TNF-α and IL-1β Increase Pericyte/Endothelial Cell Co-Culture Permeability

Abstract

Pericytes (PC) have a unique synergistic relationship with microvascular endothelial cells (MVEC) in the regulation of capillary permeability. This study investigates the effect of TNF-alpha, IL-1beta, and IL-6 on the microvasculature by measuring changes in PC contractility, and also, albumin permeability across MVEC/PC co-cultures. Semi-permeable inserts were plated first with rat lung MVEC and then PCs (on the fourth day) at a ratio of 10:1 MVEC/PC. On day 5, 50 ng/ml of TNF-alpha, IL-1beta, and IL-6 were added with or without a secretory phospholipase A(2)-IIA (sPLA(2)-IIA) inhibitor for 24 h. After treatments, albumin clearances were quantified. For measuring contractility, PCs were cultured on collagen matrices and exposed for 24 h to TNF-alpha, IL-1beta, and IL-6 at 1 ng/ml, 10 ng/ml, and 50 ng/ml with/without inhibitors for sPLA(2)-IIA, phospholipase A(2) (PLA(2)), and cyclooxygenase-II (COX-II). After treatments, the surface area of the collagen disks was digitally quantified. TNF-alpha and IL-1beta significantly increased albumin clearance in MVEC/PC co-cultures (P < 0.05) and induced dose-dependent relaxation of PCs (P < 0.05). PC relaxation was completely attenuated with the sPLA(2)-IIA and pLA(2) inhibitors; the COX-II inhibitor provided partial blockade. IL-6 had no effect on PC contractility or permeability. TNF-alpha and IL-1beta directly increased microvascular permeability in co-cultures. They also induced relaxation of PCs through a sPLA(2)-IIA dependent mechanism. Interestingly, IL-6 had no effect, although its presence in high levels has been demonstrated in inflamed lungs. These findings may help elucidate the significance of PC in regulating the capillary response to various pro-inflammatory cytokines.