Extracellular flux analysis in intact cardiac tissue slices-A novel tool to investigate cardiac substrate metabolism in mouse myocardium.

AIM: Cardiac pathologies are accompanied by alterations in substrate metabolism, and extracellular flux analysis is a standard tool to investigate metabolic disturbances, especially in immortalized cell lines. However, preparations of primary cells, such as adult cardiomyocytes require enzymatic dissociation and cultivation affecting metabolism. Therefore, we developed a flux analyzer-based method for the assessment of substrate metabolism in intact vibratome-sliced mouse heart tissue. METHODS: Oxygen consumption rates were determined using a Seahorse XFe24-analyzer and "islet capture plates." We demonstrate that tissue slices are suitable for extracellular flux analysis and metabolize both free fatty acids (FFA) and glucose/glutamine. Functional integrity of tissue slices was proven by optical mapping-based assessment of action potentials. In a proof-of-principle approach, the sensitivity of the method was tested by analyzing substrate metabolism in the remote myocardium after myocardial infarction (I/R). RESULTS: Here, I/R increased uncoupled OCR compared with sham animals indicating a stimulated metabolic capacity. This increase was caused by a higher glucose/glutamine metabolism, whereas FFA oxidation was unchanged. CONCLUSION: In conclusion, we describe a novel method to analyze cardiac substrate metabolism in intact cardiac tissue slices by extracellular flux analysis. The proof-of-principle experiment demonstrated that this approach has a sensitivity allowing the investigation of pathophysiologically relevant disturbances in cardiac substrate metabolism.

Insulin-Like Growth Factor 1 Attenuates the Pro-Inflammatory Phenotype of Neutrophils in Myocardial Infarction.

Acute myocardial infarction (MI) induces an extensive sterile inflammation, which is dominated in the early phase by invading neutrophils and monocytes/macrophages. The inflammatory response after MI critically affects infarct healing and cardiac remodeling. Therefore, modulation of cardiac inflammation may improve outcome post MI. Insulin-like growth factor 1 (IGF1) treatment reduces infarct size and improves cardiac function after MI via IGF1 receptor mediated signaling in myeloid cells. Our study aimed to investigate the effect of IGF1 on neutrophil phenotype both in vitro and in vivo after MI. We show that IGF1 induces an anti-inflammatory phenotype in bone marrow derived neutrophils. On the molecular and functional level IGF1 treated neutrophils were indistinguishable from those induced by IL4. Surprisingly, insulin, even though it is highly similar to IGF1 did not create anti-inflammatory neutrophils. Notably, the IGF1 effect was independent of the canonical Ras/Raf/ERK or PI3K/AKT pathway, but depended on activation of the JAK2/STAT6 pathway, which was not activated by insulin treatment. Single cell sequencing analysis 3 days after MI also showed that 3 day IGF1 treatment caused a downregulation of pro-inflammatory genes and upstream regulators in most neutrophil and many macrophage cell clusters whereas anti-inflammatory genes and upstream regulators were upregulated. Thus, IGF1 acts like an anti-inflammatory cytokine on myeloid cells in vitro and attenuates the pro-inflammatory phenotype of neutrophils and macrophages in vivo after MI. IGF1 treatment might therefore represent an effective immune modulatory therapy to improve the outcome after MI.

Full-length transcriptomic analysis in murine and human heart reveals diversity of PGC-1α promoters and isoforms regulated distinctly in myocardial ischemia and obesity.

BACKGROUND: Peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) acts as a transcriptional coactivator and regulates mitochondrial function. Various isoforms are generated by alternative splicing and differentially regulated promoters. In the heart, total PGC-1α deficiency knockout leads to dilatative cardiomyopathy, but knowledge on the complexity of cardiac isoform expression of PGC-1α remains sparse. Thus, this study aims to generate a reliable dataset on cardiac isoform expression pattern by long-read mRNA sequencing, followed by investigation of differential regulation of PGC-1α isoforms under metabolic and ischemic stress, using high-fat-high-sucrose-diet-induced obesity and a murine model of myocardial infarction. RESULTS: Murine (C57Bl/6J) or human heart tissue (obtained during LVAD-surgery) was used for long-read mRNA sequencing, resulting in full-length transcriptomes including 58,000 mRNA isoforms with 99% sequence accuracy. Automatic bioinformatic analysis as well as manual similarity search against exonic sequences leads to identification of putative coding PGC-1α isoforms, validated by PCR and Sanger sequencing. Thereby, 12 novel transcripts generated by hitherto unknown splicing events were detected. In addition, we postulate a novel promoter with homologous and strongly conserved sequence in human heart. High-fat diet as well as ischemia/reperfusion (I/R) injury transiently reduced cardiac expression of PGC-1α isoforms, with the most pronounced effect in the infarcted area. Recovery of PGC-1α-isoform expression was even more decelerated when I/R was performed in diet-induced obese mice. CONCLUSIONS: We deciphered for the first time a complete full-length transcriptome of the murine and human heart, identifying novel putative PGC-1α coding transcripts including a novel promoter. These transcripts are differentially regulated in I/R and obesity suggesting transcriptional regulation and alternative splicing that may modulate PGC-1α function in the injured and metabolically challenged heart.

4-hydroxytamoxifen does not deteriorate cardiac function in cardiomyocyte-specific MerCreMer transgenic mice.

Conditional, cell-type-specific transgenic mouse lines are of high value in cardiovascular research. A standard tool for cardiomyocyte-restricted DNA editing is the αMHC-MerCreMer/loxP system. However, there is an ongoing debate on the occurrence of cardiac side effects caused by unspecific Cre activity or related to tamoxifen/oil overload. Here, we investigated potential adverse effects of DNA editing by the αMHC-MerCreMer/loxP system in combination with a low-dose treatment protocol with the tamoxifen metabolite 4-hydroxytamoxifen (OH-Txf). αMHC-MerCreMer mice received intraperitoneally OH-Txf (20 mg/kg) for 5 or 10 days. These treatment protocols were highly efficient to induce DNA editing in adult mouse hearts. Multi-parametric magnetic resonance imaging revealed neither transient nor permanent effects on cardiac function during or up to 19 days after 5 day OH-Txf treatment. Furthermore, OH-Txf did not affect cardiac phosphocreatine/ATP ratios assessed by in vivo 31P MR spectroscopy, indicating no Cre-mediated side effects on cardiac energy status. No MRI-based indication for the development of cardiac fibrosis was found as mean T1 relaxation time was unchanged. Histological analysis of myocardial collagen III content after OH-Txf confirmed this result. Last, mean T2 relaxation time was not altered after Txf treatment suggesting no pronounced cardiac lipid accumulation or tissue oedema. In additional experiments, cardiac function was assessed for up to 42 days to investigate potential delayed side effects of OH-Txf treatment. Neither 5- nor 10-day treatment resulted in a depression of cardiac function. Efficient cardiomyocyte-restricted DNA editing that is free of unwanted side effects on cardiac function, energetics or fibrosis can be achieved in adult mice when the αMHC-MerCreMer/loxP system is activated by the tamoxifen metabolite OH-Txf.

FTO affects hippocampal function by regulation of BDNF processing.

Initially, the function of the fat mass and obesity associated (Fto) gene seemed to be primarily the regulation of the body weight. Here we show that loss of Fto results in a hyperactivation of the hypothalamic-pituitary-adrenal (HPA) axis. In consequence, Fto-/- mice display an anxiety-like behavior and impairments in working memory. Furthermore, differentiation of neurons is affected in the hippocampus. As a cause of these impairments we identified a processing defect of the neurotrophin BDNF which is most likely the result of a reduced expression of MMP-9. Therefore, we propose FTO as a possible new target to develop novel approaches for the treatment of diseases associated with hippocampal disorders. In parallel, we also would like to make the point that any anti-obesity therapy via blocking FTO function can have negative effects on the proper function of the hippocampus.

IGF1 Treatment Improves Cardiac Remodeling after Infarction by Targeting Myeloid Cells.

Insulin-like growth factor 1 (IGF1) is an anabolic hormone that controls the growth and metabolism of many cell types. However, IGF1 also mediates cardio-protective effects after acute myocardial infarction (AMI), but the underlying mechanisms and cellular targets are not fully understood. Here we demonstrate that short-term IGF1 treatment for 3 days after AMI improved cardiac function after 1 and 4 weeks. Regional wall motion was improved in ischemic segments, scar size was reduced, and capillary density increased in the infarcted area and the border zone. Unexpectedly, inducible inactivation of the IGF1 receptor (IGF1R) in cardiomyocytes did not attenuate the protective effect of IGF1. Sequential cardiac transcriptomic analysis indicated an altered myeloid cell response in the acute phase after AMI, and, notably, myeloid-cell Igf1r-/- mice lost the protective IGF1 function after I/R. In addition, IGF1 induced an M2-like anti-inflammatory phenotype in bone marrow-derived macrophages and enhanced the number of anti-inflammatory macrophages in heart tissue on day 3 after AMI in vivo. In summary, modulation of the acute inflammatory phase after AMI by IGF1 represents an effective mechanism to preserve cardiac function after I/R.

Cell type-specific regulation of ciliary transition zone assembly in vertebrates.

Ciliopathies are life-threatening human diseases caused by defective cilia. They can often be traced back to mutations of genes encoding transition zone (TZ) proteins demonstrating that the understanding of TZ organisation is of paramount importance. The TZ consists of multimeric protein modules that are subject to a stringent assembly hierarchy. Previous reports place Rpgrip1l at the top of the TZ assembly hierarchy in Caenorhabditis elegans By performing quantitative immunofluorescence studies in RPGRIP1L-/- mouse embryos and human embryonic cells, we recognise a different situation in vertebrates in which Rpgrip1l deficiency affects TZ assembly in a cell type-specific manner. In cell types in which the loss of Rpgrip1l alone does not affect all modules, additional truncation or removal of vertebrate-specific Rpgrip1 results in an impairment of all modules. Consequently, Rpgrip1l and Rpgrip1 synergistically ensure the TZ composition in several vertebrate cell types, revealing a higher complexity of TZ assembly in vertebrates than in invertebrates.