Mesangial cell matrix deposition in high glucose as a model of glomerulosclerosis

Abstract

The filtration unit of the kidney is the glomerulus, a capillary network supported by mesangial cells and their extracellular matrix (ECM). Glomerular function is compromised in diabetic nephropathy (DN) by uncontrolled buildup of ECM components, especially collagen IV, which progressively occlude the capillaries. Increased levels of the ECM protein fibronectin (FN) are also present at early stages of DN, however its role is unknown. Mesangial cells cultured under high glucose conditions provide a model system for studying the effect of elevated glucose levels on deposition of FN and type IV collagen, the predominant ECM component of glomerular lesions. Quantitative imaging of mesangial cell cultures and analysis of detergent-insoluble matrix showed that high glucose induced mesangial cells to assemble significantly more FN matrix, independent of FN protein levels. Mn2+-induced activation of integrins stimulated FN assembly in normal glucose, suggesting that high glucose affects integrin activity. Collagen IV matrix was also increased and co-localized with FN fibrils. An inhibitor of FN matrix assembly also prevented collagen IV deposition, demonstrating the dependence of collagen IV on FN matrix. We conclude that high glucose induces FN assembly, which contributes to collagen IV accumulation. Enhanced assembly of FN might facilitate dysregulated ECM accumulation in DN.