Reactive oxygen metabolites induce a biphasic contractile response in microvascular lung pericytes

Research advances in pericyte function and their roles in diseases

Pericyte, a kind of pluripotent cell, may regulate the irrigation flow and permeability of microcirculation. Pericytes are similar to the smooth muscle cells, which express several kinds of contractile proteins and have contractility. The dysfunction of pericytes is related to many microvascular diseases, including hypoxia, hypertension, diabetic retinopathy, fibrosis, inflammation, Alzheimer's disease, multiple sclerosis, and tumor formation. For a long time, their existence and function have been neglected. The distribution, structure, biomarker, related signaling pathways as well as the roles of pericytes on vascular diseases will be introduced in this review.

Bone marrow derived mesenchymal stem cells inhibit inflammation and preserve vascular endothelial integrity in the lungs after hemorrhagic shock

Hemorrhagic shock (HS) and trauma is currently the leading cause of death in young adults worldwide. Morbidity and mortality after HS and trauma is often the result of multi-organ failure such as acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), conditions with few therapeutic options. Bone marrow derived mesenchymal stem cells (MSCs) are a multipotent stem cell population that has shown therapeutic promise in numerous pre-clinical and clinical models of disease. In this paper, in vitro studies with pulmonary endothelial cells (PECs) reveal that conditioned media (CM) from MSCs and MSC-PEC co-cultures inhibits PEC permeability by preserving adherens junctions (VE-cadherin and β-catenin). Leukocyte adhesion and adhesion molecule expression (VCAM-1 and ICAM-1) are inhibited in PECs treated with CM from MSC-PEC co-cultures. Further support for the modulatory effects of MSCs on pulmonary endothelial function and inflammation is demonstrated in our in vivo studies on HS in the rat. In a rat “fixed volume” model of mild HS, we show that MSCs administered IV potently inhibit systemic levels of inflammatory cytokines and chemokines in the serum of treated animals. In vivo MSCs also inhibit pulmonary endothelial permeability and lung edema with concurrent preservation of the vascular endothelial barrier proteins: VE-cadherin, Claudin-1, and Occludin-1. Leukocyte infiltrates (CD68 and MPO positive cells) are also decreased in lungs with MSC treatment. Taken together, these data suggest that MSCs, acting directly and through soluble factors, are potent stabilizers of the vascular endothelium and inflammation. These data are the first to demonstrate the therapeutic potential of MSCs in HS and have implications for the potential use of MSCs as a cellular therapy in HS-induced lung injury.

Pericytes and their role in microvasculature homeostasis

BACKGROUND

The microvascular pericyte was first described in 1873, though it is a cell that has largely been ignored in the clinical literature. Pericytes are multifunctional, polymorphic, perivascular cells that lie within, and contribute to the production of the microvessel basil lamina.

MATERIALS

The pericyte is the second cell that comprises the capillary wall, and is in a prime location to be involved with microvascular permeability. The exact sequence of events in Acute Respiratory Distress Syndrome (ARDS) is unknown, though increased permeability (pulmonary edema) is the primary physiological abnormality seen in the early stages. Pericytes are crucial in the development of capillary leak and pulmonary edema seen in ARDS. Pericytes regulate permeability through contractility and apoptosis.

RESULTS

Changes in pericyte contractility alter the physical capillary barrier by opening the endothelial junctional space, and are reversible. Pericyte apoptosis leads to a compromise of the barrier effect of the capillary wall, and is a more permanent change.

CONCLUSIONS

The purpose of this paper is to review publications of pericyte physiological and pathophysiologic interactions in regards to contractility, apoptosis, and permeability.

Vascular endothelial growth factor modulates contractile response in microvascular lung pericytes

BACKGROUND

Pericytes are capillary support cells that may play a role in regulating permeability by their contractile responses. Vascular endothelial growth factor (VEGF) may play a role in the increased permeability found in sepsis and other inflammatory conditions. The purpose of this study was to evaluate the role of VEGF in regulating pericyte contraction.

METHODS

Rat microvascular lung pericytes were isolated according to previously described methods and cultured on collagen gel matrices. Cells were exposed to VEGF (10, 100, and 1000 pg/mL) for varying time periods (0, 10, 30, 60, and 120 minutes). The gels were released and their contractile responses digitally quantified.

RESULTS

At all doses, VEGF induced initial pericyte relaxation (contraction 85% to 90% of controls; P < .001). This was followed-up by increased and sustained contraction (107% to 120% of controls; P < .01).

CONCLUSIONS

VEGF modifies the contractile response of microvascular lung pericytes. This mechanism may play a role in the increased permeability demonstrated in inflammatory states.

The Roles of Cyclic Adenosine Monophosphate- and Cyclic Guanosine Monophosphate-Dependent Protein Kinase Pathways in Hydrogen Peroxide-Induced Contractility of Microvascular Lung Pericytes

BACKGROUND

Sepsis and posttraumatic inflammatory processes are accompanied by definite changes in microvascular permeability, particularly in the lung. These permeability changes may occur because of damaged regulatory mechanisms at the level of the capillary wall. Pericytes are adventitial cells located within the basement membrane of capillaries. These cells contain multiple cytoplasmic processes that envelope endothelial cells, and are consequently thought to stabilize capillary walls and participate in microcirculation and endothelial cell permeability. Data from this laboratory and other laboratories have confirmed that pericytes are contractile cells, adding to the evidence that pericytes may influence or help regulate capillary permeability. We have already determined that hydrogen peroxide (H2O2) causes dose-dependent relaxation in microvascular lung pericytes (MLPs) at 10 minutes and, conversely, dose-dependent contraction at 30 minutes. It is the aim of this study to determine the mechanism of this biphasic contractile response. Specifically, we will determine whether cyclic adenosine monophosphate (cAMP)- or cyclic guanosine monophosphate (cGMP)-dependent protein kinase intracellular pathways are responsible for the hydrogen peroxide-induced contractility of MLPs.

METHODS

Rat MLPs were isolated by previously published protocol and cultured on collagen gel matrices. MLPs were pretreated with either ODQ, a soluble guanylate cyclase inhibitor (100 mumol/L), for 15 minutes; GKIP, a protein kinase G inhibitor (100 mumol/L), for 1 hour; SQ22536, an adenylate cyclase inhibitor (100 mumol/L), for 15 minutes; or H89, a protein kinase A inhibitor (10 mumol/L), for 1 hour. Hydrogen peroxide was then introduced to each MLP culture at 10 mumol/L, 100 mumol/L, and 1 mmol/L. After each of these treatments, the surface area of the collagen gels was digitally quantified at 10 and 30 minutes.

RESULTS

SQ22536 attenuated both relaxation at 10 minutes and the contraction seen at 30 minutes for all concentrations of H2O2. H89 caused a marked basal relaxation and prevented the cells from contracting at 30-minute exposures to all concentrations of H2O2. Both ODQ and GKIP attenuated the relaxation at 10 minutes but had no affect on the later contraction.

CONCLUSION

The cGMP-dependent protein kinase pathway is a mechanism for H2O2-induced relaxation of MLPs. Up-regulation of cAMP and cGMP is responsible for early H2O2-induced relaxation and late contraction. Protein kinase A (cAMP-dependent protein kinase pathway) may be an important intracellular signaling protein in the H2O2-induced contraction of MLPs or may be unable to down-regulate cAMP once inhibited. This evidence further supports the concept that there are separate intracellular pathways that regulate divergent cellular responses. This idea parallels the clinical concept of reversible and irreversible dysfunction of cellular processes in shock, and that the cellular dysfunction is initiated by separate intracellular pathways.