Hypermethylation of mitochondrial DNA in vascular smooth muscle cells impairs cell contractility

Yue-Feng Liu,Juan-Juan Zhu,Yun-Peng Zhang,Si-An Xie,Wei Kong,Han Liu,Wei Pang,Tao Zhang,Yuan-Jun Tang,Wei-Juan Yao,Ming Zheng,Xiao Yu Tian,Chuan-Rong Zhao,Jing Zhou

doi:10.1038/s41419-020-2240-7

Abstract

Vascular smooth muscle cell (SMC) from arterial stenotic-occlusive diseases is featured with deficiency in mitochondrial respiration and loss of cell contractility. However, the regulatory mechanism of mitochondrial genes and mitochondrial energy metabolism in SMC remains elusive. Here, we described that DNA methyltransferase 1 (DNMT1) translocated to the mitochondria and catalyzed D-loop methylation of mitochondrial DNA in vascular SMCs in response to platelet-derived growth factor-BB (PDGF-BB). Mitochondrial-specific expression of DNMT1 repressed mitochondrial gene expression, caused functional damage, and reduced SMC contractility. Hypermethylation of mitochondrial D-loop regions were detected in the intima-media layer of mouse carotid arteries subjected to either cessation of blood flow or mechanical endothelial injury, and also in vessel specimens from patients with carotid occlusive diseases. Likewise, the ligated mouse arteries exhibited an enhanced mitochondrial binding of DNMT1, repressed mitochondrial gene expression, defects in mitochondrial respiration, and impaired contractility. The impaired contractility of a ligated vessel could be restored by ex vivo transplantation of DNMT1-deleted mitochondria. In summary, we discovered the function of DNMT1-mediated mitochondrial D-loop methylation in the regulation of mitochondrial gene transcription. Methylation of mitochondrial D-loop in vascular SMCs contributes to impaired mitochondrial function and loss of contractile phenotype in vascular occlusive disease.

Highlights

Vascular smooth muscle cells (SMCs) that constitute the majority of contractile cells of blood vessels, are responsible for maintaining vascular homeostasis through active contraction and relaxation
Immunoblots of nuclear versus mitochondrial fractions showed DNA methyltransferase 1 (DNMT1) and DNMT3A proteins exist both in nuclei and mitochondria (Fig. 1a), whereas DNMT3B were found exclusively in the nuclei (Fig. 1a), indicated by nuclear marker Histone 3 and mitochondrial marker VDAC1 (Fig. 1a)
Recent years, accumulating evidence showed the presence of DNMT1 and DNMT3A inside mitochondria in support of the occurrence of mitochondrial DNA (mtDNA) methylation[15,28,29]

Summary

Introduction

Vascular smooth muscle cells (SMCs) that constitute the majority of contractile cells of blood vessels, are responsible for maintaining vascular homeostasis through active contraction and relaxation. SMC contraction depends on energy provided by adenosine triphosphate (ATP) mainly generated through oxidative phosphorylation in the mitochondrion, the cellular powerhouses, or through anaerobic glycolysis. Previous study on arteries from rat, rabbit, dog, and pig indicated that SMC contraction is dependent rather exclusively on ATP derived from mitochondrial respiration[4]. Mitochondrial function is crucial for normal function of SMCs. Mitochondrial dysfunction indicated by reduced mitochondrial DNA (mtDNA) copy number and decreased mitochondrial oxygen consumption rate (OCR), is present in human atherosclerotic SMCs5. Mitochondrial dysfunction indicated by reduced mitochondrial DNA (mtDNA) copy number and decreased mitochondrial oxygen consumption rate (OCR), is present in human atherosclerotic SMCs5 These evidence suggested the association between mitochondrial abnormality and loss of contractile phenotype in SMC during the development of vascular diseases

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Conclusion