A Remarkable Adaptive Paradigm Of Heart Performance And Protection Emerges In Response To The Constitutive Challenge Of Marked Cardiac-Specific Overexpression Of Adenylyl Cyclase Type 8

Adult mice with cardiac-specific overexpression of adenylyl cyclase (AC) type VIII (TG^AC8) adapt to an incessantly increased cAMP-induced cardiac workload (∼30% increases in heart rate, ejection fraction and cardiac output) for up to a year without signs of heart failure or excessive mortality. Here we show that despite markedly increased cardiac work, classical cardiac hypertrophy markers were absent in TG^AC8, total left ventricular (LV) mass was not increased: a reduced LV cavity volume in TG^AC8was encased by thicker LV walls harboring an increased number of small cardiac myocytes and a network of small interstitial non-cardiac myocytes, manifesting increased proliferation markers and compared to WT. Protein synthesis, proteosome activity, autophagy, and Nrf-2, Hsp90α, ACC2 protein levels were increased in TG^AC8, but LV ATP and phosphocreatine levels in vivo did not differ by genotype. 2,323 transcripts and 2,184 proteins identified in unbiased omics analyses, spanning a wide array of biological processes and molecular functions in numerous cellular compartments differed in TG^AC8vs WT; and over 250 canonical signaling pathways characteristic of adaptive survival circuitry of cancers, including PI3K and growth factor signaling, cytokine and T cell receptor signaling, immune responses, ROS scavenging, proliferation, protection from apoptosis, and nutrient sensing, were activated in TG^AC8; and compared to WT there was a shift from fatty acid oxidation to increased aerobic glycolysis in the context of increased utilization of the pentose phosphate shunt and nucleotide synthesis. Thus, the adaptive paradigm, that becomes activated in the LV of TG^AC8in response to severe chronic, intense AC/PKA/Ca²⁺signaling embodies many hallmarks of cancer.