Low density lipoprotein enhances the cellular action of arginine vasopressin in rat glomerular mesangial cells in culture

MAPK signaling and the kidney

Following an overview of the biochemistry of mitogen-activated protein kinase (MAPK) pathways, the relevance of these signaling events to specific models of renal cell function and pathophysiology, both in vitro and in vivo, will be emphasized. In in vitro model systems, events activating the principal MAPK families [extracellular signal-regulated and c-Jun NH(2)-terminal kinase and p38] have been best characterized in mesangial and tubular epithelial cell culture systems and include peptide mitogens, cytokines, lipid mediators, and physical stressors. Several in vivo models of proliferative or toxic renal injury are also associated with aberrant MAPK regulation. It is anticipated that elucidation of downstream effector signaling mechanisms and a clearer understanding of the immediate and remote upstream activating pathways, when applied to these highly clinically relevant model systems, will ultimately provide much greater insight into the basis for specificity now seemingly absent from these signaling events.

Involvement of protein kinase C in the supersensitivity to 5-HT caused by oxidized low-density lipoproteins

The effect of native (n-LDL) and oxidized (ox-LDL) low-density lipoproteins and lysophosphatidylcholines (LPCs) on: (1) vasodilator responses induced by acetylcholine (ACh) in intact rabbit aorta segments, and (2) vasoconstrictor responses to serotonin (5-HT), and potassium (K+) in endothelium denuded segments was investigated. In intact vessels, 100 microg/ml ox-LDL did not modify ACh-induced relaxation, while it was diminished by 300 microg/ml ox-LDL and abolished by 50 microM LPCs. In contrast, this relaxation was unaltered by n-LDL (100 or 300 microg/ml). In deendothelialized arteries, 100 and 300 microg/ml n-LDL as well as 50 microM LPCs did not modify the contractions induced by 5-HT or K+, while 100 or 300 microg/ml ox-LDL increased the 5-HT-induced contraction, without altering those induced by 75 mM K+. Incubation with 100 or 300 microg/ml ox-LDL increased the contractile response to the protein kinase C (PKC) activator phorbol 12,13-dibutyrate (PDB) (0.1-1 microM) in a concentration-dependent manner, which was blocked by staurosporine (0.1 microM), and unaltered by (50 microM) calphostin C or (50 microM) chelerythrine, the three are PKC inhibitors. Preincubation with 0.05 microM PDB increased the contraction elicited by 5-HT, while staurosporine decreased the PDB-induced contraction, and prevented the 5-HT response increase caused by 300 microg/ml ox-LDL. These results suggest that only ox-LDL reduces endothelium-dependent relaxation and elicits PKC activation, and that this activation mediates, at least in part, the vasoconstrictor response to 5-HT.

Tranilast inhibits the growth of rat mesangial cells

We investigated the effects of tranilast on the growth of cultured rat mesangial cells. The number of mesangial cells increased fivefold during a 5-day incubation in RPMI 1640 with 20% fetal bovine serum. The number of cells was significantly lower in the presence of tranilast than in its abscence. Tranilast (0 approximately 500 microM) inhibited platelet-derived growth factor (PDGF)-induced DNA synthesis of rat mesangial cells cultured in RPMI 1640 medium containing 0.5% fetal bovine serum in a dose-dependent manner. The inhibition of DNA synthesis by tranilast was not affected by the presence of indomethacin (1 microg/ml) or N(G)-monomethyl-L-arginine (0.5 mM). Tranilast did not stimulate nitrite oxide synthesis in PDGF-stimulated cells. Mitogen-activated protein kinase activity in mesangial cells was significantly increased by exposure to PDGF, while the effect was significantly suppressed in the presence of tranilast. The present study revealed that tranilast inhibits the growth of rat mesangial cells, independently of nitric oxide or prostacycline synthesis.

Cellular signaling and proliferative action of AVP in mesangium of SHR: effect of low density lipoprotein

The present study was undertaken to determine whether low density lipoprotein (LDL) modulates the cellular action of arginine vasopressin (AVP) in cultured glomerular mesangial cells of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). The AVP-induced cellular signal transduction, including inositol 1,4,5-trisphosphate (IP3) production, fura-2 intracellular calcium measurements and cellular alkalinization, was significantly greater in cells of SHR than those of WKY. This is based on an increase in AVP V1 receptor number in cells of the SHR. Also, the AVP activation of mitogen-activated protein (MAP) kinase and [3H]thymidine incorporation was significantly exaggerated in cells of SHR compared with those of WKY. LDL at a concentration of 10 micrograms/ml augmented the cellular signaling and proliferative action of AVP in cells of WKY, but not in those of SHR. Since [3H]AVP receptor binding was not affected by the LDL pretreatment, LDL modulates the signal transduction between a location distal to the AVP receptors and proximal from the production of IP3 and diacylglycerol. These results indicate that an increase in AVP receptor capacity has a profound effect on the AVP-induced cellular signaling and proliferation, and that LDL has a slight alteration on the action of AVP in glomerular mesangial cells of SHR.