Iron-Dependent KDM4D Activity Controls the Quiescence-Activity Balance of MSCs via the PI3K-Akt-Foxo1 Pathway [CUT&Tag]

Iron deficiency is a common nutritional deficit that can lead to organ damage or dysfunction. Research is increasingly linking iron deficiency to dysfunction of bone metabolism, although the exact mechanisms remain unclear. Some studies suggest that iron-dependent methylation-erasing enzyme activity regulates cell proliferation and differentiation under physiological or pathological conditions. Whether iron deficiency inhibits the activation of quiescent mesenchymal stem cells (MSCs) by affecting histone demethylase activity is unclear. In our study, we discovered that KDM4D plays a pivotal role in the activation of quiescent MSCs. Under conditions of iron deficiency, the H3K9me3 demethylase activity of KDM4D significantly decreased. This change led to increased heterochromatin with H3K9me3 near the PIK3R3 promoter, hindering the expression of PIK3R3. Subsequently, the activation of quiescent MSCs was inhibited via the PI3K-Akt-Foxo1 pathway. Iron-deficient mice exhibited significantly inhibited bone marrow MSC activation and reduced bone mass compared to normal mice. Modulating the PI3K-Akt-Foxo1 pathway could reverse iron deficiency-induced bone loss. Overall design: CUT&Tag-seq for histone modification H3K9me3 in MSCs

铁缺乏是一种常见的营养缺乏症，可引发器官损伤或功能异常。越来越多的研究将铁缺乏与骨代谢功能紊乱联系起来，但其具体机制仍不明确。部分研究表明，铁依赖性去甲基化酶活性可在生理或病理条件下调控细胞增殖与分化。目前尚不清楚铁缺乏是否通过影响组蛋白去甲基化酶活性，抑制静息态间充质干细胞（MSCs）的激活。本研究发现，赖氨酸去甲基化酶4D（KDM4D）在静息态间充质干细胞的激活过程中发挥关键作用。在铁缺乏条件下，KDM4D的组蛋白H3赖氨酸9三甲基化（H3K9me3）去甲基化酶活性显著降低。这一变化导致磷脂酰肌醇3-激酶调节亚基3（PIK3R3）启动子区域附近携带H3K9me3标记的异染色质水平升高，阻碍了PIK3R3的基因表达。随后，静息态间充质干细胞的激活通过PI3K-Akt-Foxo1信号通路受到抑制。与正常小鼠相比，铁缺乏小鼠的骨髓间充质干细胞激活显著受抑，骨量也明显减少。调控PI3K-Akt-Foxo1信号通路可逆转铁缺乏诱导的骨丢失。实验总体设计：对间充质干细胞中的组蛋白修饰H3K9me3进行CUT&Tag测序。