Pericytes Augment The Capillary Barrier In
In Vitro Cocultures
Dente CJ, Steffes CP, Speyer C, Tyburski JG
J Surg Res 2001 May 1;97(1):85-91
Wayne State University, Department of Surgery, Detroit, Michigan 48201, USA
Most in vitro studies of Capillary permeability focus on Endothelial Cell (MVEC) MonoLayers and ignore the second cell that forms the Capillary Wall: the MicroVascular Pericyte (PC).
We describe a model to study the permeability characteristics of MVEC, PC, and MVEC:PC cocultures.
Semipermeable culture inserts were coated with Collagen and then plated with early passage bovine pulmonary MVEC.
On Day 3, bovine pulmonary PC were added at concentrations to approximate MVEC:PC ratios of 1:1, 5:1, and 10:1.
Electrical resistance was measured on subsequent days and fluorescently labeled (FITC) Albumin was used in a permeability assay to calculate an Albumin clearance for each culture.
The results for electrical resistance measurements and Albumin assays showed a similar pattern.
Resistance for Endothelial Cell MonoLayers was significantly higher and Albumin permeability was significantly lower than that of controls.
Addition of Pericytes at a 10:1 and 5:1 ratios increased the Permeability Barrier compared to Endothelial Cells alone, although these cultures were not significantly different from one another.
Cocultures at a 1:1 ratio had the best barrier, significantly better than all other cultures.
Endothelial Cell MonoLayers are an inadequate model of the MicroCirculation.
As PC form a key component of the Capillary Wall in vivo and as addition of PC to MVEC monolayers in vitro, optimally at a 1:1 ratio, increase their barrier effect to large and small molecules.
We believe it is necessary to include both cells in future in vitro studies.
Copyright 2001 Academic Press.
Contractile Proteins In Pericytes At The Blood-Brain And Blood-Retinal Barriers
Bandopadhyay R, Orte C, Lawrenson JG, Reid AR, De Silva S, Allt G
J NeuroCytol 2001 Jan;30(1):35-44
Weston Institute of Neurological Studies, Windeyer Building, University College Medical School, Cleveland Street, London W1P 6DB, UK
Evidence from a variety of sources suggests that Pericytes have contractile properties and may therefore function in the regulation of Capillary blood flow.
However, it has been suggested that contractility is not a ubiquitous function of Pericytes, and that Pericytes surrounding true Capillaries apparently lack the machinery for contraction.
The present study used a variety of techniques to investigate the expression of contractile proteins in the Pericytes of the CNS.
The results of ImmunoCytoChemistry on CryoSections of Brain and Retina, Retinal whole-mounts and ImmunoBlotting of isolated Brain Capillaries indicate strong expression of the smooth muscle isoform of Actin (alpha-SM Actin) in a significant number of Mid-Capillary Pericytes.
ImmunoGold labelling at the ultrastructural level showed that alpha-SM Actin expression in Capillaries was exclusive to Pericytes, and Endothelial Cells were negative. Compared to alpha-SM Actin, non-muscle Myosin was present in lower concentrations.
By contrast, smooth muscle Myosin isoforms, were absent. Pericytes were strongly positive for the intermediate filament protein Vimentin, but lacked Desmin which was consistently found in Vascular smooth muscle cells.
These results add support for a contractile role in Pericytes of the CNS MicroVasculature, similar to that of Vascular smooth muscle cells.
Pericyte Migration From The Vascular Wall
In Response To Traumatic Brain Injury
Dore-Duffy P, Owen C, Balabanov R, Murphy S, Beaumont T, Rafols JA
MicroVasc Res 2000 Jul;60(1):55-69
Detroit Medical Center, Department of Neurology, MI 48201, USA
Any perturbation of the Blood-Brain Barrier, whether from changes in cell physiology or from direct injury, may result in MicroVascular Dysfunction and disease.
We examined, at the ultrastructural level, MicroVascular Pericyte responses in a well-defined model of Traumatic Brain Injury in the rat.
In areas close to the site of impact Cortical Pericytes underwent a number of changes within the first hour. Approximately 40% of Pericytes migrated from their MicroVascular location.
Migration occurred concomitant with a thinning of the Abluminal surface of the Basal Lamina and an accumulation of the Receptor for the Urokinase PlasMinogen Activator on the leading surface of the migrating cell.
Migrated Pericytes appeared viable and remained in a PeriVascular location in the adjacent Neuropil.
Nonmigrating Pericytes in the same section displayed Cytoplasmic alterations and Nuclear Chromatin changes consistent with a rapid degenerative process.
Copyright 2000 Academic Press.
Cellular Mechanisms Of CNS Pericytes
Rucker HK, Wynder HJ, Thomas WE
Brain Res Bull 2000 Mar 15;51(5):363-9
Meharry Medical College, Department of Anatomy and Physiology, Nashville, TN, USA
Three major functional roles have been ascribed to Pericytes associated with Central Nervous System MicroVasculature: Contractility, regulation of Endothelial Cell activity, and Macrophage activity.
A host of different cell factors and signalling agents appear to be involved with these cellular functions, some effecting the Pericyte and others produced by this cell.
These include NeuroModulators, Vasoactive Peptides, Metabolic Factors, Growth Factors and Cytokines.
The specific compounds and their actions are collectively viewed in an effort to provide an overall picture of the regulation of Pericyte functional activity.
This small Vascular Cell is emerging as a significant entity in several Physiological processes through the functions of above.
These processes include control of blood flow, regulation of Vascular development and Immune Responses. Defining the regulatory agents and their mechanisms is key to understanding the role that Pericytes play in these processes.
Because these cells have begun to receive increasing attention in NeuroBiological studies, an overview of signalling properties should be timely and beneficial.
Role Of Central Nervous System MicroVascular Pericytes In Activation Of Antigen-Primed Splenic T-Lymphocytes
Balabanov R, Beaumont T, Dore-Duffy P
J NeuroSci Res 1999 Mar 1;55(5):578-87
Wayne State University School of Medicine and Detroit Medical Center, Department of Neurology, Michigan 48201, USA
The cellular constituents of the Blood-Brain Barrier (BBB) must make finely tuned, regulatory responses to maintain MicroVascular Homeostasis.
The mechanisms by which this task is accomplished are largely unknown.
However, it is thought they involve a series of cross-talk mechanisms among Endothelial Cells (EC), Pericytes (PC), and Astrocytes.
During inflammation, the BBB is exposed to a number of biological response modifiers including Cytokines released by infiltrating Leukocytes.
The response to Inflammatory Cytokine may alter the normal regulatory function of EC and PC.
These changes may account for some of the pathological findings in Central Nervous System (CNS) Inflammatory Disease.
Previous studies have shown that PC and EC may have Immune potential. We have investigated the response of the PC to a variety of Inflammatory Cytokines.
Primary rat PC constitutively express low levels of InterCellular Adhesion Molecule-1 (ICAM-1) and Major Histocompatibility Complex (MHC) Class I molecule.
Which can be upregulated in response to the Cytokine Interferon-gamma (IFN-γ). IFN-γ also induced the expression of MHC Class II molecule.
After induction of MHC Class II molecule, CNS PC acquired the capacity to present Antigen to primed syngeneic rat T-Lymphocytes.
Antigen presentation by PC was comparable to that seen with classic Antigen-Presenting Cells.
A small number of primary PC constitutively express low levels of Vascular Cell Adhesion Molecule-1 (VCAM-1), which was increased on exposure to Tumor Necrosis Factor-alpha (TNF-).
Results suggest that CNS PC respond to Inflammatory Cytokines, are involved in T-Lymphocyte activation, and express cell surface Adhesion Molecules (VCAM-1, ICAM-1).
That may provide costimulatory activity. It is likely that CNS PC are important in NeuroImmune Networks at the BBB.
CNS MicroVascular Pericytes Express Macrophage-Like Function, Cell Surface Integrin alpha M, And Macrophage Marker ED-2
Balabanov R, Washington R, Wagnerova J, Dore-Duffy P
MicroVasc Res 1996 Sep;52(2):127-42
Wayne State University School of Medicine, Department of Neurology, Detroit, Michigan 48201, USA
CNS Pericytes are an integral part of the Blood-Brain Barrier (BBB), but their function is not well understood. We questioned whether primary cultured CNS Pericytes have Immune potential.
Primary cultured Pericytes exhibit Phagocytic activity when exposed to FluoroChrome-conjugated polystyrene beads and AntiBody-coated Zymosan. Maximum Phagocytic activity occurred by 3 hr.
Pericytes were found to express the Macrophage markers ED-2 and the Integrin subunit CD11b (alpha M) in culture as well as on isolated MicroVessels.
Pericytes did not express the Macrophage marker ED-1. We confirm the heterogeneity of cultured CNS Pericytes with regard to expression of alpha-smooth muscle Actin.
In conclusion, Pericytes express Macrophage surface Antigens and have the ability to perform at least some Immune function.
CNS Pericytes may therefore have a role in NeuroImmune Networks at the BBB.