Loss of smooth muscle SDF-1/CXCL12 leads to cardiac hypertrophy and aortic valve stenosis

Background

Stromal cell-derived factor-1 (SDF-1 or CXCL12) and its receptors CXCR4/CXCR7 have prominent role in cardiovascular development and myocardial repair following ischemic injury. Nevertheless, detailed mechanisms of the cell specific role of SDF-1 are poorly understood. Since SDF-1-EGFP lineage tracking revealed high expression of SDF-1 in smooth muscle cells, we aimed to investigate the cell specific role by generating a smooth muscle cell specific SDF-1 (SM-SDF-1−/−) knockout mouse model.

Methods

SDF-1 expression was analyzed utilizing SDF-1-EGFP reporter mice. Conditional SM-SDF-1 KO mice were generated using Tagln-Cre; SDF-1fl/fl mice. Hearts were analysed with histology and high-resolution episcopic microscopy. Cardiac function was assessed utilizing echocardiography. RNAseq, qRT-PCR, flow cytometry and western blotting were performed. Cardiac fibrosis, apoptotic index, cell proliferation, aortic valve calcification were analyzed. SM-SDF-1−/− mice were treated with the CXCR7 agonist TC14012 (10mg/kg/I.P).

Results

SDF-1-EGFP lineage tracking and immunofluorescence revealed high expression of SDF-1 particularly in smooth muscle cells and less frequently in perivascular and endothelial cells. Conditional SM-SDF-1−/− mice showed a high pre- and perinatal mortality (50%). Immunohistochemistry of SM-SDF-1−/− mice revealed severe cardiac hypertrophy, associated with increased cardiac fibrosis, apoptotic cell death, thinned and dilated arteries and significantly decreased M2 like CD11b+/CD206+ cells. Echocardiography confirmed concentric hypertrophy, with decreased stroke volume. As a possible reason for cardiac hypertrophy, SDF-1 mutants exhibited aortic stenosis due to aortic valve thickening associated with downregulation of the SDF-1 co-receptor CXCR7. We further noticed increased plasma levels of SDF-1 in aortic stenosis patients suggesting a cardioprotective role. Transcriptome analyses from KO hearts showed an abnormal extracellular matrix (ECM) remodelling with a specific upregulation of the important valve related proteoglycans Versican, Glycan. Western blot analysis revealed activation of AKT and ERK, whereas CXCR7 expression was significantly downregulated in KO mice. To rescue the phenotype we treated KO mice with the CXCR7 agonist (TC14012) which partially attenuated aortic valve remodelling through activation of the ERK signalling pathway.

Conclusion

Our data suggest that SDF-1 is critically involved in maintaining the homeostasis of the aortic valve by regulating CXCR7 signalling. Pharmacological activation of CXCR7 might be a promising therapeutic target to limit the progression of aortic valve stenosis.

Ghadge_SM-SDF-1−/−

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): Austrian Science Fund, Austrian research promotion agency

6090Conditional ablation of SDF-1/CXCL12 in smooth muscle cells leads to severe cardiac hypertrophy and aortic valve stenosis

Background

Stromal cell derived factor-1 (SDF-1) and its corresponding receptors CXCR4 & CXCR7 have been shown to play pivotal roles during cardiovascular development, cardiac repair and tissue homeostasis after ischemia. Stabilization of the SDF-1/CXCR4+ axis has been shown to provide beneficial effects on myocardial repair. Nevertheless, detailed mechanisms of the cell specific role of SDF-1 are poorly understood. Since SDF-1-EGFP lineage tracking revealed high expression of SDF-1 in smooth muscle cells, we aimed to investigate the cell specific role by generating a smooth muscle cell specific SDF-1 (SM-SDF-1 KO) knockout mouse model.

Methods

SDF-1 expression was analyzed utilizing SDF-1-EGFP reporter mice. SM-SDF-1 KO mice were generated using Cre/LoxP technology (SM22a-Cre; SDF-1fl/fl). Morphology was analysed with immunohistochemistry and immunofluorescence. Cardiac function was assessed utilizing echocardiography and millar tip catheterization. Whole transcriptome analysis, qRT-PCR and western blotting were performed. Further, apoptotic index and cell proliferation were quantified by TUNEL assay and PH3 immunostaining, respectively.

Results

SDF-1-EGFP lineage tracking and immunofluorescence analysis revealed high expression of SDF-1 particularly in smooth muscle cells and less frequently in perivascular and endothelial cells. Conditional SM-SDF-1 KO mice showed a high pre- and perinatal mortality (50%). Immunohistochemistry in surviving adult SM-SDF-1 KO mice revealed a severe cardiac hypertrophy phenotype, associated with increased cardiac fibrosis and apoptotic cell death. SM-SDF-1 KO mice revealed very thin and dilated arteries. Echocardiography measurements confimed concentric hypertrophy, and decreased stroke volume reflecting restrictive hypertrophic cardiomyopathy. Immunohistochemistry confirmed pronounced hypertrophy of cardiomyocytes. Additionally, we found evidence for enhanced proliferation markers in cardiomyocytes of SM-SDF-1 KO mice. Transcriptome analyses from KO hearts vs. non-ablated littermates identified over 150 significantly up- and downregulated genes. Western blot analysis for HIF-1α, AKT and ERK cell-signalling pathways were significantly elevated, whereas Rho Kinase signalling was specifically downregulated in SM-SDF-1 KO mice. As a possible reason for the hypertrophic phenotype, SDF-1 mutants exhibited aortic stenosis due to aortic valve thickening associated with upregulation of the extracellular proteoglycan versican anddownregulation of the SDF-1 co-receptor CXCR7. We further noticed increased plasma levels of SDF-1 in aortic stenosis patients suggesting a cardioprotective role.

Conclusion

Our data suggest that smooth muscle cell specific expression of SDF-1 plays a prominent role in cardiovascular development leadingto cardiac hypertrophy in adult animals. Our data further suggest that SDF-1 is involved in maintaining the homeostasis of the aortic valve, possibly by regulating versican.

Acknowledgement/Funding

FWF Austria

Computational meta'omics for microbial community studies

Complex microbial communities are an integral part of the Earth's ecosystem and of our bodies in health and disease. In the last two decades, culture-independent approaches have provided new insights into their structure and function, with the exponentially decreasing cost of high-throughput sequencing resulting in broadly available tools for microbial surveys. However, the field remains far from reaching a technological plateau, as both computational techniques and nucleotide sequencing platforms for microbial genomic and transcriptional content continue to improve. Current microbiome analyses are thus starting to adopt multiple and complementary meta'omic approaches, leading to unprecedented opportunities to comprehensively and accurately characterize microbial communities and their interactions with their environments and hosts. This diversity of available assays, analysis methods, and public data is in turn beginning to enable microbiome-based predictive and modeling tools. We thus review here the technological and computational meta'omics approaches that are already available, those that are under active development, their success in biological discovery, and several outstanding challenges.