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Hypoxia-induced adrenomedullin production in the kidney
1Second Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
Background:
Adrenomedullin (AM) is a newly discovered peptide that has a potent vasorelaxant activity. To investigate its potential roles in hypoxia-induced renal injury, we examined whether AM production in the kidney increased under hypoxic conditions.
Methods:
The AM transcript levels in Madin-Darby canine kidney (MDCK) cells, rat vascular smooth muscle cells (VSMCs), and rat mesangial cells were assessed by Northern blot analyses under normoxic and hypoxic conditions. The AM peptide in culture media was measured by radioimmunoassay. The effects of hypoxia on accumulation of cAMP in VSMCs were also examined. The stability of AM transcripts under normoxic and hypoxic conditions was compared in the presence of actinomycin D. The effects of hypoxia on AM promoter activity was assessed by transient transfection assays using the AM promoter subcloned upstream of luciferase gene.
Results:
The expression of AM transcripts increased significantly in MDCK cells, rat VSMCs, and rat mesangial cells under hypoxic conditions without changes in the stability of AM transcripts; however, the AM promoter activity under hypoxic was not elevated significantly. The accumulation of AM peptide in culture media also increased significantly under hypoxic conditions in MDCK cells (2.2 +/- 0.1 fmol/10(5) cells in normoxia vs. 3.5 +/- 0.3 fmol/10(5) cells in hypoxia, 6 hr after hypoxia induction, P < 0.001), and in rat VSMCs (5.5 +/- 0.3 fmol/10(5) cells in normoxia vs. 7.8 +/- 0.4 fmol/10(5) cells in hypoxia, 8 hr after hypoxia induction, P < 0.01). Under hypoxic conditions, cAMP levels in rat VSMCs increased significantly compared with those under normoxic conditions (13.3 +/- 1.4 pmol/well vs. 4.6 +/- 0.4 pmol/well, P < 0.01).
Conclusions:
Renal parenchymal cells as well as renal vessels may produce AM under hypoxic conditions.
Insights
Hypoxia increases adrenomedullin (AM) production in kidney cells and vessels, suggesting a role for AM in mitigating hypoxia-induced renal injury. This study investigated AM
Area of Science:
- Nephrology
- Cardiovascular Biology
- Molecular Biology
Background:
- Adrenomedullin (AM) is a peptide with potent vasorelaxant properties.
- Its role in hypoxia-induced renal injury requires further investigation.
- This study examines AM production in the kidney under hypoxic conditions.
Purpose of the Study:
- To determine if kidney cells and renal vessels increase adrenomedullin (AM) production during hypoxia.
- To investigate the cellular mechanisms regulating AM expression under hypoxic stress.
Main Methods:
- Assessed AM transcript levels using Northern blot analysis in kidney cells (MDCK) and vascular smooth muscle cells (VSMCs).
- Measured AM peptide accumulation in cell culture media via radioimmunoassay.
- Evaluated AM promoter activity and transcript stability under normoxic and hypoxic conditions.
Main Results:
- Hypoxia significantly increased AM transcript and peptide levels in MDCK cells and VSMCs.
- AM transcript stability remained unchanged, but promoter activity showed no significant elevation.
- Hypoxia led to increased cyclic AMP (cAMP) levels in VSMCs.
Conclusions:
- Renal parenchymal cells and renal vessels produce increased adrenomedullin (AM) under hypoxic conditions.
- AM may play a protective role in the kidney during hypoxia.