Gαi-biased apelin analog protects against isoproterenol-induced myocardial dysfunction in rats.

Apelin receptor (APJ) activation by apelin-13 (APLN-13) engages both Gαi proteins and ß-arrestins, stimulating distinct intracellular pathways and triggering physiological responses like enhanced cardiac contractility. Substituting the C-terminal phenylalanine of APLN-13 with α-methyl-l-phenylalanine [(l-α-Me)Phe] or p-benzoyl-l-phenylalanine (Bpa) generates biased analogs inducing APJ functional selectivity toward Gαi proteins. Using these original analogs, we proposed to investigate how the canonical Gαi signaling of APJ regulates the cardiac function and to assess their therapeutic impact in a rat model of isoproterenol-induced myocardial dysfunction. In vivo and ex vivo infusions of either Bpa or (l-α-Me)Phe analogs failed to enhance rats' left ventricular (LV) contractility compared with APLN-13. Inhibition of Gαi with pertussis toxin injection optimized the cardiotropic effect of APLN-13 and revealed the inotropic impact of Bpa. Moreover, both APLN-13 and Bpa efficiently limited the forskolin-induced and PKA-dependent phosphorylation of phospholamban at the Ser16 in neonatal rat ventricular myocytes. However, only Bpa significantly reduced the inotropic effect of forskolin infusion in isolated-perfused heart, highlighting its efficient bias toward Gαi. Compared with APLN-13, Bpa also markedly improved isoproterenol-induced myocardial systolic and diastolic dysfunctions. Bpa prevented cardiac weight increase, normalized both ANP and BNP mRNA expressions, and decreased LV fibrosis in isoproterenol-treated rats. Our results show that APJ-driven Gαi/adenylyl cyclase signaling is functional in cardiomyocytes and acts as negative feedback of the APLN-APJ-dependent inotropic response. Biased APJ signaling toward Gαi over the ß-arrestin pathway offers a promising strategy in the treatment of cardiovascular diseases related to myocardial hypertrophy and high catecholamine levels.NEW & NOTEWORTHY By using more potent Gαi-biased APJ agonists that strongly inhibit cAMP production, these data point to the negative inotropic effect of APJ-mediated Gαi signaling in the heart and highlight the potential protective impact of APJ-dependent Gαi signaling in cardiovascular diseases associated with left ventricular hypertrophy.

Structure-Activity Relationship and Bioactivity of Short Analogues of ELABELA as Agonists of the Apelin Receptor.

ELABELA (ELA) is the second endogenous ligand of the apelin receptor (APJ). Although apelin-13 and ELA both target APJ, there is limited information on structure-activity relationship (SAR) of ELA. In the present work, we identified the shortest bioactive C-terminal fragment ELA23-32, which possesses high affinity for APJ (Ki 4.6 nM) and produces cardiorenal effects in vivo similar to those of ELA. SAR studies on conserved residues (Leu25, His26, Val29, Pro30, Phe31, Pro32) show that ELA and apelin-13 may interact differently with APJ. His26 and Val29 emerge as important for ELA binding. Docking and binding experiments suggest that Phe31 of ELA may bind to a tight groove distinct from that of Phe13 of Ape13, while the Phe13 pocket may be occupied by Pro32 of ELA. Further characterization of signaling profiles on the Gαi1, Gα12, and ß-arrestin2 pathways reveals the importance of aromatic residue at the Phe31 or Pro32 position for receptor activation.

Gene deletion of protein tyrosine phosphatase 1B protects against sepsis-induced cardiovascular dysfunction and mortality.

OBJECTIVE: Cardiovascular dysfunction is a major cause of mortality in patients with sepsis. Recently, we showed that gene deletion or pharmacological inhibition of protein tyrosine phosphatase 1B (PTP1B) improves endothelial dysfunction and reduces the severity of experimental heart failure. However, the cardiovascular effect of PTP1B invalidation in sepsis is unknown. Thus, we explored the beneficial therapeutic effect of PTP1B gene deletion on lipopolysaccharide (LPS)-induced cardiovascular dysfunction, inflammation, and mortality. APPROACH AND RESULTS: PTP1B(-/-) or wild-type mice received LPS (15 mg/kg) or vehicle followed by subcutaneous fluid resuscitation (saline, 30 mL/kg). α-1-dependent constriction and endothelium-dependent dilatation, assessed on isolated perfused mesenteric arteries, were impaired 8 hours after LPS and significantly improved in PTP1B(-/-) mice. This was associated with reduced vascular expression of interleukin1-ß, intercellular adhesion molecule-1, vascular cell adhesion molecule-1, cyclooxygenase-2, and inducible nitric oxide synthase mRNA. PTP1B gene deletion also limited LPS-induced cardiac dysfunction assessed by echocardiography, left ventricular pressure-volume curves, and in isolated perfused hearts. PTP1B(-/-) mice also displayed reduced LPS-induced cardiac expression of tumor necrosis factor-α, interleukin1-ß, intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and Gp91phox, as well as of several markers of cellular infiltration. PTP1B deficiency also reduced cardiac P38 and extracellular signal-regulated protein kinase 1 and 2 phosphorylation and increased phospholamban phosphorylation. Finally, PTP1B(-/-) mice displayed a markedly reduced LPS-induced mortality, an effect also observed using a pharmacological PTP1B inhibitor. PTP1B deletion also improved survival in a cecal ligation puncture model of sepsis. CONCLUSIONS: PTP1B gene deletion protects against septic shock-induced cardiovascular dysfunction and mortality, and this may be the result of the profound reduction of cardiovascular inflammation. PTP1B is an attractive target for the treatment of sepsis.