AMP-activated protein kinase inhibits IL-6-stimulated inflammatory response in human liver cells by suppressing phosphorylation of signal transducer and activator of transcription 3 (STAT3)

Abstract

Aim/hypothesis The aim of the study was to examine the possible role of AMP-activated protein kinase (AMPK) in the regulation of the inflammatory response induced by cytokine action in human liver cells. Methods IL-6-stimulated expression of the genes for acutephase response markers serum amyloid A (SAA1, SAA2) and haptoglobin (HP) in the human hepatocarcinoma cell line HepG2 were quantified after modulation of AMPK activity by pharmacological agonists (5-amino-4-imidazolecarboxamideriboside [AICAR], metformin) or by using small interfering (si) RNA transfection. The intracellular signalling pathway mediating the effect of AMPK on IL-6-stimulated acute-phase marker expression was characterised by assessing the phosphorylation levels of the candidate protein signal transducer and activator of transcription 3 (STAT3) in response to AMPK agonists. Results AICAR and metformin markedly blunt the IL-6-stimulated expression of SAA cluster genes as well as of haptoglobin in a dose-dependent manner. Moreover, the repression of AMPK activity by siRNA significantly reversed the inhibition of SAA expression by both AICAR and metformin, indicating that the effect of the agonists is dependent on AMPK. For the first time we show that AMPK appears to regulate IL-6 signalling by directly inhibiting the activation of the main downstream target of IL-6, STAT3. Conclusions/interpretation We provide evidence for a key function of AMPK in suppression of the acute-phase response caused by the action of IL-6 in liver, suggesting that AMPK may act as an intracellular link between chronic low-grade inflammation and metabolic regulation in peripheral metabolic tissues.

Phosphorylation of Janus kinase 1 (JAK1) by AMP-activated protein kinase (AMPK) links energy sensing to anti-inflammatory signaling

“…For example, others have shown that chronic AMPK activation in hepatocytes with metformin for 12 hr is able to increase levels of the orphan nuclear receptor small heterodimer partner (SHP), which reduces STAT3 phosphorylation on Tyr705 and co-localizes with nuclear STAT3 to reduce its binding to target gene promoters (53) (54). Similarly, others have demonstrated that chronic treatment of hepatocytes with AICAR suppresses IL-6 signaling, and was thought to involve an AMPK-mediated inhibition of IL-6-stimulated Tyr phosphorylation and activation of JAK1 and JAK2, and that depletion of AMPKα1 and α2 subunits could block the inhibitory effects of AMPK activators on cytokine-stimulated signaling without significantly altering basal activation (55) (56). However the underlying mechanisms were not investigated.…”

Metformin prevents ischemia reperfusion-induced oxidative stress in the fatty liver by attenuation of reactive oxygen species formation

“…The direct anti-inflammatory action of metformin has been reported in several animal experimental studies, both in the liver (69,54,47) and in circulating polymorphonuclear cells (9). In contrast to these experimental findings, metformin efficiency in human NASH treatment is the subject of open debate (58,60).…”

Serine/threonine protein kinase 25 (STK25): a novel negative regulator of lipid and glucose metabolism in rodent and human skeletal muscle

“…Western blot analysis Western blot analysis was performed as previously described [10]. See the ESM Methods for further details on procedures and antibodies used.…”