C-peptide increases the expression of vasopressin-activated calcium-mobilizing receptor gene through a G protein-dependent pathway.
OBJECTIVE
Although an increasing number of reports suggest that physiological concentrations of C-peptide protect against the development of diabetic nephropathy, possibly through the modulation of Na-K pump activity, the intracellular pathways controlled by C-peptide are still unrecognized. C-peptide and vasopressin share similar intracellular effects including the activation of calcium influx and endothelial nitric oxide synthase. Both hormones stimulate also the activity of Na-K pump activity. Whether the activity of C-peptide is mediated by the recently identified vasopressin-activated calcium-mobilizing receptor (VACM-1) has never been previously investigated.


METHODS
To clarify this issue, we evaluated the effect of C-peptide on VACM-1 RNA (measured by semiquantitative RT-PCR) and protein expression (measured by immunoblotting) in human skin fibroblasts (where a specific binding of C-peptide was demonstrated) and in human mesangial cells, the cellular target of diabetic nephropathy.


RESULTS
C-peptide-induced activation of VACM-1 was demonstrated in fibroblasts from six healthy individuals (0.51+/-0.1 vs 1.48+/-0.4, arbitrary units+/-s.e., P = 0.025). This finding was paralleled by an increased VACM-1 protein expression (5.64+/-1.0 vs 8.47+/-1.2, arbitrary units+/-s.e., P= 0.043). Similar results were confirmed in three independent cultures of human mesangial cells. VACM-1 activation in fibroblasts was insensitive to phosphatidylinositol-3-kinase inhibitor LY294002, but was inhibited by pertussis toxin, suggesting that activation of VACM-1 could be mediated by a G protein-coupled receptor.


CONCLUSIONS
This study demonstrates for the first time that C-peptide activates VACM-1, possibly through a G protein-coupled receptor. Further studies are needed to clarify whether VACM-1 is involved in the protective effect of C-peptide against the development of diabetic nephropathy.
Maestroni
Anna
A
Renal Pathophysiology Laboratory, Section Nutrition-Metabolism, Department of Medicine, San Raffaele Scientific Institute, Milan, Italy.
Ruggieri
Dora
D
Dell'Antonio
Giacomo
G
Luzi
Livio
L
Zerbini
Gianpaolo
G
D065092:Antidiuretic Hormone Receptor Antagonists; D015153:Blotting, Western; D002096:C-Peptide / Q000097:blood / Q000494:pharmacology*; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D044842:Cullin Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D003928:Diabetic Nephropathies / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology; D005920:Glomerular Mesangium / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D006801:Humans; D009025:Morpholines / Q000494:pharmacology; D037342:Pertussis Toxin / Q000494:pharmacology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D012313:RNA / Q000737:chemistry / Q000235:genetics; D017483:Receptors, Vasopressin / Q000096:biosynthesis* / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012867:Skin / Q000166:cytology
D065092:Antidiuretic Hormone Receptor Antagonists; D002096:C-Peptide; C496871:CUL5 protein, human; D002867:Chromones; D044842:Cullin Proteins; D004791:Enzyme Inhibitors; D009025:Morpholines; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017483:Receptors, Vasopressin; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D012313:RNA; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins