Current and emerging clinical research studies suggest that the penile vascular bed is a sensitive indicator of early vascular dysfunction, i.e., ED is an early clinical manifestation of generalized vascular disease and carries an independent risk for cardiovascular events. Tumor necrosis factor-alpha (TNF-1), a pro- inflammatory cytokine, is an important contributor to many cardiovascular diseases (hypertension, diabetes and metabolic disorders). TNF-1 levels are also increased in patients with erectile dysfunction (ED) (with or without cardiovascular disease), but so far no study has addressed the role of TNF-1 on erectile (dys)function. This project proposes to investigate the effects of TNF-1 on erectile function and how TNF-1 leads to hypertension-associated ED. More specifically, we will test the hypothesis that the pro-inflammatory cytokine TNF-1 increases contractile responses of cavernosal smooth muscle cells and plays a direct role in hypertension-associated ED.
Three specific aims are proposed, all providing a definition of the specific mechanisms by which TNF-1 increases cavernosal contractile responses and leads to eretile dysfunction:
Specific aim 1 : To test the hypothesis that TNF-1 enhances the constrictor sensitivity of cavernosal smooth muscle cells, leading to impaired erectile function.
Specific aim 2 : To test the hypothesis that decreased NO bioavailability and augmented RhoA/Rho kinase signaling provide mechanisms for impaired erectile function associated with increased TNF-1 levels.
Specific aim 3 : To test the hypothesis that TNF-1 plays a major role in ED associated with salt-sensitive hypertension and that TNF-1 effects are partially mediated by increased ET-1 expression. The proposed studies, integrating physiological, pharmacological, biochemical, molecular and cellular techniques, will help to better understand the effects of TNF-1 on penile function, as well as the contribution of abnormal TNF-1 levels to functional vascular changes associated with erectile dysfunction. Identification of causal factors and mechanisms responsible for increased vascular content of TNF-1 in ED and cardiovascular disease may advance disease treatment. Since cardiovascular diseases and ED are a major public health challenge worldwide and are being fueled mainly by increasing obesity and ageing of the population, our proposal is very much in accordance with the mission of the NIH.
Thirty million men in the United States suffer from ED and this number is expected to double by 2025. Considered a major public health problem, which seriously affects the quality of life of patients and their partners, ED becomes increasingly prevalent with age. In addition, an undetermined number of women also suffer from sexual dysfunction based on many of the same etiologies. A wide variety of therapeutic options are available for the treatment of ED, including vacuum therapy, intracavernous and transurethral drug therapy, surgery, and recently developed oral medications. Unfortunately, despite these options, ED persists in many patients. Sildenafil and other PDE-5 inhibitors have been successful in the treatment of many forms of ED, but often, patients fail to benefit from use of these agents. Furthermore, patients with cardiovascular disease very often are under nitrate therapy, which precludes the use of PDE-5 inhibitors. The studies outlined in this proposal aim to determine how TNF-alpha, a pro-inflammatory cytokine whose levels are elevated in plasma from patients with cardiovascular diseases and ED, changes cavernosal reactivity and leads to ED. Understanding the components of the signaling pathways activated by cytokines and how they link together is necessary for a complete comprehension of the mechanisms leading to ED. Thus, this work will greatly assist in a better understanding of mechanisms of erectile disease, as well as in the identification of novel and more efficacious therapeutic options for restoration of erectile function.
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