Novel role for endogenous hepatocyte growth factor in the pathogenesis of intracranial aneurysms

Abstract

Inflammation plays a key role in formation and rupture of intracranial aneurysms. Because hepatocyte growth factor (HGF) protects against vascular inflammation, we sought to assess the role of endogenous HGF in the pathogenesis of intracranial aneurysms. Circulating HGF concentrations in blood samples drawn from the lumen of human intracranial aneurysms or femoral arteries were compared in 16 patients. Tissue from superficial temporal arteries and ruptured or unruptured intracranial aneurysms collected from patients undergoing clipping (n=10) were immunostained with antibodies to HGF and its receptor c-Met. Intracranial aneurysms were induced in mice treated with PF-04217903 (a c-Met antagonist) or vehicle. Expression of inflammatory molecules was also measured in cultured human endothelial, smooth muscle cells and monocytes treated with lipopolysaccharides in presence or absence of HGF and PF-04217903. We found that HGF concentrations were significantly higher in blood collected from human intracranial aneurysms (1076±656 pg/mL) than in femoral arteries (196±436 pg/mL; P<0.001). HGF and c-Met were detected by immunostaining in superficial temporal arteries and in both ruptured and unruptured human intracranial aneurysms. A c-Met antagonist did not alter the formation of intracranial aneurysms (P>0.05), but significantly increased the prevalence of subarachnoid hemorrhage and decreased survival in mice (P<0.05). HGF attenuated expression of vascular cell adhesion molecule-1 (P<0.05) and E-Selectin (P<0.05) in human aortic endothelial cells. In conclusion, plasma HGF concentrations are elevated in intracranial aneurysms. HGF and c-Met are expressed in superficial temporal arteries and in intracranial aneurysms. HGF signaling through c-Met may decrease inflammation in endothelial cells and protect against intracranial aneurysm rupture.

Keywords: C-met; E-selectin; VCAM-1; hepatocyte growth factor; inflammation; intracranial aneurysm; subarachnoid hemorrhage.

Figure 1

Higher plasma levels of HGF in samples drawn from aneurysm lumens vs. femoral arteries. (* =p<0.05)

Figure 2

Examples of expression of c-Met and HGF in human superficial temporal arteries and intracranial aneurysms (ruptured and unruptured). Positive immunostaining for C-Met and HGF was noted in the endothelium and smooth muscle layers of the examined samples. Negative control excluded the primary antibody for c-Met or HGF. Similar findings were observed in tissues from 10 other patients. Scale bar=100μm.

Figure 3

Effect of a c-Met antagonist on intracranial aneurysm formation and rupture in mice. (A) Cerebral arteries and intracranial aneurysm in situ (left) and after dissection (right). Note the hemorrhage surrounding the aneurysm. Survival (B), systolic blood pressure (C), weight loss (D), aneurysm formation (E) and prevalence of subarachnoid hemorrhage (F) in sham controls (n=5), and after induction of aneurysms in mice treated with PF-04217903 (n=16) or vehicle (n=14). *=p<0.05 vs sham; ψ=P<0.05 vs baseline. ϕ=P<0.05 vs. vehicle.

Figure 4

Lower levels of VCAM-1 and E-selectin in HAECs incubated with HGF+LPS vs. LPS alone. Addition of c-Met antagonist abolishes the effect of HGF on inflammatory markers. (One-way ANOVA analysis; P=0.01 for VCAM-1 and P=0.036 for E-selectin)

Figure 5

Schematic figure of potential pathways by which HGF acts on cerebral endothelial cells to decrease the expression of adhesion molecules and inflammatory molecules such as E-selectin and VCAM-1. This attenuates the inflammatory response, stabilizes aneurysm walls, and prevents aneurysm rupture.