Interleukin-6 stimulates α-MG uptake in renal proximal tubule cells:: involvement of STAT3, PI3K/Akt, MAPKs, and NF-κB

Recent studies have shown that interleukin 6 (IL-6) acts on the cellular proliferation-activating transduction signals during cellular regeneration. Therefore, this study examined the effect of IL-6 on the activation of Na+/glucose cotransporters (SGLTs) and its related signaling pathways in primary cultured renal proximal tubule cells (PTCs). IL-6 increased the level of alpha-methyl-D-[C-14] glucopyranoside (alpha-MG) uptake in time- and dosedependent manners. IL-6 also increased SGLT1 plus SGLT2 mRNA and protein expression level. The IL-6 receptors (IL-6R alpha and gp130) were expressed in PTCs. In addition, genistein and herbimycin A completely blocked the IL-6-induced increases in alpha-MG uptake and the protein expression level of SGLTs. On the other hand, IL-6 increased the level of 5-(and-6)-chloromethyl-2', 7'-dichlorodihydrofluoresceindiacetate- sensitive cellular reactive oxygen species (ROS), and IL-6-induced increases in alpha-MG uptake and the protein expression level of SGLTs were blocked by ascorbic acid or taurine (antioxidants). IL-6 also increased the phosphorylation of signal transducer and activator of transcription-3 (STAT3), phosphoinositide3 kinase (PI3K)/Akt, and mitogen-activated protein kinases (MAPKs) in a time-dependent manner. A pretreatment with STAT3 inhibitor LY 294002, an Akt inhibitor, or MAPK inhibitors significantly blocked the IL-6-induced increase in alpha-MG uptake. In addition, IL-6 increased the level of nuclear factor-kappa B (NF-kappa B) phosphorylation. A pretreatment with SN50 or BAY 11-7082 also blocked the IL-6-induced increase in alpha-MG uptake. In conclusion, IL- 6 increases the SGLT activity through ROS, and its action in renal PTCs is associated with the STAT3, PI3K/Akt, MAPKs, and NF-kappa B signaling pathways.