ALKBH5 Induces Fibroblast-to-Myofibroblast Transformation During Hypoxia to Protect Against Cardiac Rupture After Myocardial Infarction
Objectives: To investigate the role of ALKBH5 in fibroblasts during post-myocardial infarction (MI) repair. Background: N6-methyladenosine (m6A) mRNA modification has been shown to play an important role in cardiovascular diseases. The RNA demethylase, AlkB homolog 5 (ALKBH5), is an m6A "eraser" that is responsible for decreased m6A methylation. However, its role in cardiac fibroblasts during the post-MI healing process remains elusive. Methods: MI was mimicked by permanent left anterior descending artery ligation in global ALKBH5-knockout, ALKBH5-knockin, and fibroblast-specific ALKBH5-knockout mice to study the function of ALKBH5 during post-MI collagen repair. Methylated RNA immunoprecipitation sequencing was performed to explore potential ALKBH5 targets. Results: Dramatic alterations in ALKBH5 expression were observed during the early stage post-MI and in hypoxic fibroblasts. Global ALKBH5 knockin reduced infarct size and improved cardiac function after MI. The global and fibroblast-specific ALKBH5-knockout mice both exhibited low survival rates along with poor collagen repair, impaired cardiac function, and cardiac rupture. Both in vivo and in vitro ALKBH5 loss led to impaired fibroblast activation and decreased collagen deposition. Additionally, hypoxia, but not TGF-ß1 or Ang II, upregulated ALKBH5 expression in myofibroblasts in a HIF-1a-dependent transcriptional manner. Mechanistically, ALKBH5 promoted the stability of ErbB4 mRNA and the degradation of ST14 mRNA via m6A demethylation. Fibroblast-specific ErbB4 overexpression ameliorated the impaired fibroblast-to-myofibroblast transformation and poor post-MI repair due to ALKBH5 knockout. Conclusions: Fibroblast ALKBH5 positively regulates post-MI healing via post-transcriptional modification and stabilization of ErbB4 mRNA in an m6A-dependent manner. Targeting ALKBH5/ERBB4 may be a potential therapeutic option for post-MI cardiac rupture. Overall design: To identify the m6A demethylation targets of ALKBH5 in response to acute MI, MeRIP-seq and RNA-seq were performed using RNA isolated from the infarct areas of ALKBH5-KO and WT mice 5 days after MI surgery (WT, n=3 vs. KO, n=3).