Role of the sodium‐dependent phosphate co‐transporter PiT‐1 in mouse development and vascular calcification

Abstract

Vascular calcification is correlated with morbidity and mortality in coronary artery disease, diabetes and chronic kidney disease. In vitro, elevated phosphate levels induced smooth muscle cell calcification in a PiT‐dependent manner. To determine the in vivo role of PiT‐1, a mouse conditional allele was generated in which loxP sites flanked exons 3 and 4 of the PiT‐1 gene. Recombination occurred in the presence of Cre driven by the ubiquitous Sox‐2 promoter, and the resulting PiT‐1Δ allele would produce a nonfunctional protein with a shift in the reading frame and production of a stop codon at amino acid 121. Wild‐type and PiT‐1Δ/+ mice were produced at expected Mendelian ratios, but no PiT‐1Δ/Δ mice were born. Examination of early development revealed that the PiT‐1Δ/Δ embryos were arresting at embryonic stage 10.5 and most were resorbed by E13.5. Affected embryos displayed cardiac defects and an under‐vascularized yolk sac as compared to siblings. Semi‐quantitative RT‐PCR analysis confirmed that PiT‐1Δ/Δ embryos expressed a truncated form of mRNA, but only embryos harboring at least one wild‐type allele expressed wild‐type mRNA. Thus, we have successfully generated conditional and null PiT‐1 alleles and confirmed that PiT‐1 is required for normal mouse embryonic development.