Inhibition of proNGF pathway restores erectile function through dual angiogenic and neurotrophic effects in the diabetic mouse
Patients with diabetic erectile dysfunction (ED) usually respond poorly to oral PDE5 inhibitors due to a lack of bioavailable nitric oxide from severe endothelial and neural dysfunction. ProNGF and its receptor p75NTR are known to be up-regulated in diabetic condition and to induce endothelial cell apoptosis and neuronal degeneration. The aim of this study was to investigate effectiveness of anti-proNGF neutralizing antibody (proNGF-Ab) in restoring erectile function in streptozotocin-induced diabetic mouse.
Diabetes was induced by intraperitoneal injection of streptozotocin (50 mg/kg) into 8-week-old C57BL/6 male mice for 5 consecutive days. At 8 weeks after the induction of diabetes, the animals were distributed into 3 groups: controls, streptozotocin-induced diabetic mice receiving repeated intracavernous injections of PBS (days -3 and 0; 20 µL) or proNGF-Ab (days -3 and 0; 20 µg in 20 µL of PBS). We measured erectile function by electrical stimulation of the cavernous nerve at 2 weeks after treatment. The penis was harvested and stained with antibodies to proNGF, CD31, VE-cadherin, and βIII-tubulin. We also performed TUNEL assay and Western blot analysis for p75NTR.
The cavernous expression of proNGF and p75NTR was up-regulated in diabetic mice. Local delivery of proNGF-Ab into the corpus cavernosum of diabetic mice was effective to neutralize proNGF and profoundly down-regulated expression of p75NTR. Intracavernous injection of proNGF-Ab induced significant restoration of erectile function in diabetic mice, which reach up to 90-100% of control values. ProNGF-Ab significantly increased cavernous endothelial cell content and endothelial cell-cell junction proteins; decreased endothelial cell apoptosis; and restored neuronal cell content in the cavernous tissue of diabetic mice.
Our findings suggest that inhibition of proNGF pathway is a promising therapeutic strategy for diabetic ED.
Funding: This research was supported by a grant of the Korean Health Technology R&D Project, Ministry of Health & Welfare, Republic of Korea (Ji-Kan Ryu, HI15C0508) and The National Research Foundation of Korea(NRF) funded by the Ministry of Education (Kang-Moon Song, 2017R1A6A3A11030261).