Sustained ligand-activated preconditioning (SLP), induced with chronic opioid receptor (OR) agonism, enhances tolerance to ischemia/reperfusion injury in young and aged hearts. Underlying mechanisms remain ill-defined, although early data implicate phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) during the induction phase, and b 2 -adrenoceptor (b 2 -AR), G s alpha subunit (Ga s ), and protein kinase A (PKA) involvement in subsequent cardioprotection. Here, we tested for induction of a protective b 2 -AR/Ga s /PKA signaling axis with SLP to ascertain whether signaling changes were PI3K-dependent (by sustained cotreatment with wortmannin), and whether the downstream PKA target Rho kinase (ROCK) participates in subsequent cardioprotection (by acute treatment with fasudil). A protected phenotype was evident after 5 days of OR agonism (using morphine) in association with increased membrane versus reduced cytosolic levels of total and phosphorylated b 2 -ARs; increased membrane and cytosolic expression of 52 and 46 kDa Ga s isoforms, respectively; and increased phosphorylation of PKA and Akt. Nonetheless, functional sensitivities of b 2 -ARs and adenylyl cyclase were unchanged based on concentration-response analyses for formoterol, fenoterol, and 6-[3-(dimethylamino)propionyl]-forskolin. Protection with SLP was not modified by ROCK inhibition, and changes in b 2 -AR, Ga s , and PKA expression appeared insensitive to PI3K inhibition, although 5 days of wortmannin alone exerted unexpected effects on signaling (also increasing membrane b 2 -AR and PKA expression/phosphorylation and Ga s levels). In summary, sustained OR agonism upregulates cardiac membrane b 2 -AR expression and phosphorylation in association with increased Ga s subtype levels and PKA phosphorylation. While Akt phosphorylation was evident, PI3K activity appears nonessential to OR upregulation of the b 2 -AR signal axis. This opioidergic remodeling of b 2 -AR signaling may explain b 2 -AR, Ga s , and PKA dependence of SLP protection.
|Number of pages||10|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|Publication status||Published - 1 Apr 2019|