Role of cardiac mast cells in exercise training-mediated cardiac remodeling in angiotensin II-infused ovariectomized rats

[mRNA Expression Profile Changes in Angiotensin-Ⅱ-Induced Atrial Myocardial Fibrosis in Rats]

Objective

To study the differences between the mRNA expression profile in angiotensin Ⅱ (Ang Ⅱ)-induced fibrotic cardiomyocytes and that of normal cardiomyocytes and the relevant signaling pathways.

Methods

Six 8-week-old male Sprague-Dawley (SD) rats were randomly assigned to a control group and an Ang Ⅱ group, with 3 rats in each group. Rats in the control group were injected via caudal vein with 0.9% normal saline at 2 mg/kg per day, while rats in the Ang Ⅱ group were injected with Ang Ⅱ via caudal vein at 2 mg/kg per day. The medications were continuously administered in the two groups for 14 days. The degree of myocardial fibrosis was determined by Masson's Trichrome staining and the content of collagen Ⅰ was determined by immunohistochemistry. High throughput sequencing was performed to measure the mRNA expression of rat cardiomyocytes in the two groups and to screen for differentially-expressed mRNAs. The differentially-expressed mRNAs were analyzed by Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis.

Results

Compared with those of the control group, the degree of myocardial fibrosis and the content of collagen Ⅰ in Ang Ⅱ group were significantly higher ( P<0.05). Through sequencing, 313 differentially-expressed mRNAs were identified, with 201 being up-regulated and 112 being down-regulated. Go and KEGG analyses showed that these differentially-expressed mRNA were involved in a variety of biological regulatory functions and pathways of myocardial fibrosis.

Conclusion

Ang Ⅱ can cause myocardial fibrosis in rats. There are significant differences in mRNA expression between fibrotic cardiomyocytes and normal cardiomyocytes. The differentially expressed mRNAs may play an important role in biological processes, including immune response, cell remodeling, and extracellular matrix deposition.

Beyond cardiomyocytes: Cellular diversity in the heart's response to exercise

Cardiomyocytes comprise ∼70% to 85% of the total volume of the adult mammalian heart but only about 25% to 35% of its total number of cells. Advances in single cell and single nuclei RNA sequencing have greatly facilitated investigation into and increased appreciation of the potential functions of non-cardiomyocytes in the heart. While much of this work has focused on the relationship between non-cardiomyocytes, disease, and the heart's response to pathological stress, it will also be important to understand the roles that these cells play in the healthy heart, cardiac homeostasis, and the response to physiological stress such as exercise. The present review summarizes recent research highlighting dynamic changes in non-cardiomyocytes in response to the physiological stress of exercise. Of particular interest are changes in fibrotic pathways, the cardiac vasculature, and immune or inflammatory cells. In many instances, limited data are available about how specific lineages change in response to exercise or whether the changes observed are functionally important, underscoring the need for further research.

Exercise training attenuates angiotensin II-induced cardiac fibrosis by reducing POU2F1 expression

PURPOSE

Exercise training protects against heart failure. However, the mechanism underlying the protective effect of exercise training on angiotensin II (Ang II)-induced cardiac fibrosis remains unclear.

METHODS

An exercise model involving C57BL/6N mice and 6 weeks of treadmill training was used. Ang II (1.44 mg/kg/day) was administered to induce cardiac fibrosis. RNA sequencing and bioinformatic analysis were used to identify the key factors mediating the effects of exercise training on cardiac fibrosis. Primary adult mouse cardiac fibroblasts (CFs) were used in vitro. Adeno-associated virus serotype 9 was used to overexpress POU domain, class 2, transcription factor 1 (POU2F1) in vivo.

RESULTS

Exercise training attenuated Ang II-induced cardiac fibrosis and reversed 39 gene expression changes. The transcription factor regulating the largest number of these genes was POU2F1. Compared to controls, POU2F1 was shown to be significantly upregulated by Ang II, which is itself reduced by exercise training. In vivo, POU2F1 overexpression nullified the benefits of exercise training on cardiac fibrosis. In CFs, POU2F1 promoted cardiac fibrosis. CCAAT enhancer-binding protein β (C/EBPβ) was predicted to be the transcription factor of POU2F1 and verified using a dual-luciferase reporter assay. In vivo, exercise training activated AMP-activated protein kinase (AMPK) and alleviated the increase in C/EBPβ induced by Ang II. In CFs, AMPK agonist inhibited the increase in C/EBPβ and POU2F1 induced by Ang II, whereas AMPK inhibitor reversed this effect.

CONCLUSION

Exercise training attenuates Ang II-induced cardiac fibrosis by reducing POU2F1. Exercise training inhibits POU2F1 by activating AMPK, which is followed by the downregulation of C/EBPβ, the transcription factor of POU2F1.

Hyperbaric oxygen therapy mitigates left ventricular remodeling, upregulates MMP-2 and VEGF, and inhibits the induction of MMP-9, TGF-β1, and TNF-α in streptozotocin-induced diabetic rat heart

AIMS

Hyperbaric oxygen (HBO) therapy has been widely used for the adjunctive treatment of diabetic wounds, and is currently known to influence left ventricular (LV) function. However, morphological and molecular repercussions of the HBO in the diabetic myocardium remain to be described. We aimed to investigate whether HBO therapy would mitigate adverse LV remodeling caused by streptozotocin (STZ)-induced diabetes.

MAIN METHODS

Sixty-day-old Male Wistar rats were divided into four groups: Control (n = 8), HBO (n = 7), STZ (n = 10), and STZ + HBO (n = 8). Diabetes was induced by a single STZ injection (60 mg/kg, i.p.). HBO treatment (100% oxygen at 2.5 atmospheres absolute, 60 min/day, 5 days/week) lasted for 5 weeks. LV morphology was evaluated using histomorphometry. Gene expression analyzes were performed for LV collagens I (Col1a1) and III (Col3a1), matrix metalloproteinases 2 (Mmp2) and 9 (Mmp9), and transforming growth factor-β1 (Tgfb1). The Immunoexpression of cardiac tumor necrosis factor-α (TNF-α) and vascular endothelial growth factor (VEGF) were also quantified.

KEY FINDINGS

HBO therapy prevented LV concentric remodeling, heterogeneous myocyte hypertrophy, and fibrosis in diabetic rats associated with attenuation of leukocyte infiltration. HBO therapy also increased Mmp2 gene expression, and inhibited the induction of Tgfb1 and Mmp9 mRNAs caused by diabetes, and normalized TNF-α and VEGF protein expression.

SIGNIFICANCE

HBO therapy had protective effects for the LV structure in STZ-diabetic rats and ameliorated expression levels of genes involved in cardiac collagen turnover, as well as pro-inflammatory and pro-angiogenic signaling.