Restoration Of AMP-activated Protein Kinase Activation Research Articles

Reducing NADPH Synthesis Counteracts Diabetic Nephropathy through Restoration of AMPK Activity in Type 1 Diabetic Rats

Diabetic nephropathy (DN) is a major complication of diabetes mellitus and a primary cause of end-stage renal failure. Clinical studies indicate that metabolic surgery improves DN; however, the mechanism remains unclear. Here, we report that Roux-en-Y Gastric Bypass (RYGB) surgery significantly blocked and reversed DN without affecting the insulin signaling pathway. This protective role of RYGB surgery is almost blocked by either inhibition or knockout of 5'AMP-activated protein kinase (AMPK) in podocytes. Furthermore, mRNA microarray data reveal that RYGB surgery obviously reduced the gene expression involved in nicotinamide adenine dinucleotide phosphate (NAPDH) synthesis. The expression of a key NADPH synthase, hexose-6-phosphate dehydrogenase (H6PD), was inhibited by the low plasma corticosterone level after surgery. In addition, blocking NAPDH synthesis by knocking down H6PD mimicked the beneficial role of RYGB surgery through activation of AMPK in podocytes. Therefore, this study demonstrates that reducing NADPH production is critical for renal AMPK activation in response to RYGB surgery.

Impaired efferocytosis and neutrophil extracellular trap clearance by macrophages in ARDS.

Exaggerated release of neutrophil extracellular traps (NETs) along with decreased NET clearance and inability to remove apoptotic cells (efferocytosis) may contribute to sustained inflammation in acute respiratory distress syndrome (ARDS). Recent studies in experimental models of ARDS have revealed the crosstalk between AMP-activated protein kinase (AMPK) and high-mobility group box 1 (HMGB1), which may contribute to effectiveness of efferocytosis, thereby reducing inflammation and ARDS severity.We investigated neutrophil and NET clearance by macrophages from control and ARDS patients and examined how bronchoalveolar lavage (BAL) fluid from control and ARDS patients could affect NET formation and efferocytosis. Metformin (an AMPK activator) and neutralising antibody against HMGB1 were applied to improve efferocytosis and NET clearance.Neutrophils from ARDS patients showed significantly reduced apoptosis. Conversely, NET formation was significantly enhanced in ARDS patients. Exposure of neutrophils to ARDS BAL fluid promoted NET production, while control BAL fluid had no effect. Macrophage engulfment of NETs and apoptotic neutrophils was diminished in ARDS patients. Notably, activation of AMPK in macrophages or neutralisation of HMGB1 in BAL fluid improved efferocytosis and NET clearance.In conclusion, restoration of AMPK activity with metformin or specific neutralisation of HMGB1 in BAL fluid represent promising therapeutic strategies to decrease sustained lung inflammation during ARDS.

Sestrin2 Protects Dopaminergic Cells against Rotenone Toxicity through AMPK-Dependent Autophagy Activation.

Dysfunction of the autophagy-lysosomal pathway (ALP) and the ubiquitin-proteasome system (UPS) was thought to be an important pathogenic mechanism in synuclein pathology and Parkinson's disease (PD). In the present study, we investigated the role of sestrin2 in autophagic degradation of α-synuclein and preservation of cell viability in a rotenone-induced cellular model of PD. We speculated that AMP-activated protein kinase (AMPK) was involved in regulation of autophagy and protection of dopaminergic cells against rotenone toxicity by sestrin2. The results showed that both the mRNA and protein levels of sestrin2 were increased in a TP53-dependent manner in Mes 23.5 cells after treatment with rotenone. Genetic knockdown of sestrin2 compromised the autophagy induction in response to rotenone, while overexpression of sestrin2 increased the basal autophagy activity. Sestrin2 presumably enhanced autophagy in an AMPK-dependent fashion, as sestrin2 overexpression activated AMPK, and genetic knockdown of AMPK abrogated autophagy induction by rotenone. Restoration of AMPK activity by metformin after sestrin2 knockdown recovered the autophagy activity. Sestrin2 overexpression ameliorated α-synuclein accumulation, inhibited caspase 3 activation, and reduced the cytotoxicity of rotenone. These results suggest that sestrin2 upregulation attempts to maintain autophagy activity and suppress rotenone cytotoxicity through activation of AMPK, and that sestrin2 exerts a protective effect on dopaminergic cells.

The dipeptidyl peptidase-4 inhibitor sitagliptin protects against dyslipidemia-related kidney injury in Apolipoprotein E knockout mice.

The goal of this study was to investigate the possible protective effects of sitagliptin against dyslipidemia-related kidney injury in apolipoprotein E knockout (apoE−/−) mice. Eight-week-old male apoE−/− mice were randomized to receive either a high fat diet (HFD, apoE−/− group) or HFD mixed with sitagliptin (sita + apoE−/− group) for 16 weeks. A control group of age- and gender-matched C57BL/6J mice were fed a HFD. The apoE−/− group exhibited increases in body weight and serum lipid levels in addition to high-density lipoprotein, and increases in 24-h urinary 8-hydroxy-2-deoxyguanosine and albuminuria excretion. Decreased insulin sensitivity was also observed in the apoE−/− group. These mice additionally contained enlargements of the glomerular mesangial matrix area, lipid deposition area, and renal interstitium collagen area. The apoE−/− group also demonstrated down-regulation of phosphorylated AMP-activated protein kinase (AMPK), increases in renal mRNA expression of transforming growth factor-beta 1 (TGF-β1) and fibronectin (FN), and increased protein expression of Akt, TGF-β1, FN and p38/ERK mitogen-activated protein kinase (MAPK). Sitagliptin treatment successfully ameliorated all the deleterious effects of dyslipidemia tested. To our knowledge, this is the first time that sitagliptin has been shown to reverse the renal dysfunction and structural damage induced by dyslipidemia in apoE−/− mice. Our results suggest that the renoprotective mechanism of sitagliptin may be due to a reduction in Akt levels, a restoration of AMPK activity, and inhibition of TGF-β1, FN, and p38/ERK MAPK signaling pathways.

The protective role of AMP-activated protein kinase in alpha-synuclein neurotoxicity in vitro

In the present study, we investigated the role of the main intracellular energy sensor, AMP-activated protein kinase (AMPK), in the in vitro neurotoxicity of α-synuclein (ASYN), one of the key culprits in the pathogenesis of Parkinson's disease. The loss of viability in retinoic acid-differentiated SH-SY5Y human neuroblastoma cells inducibly overexpressing wild-type ASYN was associated with the reduced activation of AMPK and its activator LKB1, as well as AMPK target Raptor. ASYN-overexpressing rat primary neurons also displayed lower activity of LKB1/AMPK/Raptor pathway. Restoration of AMPK activity by metformin or AICAR reduced the in vitro neurotoxicity of ASYN overexpression, acting independently of the prosurvival kinase Akt or the induction of autophagic response. The conditioned medium from ASYN-overexpressing cells, containing secreted ASYN, as well as dopamine-modified or nitrated recombinant ASYN oligomers, all inhibited AMPK activation in differentiated SH-SY5Y cells and reduced their viability, but not in the presence of metformin or AICAR. The RNA interference-mediated knockdown of AMPK increased the sensitivity of SH-SY5Y cells to the harmful effects of secreted ASYN. AMPK-dependent protection from extracellular ASYN was also observed in rat neuron-like pheochromocytoma cell line PC12. These data demonstrate the protective role of AMPK against the toxicity of both intracellular and extracellular ASYN, suggesting that modulation of AMPK activity may be a promising therapeutic strategy in Parkinson's disease.