Abstract
Others and we showed the increased levels of intrarenal angiotensinogen (AGT) in diabetic humans, mice, and rats. However, the precise localization of the augmented AGT mRNA and protein in proximal tubule segments of kidneys in diabetes remains to be established. To investigate the detailed localization of AGT in 3 proximal tubule segments of the kidneys in diabetes, the Otsuka Long-Evans Tokushima fatty (OLETF) rat (15 weeks) and the age-matched genetic control, the Long-Evans Tokushima Otsuka (LETO) rat were used. Kidney tissues were also prepared from OLETF rats that were administered with angiotensin II type 1 receptor blocker, olmesartan (0.02% in chow) or a combination of vasodilator agents (0.03% hydralazine, 0.006% reserpine, and 0.012% hydrochlorothiazide in chow; HRH). Moreover, biopsied samples of human kidney cortex were obtained by fine-needle aspiration to confirm the below-mentioned results of the rat localization study. Using 3-μm sections of zinc-saturated formalin-fixed paraffin-embedded slides, we examined the co-localization of AGT mRNA or protein with segment-specific protein markers (Segment (S)1-specific anti-sodium glucose cotransporter 2 antibody, S2-specific anti-carbonic anhydrase IV antibody, and S3-specific anti-ecto-adenosine triphosphatase antibody) by double staining using fluorescence in situ hybridization and/or immunofluorescence. AGT mRNA expression was not recognized much in S1 segments of either OLETF or LETO rat kidneys. In S3 segments, the AGT mRNA expression area was augmented in the OLETF rats than in the LETO rats (2.31 ± 0.02-fold; P = 0.0029). AGT protein expression areas in S1 and S3 segments were also increased (8.50 ± 2.78-fold; P = 0.0476, and 3.71 ± 0.83-fold; P = 0.0317, respectively). Chronic treatment with olmesartan, but not with HRH, ameliorated the augmented AGT mRNA and protein expression areas. AGT mRNA and protein expression areas in S2 segments were unchanged in OLETF rats compared with LETO rats. Biopsied samples of human kidney cortex showed the same results as for rat AGT mRNA and protein expression in the S1 and S2 segments. These data suggest that the augmented AGT mRNA in S3 and AGT protein in S1 and S3 play an important role in the development and the progression of diabetic nephropathy.
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