Overexpression of DNMT1 leads to hypermethylation of H19 promoter and inhibition of Erk signaling pathway in disuse osteoporosis

Bing Li  ¹ , Jie Zhao  ² , Jian-Xiong Ma  ³ , Guo-Min Li  ⁴ , Yang Zhang  ³ , Guo-Sheng Xing  ³ , Jun Liu  ⁵ , Xin-Long Ma  ⁶

Affiliations

• ¹ Joint Department, Tianjin Hospital, Tianjin 300211, People’s Republic of China.
• ² Orthopedic Department, Tianjin Hospital, Tianjin 300211, People’s Republic of China.
• ³ Orthopedic Research Institute, Tianjin Hospital, Tianjin 300050, People’s Republic of China.
• ⁴ Graduate School, Tianjin Medical University, Tianjin 300070, People’s Republic of China.
• ⁵ Joint Department, Tianjin Hospital, Tianjin 300211, People’s Republic of China. Electronic address: drliujun@hotmail.com.
• ⁶ Joint Department, Tianjin Hospital, Tianjin 300211, People’s Republic of China; Orthopedic Research Institute, Tianjin Hospital, Tianjin 300050, People’s Republic of China. Electronic address: maxinlong99@163.com.

Abstract

Disuse osteoporosis (DOP) is a common complication of the lack of mechanical loading. The precise mechanism underlying DOP remains unknown, although epigenetic modifications may be a major cause. Recently, cumulative research has revealed that DNA methyltransferase (DNMT) proteins can catalyze the conversion of cytosine to 5-methylcytosine (5mC), altering the epigenetic state of DNA. Here, we report that DNMT1 expression and lncRNA-H19 methylation are upregulated in the femoral tissues of DOP rats, accompanied with inhibited Erk signaling pathway. Overexpression of DNMT1 in UMR-106 cells mimics 5mC enrichment in the H19 promoter, inhibition of Erk signaling and impairment of osteogenesis, which can be rescued by 5′-aza-deoxycytidine (5′-Aza) treatment. Moreover, local intramedullary injection of Dnmt1 siRNA (siDNMT1) in Sprague-Dawley (SD) rats abrogated disuse lncRNA-H19 (H19) downregulation, Erk signaling inhibition, histopathological changes, and bone microstructure declines in the distal femur in vivo. Therefore, our data identify for the first time a new signaling cascade in DOP: mechanical unloading causes upregulation of DNMT1 and hypermethylation of H19 promoter, which subsequently leads to downregulation of lncRNA-H19 and inhibition of the ERK signaling, suggesting a new potential therapeutic target.

Keywords: DNA methylation; DNMT1; Disuse osteoporosis; Long-noncoding RNA-H19, Erk-MAPK signaling pathway.