A missense mutation in the sodium phosphate co-transporter Slc34a1 impairs phosphate homeostasis.

The sodium phosphate co-transporters Npt2a and Npt2c play important roles in the regulation of phosphate homeostasis. Slc34a1, the gene encoding Npt2a, resides downstream of the gene encoding coagulation factor XII (f12) and was inadvertently modified while generating f12(-/-) mice. In this report, the renal consequences of this modification are described.

Renal phosphaturia during metabolic acidosis revisited: molecular mechanisms for decreased renal phosphate reabsorption.

During metabolic acidosis (MA), urinary phosphate excretion increases and contributes to acid removal. Two Na(+)-dependent phosphate transporters, NaPi-IIa (Slc34a1) and NaPi-IIc (Slc34a3), are located in the brush border membrane (BBM) of the proximal tubule and mediate renal phosphate reabsorption. Transcriptome analysis of kidneys from acid-loaded mice revealed a large decrease in NaPi-IIc messenger RNA (mRNA) and a smaller reduction in NaPi-IIa mRNA abundance.

Fibroblast growth factor 23 impairs phosphorus and vitamin D metabolism in vivo and suppresses 25-hydroxyvitamin D-1alpha-hydroxylase expression in vitro.

Fibroblast growth factor-23 (FGF-23) is critical to the pathogenesis of a distinct group of renal phosphate wasting disorders: tumor-induced osteomalacia, X-linked hypophosphatemia, and autosomal dominant and autosomal recessive hypophosphatemic rickets. Excess circulating FGF-23 is responsible for their major phenotypic features which include hypophosphatemia due to renal phosphate wasting and inappropriately low serum 1,25(OH)2D concentrations. To characterize the effects of FGF-23 on renal sodium-phosphate (Na/P(i)) cotransport and vitamin D metabolism, we administered FGF-23(R176Q) to normal mice.

Phosphate transport: molecular basis, regulation and pathophysiology.

Inorganic phosphate (Pi) is fundamental to cellular metabolism and skeletal mineralization. Ingested Pi is absorbed by the small intestine, deposited in bone, and filtered by the kidney where it is reabsorbed and excreted in amounts determined by the specific needs of the organism. Two distinct renal Na-dependent Pi transporters, type IIa (NPT2a, SLC34A1) and type IIc (NPT2c, SLC34A3), are expressed in brush border membrane of proximal tubular cells where the bulk of filtered Pi is reabsorbed.

SLC34A3 mutations in patients with hereditary hypophosphatemic rickets with hypercalciuria predict a key role for the sodium-phosphate cotransporter NaPi-IIc in maintaining phosphate homeostasis.

Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is a rare disorder of autosomal recessive inheritance that was first described in a large consanguineous Bedouin kindred. HHRH is characterized by the presence of hypophosphatemia secondary to renal phosphate wasting, radiographic and/or histological evidence of rickets, limb deformities, muscle weakness, and bone pain. HHRH is distinct from other forms of hypophosphatemic rickets in that affected individuals present with hypercalciuria due to increased serum 1,25-dihydroxyvitamin D levels and increased intestinal calcium absorption.