Galanin mediates endogenous nitrinergic nerve outgrowth in vitro and partially restores erectile function after cavernous nerve injury in vivo
Weyne, E1; Hannan, JL2; Matsui, H3; Sopko, N4; De Ridder, D5; Bivalacqua, TJ4; Van der Aa, F5; Albersen, M5
1: KU Leuven University and University Hospitals, Belgium; 2: East Carolina University, Department of Physiology, Greenville, United States of America; 3: University of Tokyo, Department of Urology, Tokyo, Japan; 4: Johns Hopkins, Brady Urological Institute, Baltimore,United States of America; 5: KU Leuven and University Hospitals, Department of Urology, Leuven, Belgium
Introduction and objectives: New therapies are needed to treat erectile dysfunction (ED) after radical prostatectomy (RP) due to cavernous nerve injury (CNI). Previously, we have shown that the neurotrophin galanin(gal) is 180-fold upregulated in the major pelvic ganglion (MPG) after CNI and mediates neurite outgrowth in a whole mount in-vitro nerve culture. Now, we investigate if exogenous administration of galanin restores erectile function in vivo and mediates neurite outgrowth of nitrinergic and sympathetic pelvic neurons in vitro.
Material and methods: Firstly, a dissociated nerve culture of the MPG was used with addition of 1µM galanin (non-selective gal agonist), 1µM M871(selective gal receptor 2 (galR2) antagonist) and vehicle. Differences in neurite outgrowth of nitrinergic and sympathetic neurons were measured after staining for nNOS and TH respectively. Secondly, rats were divided in 3 groups: sham (receiving a laparotomy without crush), CNI+vehicle (H2O), and CNI+galanin. H20 and M1145 (galR2 selective agonist, 3 µg/kg/day) were delivered subcutaneously via an osmotic pump (Alzet 2ML4). Four weeks later, erectile responses to CN electrostimulation (2,5V; 5V; 7,5V) were measured and qPCR was performed on the MPG and corpus cavernosum (CC) for nerve and structural markers. There was no washout period.
Results: Pharmacological stimulation with galanin did not significantly increase neurite outgrowth of nNOS- and TH-positive neurons compared to vehicle treatment. Inhibition of galanin signaling by M871, a galR2-specific antagonist resulted in significant decreased neurite outgrowth of nitrinergic (879µm vs 681 µm; p<0,05) but not of sympathetic neurons (6707pixels/neuron vs 6974pixels/neuron; p>0,05) compared to vehicle. In rats treated with M1145 (galanin R2 agonist), detectable doses were found in blood serum using mass spectrometry. Erectile responses (ICP/MAP) were significantly increased 4 weeks after CNI in the M1145 group compared to vehicle for all voltages (7,5V; 0,33 vs 0,11; p<0,01). No significant differences were found in expression of nNOS, TH and B3-tubulin in the MPG of vehicle and M1145-treated rats. A drastic increase of endogenous galanin gene expression was seen in vehicle and galanin group compared to non-nerve injured animals. No differences were found in the gene expression of nNOS, TH, aSMA, coll I and III in the CC of vehicle and M1145-treated rats.
Conclusion: In vivo treatment after CNI with a galanin agonist for 4 weeks resulted in a partial recovery of erectile function in rats. Differences in expression of structural muscular and neuronal markers by galanin treatment could not be detected. Inhibition of endogenous galanin signaling impairs nitrinergic but not sympathetic nerve outgrowth in vitro. Our results suggest the galanin pathway as an important mediator for endogenous neuroregeneration after CNI.
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