Co-Regulation of Transcellular and Paracellular Leak Across Microvascular Endothelium by Dynamin and Rac

Abstract

Increased permeability of the microvascular endothelium to fluids and proteins is the hallmark of inflammatory conditions such as sepsis. Leakage can occur between (paracellular) or through (transcytosis) endothelial cells, yet little is known about whether these pathways are linked. Understanding the regulation of microvascular permeability is essential for the identification of novel therapies to combat inflammation. We investigated whether transcytosis and paracellular leakage are co-regulated. Using molecular and pharmacologic approaches, we inhibited transcytosis of albumin in primary human microvascular endothelium and measured paracellular permeability. Blockade of transcytosis induced a rapid increase in paracellular leakage that was not explained by decreases in caveolin-1 or increases in activity of nitric oxide synthase. The effect required caveolin-1 but was observed in cells depleted of clathrin, indicating that it was not due to the general inhibition of endocytosis. Inhibiting transcytosis by dynamin blockade increased paracellular leakage concomitantly with the loss of cortical actin from the plasma membrane and the displacement of active Rac from the plasmalemma. Importantly, inhibition of paracellular leakage by sphingosine-1-phosphate, which activates Rac and induces cortical actin, caused a significant increase in transcytosis of albumin in vitro and in an ex vivo whole-lung model. In addition, dominant-negative Rac significantly diminished albumin uptake by endothelia. Our findings indicate that transcytosis and paracellular permeability are co-regulated through a signaling pathway linking dynamin, Rac, and actin.

Barriers to drug delivery in solid tumors

“…Although ‘leakage’ of molecules through the vascular endothelium may occur through trans- and para-cellular pathways, 34 NPs generally bigger than 5–6 nm would not be able to cross healthy vessels characterized by a continuous endothelium. However, under pathological states like inflammation, infarcts and tumors, the endothelial lining tends to become more permeable leading to ‘gaps’ in the lining.…”

Dynamic interactions ofPlasmodiumspp. with vascular endothelium

“…7 Besides SFK, pathologic increases in transcytosis of albumin (transcellular leak) and paracellular leak are co-regulated by dynamin and Rac1. 8 In addition to albumin, transcytosis transports immunoglobulins, transferrin, aminopeptidase P and numerous other molecules. Microvascular endothelial cells can regulate permeability by both transcellular and paracellular routes except for brain microvascular endothelial cells that have few caveolae under basal conditions.…”

Palmitate-induced inflammatory pathways in human adipose microvascular endothelial cells promote monocyte adhesion and impair insulin transcytosis

“…Moreover, the access of insulin to its target tissues is markedly diminished in high-fat-fed dogs (16,27) and in diabetic humans (47), suggesting that endothelial cells play a crucial role in regulating insulin-induced glucose uptake. The delivery of proteins across the microvascular endothelium can in principle occur between (paracellular) or through (transcytosis) endothelial cells (3). Importantly the endothelium lining the microvasculature of muscle and adipose tissue is continuous in nature, with circumferential tight junctions and no gaps between cells.…”