High phosphorus diet-induced changes in NaPi-IIb phosphate transporter expression in the rat kidney: DNA microarray analysis.

The mechanism by which phosphorus levels are maintained in the body was investigated by analyzing changes in gene expression in the rat kidney following administration of a high phosphorus (HP) diet. Male Wistar rats were divided into two groups and fed a diet containing 0.3% (control) or 1.2% (HP) phosphorous for 24 days. Phosphorous retention was not significantly increased in HP rats, but fractional excretion of phosphorus was significantly increased in the HP group compared to controls, with an excessive amount of the ingested phosphorus being passed through the body. DNA microarray analysis of kidney tissue from both groups revealed changes in gene expression profile induced by a HP diet. Among the genes that were upregulated, Gene Ontology (GO) terms related to ossification, collagen fibril organization, and inflammation and immune response were significantly enriched. In particular, there was significant upregulation of type IIb sodium-dependent phosphate transporter (NaPi-IIb) in the HP rat kidney compared to control rats. This upregulation was confirmed by in situ hybridization. Distinct signals for NaPi-IIb in both the cortex and medulla of the kidney were apparent in the HP group, while the corresponding signals were much weaker in the control group. Immunohistochemical analysis showed that NaPi-IIb localized to the basolateral side of kidney epithelial cells surrounding the urinary duct in HP rats but not in control animals. These data suggest that NaPi-IIb is upregulated in the kidney in response to the active excretion of phosphate in HP diet-fed rats

GO terms that were significantly enriched (<i>p</i><0.05) in the top 1056 genes upregulated in response to a HP diet.

<p>*GO term with no <i>p</i>-value means not significant.</p><p>**FDR-corrected <i>p</i>-values of the GO terms appearing in the deepest hierarchy are represented by bold style.</p

Phosphorus and calcium balance and net absorption for control and HP diets.

<p>Data represent means ± SE (<i>n</i> = 5).</p><p>*<i>p</i><0.05 compared to the control group.</p><p>Net absorption and retention were calculated as follows:</p><p>Net absorption (mg/day) = intake – fecal excretion.</p><p>Retention (mg/day) = net absorption – urinary excretion.</p

Body weight, weight gain and food intake in control and HP rats.

<p>Data represent means ± SE (<i>n</i> = 5).</p

Effect of a HP diet on fractional excretion of calcium and phosphate in the kidney.

<p>Data represent means ± SE (<i>n</i> = 6 or 7). *<i>p</i><0.05 compared to the control group.</p

GO terms that were significantly enriched (<i>p</i><0.05) in the top 712 genes downregulated in response to a HP diet.

<p>*GO term with no <i>p</i>-value means not significant.</p><p>**FDR-corrected <i>p</i>-values of the GO terms appearing in the deepest hierarchy are represented by bold style.</p

Histological analysis of kidney tissue sections from rats fed a control or HP diet.

<p>Kidney sections from control rats (A, B, C) and HP rats (D, E, F) were stained with H&E and visualized by microscopy. Sections correspond to cortex (A, D), the corticomedullary junction (B, E) and the medullary region (C, F). Arrowheads indicate representative cyst-like areas; dotted circles indicate representative fibrosis-like areas. Scale bar = 100 µm.</p

Expression of NaPi-IIb in the kidney in control and HP rats.

<p>Kidney sections from control (A, B) and HP (C, D) rats were analyzed by <i>in situ</i> hybridization using a NaPi-IIb-specific probe. Sections represent the cortex (A, C) and medulla (B, D). Scale bar = 200 µm.</p

Genes related to water, phosphorus and calcium transport whose expression was altered in response to a HP diet.

<p>Genes related to water, phosphorus and calcium transport whose expression was altered in response to a HP diet.</p