High glucose levels enhance TGF-beta1-thrombospondin-1 pathway in cultured human mesangial cells via mechanisms dependent on glucose-induced PKC activation.
We have previously demonstrated that thrombospondin-1 (TSP-1) promotes activation of latent TGF-beta1 in cultured human mesangial cells (MCs) [Nephron 79 (1998) 38.]. This study was performed to clarify the relationship between protein kinase C (PKC) activity and activation of TGF-beta1 and TSP-1 production in cultured human MCs exposed to high glucose levels. MCs grown in 33 mmol/l glucose demonstrated a significant (P< .01) increase in activation of TGF-beta1 compared with those in 5 mmol/l glucose, which were evaluated by both an ELISA and a bioassay. High glucose-induced increase in active TGF-beta1 was completely inhibited by coincubation with 5 micromol/l GFX, a PKC inhibitor, and was mimicked by the addition of 0.1 micromol/l phorbol 12,13-dibutyrate (PDBu). On the other hand, increased TSP-1 production from MCs stimulated by 0.1 nmol/l recombinant TGF-beta1 and 0.1 micromol/l PDBu were significantly (P< .01) reduced by the addition of 10 nmol/l latency-associated peptide (LAP), a specific inhibitor of TGF-beta1 activity. The amount of TSP-1 secreted from MCs increased by a high ambient glucose. The glucose-induced increase in TSP-1 production was markedly attenuated by the treatment with GFX and LAP, while those agents did not affect TSP-1 production in low-glucose concentrations. Taken together, our results suggest that glucose-induced activation of TGF-beta1 is dependent on PKC activity, leading to a sequential increase in TSP-1 synthesis in cultured human MCs. Thus, we propose that high glucose conditions induce an increase in PKC-TGF-beta1 activity-TSP-1 pathway, and that glucose-induced increase in TSP-1 may synergistically facilitate TGF-beta1 activation in an autocrine manner in MCs.
Tada
H
H
Department of Internal Medicine, Shironishi Hospital, Shironishi Medical Foundation, 1-5-16 Shironishi, Matsumoto 390-8648, Nagano, Japan.
Kuboki
K
K
Nomura
K
K
Inokuchi
T
T
D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005920:Glomerular Mesangium / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D007672:Kidney Cortex / Q000502:physiology; D008301:Maleimides / Q000494:pharmacology; D009399:Nephrons / Q000502:physiology; D010446:Peptide Fragments / Q000494:pharmacology; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011498:Protein Precursors / Q000494:pharmacology; D011994:Recombinant Proteins / Q000494:pharmacology; D019700:Thrombospondin 1 / Q000096:biosynthesis / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000494:pharmacology / Q000502:physiology*; D053773:Transforming Growth Factor beta1
D004791:Enzyme Inhibitors; D007211:Indoles; D008301:Maleimides; D010446:Peptide Fragments; D011498:Protein Precursors; D011994:Recombinant Proteins; D019700:Thrombospondin 1; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D015240:Phorbol 12,13-Dibutyrate; D011493:Protein Kinase C; D005947:Glucose; C070515:bisindolylmaleimide I