Abstract P3066: Macrophage-derived Ccl24 Worsens Cardiac Dysfunction Following Pressure-overload

Heart failure (HF) is the leading cause of death worldwide. Systemic inflammation is associated with HF and is considered an independent predictor of adverse cardiac outcomes. Macrophages are the most abundant immune cells in the heart and have integral roles in cardiac homeostasis and remodeling. Despite their unique identity and homeostatic functions, the precise role of cardiac macrophages during cardiac remodeling is poorly understood. We have previously reported that cardiac resident macrophages expand early in response to pressure overload injury and provide cardioprotection. Using single-cell mRNA sequencing, we revealed that these macrophages consist of distinct subsets including a population that highly expresses C-C Motif Chemokine Ligand 24 (CCL24). CCL24 is a chemokine that promotes immune cell trafficking and activation through its receptor expressed on immune cells, fibroblasts, and cardiomyocytes. Here, we tested whether CCL24 regulates cardiac adaptation to pressure overload by performing transverse aortic constriction (TAC) in whole-body CCL24 knockout (CCL24KO) mice. Aortic constriction during TAC increases the pressure overload in ventricular chambers leading to an early compensated hypertrophy and diastolic dysfunction followed by systolic dysfunction and decompensated heart failure. Despite no differences at steady state, CCL24KO mice showed an improved cardiac function after TAC-induced pressure overload. Compared with WT controls, CCL24KO mice had a higher ejection fraction and fractional shortening. Furthermore, CCL24KO mice had increased hypertrophy but improved diastolic function. These results suggest that CCL24 worsens cardiac dysfunction leading to decompensated HF in response to pressure overload. Interestingly, CCL24KO mice have higher proportions of neutrophils and eosinophils at steady state, suggesting that the presence of these cells may facilitate cardiac repair. Overall, our findings indicate that macrophage-derived CCL24 is detrimental to cardiac function in response to pressure overload injury. The results of this study uncover CCL24 as a central mechanism by which cardiac resident macrophages promote cardiac inflammation and HF.

Exercise of high intensity ameliorates hepatic inflammation and the progression of NASH

Objective

Non-alcoholic fatty liver disease (NAFLD) covers a wide spectrum of liver pathology ranging from simple fatty liver to non-alcoholic steatohepatitis (NASH). Notably, immune cell-driven inflammation is a key mechanism in the transition from fatty liver to the more serious NASH. Although exercise training is effective in ameliorating obesity-related diseases, the underlying mechanisms of the beneficial effects of exercise remain unclear. It is unknown whether there is an optimal modality and intensity of exercise to treat NAFLD. The objective of this study was to determine whether high-intensity interval training (HIIT) or moderate-intensity continuous training (MIT) is more effective at ameliorating the progression of NASH.

Methods

Wild-type mice were fed a high-fat, high-carbohydrate (HFHC) diet for 6 weeks and left sedentary (SED) or assigned to either an MIT or HIIT regimen using treadmill running for an additional 16 weeks. MIT and HIIT groups were pair-fed to ensure that energy intake was similar between the exercise cohorts. To determine changes in whole-body metabolism, we performed insulin and glucose tolerance tests, indirect calorimetry, and magnetic resonance imaging. NASH progression was determined by triglyceride accumulation, expression of inflammatory genes, and histological assessment of fibrosis. Immune cell populations in the liver were characterized by cytometry by time-of-flight mass spectrometry, and progenitor populations within the bone marrow were assessed by flow cytometry. Finally, we analyzed the transcriptional profile of the liver by bulk RNA sequencing.

Results

Compared with SED mice, both HIIT and MIT suppressed weight gain, improved whole-body metabolic parameters, and ameliorated the progression of NASH by reducing hepatic triglyceride levels, inflammation, and fibrosis. However, HIIT was superior to MIT at reducing adiposity, improving whole-body glucose tolerance, and ameliorating liver steatosis, inflammation, and fibrosis, without any changes in body weight. Improved NASH progression in HIIT mice was accompanied by a substantial decrease in the frequency of pro-inflammatory infiltrating, monocyte-derived macrophages in the liver and reduced myeloid progenitor populations in the bone marrow. Notably, an acute bout of MIT or HIIT exercise had no effect on the intrahepatic and splenic immune cell populations. In addition, bulk mRNA sequencing of the entire liver tissue showed a pattern of gene expression confirming that HIIT was more effective than MIT in improving liver inflammation and lipid biosynthesis.

Conclusions

Our data suggest that exercise lessens hepatic inflammation during NASH by reducing the accumulation of hepatic monocyte-derived inflammatory macrophages and bone marrow precursor cells. Our findings also indicate that HIIT is superior to MIT in ameliorating the disease in a dietary mouse model of NASH.

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High-intensity is more effective than moderate-intensity exercise at reducing NASH.

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High-intensity exercise lowers the infiltration of inflammatory macrophages in the liver.

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Reduced macrophage accumulation was associated with lower progenitor cells.