Glomerular mRNA expression of angiotensinase A after renal ablation.

The local concentration of angiotensin II (ANG II) in the renal microenvironment is not only controlled by the generation of this peptide but also by its enzymatic degradation. Angiotensinase A (ATA; aminopeptidase A, A.C.3.4.11.7) is a major exopeptidase of the glomerulus involvement in the metabolism of ANG II. We studied the glomerular mRNA levels of ATA in a remnant kidney model 1-12 weeks after 1 1/3 nephrectomy. Functional parameters (systolic blood pressure and albuminuria) demonstrated the progression of renal disease in this model. Glomerular ATA enzyme activity significantly increased 1-5 weeks after nephrectomy and returned to control levels 12 weeks after ablation. In general, changes in steady-state mRNA expression for ATA were rather small. mRNA expression for ATA in isolated glomeruli as evaluated by northern blots was slightly increased 1 and 3 weeks after 1 1/3 nephrectomy but was suppressed 5 and 12 weeks after renal ablation compared to age-matched 2-kidney controls. Treatment of animals with the ACE inhibitor ramipril for 5 and 12 weeks partly inhibited the decrease in ATA transcripts after 1 1/3 nephrectomy and stimulated expression in 2-kidney controls whereas the ACE inhibitor decreased glomerular ATA enzyme activity in nephrectomized rats at 5 weeks. Isolated glomeruli from normal controls superfused with 10(-6) M ANG II for 60 min demonstrated no change in ATA transcripts. Our results show that ATA steady-state mRNA levels are slightly elevated early (1-3 weeks) after renal ablation, and are subsequently suppressed (5-12 weeks). ATA enzyme activity is also increased early and returned (12 weeks) to levels measured in age-matched 2-kidney controls.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of prostaglandin E2 on mRNA expression and secretion of collagens I, III, and IV and fibronectin in cultured rat mesangial cells.

The possible role of prostaglandin E2 (PGE2) on the formation of collagens and fibronectin in cultured rat mesangial cells (MC) was studied. The effect of exogenous PGE2 was analyzed by the measurement of steady-state mRNA levels of the extracellular matrix components and by the secretion of these matrix components into cell culture supernatants. PGE2, in a dose-dependent manner, reduced mRNA levels of alpha 1(I) and alpha 1(III) procollagens but had little effect on alpha 1(IV) procollagen and fibronectin mRNA. In addition to its role on mRNA levels, PGE2 reduced the secretion of all studied collagen types into the cell culture supernatants. To evaluate a possible role of intracellular cAMP in the mediation of the PGE2 effects, MC were incubated with the cAMP analogue 8-bromo-cAMP (8brcAMP). In contrast to PGE2, 8brcAMP (1 mM) had no effect on mRNA expression of procollagen Types I and III over the studied time period (1 to 48 h). Furthermore, 8brcAMP stimulated collagen secretion into the cell supernatant after 48 h of incubation. These data demonstrate that PGE2 reduces mRNA levels of procollagen Types I and III in cultured MC, although the biosynthesis of all studied extracellular matrix components is inhibited. These alterations seem to be independent of intracellular cAMP, because the cAMP analogue 8brcAMP does not mimic the PGE2 effects on steady-state mRNA expression and collagen secretion of the studied extracellular matrix components.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased expression of monocyte chemoattractant protein-1 in anti-thymocyte antibody-induced glomerulonephritis.

The infiltration of monocytes-macrophages in the glomerulus is one of the hallmarks of glomerulonephritis and may play an important pathogenetic role. Monocyte chemoattractant protein-1 (MCP-1) and colony stimulating factor-1 (CSF-1) are monocyte-specific cytokines with chemoattractant and activating activities for monocytes. MCP-1 and CSF-1 can be generated by several cell types, including glomerular mesangial cells, and can be stimulated by cytokines and immune complexes. To study the expression of CSF-1 and MCP-1 in a model of proliferative glomerulonephritis we used Northern blot analysis and immuno-histochemistry. The glomerular lesion was induced in rats by the i.v. injection of a heterologous anti-thymocyte antiserum (ATS), directed against an antigen which is localized on glomerular mesangial cells. Northern blot analysis revealed comparable amounts of CSF-1 in glomeruli isolated from control untreated rats, and from rats after 30 minutes to three weeks of injection of ATS antibody. In control glomeruli no mRNA levels for MCP-1 were detectable, but increased markedly 30 minutes after the induction of the nephritis, were then reduced at 24 hours and increased again at 5 and 21 days after induction of the disease. The increase in mRNA levels for MCP-1 30 minutes or 24 hours after ATS injection was markedly attenuated if rats were complement depleted by cobra venom injection. These time points following antibody injection were associated with mesangial immune complex formation (30 min), mesangiolysis (24 hr) and proliferative glomerulonephritis (5 and 21 days). By immunohistology the presence of MCP-1 was demonstrated in glomeruli with a predominant mesangial distribution. The mesangial immunofluorescence for MCP-1 followed a pattern similar to that of the mRNA for MCP-1 after induction of the disease process, that is, it increased after 30 minutes, decreased after 24 hours and was increased again at three weeks. Within 30 minutes of the antibody injection an increased infiltration of monocytes-macrophages was observed in the glomeruli, which was maintained up to three weeks of induction of the glomerulonephritis. When the rats were decomplemented with cobra venom factor prior to the i.v. injection of ATS, the expression of MCP-1 in glomeruli remained low and the influx of monocytes/macrophages did not appear. We conclude that MCP-1 is increased early on in glomeruli of rats with immune-mediated mesangial proliferative glomerulonephritis. This increase is mediated by complement activation secondary to the in situ immune complex formation at the glomerular mesangium.(ABSTRACT TRUNCATED AT 400 WORDS)

TGF-beta stimulates rat mesangial cell proliferation in culture: role of PDGF beta-receptor expression.

Transforming growth factor (TGF)-beta is known to increase mesangial cell (MC) matrix; however, its possible role on MC proliferation is controversial. We therefore studied the influence of TGF-beta on MC proliferation in culture and evaluated its effect on the platelet-derived growth factor (PDGF) B-chain as well as the expression of the PDGF beta-receptor. TGF-beta (1 ng/ml) increases MC DNA synthesis by approximately threefold after 48 h of incubation. TGF-beta-induced MC proliferation was also confirmed by cell counts. A neutralizing anti-TGF-beta antibody completely blocked this growth promoting activity. The levels of PDGF beta-receptor steady-state mRNA were increased by TGF-beta at 48 h. This was associated with an increase in receptor density per cell as measured by receptor kinetic studies. PDGF B-chain mRNA was also increased by TGF-beta at 48 h. A neutralizing anti-PDGF B-antibody causes no reduction of TGF-beta-induced DNA synthesis; however, suramin completely inhibited the mitogenic effect of TGF-beta. We conclude that TGF-beta stimulates MC growth in long-term culture, a process in which upregulation of the PDGF beta-receptor and enhanced synthesis of PDGF B-chain might be involved.