Background: Fibulin-1, an extracellular matrix component and mediator in cardiac fibrosis, is expressed in cardiac valves, heart muscles and blood vessels and may contribute to different cardiovascular pathological conditions such as hypertension, aortic valve stenosis, atrial fibrillation and coronary artery disease. The most conspicuous functions of fibulin-1 include cell adhesion and cell migration within the extracellular matrix (ECM). This was found to reflect vascular dysfunction contributing to the development of fibrosis in the myocardium by means of changes in the ECM, possibly as a result of inflammation. Inflammatory mediators such as C-reactive protein (CRP) and albumin have been investigated over the years for the role they play in the inflammatory processes. However, one inflammatory mediator, soluble urokinase-type plasminogen activator receptor (suPAR), only emerged as a potential biomarker in the development of sclerotic disease. SuPAR is a soluble bioactive form of the urokinase-type plasminogen activator receptor (uPAR) secreted by inflammatory cells such as macrophages, endothelial cells and monocytes. The most profound functions of suPAR such as cell migration and cell adhesion contribute to the development of diseases such as infection, autoimmune diseases, cancer and atherosclerosis. Motivation and aim: This study was motivated by an awareness of the limited data on the potential link between fibulin-1 and suPAR, along with other markers of inflammation (CRP and albumin). We aimed to compare the levels of a marker of cardiac fibrosis (fibulin-1) and inflammatory mediators (suPAR, CRP and albumin) in African and Caucasian men and women. A second aim was to explore fibulin-1 and its potential association with these inflammatory markers independent of haemodynamic and metabolic risk factors in a bi-ethnic cohort from South Africa. Methodology: Data from the cross-sectional SAfrEIC study (South African study regarding the role of Sex, Age and Ethnicity on Insulin sensitivity and Cardiovascular function) were used, which initially included 756 participants. Our study population comprised 290 Africans (men: n=130; women: n=160) and 343 Caucasians (men: n=160; women: n=183). We excluded HIV-infected participants (n=115) as well as those with missing data (n=8). Traditional cardiovascular measurements together with the relevant biochemical analyses were done. T-tests and Chi-square tests were used to compare means and proportions between groups, respectively. Single and partial correlations were performed to determine the relationship of fibulin-1 with suPAR, CRP and albumin, with adjustments for age. SuPAR, CRP and albumin were divided into tertiles to explore the association with fibulin-1 levels, while adjusting for age, body mass index (BMI) and diastolic blood pressure (DBP) by using analysis of covariance (ANCOVA). Multiple regression analysis was performed to explore independent associations. Results: Participants were divided into African and Caucasian men and women due to significant interactions of the main effects of ethnicity and gender on the association of fibulin-1 with suPAR (ethnicity: F(633)=7.29; p<0.001 and gender: F(633)=7.99; p<0.001). Fibulin-1 levels were higher in African men (p=0.010), whereas CRP was higher in African women (p<0.001) compared to their Caucasian counterparts. In both gender groups suPAR levels were higher and albumin lower in Africans compared to Caucasians (p<0.006). In single regression analyses, a positive correlation existed between fibulin-1 and suPAR in African (r=0.19; p=0.028) and Caucasian men (r=0.37; p<0.001), also in African (r=0.193; p=0.028) and Caucasian women (r=0.14; p=0.036). After adjustments were applied for age, this correlation remained in African (r=0.23; p=0.010) and Caucasian men (r=0.22; p=0.005) only. An inverse correlation was found between fibulin-1 and albumin in African men (r=-0.28; p=0.002), but not in Caucasian men (r=-0.09; p=0.245). No significant correlation was found between fibulin-1 and CRP in any group. Forward stepwise regression analysis was performed in men and the previous associations between fibulin-1 and suPAR were confirmed in African and Caucasian men; along with the inverse relationship of fibulin-1 with albumin (Adj. R2=0.217; β=–0.210; p=0.013) in African men only. Conclusion: Fibulin-1 was positively associated with suPAR in African and Caucasian men, but not in women. We also found fibulin-1 to be negatively associated with albumin in African men only. These results are indicative of the presence of potential subclinical low-grade inflammation as depicted by suPAR within the extracellular matrix. This low-grade inflammation may contribute to the potential onset of cardiac fibrosis or vascular sclerosis among these South African men with lower albumin levels. / MSc (Physiology), North-West University, Potchefstroom Campus, 2014

Dans le système nerveux central, le récepteur inhibiteur GABAB est un archétype des RCPGs hétérodimériques. Il est composé en effet de deux sous-unités, la sous-unité GABAB1 (B1a ou B1b) qui lie l’agoniste et la sous-unité GABAB2 couplée aux protéines G. L’activation de ce récepteur a un effet antinociceptif bien établi concernant les douleurs aiguës mais son effet reste cependant très limité en cas de douleurs neuropathiques. Notre hypothèse est que son activation et sa signalisation peuvent être altérées par des protéines partenaires, aboutissant à des processus de désinhibition dans la moelle épinière en conditions de neuropathie. Nos résultats mettent en évidence le rôle de deux protéines partenaires qui sont surexprimées en conditions douloureuses et qui diminuent l’activation du récepteur GABAB via deux mécanismes différents. D’un part, la protéine cytosolique 14-3-3? induit la dissociation de l’hétérodimère B1b/B2. Cette action a lieu principalement dans les compartiments post-synaptiques. D’autre part, la fibuline-2, protéine de la matrice extracellulaire diminue l’activation de l’hétérodimère B1a/B2. Il s’agit cette fois préférentiellement d’une action dans les compartiments pré-synaptiques. Des stratégies anti-sens (siRNA anti-14-3-3? ou anti-fibuline-2) ou des peptides de compétition sélectifs de l’interaction B1b/14-3-3? permettent de potentialiser les effets antinociceptifs d’un agoniste du récepteur sur un modèle animal de neuropathie. L’ensemble de ces résultats suggèrent que l’état d’oligomérisation des RCPGs peut être modulé in vivo par des protéines partenaires endogènes impliquées dans le développement ou le maintien d’états pathologiques de sensibilisation à la douleur. / In the central nervous system, the inhibitory GABAB receptor is an obligate heterodimeric GPCR that requires the association between GABAB1 (B1a or B1b) and GABAB2 subunits. The heterodimeric GABAB receptor activation has a well-known antinociceptive action in acute pain but its effect appears limited in pathological states. Our hypothesis is that the GABAB activation and signaling could be altered by partner proteins, thus resulting in desinhibition processes in the spinal cord. In the present study, we investigated the role of two partner proteins overexpressed in neuropathic states which decrease GABAB activation through two different mechanisms. On the one hand, the cytosolic 14-3-3? protein induces the dissociation of the heterodimer B1b/B2. This effect occurs in post-synaptic compartments. On the other hand, fibulin-2, an extracellular matrix protein, which decreases the activation of the heterodimer B1a/B2 localized preferentially in presynaptic compartments. Anti-sens strategies (anti-14-3-3? or anti-fibulin-2 siRNA) or competing peptides specific of 14-3-3?/B1b interaction, potentiate the antinociceptive effects of GABAB agonist in an animal model of neuropathic pain. Taken together, our data suggest that GPCR oligomeric state can be modulated in vivo by endogenous partners proteins that are involved in the development and the maintenance of pain sensitization.