The principal effectors of the two systems, angiotensin II and BK, exert opposing effects on vascular tone, with angiotensin II directly promoting VSMC contraction and BK indirectly causing vasodilation through BK receptor-mediated NO generation by vascular endothelial http://www.selleckchem.com/products/crenolanib-cp-868596.html cells. Despite the generally salutary effects of BK, it is clear that dysregulation of the KKS is associated with progression of the vascular and renal complications of diabetes mellitus (40). In the setting of endothelial denudation, BK can act directly on B1 and B2 bradykinin receptors expressed by VSMC to promote vasoconstriction in a manner similar to angiotensin II (13). The complex roles of the KKS in health and disease and its potential as a therapeutic target underscore the importance of understanding its mechanisms of action in vascular tissue.

Under normal physiologic conditions, VSMCs are not directly exposed to plasma PK due to the presence of an intact endothelial barrier. As we demonstrate, endothelial cells lack the ability to activate PK in the absence of factor XIIa generated through activation of the intrinsic clotting system (1,�C3). In contrast, we find that VSMCs, which could be exposed to PK in the setting of vascular injury and endothelial denudation, do not require exogenous clotting cascade factors to generate KK. Activation of plasma PK by VSMC does involve proteolysis, as incubation of PK with VSMC leads to the generation of cleaved PK fragments, which is similar to that produced when PK is activated by factor XIIa in a cell-free system (data not shown).

However, the identity of the VSMC protease(s) responsible for PK activation remains to be determined. Unlike endothelial cells, activation of PK by VSMC also does not require HMWK, which mediates the binding of PK to endothelial cell membranes, indicating that the mechanism of PK binding, as well as its cleavage/activation by VSMC is distinct from that employed by endothelial cells. Our data suggest that PK activation by VSMC initiates a cascade of signaling events leading to EGF receptor transactivation and activation of the ERK1/2 and JNK cascades that, ironically, involves neither BK or B1/B2 receptors. As depicted schematically in Fig. 8, PK binding to an as yet unknown PK activator on the surface of VSMCs generates KK. Among the substrates cleaved by KK are the N termini of PAR1/2.

One consequence of PAR activation is increased ADAM activity, specifically including ADAM17/TACE, which acts on cell surface EGF receptor ligand precursors, including AR, to trans-activate Batimastat EGF receptors, and on unprocessed TNF�� to enhance its release. Although it is likely that in vivo activation of PK on VSMC also leads to BK production and B1/B2 receptor activation, our results demonstrate a direct role for plasma KK in the activation of PAR1/2 and stimulation of pathways involved in the control of cell proliferation, apoptosis, and inflammation. FIGURE 8.