Angiotensin-(1-7) activates a tyrosine phosphatase and inhibits glucose-induced signalling in proximal tubular cells.
BACKGROUND
In the diabetic kidney, stimulation of mitogen-activated protein kinases (MAPKs) leads to extracellular matrix protein synthesis. In the proximal tubule, angiotensin-(1-7) [Ang-(1-7)] blocks activation of MAPKs by angiotensin II. We studied the effect of Ang-(1-7) on signalling responses in LLC-PK(1) cells in normal (5 mM) or high (25 mM) glucose.


METHODS
The p38 MAPK was assayed by immunoblot, Src homology 2-containing protein-tyrosine phosphatase-1 (SHP-1) activity was measured after immunoprecipitation, cell protein synthesis was determined by [(3)H]-leucine incorporation and transforming growth factor-beta1 (TGF-beta1), fibronectin and collagen IV were assayed by immunoblots and/or ELISA.


RESULTS
High glucose stimulated p38 MAPK. This response was inhibited by Ang-(1-7) in a concentration-dependent fashion, an effect reversed by the receptor Mas antagonist A-779. Ang-(1-7) increased SHP-1 activity, via the receptor Mas. An inhibitor of tyrosine phosphatase, phenylarsine oxide, reversed the inhibitory effect of Ang-(1-7) on high glucose-stimulated p38 MAPK. Ang-(1-7) inhibited high glucose-stimulated protein synthesis, and blocked the stimulatory effect of glucose on TGF-beta1. Conversely, Ang-(1-7) had no effect on glucose-stimulated synthesis of fibronectin or collagen IV.


CONCLUSIONS
These data indicate that in proximal tubular cells, binding of Ang-(1-7) to the receptor Mas stimulates SHP-1, associated with the inhibition of glucose-stimulated p38 MAPK. Ang-(1-7) selectively inhibits glucose-stimulated protein synthesis and TGF-beta1. In diabetic nephropathy, Ang-(1-7) may partly counteract the profibrotic effects of high glucose.
Gava
Elisandra
E
Division of Nephrology, Department of Medicine, Kidney Research Centre, Ottawa Health Research Institute, University of Ottawa, Ottawa, Ontario, Canada.
Samad-Zadeh
Arman
A
Zimpelmann
Joseph
J
Bahramifarid
Nasim
N
Kitten
Gregory T
GT
Santos
Robson A
RA
Touyz
Rhian M
RM
Burns
Kevin D
KD
D000803:Angiotensin I / Q000494:pharmacology*; D000818:Animals; D024141:Collagen Type IV / Q000378:metabolism; D003928:Diabetic Nephropathies / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D004789:Enzyme Activation / Q000187:drug effects; D005353:Fibronectins / Q000378:metabolism; D005947:Glucose / Q000502:physiology*; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000378:metabolism* / Q000473:pathology; D018374:LLC-PK1 Cells; D010446:Peptide Fragments / Q000494:pharmacology*; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6 / Q000378:metabolism; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013552:Swine; D053773:Transforming Growth Factor beta1 / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D024141:Collagen Type IV; D005353:Fibronectins; D010446:Peptide Fragments; D053773:Transforming Growth Factor beta1; D000803:Angiotensin I; D048051:p38 Mitogen-Activated Protein Kinases; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; C118790:angiotensin I (1-7); D005947:Glucose