The promoter activity of human Mfn 2 depends on Sp

Aims: Mitofusin-2 (Mfn2) expression is dysregulated in vascular proliferative disorders and its over-expression attenuates the proliferation of vascular smooth muscle cells (VSMCs) and neointimal lesion development after balloon angioplasty. We sought to gain insight into the mechanisms that control Mfn2 expression in VSMCs. Methods and Results: We cloned and characterized 2 kb of the 5'-flanking region of the human Mfn2 gene. Its TATA-less promoter contains a CpG island. In keeping with this, 5’-RACE, revealed 6 transcriptional start sites (TSSs), of which TSS2 and TSS5 were the most frequently used. The strong CpG island was found non methylated under conditions characterized by large differences in Mfn2 gene expression. The proximal Mfn2 promoter contains 6 putative Sp1 motifs. Sp1 binds to the Mfn2 promoter and its over-expression activates Mfn2 promoter in VSMCs. Inhibition of Sp1 by WP631 reduced Mfn2 expression, and Sp1 silencing reduced transcriptional activity of the Mfn2 promoter. In keeping with this view, Sp1 and Mfn2 mRNA levels were down-regulated in aorta early after an atherogenic diet in Apolipoprotein E-knockout mice or in VSMCs cultured in the presence of low serum. Conclusions: Sp1 is a key factor in maintaining basal Mfn2 transcription in VSMCs. Given the anti-proliferative actions of Mfn2, Sp1-induced Mfn2 transcription may represent a mechanism for prevention of VSMCs proliferation and neointimal lesion and development. Abstract