Involvement of osteopontin upregulation on mesangial cells growth and collagen synthesis induced by intermittent high glucose

Abstract

Glucose fluctuations are strong predictor of diabetic vascular complications. We explored the effects of constant and intermittent high glucose on the proliferation and collagen synthesis of cultured rat mesangial cells. Furthermore, the possible involvement of osteopontin (OPN) was assessed. In rat mesangial cells cultured in 5, 25, or 5 mmol/L alternating with 25 mmol/L glucose in the absence or presence of neutralizing antibodies to OPN, beta3 integrin receptor and beta5 integrin receptor, the cell proliferation, collagen synthesis, and the expression of OPN and type IV collagen were assessed. In cultured mesangial cells, treatment with constant or intermittent high glucose significantly increased [(3)H]thymidine incorporation in a time-dependent manner. A modest increase was observed at 12 h, and further deteriorated afterwards, and reached the maximum incorporation at 48 h. Treatment with constant high glucose for 48 h resulted in significant increases in [(3)H]thymidine incorporation, cell number, [(3)H]proline incorporation, mRNA, and protein levels of type IV collagen and OPN compared with mesangial cells treated with the normal glucose, which were markedly enhanced in cells exposed to intermittent high glucose medium. In addition, neutralizing antibodies to either OPN or its receptor beta3 integrin but not neutralizing antibodies to beta5 integrin can effectively prevented proliferation and collagen synthesis of mesangial cells induced by constant or intermittent high glucose. Intermittent high glucose exacerbates mesangial cells growth and collagen synthesis by upregulation of OPN expression, indicating that glycemic variability have important pathological effects on the development of diabetic nephropathy, which is mediated by the stimulation of OPN expression and synthesis.