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Pro-inflammatory sPLA2, integrins, and smoking

Institution: University of California, Davis
Investigator(s): Yoshikazu Takada, M.D., Ph.D.
Award Cycle: 2009 (Cycle 18) Grant #: 18XT-0169 Award: $250,000
Subject Area: Cardiovascular Disease
Award Type: Exploratory/Developmental Award

Initial Award Abstract
Background: Smoking is a prime factor in heart disease, stroke, and chronic lung disease, which cost the United States more than $150 billion a year. The relationship between smoking and cardiovascular disease is well documented, as is the association of smoking with increased blood levels of inflammatory markers and accelerated atherosclerosis. Blood levels of C-reactive protein (CRP) are positively associated with the number of cardiovascular risk factors. The secretory phospholipase A2 group IIA (sPLA2) is an inflammatory protein known to play a role in the pathogenesis of many inflammatory diseases. Recent studies have suggested that sPLA2 is critically involved in atherosclerosis formation. Notably the blood levels of CRP and those of sPLA2 correlate well in patients with coronary artery disease (CAD). Elevated levels of sPLA2 are associated with an increased risk of future CAD in apparently healthy individuals. Importantly, sPLA2 (and CRP) may indirectly play a role in inducing inflammation, but it also directly mediates atherosclerosis formation. The mechanism of pro-inflammatory action by sPLA2 has, however, not been fully established. sPLA2 breaks down the glyceroacyl phospholipids present in lipoproteins and cell membranes forming arachidonic acid, which is further metabolized into potent mediators for inflammation. However, some biological effects of sPLA2 are independent of its action to break down phospholipids, suggesting that they are mediated by sPLA2 binding to specific receptors on the cell surface. The sPLA2 receptor in human has not been established.

Preliminary studies: We recently discovered that human sPLA2 specifically binds to cell surface receptor proteins (called integrins). We generated a sPLA2 mutant that is defective in binding to the receptors. Notably, we showed that sPLA2 induced cell proliferation and proliferative signaling in monocytic cells, which play a key role in atherosclerosis formation. This process required the receptors (integrins) since the sPLA2 mutant, which can not bind to the receptors, did not induce cell proliferation or signals.

Hypothesis: We hypothesize that the receptors (integrins) mediate pro-inflammatory signals by sPLA2, and that sPLA2-integrin interaction is a novel therapeutic target for inflammation and atherogenesis. If this is the case we will be able to suppress inflammation and atherosclerosis by inhibiting sPLA2 binding to the receptors (integrins).

Research design: To address this hypothesis, we propose to: 1) Test if sPLA2 binding to integrins induces known pro-inflammatory action (e.g., production of cytokines and other proteins) in monocytic cells. 2) Identify the signaling events induced by sPLA2- integrin interaction to cell proliferation and gene expression in monocytic cells.

Expected results: The proposed project will determine if the known sPLA2-induced pro-inflammatory actions are mediated by the binding of sPLA2 to receptors and subsequent signaling processes, and identify components in the signaling pathways that are involved in this process. The proposed project will establish that sPLA2-integrin interaction is a critical component of pro-inflammatory sPLA2 signaling, and that sPLA2-integrin interaction is a novel target for drug discovery. Based on the information obtained by the proposed project, we will be able to screen for drugs that block sPLA2 binding to the receptors (integrins), which we expect to inhibit inflammation and atherosclerosis formation induced by sPLA2, in future experiments.