Related Experiment Video
Updated: Jun 5, 2025
Methods for Analyzing the Impacts of Natural Uranium on In Vitro Osteoclastogenesis
Published on: January 30, 2018
The uremic toxin indoxyl sulfate decreases osteocyte RANKL/OPG and increases Wnt inhibitor RNA expression that is
Neal X Chen1, Kalisha D O'Neill1, Hannah E Wilson2
1Department of Medicine, Division of Nephrology and Indiana University School of Medicine, Indianapolis, IN 46202, United States.
Abstract:
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 Cyp1a1 and Cyp1b1 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.
Insights
Indoxyl sulfate (IS) contributes to low bone turnover in chronic kidney disease (CKD) by disrupting osteocyte function. It reduces bone formation and mineralization, potentially worsening bone disease in CKD patients.
Area of Science:
- Nephrology
- Endocrinology
- Bone Biology
Background:
- Renal osteodystrophy (ROD) in chronic kidney disease (CKD) is linked to low bone turnover and increased fracture risk.
- Indoxyl sulfate (IS), a uremic toxin and aryl hydrocarbon receptor (AhR) ligand, is elevated in CKD and suspected to contribute to ROD.
- Osteocyte dysfunction is a potential mechanism for the altered bone remodeling observed in ROD.
Purpose of the Study:
- To investigate the direct effects of indoxyl sulfate (IS) on osteocyte function and its role in renal osteodystrophy (ROD).
- To determine if IS-induced changes in osteocyte gene expression and function are mediated by the aryl hydrocarbon receptor (AhR).
- To explore the interaction between IS and parathyroid hormone (PTH) in modulating osteocyte activity.
Main Methods:
- Cultured early (14-day) and mature (35-day) IDG-SW3 osteocytes.
- Incubated osteocytes with indoxyl sulfate (IS) and/or AhR inhibitor (CH223191) or parathyroid hormone (PTH).
- Assessed osteocyte gene expression (RANKL/OPG ratio, Wnt inhibitors), mineralization, and alkaline phosphatase (ALP) activity.
Main Results:
- IS exposure decreased RANKL/OPG ratio and increased Wnt inhibitors (Sost, Dkk1), reducing mineralization and ALP activity in osteocytes.
- AhR inhibition partially restored mineralization and ALP activity but did not affect RANKL/OPG or Wnt inhibitor expression.
- In the presence of PTH, IS enhanced PTH-induced RANKL/OPG increase and further activated AhR, while reversing IS-induced Wnt inhibitor upregulation.
Conclusions:
- Indoxyl sulfate (IS) directly impairs osteocyte function, contributing to low bone turnover in CKD when parathyroid hormone (PTH) levels are not elevated.
- IS-induced changes in osteocyte Wnt inhibitor and RANKL/OPG expression promote decreased bone formation and resorption.
- When PTH is elevated, IS exacerbates osteoclast activity by further increasing the RANKL/OPG ratio, worsening bone resorption in CKD.
More Related Videos
Related Concept Videos
01:17Hormones and Bone Tissue
Hormones That Influence Osteoblasts and/or Maintain the Matrix
Several hormones are necessary for controlling bone growth and maintaining the bone matrix. The pituitary gland secretes growth hormone (GH), which, as its name implies, controls bone growth. This happens in several ways: first, it triggers chondrocyte...
01:31Osteoclasts in Bone Remodeling
01:21Skeleton and Calcium Homeostasis
00:59The Parathyroid Glands
Oxyphil cells, whose functions remain elusive, emerge during late puberty, adding a layer of complexity to the parathyroid gland's intricacies. In contrast, principal parathyroid cells undertake a vital role by...
01:40Bone Remodeling
01:27Roles of Electrolytes: Calcium and Phosphate
The calcium concentration in blood plasma is primarily...