Increased Osteoclast and Decreased Osteoblast Activity Causes Reduced Bone Mineral Density and Quality in Genetic Hypercalciuric Stone‐Forming Rats

Abstract

To study human idiopathic hypercalciuria (IH), we developed an animal model, genetic hypercalciuric stone‐forming (GHS) rats, whose pathophysiology parallels that in IH. All GHS rats form kidney stones and have decreased BMD and bone quality compared with the founder Sprague–Dawley (SD) rats. To understand the bone defect, we characterized osteoclast and osteoblast activity in the GHS compared with SD rats. Bone marrow cells were isolated from femurs of GHS and SD rats and cultured to optimize differentiation into osteoclasts or osteoblasts. Osteoclasts were stained for TRAcP (tartrate resistant acid phosphatase), cultured to assess resorptive activity, and analyzed for specific gene expression. Marrow stromal cells or primary neonatal calvarial cells were differentiated to osteoblasts, and osteoblastic gene expression as well as mineralization was analyzed. There was increased osteoclastogenesis and increased resorption pit formation in GHS compared with SD cultures. Osteoclasts had increased expression of cathepsin K, Tracp, and MMP9 in cells from GHS compared with SD rats. Osteoblastic gene expression and mineralization was significantly decreased. Thus, alterations in baseline activity of both osteoclasts and osteoblasts in GHS rats, led to decreased BMD and bone quality, perhaps because of their known increase in vitamin D receptors. Better understanding of the role of GHS bone cells in decreased BMD and quality may provide new strategies to mitigate the low BMD and increased fracture risk found in patients with IH. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Effect of Osteoblast‐Specific Deletion of the Proton Receptor OGR1

“…Bone marrow stromal cells (BMSC) from femurs of 10‐ to 12‐week‐old female OB‐cKO and OGR1 flox/flox (WT) mice were cultured to near confluence and then differentiated to OB by incubation with 50 μg/mL ascorbic acid and 10 mM β‐glycerophosphate. ( 30 ) After 1 week in differentiation medium, DNA was collected from the cells and genotyping was used to determine the presence of the mutant OGR1. As an additional control, mesenchymal stem cells from bone marrow of WT and OB‐cKO mice were differentiated to osteoclasts (see below) to determine whether OGR1 was deleted specifically only in OB cells but not in OC cells.…”

“…After 2 weeks in differentiation medium, cells were washed, fixed with 10% neutral buffered formalin, and then stained with BCIP/NBT solution (Thermo Fisher Scientific, Waltham, MA, USA) to measure alkaline phosphatase or after 3 weeks were washed, fixed, and stained with alizarin red. ( 30 ) Quantitation was carried out with a ChemiDoc MP imaging system (Bio‐Rad, Hercules, CA, USA). After 2 weeks in differentiation medium, cells on other plates were collected for RNA measurements of specific gene expression or used to test responsiveness to MET.…”

Associations between lumbar bone mineral density, serum 25-hydroxyvitamin D and history of kidney stones in adults aged 30–69 years in the USA (NHANES 2011–2018)

“…This non-invasive examination is convenient and efficient; however, the mechanisms underlying this effect remain unclear. Stones are common in patients with high calcium levels in the urine 20. Hypercalciuria occurs because of a net loss of calcium from the body; therefore, patients usually excrete more calcium than they absorb.…”

“…Stones are common in patients with high calcium levels in the urine. 20 Hypercalciuria occurs because of a net loss of calcium from the body; therefore, patients usually excrete more calcium than they absorb. Some researchers have speculated that this extra urinary calcium is derived from bone.…”

Phosphatidyl Inositol 3-Kinase (PI3K)-Inhibitor CDZ173 protects against LPS-induced osteolysis

“…Osteoclast-specific genes are up-regulated during RANKLinduced osteoclast formation (Zhou et al, 2015;Krieger et al, 2020). These genes include transcription factors c-Fos and NFATc1 in the osteoclast nucleus, dendritic cell-specific transmembrane protein (DC-STAMP), matrix metallopeptidase 9 (MMP 9), tartrate resistant acid phosphatase (Tracp), and cathepsin K (CTSK) involved in absorption function.…”