Decreased transcription of the sodium-phosphate transporter gene in the hypophosphatemic mouse
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J F Collins1, L A Scheving, F K Ghishan
1Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-2576, USA.
Abstract:
Recently, it has been hypothesized that the proximal tubular Na(+)-Pi transporter may play a role in murine X-linked hypophosphatemic vitamin D-resistant rickets. In the present investigation, Western blot analysis of renal brush-border membrane proteins, utilizing polyclonal antisera raised against the mouse Na(+)-Pi transporter, revealed a predominant band at 87 kDa in normal and hypophosphatemic (Hyp) mice. The intensity of this band was reduced in the Hyp mouse by 4.5-fold (Hyp/normal = 0.22 +/- 0.04, n = 3, P < 0.05). Additionally, immunohistochemical analysis of kidney cortex in both mice localized the protein to the apical membrane of the proximal tubules. Relative transcription rates of the Na(+)-Pi transporter gene in the normal and Hyp mouse were then investigated. Nuclear run-on assays showed a 51 +/- 0.02% decreased rate of transcription of the Na(+)-Pi transporter gene in the Hyp mice (n = 3). Thus abnormal transcriptional control of this gene in the Hyp mouse likely plays a role in X-linked hypophosphatemia.
Insights
The sodium-phosphate (Na(+)-Pi) transporter is reduced in X-linked hypophosphatemia mice. Abnormal gene transcription of this transporter likely contributes to this condition.
Area of Science:
- Biochemistry
- Genetics
- Nephrology
Background:
- X-linked hypophosphatemia is a genetic disorder characterized by impaired phosphate reabsorption.
- The proximal tubular sodium-phosphate (Na(+)-Pi) transporter is crucial for phosphate homeostasis.
Purpose of the Study:
- To investigate the role of the Na(+)-Pi transporter in murine X-linked hypophosphatemia.
- To determine if alterations in Na(+)-Pi transporter expression or gene transcription contribute to the disease phenotype.
Main Methods:
- Western blot analysis of renal brush-border membrane proteins to quantify Na(+)-Pi transporter levels.
- Immunohistochemical analysis to localize the transporter in kidney cortex.
- Nuclear run-on assays to assess gene transcription rates.
Main Results:
- Western blot revealed a 4.5-fold reduction in Na(+)-Pi transporter protein levels in hypophosphatemic (Hyp) mice compared to normal mice.
- Immunohistochemistry confirmed transporter localization to the apical membrane of proximal tubules in both groups.
- Nuclear run-on assays demonstrated a 51% decrease in Na(+)-Pi transporter gene transcription rate in Hyp mice.
Conclusions:
- Reduced expression of the Na(+)-Pi transporter in the kidney is a key feature of murine X-linked hypophosphatemia.
- Abnormal transcriptional control of the Na(+)-Pi transporter gene likely underlies the development of X-linked hypophosphatemia.