Glucose-induced fibronectin expression in endothelial cells is mediated by Protein Kinase C

Summary

One of the crucial pathophysiological changes in diabetic angiopathy might be the glucose-induced synthesis of components of the extracellular matrix-like fibronectin. This effect has been described for endothelial and mesangial cells. In order to gain further insight into the mechanisms how glucose-induced fibronectin expression is regulated, confluent monolayers of human umbilical vein endothelial cells (HUVEC) were incubated with varying concentrations of D-glucose (5 — 30mM) in a time-dependent manner. Using Westernblotting techniques with a monoclonal antibody, a 3 ± 0.2-fold increase of the 220 kDa-signal corresponding to human fibronectin was visible after an incubation time of 6 h indicating de-novo synthesis. Using incubation times of 6 or 10 days, glucose-mediated fibronectin overexpression was still visible, reaching a maximum at 15 mM D-glucose. The corresponding maximum values were 2.4 ± 0.3 (6 d) and 2.3 ± 0.2 (10 d). There was a concomitant glucose-dependent onset of expression of Protein Kinase C (PKC)-isoforms PKC-delta (2.5 ± 0.3-fold), PKC-epsilon (2 ± 0.2-fold) and PKC-zeta (1.8 ± 0.2-fold), which reached a maximum after 12 h and was still visible during long-term culture. Induction of fibronectin expression was also obtained using the PKC-activating phorbolester Phorbol-12-myristat-13-acetat (PMA) which mimicks glucose-induced PKC activation. Glucose-induced fibronectin expression was decreased by the PKC-inhibitor H-7 (1-[5-isoquinolinylsulfonyl]-2-methylpiperazine). These experiments suggest that: 1. Short-term induction of fibronectin expression mediated by glucose is probably PKC-triggered since concomitant induction of PKC-isoforms PKC-delta, PKC-epsilon and PKC-zeta was observed. 2. Long-term incubation with D-glucose leads to an ongoing concentration-dependent coexpression of fibronection and various PKC-isoforms. If glucose-induced, PKC-mediated de-novo synthesis of components of the connective tissue or the extracellular matrix may be important in the pathomechanism of diabetic angiopathy, has to be proven.

Key words

Endothelium - fibronectin - D-glucose - Protein Kinase C