Abstract
Valve remodeling is a process involving extracellular matrix organization and elongation of valve leaflets. Here, through single-cell RNA sequencing of human fetal valves, we identified an elastin-producing valve interstitial cell (VIC) subtype (apolipoprotein E (APOE)+, elastin-VICs) spatially located underneath valve endothelial cells (VECs) sensing unidirectional flow. APOE knockdown in fetal VICs resulted in profound elastogenesis defects. In valves with pulmonary stenosis (PS), we observed elastin fragmentation and decreased expression of APOE along with other genes regulating elastogenesis. Cell–cell interaction analysis revealed that jagged 1 (JAG1) from unidirectional VECs activates elastogenesis in elastin-VICs through NOTCH2. Similar observations were made in VICs cocultured with VECs under unidirectional flow. Notably, a drastic reduction of JAG1–NOTCH2 was also observed in PS valves. Lastly, we found that APOE controls JAG1-induced NOTCH activation and elastogenesis in VICs through the extracellular signal-regulated kinase pathway. Our study suggests important roles of both APOE and NOTCH in regulating elastogenesis during human valve remodeling.
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Data availability
The raw and processed data from single-cell RNA sequencing in this study have been deposited to the Gene Expression Omnibus database (https://www.ncbi.nlm.nih.gov/geo/) under accession number GSE228638. The datasets are open to the public for research purposes without restriction. GSE117011 (Hulin et al.21, PMID: 30796046) and GSE106118 (Cui et al.19, PMID: 30759401) were also used as published source data. Source data are provided with this paper.
Code availability
Code for scRNA-seq CCA integration and cell–cell interaction can be accessed via GitHub at https://github.com/ly19901105/-APOE-NOTCH-Axis-Governs-Elastogenesis-During-Human-Cardiac-Valve-Remodeling.git.
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Acknowledgements
This work was supported by Additional Ventures (1019125), a CCRF Endowed Scholar Award (M. Gu) and the Chan Zuckerberg Initiative (CZF2019-002440 and CZF2021-237566) (J.R.S.). N.P. received the American Heart Association Predoctoral Fellowship grant 1013861. Z.Y. received the American Heart Association Predoctoral Fellowship grant 906513. We greatly appreciate M. Faust, L. Fist and O. Croweak from the Heart Institute Biorepository (HIBR), Cincinnati Children’s Hospital Medical Center (CCHMC) for collecting and providing human pulmonary valve samples; B. DiPasquale and J. Reuss from Pathology Core, the Discover Together Biobank, CCHMC for support to the study; M. Kofron from Confocal Imaging Core (CIC), CCHMC and J. Kitzmiller from the Division of Pulmonary Biology, CCHMC for providing access to and assistance with the confocal microscope and image processing; and J.C. Wu from Stanford University for providing guidance and support to the project.
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Z.L., Z.Y., C.T., Y.M. and M. Gu conceived and designed experiments. Y.M., Z.Y., I.G., A.W. and J.R.S. collected and dissected human heart samples. Z.L. and Y.L. performed the bioinformatics analysis supervised by M. Guo. Y.-W.C. performed prenatal-based immunofluorescence analysis. Z.L. and Z.Y. performed postnatal valve immunofluorescence analysis supervised by A.O’D. and D.S.W. Z.Y., C.T. and Z.L. performed and analyzed cell-based experiments. K.E.Y. provided suggestions for the experimental design. Z.L., Z.Y., N.P., Y.M. and M. Gu wrote the manuscript with contributions from all other authors. M. Gu and Y.M. oversaw the project. All authors read and approved the manuscript.
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Nature Cardiovascular Research thanks Jae-Hoon Choi, Joy Lincoln and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Extended data
Extended Data Fig. 1 scRNA-seq of Normal Human Fetal Heart Valves.
a. Violin plot of doublet score, mitochondria percentage, number of counts, and number of features across all valves after quality control: nCount RNA < 1e5, nFeature RNA > = 1000, pMT < 10, Doublet score <0.3. A/P/M/T represent Aortic, Pulmonary, Mitral, Tricuspid valves respectively; b. UMAP visualization of cells from four different human fetal valves from two week-15 healthy hearts after integration by Canonical Correlation Analysis (CCA); c. Left: Cell number and proportion of each valve in each cell type. Right: Dot plot of representative marker genes within each valve cell type; d. Feature plot of representative marker genes in each valve cell type; e. UMAP visualization of four different human fetal valves within VICs; f. Left: Bar graph showing proportions of each valve within each VIC subtype. Right: Bar graph showing proportions of each VIC subtype within each valve; g. Feature plots for marker genes for each VIC subtype in VICs.
Extended Data Fig. 2 Re-analysis of Public Human Fetal and Mouse Postnatal Heart Valve scRNA-seq Datasets.
a. UMAP visualization of postnatal mouse valve cell types (Hulin et al., 2019); b. Feature plot of representative marker genes within each cell type within mouse valves; c. Development stage visualization (P7 and P30) and feature plots of representative marker genes for each VIC subtype; d. UMAP visualization showing mouse VIC subtypes similar to human GAG-VICs (Left) and Collagen-VICs (Right) through reverse projection; e. UMAP presentation of newly discovered Elastin-VICs, CLDN11-VICs, and Proliferative-VICs; f. UMAP visualization of human fetal valve in W22, W23, and W25 (Cui et al., 2019) integrated by CCA; g. Feature plot of representative marker genes of each cell type in Cui et al, 2019. h. UMAP visualization of VICs in W22, W23, and W25 (Cui et al., 2019).
Extended Data Fig. 3 APOE Expression and Functions in VICs During Elastogenesis.
a. Left: Representative immunofluorescence staining and RNA in situ hybridization of APOE in four human fetal valves. n = 3 different valves. White arrows represent unidirectional flow directions. Right: Violin plots of APOE and ELN expression within Elastin-VICs across each valve, A/P/M/T represent Aortic, Pulmonary, Mitral, Tricuspid valve respectively; b. Violin plots of elastogenesis-related genes (EMILIN1, LOXL1, FBN1, LTBP1) expression within Elastin-VICs across each valve; c. PCA analysis comparing four valves transcriptome in each VIC subtype; d. qPCR detection of VIC-related marker genes in cultured human fetal VICs, VECs, and HUVECs. Expression levels are normalized to HUVECs; e. Flow cytometry analysis of PECAM1 (VECs) and COL1A1 (VICs) expression in culture VICs; f. immunofluorescence staining of α-SMA (VICs) and PECAM1 (VECs) on cultured VICs; g. qPCR analysis APOE in VICs after APOE KD; h. Quantification of total elastin (both tropo-elastin(soluble) and mature elastin (insoluble)) in VICs after APOE KD. The elastin content was normalized to the total protein content; i. qPCR analysis of elastogenesis-related genes in VICs after APOE KD; j. Violin plot and feature plot of ACTA2 expression in VIC subtypes. FDR: Elastin vs. other VIC subclusters; k. Representative immunofluorescence staining of α-SMA and Elastin in four human fetal valves. White arrows represent unidirectional flow directions. Yellow arrowhead: Elastin-VIC positive for α-SMA. White arrowhead: VICs positive for α-SMA but not Elastin. n = 3; l. Contraction assay comparing scramble and APOE KD in VICs; m. qPCR analysis of contraction-related gene expressions in VICs comparing scramble and APOE KD. Data are shown as the mean ± SEM. n = 3 biological repeats. ns p > 0.05, *p < 0.05, **p < 0.01, ***p < 0.001. For g-i, l-m, scramble vs. APOE KD; d-e, VICs vs. VECs. Statistics in d-e, g-i, l-m: Unpaired 2-tailed t-test (2 groups). P values in d: COL1A1: p = 0.0121, ACTA2: p = 0.0437; in e: p < 0.0001; in g: p = 0.0023; in i: FBN2: p = 0.0265, LTBP2: p = 0.6162, LTBP4: p = 0.0422, FBLN1: p = 0.0327, FBLN2: p = 0.0526, LOX: p = 0.0003; in l: p = 0.0362; in m: ACTA2: p = 0.0011, MYH11: p = 0.0223, SMTN: p = 0.1664, CNN1: p = 0.0247. For j: Statistics adhered to a two-sided approach. Significance was determined by adjusted p-values (FDRs) < 0.05. FDR for j: FDR = 8.43E-203. FDR: False Discovery Rate. HUVECs: Human Umbilical Vein Endothelial Cells. KD: Knockdown.
Extended Data Fig. 4 Overview of Elastin-related Staining and scRNA-seq for PV with Pulmonary Stenosis.
a. Left: Verhoeff staining of pulmonary valves from the other two healthy control and age-matched Pulmonary Stenosis (PS) patients. The black staining within the dashed area indicated the elastin fiber. Right: Quantification of positive staining area of elastin fiber within elastin layer. Age of the sample were from 5-months to 10-years; b. Immunofluorescence staining of ELN, APOE, EMILIN1, and LOXL1 in pulmonary valves from control and PS. White dashed boxes corresponded to the zoom-in figures shown in Fig. 3b. n = 3 different valves; c. UMAP projection of valve cell types within pulmonary valves (PVs) from one healthy control and one patient with PS; d. Feature plots of representative marker genes within each cell type and subtype from c; e. Feature plots of representative marker genes of VIC subtypes comparing PVs from one control and one PS; f. Heatmap demonstrating the gene expression changes of elastase (MMPs) and elastase inhibitors (TIMPs) within each PV-VIC subcluster; g. qPCR of MMPs and TIMPs gene expressions in cultured human VICs comparing scramble vs. APOE KD. n = 3 biological repeats. Data shown as mean ± SEM. ns p > 0.05, *p < 0.05. For a: control vs. PS; For g: scramble vs. APOE KD. Statistics in a, g: Unpaired 2-tailed t-test (2 groups). P value in a: p = 0.0407; in g: MMP1: p = 0.2031, MMP2: p = 0.0649, MMP3: p = 0.1083, MMP9: p = 0.0635; MMP12: p = 0.1017, MMP13: p = 0.2405, MMP14: p = 0.2096, TIMP2: p = 0.0198, TIMP3: p = 0.0313, TIMP4: p = 0.8384.
Extended Data Fig. 5 Overview of VEC Populations from Human and Mouse scRNA-seq and Spatial Location.
a. UMAP demonstrating the distribution of four valves within VECs; b. Left: Bar graph showing proportions of each valve within each VEC subtype. Right: Bar graph showing proportions of each VEC subtype within each valve; c. Feature plots of marker genes for each VEC subtype; d. UMAP visualization of mouse VEC subtypes and timepoint distribution (Hulin et al., 2019); e. Feature plots of marker genes for each VEC subtype from mouse dataset; f-g. UMAP demonstration of the similarity of VEC subtypes between human and mouse VECs through reverse projection; h-i. Immunofluorescence staining of FOXC2 in four human fetal valves at W15 (h). Zoom out of immunofluorescence staining of FOXC2, CD55 and RNA in situ hybridization of PTGDS in four human fetal valves at W15 (i). White arrows represent unidirectional flow directions. n = 3 different hearts; j. UMAP visualization of each VEC subtype (Upper), and violin plot of CD55, PTGDS, FOXC2 expression among four valves (Lower); k. RNA in situ hybridization of PTGDS, APOE, PECAM1, and immunofluorescence staining of CD55, APOE, and PECAM1 in four human fetal valves at W15. n = 3 different hearts; l. Quantification of PTGDS+ VECs from Fig. 4d; m. PCA Analysis comparing four different valves in each VECs subtype. For l: Data shown as mean ± SEM. ***p < 0.001. SL vs. AV. Statistics: Unpaired 2-tailed t-test (two groups). P value in l: p = 0.0007. SL valves: Semilunar valves, A-V valves: Atrioventricular valves.
Extended Data Fig. 6 JAG1-NOTCH2 Mediated Notch Signal Between UDVECs and Elastin-VICs.
a. Major Extracellular Matrix (ECM)-related Ligand-Receptor (L-R) pairs between Elastin-VICs and unidirectional VECs (UDVECs) subtypes; b. Total L-R pair numbers between UDVECs and Elastin-VICs; c. Notch-related signaling patterns from UDVECs to Elastin-VICs; d. Gene Ontology (GO) enrichment analysis of differential expressed genes within each VIC subtype; e. Violin plot of DLL1 in VECs. FDR: PTGDS-VECs vs. other VEC subtypes; f. RNA in situ hybridization staining of PTGDS, JAG1, and NOTCH3 in four human fetal valves at W15, n = 3 different hearts; g. Violin plots of NOTCH1-3, HES1, HES4, and HEY2 in VICs. FDR: Elastin-VICs vs. other VIC subtypes; h. Immunofluorescence staining of NOTCH3, NOTCH1, HES1, and Elastin in four different valves; i. Violin plots of Notch receptors and downstream target gene expressions within Elastin-VICs (Left), and Notch ligands in UDVECs (Right) across each valve; j. qPCR analysis of Notch target genes in VICs with Jag1 (15 μg/ml) treatment; k. qPCR analysis of Notch receptors and target genes in cultured human VICs after combinational KD of NOTCH receptors. Jag1 (15ug/ml) was included; n = 3 biological repeats. Data shown as mean ± SEM. ns p > 0.05, *p < 0.05, **p < 0.01, ***p < 0.001. For g, i: Statistics adhered to a two-sided approach. Significance was determined by adjusted p-values (FDRs) < 0.05. For j, Control vs. Jag1 treatment. Unpaired 2-tailed t-test (two groups); P values for j: HEY2: p = 0.0006, HEYL: p = 0.0265, HES1: p = 0.2450. For k: one-way ANOVA followed by Tukey’s test, vs Scramble. P values for k: NOTCH2: Scramble vs. siN1: p > 0.9999, vs. siN2: p = 0.0008, vs. siN3: p = 0.1982, vs. siN1 + N2: p = 0.0024, vs. siN1 + N3: p > 0.9999, vs. siN2 + N3: p = 0.0008, vs. siN1 + N2 + N3: p = 0.0004, NOTCH1: Scramble vs. siN1: p < 0.0001, vs. siN2: p = 0.0025, vs. siN3: p = 0.0095, vs. siN1 + N2: p < 0.0001, vs. siN1 + N3: p < 0.0001, vs. siN2 + N3: p = 0.0206, vs. siN1 + N2 + N3: p < 0.0001, NOTCH3: Scramble vs. siN1: p = 0.3875, vs. siN2: p = 0.0053, vs. siN3: p < 0.0001, vs. siN1 + N2: p = 0.0038, vs. siN1 + N3: p < 0.0001, vs. siN2 + N3: p < 0.0001, vs. siN1 + N2 + N3: p < 0.0001, HEY2: Scramble vs. siN1: p = 0.6668, vs. siN2: p = 0.0413, vs. siN3: p = 0.9996, vs. siN1 + N2: p = 0.0510, vs. siN1 + N3: p = 0.9210, vs. siN2 + N3: p = 0.0238, vs. siN1 + N2 + N3: p = 0.0122, HEYL: Scramble vs. siN1: p = 0.2549, vs. siN2: p = 0.0001, vs. siN3: p = 0.0745, vs. siN1 + N2: p < 0.0001, vs. siN1 + N3: p = 0.0014, vs. siN2 + N3: p = 0.0001, vs. siN1 + N2 + N3: p < 0.0001. ECM: Extracellular Matrix, L-R: Ligand-Receptors.
Extended Data Fig. 7 Flow-induced JAG1-NOTCH2 Activation Between VICs and VECs in vitro.
a. qPCR detection of VEC-related genes in cultured VECs, VICs, and HUVECs. Expression levels are normalized to HUVECs; b. Flow cytometry analysis of PECAM1 (VECs) and COL1A1 (VICs) expression in culture VECs; c. Immunostaining of PECAM1 (VECs) and α-SMA (VICs) on cultured VECs; d. Representative bright field imaging of VECs under static, disturbed, and unidirectional/laminar flow conditions for 48 hours; e. Western blot and statistical analysis of JAG1 and GAPDH in VECs under different flow conditions. Unidirectional shear stress: 8.52 dynes/cm2; f. qPCR analysis of flow responsive genes and JAG1 expression in VECs under static or unidirectional laminar flow; g. Demonstration figure of VECs-VICs co-cultured in no-contacting condition under laminar flow; h. Immunofluorescence staining of α-SMA, NOTCH2, HES1, and EMILIN1 in VICs co-cultured with non-contacting VECs; i. qPCR detection of HEYL and HES1 in VICs co-cultured with VECs under flow conditions in partial-contact manner; j. Demonstration figure of VICs co-cultured with VEC under JAG1 KD in partial-contacting condition under laminar flow; k. qPCR detection of JAG1 in VECs under scramble or JAG1 KD; l-m. Immunofluorescence staining of α-SMA,NOTCH2 (l), and HES1 (m) in VICs co-cultured with partial-contacting VECs with JAG1 KD; n. Demonstration figure of VICs co-cultured with VECs after JAG1 overexpression (OE) in partial-contacting conditions under static flow; o. Western blot and statistical analysis of JAG1 in VECs with empty vector or JAG1 OE; p. Immunofluorescence staining of NOTCH2, NOTCH3, HES1, α-SMA, and PECAM1 in VICs co-cultured with VECs with JAG1 OE under static flow. n = 3 biological repeats. Data shown as ± SEM. ns p > 0.05, *p < 0.05, **p < 0.01, ***p < 0.001. For a-b: VICs vs. VECs; f, i: Static vs. Laminar flow; P values in a: PECAM1: p < 0.0001, CDH5: p = 0.0002; in b: p < 0.0001; k: scramble vs. JAG1 KD; o: empty vector vs. JAG1 OE. Statistics in a-b, f, i, k, o: Unpaired 2-tailed t-test (two groups), in e: one-way ANOVA followed by Tukey’s test, vs. Static flow. P values in e: Static vs. Disturbed flow: p = 0.6939, Static vs. Unidirectional flow: p = 0.0038; in f: JAG1: p = 0.0331, KLF2: p = 0.0065, KLF4: p = 0.0183, NOS3: p = 0.0129; in i: HEYL: p = 0.0412, HES1: p = 0.0818; in k: p < 0.0001; in o: p = 0.0224. Panels g, j and n created with BioRender.com.
Extended Data Fig. 8 APOE Controlled Jag1-induced Elastogenesis and Contraction in VICs.
a. qPCR analysis of elastogenesis-related genes in VICs with Jag1 treatment; b. Contraction assay of VICs with Jag1 treatment; c. qPCR analysis of contraction-related genes in VICs with Jag1 treatment. Jag1: 15 μg/ml; d. qPCR analysis of FBN2, LTBP1, FBLN2 and EMILIN1 expressions in each NOTCH receptor KD condition; e. Contraction assay of VICs with Jag1 treatment and APOE KD; f. qPCR analysis of contraction-related genes in VICs with Jag1 treatment and APOE KD. Jag1: 15 μg/ml. n = 3 biological repeats in each panel. Data shown as ± SEM. ns p > 0.05, *p < 0.05, **p < 0.01, ***p < 0.001. For a-c, control vs. Jag1 treatment. unpaired 2-tailed t-test (two groups). P value in a: ELN: p = 0.4570, FBN1: p = 0.0902, LTBP1: p = 0.0023, EMILIN1: p = 0.0060, LOXL1: p = 0.0083, FBN2: p = 0.0384, LTBP2: p = 0.7548, LTBP4: 0.0451, FBLN1: p = 0.4267, FBLN2: p = 0.0126, LOX: p = 0.0217; in c: ACTA2: p = 0.0185, MYH11: p = 0.0101, SMTN: p = 0.4497, CNN1: p = 0.0974, TAGLN: p = 0.0096. In d-f: one-way ANOVA followed by Tukey’s test, vs. Scramble. P values in d: FBN2: Scramble vs. siN1: p > 0.9999, vs. siN2: p = 0.0319, vs. siN3: p = 0.9288, vs. siN1 + N2: p = 0.0937, vs. siN1 + N3: p > 0.9999, vs. siN2 + N3: p = 0.0525, vs. siN1 + N2 + N3: p = 0.0029, LTBP1: Scramble vs. siN1: p = 0.7849, vs. siN2: p = 0.0178, vs. siN3: p = 0.2424, vs. siN1 + N2: p = 0.0004, vs. siN1 + N3: p = 0.9567, vs. siN2 + N3: p = 0.0098, vs. siN1 + N2 + N3: p = 0.0035, FBLN2: Scramble vs. siN1: p > 0.9999, vs. siN2: p = 0.0147, vs. siN3: p = 0.7622, vs. siN1 + N2: p = 0.0084, vs. siN1 + N3: p = 0.6843, vs. siN2 + N3: p = 0.0968, vs. siN1 + N2 + N3: p = 0.0022, EMILIN1: Scramble vs. siN1: p = 0.9949, vs. siN2: p = 0.5744, vs. siN3: p = 0.9886, vs. siN1 + N2: p = 0.1343, vs. siN1 + N3: p = 0.9997, vs. siN2 + N3: p = 0.0356, vs. siN1 + N2 + N3: p = 0.0235; in e: Ctrl vs. Jag1: p = 0.3496, Jag1 vs. Jag1+APOE KD: p = 0.0060; in f: ACTA2: Ctrl vs. Jag1: p = 0.0125, Jag1 vs. Jag1+APOE KD: p = 0.0035, CNN1: Ctrl vs. Jag1: p = 0.0002, Jag1 vs. Jag1+APOE KD: p = 0.0006.
Extended Data Fig. 9 Overview of VEC scRNA-seq from Pulmonary Valves with Pulmonary Stenosis.
a. Feature plots of markers genes for each VEC subtype combining valves from one control and one patient with PS; b. Violin plots comparing JAG1 expression between three VEC subtypes; c. Immunofluorescence staining and percentage of NOTCH1+ & NOTCH3+ VICs in Elastin layer VICs in pulmonary valve tissues from control vs. PS. n = 3 different samples in each group. Data shown as ± SEM. **p < 0.01, ***p < 0.001, control vs. PS. Statistics in c: Unpaired 2-tailed t-test (two groups). P value in c: NOTCH1: p = 0.0493, NOTCH3: p = 0.0002.
Extended Data Fig. 10 APOE Showed No Effect on Notch Degradation or Akt Signaling.
a-b. Quantification of NOTCH2 nuclei positive signals per cell in Fig. 7b,e. c. Western blot of NOTCH2 and GAPDH in VICs treated with 20 μg/ml cycloheximide (CHX) and harvested at the indicated time points; d. Western blot of p-AKT and pan AKT in VICs with empty vector and APOE OE; e. Demonstration figure: On one side, unidirectional flow induced Jag1 production in VECs, which activated NOTCH2-mediated Notch signaling in contacting Elastin-VICs, and promoted downstream elastogenesis-related protein expressions. On the other side, APOE facilitated NOTCH2 and its downstream signaling and elastogenesis protein expressions through MAPK/ERK pathway. Insufficient APOE found in PS patients suppressed Notch signaling, leading to elastogenesis defects. n = 3 biological repeats in each panel. Data shown as ± SEM. ns p > 0.05, **p < 0.01. For a, Jag1 treatment (15 μg/ml) vs. Jag1 treatment and APOE KD. For b, d, Empty vector vs. APOE OE. In a, b, d, unpaired two-tailed t-test. P values in a: p = 0.0048; in b: p = 0.0035; In c, Scramble vs. APOE KD (upper), empty vectors vs. APOE OE (lower), unpaired 2-tailed t-test (two groups), comparing conditions within each time point. Panel e created with BioRender.com.
Supplementary information
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Liu, Z., Liu, Y., Yu, Z. et al. APOE–NOTCH axis governs elastogenesis during human cardiac valve remodeling. Nat Cardiovasc Res 3, 933–950 (2024). https://doi.org/10.1038/s44161-024-00510-3
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DOI: https://doi.org/10.1038/s44161-024-00510-3
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