Abstract: FR-PO281

Severe CKD Environment Affects CaSR Gene Expression and the Cascade of Genes in Parathyroid Glands Even without High Phosphorus Diets

Session Information

Category: Mineral Disease

  • 1202 Mineral Disease: Vitamin D, PTH, FGF-23

Authors

  • Uchiyama, Taketo, Division of Nephrology and Hypertension, Department of Internal Medicine, Jikei University School of Medicine, Tokyo, Japan
  • Ohkido, Ichiro, Division of Nephrology and Hypertension, Department of Internal Medicine, Jikei University School of Medicine, Tokyo, Japan
  • Kamejima, Sahoko, Jikei University School of Medicine, Tokyo, Japan
  • Nakashima, Akio, Division of Kidney and Hypertension, Department of Internal Medicine, The Jikei University School of Medicine, Tokyo, Japan
  • Yokoo, Takashi, The Jikei University School of Medicine, Tokyo, Japan
Background

Chronic kidney disease (CKD) disrupts mineral homeostasis and its representative pathosis is defined as secondary hyperparathyroidism (SHPT). SHPT occurs during the early course of progressive renal insufficiency, and is associated with mortality and cardiovascular events. Reduction of the calcium-sensing receptor (CaSR) occurs slowly and progressively throughout this process, although the underlying mechanism remains largely unknown.

Methods

CKD was induced by 0.75% adenine-containing diet. CKD rats and control rats were maintained for 2 weeks on diets containing 0.7% phosphorus or 1.3% phosphorus. In a gene expression analysis, TaqMan probes were used to do the quantitative real-time polymerase chain reactions. CaSR and glial cells missing-2 (Gcm2) protein expressions were analyzed using immunohistochemistry and western blotting. DNA methylation analysis was performed using a restriction digestion and quantitative PCR.

Results

CaSR mRNA was reduced in CKD rats fed the normal and high phosphorus diets (CKD NP and CKD HP, respetctively) (Figure 1), and the amount of CaSR protein was compatible with the gene expression assay. There is no significant difference in the DNA methylation status in the promoters of CaSR between the four groups. Gcm2, which has been shown to directly regulate CaSR and also to transactivate CaSR through Gcm2 response elements in the CaSR promoter, was significantly decreased in CKD NP and CKD HP rats (Figure 2), and using western blotting the expression of Gcm2 was shown to be compatible.

Conclusion

A reduction of CaSR expression in parathyroid glands was observed in CKD NP and CKD HP rats; however, the DNA hypermethylaton was not demonstrated. We then analyzed the Gcm2 gene and its protein expression, as upstream transcription factor of CaSR, and we verified its depression in CKD NP and CKD HP rats. Consequently, our data suggest that Gcm2 was responsible for the reduction in mRNA and protein levels of CaSR and VDR in PTGs of CKD HP rats.