Kidney Week

Abstract: SA-OR021

Protective Role of Type III Sodium-Dependent Phosphate Transporter, PiT-2, in Uremic Vascular Calcification

Session Information

• Mineral Disease: Bones, Vessels, Stones
  November 04, 2017 | Location: Room 273, Morial Convention Center
  Abstract Time: 04:30 PM - 04:42 PM

Category: Mineral Disease

• 1205 Vascular Calcification

Authors

• Yamada, Shunsuke, University of Washington, Seattle, Washington, United States

Shunsuke Yamada, MD

• Soberg, Elizabeth M., University of Washington, Seattle, Washington, United States

Elizabeth M. Soberg,

• Cox, Timothy C, University of Washington, Seattle, Washington, United States

Timothy C Cox,

• Speer, Mei Y., University of Washington, Seattle, Washington, United States

Mei Y. Speer,

• Giachelli, Cecilia M., University of Washington, Seattle, Washington, United States

Cecilia M. Giachelli,

Background

Vascular calcification (VC) is prevalent in patients with chronic kidney disease (CKD) and increases the risk of cardiovascular deaths. PiT-2 is a type III sodium-dependent phosphate (Pi) transporter expressed in various tissues and a causative gene for familial basal ganglion arterial calcification. However, it is unknown whether PiT-2 plays a role in the pathogenesis of VC related to CKD.

Methods

To determine the role of PiT-2 in VC, wild-type (WT) and global PiT-2 heterozygous (HET) knockout mice were challenged with CKD. At two weeks after the two-step 5/6^th nephrectomy, mice were fed a normal (0.5%) or high (1.5%) Pi diet for 11 days and terminated. At termination, blood, aorta, kidney, and femur were collected. Serum chemistry, histology, and micro CT analyses were performed. Primary vascular smooth muscle cells (VSMCs) isolated from the aortas of WT and PiT-2 HET mice were used for in vitro Pi-induced calcification and P-uptake assays. WT-derived VSMCs were also treated with scramble or PiT-2 small interfering RNA (siRNA) and used for gene and protein expression analysis.

Results

Uremic mice fed a high Pi diet developed VC in the medial layer of the aorta, which was exemplified by Alizarin red staining and calcium quantification of the blood vessel. PIT-2 haploinsufficiency greatly enhanced VC in the setting of CKD and high Pi diet. No differences were observed in the serum levels of calcium, Pi, and FGF23, kidney function, and renal mRNA expression of SLC34A1 and SLC34A3 between the WT and PiT-2 HET mice with CKD. MicroCT analyses showed that haploinsufficiency of PiT-2 decreased trabecular bone mineral density and thickness in CKD. In vitro, Pi uptake activity was decreased in the cultured VSMCs isolated from the PiT-2 HET mice compared with those from the WT mice. Under high Pi medium condition, PiT-2 haploinsufficiency increased calcification of the cultured VSMCs. Similar results were also found in WT VSMCs treated with PiT-2 siRNA. Finally, mRNA expression and protein levels of osteoprotegerin, an inhibitor of VC, were decreased in VSMCs treated with PiT-2 siRNA compared to scramble controls.

Conclusion

PiT-2 plays a protective role in the pathogenesis of VC and bone disorders in CKD mice, and can be a promising therapeutic target in the CKD population.

Funding

• NIDDK Support