Summary
Conditioning of endothelial cells by shear stress suppresses their response to inflammatory
cytokines. We questioned whether signalling through different integrin-matrix interactions,
previously associated with the pathogenic effects of disturbed flow, supported the
anti-inflammatory action of steady shear. Primary human endothelial cells were cultured
on different substrates and exposed to shear stress (2.0Pa) for varying periods before
stimulation with tumour necrosis factor-α (TNF). Shear-conditioning inhibited cytokine-induced
recruitment of flowing neutrophils. However, the effect was similar for culture on
collagen, laminin or fibronectin, even when seeding was reduced to 2hours, and shear
to 3hours before TNF treatment (to minimise deposition of endothelial matrix). Nevertheless,
in short- or longer- term cultures, reduction in expression of β1-integrin (but not β3-integrin) using siRNA essentially ablated the effect of shear-conditioning on neutrophil
recruitment. Studies of focal adhesion kinase (FAK) phosphorylation, siRNA against
FAK and a FAK-inhibitor (PF573228) indicated that FAK activity was an essential component
downstream of β1-integrin. In addition, MAP-kinase p38 was phosphorylated downstream of FAK and also
required for functional modification. Mechanotransduction through β1-integrins, FAK and p38 is required for anti-inflammatory effects of steady shear
stress. Separation of the pathways which underlie pathological versus protective responses
of different patterns of flow is required to enable therapeutic modification or mimicry,
respectively.
Keywords
Endothelial cells - shear stress - integrin - inflammation