Direct evidence for cytokine involvement in neointimal hyperplasia

Tumor necrosis factor-alpha (TNF-alpha) and interleukin 1 (IL-1) are proximal inflammatory cytokines that stimulate expression of adhesion molecules and induce synthesis of other proinflammatory cytokines. In addition, TNF-alpha and IL-1 influence vascular smooth muscle cell migration and proliferation in vitro. In view of the inflammatory nature of neointimal hyperplasia (NIH), we tested the hypothesis that endogenous TNF-alpha and IL-1 modulate low shear stress-induced NIH.

Mice underwent unilateral common carotid artery (CCA) ligation. Low shear stress in the patent ligated CCA has previously been shown to result in remodeling and NIH. Reverse transcriptase-polymerase chain reaction for TNF-alpha and IL-1alpha mRNA demonstrated both TNF-alpha and IL-1alpha mRNA in ligated CCAs, whereas normal and sham-operated CCAs had none. Mice lacking functional TNF-alpha (TNF-/-) developed 14-fold less neointimal area than WT controls (P:<0.05). p80 IL-1 type I receptor knockout (IL-1RI-/-) mice tended to develop less (7-fold, P:>0.05) neointimal area than WT controls. Furthermore, no IL-1alpha mRNA expression was detected in CCAs from TNF-/- mice; however, TNF-alpha mRNA expression was found in the IL-1RI-/- mice. Mice that overexpress membrane-bound TNF-alpha but produce no soluble TNF-alpha display an accentuated fibroproliferative response to low shear stress (P:<0.05).

These results directly demonstrate that TNF-alpha and IL-1 modulate NIH induced by low shear stress. NIH can proceed by way of soluble TNF-alpha-independent mechanisms. Specific anti-TNF-alpha and anti-IL-1 therapies may lessen NIH.