Lack of Gαi2 leads to dilative cardiomyopathy and increased mortality in β1-adrenoceptor overexpressing mice

Aims Inhibitory G (Gi) proteins have been proposed to be cardioprotective. We investigated effects of Gαi2 knockout on cardiac function and survival in a murine heart failure model of cardiac β1-adrenoceptor overexpression. Methods and results β1-transgenic mice lacking Gαi2 (β1-tg/Gαi2 -/-) were compared with wild-type mice and littermates either overexpressing cardiac β1-adrenoceptors (β1-tg) or lacking Gαi2 (Gαi2 -/-). At 300 days, mortality of mice only lacking Gαi2 was already higher compared with wild-type or β1-tg, but similar to β1-tg/Gαi2 -/-, mice. Beyond 300 days, mortality of β1-tg/Gαi2 -/- mice was enhanced compared with all other genotypes (mean survival time: 363 ± 21 days). At 300 days of age, echocardiography revealed similar cardiac function of wild-type, β1-tg, and Gαi2 -/- mice, but significant impairment for β1-tg/Gαi2 -/- mice (e.g. ejection fraction 14 ± 2 vs. 40 ± 4% in wild-type mice). Significantly increased ventricle-to-body weight ratio (0.71 ± 0.06 vs. 0.48 ± 0.02% in wild-type mice), left ventricular size (length 0.82 ± 0.04 vs. 0.66 ± 0.03 cm in wild types), and atrial natriuretic peptide and brain natriuretic peptide expression (mRNA: 2819 and 495% of wild-type mice, respectively) indicated hypertrophy. Gαi3 was significantly up-regulated in Gαi2 knockout mice (protein compared with wild type: 340 ± 90% in Gαi2 -/- and 394 ± 80% in β1-tg/Gαi2 -/-, respectively). Conclusions Gαi2 deficiency combined with cardiac β1-adrenoceptor overexpression strongly impaired survival and cardiac function. At 300 days of age, β1-adrenoceptor overexpression alone had not induced cardiac hypertrophy or dysfunction while there was overt cardiomyopathy in mice additionally lacking Gαi2. We propose an enhanced effect of increased β1-adrenergic drive by the lack of protection via Gαi2. Gαi3 up-regulation was not sufficient to compensate for Gαi2 deficiency, suggesting an isoform-specific or a concentration-dependent mechanism.Fil: Keller, Kirsten. Universitat Zu Köln; AlemaniaFil: Maass, Martina. University Hospital of Cologne; AlemaniaFil: Dizayee, Sara. Universitat Zu Köln; AlemaniaFil: Leiss, Veronika. Eberhard Karls University Hospitals and Clinics; AlemaniaFil: Annala, Suvi. Universitat Zu Köln; AlemaniaFil: Köth, Jessica. Universitat Zu Köln; AlemaniaFil: Seemann, Wiebke K.. Universitat Zu Köln; AlemaniaFil: Müller Ehmsen, Jochen. Asklepios Klinik Altona; AlemaniaFil: Mohr, Klaus. Universitaet Bonn; AlemaniaFil: Nürnberg, Bernd. Eberhard Karls University Hospitals and Clinics; AlemaniaFil: Engelhardt, Stefan. Universitat Technical Zu Munich; AlemaniaFil: Herzig, Stefan. Universitat Zu Köln; AlemaniaFil: Birnbaumer, Lutz. National Institutes of Health; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Matthes, Jan. Universitat Zu Köln; Alemani

Engineered Context-Sensitive Agonism: Tissue-Selective Drug Signaling through a G Protein-Coupled Receptor

Drug discovery strives for selective ligands to achieve targeted modulation of tissue function. Here we introduce engineered context-sensitive agonism as a postreceptor mechanism for tissue-selective drug action through a G protein-coupled receptor. Acetylcholine M2-receptor activation is known to mediate, among other actions, potentially dangerous slowing of the heart rate. This unwanted side effect is one of the main reasons that limit clinical application of muscarinic agonists. Herein we show that dualsteric (orthosteric/allosteric) agonists induce less cardiac depression ex vivo and in vivo than conventional full agonists. Exploration of the underlying mechanism in living cells employing cellular dynamic mass redistribution identified context-sensitive agonism of these dualsteric agonists. They translate elevation of intracellular cAMP into a switch from full to partial agonism. Designed context-sensitive agonism opens an avenue toward postreceptor pharmacologic selectivity, which even works in target tissues operated by the same subtype of pharmacologic receptor

Rational Design of Partial Agonists for the Muscarinic M-1 Acetylcholine Receptor

Aiming to design partial agonists for a G-protein-coupled receptor based on dynamic ligand binding, we synthesized three different series of bipharmacophoric ligands composed of the orthosteric building blocks iperoxo and 1 linked to allosteric modulators (BQCA-derived compounds, BQCAd; TBPB-derived compound, TBPBd). Their interactions were studied with the human muscarinic acetylcholine M-1-receptor (hM(1)) with respect to receptor binding and G(q)-protein signaling. Results demonstrate that iperoxo/BQCAd (2, 3) and 1/BQCAd hybrids (4) act as M1 partial agonists, whereas 1/TBPBd hybrids (5) did not activate M-1-receptors. Among the iperoxo/BQCAd-hybrids, spacer length in conjunction with the pattern of substitution tuned efficacy. Most interestingly, a model of dynamic ligand binding revealed that the spacer length of 2a and 3a controlled the probability of switch between the inactive purely allosteric and the active bitopic orthosteric/allosteric binding pose. In summary, dynamic ligand binding can be exploited in M-1 receptors to design partial agonists with graded efficacy