Lipoprotein(a) stimulates growth of human mesangial cells and induces activation of phospholipase C via pertussis toxin-sensitive G proteins

Background. Renal disease is commonly associated with hyperlipidemia and correlates with glomerular accumulation of atherogenic lipoproteins, for example, lipoprotein(a) [Lp(a)], and mesangial hypercellularity. Specific binding of Lp(a) to mesangial cells and induction of c-myc and c-Sos expression has been demonstrated. Therefore, in this study, we investigated a possible growth stimulatory effect and mode of action of Lp(a) in human mesangial cells. Methods. Lp(a) was purified from the regenerate fluid of a dextran sulfate column-based low-density lipoprotein apheresis system. Human mesangial cells were isolated by a sequential sieving technique from patients undergoing tumor nephrectomy. DNA synthesis was measured by [H-3]-thymidine incorporation. The intracellular calcium concentration ([Ca2+](i)) was determined by Fura 2-fluorescence, and inositol 1,4,5-trisphosphate (1,4,5-IP3) concentration was measured by a radioreceptor assay. Results. The data show that Lp(a) bound to the cells with a K-d of 17.0 mu g/ml and increased DNA synthesis and cell proliferation. Lp(a) caused a rapid increase in 1,4,5-IP3 and [Ca2+](i) via a pertussis toxin-sensitive mechanism. The phospholipase C (PLC) inhibitor U73122 abolished Lp(a)-induced cell proliferation. In contrast, vasopressin-induced increase in 1,4,5-IP3 and [Ca2+](i) was pertussis toxin insensitive. Conclusion. This study revealed that Lp(a) stimulates growth of human mesangial cells. Lp(a)-induced signaling involves binding to a receptor and stimulation of PLC via G(i) proteins. Stimulation of PLC appears to be essential for the growth stimulatory effect of Lp(a). Whether these effects of Lp(a) contribute to the pathophysiology of renal disease needs to be determined.