Abstract
Purpose::
Complications of diabetic retinopathy, such as macular edema, appear to be generated by multiple inflammatory factors that affect the retinal microcirculation. To elucidate the cell types and mechanisms underlying the therapeutic effects of glucocorticoids in this pathology, human retinal microvascular pericytes (HRMP), monocytes (THP-1), and retinal endothelial cells (HREC) were treated with TNF-α- or IL-1ß to induce an inflammatory phenotype, and protein secretion was measured in the presence or absence of dexamethasone (DEX).
Methods::
For cell characterization studies, cells were loaded with the fluorescent calcium indicator dye fluo-4 and then treated with VEGF-165, VEGF-121, PlGF, VEGF-E or PDGF-BB (1-100 ng/ml). A Fluorometric Imaging Plate Reader was used to measure changes in intracellular calcium. In order to confirm glucocorticoid receptor (GR) activation, an anti-phospho-Ser(211) antibody was used to detect phosphorylation-dependent nuclear translocation. In transrepression studies, cells were incubated for 5 hr (THP-1) or 24 hr (HRMP, HREC) with medium (control), TNF-α- (10 ng/ml) or IL-1ß (10 ng/ml), in the presence or absence of dexamethasone (10 nM-1 µM). The secretion of 89 pre-selected proteins was measured from each sample by a commercial vendor using a validated Luminex Multi-analyte Profile technology.
Results::
Consistent with the expected expression of growth factor receptors, calcium mobilization was induced in HREC by VEGF-165, VEGF-121, or VEGF-E, and in HRMP by PDGF-BB. Phosphorylation at Ser(211) on the GR, a marker of nuclear translocation, was observed in all three cell types with DEX treatment. Compared to control responses, TNF-α or IL-1ß induced a five-fold or more increase in several inflammation-associated proteins in each cell type. The number of mediators and extent of increased secretion were greatest in HRMP (≥ five-fold increase in 33 proteins with TNF-α and 29 proteins with IL-1ß). In HRMP and THP-1 cells, DEX inhibited the secretion of several inflammation-associated proteins in a dose-dependent manner. The IC-50 for DEX inhibition ranged from 2 nM for some proteins to 1 µM for others, and this differential effect was dependent on cell type and inflammatory stimulator.
Conclusions::
This is the first report of glucocorticoids inhibiting inflammation-associated protein secretion in retinal pericytes. In addition, the results suggest that delivering a high dose of dexamethasone (~1 µM or higher) to the vitreous may inhibit a broad range of pathologic mediators.
Keywords: corticosteroids • cytokines/chemokines • vascular cells