Murine neonatal cardiac B cells promote cardiomyocyte proliferation and heart regeneration

Abstract

The irreversible loss of cardiomyocytes in the adult heart following cardiac injury leads to adverse cardiac remodeling and ventricular dysfunction. However, the role of B cells in cardiomyocyte proliferation and heart regeneration has not been clarified. Here, we found that the neonatal mice with B cell depletion showed markedly reduced cardiomyocyte proliferation, leading to cardiac dysfunction, fibrosis scar formation, and the complete failure of heart regeneration after apical resection. B cell depletion also significantly impaired heart regeneration and cardiac function in neonatal mice following myocardial infarction (MI). However, B cell depletion in adult mice suppressed tissue inflammation, inhibited myocardial fibrosis, and improved cardiac function after MI. Interestingly, B cell depletion partially restricted cardiomyocyte proliferation in adult mice post-MI. Single-cell RNA sequencing showed that cardiac B cells possessed a more powerful ability to inhibit inflammatory responses and enhance angiogenesis in the postnatal day 1 (P1) mice compared with P7 and adult mice. Besides, the proportion of cardioprotective B cell clusters with high expression levels of S100a6 (S100 calcium-binding protein A6) and S100a4 (S100 calcium-binding protein A4) was greatly decreased in adult heart tissues compared with neonatal mice after cardiac damage. Thus, our study discovers that cardiac B cells in neonatal mice are required for cardiomyocyte proliferation and heart regeneration, while adult B cells promote inflammation and impair cardiac function after myocardial injury.

Fig. 1. Murine neonatal cardiac B cells promote cardiomyocyte proliferation and heart regeneration.

a Representative images and quantification of heart sections stained with Masson’s trichrome from the neonatal CD19^DTR or WT mice with DT or PBS administration 3 weeks after AR. Scale bars, 1000 μm (left) or 100 μm (right). Each symbol in quantification represents one mouse (n = 5 mice for each group, one-way ANOVA). b Echocardiographic measurement of LVEF and LVFS of the neonatal CD19^DTR or WT mice with DT or PBS administration 3 weeks after AR. Each symbol represents one mouse (n = 14 or 15 mice for each group, one-way ANOVA). c Representative images and quantification of heart sections stained with Masson’s trichrome from the neonatal CD19^DTR mice with DT or PBS administration 3 weeks after MI. Scale bars, 1000 μm (left) or 100 μm (right). Each symbol in quantification represents one mouse (n = 5 mice for each group, unpaired Student’s t-test). d Echocardiographic measurement of LVEF and LVFS of the neonatal CD19^DTR mice with DT or PBS administration 3 weeks after MI. Each symbol in quantification represents one mouse (n = 11 or 12 mice for each group, unpaired Student’s t-test). e–g Representative immunofluorescent staining images and quantification of EdU⁺, pH3⁺, or Ki67⁺ cardiomyocytes from myocardial tissues of the neonatal CD19^DTR mice with DT or PBS administration at day 7 post-AR. Scale bars, 20 μm. Each symbol in quantification indicates one representative image from one heart section of one mouse (n = 10 mice for each group in e; n = 6 mice for each group in f and g; unpaired Student’s t-test). The data were shown as mean ± SD. *p < 0.05. **p < 0.01, and ***p < 0.001.

Fig. 2. Murine neonatal cardiac B cells possess the greater ability to inhibit inflammatory responses and promote angiogenesis after cardiac injury.

a Representative immunofluorescent staining images and quantification of EdU⁺ cardiomyocytes from myocardial tissues of adult CD19^DTR mice with DT or PBS administration at day 7 post-MI. Each symbol in quantification indicates one representative image from one heart section of one mouse (MI + PBS group, n = 7 mice; MI + DT group, n = 9 mice; mean ± SD; unpaired Student’s t-test). Scale bars, 20 μm. b Violin plots showing the expression scores of cell proliferation-associated genes (Slpi, Ighg1, Lcn2, S100a8, S100a9, and Cxcl2) in cardiac B cells from adult mice subjected to MI or sham operation (GSE163465). c GO enrichment analysis of DEGs in B cells from heart tissues at day 7 after AR operated on P1 and P7 mice. d Heatmap of DEGs enriched in angiogenesis, inflammatory responses, and chemokine signaling pathway of cardiac B cells prepared as in c and from adult mouse heart after MI (GSE163465). e Heatmap of top DEGs from cardiac B cells prepared as in c and from adult mouse heart after MI (GSE163465). f UMAP plots displaying B cell clusters in heart tissues prepared as in c and from adult mouse heart after MI (GSE163465). g Distribution of B cell proportions in each of the nine clusters from heart tissues prepared as in c and from adult mouse heart after MI (GSE163465). **p < 0.01.