Abstract
Purpose: :
Peroxisome proliferator-activated receptors (PPARs) are nuclear membrane receptors that exist as three subtypes - a, b and g. PPARs are activated by a number of ligands, including naturally occurring fatty acids, NSAIDs, and prostaglandins. Of the three PPAR subtypes, PPAR-b appears to play a role in cell proliferation. The purpose of this study was to determine whether PPAR-b is pro-angiogenic in the retina.
Methods: :
In vitro, retinal Müller cells were subjected to normoxia or hypoxia for 24 hrs. Retinal microvascular endothelial cells (RMEC) were treated with and without VEGF for 24 hrs. Microarray analysis of PPAR-b-related genes was performed. Müller cells were treated with a PPAR-b inhibitor, sulindac sulfide (SS), or with siRNA directed against PPAR-b, and hypoxia-induced VEGF production was measured. RMEC were treated with SS, or with PPAR-b-directed siRNA, and VEGF-induced proliferation and tube formation were measured. RMEC were treated with cPGI, a stable analog of PGI2 (a known ligand for PPAR-b), and PPAR-b activation was measured. In vivo, rats were subjected to OIR, treated with SS, and neovascular (NV) area was measured.
Results: :
Hypoxic Müller cells and VEGF-treated RMEC demonstrated a significant increase (p = 0.01) in PPAR-b expression. Expression of adipose differentiation-related protein (ADRP), a protein exclusively regulated by PPAR-b, demonstrated a 6-fold increase in hypoxic Müller cells. SS and PPAR-b-directed siRNA resulted in dose-dependent inhibition of hypoxia-induced VEGF production in Müller cells and VEGF-induced proliferation (p= 0.005) and tube formation in RMEC. RMEC treated with cPGI demonstrated a 3.5-fold increase in PPAR-b activation, measured by ADRP expression. In OIR rats, SS demonstrated a dose-dependent reduction in NV area that reached 50%.
Conclusions: :
In vitro, inhibiting PPAR-b led to both an inhibition of Müller cell and RMEC angiogenic cell behaviors, suggesting that it may play multiple roles in regulating angiogenesis. In vivo, PPAR-b inhibition reduced pathological retinal NV. These findings suggest that PPAR-b may constitute a novel and rational target for chemotherapeutic intervention in ocular angiogenesis.
Keywords: retinal neovascularization • transcription factors • vascular endothelial growth factor