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Sources of Funding: supported by MW (Ji-Kan Ryu, HI15C0508), Republic of Korea.

Introduction

Patients with diabetic erectile dysfunction (ED) often have severe endothelial dysfunction, which results in poor response to oral phosphodiesterase-5 inhibitors. Dickkopf-3 (DKK3), originally reported to interact Wnt signaling pathway during embryonic development, is known to involve in the endothelial cell proliferation. However, the role of DKK3 in ED is as yet not reported. The aim of this study was to investigate whether and how DKK3 gene or peptide restores erectile function in diabetic mice.

Methods

Eight-week-old C57BL/6 mice were used, and diabetes was induced by intraperitoneal injection of streptozotocin. At 8 weeks after the diabetes induction, the efficacy of DKK3 peptide or gene were determined by three independent experiments: Experiment 1 (DKK2 peptide; Control, DM + PBS, DM + DKK3 peptide [5 μg/20 μL]); Experiment 2 (DKK2 plasmid DNA with electroporation; Control, DM + empty vector (100 μg/20 μL), DM + DKK3 plasmid (10 μg, 40 μg, or 100 μg/20 μL, respectively); and Experiment 3 (DKK3 adenovirus; Control, DM + PBS, DM + Ad-GPF (1 x 10⁹ vp/20 μL), DM + Ad-DKK3 (1 x 10⁷, 1 x 10⁸, 1 x 10⁹ vp/20 μL, respectively). One (peptide) or two weeks (gene) after treatment, we measured erectile function by electrical stimulation of the cavernous nerve. The penis was then harvested for histologic examination. We also determined angiogenic activity of DKK3 in primary cultured mouse cavernous endothelial cells (MCECs).

Results

The protein expression of DKK3 was significantly lower in cavernous tissue of diabetic mice than in controls. Intracavernous injection of DKK3 peptide or gene partially restored erectile function in diabetic mice, which reached up to 70-80% of the control values. DKK3 significantly restored cavernous endothelial cell content and endothelial cell-cell junction proteins (ZO-1 and claudin-5) in diabetic mice. Treatment of MCECs with DKK3 peptide significantly increased the expression of basic fibroblast growth factor and angiopoietin-1, which accelerated tube formation and endothelial migration, and restored integrity of the endothelial cell-cell junction.

Conclusions

DKK3 restored erectile function in diabetic mouse through the restoration of cavernous endothelial cells and the integrity of endothelial cell-cell junction. Therapeutic cavernous endothelial regeneration by use of DKK3 may provide a good opportunity for treating ED from vascular causes.

Funding

supported by MW (Ji-Kan Ryu, HI15C0508), Republic of Korea.