Minutes that matter: time-efficient high-intensity interval training improves cardiac function with transcriptomic evidence in post–myocardial infarction mice

FIGURE 1. HIIT improved exercise capacity in mice with infarcted hearts. (A) The experimental protocol is illustrated as a schematic. Mice were familiarized with the treadmill apparatus for 5 days; then, mice in the Sham, MI-only, and MI + HIIT groups underwent the corresponding surgical procedures, and all animals remained sedentary for 1 week. The HIIT regimen was initiated in HIIT-only and MI + HIIT mice at Week 0 and continued until Week 6, while animals in the other three groups remained sedentary. (B–D) Exercise capacity was assessed by measuring running (B) distance, (C) speed, and (D) time to exhaustion at Week 0 and Week 6. Data are presented as mean ± SD. Group differences were evaluated using one-way ANOVA for comparisons across all five experimental groups, followed by post hoc analysis where applicable. For comparisons between two groups, independent two-tailed t-tests were performed, with p-values adjusted for multiple comparisons using the Benjamini-Hochberg false discovery rate (FDR) correction. An adjusted p-value of less than 0.05 was considered statistically significant. The sample size for each group was: Control (n = 10), HIIT-only (n = 10), Sham (n = 8), MI-only (n =…

FIGURE 2. HIIT improved heart function and limited adverse cardiac remodeling in mice with infarcted hearts. (A) Echocardiographic images were collected at Week 0 and Week 6 and used to determine measurements of left ventricular (B) ejection fraction (LVEF) and (C) fractional shortening (LVFS), left-ventricular internal dimensions at (D) diastole (LVIDd) and (E) systole (LVIDs). Representative echocardiographic images are displayed in A for mice in the MI-only and MI + HIIT groups at both time points. Data are presented as mean ± SD. Group differences were evaluated using one-way ANOVA for comparisons across all five experimental groups, followed by post hoc analysis where applicable. For comparisons between two groups, independent two-tailed t-tests were performed, with p-values adjusted for multiple comparisons using the Benjamini-Hochberg false discovery rate (FDR) correction. An adjusted p-value of less than 0.05 was considered statistically significant. (n = 9 mice per experimental group).

FIGURE 3. HIIT increased myocardial mass and reduced fibrosis in infarcted mouse hearts. (A) Mouse bodyweights were measured at Week 0 and immediately after animals were sacrificed at Week 6. (B) Heart weights were measured after harvesting at Week 6, and (C) heart-weight-to-bodyweight ratios were calculated and expressed as a percentage. (D) Cardiac tissue sections were obtained from the LVs of mice sacrificed at Week 6 and stained with Masson’s trichrome to identify fibrotic (blue) and nonfibrotic (red) regions; then, (E) the ratio of the area of fibrosis to the area of the entire LV was calculated and presented as a percentage. Representative images are displayed in panel D (Scale bar = 100 μm). Data are presented as mean ± SD. Group differences were evaluated using one-way ANOVA for comparisons across all five experimental groups, followed by post hoc analysis where applicable. For comparisons between two groups, independent two-tailed t-tests were performed, with p-values adjusted for multiple comparisons using the Benjamini-Hochberg false discovery rate (FDR) correction. An adjusted p-value of less than 0.05 was considered statistically significant. (n = 8–10 mice per experimental…

FIGURE 4. HIIT increased cardiomyocyte DNA synthesis and cell-cycle activity in infarcted mouse hearts. Mice in all groups received intraperitoneal injections of 5-ethynyl-2′-deoxyuridine (EdU) once per week at Weeks 3, 4, and 5; then, after sacrifice at Week 6, (A) sections of LV tissue were stained for the presence of EdU (red), for the expression of cardiac troponin T (cTnT, green) to visualize cardiomyocytes, and with Hoechst 33,342 (blue) to label nuclei. (B) Cardiomyocyte proliferation was summarized as the proportion of cTnT-expressing cells that were also positive for EdU and expressed as a percentage. Representative images are displayed in panel A (Scale bar = 20 μm). Data are presented as mean ± SD. Group differences were evaluated using one-way ANOVA for comparisons across all five experimental groups, followed by post hoc analysis where applicable. For comparisons between two groups, independent two-tailed t-tests were performed, with p-values adjusted for multiple comparisons using the Benjamini-Hochberg false discovery rate (FDR) correction. An adjusted p-value of less than 0.05 was considered statistically significant. (n = 8 mice per experimental group).

FIGURE 5. Gene Ontology enrichment and KEGG Pathway analysis of bulk RNA sequencing data suggest that HIIT altered the activity of pathways that regulate myocardial contractility, cardiac metabolism, cardiomyocyte proliferation, apoptosis, and inflammation in infarcted mouse hearts. Bulk RNA sequencing analysis was performed with LV tissues collected after sacrifice at Week 6 (n = 3 mice per experimental group). (A) The abundance of expression for genes that improve cardiac contraction (Mylk3, Mylk4, Ryr2, Hrc, Cacna1s), increase myocardial metabolic efficiency (Gck, Pfkm, Pkm, Cybb, Ncf4), promote (Notch4, Erbb3, Erbb4, Epas1) or inhibit (Cdkn2a, Cdkn2c, Rbl1) cardiomyocyte proliferation, and reduce apoptosis or promote inflammation (Casp1, Casp3, Tnfα, Il6, Tlr2, Olr1, Mmp9) is summarized as a heat map. (B) Data for the MI-only and MI + HIIT groups were compared via Gene Ontology (GO) enrichment analysis, and the 30 terms that were most significantly (p < 0.05) upregulated in the MI + HIIT group were identified. (C) Data for the MI-only and MI + HIIT groups were compared via KEGG pathway analysis to identify pathway classifications that were significantly (p < 0.05) upregulated in the MI…

FIGURE 6. FPKM normalization of bulk RNA sequencing data suggests that HIIT led to changes in gene expression that are associated with increases in cardiomyocyte proliferation, improvements in myocardial contractility and metabolism, and declines in apoptosis and inflammation in infarcted mouse hearts. Bulk RNA sequencing data were normalized according to Fragments Per Kilobase of transcript per Million mapped reads (FPKM), and results are displayed for (A) genes that contribute to cardiac contractile activity (Mylk3, Mylk4, Ryr2, Hrc, Cacna1s), (B) genes that regulate myocardial metabolism (Gck, Pfkm, Pkm, Cybb, Ncf4), (C) genes that promote cardiomyocyte proliferation (Notch4, Erbb3, Erbb4, Epas1), (D) genes that inhibit cardiomyocyte cell-cycle activity (Cdkn2a, Cdkn2c, Rbl1), and (E) genes that promote inflammation or apoptosis (Casp1, Casp3, Tnfα, Il6, Tlr2, Olr1, Mmp9). Data are presented as mean ± SD; p-values were determined via independent two-tailed t-tests, with p-values adjusted for multiple comparisons using the Benjamini-Hochberg false discovery rate (FDR) correction. An adjusted p-value of less than 0.05 was considered statistically significant. (n = 3 mice per experimental…