Paul Fransen

Cardiac endothelium and myocardial function

Endocardial endothelium and vascular endothelium of myocardial capillaries share common features as modulators of cardiac performance, rhythmicity and growth. Growing evidence suggests differences between these two cardiac endothelial cell types with regard to developmental, morphological and functional properties. A major difference probably resides in the way and extent by which these endothelial cells perceive and transmit signals.

Neuregulin-1 Induces a Negative Inotropic Effect in Cardiac Muscle Role of Nitric Oxide Synthase

Background—Deficient cardiac neuregulin/ErbB signaling increases susceptibility to heart failure. In this study, we examined the effects of neuregulin-1 (NRG-1) on myocardial contractility. Methods and Results—NRG-1 (&agr; and &bgr; isoforms) induced a negative inotropic effect in isolated rabbit papillary muscles and a rightward shift of the dose-response curve to isoproterenol. Both effects were attenuated by L-NMMA, which suggests a role for NO synthase. In cultured rat cardiomyocytes, NRG-1&bgr; enhanced nitrite production and resulted in phosphorylation of endothelial NO synthase and the serine/threonine kinase Akt. Conclusions—NRG-1 has negative inotropic effects that are preserved during &bgr;-adrenergic stimulation and activates endothelial NO synthase in cardiomyocytes.

Elastin fragmentation in atherosclerotic mice leads to intraplaque neovascularization, plaque rupture, myocardial infarction, stroke, and sudden death

Our study underscores the importance of elastin fragmentation in the vessel wall as an accelerator of atherosclerosis with enhanced inflammation and increased neovascularization, thereby promoting the development of unstable plaques that eventually may rupture. The present mouse model offers the opportunity to further investigate the role of key factors involved in plaque destabilization and potential targets for therapeutic interventions.

Vasodilator efficacy of nitric oxide depends on mechanisms of intracellular calcium mobilization in mouse aortic smooth muscle cells

Background and purpose:  Reduction of intracellular calcium ([Ca2+]i) in smooth muscle cells (SMCs) is an important mechanism by which nitric oxide (NO) dilates blood vessels. We investigated whether modes of Ca2+ mobilization during SMC contraction influenced NO efficacy.

The cardiac endothelium: functional morphology, development, and physiology.

Cardiac endothelial cells, regardless of whether they are from endocardial or from coronary (micro)vascular origin, directly modulate performance of the subjacent cardiomyocytes, resulting in control of the onset of ventricular relaxation and rapid filling of the heart. This review summarizes major features of the morphology, embryology, and comparative physiology of cardiac endothelial cells as well as the experimental observations on how cardiac endothelial cells affect the mechanical performance of the heart. As for the underlying mechanisms of the interaction between cardiac endothelial cells and cardiomyocytes, two working hypotheses have been postulated over the past years; (1) interaction mediated through a trans-endothelial physicochemical gradient for various ions (active blood-heart barrier), and (2) interaction mediated through the release by the cardiac endothelial cells of various cardioactive substances, eg, nitric oxide, endothelin, and prostacyclin. These two mechanisms may act in concert or in parallel.

Endothelium-dependent relaxation evoked by ATP and UTP in the aorta of P2Y2-deficient mice

Based on pharmacological criteria, we previously suggested that in the mouse aorta, endothelium‐dependent relaxation by nucleotides is mediated by P2Y1 (adenosine diphosphate (ADP)), P2Y2 (adenosine triphosphate (ATP)) and P2Y6 (uridine diphosphate (UDP)) receptors. For UTP, it was unclear whether P2Y2, P2Y6 or yet another subtype was involved. Therefore, in view of the lack of selective purinergic agonists and antagonists, we used P2Y2‐deficient mice to clarify the action of UTP. Thoracic aorta segments (width 2 mm) of P2Y2‐deficient and wild‐type (WT) mice were mounted in organ baths to measure isometric force development and intracellular calcium signalling. Relaxations evoked by ADP, UDP and acetylcholine were identical in knockout and WT mice, indicating that the receptors for these agonists function normally. P2Y2‐deficient mice showed impaired ATP‐ and adenosine 5′[γ‐thio] triphosphate (ATPγS)‐evoked relaxation, suggesting that in WT mice, ATP and ATPγS activate predominantly the P2Y2 subtype. The ATP/ATPγS‐evoked relaxation and calcium signals in the knockout mice were partially rescued by P2Y1, as they were sensitive to 2′‐deoxy‐N6‐methyladenosine 3′,5′‐bisphosphate (MRS2179), a P2Y1‐selective antagonist. In contrast to ATP, the UTP‐evoked relaxation was not different between knockout and WT mice. Moreover, the action of UTP was not sensitive to MRS2179. Therefore, the action of UTP is probably mediated mainly by a P2Y6(like) receptor subtype. In conclusion, we demonstrated that ATP‐evoked relaxation of the murine aorta is mainly mediated by P2Y2. But this P2Y2 receptor has apparently no major role in UTP‐evoked relaxation. The vasodilator effect of UTP is probably mediated mainly by a P2Y6(like) receptor.

Paraoxonase 1 gene transfer lowers vascular oxidative stress and improves vasomotor function in apolipoprotein E-deficient mice with pre-existing atherosclerosis

Transgenesis of human paraoxonase 1 (PON1), a HDL‐associated enzyme that destroys lipid peroxides, has been reported to reduce early atherogenesis in mice. The present study explored the therapeutic potential of human PON1 gene transfer in old apolipoprotein E‐deficient (apoE−/−) mice with advanced atherosclerosis.

Agonists of the P2YAC-receptor activate MAP kinase by a ras-independent pathway in rat C6 glioma

We have previously shown that an ecto‐NPPase modulates the ATP‐ and ADP‐mediated P2YAC‐receptor activation in rat C6 glioma. In the present study, 2MeSADP and Ap3A induced no detectable PI turnover and were identified as specific agonists of the P2YAC‐receptor with EC50 values of 250 ± 37 pm and 1 ± 0.5 µm, respectively. P2YAC‐receptor stimulation increased MAP kinase (ERK1/2) activation that returned to the basal level 4 h after stimulation and was correlated with a gradual desensitization of the P2YAC‐purinoceptor. The purinoceptor antagonists DIDS and RB2 blocked MAP kinase activation. An IP3‐independent Ca2+‐influx was observed after P2YAC‐receptor activation. Inhibition of this influx by Ca2+‐chelation, did not affect MAP kinase activation. Pertussis toxin, toxin B, selective PKC‐inhibitors and a specific MEK‐inhibitor inhibited the 2MeSADP‐ and Ap3A‐induced MAP kinase activation. In addition, transfection with dominant negative RhoAAsn19 rendered C6 cells insensitive to P2YAC‐receptor‐mediated MAP kinase activation whereas dominant negative ras was without effect. Immunoprecipitation experiments indicated a significant increase in the phosphorylation of raf‐1 after P2YAC‐receptor activation. We may conclude that P2YAC‐purinoceptor agonists activate MAP kinase through a Gi‐RhoA‐PKC‐raf‐MEK‐dependent, but ras‐ and Ca2+‐independent cascade.

P2Y receptors and atherosclerosis in apolipoprotein E‐deficient mice

Background and purpose:  P2Y nucleotide receptors are involved in the regulation of vascular tone, smooth muscle cell (SMC) proliferation and inflammatory responses. The present study investigated whether they are involved in atherosclerosis.

Inhibition of inositol monophosphatase by lithium chloride induces selective macrophage apoptosis in atherosclerotic plaques

BACKGROUND AND PURPOSE Lithium chloride (LiCl) inhibits inositol monophosphatase (IMPase) at therapeutic concentrations. Given that LiCl induces death in cultured macrophages and that macrophages play an active role in atherosclerotic plaque destabilization, we investigated whether LiCl would induce selective macrophage death to stabilize the structure of the plaque.