Monocyte-mesangial cell interactions in high-glucose co-cultures

Background. Monocytes bind to human mesangial cells (HMC) in a co-culture m odel of leukocyte/glomerular cell interactions. Since monocytic infiltratio n has been demonstrated in the early stages of diabetic glomerulopathy, we examined whether co-culture with myelomonocytes of the U937 cell line in me dia mimicking the diabetic microenvironment modulated phenotype, growth, an d extracellular matrix production patterns of HMC. Methods. HMC monolayers grown for 5 daps in 5.5 mmol/l (NG) or 30 mmol/l (H G) glucose media were examined 3, 24 and 48 h after addition of U937 cells by computer-assisted image analysis/fluorescence microscopy following fixat ion, staining for cell adhesion, and TUNEL/propidium iodide labelling for a poptosis. As matrix components may be relevant to both phenotype of culture d HMC and monocyte adhesion, reverse transcription-polymerase chain reactio n. zymography, and ELISA were used to detect urokinase-plasminogen activato r (uPa), collagen type IV (COL IV), transforming growth factor beta1 (TGF-b eta1), matrix metalloproteinases (MMP), and relative inhibitors (tissue inh ibitor of MMP (TIMP)) expression in co-cultures in NG/HG. Results. U937 adhesion at 1-3 h was increased in HG (from 54.9 +/- 6.6 to 8 7.1 +/- 5.8% U937/HMC). Control HMC proliferating in NG supplemented with 1 0% fetal bovine serum had an average cross-sectional area of 9993 +/- 505 m u (2) with 1.2 +/- 0.1 hillocks/high-power field, which increased to 13 651 +/- 1114 mu (2) with 0.5 +/- 0.2 hillocks/high-power field in HG (P < 0.05 ). TUNEL + HMC were nearly identical (4.9 <plus/minus> 1.7 vs 4.2 +/- 0.4% in HG, P = NS). Enhanced transcription and secretion of urokinase (uPA, +65 6%), COL IV (+137%), TGF-beta1 (+590%) were observed in co-cultures in HG. COL IV and TGF-beta1, but not uPA, were also increased in HMC alone, expose d to HG for 5 days, MMP-2/TIMP-2 ratio was decreased while MMP-1/TIMP-1 was increased in KG co-cultures. In both NG and HG, U937 adhesion reduced HMC number and hillocks at 24 h, with constant apoptosis. The effects of U937 w ere no longer detectable at 48 h, when apoptosis was 2.1 +/- 0.6 vs 4.0 +/- 0.4% in HG, and cell counts returned above basal, possibly due to a delaye d proliferative response. Conclusions. High glucose medium increases U937 cell adhesion to HMC. In tu rn, monocytes modulate number and spatial distribution of HMC, which are al so markedly affected by ambient glucose levels. These interactions may be r elevant to leukocyte infiltration, mesangial expansion, and glomerulosclero sis in diabetes.