The therapeutic value of mesenchymal stromal cells (MSCs) for various regenerative medicine applications, including hematopoietic stem cell transplantations (HSCT), has been well-established. Owing to their small numbers in vivo, it becomes necessary to expand them in vitro, which leads to a gradual loss of their regenerative capacity. Stress-induced mitogen-activated protein kinase p38 (p38 MAPK) signaling has been shown to compromise the MSC functions. Therefore, we investigated whether pharmacological inhibition of p38 MAPK signaling rejuvenates the cultured MSCs and boosts their functionality. Indeed, we found that the ex vivo expanded MSCs show activated p38 MAPK signaling and exhibit increased oxidative stress. These MSCs show a decreased ability to secrete salutary niche factors, thereby compromising their ability to support hematopoietic stem cell (HSC) self-renewal, proliferation, and differentiation. We, therefore, attempted to rejuvenate the cultured MSCs by pharmacological inhibition of p38 MAPK – a strategy broadly known as “priming of MSCs”. We demonstrate that priming of MSCs with a p-38 MAPK inhibitor, PD169316, boosts their niche-supportive functions via upregulation of various HSC-supportive transcription factors. These primed MSCs expand multipotent HSCs having superior homing and long-term reconstitution ability. These findings shed light on the significance of non-cell-autonomous mechanisms operative in the hematopoietic niche and point towards the possible use of pharmacological compounds for rejuvenation of ex vivo cultured MSCs. Such approaches could improve the outcome of regenerative therapies involving in vitro cultured MSCs.

Graphical abstract

中文翻译：

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p38 MAPK 的药理抑制作用使骨髓来源的间充质基质细胞恢复活力并增强其造血干细胞支持能力

间充质基质细胞 (MSCs) 在各种再生医学应用中的治疗价值，包括造血干细胞移植 (HSCT)，已得到充分证实。由于它们在体内的数量很少，因此有必要在体外扩增它们，这导致它们的再生能力逐渐丧失。应激诱导的丝裂原活化蛋白激酶 p38 (p38 MAPK) 信号传导已被证明会损害 MSC 功能。因此，我们研究了对 p38 MAPK 信号的药理学抑制是否可以使培养的 MSCs 恢复活力并增强其功能。事实上，我们发现体外扩增的 MSCs 显示出激活的 p38 MAPK 信号并表现出增加的氧化应激。这些间充质干细胞分泌有益利基因子的能力下降，从而损害它们支持造血干细胞 (HSC) 自我更新、增殖和分化的能力。因此，我们试图通过药理学抑制 p38 MAPK 来使培养的 MSCs 恢复活力——一种广泛称为“MSCs 启动”的策略。我们证明，用 p-38 MAPK 抑制剂 PD169316 引发 MSCs 通过上调各种 HSC 支持性转录因子来增强其生态位支持功能。这些引发的 MSC 扩展了具有卓越归巢和长期重建能力的多能 HSC。这些发现揭示了在造血生态位中起作用的非细胞自主机制的重要性，并指出了可能使用药理学化合物来恢复体外培养的 MSCs。

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