Attenuated RhoA/Rho-kinase Signaling in Penis of Transgenic Sickle Cell Mice

Abstract

Objectives RhoA and its main downstream effector, Rho-kinase (ROCK) are important in maintaining the penis in the flaccid state. The pathophysiology of Sickle cell disease-associated priapism is not well defined. We hypothesize that RhoA/ROCK vasoconstrictive pathways may be involved in the development of priapism. Therefore, the objective of this study was to evaluate molecular changes in RhoA and ROCK in an established transgenic sickle cell mouse model of priapism. Methods Two groups of mice were utilized: 1) wild type (WT; C57BL/6), and 2) transgenic Sickle cell mice (Sickle). We evaluated RhoA GTPase and total ROCK activities as well as ROCK1 and ROCK2 protein expression in WT and Sickle mice penes. We also evaluated in vivo erectile responses to cavernous nerve stimulation (CNS) and the frequency and duration of spontaneous erections both pre- and post-CNS. Results Sickle mice demonstrated significantly (p<0.05) enhanced erectile responses to CNS and frequency of spontaneous erections both pre- and post-CNS when compared to WT. Sickle mice penes had a significant decline in RhoA GTPase (p<0.01) and total ROCK activities (p<0.05) when compared to WT mice. There was a significant (p<0.05) reduction in ROCK2 protein expression in Sickle mice penes when compared to WT mice protein expression. No change in ROCK1 protein expression was observed in both cohort’s of mice penes. Conclusion These data suggest that Sickle cell disease associated-priapism may be contributed by a lack of RhoA/ROCK mediated vasoconstriction and highlight a novel molecular mechanism in the pathophysiology of priapism.

Molecular Analysis of Erection Regulatory Factors in Sickle Cell Disease Associated Priapism in the Human Penis

“…It has been well established that the Rho pathway, consisting of RhoA and its downstream effector, ROCK (with two isoforms, ROCK1 and ROCK2), plays a major role in maintaining the penis in its flaccid state through vasoconstriction and eNOS regulation 25, 26 . In fact, recently, Bivalacqua et al demonstrated that the RhoA/ROCK pathway is downregulated in the penis of SCD mice and thus contributes to uncontrolled cavernosal vasorelaxation producing priapism 11 . Specifically, they showed that the SCD mouse penis has a significant decline in both RhoA and total ROCK activities compared with that of the WT mouse penis.…”

“…Therefore, upon psychogenic or reflexogenic neuronal stimulation, prolonged erection occurs because of uncontrolled nNOS-dependent cGMP-induced vasodilation of the corpora cavernosa owing to deficient PDE5-specific cGMP hydrolysis 9 . More recently, priapism in SCD mice has also been shown to be associated with dysfunctional signaling of RhoA, and its downstream effector ROCK, which both mediate vasoconstriction of the penile vasculature 11 . In addition, dysregulation of opiorphin and adenosine signaling, as well as increased oxidative stress in the penis, are proposed contributory mechanisms based on experimental studies using animal models of priapism 11–16 .…”

“…More recently, priapism in SCD mice has also been shown to be associated with dysfunctional signaling of RhoA, and its downstream effector ROCK, which both mediate vasoconstriction of the penile vasculature 11 . In addition, dysregulation of opiorphin and adenosine signaling, as well as increased oxidative stress in the penis, are proposed contributory mechanisms based on experimental studies using animal models of priapism 11–16 .…”

Molecular Pathophysiology of Priapism: Emerging Targets

“…Bivalacqua et al reported that total ROCK activity in eNOS knock-out mice, which demonstrate a priapism phenotype, was reduced, with no change in RhoA activity [20]. Bivalacqua et al later reported attenuated RhoA/ROCK signaling in penes of transgenic SCD mice contributing to priapism [35]. Penes of SCD mice display a reduction in RhoA activity and specifically ROCK2 protein expression compared to that of the wild-type mouse penis.…”

How I treat priapism

“…Recognition of the roles of NO, RhoA/ROCK, adenosine, and opiorphins may lead to the development of future agents potentially targeting these molecular effectors. 39,[46][47][48]105,106 Strategies involving the use of PDE5 inhibitors to correct the underlying aberrations in NO balance have met with some success, as well as challenges regarding cost and patient adherence. [51][52][53]107 Preclinical investigations in animal models of SCD have uncovered alternative methods of restoring NO balance through the use of sustained NO-releasing compounds.…”