The THO Complex-Dependent Posttranscriptional Control Contributes to Vascular Smooth Muscle Cell Fate Decision

We applied RNA-Seq to analyze the effects of silencing of Thoc2 or Thoc5, two components of the THO complex, in cultured VSMC. The result revealed that Thoc5 silencing closely resembled the gene expression changes induced upon PDGF-BB/PDGF-DD treatments in cultured VSMCs. Mechanistically, our RIP-Seq data revealed both Thoc2 and Thoc5 preferentially interacted with VSMC marker gene mRNAs and mediated their expression. Interestingly, mRNAs that lost Thoc2 or Thoc5 binding during VSMC dedifferentiation were enriched for genes important for VSMC identity. In addition, silencing of Thoc2 or Thoc5 led to dedifferentiation of VSMCs in vitro, characterized by decreased VSMC marker gene expression and increased migration and proliferation. Furthermore, we performed immuno-histochemical staining against Thoc2 and Thoc5, and found a dramatic reduction in their expression in human arteries undergoing carotid endarterectomy (CEA) compared to normal internal mammary arteries (IMA). Notably, Thoc5 overexpression in injured rat carotid arteries significantly repressed loss of VSMC marker gene expression and neointima formation. Together, our data introduce dynamic binding of THO to VSMC marker gene mRNAs as a novel mechanism contributing to VSMC fate decisions, and imply Thoc5 as a potential intervention node for vascular diseases. RNA-Seq of Thoc2 or Thoc5 silencing in cultured mVSMC; ChIP-seq of Thoc5 in wild-type cultured mVSMC; RIP-Seq of Thoc2 or Thoc5 in cultured mVSMC.