Matrix protein glycation impairs agonist-induced intracellular Ca2+ signaling in endothelial cells

Studies have shown diabetes to be associated with alterations in composition of extracellular matrix and that such proteins modulate signal transduction. The present studies examined if non-enzymatic glycation of fibronectin or a mixed matrix preparation (EHS) alters endothelial cell Ca2+ signaling following agonist stimulation. Endothelial cells were cultured from bovine aorta and rat heart. To glycate proteins, fibronectin (10 mug/ml), or EHS (2.5 mg/ml) were incubated (37 degreesC, 30 days) with 0.5 M glucose-6-phosphate. Matrix proteins were coated onto cover slips after which cells (10(5) cells/ml) were plated and allowed to adhere for 16 h. For measurement of intracellular Ca2+, cells were loaded with fura 2 (2 PM) and fluorescence intensity monitored. Bovine cells on glycated EHS showed decreased ability for either ATP (10(-6) M) or bradykinin (10(-7) M) to increase Ca-i(2+). In contrast, glycated fibronectin did not impair agonist-induced increases in Ca-i(2+). In the absence of extracellular Ca2+, ATP elicited a transient increase in Ca-i(2+) consistent with intracellular release. Re-addition of Ca2+ resulted in a secondary rise in Ca-i(2+) indicative of store depletion-mediated Ca entry. Both phases of Ca2+ mobilization were reduced in cells on glycated mixed matrix; however, as the ratio of the two 2 components was similar in all cells, glycation appeared to selectively impair Ca2+ release from intracellular stores. Thapsigargin treatment demonstrated an impaired ability of cells on glycated EHS to increase cytoplasmic Ca2+ consistent with decreased endoplasmic reticulum Ca2+ stores. Further support for Ca2+ mobilization was provided by increased baseline IP3 levels in cells plated on glycated EHS. impaired ATP-induced Ca2+ release could be induced by treating native EHS with laminin antibody or exposing cells to H2O2 (20-200 muM). Glycated EHS impaired Ca2+ signaling was attenuated by treatment with aminoguanidine or the antioxidant alpha-lipoic acid. The results demonstrate that matrix glycation impairs agonist-induced Ca-i(2+) increases which may impact on regulatory functions of the endothelium and implicate possible involvement of oxidative stress. (C) 2002 Wiley-Liss, Inc.