Fibronectin-Induced Increase in Mesangial Cell Prostaglandin Release: Effect of Hyperglycemia and PKC Inhibition

Glomerular accumulation of extracellular matrix in diabetes is a potential regulator of mesangial cell-matrix interactions through transmembrane matrix receptors. We now provide evidence that PG production from rat glomerular mesangial cells is increased by Fn. An increase in PG (measured as PGE) was demonstrated in mesangial cell-enriched glomerular cores after 1-h exposure (149 ± 8% of timed control) and was sustained over a 24-h period (214 ±7%). Increased PG production followed exposure to a chymotryptic fragment (120,000 Mr) of Fn and occurred concomitant with an increase in participate PKC activity. A tetrapeptide (Arg-Gly-Asp-Ser) with the Arg-Gly-Asp sequence, contained in Fn and the chymotryptic fragment and recognized by specific membrane receptors (integrin matrix-binding proteins), also raised PG levels. As has been shown previously, exposure to high glucose concentration can increase mesangial cell PGE production (from 677 ± 61 pg mg protein⁻¹ · 2 h⁻¹ at 5.6 mM glucose to 1561 ± 132 pg · mg protein⁻¹ · 2 h⁻¹ at 50 mM glucose, P < 0.001). The response to the chymotryptic fragment of Fn also was enhanced by concurrent exposure to high glucose concentration (from 2560 ± 199 pg · mg protein⁻¹ · 2 h⁻¹ at 5.6 mM glucose to 4672 ± 358 pg · mg protein⁻¹ · 2 h at 50 mM glucose, P < 0.001). Coincubation with H-7, an inhibitor of PKC, abolished the PG response to glucose and the chymotryptic fragment. Involvement of PKC was supported further by abrogation of the effect of chymotryptic fragment in mesangial cells cultured for a prior prolonged period with phorbol ester. Additionally, heparin significantly reduced the Fn- and chymotryptic fragment-induced response. Thus, the autocrine environment of the mesangial cell is altered in the presence of Fn. We propose that this mechanism contributes to the raised PG levels seen in diabetes and the attendant hemodynamic consequences.