Hexosamines and TGF-β₁use similar signaling pathways to mediate matrix protein synthesis in mesangial cells

Abstract

Hyperglycemia-induced alterations in mesangial (MES) cell function and extracellular matrix (ECM) protein accumulation are seen in diabetic glomerulopathy. Transforming growth factor-beta1 (TGF-beta1) mediates high-glucose-induced matrix production in the kidney. Recent studies demonstrated that some of the effects of high glucose on cellular metabolism are mediated by the hexosamine biosynthesis pathway (HBP) in which fructose-6-phosphate is converted to glucosamine (GlcN) 6-phosphate. We previously showed that the high-glucose-mediated fibronectin and laminin synthesis in MES cells is mediated by the HBP and that GlcN is more potent than glucose in inducing TGF-beta1 promoter luciferase activity. In this study, we investigated the hypothesis that the effects of glucose on MES matrix production occur via hexosamine regulation of TGF-beta1. Culturing simian virus (SV)-40-transformed rat kidney MES cells in 25 mM glucose (HG) for 48 h increases cellular fibronectin and laminin levels about twofold on Western blots compared with low glucose (5 mM). GlcN (1.5 mM) or TGF-beta1 (2.5-5 ng/ml) for 24-48 h also increases ECM synthesis. However, the effects of HG or GlcN with TGF-beta1 are not additive. The presence of anti-TGF-beta1 antibodies (20 microg/ml) blocks both TGF-beta1- and GlcN-induced fibronectin synthesis. TGF-beta1 increased ECM levels via PKA (laminin and fibronectin) and PKC (fibronectin) pathways. Similarly, TGF-beta1 and hexosamines led to nonadditive increases in phosphorylation of the cAMP responsive element binding transcription factor. These results suggest that the effects of excess glucose on MES ECM synthesis occur via HBP-mediated regulation of TGF-beta1.

Molecular mechanisms of glutamine action

“…Hyperglycemia induces marked changes in mesangial cell function and ECM protein accumulation as seen in diabetic glomerulopathy (Isono et al, 2000;Singh et al, 2004). The hexosamine biosynthesis pathway is implicated in mediating several metabolic effects of high glucose and glutamine in cells.…”

Hexosamine induction of oxidative stress, hypertrophy and laminin expression in renal mesangial cells: effect of the anti‐oxidant α‐lipoic acid

“…29 We have previously shown that high glucose, glucosamine and TGF-b1 increase PKC and PKA activities in renal mesangial cells and that downstream transcription factor CREB participates in fibronectin and laminin expression. [30][31][32] Nonetheless, the molecular basis for high glucose and hexossamineinduced cell-cycle arrest, mesangial ECM regulation and apoptosis are not fully understood.…”

PPARγ agonists inhibit TGF-β-PKA signaling in glomerulosclerosis

“…For example, TGF-β induced apoptosis and Epithelial-to-Mesenchymal Transition (EMT) in AML-12 murine hepatocytes was associated with PKA activation [31] . Singh et al reported that laminin and fibronectin (Fn) expression induced by TGF-β1 could be down-regulated by PKA signaling blockage; however, the inhibition of PKC did not have significant effects on TGF-β1 [32] .…”

“…After TGF-β combines with its receptor, the receptor phosphorylates PKA directly, with the formation of complexes between Smads and the regulatory subunits of PKA. Inhibition of the PKA signal pathway could block the matrix protein synthesis stimulated by TGF-β [9] .…”