Objective: 

Endothelial nitric oxide synthase (NOS-3) is crucial for endothelial cell (EC) function. The T-786C single nucleotide polymorphism (SNP) of the nos-3 gene constitutes a risk factor for coronary heart disease and rheumatoid arthritis in individuals homozygous for the C-variant of the gene. This increased risk is due to the fact that the expression of the C-variant of the nos-3 gene is less sensitive fluid shear stress (FSS), resulting in a reduced capacity to synthesise NO. The aim of this study was to investigate leukocyte-endothelial cell interactions in the light of this endothelial dysfunction.

Methods: 

Primary human umbilical cord vein endothelial cells were isolated and genotyped for the nos-3 geneT-786C SNP. The abundance of arachidonic acid (AA)-metabolizing enzymes was investigated by both real-time RT-PCR and Western blot analysis. For transmigration studies, the human monocytic cell line THP-1 and genotyped ECs exposed to FSS and subsequently seeded on filter inserts, were used. As readouts the number of transmigrated cells and pro-inflammatory gene expression were analysed in the THP-1 cells.

Results: 

Unexpectedly, exposure to FSS effectively reduced monocyte migration not only through TT but also through CC genotype ECs, in spite of their impaired NO formation. Consequently, (a) compensatory mechanism(s) must exist in CC cells. We hypothesised that AA metabolites may play a role therein, acknowledging their anti-inflammatory functions. Interestingly, cyclooxygenase-2, normally primarily expressed in a pro-inflammatory context and lipocalin-type prostaglandin D synthase (L-PGDS) were selectively FSS-induced in CC genotype ECs. Finally, siRNA-based blockade of L-PGDS significantly enhanced THP-1 cell migration through the CC genotype EC monolayer, suggesting that a product of this isomerase is responsible for the observed compensatory mechanism.

Conclusion: 

Despite an impaired NO synthesis capacity, CC genotype ECs reveal a robust FSS-dependent anti-inflammatory phenotype pointing towards compensatory mechanisms that include up-regulation of the COX-2/L-PGDS axis and, possibly, an enhanced release of the anti-inflammatory prostaglandins D₂ and J₂.