Myocardial fibrosis after myocardial infarction (MI) is a leading cause of heart diseases. MI activates cardiac fibroblasts (CFs) and promotes CF to myofibroblast transformation (CMT). This study aimed to investigate the role of miR‐21 in the regulation of CMT and myocardial fibrosis. Primary rat CFs were isolated from young SD rats and treated with TGF‐β1, miR‐21 sponge or Jagged1 siRNA. Cell proliferation, invasion and adhesion were detected. MI model was established in male SD rats using LAD ligation method and infected with recombinant adenovirus. The heart function and morphology was evaluated by ultrasonic and histological analysis. We found that TGF‐β1 induced the up‐regulation of miR‐21 and down‐regulation of Jagged1 in rat CFs. Luciferase assay showed that miR‐21 targeted 3′‐UTR of Jagged1 in rat CFs. miR‐21 sponge inhibited the transformation of rat CFs into myofibroblasts, and abolished the inhibition of Jagged1 mRNA and protein expression by TGF‐β1. Furthermore, these effects of miR‐21 sponge on rat CFS were reversed by siRNA mediated knockdown of Jagged1. In vivo, heart dysfunction and myocardial fibrosis in MI model rats were partly improved by miR‐21 sponge but were aggravated by Jagged1 knockdown. Taken together, these results suggest that miR‐21 promotes cardiac fibroblast‐to‐myofibroblast transformation and myocardial fibrosis by targeting Jagged1. miR‐21 and Jagged1 are potential therapeutic targets for myocardial fibrosis.

Mitochondrial quality control is a new target for myocardial protection. Notch signaling plays an important role in heart development, maturation, and repair. However, the role of Notch in the myocardial mitochondrial quality control remains elusive. In this study, we isolated myocardial cells from rats and established myocardial ischemia reperfusion injury (IRI) model. We modulated Notch1 expression level in myocardial cells via infection with recombinant adenoviruses Ad‐N1ICD and Ad‐shN1ICD. We found that IR reduced myocardial cells viability, but Notch1 overexpression increased the viability of myocardial cells exposed to IRI. In addition, Notch1 overexpression improved ATP production, increased mitochondrial fusion and decreased mitochondrial fission, and inhibited mitophagy in myocardial cells exposed to IRI. However, N1ICD knockdown led to opposite effects. The myocardial protection role of Notch1 was related to the inhibition of Pink1 expression and Mfn2 and Parkin phosphorylation. In conclusion, Notch1 exerts myocardial protection and this is correlated with the maintenance of mitochondrial quality control and the inhibition of Pink1/Mfn2/Parkin signaling.

Purpose During myocardial infarction (MI), cardiac fibroblasts (CFs) transform into myofibroblast (CMT). This study aimed to investigate the crosstalk of Notch1 and transforming growth factor‐β1 (TGF‐β1)/Smad3 signaling in the regulation of CMT and myocardial fibrosis. Methods Primary CFs were isolated from young rats and treated with TGF‐β1 or adenovirus to overexpress or knockdown Notch1 intracellular domain (N1ICD) or Smad3. Results TGF‐β1 decreased the expression of fibroblast markers but increased the expression of myofibroblast markers in rat CFs. TGF‐β1 increased the proliferation, invasion, and adhesion, and the secretion of collagen I of CFs, and these effects were inhibited by N1ICD overexpression. Moreover, endogenous Smad3 phosphorylation in CFs was enhanced by N1ICD knockdown, whereas TGF‐β1 induced Smad3 phosphorylation was antagonized by the N1ICD overexpression. Conversely, endogenous N1ICD activation in CFs was antagonized by Smad3, whereas TGF‐β1 induced N1ICD inactivation was antagonized by Smad3 knockdown. Coimmunoprecipitation showed that N1ICD interacted with Smad3 and immunostaining revealed the colocalization of N1ICD and Smad3 in the nuclei of CFs. Moreover, we demonstrated the functional antagonism of N1ICD and Smad3 on the phenotypes of CFs. Finally, TGF‐β1/Smad3 signaling promoted whereas Notch signaling inhibited myocardial fibrosis in rat MI model. Conclusion Notch signaling inhibits CMT by antagonizing TGF‐β1/Smad3 signaling. Notch signaling activators and TGF‐β1/Smad3 signaling inhibitors could be exploited for therapeutic intervention to inhibit myocardial fibrosis after MI.

Pulmonary arterial hypertension (PAH) is a fatal disease whose molecular mechanism is unknown. The trimethylation of lysine 36 on histone 3 (H3K36me3) catalyzed by SETD2 and the modification of N6-methyladenine (m 6 A) mRNA mediated by METTL14 play important roles in a variety of normal and pathological biological processes. However, the role of these epigenetic controls in the pathogenesis of PAH remains unclear. In this study, the expression of SETD2 and METTL14 was elevated in pulmonary artery smooth muscle cells (PASMCs) of hypoxia-induced PAH mice. We further constructed a mouse model with SETD2 specific knockout in smooth muscle cells (SETD2 SM22α Cre ). Our results suggest that the lack of SETD2 in SMCs protected mice from hypoxia-induced PAH and significantly reduced right ventricular systolic pressure (RVSP), right ventricular/left ventricular plus septum [RV/(LV+S)] weight ratio, and pulmonary median width. In addition, the absence of SETD2 in SMCs alleviates the level of METTL14 expression and the m 6 A RNA methylation level in PAH SMCs. These results obtained from mice suggest that strategies that target the inhibition of SETD2/METTL14 activity may be a viable treatment for PAH in a clinical setting.

Mitochondrial fusion and fission dynamic are critical to the myocardial protection against ischaemia‐reperfusion injury. Notch1 signalling plays an important role in heart development, maturation and repair. However, the role of Notch1 in the myocardial mitochondrial fusion and fission dynamic remains elusive. Here, we isolated myocardial cells from rats and established myocardial ischaemia‐reperfusion injury (IRI) model. We modulated Notch1, MFN1 and DRP1 expression levels in myocardial cells via infection with recombinant adenoviruses. The results showed that Notch1 improves the cell viability and mitochondrial fusion in myocardiocytes exposed to IRI. These improvements were dependent on the regulation of MFN1 and DRP1. On the mechanism, we found that MNF1 is transcriptionally activated by RBP‐Jk in myocardiocytes. Notch1 also improves the mitochondrial membrane potential in myocardiocytes exposed to IRI. Moreover, we further confirmed the protection of the Notch1‐MFN1/Drp1 axis on the post‐ischaemic recovery of myocardial performance is associated with the preservation of the mitochondrial structure. In conclusion, this study presented a detailed mechanism by which Notch1 signalling improves mitochondrial fusion during myocardial protection.