內皮細胞胞外基質維持骨髓間葉幹細胞之幹細胞特性

Abstract

Mesenchymal stem cells (MSCs) hold great potential in cell therapies by virtue of the regenerative effects and immunomodulatory properties, but the scarce nature of MSCs makes ex vivo expansion indispensable prior to transplantation purposes. However, potential loss of stemness ensuing culture expansion has hindered the advancements in MSCs-based treatments. In principles, stemness can be preserved by reconstructing the stem cell niche, but the physiological nature including the endogenous stem cell niche of MSCs remains elusive. Emerging hypotheses suggested that pericytes residing subendothelium might be one of the primitive origins of MSCs, and accordingly, we speculated that endothelial cells (ECs) might participate in the constitution of the stem cell niche for MSCs. In this study, ECs derivatives including extracellular matrix (ECM) and paracrine factors collected from conditioned medium (CM) of aortic endothelial cells (AECs) and Mile Sven 1 endothelial cell line (MS1) were investigated for the potential to maintain MSCs stemness. When compared with MSCs cultured alone, on MSCECM and in endothelial CMs, MSCs on endothelial ECMs especially on MS1ECM possessed the morphology of more juvenile cells, showed quiescence in proliferation, in agreement with general description of primitive MSCs. Besides, MSCs expanded on MS1ECM possess greater osteogenic, adipogenic and chondrogenic potential under proper stimuli. These results indicated that MS1ECM preserved the stemness of MSCs. We further discovered that the possible mechanism resulted from MSCs expanded on MS1ECM had significantly higher H3K27me3 mark with significantly lower expression of Kdm6b, a specific H3K27 demethylase. Higher H3K27me3 mark in MS1ECM can be interpreted as transcriptional inactivation, and it probably explained proliferative quiescence and better differentiation plasticity. Taken together, MS1ECM retained MSCs stemness by shaping an inhibitory chromatin signature via maintaining lower expression of Kdm6b. Our work provided not only a supportive evidence that MSCs can reside in perivascular niche, but also a feasible novel approach for MSCs ex vivo expansion. The detailed signal between extracellular environment and intracellular chromatin signature requires further investigation.