Abstract 20504: Dysfunctional cAMP-Dependent Protein Kinase (PKA) Signaling Causes Impaired Autonomic Control in Diabetic Heart Failure
Autonomic control of cardiac function primarily occurs through the regulation of cAMP-dependent protein kinase (PKA) via the adrenergic and muscarinic pathways. The diabetic heart has a suppressed β-adrenergic response that is classically attributed to β-adrenergic receptor internalization, but little is known about how the PKA signaling pathway is affected. We assessed the hypothesis that β-adrenergic impairment in diabetes occurs through PKA signaling dysfunction. Four-month streptozotocin (STZ)-induced diabetic mice were used in this study as a model of diabetic cardiomyopathy. Although the diabetic mice have substantial cardiac impairment, as measured by pressure catheter, cAMP levels are not reduced, suggesting the pathway upstream of PKA is intact. We next developed a novel system using acute 8-min treatments with a cAMP analog, 8Br-cAMP, to activate PKA in a receptor-independent manner and increase ventricular inotropy. Diabetic mice have an impaired response to 8Br-cAMP treatment as shown by minimal change in PKA substrate phosphorylation (Fig. 1) and PKA activity by enzyme assay (% increase, C: 65±3.5, STZ: 30±5, n=5). Interestingly, cytosolic phosphorylation of PFK-2 is absent (% increase, C: 142±32, STZ: -15.7±13, n=5), yet nuclear phosphorylation of CREB is maintained suggesting a difference in localization of PKA. Although total PKA content is not different in the diabetic hearts, there is reduced cytosolic content of PKA (-35±1%, n=5) and an increase in nuclear translocation of PKA with treatment. The improper localization of PKA in the diabetic mice explains the differing phosphorylation. A major contributor is the reduction of nuclear PKA inhibitors/exporters, PKIα (-33±6.2%, n=5) and PKIγ (-20±7.2%, n=5), which normally regulate the nuclear content of PKA. In conclusion, PKA signaling is greatly impaired in diabetes and is attributable to altered enzyme localization, which is at least in part a result of PKI loss.
Author Disclosures: L. Bockus: None. K. Humphries: None.
- © 2014 by American Heart Association, Inc.