Diabetic nephropathy is characterized by mesangial cells early proliferation, mesangial expansion, hypertrophy and most importantly extra cellular matrix (ECM) accumulation. Recent data have linked the serine/threonine kinase PKB (Akt) and the extracellular signal regulated kinases 1/2 (ERK1/2) to mesangial matrix modulation. The non-toxic immunomodulator AS101 (ammonium trichloro(dioxoethylene-o,o')tellurate) has been previously shown to favorably affect renal pathology in various animal models. In addition, AS101 was shown to inhibit Akt activity in leukemic cells. Here, we studied the role of AS101 in regulating high glucose-induced Collagen elaboration by mesangial cells and the molecular mechanism mediating this effect.
Treatment of primary rat mesangial cells with high glucose (HG) levels (30 mmol/l) in the presence of AS101 significantly reduced their elevated proliferative ability, as assessed by XTT assay and cell cycle analysis. Furthermore, this reduction was associated with decreased protein expression of Phosphorylated Akt at S473, corresponding to Akt activation, increased level of PTEN, followed by decreased pGSK-3β (inactivated form) and pFoxO3a (inactivated form) expression, known to induce ECM accumulation in renal cells. In addition, AS101 inhibited HG-induced cell growth which was correlated to mTOR and rpS6 de-phosphorylation. Surprisingly, HG treatment caused downregulation of ERK1/2 phosphorylation in a non-correlative fashion to AKT activation. This downregulation was also inhibited by the introduction of AS101 to HG treated cells.
Moreover, pharmacological inhibition of PI3K; mTORC1 and SMAD3 decreased HG-induced collagen accumulation while inhibition of GSK3-β and MEK1/2 didn’t change its elevated levels. This further established ERK1/2 role as an anti-fibrotic mediator rather than a pro-fibrotic one.
Finally, we suggest that pharmacological inhibition of PI3K/Akt/mTOR axis combining with the activation of ERK1/2 - MAPK pathway by non-toxic compounds like AS101, which is currently undergoing phase II clinical trials, has a clinical potential in alleviating diabetic nephropathy.