Osteopontin: correlation with interstitial fibrosis in human diabetic kidney and PI3-kinase-mediated enhancement of expression by glucose in human proximal tubular epithelial cells.
OBJECTIVE
To examine the expression and localization of osteopontin (OPN), a secreted phosphoprotein implicated in the development of tubulointerstitial inflammation in various models of renal disease, in human diabetic kidneys, and to study the regulation of OPN expression in primary cultures of human renal proximal tubular epithelial cells (RPTEC).


RESULTS
Differential gene expression profiling through subtractive hybridization demonstrated increased renal OPN mRNA expression in a patient with diabetic nephropathy. Immunohistochemical staining of normal and diabetic human kidney samples confirmed that OPN was localized to cortical tubular, interstitial and juxtaglomerular compartments. Quantification of OPN immunostaining revealed a marked increase in the percentage of OPN-positive tubular profiles in diabetic kidneys (47 +/- 9% versus 5 +/- 3%, diabetic versus minimal change disease) that correlated strongly with the degree of cortical scarring (r2 = 0.91). Results of Northern hybridization, flow cytometry and Western blotting indicated that glucose up-regulates OPN mRNA and protein expression in primary cultures of human RPTECs. This effect was independent of the osmotic effects of glucose and independent of insulin. Finally, glucose-stimulated OPN expression was inhibited by LY294002, an inhibitor of phosphatidylinositol 3-kinase activity, in a dose-dependent manner.


CONCLUSIONS
OPN is expressed in human diabetic kidneys and regulation of OPN expression is via a glucose-mediated, phosphatidylinositol 3-kinase-dependent pathway.
Junaid
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A
Department of Internal Medicine, University of Manitoba and St Boniface Hospital Research Centre, Winnipeg, Canada. junaid@cc.umanitoba.ca
Amara
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FM
D000368:Aged; D000595:Amino Acid Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D002478:Cells, Cultured; D003928:Diabetic Nephropathies / Q000150:complications* / Q000378:metabolism / Q000473:pathology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D005355:Fibrosis / Q000209:etiology / Q000378:metabolism* / Q000473:pathology; D005434:Flow Cytometry; D020869:Gene Expression Profiling; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008969:Molecular Sequence Data; D009395:Nephritis, Interstitial / Q000378:metabolism / Q000473:pathology; D053495:Osteopontin; D019869:Phosphatidylinositol 3-Kinases / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D017386:Sequence Homology, Amino Acid; D012795:Sialoglycoproteins / Q000187:drug effects / Q000378:metabolism*
D004791:Enzyme Inhibitors; D012333:RNA, Messenger; C506895:SPP1 protein, human; D012795:Sialoglycoproteins; D053495:Osteopontin; D019869:Phosphatidylinositol 3-Kinases; D005947:Glucose