Interleukin 1 activates jun N-terminal kinases JNK1 and JNK2 but not extracellular regulated MAP kinase (ERK) in human glomerular mesangial cells

Interleukin 1 (IL-1) potently activates human glomerular mesangial cells (HMC). In cytosolic extracts of IL-1-stimulated HMC or in anion exchange chromatography fractions we could not find any change in phosphorylation of myelin basic protein (MBP), a good substrate for extracellular regulated kinase (ERK). In contrast, IL-1 stimulated GST-jun kinase activity at least 10-fold. The jun kinase activity could be characterised as JNK1 and JNK2 at the protein and mRNA level. IL-1, TNF, UV light and osmotic stress, but not PMA, LPS, IL-3, IL-4, IL-6, IL-8, IL-10, IL-13, GM-CSF, PDGF, bFGF, TGF-beta and interferon-gamma were able to stimulate jun kinase activity in HMC, suggesting that jun kinase is selectively mediating signal transduction of the proinflammatory cytokines IL-1 and TNF as well as of cellular stress in HMC.

Autocrine growth regulation of human glomerular mesangial cells is primarily mediated by basic fibroblast growth factor

For various forms of human glomerulonephritis a close relationship between inflammatory injury and a local mesangial proliferative response has been described. Herein, we used primary cultures of human glomerular mesangial cells (HMCs) from five different donors to determine the autocrine growth-inducing capacity of their supernatants after stimulation with different cytokines and lipopolysaccharide (LPS) to determine whether this effect is due to basic fibroblast growth factor (bFGF). The basal growth-inducing capacity of supernatants collected from serum-free cultured HMC and concentrated 100-fold above a cut-off size of 10 kd was significantly increased by interleukin (IL)-1 beta, platelet-derived growth factor (PDGF), and LPS up to 15-fold, but not by IL-1 alpha, IL-6, or bFGF. An anti-human bFGF antibody blocked the majority of IL-1 or LPS-induced proliferative effect of supernatants; complete inhibition was achieved by a combination of anti-human bFGF- and anti-human platelet-derived growth factor antibodies. HMCs express different isoforms of bFGF (18, 21.5, and 24 kd) in membrane, cytosolic, and nuclear fractions. All isoforms of bFGF were found in the nuclear fraction of HMC, whether stimulated or not. Immunoblots for bFGF protein of HMC demonstrated that only a approximate to 16 kd bFGF protein was released into HMC supernatants after stimulation with IL-1 beta, platelet-derived growth factor-BB, and LPS. The 18 kd isoform of bFGF accumulated in the membranes but was not released after stimulation with IL-1 alpha, IL-6, and bFGF, suggesting that its release was a prerequisite for autocrine growth stimulation. By means of reverse transcription polymerase chain reaction controlled by Southern blots, bFGF-mRNA expression of HMC was enhanced by IL-1 alpha, IL-1 beta, and LPS. Finally, we were able to show that HMCs are expressing bFGF receptors. In summary, our data demonstrate for the first time that the autocrine proliferative response of HMC to major inflammatory factors may primarily be mediated by bFGF.

Activation of autoreactive T-lymphocytes by cultured syngeneic glomerular mesangial cells

The capacity of intrinsic, glomerular mesangial cells (MC) to cause an autoreactive response of syngeneic lymphocytes in vitro are presented. Initial experiments demonstrated the MHC class II dependent capacity of MC to present exogenous antigen to sensitized lymph node lymphocytes (LN) and to activate naive, allogeneic LN in the absence of a nominal antigen. However, the most striking finding of the present investigation was that mouse MC (C57BL/6 or DBA/2) augmented a significant activation of naive, syngeneic lymphocytes. The extent of the proliferative lymphocyte response was comparable to that observed after stimulation with allogeneic MC. Moreover, during syngeneic coculture substantial amounts of interferon bioactivity were generated. Equipotent concentrations of rm IFN-gamma were sufficient to induce class II MHC expression of mouse MC. In control experiments the macrophage cell line, IC-21 (C57BL/6), or freshly prepared DBA/2 mouse peritoneal macrophages did not elicit a syngeneic LN response. Using MC, which had not been pretreated, the MC-specific LN stimulation occurred after prolonged periods of coculture. The stimulation index (S.I.) was 9.77 after 144 hours compared with LN controls (S.I. = 1). However, a 48 hour pretreatment of MC with either rm IFN-gamma alone or in combination with rh TNF-alpha and/or the continuous presence of rm IL-1 alpha during coculture periods from 72 to 144 hours substantially enhanced the proliferative LN response. Analysis of non-adherent LN by flow cytometry (FACS) after 96 or 120 hours coculture with MC revealed an increased ratio of Thy1.2+ to B220+ cells with a predominant rise of L3T4+ T-helper cells compared to Lyt2+ cytotoxic T-cells. Furthermore, immune fluorescence microscopy showed that a fraction of Thy1.2+ lymphoblasts adhered to MC. FACS analysis of these adherent LN after detachment demonstrated that in comparison to cocultures with untreated MC, cocultures of LN with IFN-gamma/TNF-alpha pre-treated MC resulted in a 24.4% increase of Thy1.2+ cells, with 89% of these being L3T4+ T-helper lymphocytes. In conclusion, autoreactivity of preferentially T-helper cells to cocultured glomerular MC was shown, which may represent a useful model of T-lymphocyte dependent glomerulonephritis.