Activation of AMP-Activated Protein Kinase Inhibits Albumin-Induced Endoplasmic Reticulum Stress and Apoptosis through Inhibition of Reactive Oxygen Species

Abstract

Background: Endoplasmic reticulum (ER) stress induced by urinary albumin plays an important role in tubulointerstitial injury. We have shown that albumin-induced ER stress is regulated through reactive oxygen species (ROS)-c-Src kinase-mTOR signaling pathways. We postulated that peroxisome proliferator-activated receptor-γ (PPAR-γ) might also act as an upstream signaling molecule between c-Src kinase and mTOR. It has been suggested that AMP-activated protein kinase (AMPK) is involved in attenuation of ER stress. We examined whether and how activation of AMPK suppressed the albumin-induced ER stress and apoptosis in tubular epithelial cells. Method: HK-2 cells, a proximal tubular cell line, were used. Protein expressions were measured by Western blot analysis. Intracellular ROS and apoptosis were analyzed by flow cytometry. Results: Albumin-induced PPAR-γ expression and PPAR-γ inhibitor (GW9662) suppressed the albumin-induced ER stress. c-Src kinase inhibitor and GW9662 reduced the albumin-induced PPAR-γ and mTOR, respectively. Metformin (the best known clinical activator of AMPK) and another AMPK activator (AICAR) suppressed the albumin-induced ER stress via inhibition of ROS through induction of endogenous antioxidant thioredoxin. AMPK inhibitor blocked the effect of metformin and AICAR. Our in vivo animal study showed that metformin reduced the renal cortical expression of ER stress protein (GRP78) in protein-overload proteinuria rats. Metformin also reducedthe caspase 3-dependent apoptosis induced by albumin. Conclusion: PPAR-γ was involved in albumin-induced ER stress as an upstream signaling molecule between c-Src kinase and mTOR. AMPK activation might be beneficial in attenuating the tubulointerstitial injury induced by albumin.

Knockdown of RTN1A attenuates ER stress and kidney injury in albumin overload-induced nephropathy

“…Proteinuria plays an important role in the progression of tubulointerstitial injury (10,24). It has been recognized that excessive protein in urine is not merely a marker of the kidney injury but has intrinsic cell toxicity that contributes to tubular injury and fibrosis (28).…”

“…Albumin-induced ER stress in cultured tubular cells has also been previously reported (10,11). To determine whether RTN1A is a key mediator of albumininduced ER stress and apoptosis in renal tubular cells, RTN1A expression was knocked down in HK2 cells using a lentiviral vector expressing RTN1A shRNA [clone4 or a mixture of clone (1ϩ4)], as we have previously described (7).…”

“…Endoplasmic reticulum (ER) stress has been shown to contribute to the development and progression of CKD (9,10). Cells respond to ER stress by activating the unfolded protein response (UPR), and glucose-regulated protein of 78 kDa (GRP78) serves as a central regulator of three main UPR sensors, namely, activating transcription factor (ATF)6, inositol-requiring enzyme (IRE)-1␣, and protein kinase RNA-like ER kinase (PERK), that initiate the UPR signaling pathway under ER stress.…”

Colorectal and Prostate Cancer Risk in Diabetes: Metformin, an Actor behind the Scene

“…Metformin arrests hyperinsulinemia-induced free radicals (superoxide anion radical, hydroxyl radicals) and reactive oxygen species (ROS, hydrogen peroxide), which are integral to oxidative stress (imbalance between oxidants and antioxidants) and play an active mechanistic role in most cancers, and cell death is associated with generation of ROS 50, 58-61. AMPK in conjunction with the transcription factor FOXO3 lessens the fatty acid-induced generation of intracellular ROS by up-regulating the expression of the antioxidant thioredoxin 62-64, and the reduction in NADPH oxidase activity 65.…”

Altering Fate Determination of Human Bone Marrow-Derived Mesenchymal Stem Cells through Environmental and Transcriptional Cues

“…88 Metformin, an AMPK activator, has been shown to decrease reprogramming efficiency in multiple studies, 117 despite the fact that AMPK activation induces endogenous antioxidant expression and reduces intracellular reactive oxygen species. 248 because of their ability to rely heavily on glycolysis (provided they are not calorically restricted), but the discovery that a particular metabolic phenotype is required for supporting the energetic requirements of the reprogramming process has resulted in the understanding that being able to readily shift to a glycolytic metabolic phenotype is a defining property of stem cells. The implications of these findings to the study of stem cells in aging are enormous, because manipulating the metabolic phenotype of a cell as a strategy to restore its function is an approachable problem.…”