Soluble uric acid increases intracellular calcium through an angiotensin II-dependent mechanism in immortalized human mesangial cells.

Hyperuricemia is associated with increases in cardiovascular risk and renal disease. Mesangial cells regulate glomerular filtration rates through the release of hormones and vasoactive substances. This study evaluates the signaling pathway of uric acid (UA) in immortalized human mesangial cells (ihMCs). To evaluate cell proliferation, ihMCs were exposed to UA (6-10 mg/dL) for 24-144 h. In further experiments, ihMCs were treated with UA (6-10 mg/dL) for 12 and 24 h simultaneously with losartan (10(-7) mmol/L). Angiotensin II (AII) and endothelin-1 (ET-1) were assessed using the enzyme-linked immunosorbent assay (ELISA) technique. Pre-pro-ET mRNA was evaluated by the real-time PCR technique. It was observed that soluble UA (8 and 10 mg/dL) stimulated cellular proliferation. UA (10 mg/dL) for 12 h significantly increased AII protein synthesis and ET-1 expression and protein production was increased after 24 h. Furthermore, UA increased [Ca(2+)](i), and this effect was significantly blocked when ihMCs were preincubated with losartan. Our results suggested that UA triggers reactions including AII and ET-1 production in mesangial cells. In addition, UA can potentially affect glomerular function due to UA-induced proliferation and contraction of mesangial cells. The latter mechanism could be related to the long-term effects of UA on renal function and chronic kidney disease.

Escherichia coli lipopolysaccharide inhibits renin activity in human mesangial cells.

Hyperactivation of systemic renin-angiotensin system (RAS) during sepsis is well documented. However, the behavior of intrarenal RAS in the context of endotoxemia is yet to be defined. The present study evaluates the direct effect of Escherichia coli lipopolysaccharide (LPS) on immortalized human mesangial cell (HMC) RAS. Quiescent HMC were incubated with vehicle or LPS (1-100 microg/ml), and levels of angiotensin I and II (Ang I and II) and their metabolites were analyzed by high-performance liquid chromatography. In addition, angiotensin-converting enzyme (ACE) and renin activity were also investigated. Cell lysate and extracellular medium levels of Ang II were rapidly reduced (1 h) in a time- and concentration-dependent manner, reaching a significant -9 fold-change (P<0.001) after 3 h of LPS incubation. Similar results were obtained for Ang I levels (-3 fold-change, P<0.001). We ruled out Ang I and II degradation, as levels of their metabolic fragments were also significantly decreased by LPS. ACE activity was slightly increased following LPS incubation. On the other hand, renin activity was significantly inhibited, as Ang I concentration elevation following exogenous angiotensinogen administration was blunted by LPS (-60% vs vehicle, P<0.001). Renin and angiotensinogen protein levels were not affected by LPS according to Western blot analysis. Taken together, these data demonstrate for the first time that LPS significantly downregulates HMC RAS through inhibition of renin or renin-like activity. These findings are potentially related to the development of and/or recovery from acute renal failure in the context of sepsis.

Increased IL-6 in supernatant of rat mesangial cell cultures treated with erythrogenic toxin type B and its precursor isolated from nephritogenic streptococci.

BACKGROUND/AIMS: Previous reports have shown the presence of streptococcal erythrogenic toxin type B (ETB), IL-8, transforming growth factor-beta (TGF-beta) and glomerular proliferation in renal biopsies from patients with acute poststreptococcal glomerulonephritis (APSGN). In addition, increased levels of plasma IL-6 and tumor necrosis factor-alpha (TNFalpha) and urinary IL-6 have also been reported in this disease. To determine the effect of ETB in mesangial cell cytokine production and proliferation, the concentration of several cytokines (IL-6, IL-1beta, TNFalpha, IL-10, IL-4, RANTES), soluble TNF receptor I (STNFR-I), soluble TNF receptor II (STNFR-II) and proliferation were measured in rat mesangial cells cultures after treatment with ETB or its precursor (ETBP). METHODS: To analyze the levels of cytokines and production of soluble receptors as well as proliferation, rat mesangial cells were cultured with ETB or ETBP (50 microg/ml). After 24, 48 and 96 h of incubation, culture supernatants were assessed for cytokines and receptors by ELISA and for proliferation by incorporation of radioactive thymidine. RESULTS: A significant increase in IL-6 levels was found in mesangial cell cultures treated with either ETBP or ETB when compared with controls. Streptococcal proteins treated mesangial cells also showed elevated levels of proliferation at 96 h. Increased production of IL-6 was not correlated with proliferation. A polyclonal anti-ETB antibody abolished the IL-6 stimulatory effect of ETB on mesangial cells. ETB/ETBP failed to increase the levels of other cytokines and cytokine soluble receptors. CONCLUSION: Streptococcal ETB/ETBP is capable of inducing increased production of IL-6 and proliferation on mesangial cells. These findings could be relevant in a possible early interaction of streptococcal proteins with mesangial cells and during the course of APSGN.