Inflammation and vascular injury: basic discovery to drug development.

The invited special lecture at the 76(th) Annual Scientific Meeting of the Japanese Circulation Society focused on the central role of inflammation in vascular injury and repair. Early studies pioneered the concept that mechanical injury, such as balloon angioplasty and endovascular stent deployment, elicits an inflammatory response from the vessel wall. This hypothesis was developed and substantiated at a time when the prevailing dogma viewed restenosis following angioplasty as a primarily proliferative smooth muscle cell disease. Antibody targeting of Mac-1 reduced leukocyte accumulation and limited neointimal formation following balloon injury or stent implantation. Genetic absence of Mac-1 resulted in diminished leukocyte accumulation and neointimal thickening after carotid artery injury in mice. In the course of those studies, our laboratory made fundamental discoveries regarding the mechanism of leukocyte recruitment at sites of vascular injury and identified platelet glycoprotein (GP) Ibα, a component of the GPIb-IX-V complex, as the previously unknown platelet counter-receptor for Mac-1. Follow-on studies have focused extensively on the structure, function, and signaling of the leukocyte integrin Mac-1. The binding site for GPIbα in Mac-1 has been mapped and subsequently showed that leukocyte engagement of platelet GPIbα via Mac-1 is critical not only for the biological response to vascular injury, but also for thrombosis, vasculitis, glomerulonephritis, and multiple sclerosis, thereby advancing the hypothesis that virtually all inflammation is platelet-dependent. Furthermore, ligand engagement of Mac-1 initiates a novel gene program that promotes inflammation by activating NFκB and downregulating the expression of the forkhead transcription factor Foxp1 that controls monocyte differentiation. Small molecule inhibitors of Mac-1 function have been pursued, including targeting of Mac-1-GPIbα binding or the downstream tyrosine kinase spleen tyrosine kinase. Drs Teruo Inoue, Koichi Node, Tatsuya Fukotomi, Masashi Sakuma, Toshifumi Morooka, and Kohsuke Nakajima, valued Japanese collaborators and post-doctoral fellows, have contributed enormously to these discoveries.