Increased Levels of Dickkopf 3 in the Aqueous Humor of Patients With Diabetic Macular Edema

PURPOSE: To investigate associations between diabetic macular edema (DME) and levels of the Wnt modulator Dickkopf 3 (DKK-3) in the aqueous humor (AH) of patients with DME and to analyze the clinical implications of this association. METHODS: Forty-four eyes of 39 patients with DME and 27 eyes of 27 controls were studied. Aqueous humor DKK-3 levels were measured by ELISA before the first intravitreal injection of bevacizumab (IVB). Visual acuity assessments and spectral-domain optical coherence tomography (SD-OCT) were performed before and 3 months after the first IVB. DKK-3 expression in high glucose-treated human Muller cells was examined by Western blot and immunofluorescence. Concentration of secreted DKK-3 in conditioned medium from human Muller cell cultures were analyzed by ELISA. RESULTS: ELISA showed increased DKK-3 levels in the eyes of DME patients compared with control subjects (median 207.86 ng/mL, range, 66.75-499.64 vs. 94.94 ng/mL, 33.34-164.45 ng/mL; P < 0.001). Based on multivariate analyses, elevated DKK-3 levels were associated with increased inner nuclear layer (INL) volume on SD-OCT before IVB. Western blot and immunofluorescence analyses showed higher DKK-3 expression in high glucose-treated Muller cells than in control cells, with DKK-3 secretion also being increased. CONCLUSIONS: DKK-3 expression was elevated in the AH of DME patients and in high glucose-treated human Muller cells. The observation of increased DKK-3 expression levels in the AH of DME patients with prominent edema in the INL suggests that the area of INL thickening might correlate with the area of reactive responses by Muller cells in these patients.