Sofie Nimmegeers

Role of the soluble guanylyl cyclase |[alpha]|1-subunit in mice corpus cavernosum smooth muscle relaxation

Soluble guanylyl cyclase (sGC) is the major effector molecule for nitric oxide (NO) and as such an interesting therapeutic target for the treatment of erectile dysfunction. To assess the functional importance of the sGCα1β1 isoform in corpus cavernosum (CC) relaxation, CC from male sGCα1−/− and wild-type mice were mounted in organ baths for isometric tension recording. The relaxation to endogenous NO (from acetylcholine, bradykinin and electrical field stimulation) was nearly abolished in the sGCα1−/− CC. In the sGCα1−/− mice, the relaxing influence of exogenous NO (from sodium nitroprusside and NO gas), BAY 41-2272 (NO-independent sGC stimulator) and T-1032 (phosphodiesterase type 5 inhibitor) were also significantly decreased. The remaining exogenous NO-induced relaxation seen in the sGCα1−/− mice was significantly decreased by the sGC-inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one. The specificity of the impairment of the sGC-related responses was demonstrated by the unaltered relaxations seen with forskolin (adenylyl cyclase activator) and 8-pCPT-cGMP (cGMP analog). In conclusion, the sGCα1β1 isoform is involved in corporal smooth muscle relaxation in response to NO and NO-independent sGC stimulators. The fact that there is still some effect of exogenous NO in the sGCα1−/− mice suggests the contribution of (an) additional pathway(s).

NO-insensitive sGCbeta1 H105F knockin mice: if NO has no place to go

Address: 1Department of Molecular Biomedical Biology, Faculty of Sciences, Ghent University, Gent, Belgium, 2Department of Molecular Biomedical Research, Molecular Pathology and Experimental Therapy Unit, VIB, Gent-Zwijnaarde, Belgium, 3Cardiovascular Research Center, Massachusetts General Hospital, Charlestown, USA, 4Department of General Physiology and Human Physiology and Pathophysiology, Ghent University, Gent, Belgium and 5Cardiovascular Research, Bayer Schering Pharma AG, Aprather Weg 18a, 42096 Wuppertal, Germany

Phenotypes of sGC mutant mice in basic conditions, disease and shock

To evaluate the role of sGC in physiology and pathogenesis, we generated sGCα1-/- mice and sGCβH105F knock in mice. The latter have a heme-less and hence NO-resistant sGC, and are a model for the situation in oxidative stress, where the sGC loses its sensitivity to NO. We observed that some of the phenotypic differences observed in sGCα1-/- are dependent on the genetic background while others are not. So, the gender-specific testosterone hypertension was obvious in male sGCα1-/- mice on a 129Sv background but not on a C57Bl/6 background, while the changes in relaxation of gastro-intestinal smooth muscle are identical in sGCα1-/- mice on both genetic backgrounds. Furthermore, while the presence of the sGCα2 β1 isoform is sufficient to retain NO responsiveness in a number of situations, the sGCα1β isoform seems to have exclusive roles. sGCβ1H105F mice show a reduced viability, anatomical abnormalities, growth retardation, and hypertension. The blood pressure is no longer sensitive to NO donor compounds or L-NAME but the action of the sGC activator BAY58-2667 was preserved, confirming the thesis that BAY58-2667 preferentially activates the heme-free form of sGC, also in vivo. The cardiovascular collapse in inflammatory shock (sepsis, anaphylaxis,...) is considered to depend on the NOS-2-sGC-cGK axis. However, except for NOS-3 dependent anaphylactic shock, which was partially inhibited in sGCα1-/- mice, various other forms of shock (LPS, TNF) were not attenuated in the absence of sGC, rather in contrast. In addition, we observed that in some situations, as much NOS-2 and NOS-2 derived NO is present as in lethal septic shock, without having hemodynamic consequences. These results imply that at least part of the protective properties of NO in shock are sGC dependent. They however also question the paradigm that the NO-sGC-cGK axis is the mediator of distributive shock. Indeed, we obtained evidence that some Reactive Oxygen Species might be an alternative candidate mediator, and might influence the NOS or sGC in shock.

Characterization of the effect of histamine on mouse corpus cavernosum

Widespread clinical use of H2-antagonists for treatment of peptic ulcer disease has been associated with reports of erectile failure [1]. Injections of histamine intracavernously in humans cause erection in all patients [2, 3]. This plus histamine-containing mastocytes being identifi ed in erectile tissue, indicate that histamine may play a role in penile erection [4]. However, mechanisms involved (whether on smooth muscle cells, endothelial control, neural activity or an action on receptors) are not fully established. Corpora cavernosa from New Zealand White rabbits showed only contraction following activation of H1-receptors [5] while in human corpora cavernosa variable responses have been demonstrated in vitro [2, 3]. Histamine-induced relaxation of human isolated corpora cavernosa has been reported to be only in part due to H2-receptor activation [3]. As mouse cavernosal tissue exhibits very similar characteristics to human tissue, it has been proposed as a suitable model for human tissue [6]. Therefore this study aimed to investigate the effect of histamine on activity of mouse corpora cavernosa.

Targeting the NO – cGMP pathway: phenotyping of NO-insensitive sGCbeta1 H105F knockin mice

Address: 1Department of Molecular Biology, Faculty of Sciences, Ghent University, Gent, Belgium, 2Department of Molecular Biomedical Research, Molecular Pathology and Experimental Therapy unit, VIB, Gent-Zwijnaarde, Belgium, 3Cardiovascular Research Center, Massachusetts General Hospital, Charlestown, USA and 4Department of General physiology and human physiology and pathopyphysiology, Ghent University, Gent, Belgium

In vitro and in vivo studies on the importance of the soluble gyanylyl cyclase alpha 1 subunit in penile erection

Purpose Soluble guanylyl cyclase (sGC), which plays a pivotal role in penile erection, is a heterodimer build up by an α and a β subunit. For both subunits two isoforms have been characterized, but only the sGCα1β1 and sGCα2β1 isoforms seem to be functionally active. To elucidate the functional role of the sGCα1β1 heterodimer in the mechanism of erection, experiments were performed in vivo and on isolated corpora cavernosa (CC) using sGCα 1 −/− mice.

NO-mediated vascular smooth muscle relaxation in sGCα1 knock-out mice

Background Nitric oxide (NO) is the active metabolite responsible for the relaxing influence of several endogenous and exogenous vasodilators. The predominant intracellular receptor for NO is soluble guanylyl cyclase (sGC), that consists of an α and a β subunit, each existing in 2 isoforms (α1/α2 and β1/β2). The α1β1 isoform is most abundantly expressed and widely distributed. We investigated the functional importance of the α1-subunit in vasorelaxations induced by endogenous NO and exogenous NOdonors.