“Cardiac Specific Adenyl Cyclase Type 8 Overexpression Induces Chronic Cardiac Exercise and Leads to a Unique Form of Cardiac Growth.”
Authors: Lammons John , Tarasov Kirill , Wang Mingyi , Ahmet Ismayil , Riordon Daniel , Zhang Jing , Chakir Khalid , Lukyanenko Yevgeniya , Lyashkov Alexey , Lakatta Edward 
Published: April 2020

IntroductionCardiac specific overexpression of adenylate cyclase type 8 (TGAC8) induces a robust, chronic increase in AC‐PKA‐cAMP signaling. Due elevated cardiac AC8‐ PKA‐cAMP signaling, TGAC8 mice experience a 30% increase in heart rate and a roughly 60% increase in ejection fraction1. This continuously elevated cardiac workload places a significant stress on TGAC8 mice hearts. We employed unbiased multiomics on left ventricle (LV) tissue to deduce the diverse molecular adaptions utilized by TGAC8 mice to adapt to this stress. We utilized echocardiogram to measure cardiac structure in TGAC8 and wildtype (WT) littermates, assessed changes in LV histology, and assessed key growth targets using western blotting to further study the cardiac growth phenotype of TGAC8 mice.ResultsPosterior wall thickness and interventricular septal thickening was increased by roughly 1mm and 2mm (p‐value < .05) respectively in TGAC8 vs WT. Despite wall thickening, total LVM was not significantly different, due to smaller ventricular chamber volume in TGAC8 mice. Cross‐sectional area of left ventricle cells in TG mice were significantly reduced on average by 100 um2 (p‐value < .05). Cells with an area less than 400 um2 were increased by 56% in TGAC8 mice compared to WT. Proteomic and RNA sequencing analyses reveals enrichment of transcripts and proteins involved in cell cycle regulation, cardiac growth, and cardiomyocyte development. Enrichment of standard cardiac hypertrophy markers such as ACTA2, ANP, MHY7, and BNP, however, were not observed. Western blotting results verified enrichment of regulators associated with growth signaling and cardiomyocyte proliferation, such as CITED4 and phospho‐AKT, previously not identified in our proteomics analysis.ConclusionThe cardiac growth response to chronically activated AC‐PKA‐cAMP signaling in TGAC8 mice is a key adaption to chronically elevated cardiac workload. Myocardial growth in TGAC8 mice is not mediated through classical pathological or physiological hypertrophy mechanisms, considering the average cardiac cell size is decreased in the LV of TGAC8 mice. Our findings suggest myocardial growth in TGAC8 mice is mediated through cardiac cell proliferation and maturation rather than cardiomyocyte physiological hypertrophic growth. While the various cell types that mediate proliferation remain to be studied, alterations in the activity of cardiac developmental regulators and PI3K‐AKT signaling are likely mediating this process. This unique phenotype makes TGAC8 mice a novel model for cardiac growth.Support or Funding InformationThis research was supported by the Intramural Research Program of National Institutes of Health, National Institute on Aging.Proteomic Analysis of Enriched Growth Signaling in TGACB MiceFigure 1
Multiomics Data for Myocardial Developmental Markers and Cell Cycle Regulators

Gene name

symbol

Protein

Protein

RNA

RNA

Delta Percent Change

p‐value

Log2fold

q‐value

Neurogenic locus notch homolog protein 1

Notch 1

11.61042795

0.034634

−0.10343

0.543742

Recombining binding protein suppressor of hairless

Rbpj

15.20

0.022

−0.11919

0.309147

Histone‐lysine N‐methyltransferase Smyd1

Smyd1

6.782540441

0.007642

0.107033

0.17192

T‐box transcription factor TBX5

Tbx5

15.7334461

0.039575

0.394611

0.000553

T‐box transcription factor TBX20

Mef2a

14.5453468

0.008824

0.394066

0.000553

Myocyte‐specific enhancer factor 2A

Tbx20

9.838421742

0.068529

*

Myocyte Enhancer Factor 2C

Mef2c

*

−0.17984

0.038123

Homeobox protein Nkx‐2.5

Nkx2‐5

*

0.559012

0.041448

Heart‐ and neural crest derivatives‐expressed protein 2

HAND2

*

1.04129

0.000553

cyclin d1

Ccnd 1

8.20

0.325

−0.22628

0.01724

cyclin d2

Ccnd2

10.10

0.515

−0.01038

0.937869

Cyclin‐dependent kinase 2

Cdk2

18.92

0.008

0.221418

0.427878

Cyclin‐dependent kinase 6

Cdk6

31.41

0.001

0.401706

0.000553

Proliferating Cell Nuclear Antigen

Pena

11.59

0.019

−0.05709

0.783869

P27

CDKN1B

12.13

0.270

0.003132

0.987798

P21

CDKN1A

*

0.32033

0.934763

Meis Homeobox 1

Meis1

*

−0.28486

0.018269

*Not Identified