Purpose: We recently reported that Vcsa1 is one of the most down-regulated genes in the corpora of rats in 3 distinct models of erectile dysfunction. Since gene transfer of plasmids expressing Vcsa1 or intracorporeal injection of its mature peptide product sialorphin into the corpora of aging rats was shown to restore erectile function, we proposed that the Vcsa1 gene has a direct role in erectile function. To determine if similar changes in gene expression occur in the corpora of human subjects with erectile dysfunction we identified a human homologue of Vcsa1 (hSMR3A) and determined the level of expression of hSMR3A in patients.
Materials and methods: hSMR3A was identified as a homologue of Vcsa1 by searching protein databases for proteins with similarity. hSMR3A cDNA was generated and subcloned into the plasmid pVAX to generate pVAX-hSMR3A. pVAX-hSMR3A (25 or 100 microg) was intracorporeally injected into aging rats. The effect on erectile physiology was compared histologically and by measuring intracorporeal pressure/blood pressure with controls treated with the empty plasmid pVAX. Total RNA was extracted from human corporeal tissue obtained from patients undergoing previously scheduled penile surgery. Patients were grouped according to normal erectile function (3), erectile dysfunction and diabetes (5) and patients without diabetes but with erectile dysfunction (5). Quantitative reverse-transcriptase polymerase chain reaction was used to determine the hSMR3A expression level.
Results: Intracorporeal injection of 25 microg pVAX-hSMR3A was able to significantly increase the intracorporeal pressure-to-blood pressure ratio in aging rats compared to age matched controls. Higher amounts (100 microg) of gene transfer of the plasmid caused less of an improvement in the intracorporeal pressure-to-blood pressure ratio compared to controls, although there was histological and visual evidence that the animals were post-priapitic. These physiological effects were similar to previously reported effects of intracorporeal injection of pVAX-Vcsa1 into the corpora of aging rats, establishing hSMR3A as a functional homologue of Vcsa1. More than 10-fold down-regulation in hSMR3A transcript expression was observed in the corpora of patients with vs without erectile dysfunction. In patients with diabetes associated and nondiabetes associated erectile dysfunction hSMR3A expression was found to be down-regulated.
Conclusions: These results suggest that hSMR3A can act as a marker for erectile dysfunction associated with diabetic and nondiabetic etiologies. Given that our previous studies demonstrated that gene transfer of the Vcsa1 gene and intracorporeal injection of its protein product in rats can restore erectile function, these results suggest that therapies that increase the hSMR3A gene and product expression could potentially have a positive impact on erectile function.