Abstract Body (Do not enter title and authors here): Background: In an aging population, heart failure (HF) remains a leading cause of mortality worldwide. This study utilized genetically modified mice to investigate cardiac hypertrophy and HF, exploring potential age and sex-related differences. The focus was on understanding proteomic changes, functional impairment, and cardiac remodeling to gain deeper insights into the molecular intricacies of HF.

Experimental Approach: Double transgenic (DTG) male and female mice overexpressing both Cyclin T1 and Gαq under the control of the cardiac-specific α-myosin heavy chain promoter, show pathological myocardial cell growth and develop hypertrophy, eventually progressing to HF. Comparative analyses were conducted between DTG mice and respective wild-type (WT) littermates at the age of 5 and 9 weeks (n=4 per group, time point and sex). Heart function was evaluated via small animal echocardiography. Proteomes of the left ventricles (LV) of DTG and WT mice were analyzed by mass spectrometry and altered proteins categorized using Ingenuity Pathway Analysis.

Results: DTG mice showed a decrease in heart function over time. Independent of sex, DTG mice exhibited a significant decrease in left ventricular ejection fraction (LVEF) after 9 weeks compared to WT (DTG vs. WT: LVEF: 38.4±10.2% vs. 63.3±4.3%; p<0.001) and in relation to younger 5-week-old animals (DTG vs. WT: LVEF: 61.1±2.7% vs. 68.6±4%; p=0.16). Functional and morphological changes were clearly visible earlier in DTG males at 5 weeks compared to females. Also, LV proteomes showed differences between DTG and WT, and between sexes. The most and strongest changes in protein abundance (q<0.05, FC≥|1.5|) were observed after 9 weeks in DTG compared to WT, and much stronger in females (overall: 450↑, 437↓; males: 312↑, 347↓; females: 464↑, 463↓). Regarding age and sex differences, effects were again more pronounced at a younger age in males (5 weeks; altered proteins: 761 in males, 572 in females). These differences became even more apparent from further enrichment analyses of significantly altered proteins categorized into functional pathways such as energy metabolism and CVD-related categories.

Conclusion: Female mice tend to be more resistant to a down-regulation of mitochondrial oxidative capacity during pathological hypertrophy at earlier stages of disease progression. These sex differences emphasize the complexity of HF, pointing to the need of sex-specific considerations in therapeutic approaches.