Gender- and age-dependent changes in kidney androgen protein mRNA expression in a knockout mouse model for nephrolithiasis

Adenine phosphoribosyl transferase (APRT) deficiency and a novel sequence variant in APRT with phenotypic diversity and a literature review

Adenine phosphoribosyl transferase (APRT) deficiency is an autosomal recessive disorder and a rare cause of urolithiasis due to mutations in APRT (OMIM #102600). APRT deficiency results in increased urinary excretion of 2,8-dihydroxyadenine (DHA) which can cause urolithiasis and kidney failure. However, with prompt diagnosis, patients with APRT deficiency can be treated with xanthine oxidoreductase inhibitors which decrease urinary DHA excretion and improve outcomes. We report a pair of siblings, an 11-year-old brother and his 14-year-old sister with compound heterozygous variants c.270del (p.Lys91Serfs*46) and c.484_486del (p.Leu162del) in APRT with variable clinical presentation of APRT deficiency. The brother presented at 17 months of age with urolithiasis and severe acute kidney injury. His elder sister remained well and asymptomatic with normal kidney function and did not develop renal calculi. Brownish disk or sphere-like crystals with both concentric and radial markings were reported on urine microscopy in the sister on screening. The sister's diagnosis was confirmed with further laboratory evidence of absent red cell lysate APRT activity with corresponding elevated levels of urinary DHA. In conclusion, we identified a novel mutation in the APRT gene in a pair of siblings with greater phenotypic severity in the male.

Effects of antifibrotic agents on TGF-beta1, CTGF and IFN-gamma expression in patients with idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a deadly disease, largely unresponsive to treatment with corticosteroids and immunosuppressives. The aim of this randomized, prospective, open-label study was to characterize the molecular effects of IFN-gamma-1b and colchicine, on biomarkers expression associated with fibrosis (TGF-beta, CTGF) and immunomodulatory/antimicrobial activity (IFN-gamma), in the lungs of patients with IPF. Fourteen (14) patients with an established diagnosis of IPF received either 200 microg of IFN-gamma-1b subcutaneously three times per week, or 1mg of oral colchicine per day, for 24 months. Using RT-PCR assay, we evaluated the transcription levels of transforming growth factor beta1 (TGF-beta1), connective-tissue growth factor (CTGF), and interferon-gamma (IFN-gamma) genes in lung tissue before and after treatment with IFN-gamma-1b or colchicine. Marked mRNA expression of TGF-beta1 and CTGF, but complete lack of interferon-gamma was detected in fibrotic lung tissue at entry. After treatment, both groups exhibited increased expression of IFN-gamma gene at 6 months that was sustained at 24 months. The expression of CTGF and TGF-beta1 remained almost stable before and after treatment, in the IFN-gamma-1b group, while TGF-beta1 was statistically decreased after therapy, in the colchicine group (p=0.0002). Significant difference in DLCO (% pred), was found between the two treatment groups in favor of IFN-gamma-1b group (p=0.04). In addition, the IFN-gamma-1b group showed stability in arterial PO2 while the colchicine group significantly deteriorated (p=0.02). In conclusion, we report the effect of antifibrotic agents (IFN-gamma-1b and colchicine) in TGF-beta, CTGF, and endogenous IFN-gamma gene expression, in human fibrosis. However, extended studies are needed to verify the pathophysiological consequences of these findings.

Aprt/Opn double knockout mice: osteopontin is a modifier of kidney stone disease severity

BACKGROUND

Osteopontin (OPN) is reported to have two distinct functions in kidney disease: Promotion of inflammation at sites of tissue injury, and inhibition of calcium oxalate monohydrate stone formation. However, many of the studies supporting these functions were carried out in animal models of acute renal injury or in cultured cells; thus, the role of OPN in chronic renal disease is not well defined. We examined the role of OPN in adenine phosphoribosyltransferase (Aprt) knockout mice, in which inflammation and formation of 2,8-dihydroxyadenine (DHA) kidney stones are prominent features, by generating Aprt/Opn double knockout mice.

METHODS

We characterized the phenotypes of six- and 12-week-old Aprt-/- Opn-/-, Aprt-/- Opn+/+, Aprt+/+ Opn-/-, and Aprt+/+ Opn+/+ male and female mice using biochemical, histologic, immunohistochemical, and in situ hybridization techniques.

RESULTS

At 6 weeks of age, there was no difference in phenotype between double knockout and Aprt knockout mice. At 12 weeks, there was increased adenine and DHA excretion, renal crystal deposition, and inflammation in double knockout versus Aprt knockout male mice. Double knockout and Aprt knockout female mice at 12 weeks had less pathology than their male counterparts, but kidneys from double knockout females showed more inflammation compared with Aprt knockout females; both genotypes had similar levels of DHA crystal deposition.

CONCLUSION

We conclude that (1) OPN is a major inhibitor of DHA crystal deposition and inflammation in male mice; and (2) OPN is a major modifier of the inflammatory response but not of crystal deposition in female mice. Thus, separate mechanisms appear responsible for the tissue changes seen in DKO males versus females.

Impaired expression of an organic cation transporter, IMPT1, in a knockout mouse model for kidney stone disease

The imprinted multimembrane-spanning polyspecific transporter-like gene 1 ( IMPT1) encodes a predicted protein with organic cation transport capabilities. As a first step in understanding the function of IMPT1, we identified the renal structures expressing this gene in knockout mice with adenine phosphoribosyltransferase (APRT) deficiency and 2,8-dihydroxyadenine (DHA) nephrolithiasis. IMPT1 mRNA was not detected using a standard in situ hybridization (ISH) protocol, but we observed intense staining in cortico-medullary tubules and glomeruli in wild-type mice using an improved reverse transcription-polymerase chain reaction (RT-PCR) ISH procedure. IMPT1 mRNA expression was significantly decreased in the cortical region in kidney sections from APRT-deficient male mice. APRT-deficient female mice are less severely affected by DHA-induced kidney stone disease, and we observed only a modest reduction in IMPT1 expression in kidneys from these mice. IMPT1 expression in APRT heterozygous mice was comparable to that in wild-type mice, suggesting imprinting of one of the parental alleles. These findings suggest that decreased IMPT1 mRNA expression may contribute to the impaired renal function in APRT-deficient male mice, and that RT-PCR ISH is a valuable tool for localizing the site of expression of transcripts that are not detectable using standard ISH procedures.