Factors influencing osteogenic differentiation of human aortic valve interstitial cells

Human aortic valve interstitial cells redifferentiate into an osteoblast-like phenotype, which is the key cellular mechanism of aortic valve calcification. Methyltransferase-like 3, the N6-methyladenosine methylation writer, has emerged as a new layer of epigenetic regulation for osteogenic differentiation of bone mesenchymal stem cells. The current study sought to determine whether methyltransferase-like 3 also plays a role in the osteogenic differentiation of human aortic valve interstitial cells.

Aortic valves from patients with aortic stenosis (n = 50) and normal controls (n = 50) were subjected to determination of methyltransferase-like 3 expression. Mineralized bone matrix formation was assessed by Alizarin Red staining. The interaction between methyltransferase-like 3 and twist-related protein 1 was confirmed via luciferase reporter and N6-methyladenosine methylated RNA immunoprecipitation quantitative reverse-transcription polymerase chain reaction.

Methyltransferase-like 3 was highly expressed in human calcified aortic valves (1.61 ± 0.50) versus normal valves (3.07 ± 0.62; P < .0001). Osteogenic stimulation for 7 days resulted in a 2.15 ± 0.16-fold increase (P < .0001) in methyltransferase-like 3 protein level compared with the control group in human aortic valve interstitial cells. Functionally, methyltransferase-like 3 acted as a positive regulator of osteogenic differentiation of human aortic valve interstitial cells. Mechanistically, methylated RNA immunoprecipitation quantitative reverse-transcription polymerase chain reaction identified twist-related protein 1 as a target of methyltransferase-like 3-mediated m⁶A modification. Moreover, N6-methyladenosine-mediated twist-related protein 1 mRNA inhibition relied on the m⁶A binding protein YTH-domain family member 2-dependent pathway.

Methyltransferase-like 3 promotes osteogenic differentiation of human aortic valve interstitial cells by inhibiting twist-related protein 1 through an N6-methyladenosine YTH-domain family member 2-dependent pathway. Our findings provide novel mechanistic insights into a critical role of methyltransferase-like 3 in the aortic valve calcification progression and shed new light on N6-methyladenosine-directed diagnostics and therapeutics in aortic valve calcification.