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Published on: November 15, 2013
Nuclear xenobiotic receptor PXR-null mouse exhibits hypophosphatemia and represses the Na/Pi-cotransporter SLC34A2
Yoshihiro Konno1, Rick Moore, Nobuhiro Kamiya
1Pharmacogenetics Section, Laboratory of Reproductive and Developmental Toxicology, National Institute of Environmental Health Sciences, National Institutes of Health, North Carolina 27709, USA.
Objective:
We previously found that the lack of nuclear xenobiotic receptor, PXR, decreases femoral bone mineral density (BMD) in Pxr-/- mice. Our present study aims to elucidate the inherited phenotype that correlates with the decreased BMD and to identify the PXR-regulated gene that may link with this phenotype.
Methods:
Pxr+/+ and Pxr-/- mice were used to measure the serum levels of inorganic phosphate (Pi), calcium and vitamin D3. Real time PCR and western blots were used to determine the intestinal and renal expressions of Pi and calcium transporters and various other genes involved in bone homeostasis. Cell-based reporter and gel shift assays were performed to characterize the promoter of the identified PXR-regulated gene.
Results:
In both Pxr-/- male and female mice, lumbar, sternum, and skull were all also found to have decreased their BMD values. Serum Pi levels, but not calcium levels, are attenuated in Pxr-/- mice, exhibiting a phenotype of hypophosphatemia. Among the members of the Na/Pi contransporter family, only the SLC34A2 mRNA and protein are repressed in Pxr-/- mice. PXR can directly activate the transcription of the SLC34A2 gene through an ER6 motif on its promoter.
Conclusion:
Pxr-/- mice show the inherited phenotype of hypophosphatemia. The lack of PXR results in a severe repression of the Na/Pi cotransporter NaPi-IIb/Npt2b (SLC34A2), thus leading Pxr-/- males and females to develop a type of hypophosphatemia.
Insights
The absence of the pregnane X receptor (PXR) causes hypophosphatemia in mice. This is due to reduced expression of the phosphate transporter gene SLC34A2, impacting bone mineral density.
Area of Science:
- Biochemistry
- Genetics
- Physiology
Background:
- The pregnane X receptor (PXR) is a nuclear receptor involved in xenobiotic metabolism.
- Previous studies indicated that PXR deficiency leads to decreased bone mineral density (BMD).
Purpose of the Study:
- To investigate the inherited phenotype associated with reduced BMD in PXR-deficient mice.
- To identify PXR-regulated genes involved in bone homeostasis.
Main Methods:
- Serum levels of phosphate, calcium, and vitamin D3 were measured in Pxr+/+ and Pxr-/- mice.
- Gene and protein expression of transporters and bone homeostasis regulators were analyzed using RT-PCR and Western blots.
- Reporter and gel shift assays were employed to characterize gene promoter activity.
Main Results:
- Pxr-/- mice exhibited decreased BMD in multiple skeletal sites and hypophosphatemia (low serum phosphate).
- The expression of the sodium-phosphate cotransporter SLC34A2 (NaPi-IIb/Npt2b) was significantly repressed in Pxr-/- mice.
- PXR directly activates SLC34A2 transcription via an ER6 motif on its promoter.
Conclusions:
- PXR deficiency in mice results in an inherited phenotype of hypophosphatemia.
- Reduced expression of the NaPi-IIb/Npt2b (SLC34A2) cotransporter due to PXR absence contributes to hypophosphatemia and decreased BMD.
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