Osteopontin, also known as secreted phosphoprotein 1 (SPP-1), is one of the proinflammatory cytokines upregulated in kidneys of diabetic animals and patients with diabetic kidney disease. In the proximal tubules there is a proinflammatory environment associated with an increase in urinary albumin and albumin-bound fatty acids (FA) in proteinuric kidney diseases like diabetic nephropathy. In this study, we explored if FA overload stimulates SPP-1 expression and cleavage in renal tubular epithelial cells. Renal tubular SPP-1 gene and protein expression was examined in Zucker diabetic fatty (ZD) rats and in cultured renal tubular cells exposure to bovine serum albumin (BSA) or BSA overloaded with saturated fatty acid palmitic acid (PA). Real-time PCR analysis confirmed an upregulation of the renal cortical SPP-1 gene proportionate to albuminuria and nephropathy progression in ZD rats at the age of 7-20 weeks. Immunofluorescence staining of kidney sections revealed an increase in SPP-1 protein in albumin-overloaded proximal tubules of ZD rats. Western blot analysis detected an increase in both intact and matrix metalloproteinase (MMP) cleaved SPP-1 in the diabetic kidneys. When exposed to FA-free BSA, HK-2 cells exhibited an increase in protein levels of full-length and cleaved SPP-1. This increase in SPP-1 expression and cleavage was greatly enhanced in the presence of PA (250 muM). These results demonstrate a stimulatory effect of albumin and its conjugated fatty acids on SPP-1 expression and cleavage in renal tubule epithelial cells. Thus, besides lowering albuminuria/proteinuria, mitigating circulating FA levels may be an important factor in preventing tubular cell injury and tubulointerstitial inflammation in obesity and type 2 diabetes related kidney diseases.