Background: Cells that comprise the pulmonary capillary walls, the pericytes and endothelial cells, may undergo apoptosis in inflammatory states. This study examined the effects of lipopolysaccharide (LPS) on apoptosis in pericytes and endothelial cells, both individually and grown together in a coculture system.
Methods: Pericytes and endothelial cells were isolated and cultured separately and in coculture as previously described. The cells were subsequently exposed to LPS for 12, 24, 48, and 72 hours. The cellular contents were then examined by Western blot analysis for products of apoptosis. TUNEL staining was also performed to analyze for apoptosis.
Results: Pericytes alone exposed to LPS showed increased levels of p11 and p17, which are activated fragments of capase-3, a cysteine effector protease involved in cleaving cytoskeletal and nuclear proteins to induce apoptosis. When grown in coculture with endothelial cells and exposed to LPS in coculture but harvested independently, pericytes showed decreased levels of p11 and p17 and increased levels of Bcl-xL, an antiapoptotic protein that protects the integrity of mitochondria, and prevents cytochrome c release and subsequent caspase-9 activation.
Conclusions: In response to LPS, pericytes undergo apoptosis involving the caspase-3 pathway. Endothelial cells may decrease this effect through the expression of a soluble mediator.
Copyright 2004 Elsevier Inc.