Divergent localization of angiotensinogen mRNA and protein in proximal tubule segments of normal rat kidney

Objectives: Angiotensinogen in the kidneys is formed primarily in the proximal tubule cells and is secreted into the tubular fluid. Structurally, proximal tubules can be divided into three segments. The first segment, segment 1 (S1) is mainly confined to the pars convoluta, the second segment, segment 2 (S2) comprises the end of pars convoluta, and the third segment, segment 3 (S3) includes the major part of the pars recta. There are some reports describing angiotensinogen localization in kidneys; however, it remains uncertain which proximal tubule segments express angiotensinogen. To determine the detailed localization of angiotensinogen in the three proximal tubule segments, we established multistaining methods using segment-specific protein markers. Methods: Using kidneys from Wistar-Kyoto rats, we performed immunohistochemistry and double or triple staining by fluorescence in-situ hybridization and/or immunofluorescence. Results: Our results show that angiotensinogen mRNA and protein are expressed in the cortex and outer medulla of the normal rat kidney. Angiotensinogen mRNA was hardly detected in S1, detected weakly in S2 and strongly in S3 segments. In contrast, angiotensinogen protein was detected in S1 at high levels and less in S2 and S3 segments. Conclusion: These data indicate divergence of angiotensinogen mRNA transcription and angiotensinogen protein synthesis and metabolism in different segments of the normal rat proximal tubules.