Slc7a9 knockout mouse is a good cystinuria model for antilithiasic pharmacological studies.

Cystinuria is a hereditary disorder caused by a defect in the apical membrane transport system for cystine and dibasic amino acids in renal proximal tubules and intestine, resulting in recurrent urolithiasis. Mutations in SLC3A1 and SLC7A9 genes, that codify for rBAT/b(0,+)AT transporter subunits, cause type A and B cystinuria, respectively. In humans, cystinuria treatment is based on the prevention of calculi formation and its dissolution or breakage. Persistent calculi are treated with thiols [i.e., d-penicillamine (DP) and mercaptopropionylglycine (MPG)] for cystine solubilization. We have developed a new protocol with DP to validate our Slc7a9 knockout mouse model for the study of the therapeutic effect of drugs in the treatment of cystine lithiasis. We performed a 5-wk treatment of individually caged lithiasic mutant mice with a previously tested DP dose. To appraise the evolution of lithiasis throughout the treatment a noninvasive indirect method of calculi quantification was developed: calculi mass was quantified by densitometry of X-ray images from cystinuric mice before and after treatment. Urine was collected in metabolic cage experiments to quantify amino acids in DP-treated and nontreated, nonlithiasic mutant mice. We found significant differences between DP-treated and nontreated knockout mice in calculi size and in urinary cystine excretion. Histopathological analysis showed that globally nontreated mutant mice had more severe and diffuse urinary system damage than DP-treated mice. Our results validate the use of this mouse model for testing the efficacy of potential new drugs against cystinuria.

Profiling at mRNA, protein, and metabolite levels reveals alterations in renal amino acid handling and glutathione metabolism in kidney tissue of Pept2-/- mice.

PEPT2 is an integral membrane protein in the apical membrane of renal epithelial cells that operates as a rheogenic transporter for di- and tripeptides and structurally related drugs. Its prime role is thought to be the reabsorption of filtered di- and tripeptides contributing to amino acid homeostasis. To elucidate the role of PEPT2 in renal amino acid metabolism we submitted kidney tissues of wild-type and a Pept2(-/-) mouse line to a comprehensive transcriptome, proteome and metabolome profiling and analyzed urinary amino acids and dipeptides. cDNA microarray analysis identified 147 differentially expressed transcripts in transporter-deficient animals, and proteome analysis by 2D-PAGE and MALDI-TOF-MS identified 37 differentially expressed proteins. Metabolite profiling by GC-MS revealed predominantly altered concentrations of amino acids and derivatives. Urinary excretion of amino acids demonstrated increased glycine and cysteine/cystine concentrations and dipeptides in urine were assessed by amino acid analysis of urine samples before and after in vitro dipeptidase digestion. Dipeptides constituted a noticeable fraction of urinary amino acids in Pept2(-/-) animals, only, and dipeptide-bound glycine and cystine were selectively increased in Pept2(-/-) urine samples. These findings were confirmed by a drastically increased excretion of cysteinyl-glycine (cys-gly). Urinary loss of cys-gly together with lower concentrations of cysteine, glycine, and oxoproline in kidney tissue and altered expression of mRNA and proteins involved in glutathione (GSH) metabolism suggests that PEPT2 is predominantly a system for reabsorption of cys-gly originating from GSH break-down, thus contributing to resynthesis of GSH.

Phenotype analysis of mice deficient in the peptide transporter PEPT2 in response to alterations in dietary protein intake.

The peptide transporter PEPT2 mediates cellular uptake of di- and tripeptides driven by an inwardly directed electrochemical proton gradient. In mammals PEPT2 is found in a variety of organs such as kidney, lung, brain, enteric nervous system, and mammary gland. Highest expression levels are observed in renal proximal tubules where PEPT2 contributes to reabsorption of filtered di- and tripeptides. To assess the physiological importance of the transporter in overall metabolism, we have generated a Pept2-/- mouse line that lacks a functional PEPT2 protein. Here we present data on body weight, organ weights, and blood pressure. Mice were then fed diets containing either 10, 20, or 30% (w/w) protein, and food and water intake rates as well as plasma and urine parameters were determined. In spite of PEPT2 expression in a variety of tissues, only subtle phenotypic changes were observed. Male PEPT2 null mice displayed lower bodyweight and lower relative heart weight, whereas, relative kidney weight was lower in female Pept2-/- mice. No differences were found in blood pressure. When fed diets with different protein contents, Pept2-/- mice adapted food intake to dietary protein content with higher consumption rates on low protein and reduced food intake rates on the high protein diet.