Project description:Compelling evidence suggests that mitochondrial dysfunction contributes to the pathogenesis of heart failure, including defects in the substrate oxidation, and the electron transport chain (ETC) and oxidative phosphorylation (OXPHOS). However, whether such changes occur early in the development of heart failure, and are potentially involved in the pathologic events that lead to cardiac dysfunction is unknown. To address this question, we conducted transcriptomic/metabolomics profiling in hearts of mice with two progressive stages of pressure overload-induced cardiac hypetrophy: i) cardiac hypertrophy with preserved ventricular function achieved via transverse aortic constriction for 4 weeks (TAC) and ii) decompensated cardiac hypertrophy or heart failure (HF) caused by combining 4 wk TAC with a small apical myocardial infarction. Transcriptomic analyses revealed, as shown previously, downregulated expression of genes involved in mitochondrial fatty acid oxidation in both TAC and HF hearts compared to sham-operated control hearts. Surprisingly, however, there were very few changes in expression of genes involved in other mitochondrial energy transduction pathways, ETC, or OXPHOS. Metabolomic analyses demonstrated significant alterations in pathway metabolite levels in HF (but not in TAC), including elevations in acylcarnitines, a subset of amino acids, and the lactate/pyruvate ratio. In contrast, the majority of organic acids were lower than controls. This metabolite profile suggests “bottlenecks” in the carbon substrate input to the TCA cycle. This transcriptomic/metabolomic profile was markedly different from that of mice PGC-1a/b deficiency in which a global downregulation of genes involved in mitochondrial ETC and OXPHOS was noted. In addition, the transcriptomic/metabolomic signatures of HF differed markedly from that of the exercise-trained mouse heart. We conclude that in contrast to current dogma, alterations in mitochondrial metabolism that occur early in the development of heart failure reflect largely post-transcriptional mechanisms resulting in impedance to substrate flux into the TCA cycle, reflected by alterations in the metabolome. Microarray gene expression profiling was performed with bi-ventricle RNA isolated from (1) 3 month-old female C57Bl6/J mice with transverse aortic constriction (CH), vs sham-operated control (Sham-CH), (2) 3 month-old female C57Bl6/J mice with heart failure (HF), vs. sham-operated control (Sham-HF); (3) 2 month-old female C57Bl6/J mice with voluntary wheel training for 2 months (Run), vs. Sedentary control (Sed). Five biological replicates are included for each group.

Project description:Compelling evidence suggests that mitochondrial dysfunction contributes to the pathogenesis of heart failure, including defects in the substrate oxidation, and the electron transport chain (ETC) and oxidative phosphorylation (OXPHOS). However, whether such changes occur early in the development of heart failure, and are potentially involved in the pathologic events that lead to cardiac dysfunction is unknown. To address this question, we conducted transcriptomic/metabolomics profiling in hearts of mice with two progressive stages of pressure overload-induced cardiac hypetrophy: i) cardiac hypertrophy with preserved ventricular function achieved via transverse aortic constriction for 4 weeks (TAC) and ii) decompensated cardiac hypertrophy or heart failure (HF) caused by combining 4 wk TAC with a small apical myocardial infarction. Transcriptomic analyses revealed, as shown previously, downregulated expression of genes involved in mitochondrial fatty acid oxidation in both TAC and HF hearts compared to sham-operated control hearts. Surprisingly, however, there were very few changes in expression of genes involved in other mitochondrial energy transduction pathways, ETC, or OXPHOS. Metabolomic analyses demonstrated significant alterations in pathway metabolite levels in HF (but not in TAC), including elevations in acylcarnitines, a subset of amino acids, and the lactate/pyruvate ratio. In contrast, the majority of organic acids were lower than controls. This metabolite profile suggests “bottlenecks” in the carbon substrate input to the TCA cycle. This transcriptomic/metabolomic profile was markedly different from that of mice PGC-1a/b deficiency in which a global downregulation of genes involved in mitochondrial ETC and OXPHOS was noted. In addition, the transcriptomic/metabolomic signatures of HF differed markedly from that of the exercise-trained mouse heart. We conclude that in contrast to current dogma, alterations in mitochondrial metabolism that occur early in the development of heart failure reflect largely post-transcriptional mechanisms resulting in impedance to substrate flux into the TCA cycle, reflected by alterations in the metabolome.

Project description:Background: Embryonic trancription factor TBX18 re-expression has been demonstrated to be capable of converting ventricular myocytes to pacemakers cells. The goals of this study are to investigate the effects of TBX18 on myocytes and non-myocytes at day 3, day 6 and day 14, as well as tracking the key node of reprogramming process and mechanism. Methods: Neonatal rat ventricular myocytes (NRVC) were treated by adeno-TBX18 or GFP for 3 days to investigate the early effects of TBX18 on myocytes and non-myocytes. Except for these 2 treatments, Adeno-TBX18 with one specific Tgfβ inhibitor, A83-01 (0.2uM) was treated for NRVC for 14 days for explore the effects of Tgfβ inhibition on fibroblast activation and myocyte reprogramming process. Attached NRVC monolayers were digested with 0.25% trypsin (Cat# LS003707, Corning, NY) for 5 min at 37 °C, and filtered through a 100-μm cell strainer (Fischer Scientific, Waltham, MA) to generate a single-cell suspension. Single cells were resuspended to a concentration of 700-2,000 cells per microliter. Gel beads-in-emulsion (GEMs) were generated with Chromium X (10X Genomics, Pleasanton, CA) and RNA libraries were prepared using the Chromium Next GEM Single Cell 3' GEM kit, v3.1 (10X Genomics Inc., Pleasanton, CA) with a targeted cell recovery of 4,000-10,000 cells per reaction. Quality control of cDNA and scRNA-seq libraries were performed using the Bioanalyzer High Sensitivity kit (Agilent Technologies Inc., CA). Libraries were sequenced using Novaseq 6000 (Illumina Inc., CA) with a minimum depth of 50,000–65,000 read pairs per cell. Result: Upon QA/QC filtering, 13,437 cells met the quality thresholds for subsequent analysis. We focused on three cell types: cardiomyocytes (CMs, Tnni3-positive), total FBs (Pdgfrb and Tcf21-positive) with 2 subpopulations, including myoFBs (Pdgfrb, Tcf21, Acta2-high) and quiescent FBs (Pdgfrb, Tcf21, Acta2-low). Pathway analysis further revealed that upregulated DEGs by TBX18 are involved in fibroblast activation and ECM remodeling. Among those, Tgfβ signaling, which is one of the major molecular mediators of fibrosis in the heart, figured prominently in TBX18-transduced CMs and FBs. This was evidenced by upregulated expression of Tgfβ ligands and profibrotic genes such as Tgfb1, Tgfb2, and Acta2 in TBX18-NRVCs. Accordingly, higher proportion of activated myofibroblasts (39.3% vs. 25.4%) and lower proportion of quiescent FBs were observed in TBX18-NRVCs compared to control (Fig. 2F). To test the causative role of Tgfβ signaling in triggering fibrosis upon TBX18 re-expression, monolayers of NRVCs were treated with a small molecule inhibitor of type I Tgfβ receptors, A83-01. Treatment with A83-01 significantly decreased the population of myoFBs from 68.0% in TBX18-NRVC to 49.5% of total cell population at d14. Heat map analysis of all genes indicated that TBX18-CMs show upregulation of fibroblast-related genes, which is mitigated with A83-01 treatment. The upregulated DEGs in TBX18-FBs pointed to ECM remodeling as well as inflammatory response involving Tgfβ and other cytokines. Again, treatment with A83-01 abrogated the rise of these pathways. Profibrotic genes such as Tgfb2, Tgfb3, Acta2, and inflammatory genes were upregulated in FBs transduced with Ad-TBX18, which was mitigated by A83-01 treatment. The upregulated gene clusters in TBX18-FBs were also upregulated in TBX18-CMs, particularly, interferon signaling, interleukin-4 regulation of apoptosis, which may have led to the loss of TBX18-CMs over time. The inflammatory and profibrotic pathways were suppressed by treatment with A83-01 and may explain the higher population of TBX18-CMs with A83-01 at d14.We also quantified the number of de novo iPMs based on: Tnni3high, Hcn4+, Nkx2-5low, Gja1low through our scRNA-seq analysis and demonstrated the proportions of Hcn4+ iPMs was similar in TBX18-CMs regardless of Tgfβ inhibition but was higher compared to control. Conclusion: Tgfβ signaling inhibition with a83-01 prevents against myofibroblast activation, cardiomyocytes apoptosis and inflammatory response induced by TBX18, and short term treatment of A8301 does not strongly interfere the reprogramming process and efficiency.

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Developmental heterogeneity of cardiac fibroblasts does not predict pathological proliferation and activation

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