1. Cellular and Molecular Pharmacology of the urotensinergic system.
Despite successes, cardiovascular diseases (CVDs) continue to impose enormous health (around 20 million deaths per year) and financial burdens (almost 300 billion dollars per year) worldwide. While numerous G protein-coupled receptors (GPCR) are involved in the regulation of cardiac functions, only a few, including the β-adrenergic and the angiotensin II receptors, have been targeted for therapeutic intervention. Current marketed GPCR drugs are broadly classified as either agonists or antagonists. However, GPCRs couple to a multitude of intracellular signaling pathways beyond classical G-protein signals, and these signals can be independently activated by biased ligands to vastly expand the potential for new drugs. By selectively engaging only a subset of a receptor's potential intracellular partners, biased ligands or allosteric modulators may deliver more precise therapeutic benefit with fewer side effects than current GPCR-targeted drugs. For instance, TRV120027, a biased ligand for angiotensin II receptor type 1, which prevented G protein-dependent signaling, but fostered β-arrestin signaling, showed cardioprotective functions by preserving cardiac inotropic functions, while decreasing systemic vascular resistance. The urotensinergic system, by inducing similar G protein-mediated intracellular events, is now recognized as an important player in the development of atherosclerosis and pulmonary arterial hypertension (PAH), two diseases for which no cure exist. The unique nature of the urotensinergic system, composed of two endogenous peptides and one G protein-coupled receptor (UT), identifies UT as a key target for the treatment/management of CVD including atherosclerosis. Interestingly, it was observed that UII and URP exerted common but also divergent physiological actions through the recruitment of specific subsets of secondary messengers. This phenomenon, which is in accordance with the notion of functional selectivity, is dependent on the ligand-induced UT conformation. We therefore hypothesize that a better understanding of the molecular mechanism involved in UII and/or URP-associated UT activation could provide a new view of UT pharmacology in healthy and disease states. Such new knowledge could also implement the discovery of new and innovative peptide-based compounds that can control/modulate in a specific, temporal and pathway-oriented manner UT-associated signaling. Hence, our research program, focused on the urotensinergic system, aims at (1) understanding the mechanisms underlying the cellular events involved in UII and URP functional selectivity and (2) providing innovative new synthetic entities, i.e. biased agonists and allosteric modulators, for the fine-tuned control of UT functions.
2. Development of molecular tools for the control of cellular signaling associated with the anti-apoptotic effects of the PACAPergic system
Despite numerous successes at controlling GPCRs, optimizing/developing pharmacological tools for existing/potential targets continue to be a challenge for the pharmaceutical industry. Biological responses are encoded during the initial interaction step between a ligand and its cognate receptor(s). Ligand-induced receptor conformational changes, by stabilizing in different proportions various “active receptor populations”, modulate multiple G protein- and non-G protein-mediated effectors. Thus, the stabilization or disruption of molecular interactions that changes the energy setting of the system has the potential to affect the conformational ensemble in ways that modulates signaling. Pepducins were discovered in the late 1990's based on the hypothesis that the intracellular loops of a G protein-coupled receptor (GPCR) were crucial site of interactions with components of the intracellular signaling machinery. Pepducins are cell-penetrating lipidated peptides composed of a lipid moiety attached to a peptide that corresponds to an amino acid segment from one of the cytoplasmic loop of the GPCR of interest. Following the establishment of an equilibrium between the inner and outer leaflet of the lipid bilayer, pepducins interact within seconds with their cognate GPCR based on natural intra- and inter-molecular contacts. Such interactions lead to the stabilization of the receptor in one of the spectrum of conformations between the ‘on’ and ‘off’ states of the receptor. Hence, these compounds can function as allosteric agonist or positive/negative allosteric modulator of their cognate receptor, making them highly useful for the study of GPCR signaling, as reported for protease-activated receptors, chemokine receptors, and adrenergic receptors. To date, allosteric pepducin agonists have been generated against more than a dozen class A GPCR but to the best of our knowledge, no pepducin targeting class B receptors have been reported. Hence, the conception of pepducin preventing apoptosis through the specific activation of PAC1, despite enriching the armamentarium of apoptosis inhibitors, could represent important and unique research tools when investigating the cellular mechanisms underlying stroke, spinal cord injuries, artherosclerosis, and cancer. To tackle this challenge, we propose to use a newly developed approach in order to control the intracellular signaling associated with PAC1 apoptotic activities. More specifically, we propose a multidisciplinary approach focussed on: 1) developing PAC1-based pepducin that will allosterically modulate PAC1-mediated apoptosis; 2) investigating the anti-apoptotic properties of these derivatives as well as their mechanism of action, and 3) studying the relationship between the chemical or tridimensional structure of bioactive PAC1-derived pepducins and their biological activity.
