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Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): The Russian Science Foundation Introduction Aortic valve stenosis due to calcification of valve cusps is the most common valve disease in the world today. The main feature of this condition is a progressive mineralization of valve tissue. The mechanisms underlying this process is still unknown, but in recent years it has become clear that pathological mineralization of heart and blood vessels has some similarities with the physiological process of bone formation. It has been suggested that interstitial cells (VICs) are the main functional units in the valve that undergo calcification. However, the early initiating mechanisms that trigger osteogenic transformation of cells remain unclear. Purpose The aim of the present study was to elucidate the most responsive time point of osteogenic differentiation induction and to identify the main osteogenic markers that mediate pathological calcification in human aortic valve. Methods VICs were obtained from patients with aortic valve calcification and from healthy aortic valves. The effectiveness of cell cultures osteogenic differentiation was estimated by Alizarin Red staining. Investigation of gene expression changes upon osteogenic differentiation was performed by qPCR and RNA sequencing. Results We found that 48 hours after the induction of osteogenic differentiation is the most relevant time point to identify the early regulators of osteogenic transformation of the cells. That is the time when the most intensive response from osteogenic markers takes place – BGLAP, OPG, OGN, RUNX2 – in comparison to 24, 72 and 96 hours of differentiation in both patient's and healthy cells. We found out that induction of osteogenic differentiation on early stages initiates transcriptional program that serve to induce the next molecular events which recruit phenotype-specific osteogenes. We revealed that 558 and 232 genes which were up and down regulated during differentiation were the same for healthy and patient's cells. However, there was a number of genes which was specific for either patient's or healthy cells. Conclusions We presume that a great amount of the main molecular participants of osteogenic differentiation is shared between different types of cells which are prone to differentiation. However, we perform the results about specificity and difference between the mechanisms of osteogenic differentiation of patient's and healthy cells. [ABSTRACT FROM AUTHOR]