Advanced-glycation-end-product-cholesterol-aggregated-protein accelerates the proliferation of mesangial cells mediated by transforming-growth-factor-beta 1 receptors and the ERK-MAPK pathway

Hyperglycemia and hyperlipidemia are considered critical to the development of diabetic nephropathy. The aim of this study is to clarify the effect of cholesterol on advanced-glycation-end-products and the mechanisms behind the advanced-glycation-end-product-cholesterol-aggregated bovine serum albumin (BSA)-induced proliferation of mesangial cells. Mesangial cells were treated with advanced-glycation-end-product-cholesterol-aggregated-BSA, and RNA and protein were isolated. Cholesterol caused a 1.5-fold increase in fluorescent intensity and 2-fold increase in advanced-glycation-end-products in vitro. Pyridoxamine, aminoguanidine, and N-acetyl-l-cycteine suppressed the production of advanced-glycation-end-product-cholesterol-aggregated-BSA. Advanced-glycation-end-product-cholesterol-BSA was analyzed by matrix-assisted-laser-desorption/ionization-time of flight mass spectrometry, and peaks were found to shift toward a higher mass. Advanced-glycation-end-product-cholesterol-aggregated-BSA induced overexpression of the mRNA of transforming growth factor-beta1, collagen type 1, collagen type 4 and receptor for advanced-glycation-end-products, and the proliferation of mesangial cells. The injection of advanced-glycation-end-product-cholesterol-aggregated-BSA caused glomerular changes and albuminuria in non-diabetic mice. A transforming-growth-factor-beta receptor1 kinase inhibitor or Mitogen-activated-Protein-Kinase/Extracellular-Signal-regulated-Kinase kinase (ERK) inhibitor (U-0126) suppressed the proliferation of mesangial cells induced by advanced-glycation-end-product-cholesterol-aggregated-BSA dose-dependently. U-0126 inhibited the phosphorylation of ERK1/2 in advanced-glycation-end-product-cholesterol-aggregated-BSA treated mesangial cells. These findings suggested that cholesterol promotes the formation of advanced-glycation-end-products-protein and that advanced-glycation-end-product-cholesterol-aggregated protein stimulates mesangial cells to proliferate via transforming-growth-factor-beta receptors and the ERK-MAPK pathway in diabetic glomeruli.