Hypoxia-induced phenotypic switch of fibroblasts to myofibroblasts through a matrix metalloproteinase 2/tissue inhibitor of metalloproteinase-mediated pathway: implications for venous neointimal hyperplasia in hemodialysis access.
Cuvinte cheie
Abstract
OBJECTIVE
Hemodialysis grafts fail because of venous neointimal hyperplasia formation caused by adventitial fibroblasts that have become myofibroblasts (ie, alpha-smooth muscle actin [SMA]-positive cells) and migrate to the neointima. There is increased expression of hypoxia-inducible factor (HIF)-1alpha in venous neointimal hyperplasia formation in experimental animal models and clinical samples. It was hypothesized that, under hypoxic stimulus (ie, HIF-1alpha), fibroblasts will convert to myofibroblasts through a matrix metalloproteinase (MMP)-2-mediated pathway.
METHODS
Murine AKR-2B fibroblasts were made hypoxic or normoxic for 24, 48, and 72 hours. Protein expression for HIF-1alpha, alpha-SMA, MMP-2, MMP-9, tissue inhibitor of metalloproteinase (TIMP)-1, and TIMP-2 was performed to determine the kinetic changes of these proteins. Immunostaining for alpha-SMA, collagen, and fibronectin was performed.
RESULTS
At all time points, there was significantly increased expression of HIF-1alpha in the hypoxic fibroblasts compared with normoxic fibroblasts (P < .05). There was significantly increased expression of alpha-SMA at all time points, which peaked by 48 hours in hypoxic fibroblasts compared with normoxic fibroblasts (P < .05). There was a significant increase in the expression of active MMP-2 by 48-72 hours and a significant increase in TIMP-1 by 48-72 hours by hypoxic fibroblasts (P < .05). By 72 hours, there was significant increase in TIMP-2 expression (P < .05). Immunohistochemical analysis demonstrated increased expression of alpha-SMA, collagen, and fibronectin as the duration of hypoxia increased.
CONCLUSIONS
Under hypoxic conditions, fibroblasts will convert to myofibroblasts through an MMP-2-mediated pathway, which may provide insight into the mechanism of venous neointimal hyperplasia.
