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Medical Faculty of the Charité, 1Department of Anatomy, 3Nephrology/Hypertension, Franz Volhard Clinic, HELIOS Clinics and Max Delbrück Center for Molecular Medicine, and 4Department of Physiology, Berlin, Germany; and 2University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma
Submitted 21 April 2004 ; accepted in final form 19 October 2004
The Tamm-Horsfall protein (THP; uromodulin), the dominant protein in normal urine, is produced exclusively in the thick ascending limb of Henle's loop. THP mutations are associated with disease; however, the physiological role of THP remains obscure. We generated THP gene-deficient mice (THP /) and compared them with wild-type (WT) mice. THP / mice displayed anatomically normal kidneys. Steady-state electrolyte handling was not different between strains. Creatinine clearance was 63% lower in THP / than in WT mice (P < 0.05). Sucrose loading induced no changes between strains. However, water deprivation for 24 h decreased urine volume from 58 ± 9 to 28 ± 4 µl·g body wt1·24 h1 in WT mice (P < 0.05), whereas in THP / mice this decrease was less pronounced (57 ± 4 to 41 ± 5 µl·g body wt1·24 h1; P < 0.05), revealing significant interstrain difference (P < 0.05). We further used RT-PCR, Northern and Western blotting, and histochemistry to study renal transporters, channels, and regulatory systems under steady-state conditions. We found that major distal transporters were upregulated in THP / mice, whereas juxtaglomerular immunoreactive cyclooxygenase-2 (COX-2) and renin mRNA expression were both decreased in THP / compared with WT mice. These observations suggest that THP influences transporters in Henle's loop. The decreased COX-2 and renin levels may be related to an altered tubular salt load at the macula densa, whereas the increased expression of distal transporters may reflect compensatory mechanisms. Our data raise the hypothesis that THP plays an important regulatory role in the kidney.
gene-disrupted mice; thick ascending limb; renal concentrating mechanism
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