular membrane trafficking as expressed, for example, in cell polarity development. Moreover, specific roles of a variety of cofactors, regulating the intracellular dynamics of these transporters, are also becoming apparent, thereby providing further insight into their mechanism of action and overall functioning. Interestingly, organellar NHEs have been related to mental disorders, implying a potential role in the brain, thus...

Increased expression of distinct galectins in multiple sclerosis lesions.

Abstract: Aims: Multiple sclerosis (MS) is a chronic progressive degenerative disorder of the central nervous system, characterized by inflammation, demyelination, ultimate failure of remyelination and axonal loss. Current research identifies galectins, adhesion/growth-regulatory effectors binding beta-galactosides, peptide motifs and lipids, as important immunomodulators in diverse inflammatory diseases. However, little is known about their expression, cellular localization and role in human central nervous system tissue. To identify a potential role of galectins in MS, their expression and localization in control white matter (CWM) and demyelinated MS lesions were examined. Methods: qPCR, Western blot and immunohistochemical analyses were performed on human post mortem CWM and MS lesions at different stages. Cultured astrocytes, derived from healthy subjects and MS patients, were analysed similarly. Results: Among 11 different galectins tested, galectins-1, -3, -8 and -9 were present at detectable levels in CWM, and, interestingly, significantly enhanced in active MS lesions. On the cellular level, galectins localized to microglia/macrophages, astrocytes and endothelial cells. Intriguingly, galectin-9 displayed a distinctly different intracellular localization in microglia/macrophages when comparing active and inactive MS lesions, being restricted to the nuclei in active lesions, and primarily localizing in the cytoplasm in inactive lesions. Furthermore, enhanced levels of galectin-1, detected as dimers in Western blot analysis, were released by cultured astrocytes from MS patients. Conclusions: This study provides a detailed analysis of galectins in MS lesions and assigns distinct galectins to different aspects of the disease. Thus, besides being known as modulators of inflammatory processes, our findings suggest additional association of distinct galectins with MS pathology.

Functional characterization of mutations in the myosin Vb gene associated with microvillus inclusion disease.

Abstract: Objectives: Microvillus inclusion disease (MVID) is a rare autosomal recessive enteropathy characterized by intractable diarrhea and malabsorption. Recently, various MYO5B gene mutations have been identified in patients with MVID. Interestingly, several patients with MVID showed only a MYO5B mutation in 1 allele (heterozygous) or no mutations in the MYO5B gene, illustrating the need to further functionally characterize the cell biological effects of the MYO5B mutations. Patients and Methods: The genomic DNA of 9 patients diagnosed as having MVID was screened for MYO5B mutations, and quantitative polymerase chain reaction and immunohistochemistry on the material of 2 patients was performed to investigate resultant cellular consequences. Results: We demonstrate for the first time that MYO5B mutations can be correlated with altered myosin Vb messenger RNA expression and with an aberrant subcellular distribution of the myosin Vb protein. Moreover, we demonstrate that the typical and myosin Vb-controlled accumulation of Rab11a- and FIP5-positive recycling endosomes in the apical cytoplasm of the cells is abolished in MVID enterocytes, which is indicative of altered myosin Vb function. Moreover, we report 8 novel MYO5B mutations in 9 patients of various ethnic backgrounds with MVID, including compound heterozygous mutations. Conclusions: Our functional analysis indicates that MYO5B mutations can be correlated with an aberrant subcellular distribution of the myosin Vb protein, and apical recycling endosomes, which, together with the additional compound heterozygous mutations, significantly strengthen the link between MYO5B and MVID.

Differential effects of TNF (TNFSF2) and IFN-γ on intestinal epithelial cell morphogenesis and barrier function in three-dimensional culture.

Abstract: Background: The cytokines TNF (TNFSF2) and IFN gamma are important mediators of inflammatory bowel diseases and contribute to enhanced intestinal epithelial permeability by stimulating apoptosis and/or disrupting tight junctions. Apoptosis and tight junctions are also important for epithelial tissue morphogenesis, but the effect of TNF and IFN gamma on the process of intestinal epithelial morphogenesis is unknown. Methods/Principal Findings: We have employed a three-dimensional cell culture system, reproducing in vivo-like multicellular organization of intestinal epithelial cells, to study the effect of TNF on intestinal epithelial morphogenesis and permeability. We show that human intestinal epithelial cells in three-dimensional culture assembled into luminal spheres consisting of a single layer of cells with structural, internal, and planar cell polarity. Exposure of preformed luminal spheres to TNF or IFN gamma enhanced paracellular permeability, but via distinctive mechanisms. Thus, while both TNF and IFN gamma, albeit in a distinguishable manner, induced the displacement of selected tight junction proteins, only TNF increased paracellular permeability via caspase-driven apoptosis and cell shedding. Infliximab and adalumimab inhibited these effects of TNF. Moreover, we demonstrate that TNF via its stimulatory effect on apoptosis fundamentally alters the process of intestinal epithelial morphogenesis, which contributes to the de novo generation of intestinal epithelial monolayers with increased permeability. Also IFN gamma contributes to the de novo formation of monolayers with increased permeability, but in a manner that does not involve apoptosis. Conclusions: Our study provides an optimized 3D model system for the integrated analysis of (real-time) intestinal epithelial paracellular permeability and morphogenesis, and reveals apoptosis as a pivotal mechanism underlying the enhanced permeability and altered morphogenesis in response to TNF, but not IFN gamma.

Function of MRP1/ABCC1 is not dependent on cholesterol or cholesterol-stabilized lipid rafts

Abstract: MRP1 (multidrug-resistance-related protein 1)/ABCC1 (ATP-binding cassette transporter C1) has been localized in cholesterol-enriched lipid rafts, which suggests a role for these lipid rafts and/or cholesterol in MRP1 function. In the present study, we have shown for the first time that nearly complete oxidation of free cholesterol in the plasma membrane of BHK-MRP1 (MRP1-expressing baby hamster kidney) cells did not affect MRP1 localization in lipid rafts or its efflux function, using 5-carboxyfluorescein diacetate as a substrate. Inhibition of cholesterol biosynthesis, using lovastatin in combination with RO 48-8071, an inhibitor of oxidosqualene cyclase, resulted in a shift of MRP1 out of lipid raft fractions, but did not affect MRP1-mediated efflux in Neuro-2a (neuroblastoma) cells. Short-term methyl-β-cyclodextrin treatment was equally effective in removing free cholesterol from Neuro-2a and BHK-MRP1 cells, but affected MRP1 function only in the latter. The kinetics of loss of both MRP1 efflux function and lipid raft association during long-term methyl-β-cyclodextrin treatment did not match the kinetics of free cholesterol removal in both cell lines. Moreover, MRP1 activity was measured in vesicles consisting of membranes isolated from BHK-MRP1 cells using the substrate cysteinyl leukotriene C4 and was not changed when the free cholesterol level of these membranes was either decreased or increased. In conclusion, MRP1 activity is not correlated with the level of free cholesterol or with localization in cholesterol-dependent lipid rafts.