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| Author(s): |
Bruna Hitomi Inoue
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Faculdade de Medicina (FM/SBD) |
| Defense date: | 2012-10-29 |
| Examining board members: |
Adriana Castello Costa Girardi;
Joel Claudio Heimann;
Gerhard Malnic
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| Advisor: | Adriana Castello Costa Girardi |
| Abstract | |
Epidemiological evidences indicate that the presence of microalbuminuria predicts a higher frequency of cardiovascular events and mortality in essential hypertensive patients. Microalbuminuria may arise from increased glomerular permeability and/or reduced proximal tubular reabsorption of albumin. However, it remains to be determined whether the mechanisms that regulate the renal proximal tubular reabsorption of albumin are altered in essential hypertension. The purpose of this work was to investigate the molecular basis of microalbuminuria in essential hypertension, focusing on the renal tubular reabsorption of albumin. To this end, we evaluated the temporal evolution of urinary albumin excretion in spontaneously hypertensive rats (SHR) at 6 weeks of age (systolic arterial pressure, SAP, = 105 ± 4 mmHg), 14 weeks of age (SAP = 180 ± 2 mmHg) and 21 weeks of age (SAP = 202 ± 2 mmHg). Age-matched normotensive Wistar rats were used as controls. It was observed that the daily urinary excretion of albumin progressively increased with blood pressure in SHR from 6 to 21 weeks of age (10.5 ± 1.9, 92 ± 7.0 and 154 ± 27 g in SHR with 105, 180 and 202 mmHg of average SAP, respectively). This progressive increase in microalbuminuria has not been observed in age-matched normotensive Wistar rats, indicating that this phenomenon cannot be attributed to age progression over the studied period. SDS-PAGE analysis of urinary proteins showed that microalbuminuric SHR virtually excreted proteins of the size of albumin or smaller (< 70kDa), typical of tubular proteinuria. Additionally, it was verified that the protein expression levels of the endocytic receptors megalin and cubilin as well as of the chloride channel ClC-5 progressively decreased in the renal cortex of SHR from 6 to 21 weeks of age. Moreover, it was observed reduction of expression of another macromolecule that plays an important role in the process of receptor mediated endocytosis in the renal proximal tubule, the v-H+- ATPase, was reduced. However, reduced cortical expression of the B2 subunit of the v- H+-ATPase, was only statistically significant in 21-wk-old vs. 6-wk-old SHR. Expression levels of structural components of the glomerular barrier such as nephrin and podocin were unchanged. To sum up, our study demonstrates that the increase in urinary protein excretion, especially of albumin, is associated with lower expression of key components of the apical endocytic apparatus in the renal proximal tubule. It is tempting to speculate that dysfunction of the apical endocytic pathway in the renal proximal tubule may be the major mechanism underlying development of microalbuminuria in essential hypertension (AU) | |
| FAPESP's process: | 10/03398-7 - Molecular basis of microalbuminuria in essential hypertension: role of tubular albumin reabsorption |
| Grantee: | Bruna Hitomi Inoue |
| Support Opportunities: | Scholarships in Brazil - Master |