Impaired cardiac performance, protein synthesis, and mitochondrial function in tumor-bearing mice

Abstract

Background: To understand the underlying mechanisms of cardiac dysfunction in cancer, we examined cardiac function, protein synthesis, mitochondrial function and gene expression in a model of heart failure in mice injected with Lewis lung carcinoma (LLC1) cells.

Experimental design: Seven week-old C57BL/J6 male and female mice were injected with LLC1 cells or vehicle. Cardiac ejection fraction, ventricular wall and septal thickness were reduced in male, but not female, tumor-bearing mice compared to vehicle-injected control mice. Cardiac protein synthesis was reduced in tumor-bearing male mice compared to control mice (p = 0.025). Aspect ratio and form factor of cardiac mitochondria from the tumor-bearing mice were increased compared control mice (p = 0.042 and p = 0.0032, respectively) indicating a more fused mitochondrial network in the hearts of tumor-bearing mice. In cultured cardiomyocytes maximal oxygen consumption and mitochondrial reserve capacity were reduced in cells exposed to tumor cell-conditioned medium compared to non-conditioned medium (p = 0.0059, p = 0.0010). Whole transcriptome sequencing of cardiac ventricular muscle from tumor-bearing vs. control mice showed altered expression of 1648 RNA transcripts with a false discovery rate of less than 0.05. Of these, 54 RNA transcripts were reduced ≤ 0.5 fold, and 3 RNA transcripts were increased by ≥1.5-fold in tumor-bearing mouse heart compared to control. Notably, the expression of mRNAs for apelin (Apln), the apelin receptor (Aplnr), the N-myc proto-oncogene, early growth protein (Egr1), and the transcription factor Sox9 were reduced by >50%, whereas the mRNA for growth arrest and DNA-damage-inducible, beta (Gadd45b) is increased >2-fold, in ventricular tissue from tumor-bearing mice compared to control mice.

Conclusions: Lung tumor cells induce heart failure in male mice in association with reduced protein synthesis, mitochondrial function, and the expression of the mRNAs for inotropic and growth factors. These data provide new mechanistic insights into cancer-associated heart failure that may help unlock treatment options for this condition.

Fig 1. Effects of PBS- and LLC1 tumor cell-injection on ventricular echocardiography in male mice 14 days post-injection of vehicle or cells.

A. LV posterior wall (LVPW) thickness in systole. B. LVPW thickness in diastole. C. Interventricular septum (IVS) thickness in systole. D. IVS thickness in diastole. E. LV internal dimension (LVID) in systole. F. LVID in diastole. G. Ejection fraction (%) calculated by the Teichholz method. H. Ejection fraction (%) calculated by the cubed method. I. Percentage (%) fractional shortening.

Fig 2. Echocardiography in PBS- and LLC1 cell-injected female mice.

A. LVPW thickness in systole. B. LVPW thickness in diastole. C. IVS thickness in systole. D. IVS thickness in diastole. E. LVID in systole. F. LVID in diastole. G. Ejection fraction (%) calculated by the Teichholz method. H. Ejection fraction (%) calculated by the cubed method. I. Percentage (%) fractional shortening.

Fig 3

A. Protein fractional synthesis rates in the hearts of tumor-bearing and control mice. B. Heart masses of tumor-bearing and control mice. C. Heart/body mass ratios of tumor-bearing and control mice.

Fig 4. Effects of LLC1 tumor cells on cardiac myofibrillar mitochondrial morphology.

A. Ventricular tissue from PBS-injected mice (left panel) and LLC1 tumor-bearing mice (right panel). B. Average cross-sectional area (μm²) of intramyofibrillar mitochondria. C. Mitochondrial number per image. D. Mitochondrial density by area, calculated per image frame area of 43.588 μm². E. Mitochondrial aspect ratio. F. Mitochondrial form factor (FF).

Fig 5. LLC1 tumor cell conditioned medium impairs maximal and reserve mitochondrial oxygen consumption rates in cardiomyocytes.

A. Effects of LLC1 tumor cell conditioned media (CM) and non-conditioned media (NCM) on AC16 human cardiomyocyte oxygen consumption rates, normalized to total μg protein. B. Cardiomyocyte basal respiration. C. Cardiomyocyte maximal respiration. D. Cardiomyocyte mitochondrial reserve capacity.

Fig 6. Effects of LLC1 tumor cells on cardiac mitochondrial OXPHOS complexes.

A. Immunoblot of mitochondrial OXPHOS complexes derived from tumor-injected mice and vehicle-injected mice B. Densitometric analysis of complex I. C. Densitometric analysis of complex II. D. Densitometric analysis of complex IV. E. Densitometric analysis of complex III. F. Densitometric analysis of complex V. Of note, the sequence of densitometric plots corresponds to the position of the complexes on the gel.