Glutathione peroxidase-3 produced by the kidney binds to a population of basement membranes in the gastrointestinal tract and in other tissues

Abstract

Glutathione peroxidase-3 (Gpx3), the extracellular glutathione peroxidase synthesized largely in the kidney, binds to basement membranes of renal cortical epithelial cells. The present study assessed extrarenal expression of Gpx3 using RT-PCR and presence of Gpx3 protein using immunocytochemistry. Gpx3 expression was higher in kidney and epididymis than in other tissues. Gpx3 bound to basement membranes of epithelial cells in the gastrointestinal tract, the efferent ducts connecting the seminiferous tubules with the epididymis, the bronchi, and type II pneumocytes. It was not detected on the basement membrane of type I pneumocytes. Gpx3 was also present in the lumen of the epididymis. Transplantation of Gpx3(+/+) kidneys into Gpx3(-/-) mice led to Gpx3 binding to the same basement membranes to which it bound in Gpx3(+/+) mice but not to its presence in the epididymal lumen. These results show that Gpx3 from the blood binds to basement membranes of specific epithelial cells and indicate that the cells modify their basement membranes to cause the binding. They further indicate that at least two Gpx3 compartments exist in the organism. In one compartment, kidney supplies Gpx3 through the blood to specific basement membranes in a number of tissues. In the other compartment, the epididymis provides Gpx3 to its own lumen. Tissues other than kidney and epididymis express Gpx3 at lower levels and may supply Gpx3 to other compartments.

Fig. 1.

Relative quantities (RQ) of glutathione peroxidase-3 (Gpx3) mRNA in tissues of Gpx3^+/+ mice fed the diet supplemented with 0.25 mg selenium/kg. The kidney value was 106 ± 9.5 RQ, n = 3. For other tissues n was 3 or 4. Corresponding Gpx3^−/− values did not reach the threshold of significance. Hprt, hypoxanthinephosphoribosyltransferase.

Fig. 2.

Gpx3 in tissues of Gpx3^+/+ mouse gastrointestinal tract. A: stomach-arrowheads point to Gpx3-positive cells that have not been identified. B: duodenum. C: en face view of duodenal villus arrowheads point to basement membrane pores. D: liver. E: gall bladder. F: colon. Gpx3 is red; actin is green; nuclei are blue.

Fig. 3.

Gpx3 in mouse jejunum. A: from Gpx3^+/+ mouse. B: from Gpx3^−/− mouse. C: from Gpx3^−/− mouse 2 wk after transplantation of a Gpx3^+/+ kidney. Gpx3 is red; actin is green; nuclei are blue.

Fig. 4.

Gpx3 in mouse lung. In A and B Gpx3 is red, actin is green, and nuclei are blue. A: from Gpx3^+/+ mouse. B: from Gpx3^−/− mouse 2 wk after transplantation of a Gpx3^+/+ kidney. C: from Gpx3^+/+ mouse. In C, Gpx3 is green, antiprosurfactant protein C (stain for type II pneumocytes) is red, and nuclei are blue.

Fig. 5.

Gpx3 in mouse efferent ducts and initial segment of the epididymis. A: from Gpx3^+/+ mouse. B: from Gpx3^−/− mouse. C: from Gpx3^−/− mouse 2 wk after transplantation of a Gpx3^+/+ kidney. Gpx3 is red; actin is green; nuclei are blue. ED indicates efferent ducts and IS indicates the initial segment of the epididymis.

Fig. 6.

Gpx3 in mouse epididymis. A: distal caput from Gpx3^+/+ mouse. B: distal caput from Gpx3^−/− mouse. C: cauda from Gpx3^+/+ mouse. D: cauda from Gpx3^−/− mouse 2 wk after transplantation of a Gpx3^+/+ kidney. Gpx3 is red; actin is green; nuclei are blue. Arrowheads point to Gpx3 inside cells.

Fig. 7.

Appearance of Gpx3 in native kidneys of Gpx3^−/− mice after transplant of Gpx3^+/+ kidneys. Three Gpx3^−/− mice received kidney transplants from Gpx3^+/+ mice and are indicated by TR1, TR2, and TR3. Homogenates of native and transplanted kidneys were made 2 wk after the transplant and subjected to SDS/PAGE and Western blotting. Lanes 1 and 2 represent kidneys from mice that did not undergo transplant.

Fig. 8.

Gpx3 protein in plasma and kidney from mice of differing selenium nutritional status. Plasma samples and kidney homogenates were subjected to SDS/PAGE, and Western blotting was carried out. Protein (50 μg) in the form of 10% kidney homogenate or 0.5 μl plasma was loaded per lane. Density of the Gpx3 band was determined and compared with the average density from mice fed 0.25 mg selenium/kg diet. Values are means ± SD, n = 5.