Question:

Individuals homozygous for the T-786C SNP of the endothelial nitric oxide (NO) synthase gene have an increased risk to contract coronary heart disease due to the relative insensitivity of the C-variant to fluid shear stress (FSS) resulting in a reduced NO synthesis capacity. However, there are at least two mechanisms by which this genetically determined dysfunction can be overcome, one of which was investigated herein.

Methods:

Human umbilical vein endothelial cells (EC) were genotyped for the T-786C SNP, and CC genotype cells were compared to TT genotype ECs throughout. Expression of arachidonic acid-metabolizing enzymes was investigated by both quantitative PCR and Western blot analysis. 15-Deoxy-D12,14-prostaglandin J₂ (15d-PGJ₂) released was determined by EIA. Human monocytic THP-1 cells were employed to interact with the CC or TT genotype ECs.

Results:

Exposing the ECs to FSS effectively reduced THP-1 cell migration not only through TT but also through the NO-deficient CC genotype cells, pointing to the existence of a compensatory mechanism. Both cyclooxygenase-2 and lipocalin-type prostaglandin D synthase (L-PGDS) expression was up-regulated by FSS solely in CC genotype ECs, and siRNA-mediated down-regulation of L-PGDS significantly enhanced THP-1 cell migration through the CC genotype EC monolayer. Moreover, only these cells released 15d-PGJ₂, the ultimate metabolite of the L-PGDS pathway, in response to FSS, and 15d-PGJ₂ effectively abrogated pro-inflammatory activation of the THP-1 cells.

Conclusions:

Despite a reduced capacity to form NO, CC genotype ECs reveal a robust anti-inflammatory phenotype due to an up-regulation of 15d-PGJ₂ synthesis in response to FSS. Its inhibitory effect on e.g. interleukin-1b expression in monocytes is not mediated by one of the classical fatty acid signalling mechanisms but involves the activation of an as yet unidentified inhibitory transcription factor.