MEK inhibition exerts temporal and myeloid cell-specific effects in the pathogenesis of neurofibromatosis type 1 arteriopathy

Mutations in the NF1 tumor suppressor gene are linked to arteriopathy. Nf1 heterozygosity (Nf1+/–) results in robust neointima formation, similar to humans, and myeloid-restricted Nf1+/– recapitulates this phenotype via MEK-ERK activation. Here we define the contribution of myeloid subpopulations to NF1 arteriopathy. Neutrophils from WT and Nf1+/– mice were functionally assessed in the presence of MEK and farnesylation inhibitors in vitro and neutrophil recruitment to lipopolysaccharide was assessed in WT and Nf1+/– mice. Littermate 12–15 week-old male wildtype and Nf1+/– mice were subjected to carotid artery ligation and provided either a neutrophil depleting antibody (1A8), liposomal clodronate to deplete monocytes/macrophages, or PD0325901 and neointima size was assessed 28 days after injury. Bone marrow transplant experiments assessed monocyte/macrophage mobilization during neointima formation. Nf1+/– neutrophils exhibit enhanced proliferation, migration, and adhesion via p21^Ras activation of MEK in vitro and in vivo. Neutrophil depletion suppresses circulating Ly6C^low monocytes and enhances neointima size, while monocyte/macrophage depletion and deletion of CCR2 in bone marrow cells abolish neointima formation in Nf1+/– mice. Taken together, these findings suggest that neurofibromin-MEK-ERK activation in circulating neutrophils and monocytes during arterial remodeling is nuanced and points to important cross-talk between these populations in the pathogenesis of NF1 arteriopathy.