Mesenchymal Stem Cell Laboratory, Adelaide Medical School, Faculty of Health and Medical Sciences, University of Adelaide, Adelaide, SA, 5000, Australia.
South Australian Health and Medical Research Institute, Adelaide, SA, 5000, Australia.
Epigenetics Chromatin. 2019 Jan 3;12(1):3. doi: 10.1186/s13072-018-0247-4.
The 5 hydroxymethylation (5hmC) mark and TET DNA dioxygenases play a pivotal role in embryonic stem cell differentiation and animal development. However, very little is known about TET enzymes in lineage determination of human bone marrow-derived mesenchymal stem/stromal cells (BMSC). We examined the function of all three TET DNA dioxygenases, responsible for DNA hydroxymethylation, in human BMSC cell osteogenic and adipogenic differentiation.
We used siRNA knockdown and retroviral mediated enforced expression of TET molecules and discovered TET1 to be a repressor of both osteogenesis and adipogenesis. TET1 was found to recruit the co-repressor proteins, SIN3A and the histone lysine methyltransferase, EZH2 to osteogenic genes. Conversely, TET2 was found to be a promoter of both osteogenesis and adipogenesis. The data showed that TET2 was directly responsible for 5hmC levels on osteogenic and adipogenic lineage-associated genes, whereas TET1 also played a role in this process. Interestingly, TET3 showed no functional effect in BMSC osteo-/adipogenic differentiation. Finally, in a mouse model of ovariectomy-induced osteoporosis, the numbers of clonogenic BMSC were dramatically diminished corresponding to lower trabecular bone volume and reduced levels of TET1, TET2 and 5hmC.
The present study has discovered an epigenetic mechanism mediated through changes in DNA hydroxymethylation status regulating the activation of key genes involved in the lineage determination of skeletal stem cells, which may have implications in BMSC function during normal bone regulation. Targeting TET molecules or their downstream targets may offer new therapeutic strategies to help prevent bone loss and repair following trauma or disease.
5 羟甲基化（5hmC）标记和 TET DNA 双加氧酶在胚胎干细胞分化和动物发育中起着关键作用。然而，人们对 TET 酶在人类骨髓间充质干细胞/基质细胞（BMSC）谱系决定中的作用知之甚少。我们研究了负责 DNA 羟甲基化的三种 TET DNA 双加氧酶在人 BMSC 细胞成骨和成脂分化中的作用。
我们使用 siRNA 敲低和逆转录病毒介导的 TET 分子强制表达，发现 TET1 是成骨和成脂分化的抑制剂。发现 TET1 招募共抑制蛋白 SIN3A 和组蛋白赖氨酸甲基转移酶 EZH2 到成骨基因。相反，TET2 被发现是成骨和成脂分化的促进剂。数据表明，TET2 直接负责成骨和成脂谱系相关基因的 5hmC 水平，而 TET1 也在这个过程中发挥作用。有趣的是，TET3 在 BMSC 成骨/成脂分化中没有表现出功能作用。最后，在卵巢切除诱导骨质疏松症的小鼠模型中，克隆形成 BMSC 的数量显著减少，相应的小梁骨体积减少，TET1、TET2 和 5hmC 水平降低。
本研究发现了一种通过改变 DNA 羟甲基化状态介导的表观遗传机制，调节参与骨骼干细胞谱系决定的关键基因的激活，这可能对 BMSC 在正常骨调节中的功能有影响。靶向 TET 分子或其下游靶点可能为预防创伤或疾病后骨丢失和修复提供新的治疗策略。
