Kinetics of LFA-1 binding to ICAM-1 studied in a cell-free system

Integrin Regulators in Neutrophils

Neutrophils are the most abundant leukocytes in humans and are critical for innate immunity and inflammation. Integrins are critical for neutrophil functions, especially for their recruitment to sites of inflammation or infections. Integrin conformational changes during activation have been heavily investigated but are still not fully understood. Many regulators, such as talin, Rap1-interacting adaptor molecule (RIAM), Rap1, and kindlin, are critical for integrin activation and might be potential targets for integrin-regulating drugs in treating inflammatory diseases. In this review, we outline integrin activation regulators in neutrophils with a focus on the above critical regulators, as well as newly discovered modulators that are involved in integrin activation.

Ligation of ICAM-1 on human aortic valve interstitial cells induces the osteogenic response: A critical role of the Notch1-NF-κB pathway in BMP-2 expression

Calcific aortic valve disease (CAVD) is a chronic inflammatory condition and affects a large number of elderly people. Aortic valve interstitial cells (AVICs) occupy an important role in valvular calcification and CAVD progression. While pro-inflammatory mechanisms are capable of inducing the osteogenic responses in AVICs, the molecular interaction between pro-inflammatory and pro-osteogenic mechanisms remains poorly understood. This study tested the hypothesis that intercellular adhesion molecule-1 (ICAM-1) plays a role in mediating pro-osteogenic factor expression in human AVICs. AVICs were isolated from normal human aortic valves and cultured in M199 medium. Treatment with leukocyte function-associated factor-1 (LFA-1, an ICAM-1 ligand) up-regulated the expression of bone morphogenetic protein-2 (BMP-2) and resulted in increased alkaline phosphatase activity and formation of calcification nodules. Pre-treatment with lipopolysaccharide (LPS, 0.05μg/ml) increased ICAM-1 levels on cell surfaces and exaggerated the pro-osteogenic response to LFA-1, and neutralization of ICAM-1 suppressed this response. Further, ligation of ICAM-1 by antibody cross-linking also up-regulated BMP-2 expression. Interestingly, LFA-1 elicited Notch1 cleavage and NF-κB activation. Inhibition of NF-κB markedly reduced LFA-1-induced BMP-2 expression, and inhibition of Notch1 cleavage with a γ-secretase inhibitor suppressed LFA-1-induced NF-κB activation and BMP-2 expression. Ligation of ICAM-1 on human AVICs activates the Notch1 pathway. Notch1 up-regulates BMP-2 expression in human AVICs through activation of NF-κB. The results demonstrate a novel role of ICAM-1 in translating a pro-inflammatory signal into a pro-osteogenic response in human AVICs and suggest that ICAM-1 on the surfaces of AVICs contributes to the mechanism of aortic valve calcification.