Dietary phosphate restriction attenuates polycystic kidney disease in mice

Studies in rodents with reduced nephron mass have suggested a strong positive correlation between dietary phosphate consumption and CKD progression. Prior work by our group demonstrated that dietary phosphate restriction can prevent tubular injury and microcyst formation in rodents with glomerulonephritis. Tubular injury and cystic dilation of tubules are key contributors to kidney function decline in polycystic kidney disease (PKD). Here, we determined whether dietary phosphate restriction slows renal cyst growth and fibrosis in a mouse model of PKD. Pcy/pcy mice received a normal phosphate (0.54%) or a phosphate-restricted (0.02%) diet (n = 10/group) from 7 to 20 wk of age. All of the other major dietary constituents, including protein source and content, were comparable between the two diets. At 20 wk, body weight, kidney weight-to-body weight ratio (KW/BW), cystic area, cyst number, and kidney fibrosis were quantified. Pcy/pcy mice fed a phosphate-restricted diet had lower serum phosphate, fibroblast growth factor 23, and parathyroid hormone levels, along with elevated serum calcium levels and increased kidney Klotho gene expression compared with mice that consumed the control diet. Dietary phosphate restriction resulted in a 25% lower KW/BW ratio and reduced the cyst number, cystic index, and gene expression for the tubular injury markers neutrophil gelatinase-associated lipocalin and interleukin-18. Mice fed the phosphate-restricted diet exhibited lower kidney expression for pathways involved in collagen deposition and myofibroblast activation (collagen type I-α₁, phosphorylated SMAD3, and α-smooth muscle actin); however, histological differences in kidney fibrosis were not appreciated. Dietary phosphate restriction slows cystogenesis and inhibits the activation of key pathways in the generation of kidney fibrosis in PKD mice.