Single cell sequencing reveals endothelial plasticity with transient mesenchymal activation after myocardial infarction.

Endothelial cells play a critical role in the adaptation of tissues to injury. Tissue ischemia induced by infarction leads to profound changes in endothelial cell functions and can induce transition to a mesenchymal state. Here we explore the kinetics and individual cellular responses of endothelial cells after myocardial infarction by using single cell RNA sequencing. This study demonstrates a time dependent switch in endothelial cell proliferation and inflammation associated with transient changes in metabolic gene signatures. Trajectory analysis reveals that the majority of endothelial cells 3 to 7 days after myocardial infarction acquire a transient state, characterized by mesenchymal gene expression, which returns to baseline 14 days after injury. Lineage tracing, using the Cdh5-CreERT2;mT/mG mice followed by single cell RNA sequencing, confirms the transient mesenchymal transition and reveals additional hypoxic and inflammatory signatures of endothelial cells during early and late states after injury. These data suggest that endothelial cells undergo a transient mes-enchymal activation concomitant with a metabolic adaptation within the first days after myocardial infarction but do not acquire a long-term mesenchymal fate. This mesenchymal activation may facilitate endothelial cell migration and clonal expansion to regenerate the vascular network

Noncompaction of the Ventricular Myocardium Is Associated with a De Novo Mutation in the β-Myosin Heavy Chain Gene

Noncompaction of the ventricular myocardium (NVM) is the morphological hallmark of a rare familial or sporadic unclassified heart disease of heterogeneous origin. NVM results presumably from a congenital developmental error and has been traced back to single point mutations in various genes. The objective of this study was to determine the underlying genetic defect in a large German family suffering from NVM. Twenty four family members were clinically assessed using advanced imaging techniques. For molecular characterization, a genome-wide linkage analysis was undertaken and the disease locus was mapped to chromosome 14ptel-14q12. Subsequently, two genes of the disease interval, MYH6 and MYH7 (encoding the α- and β-myosin heavy chain, respectively) were sequenced, leading to the identification of a previously unknown de novo missense mutation, c.842G>C, in the gene MYH7. The mutation affects a highly conserved amino acid in the myosin subfragment-1 (R281T). In silico simulations suggest that the mutation R281T prevents the formation of a salt bridge between residues R281 and D325, thereby destabilizing the myosin head. The mutation was exclusively present in morphologically affected family members. A few members of the family displayed NVM in combination with other heart defects, such as dislocation of the tricuspid valve (Ebstein's anomaly, EA) and atrial septal defect (ASD). A high degree of clinical variability was observed, ranging from the absence of symptoms in childhood to cardiac death in the third decade of life. The data presented in this report provide first evidence that a mutation in a sarcomeric protein can cause noncompaction of the ventricular myocardium

Single cell sequencing reveals endothelial plasticity with transient mesenchymal activation after myocardial infarction

Endothelial cells play a critical role in the adaptation of tissues to injury. Tissue ischemia induced by infarction leads to profound changes in endothelial cell functions and can induce transition to a mesenchymal state. Here we explore the kinetics and individual cellular responses of endothelial cells after myocardial infarction by using single cell RNA sequencing. This study demonstrates a time dependent switch in endothelial cell proliferation and inflammation associated with transient changes in metabolic gene signatures. Trajectory analysis reveals that the majority of endothelial cells 3 to 7 days after myocardial infarction acquire a transient state, characterized by mesenchymal gene expression, which returns to baseline 14 days after injury. Lineage tracing, using the Cdh5-CreERT2;mT/mG mice followed by single cell RNA sequencing, confirms the transient mesenchymal transition and reveals additional hypoxic and inflammatory signatures of endothelial cells during early and late states after injury. These data suggest that endothelial cells undergo a transient mes-enchymal activation concomitant with a metabolic adaptation within the first days after myocardial infarction but do not acquire a long-term mesenchymal fate. This mesenchymal activation may facilitate endothelial cell migration and clonal expansion to regenerate the vascular network

Localization of R281 in a protein model of the myosin heavy chain.

<p>A, Positions of amino acids affected in NVM, HCM and DCM. The mutations were plotted on a model of chicken skeletal myosin subfragment-1 (PDB code 2MYS). Functional sites are indicated by arrows. 68 selected mutations causing HCM are indicated by yellow spheres and 4 mutations causing DCM by green spheres. The mutations were selected from the UniProt database (UniProtKB) and from two publications<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0001362#pone.0001362-Woo1" target="_blank">[33]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0001362#pone.0001362-Villard1" target="_blank">[34]</a>. The described NVM causing mutation is highlighted as a blue sphere and labeled according to the position in MYH7_HUMAN. B, Close-up view of the salt bridge between residues R281 and D325 in chicken skeletal myosin subfragment-1 (PDB code 2MYS). The amino acids are numbered according to MYH7_HUMAN. The sulfate molecule (yellow and orange) marks the ATPase active site for better orientation. The residues R281 and D325 are shown according to the CPK color scheme (grey, carbon atoms; red, oxygen atoms, i.e. acidic side chain; light blue, nitrogen atoms, i.e. basic side chain). The salt bridge between R281 and D325 is symbolized by dashed black lines that indicate potential hydrogen bonds. The helix attached to D325 is highlighted in red.</p

Multiple alignment of different myosin molecules.

<p>The interacting sites R281 and D325 (both in bold, position numbering according to MYH7_HUMAN) are highly conserved between myosin molecules of human, fruit fly, zebrafish and <i>Caenorhabditis elegans</i>, respectively (*, identical position; :, conservative exchange). Sequence names correspond to SwissProt entry names: MYH7_HUMAN-human myosin heavy chain, cardiac muscle beta isoform; MYH1_HUMAN-human myosin heavy chain, skeletal muscle, adult 1; MYH4_HUMAN-human myosin heavy chain, skeletal muscle, fetal; MYH1_MOUSE-murine myosin heavy chain, skeletal muscle, adult 1; MYH4_RABIT-rabbit myosin heavy chain, skeletal muscle, juvenile; MYSS_CHICK-chicken myosin heavy chain, skeletal muscle, adult; Q802Z4_BRARE (Q802_BRARE)-zebrafish protein Q802Z4; MYSA_DROME-fruit fly myosin heavy chain, muscle; MYO3_CAEEL-<i>Caenorhabditis elegans</i> myosin heavy chain A.</p

Imaging of NVM in the index patient (III:4, panel A) and her sister's daughter (IV:13, panel B).

<p>Shown are two-dimensional echocardiographs (ventricular part of a four-chamber view) in diastole, with (right) and without (left) color flow imaging. Arrows point to recesses in the myocardial wall.</p

Pedigree of family DU-11 with haplotypes on chromosome 14 and segregation of <i>MYH7</i> mutation R281T (c.842G>C).

<p>Family members are shown by filled black symbols (affected), by half filled symbols (partially affected), open symbols (unaffected) and gray symbols (unknown affection status). An arrow points to the index patient. The disease associated haplotype is shown by filled black bars. Markers within the minimum disease associated haplotype are boxed. Below the haplotypes of each individual the occurrence of wild-type (+) and mutant <i>MYH7</i> alleles (−) is indicated.</p

Imaging of NVM in patient III:8 of family DU-11.

<p>A, Magnetic resonance image: long-axis plane in diastole. Prominent myocardial trabeculations and deep intertrabecular recesses are seen in the apical half of the right and left ventricle as indicated by arrows. B, Magnetic resonance image: short-axis plane in diastole. In the apex region the cavum and the myocardial wall can not clearly be distinguished. Extensive trabeculations in this region produce a sponge-like appearance of the myocardium. C, Two-dimensional echocardiograph: apical four-chamber view in diastole with (right) and without (left) color flow imaging. A massive apical thickening is seen without any evidence of trabeculations in the left image. In contrast, color flow imaging (right image) shows more clearly the recesses extending deeply into the myocardial wall. D, Two-dimensional echocardiograph: parasternal short-axis view in diastole with (right) and without (left) color flow imaging. The left image shows a mesh-like morphology in the mid-region of the left ventricle. The cavum is not clearly discernable. The right image demonstrates numerous small blood-flow eddies within the sponge-like myocardium (as shown by color flow imaging). LV, left ventricle; RV, right ventricle; LA, left atrium; RA, right atrium.</p

Patient Characteristics (initial presentation)

a<p>Age at presentation in years; dc, deceased;</p>b<p>HF, chronic heart failure; NYHA, classi-fication of heart failure according to the New York Heart Association; CD, cardiac death</p>c<p>EA, Ebstein's anomaly;</p>d<p>ASD, atrial septal defect;</p>e<p>aECG, abnormal ECG;</p>f<p>NVM, non-compaction of the ventricular myocardium; +, affected; (+), partially affected; see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0001362#s4" target="_blank">Material and Methods</a> for details on the affection status; non-isolated/isolated: with/without EA and/or ASD. Listed are all carriers of the <i>MYH7</i> mutation and in addition individual III-2 who was not genotyped.</p