In vivo genetic evidence for suppressing vascular and soft-tissue calcification through the reduction of serum phosphate levels, even in the presence of high serum calcium and 1,25-dihydroxyvitamin d levels.
BACKGROUND
Klotho-knockout mice (klotho(-/-)) have increased renal expression of sodium/phosphate cotransporters (NaPi2a), associated with severe hyperphosphatemia. Such serum biochemical changes in klotho(-/-) mice lead to extensive soft-tissue anomalies and vascular calcification. To determine the significance of increased renal expression of the NaPi2a protein and concomitant hyperphosphatemia and vascular calcification in klotho(-/-) mice, we generated klotho and NaPi2a double-knockout (klotho(-/-)/NaPi2a(-/-)) mice.


RESULTS
Genetic inactivation of NaPi2a activity from klotho(-/-) mice reversed the severe hyperphosphatemia to mild hypophosphatemia or normophosphatemia. Importantly, despite significantly higher serum calcium and 1,25-dihydroxyvitamin D levels in klotho(-/-)/NaPi2a(-/-) mice, the vascular and soft-tissue calcifications were reduced. Extensive soft-tissue anomalies and cardiovascular calcification were consistently noted in klotho(-/-) mice by 6 weeks of age; however, these vascular and soft-tissue abnormalities were absent even in 12-week-old double-knockout mice. Klotho(-/-)/NaPi2a(-/-) mice also regained body weight and did not develop the generalized tissue atrophy often noted in klotho(-/-) single-knockout mice.


CONCLUSIONS
Our in vivo genetic manipulation studies have provided compelling evidence for a pathological role of increased NaPi2a activities in regulating abnormal mineral ion metabolism and soft-tissue anomalies in klotho(-/-) mice. Notably, our results suggest that serum phosphate levels are the important in vivo determinant of calcification and that lowering serum phosphate levels can reduce or eliminate soft-tissue and vascular calcification, even in presence of extremely high serum calcium and 1,25-dihydroxyvitamin D levels. These in vivo observations have significant clinical importance and therapeutic implications for patients with chronic kidney disease with cardiovascular calcification.
Ohnishi
Mutsuko
M
Departments of Oral Medicine, Infection, and Immunity and Developmental Biology, Harvard School of Dental Medicine, Boston, Mass, USA.
Nakatani
Teruyo
T
Lanske
Beate
B
Razzaque
M Shawkat
MS
D000818:Animals; D001808:Blood Vessels / Q000473:pathology*; D001842:Bone and Bones / Q000473:pathology*; D002114:Calcinosis; D002118:Calcium / Q000097:blood*; D005260:Female; D005966:Glucuronidase / Q000235:genetics / Q000378:metabolism; D006801:Humans; D017674:Hypophosphatemia / Q000097:blood / Q000235:genetics* / Q000473:pathology; D000090265:Klotho Proteins; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D010710:Phosphates / Q000097:blood*; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa / Q000235:genetics / Q000378:metabolism; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
D010710:Phosphates; C493555:Slc34a1 protein, mouse; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D014807:Vitamin D; C097949:1,25-dihydroxyvitamin D; D005966:Glucuronidase; D000090265:Klotho Proteins; D002118:Calcium