KRIT1-mediated regulation of neutrophil adhesion and motility.

Loss of Krev interaction-trapped-1 (KRIT1) expression leads to the development of cerebral cavernous malformations (CCM), a disease in which abnormal blood vessel formation compromises the structure and function of the blood-brain barrier. The role of KRIT1 in regulating endothelial function is well-established. However, several studies have suggested that KRIT1 could also play a role in regulating nonendothelial cell types and, in particular, immune cells. In this study, we generated a mouse model with neutrophil-specific deletion of KRIT1 in order to investigate the effect of KRIT1 deficiency on neutrophil function. Neutrophils isolated from adult Ly6G Krit1 mice had a reduced ability to attach and spread on the extracellular matrix protein fibronectin and exhibited a subsequent increase in migration. However, adhesion to and migration on ICAM-1 was unchanged. In addition, we used a monomeric, fluorescently-labelled fragment of fibronectin to show that integrin activation is reduced in the absence of KRIT1 expression, though β1 integrin expression appears unchanged. Finally, neutrophil migration in response to lipopolysaccharide-induced inflammation in the lung was decreased, as shown by reduced cell number and myeloperoxidase activity in lavage samples from Krit1 mice. Altogether, we show that KRIT1 regulates neutrophil adhesion and migration, likely through regulation of integrin activation, which can lead to altered inflammatory responses in vivo.