Autocrine Activation of the IGF-I Signaling Pathway in Mesangial Cells Isolated From Diabetic NOD Mice
- Ivan Tack1,
- Sharon J. Elliot2,
- Mylene Potier2,
- Ana Rivera2,
- Gary E. Striker2 and
- Liliane J. Striker2
- 1Physiology Laboratory, University of Toulouse School of Medicine, Toulouse, France
- 2Vascular Biology Institute, University of Miami School of Medicine, Miami, Florida
Abstract
Mesangial cells isolated from NOD mice after the onset of diabetes have undergone a stable phenotypic change. This phenotype is characterized by increased expression of IGF-I and downregulation of collagen degradation, which is associated with decreased MMP-2 activity. Here, we investigated the IGF-I signaling pathway in mesangial cells isolated from NOD mice before (nondiabetic NOD mice [ND-NOD]) and after (diabetic NOD mice [D-NOD]) the onset of diabetes. We found that the IGF-I signaling pathway in D-NOD cells was activated by autocrine IGF-I. They had phosphorylation of the IGF-I receptor β-subunit, phosphorylation of insulin receptor substrate (IRS)-1, and association of the p85 subunit (phosphatidylinositol 3-kinase [PI3K]) with the IGF-I receptor and IRS-1 in D-NOD cells in the basal state. This was also associated with increased phosphorylation of ERK2 in D-NOD mesangial cells. Inhibiting autocrine IGF-I from binding to its receptor using an IGF-I–neutralizing antibody or inhibiting IGF-I signaling pathways using a specific PI3K inhibitor or a specific mitogen-activated protein kinase/extracellular response kinase kinase inhibitor decreased phosphorylated ERKs in D-NOD cells. Importantly, this was associated with increased MMP-2 activity. The addition of exogenous IGF-I to ND-NOD activated signal transduction. Therefore, we conclude that the IGF-I signaling pathway is intact in both D-NOD and ND-NOD cells. However, the phenotypic change in D-NOD cells is associated with constitutive activation of the IGF-I signaling pathways, which may participate in the development and progression of diabetic glomerulosclerosis.
Footnotes
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Address correspondence and reprint requests to Sharon J. Elliot, Vascular Biology Institute, Department of Medicine, University of Miami School of Medicine, P.O. Box 019132 (R104), Miami, FL 33101. E-mail: selliot{at}med.miami.edu.
I.T. and S.J.E. contributed equally to this work.
Received for publication 31 January 2001 and accepted in revised form 22 October 2001.
BSA, bovine serum albumin; D-NOD, diabetic NOD mice; ECM, extracellular matrix; ERK, extracellular response kinase; IRS, insulin receptor substrate; MAPK, mitogen-activated protein kinase; MEK, mitogen-activated protein kinase/extracellular response kinase kinase; ND-NOD, nondiabetic NOD mice; PI3K, phosphatidylinositol 3-kinase; PMSF, phenylmethylsulfonyl fluoride.
