Chen Neal X, O'Neill Kalisha D, Wilson Hannah E, Srinivasan Shruthi, Bonewald Lynda, Moe Sharon M
Department of Medicine, Division of Nephrology and Indiana University School of Medicine, Indianapolis, IN 46202, United States.
Department of Anatomy, Cell Biology and Physiology Indiana University School of Medicine, Indianapolis, IN 46202, United States.
JBMR Plus. 2024 Oct 29;9(1):ziae136. doi: 10.1093/jbmrpl/ziae136. eCollection 2025 Jan.
Renal osteodystrophy (ROD) leads to increased fractures, potentially due to underlying low bone turnover in chronic kidney disease (CKD). We hypothesized that indoxyl sulfate (IS), a circulating toxin elevated in CKD and a ligand for the aryl hydrocarbon receptor (AhR), may target the osteocytes leading to bone cell uncoupling in ROD. The IDG-SW3 osteocytes were cultured for 14 days (early) and 35 days (mature osteocytes) and incubated with 500 μM of IS after dose finding studies to confirm AhR activation. Long-term incubation of IS for 14 days led to decreased expression of Tnfsf11/Tnfrsf11b ratio (RANKL/OPG), which would increase osteoclast activity, and increased expression of Wnt inhibitors Sost and Dkk1, which would decrease bone formation in addition to decreased mineralization and alkaline phosphatase (ALP) activity. When osteocytes were incubated with IS and the AhR translocation inhibitor CH223191, mineralization and ALP activity were restored. However, the Tnfsf11/Tnfrsf11b ratio and Sost, Dkk1 expression were not altered compared with IS alone, suggesting more complex signaling. In both early and mature osteocytes, co-culture with parathyroid hormone (PTH) and IS reversed the IS-induced upregulation of Sost and Dkk1, and IS enhanced the PTH-induced increase of the Tnfsf11/Tnfrsf11b ratio. Co-culture of IS with PTH additively enhanced the AhR activity assessed by and expression. In summary, IS in the absence of PTH increased osteocyte messenger RNA (mRNA) Wnt inhibitor expression in both early and mature osteocytes, decreased mRNA expression ofTnfsf11/Tnfrsf11b ratio and decreased mineralization in early osteocytes. These changes would lead to decreased resorption and formation resulting in low bone remodeling. These data suggest IS may be important in the underlying low turnover bone disease observed in CKD when PTH is not elevated. In addition, when PTH is elevated, IS interacts to further increase Tnfsf11/Tnfrsf11b ratio for osteoclast activity in both early and mature osteocytes, which would worsen bone resorption.
肾性骨营养不良（ROD）会导致骨折增加，这可能是由于慢性肾脏病（CKD）潜在的低骨转换所致。我们推测，硫酸吲哚酚（IS）作为CKD中升高的循环毒素及芳烃受体（AhR）的配体，可能靶向骨细胞，导致ROD中的骨细胞解偶联。在剂量探索研究以确认AhR激活后，将IDG-SW3骨细胞培养14天（早期）和35天（成熟骨细胞），并用500μM的IS孵育。IS长期孵育14天导致肿瘤坏死因子配体超家族成员11/肿瘤坏死因子受体超家族成员11b比值（RANKL/OPG）表达降低，这会增加破骨细胞活性，同时Wnt抑制剂sclerostin（Sost）和Dickkopf相关蛋白1（Dkk1）表达增加，除了矿化和碱性磷酸酶（ALP）活性降低外，还会减少骨形成。当骨细胞与IS及AhR易位抑制剂CH223191一起孵育时，矿化和ALP活性得以恢复。然而，与单独使用IS相比，肿瘤坏死因子配体超家族成员11/肿瘤坏死因子受体超家族成员11b比值以及Sost、Dkk1的表达并未改变，提示存在更复杂的信号传导。在早期和成熟骨细胞中，与甲状旁腺激素（PTH）和IS共同培养可逆转IS诱导的Sost和Dkk1上调，且IS增强了PTH诱导的肿瘤坏死因子配体超家族成员11/肿瘤坏死因子受体超家族成员11b比值增加。IS与PTH共同培养可累加增强通过 和 表达评估的AhR活性。总之，在没有PTH的情况下，IS会增加早期和成熟骨细胞中骨细胞信使核糖核酸（mRNA）Wnt抑制剂的表达，降低肿瘤坏死因子配体超家族成员11/肿瘤坏死因子受体超家族成员11b比值的mRNA表达，并降低早期骨细胞的矿化。这些变化会导致吸收和形成减少，从而导致低骨重塑。这些数据表明，当PTH未升高时，IS可能在CKD中观察到的潜在低转换骨病中起重要作用。此外，当PTH升高时，IS相互作用以进一步增加早期和成熟骨细胞中破骨细胞活性的肿瘤坏死因子配体超家族成员11/肿瘤坏死因子受体超家族成员11b比值，这会使骨吸收恶化。
