Homocysteine Metabolites Impair the PHF8/H4K20me1/mTOR/Autophagy Pathway by Upregulating the Expression of Histone Demethylase PHF8-targeting microRNAs in Human Vascular Endothelial Cells and Mice

Abstract

The inability to efficiently metabolize homocysteine (Hcy), which occurs in nutritional and genetic deficiencies, leads to hyperhomocysteinemia (HHcy) thereby causing endothelial dysfunction, a hallmark of atherosclerosis which underpins cardiovascular disease (CVD). The dysregulation of mammalian target of rapamycin (mTOR) signaling, and impaired autophagy play important roles in CVD. Biochemically, HHcy is characterized by elevated levels of Hcy and its metabolites, Hcy-thiolactone (HTL) and N-Hcy-protein (N-Hcy). However, whether these metabolites can dysregulate mTOR signaling and autophagy in endothelial cells is not known. Here, we examined the influence of HTL, N-Hcy, and Hcy on the PHF8/H4K20me1/mTOR/autophagy pathway in human umbilical vein endothelial cells (HUVEC). We found that treatments with HTL, N-Hcy, or Hcy significantly reduced PHF8 protein and mRNA expression, increased H4K20me1, and upregulated mTOR signaling. Autophagy was also impaired (significantly downregulated BECN1, ATG5, ATG7, and LC3 protein and mRNA levels). We also found that these changes were mediated by PHF8-targeting microRNA (miR): miR-22-3p and miR-1229-3p. The effects of HTL, N-Hcy, or Hcy on the miR expression and on the PHF8/H4K20me1/mTOR/autophagy pathway were abrogated by treatments with an inhibitor of miR-22 or miR-1229. Taken together, these findings show that Hcy metabolites can upregulate miR-22-3p and miR-1229-3p expression, which then dysregulate the PHF8/H4K20me1/mTOR/autophagy pathway, important for vascular homeostasis.