Alterations in angiogenic growth factors and neuronal nitric oxide synthase expression in chronic cavernosal ischemia

Abstract

Our aim was to study anatomical and molecular changes at varying time points after the induction of cavernosal ischemia (CI) in a rabbit model of arteriogenic erectile dysfunction. Tissue structure and the expression of angiogenic and neurogenic genes were examined using immunostaining and reverse transcription-polymerase chain reaction (RT-PCR) analyses. We found a progressive increase of erectile connective tissue together with a decrease in smooth muscle cell content as the duration of CI increased. Immunohistochemical staining showed an increase in vascular endothelial growth factor (VEGF) levels at the early stages and a decrease at the later stages of ischemia. RT-PCR analysis of VEGF and neuronal nitric oxide synthase (nNOS) confirmed these results and showed nearly a two-fold increase in VEGF and nNOS mRNA levels in the early stages of CI with a decrease at the later stages of CI. On the other hand, mRNA levels of VEGF receptor, KDR, decreased approximately by 50% over the course of CI. Our studies showed that the cellular and molecular responses of the erectile tissue to short-term ischemia are different than those seen after long-term ischemia. The dramatic reduction in KDR expression suggests that the cavernosal endothelium is very sensitive to ischemia. The similar changes in VEGF and nNOS expression over the course of CI suggest a tissue-defensive mechanism to CI via the VEGF and NO pathways. Taken together, this study suggests that supplementation of VEGF at earlier stages of ischemia may restore the damaged endothelial cells of the corpus cavernosum and support tissue perfusion.

Oxidative Stress and Molecular Reactions in Arteriogenic Erectile Dysfunction

“…1). 29 The nNOS levels then gradually decrease significantly in a time-dependent manner over the course of ischemia (Fig. 1).…”

“…The number of ischemic endothelial cells that stained positively for VEGF was similar to the controls. 29 Semi-quantitative RT-PCR analyses of rabbit erectile tissue have shown that VEGF gene expression initially increases in response to ischemia and then it gradually decreases over the course of ischemia reaching to a level significantly lower than the levels of the early stages of ischemia (Fig. 1).…”

“…1). 29 The initial upregulation of nNOS in the ischemic erectile tissue may be a physiologic defense mechanism to maintain NO levels; however, it seems to fail after long-term exposure to ischemia. …”

“…29 Immunohistochemical analysis with anti-VEGF antibodies have shown that positively stained areas within the corpus cavernosum are greater in the early stages of cavernosal ischemia in comparison to age-matched controls. 29 After long-term ischemia, however, the VEGF-positive stained areas within the corpus cavernosum were found to dramatically diminish. The number of ischemic endothelial cells that stained positively for VEGF was similar to the controls.…”

“…12,29,30 HIF upregulation may be a primary reaction to ischemia that appears to regulate other hypoxia sensitive genes in the penis. These molecular reactions lead to profound changes in erectile tissue structure and function and may play a central role to the pathophysiology of arteriogenic ED.…”