AMPK as a Therapeutic Target for Treating Metabolic Diseases

CD36 palmitoylation disrupts free fatty acid metabolism and promotes tissue inflammation in non-alcoholic steatohepatitis

BACKGROUND AND AIMS

Fatty acid translocase CD36 (CD36) is a membrane protein with multiple immuno-metabolic functions. Palmitoylation has been suggested to regulate the distribution and functions of CD36, but little is known about its significance in non-alcoholic steatohepatitis (NASH).

METHODS

Human liver tissue samples were obtained from patients undergoing liver biopsy for diagnostic purposes. CD36 knockout mice were injected with lentiviral vectors expressing wild-type CD36 or CD36 with mutated palmitoylation sites. Liver histology, immunofluorescence, mRNA expression profile, subcellular distributions and functions of CD36 protein were assessed.

RESULTS

The localization of CD36 on the plasma membrane of hepatocytes was markedly increased in patients with NASH compared to patients with normal liver and those with simple steatosis. Increased CD36 palmitoylation and increased localization of CD36 on the plasma membrane of hepatocytes were also observed in livers of mice with NASH. Furthermore, inhibition of CD36 palmitoylation protected mice from developing NASH. The absence of palmitoylation decreased CD36 protein hydrophobicity reducing its localization on the plasma membrane as well as in lipid raft of hepatocytes. Consequently, a lack of palmitoylation decreased fatty acid uptake and CD36/Fyn/Lyn complex in HepG2 cells. Inhibition of CD36 palmitoylation not only ameliorated intracellular lipid accumulation via activation of the AMPK pathway, but also inhibited the inflammatory response through the inhibition of the JNK signaling pathway.

CONCLUSIONS

Our findings demonstrate the key role of palmitoylation in regulating CD36 distributions and its functions in NASH. Inhibition of CD36 palmitoylation may represent an effective therapeutic strategy in patients with NASH.

LAY SUMMARY

Fatty acid translocase CD36 (CD36) is a multifunctional membrane protein which contributes to the development of liver steatosis. In the present study, we demonstrated that the localization of CD36 on the plasma membrane of hepatocytes is increased in patients with non-alcoholic steatohepatitis. Blocking the palmitoylation of CD36 reduces CD36 distribution in hepatocyte plasma membranes and protects mice from non-alcoholic steatohepatitis. The inhibition of CD36 palmitoylation not only improved fatty acid metabolic disorders but also reduced the inflammatory response in vitro and in vivo. The present study suggests that CD36 palmitoylation is important for non-alcoholic steatohepatitis development and inhibition of CD36 palmitoylation could be used to cure non-alcoholic steatohepatitis.

Metformin as an Anticancer Agent

Metformin has been a frontline therapy for type 2 diabetes (T2D) for many years. Its effectiveness in T2D treatment is mostly attributed to its suppression of hepatic gluconeogenesis; however, the mechanistic aspects of metformin action remain elusive. In addition to its glucose-lowering effect, metformin possesses other pleiotropic health-promoting effects that include reduced cancer risk and tumorigenesis. Metformin inhibits the electron transport chain (ETC) and ATP synthesis; however, recent data reveal that metformin regulates AMP-activated protein kinase (AMPK) and the mechanistic target of rapamycin complex 1 (mTORC1) by multiple, mutually nonexclusive mechanisms that do not necessarily depend on the inhibition of ETC and the cellular ATP level. In this review, we discuss recent advances in elucidating the molecular mechanisms that are relevant for metformin use in cancer treatment.

Is TAK1 a Direct Upstream Kinase of AMPK?

Alongside Liver kinase B1 (LKB1) and Ca²⁺/Calmodulin-dependent protein kinase kinase 2 (CaMKK2), Transforming growth factor-β (TGF-β)-activated kinase 1 (TAK1) has been suggested as a direct upstream kinase of AMP-activated protein kinase (AMPK). Several subsequent studies have reported on the TAK1-AMPK relationship, but the interpretation of the respective data has led to conflicting views. Therefore, to date the acceptance of TAK1 as a genuine AMPK kinase is lagging behind. This review provides with argumentation, whether or not TAK1 functions as a direct upstream kinase of AMPK. Several specific open questions that may have precluded the consensus are discussed based on available data. In brief, TAK1 can function as direct AMPK upstream kinase in specific contexts and in response to a subset of TAK1 activating stimuli. Further research is needed to define the intricate signals that are conditional for TAK1 to phosphorylate and activate AMPKα at T172.

Multivariate analysis of genomics data to identify potential pleiotropic genes for type 2 diabetes, obesity and dyslipidemia using Meta-CCA and gene-based approach

Previous studies have demonstrated the genetic correlations between type 2 diabetes, obesity and dyslipidemia, and indicated that many genes have pleiotropic effects on them. However, these pleiotropic genes have not been well-defined. It is essential to identify pleiotropic genes using systematic approaches because systematically analyzing correlated traits is an effective way to enhance their statistical power. To identify potential pleiotropic genes for these three disorders, we performed a systematic analysis by incorporating GWAS (genome-wide associated study) datasets of six correlated traits related to type 2 diabetes, obesity and dyslipidemia using Meta-CCA (meta-analysis using canonical correlation analysis). Meta-CCA is an emerging method to systematically identify potential pleiotropic genes using GWAS summary statistics of multiple correlated traits. 2,720 genes were identified as significant genes after multiple testing (Bonferroni corrected p value < 0.05). Further, to refine the identified genes, we tested their relationship to the six correlated traits using VEGAS-2 (versatile gene-based association study-2). Only the genes significantly associated (Bonferroni corrected p value < 0.05) with more than one trait were kept. Finally, 25 genes (including two confirmed pleiotropic genes and eleven novel pleiotropic genes) were identified as potential pleiotropic genes. They were enriched in 5 pathways including the statin pathway and the PPAR (peroxisome proliferator-activated receptor) Alpha pathway. In summary, our study identified potential pleiotropic genes and pathways of type 2 diabetes, obesity and dyslipidemia, which may shed light on the common biological etiology and pathogenesis of these three disorders and provide promising insights for new therapies.

Peritumoral monocytes induce cancer cell autophagy to facilitate the progression of human hepatocellular carcinoma

Macroautophagy/autophagy is an important catabolic process mediating cellular homeostasis and plays critical roles in cancer development. Whereas autophagy has been widely studied in various pathological models, little is known about the distribution, clinical significance and regulatory mechanism of this process in human hepatocellular carcinoma (HCC). In the present study, we found that tumor tissues exhibited significantly increased levels of autophagy compared with non-tumor tissues, and cancer cells with higher levels of autophagy were predominantly enriched in the invading edge regions of human HCC. Increased MAP1LC3B/LC3B expression in the invading edge regions was significantly correlated with a higher density of closely located monocytes, and TNF and IL1B derived from tumor-activated monocytes synergistically induced cancer cell autophagy in the invading edge regions of HCC. Monocyte-elicited autophagy induced the epithelial-mesenchymal transition (EMT) of cancer cells and promoted tumor metastasis by activating the NFKB-SNAI1 signaling pathway. Moreover, the increase of LC3B⁺ cancer cells in the invading edge areas was associated with high mortality and reduced survival of patients with HCC. These findings indicated that cancer cell autophagy is regulated by a collaborative interaction between tumor and immune cell components in distinct HCC microenvironments, thus allowing the inflammatory monocytes to be rerouted in a tumor-promoting direction.

Interplay of Autophagy Inducer Rapamycin and Proteasome Inhibitor MG132 in Reduction of Foam Cell Formation and Inflammatory Cytokine Expression

MG132 is a pivotal inhibitor of the ubiquitin-proteasome system (UPS), and rapamycin (RAPA) is an important inducer of autophagy. MG132 and RAPA have been shown to be effective agents that can cure multiple autoimmune diseases by reducing inflammation. Although individual MG132 and RAPA showed protective effects for atherosclerosis (AS), the combined effect of these two drugs and its molecular mechanism are still unclear. In this article we investigate the regulation of oxidative modification of low-density lipoprotein (ox-LDL) stress and foam cell formation in the presence of both proteasome inhibitor MG132 and the autophagy inducer RAPA to uncover the molecular mechanism underlying this process. We established the foam cells model by ox-LDL and an animal model. Then, we tested six experimental groups of MG132, RAPA, and 3MA drugs. As a result, RAPA-induced autophagy reduces accumulation of polyubiquitinated proteins and apoptosis of foam cells. The combination of MG132 with RAPA not only suppressed expression of the inflammatory cytokines and formation of macrophage foam cells, but also significantly affected the NF-κB signaling pathway and the polarization of RAW 264.7 cells. These data suggest that the combination of proteasome inhibitor and autophagy inducer ameliorates the inflammatory response and reduces the formation of macrophage foam cells during development of AS. Our research provides a new way to suppress vascular inflammation and stabilize plaques of late atherosclerosis.

A Method for Rapid Screening of Anilide-Containing AMPK Modulators Based on Computational Docking and Biological Validation

Adenosine 5'-monophsphate-activated protein kinase (AMPK) is a crucial energy sensor for maintaining cellular homeostasis. Targeting AMPK may provide an alternative approach in treatment of various diseases like cancer, diabetes, and neurodegenerations. Accordingly, novel AMPK activators are frequently identified from natural products in recent years. However, most of such AMPK activators are interacting with AMPK in an indirect manner, which may cause off-target effects. Therefore, the search of novel direct AMPK modulators is inevitable and effective screening methods are needed. In this report, a rapid and straightforward method combining the use of in silico and in vitro techniques was established for selecting and categorizing huge amount of compounds from chemical library for targeting AMPK modulators. A new class of direct AMPK modulator have been discovered which are anilides or anilide-like compounds. In total 1,360,000 compounds were virtually screened and 17 compounds were selected after biological assays. Lipinski's rule of five assessment suggested that, 13 out of the 17 compounds are demonstrating optimal bioavailability. Proton acceptors constituting the structure of these compounds and hydrogen bonds with AMPK in the binding site appeared to be the important factors determining the efficacy of these compounds.

Antiobesity Effects of Ginsenoside Rg1 on 3T3-L1 Preadipocytes and High Fat Diet-Induced Obese Mice Mediated by AMPK

Ginsenosides Rg1 is one of the major pharmacologically active saponins in ginseng, which as an antioxidant reduces oxidative damage in the liver and can also be used to prevent cardiovascular diseases and diabetes. However, there is no research targeting the effect of lipid metabolism in high-fat diet (HFD)-induced mice. In this study, we evaluated the anti-obesity effects of Rg1 in 3T3-L1 adipocyte cells and HFD-induced obese C57BL/6J mice. Administration of Rg1 to HFD-induced obese mice significantly decreased body weight, total cholesterol, and total triglyceride levels. In addition to effects in 3T3-L1 cells, Rg1 reduced the accumulation of lipid droplets in a dose-dependent manner. Furthermore, Rg1 exhibits an anti-adipogenic effect via regulation of the expression of the transcriptional factors and lipid metabolism-related genes in vivo and in vitro. We observed that Rg1 administration significantly increased the phosphorylation level of AMP-activated protein kinase (AMPK) in both epididymal white adipose tissue and 3T3-L1 cells. These results indicated that Rg1 works both in an anti-adipogenic and anti-obesity manner through inducing AMPK activation, inhibiting lipogenesis, and decreasing intracellular lipid content, adipocyte size, and adipose weight.

Direct Activation of Adenosine Monophosphate-Activated Protein Kinase (AMPK) by PF-06409577 Inhibits Flavivirus Infection through Modification of Host Cell Lipid Metabolism

Mosquito-borne flaviviruses are a group of RNA viruses that constitute global threats for human and animal health. Replication of these pathogens is strictly dependent on cellular lipid metabolism. We have evaluated the effect of the pharmacological activation of AMP-activated protein kinase (AMPK), a master regulator of lipid metabolism, on the infection of three medically relevant flaviviruses, namely, West Nile virus (WNV), Zika virus (ZIKV), and dengue virus (DENV). WNV is responsible for recurrent outbreaks of meningitis and encephalitis, affecting humans and horses worldwide. ZIKV has caused a recent pandemic associated with birth defects (microcephaly), reproductive disorders, and severe neurological complications (Guillain-Barré syndrome). DENV is the etiological agent of the most prevalent mosquito-borne viral disease, which can induce a potentially lethal complication called severe dengue. Our results showed, for the first time, that activation of AMPK using the specific small molecule activator PF-06409577 reduced WNV, ZIKV, and DENV infection. This antiviral effect was associated with an impairment of viral replication due to the modulation of host cell lipid metabolism exerted by the compound. These results support that the pharmacological activation of AMPK, which currently constitutes an important pharmacological target for human diseases, could also provide a feasible approach for broad-spectrum host-directed antiviral discovery.

Proteostasis in epicardial versus subcutaneous adipose tissue in heart failure subjects with and without diabetes

BACKGROUND

Cardiovascular diseases (CVDs) are leading cause of death and primary cause of morbidity and mortality in diabetic population. Epicardial adipose tissue (EAT) covers the heart's surface and is a source of biomolecules regulating heart and blood vessel physiology. The protective activation of the unfolded protein response (UPR) and autophagy allows the cardiomyocyte reticular network to restore energy and/or nutrient homeostasis and to avoid cell death. However, an excessive or prolonged UPR activation can trigger cell death. UPR activation is an early event of diabetic cardiomyopathies and deregulated autophagy is associated with CVDs.

RESULTS

An upregulation of UPR markers (glucose-regulated protein 78 KDa, glucose-regulated protein 94 KDa, inositol-requiring enzyme 1α, protein kinase RNA-like ER kinase and CCAAT/-enhancer-binding protein homologous protein (CHOP) gene) in EAT compared to subcutaneous adipose tissue (SAT), was observed as well as the UPR-related apoptosis marker caspase-4/procaspase-4 ratio but not in CHOP protein levels. Additionally, levels of ubiquitin and ubiquitinated proteins were decreased in EAT. Moreover, upregulation of autophagy markers (5' adenosine monophosphate-activated protein kinase, mechanistic target of rapamycin, Beclin 1, microtubule-associated protein light chain 3-II, lysosome-associated membrane protein 2, and PTEN-induced putative kinase 1) was observed, as well as an increase in the apoptotic Bim but not the ratio between Bim and the anti-apoptotic Bcl-2 in EAT. Diabetic patients show alterations in UPR activation markers but not in autophagy or apoptosis markers.

CONCLUSION

UPR and autophagy are increased in EAT compared to SAT, opening doors to the identification of early biomarkers for cardiomyopathies and novel therapeutic targets.

Polyacetylene From Dendropanax morbifera Alleviates Diet-Induced Obesity and Hepatic Steatosis by Activating AMPK Signaling Pathway

The extract tea of Dendropanax morbifera is popular beverages in Korea, and their preventive and therapeutic roles in metabolic disorders have been reported. However, the molecular mechanism has not been studied despite the known efficacy of D. morbifera. Eleven fractions (fr.1–fr.11) were divided by MPLC to find the active compound. Among them, Fr.5 was superior to others in that the inhibitory efficacy of de novo triglyceride (TG) biosynthesis. NMR analysis revealed that Fr.5 is composed 98% or more (9Z,16S)-16-hydroxy-9,17-octadecadiene-12,14-diynoic acid (HOD). Treatment of HOD diminished oleic acid (OA)-induced TG accumulation in HepG2 hepatocytes and differentiation of 3T3-L1 preadipocytes by activating LKB1/AMPK. In addition, we determined the effect of the oral administration of the extract of D. morbifera on obesity and hepatic steatosis in high-fat diet (HFD)-induced obese mice. This study proved that D. morbifera containing HOD, the active substance, can show preventive or therapeutic efficacy on obesity and hepatic steatosis through the targeting LKB1/AMPK axis.

AICAR inhibits NFκB DNA binding independently of AMPK to attenuate LPS-triggered inflammatory responses in human macrophages

5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) is an established pharmacological activator of AMP-activated protein kinase (AMPK). Both, AICAR and AMPK were reported to attenuate inflammation. However, AICAR is known for many AMPK-independent effects, although the mechanisms remain incompletely understood. Here we report a potent suppression of lipopolysaccharide (LPS)-induced inflammatory gene expression by AICAR in primary human macrophages, which occurred independently of its conversion to AMPK-activating 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranosyl monophosphate. Although AICAR did not interfere with activation of cytosolic signalling cascades and nuclear translocation of nuclear factor - κB (NFκB) by LPS, it prevented the recruitment of NFκB and RNA polymerase II to target gene promoters. AICAR also inhibited signal transducer and activator of transcription 3 (STAT3)-dependent induction of interleukin (IL) IL-6 and IL-10 targets, while leaving STAT6 and HIF1α-dependent gene expression in IL-4 and dimethyloxalylgylcine-treated macrophages intact. This points to a transcription factor-specific mode of action. Attenuated gene expression correlated with impaired NFκB and STAT3, but not HIF-binding in electrophoretic mobility shift assays in vitro. Conclusively, AICAR interferes with DNA binding of NFκB and STAT3 to modulate inflammatory responses.

What Can 'Brown-ing' Do For You?

Human stem cell-based models of thermogenic adipocytes provide an opportunity for the establishment of new therapeutics, modeling of disease mechanisms, and understanding of development. Pluripotent stem cells, adipose-derived stem cells/preadipocytes, and programming-reprogramming-based approaches have been used to develop cell-based platforms for drug screening and transplantable therapeutics in the metabolic disease arena. Here we provide a detailed overview of these approaches, the latest advances in this field, and the opportunities and shortcomings they present. Moreover, we comment on how stem-cell-based platforms can be best utilized in the future for the treatment and understanding of metabolic diseases, including type 2 diabetes and associated medical issues such as obesity.

Activation of Liver AMPK with PF-06409577 Corrects NAFLD and Lowers Cholesterol in Rodent and Primate Preclinical Models

Dysregulation of hepatic lipid and cholesterol metabolism is a significant contributor to cardiometabolic health, resulting in excessive liver lipid accumulation and ultimately non-alcoholic steatohepatitis (NASH). Therapeutic activators of the AMP-Activated Protein Kinase (AMPK) have been proposed as a treatment for metabolic diseases; we show that the AMPK β1-biased activator PF-06409577 is capable of lowering hepatic and systemic lipid and cholesterol levels in both rodent and monkey preclinical models. PF-06409577 is able to inhibit de novo lipid and cholesterol synthesis pathways, and causes a reduction in hepatic lipids and mRNA expression of markers of hepatic fibrosis. These effects require AMPK activity in the hepatocytes. Treatment of hyperlipidemic rats or cynomolgus monkeys with PF-06409577 for 6 weeks resulted in a reduction in circulating cholesterol. Together these data suggest that activation of AMPK β1 complexes with PF-06409577 is capable of impacting multiple facets of liver disease and represents a promising strategy for the treatment of NAFLD and NASH in humans.

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PF-06409577 is a potent activator of AMPK β1 containing complexes.

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PF-06409577 improves liver function and systemic dyslipidemia in rodents through hepatic AMPK activation.

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PF-06409577-mediated reductions in circulating cholesterol was observed in monkeys and diabetic rats.

NAFLD and NASH remain poorly treated and are diseases which are growing rapidly in societal cost. Therapeutic mechanisms that impact multiple aspects of the dysregulated metabolic regulation of NAFLD and NASH are needed. Pharmacological AMPK activation has long held promise as a treatment for NAFLD because of its impact on hepatic lipid and cholesterol synthesis, as well as its proposed anti-inflammatory and anti-lipolytic actions. Recent development of clinically viable small molecule AMPK activators, including PF-06409577, has enabled their more thorough characterization in preclinical disease models.

Palmitic and Oleic Acid: The Yin and Yang of Fatty Acids in Type 2 Diabetes Mellitus

Increased plasma non-esterified fatty acids (NEFAs) link obesity with insulin resistance and type 2 diabetes mellitus (T2DM). However, in contrast to the saturated FA (SFA) palmitic acid, the monounsaturated FA (MUFA) oleic acid elicits beneficial effects on insulin sensitivity, and the dietary palmitic acid:oleic acid ratio impacts diabetes risk in humans. Here we review recent mechanistic insights into the beneficial effects of oleic acid compared with palmitic acid on insulin resistance and T2DM, including its anti-inflammatory actions, and its capacity to inhibit endoplasmic reticulum (ER) stress, prevent attenuation of the insulin signaling pathway, and improve β cell survival. Understanding the molecular mechanisms of the antidiabetic effects of oleic acid may contribute to understanding the benefits of this FA in the prevention or delay of T2DM.

AMP-Activated Protein Kinase (AMPK) Regulates Energy Metabolism through Modulating Thermogenesis in Adipose Tissue

Obesity occurs when excess energy accumulates in white adipose tissue (WAT), whereas brown adipose tissue (BAT), which is specialized in dissipating energy through thermogenesis, potently counteracts obesity. White adipocytes can be converted to thermogenic "brown-like" cells (beige cells; WAT browning) under various stimuli, such as cold exposure. AMP-activated protein kinase (AMPK) is a crucial energy sensor that regulates energy metabolism in multiple tissues. However, the role of AMPK in adipose tissue function, especially in the WAT browning process, is not fully understood. To illuminate the effect of adipocyte AMPK on energy metabolism, we generated Adiponectin-Cre-driven adipose tissue-specific AMPK α1/α2 KO mice (AKO). These AKO mice were cold intolerant and their inguinal WAT displayed impaired mitochondrial integrity and biogenesis, and reduced expression of thermogenic markers upon cold exposure. High-fat-diet (HFD)-fed AKO mice exhibited increased adiposity and exacerbated hepatic steatosis and fibrosis and impaired glucose tolerance and insulin sensitivity. Meanwhile, energy expenditure and oxygen consumption were markedly decreased in the AKO mice both in basal conditions and after stimulation with a β3-adrenergic receptor agonist, CL 316,243. In contrast, we found that in HFD-fed obese mouse model, chronic AMPK activation by A-769662 protected against obesity and related metabolic dysfunction. A-769662 alleviated HFD-induced glucose intolerance and reduced body weight gain and WAT expansion. Notably, A-769662 increased energy expenditure and cold tolerance in HFD-fed mice. A-769662 treatment also induced the browning process in the inguinal fat depot of HFD-fed mice. Likewise, A-769662 enhanced thermogenesis in differentiated inguinal stromal vascular fraction (SVF) cells via AMPK signaling pathway. In summary, a lack of adipocyte AMPKα induced thermogenic impairment and obesity in response to cold and nutrient-overload, respectively, whereas chronic AMPK activation by A-769662 promoted WAT browning in inguinal WAT and protected against HFD-induced obesity and related metabolic dysfunction. These findings reveal a vital role for adipocyte AMPK in regulating the browning process in inguinal WAT and in maintaining energy homeostasis, which suggests that the targeted activation of adipocyte AMPK may be a promising strategy for anti-obesity therapy.

AMPK: Sensing Glucose as well as Cellular Energy Status

Mammalian AMPK is known to be activated by falling cellular energy status, signaled by rising AMP/ATP and ADP/ATP ratios. We review recent information about how this occurs but also discuss new studies suggesting that AMPK is able to sense glucose availability independently of changes in adenine nucleotides. The glycolytic intermediate fructose-1,6-bisphosphate (FBP) is sensed by aldolase, which binds to the v-ATPase on the lysosomal surface. In the absence of FBP, interactions between aldolase and the v-ATPase are altered, allowing formation of an AXIN-based AMPK-activation complex containing the v-ATPase, Ragulator, AXIN, LKB1, and AMPK, causing increased Thr172 phosphorylation and AMPK activation. This nutrient-sensing mechanism activates AMPK but also primes it for further activation if cellular energy status subsequently falls. Glucose sensing at the lysosome, in which AMPK and other components of the activation complex act antagonistically with another key nutrient sensor, mTORC1, may have been one of the ancestral roles of AMPK.

Promise and challenges for direct small molecule AMPK activators

AMP-activated protein kinase (AMPK) is an evolutionary conserved and ubiquitously expressed serine/threonine kinase playing a central role in the coordination of energy homeostasis. Based on the beneficial outcomes of its activation on metabolism, AMPK has emerged as an attractive target for the treatment of metabolic diseases. Identification of novel downstream targets of AMPK beyond the regulation of energy metabolism has renewed considerable attention in exploiting AMPK signaling for novel therapeutic targeting strategies including treatment of cancer and inflammatory diseases. The complexity of AMPK system with tissue- and species-specific expression of multiple isoform combination regulated by various inputs, post-traductional modifications and subcellular locations presents unique challenges for drug discovery. Here, we review the most recent advances in the understanding of the mechanism(s) of action of direct small molecule AMPK activators and the potential therapeutic opportunities.

Cellular Energy Sensing and Metabolism-Implications for Treating Diabetes: The 2017 Outstanding Scientific Achievement Award Lecture

The Outstanding Scientific Achievement Award recognizes distinguished scientific achievement in the field of diabetes, taking into consideration independence of thought and originality. Gregory R. Steinberg, PhD, professor of medicine, Canada Research Chair, J. Bruce Duncan Endowed Chair in Metabolic Diseases, and codirector of the Metabolism and Childhood Obesity Research Program at McMaster University, Hamilton, Ontario, Canada, received the prestigious award at the American Diabetes Association's 77th Scientific Sessions, 9-13 June 2017, in San Diego, CA. He presented the Outstanding Scientific Achievement Award Lecture, "Cellular Energy Sensing and Metabolism-Implications for Treating Diabetes," on Monday, 12 June 2017.The survival of all cells is dependent on the constant challenge to match energetic demands with nutrient availability, a task that is mediated through a highly conserved network of metabolic fuel sensors that orchestrate both cellular and whole-organism energy balance. A mismatch between cellular energy demand and nutrient availability is a key factor contributing to the development of type 2 diabetes; thus, understanding the fundamental mechanisms by which cells sense nutrient availability and demand may lead to the development of new treatments. Glucose-lowering therapies, such as caloric restriction, exercise, and metformin, all induce an energetic challenge that results in the activation of the cellular energy sensor AMP-activated protein kinase (AMPK). Activation of AMPK in turn suppresses lipid synthesis and inflammation while increasing glucose uptake, fatty acid oxidation, and mitochondrial function. In contrast, high levels of nutrient availability suppress AMPK activity while also increasing the production of peripheral serotonin, a gut-derived endocrine factor that suppresses β-adrenergic-induced activation of brown adipose tissue. Identifying new ways to manipulate these two ancient fuel gauges by activating AMPK and inhibiting peripheral serotonin may lead to the development of new therapies for treating type 2 diabetes.

Methods to Evaluate AMPK Regulation of Macrophage Cholesterol Homeostasis

Macrophages are a driving force in the development and progression of atherosclerosis, a chronic condition that can lead to cardiovascular disease. In this chapter we describe methods that monitor macrophage cholesterol homeostasis such as cholesterol synthesis, uptake, and efflux, all with the use of AMPK activators and potential genetic models that could help shed light on the role of this metabolic regulator in atherosclerosis and other chronic diseases.

AMP-Activated Protein Kinase Regulation of the NLRP3 Inflammasome during Aging

The NLRP3 inflammasome has recently emerged as an unexpected marker of stress and metabolic risk and has also been implicated in the development of major aging-related diseases such as gout, type 2 diabetes, obesity, cancer, and neurodegenerative and cardiovascular disorders. Several pathways regulating the NLRP3 inflammasome are currently being studied, but how the NLRP3 inflammasome is regulated remains unknown. AMP-activated protein kinase (AMPK), a central regulator of multiple metabolic pathways involved in the pathophysiology of aging and age-related diseases, has emerged as an important integrator of signals controlling inflammation including the inflammasome. In this Opinion article, we show that several AMPK-dependent pathways regulate NLRP3 inflammasome activation during aging, suggesting NLRP3 as a potential pharmacological target in age-related diseases.

Dipeptidyl-Peptidase 4 Inhibitor Sitagliptin Ameliorates Hepatic Insulin Resistance by Modulating Inflammation and Autophagy in ob/ob Mice

Obesity and type 2 diabetes are the most common metabolic diseases globally. They are associated with inflammation, oxidative stress, autophagy, and insulin resistance. Sitagliptin, a dipeptidyl-peptidase 4 inhibitor, has been reported to show multiple biological activities beyond the antidiabetic property. This study was aimed at investigating the effect of sitagliptin on hepatic steatosis, insulin resistance, inflammation, and autophagy and exploring the underlying molecular mechanism. In the current study, ob/ob mice, a mouse model of genetic obesity and diabetes, were administered via gavage with sitagliptin 50 mg/kg daily for 4 weeks. Changes in glycolipid metabolism, inflammatory responses, and autophagy in the liver were evaluated. Body weight gain, lipid metabolic disorder, and hepatic steatosis as well as systemic and hepatic insulin sensitivity in ob/ob mice were significantly attenuated after sitagliptin treatment. Furthermore, sitagliptin decreased inflammatory responses by regulating macrophage M1/M2 polarization and inhibiting the activities of NF-κB and JNK. Moreover, sitagliptin increased the levels of phosphorylation of AMPK and decreased those of mTOR. This study indicates that sitagliptin significantly ameliorates the development of hepatic steatosis and insulin resistance in ob/ob mice by inhibiting inflammatory responses and activating autophagy via AMPK/mTOR signaling pathway.

Melatonin alleviates oxidative stress-inhibited osteogenesis of human bone marrow-derived mesenchymal stem cells through AMPK activation

Oxidative stress plays an important role in the pathogenesis of aging-related osteoporosis through the increased bone resorption or reduced bone formation. Melatonin, which can exert beneficial actions through antioxidant, anti-inflammatory, and bone-preserving effects, shows promise in preventing oxidative stress-inhibited osteogenesis. However, specific mechanisms by which melatonin rescues oxidative stress-inhibited osteogenesis of human mesenchymal stem cells (MSCs) have not been fully elucidated yet. We therefore investigated whether activation of AMPK by melatonin regulates the antagonistic crosstalk between oxidative stress and osteogenic differentiation in human MSCs. Melatonin treatment significantly enhanced osteogenic differentiation of human MSCs through activation of AMPK and upregulation of FOXO3a and RUNX2 which were known as master transcription factors responsible for the mechanistic link between oxidative stress and osteogenic phenotype. Osteogenic differentiation determined by calcium deposition was significantly increased by melatonin treatment against oxidative stress. In addition, melatonin treatment reconstituted activation of AMPK and expression of FOXO3a and RUNX2 inhibited by oxidative stress. Overall, these results demonstrate that melatonin enhances osteogenic differentiation of human MSCs and restores oxidative stress-inhibited osteogenesis through AMPK activation in human MSCs, suggesting that activation of AMPK by melatonin may represent a promising new therapeutic strategy for treating metabolic bone diseases such as osteoporosis.

Advanced palladium free approach to the synthesis of substituted alkene oxindoles via aluminum-promoted Knoevenagel reaction

A synthetic route for the synthesis of C24, as well as for the design of focused libraries of direct AMPK activators was developed based on a convergent strategy. The proposed scheme corresponds to the current trends in C–H bond functionalization. The use of aluminum isopropoxide for the Knoevenagel condensation of oxindole with benzophenones is a noticeable point of this work.

A synthetic route for the synthesis of C24, as well as for the design of focused libraries of direct AMPK activators was developed based on a convergent strategy.

Serine prevented high-fat diet-induced oxidative stress by activating AMPK and epigenetically modulating the expression of glutathione synthesis-related genes

Serine deficiency has been observed in patients with nonalcoholic fatty liver disease (NAFLD). Whether serine supplementation has any beneficial effects on the prevention of NAFLD remains unknown. The present study was conducted to investigate the effects of serine supplementation on hepatic oxidative stress and steatosis and its related mechanisms. Forty male C57BL/6J mice (9week-old) were randomly assigned into four groups (n=10) and fed: i) a low-fat diet; ii) a low-fat diet supplemented with 1% (wt:vol) serine; iii) a high-fat (HF) diet; and iv) a HF diet supplemented with 1% serine, respectively. Palmitic acid (PA)-treated primary hepatocytes separated from adult mice were also used to study the effects of serine on oxidative stress. The results showed that serine supplementation increased glucose tolerance and insulin sensitivity, and protected mice from hepatic lipid accumulation, but did not significantly decreased HF diet-induced weight gain. In addition, serine supplementation protected glutathione (GSH) antioxidant system and prevented hypermethylation in the promoters of glutathione synthesis-related genes, while decreasing reactive oxygen species (ROS) in mice fed a HF diet. Moreover, we found that serine supplementation increased phosphorylation and S-glutathionylation of AMP-activated protein kinase α subunit (AMPKα), and decreased ROS, malondialdehyde and triglyceride contents in PA-treated primary hepatocytes. However, while AMPK activity or GSH synthesis was inhibited, the abovementioned effects of serine on PA-treated primary hepatocytes were not observed. Our results suggest that serine supplementation could prevent HF diet-induced oxidative stress and steatosis by epigenetically modulating the expression of glutathione synthesis-related genes and through AMPK activation.

A vicious circle between insulin resistance and inflammation in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) comprises a spectrum of diseases, including simple steatosis, nonalcoholic steatohepatitis (NASH), liver cirrhosis and hepatocellular carcinoma. Lipotoxicity, insulin resistance (IR) and inflammation are involved in the disease process. Lipotoxicity promotes inflammation and IR, which in turn, increase adipocyte lipolysis and exacerbates lipotoxicity. Furthermore, IR and inflammation form a vicious circle, with each condition promoting the other and accelerating the development of NAFLD in the presence of lipotoxicity. As an integrator of inflammatory pathway networks, nuclear factor-kappa B (NF-κB) regulates expression of pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), and anti-inflammatory cytokines, such as adiponectin in NAFLD. In this review, the relationships between lipotoxicity, IR and inflammation in NAFLD are discussed, with particular emphasis on the inflammatory pathways.

The emerging role of AMP-activated protein kinase in cholestatic liver diseases

AMP-activated protein kinase (AMPK), recognized as an energy sensor with three heterotrimeric subunits (α, β and γ), not only maintains basal intracellular adenosine triphosphate levels but also regulates energy-intensive pathological responses, such as neurodegenerative and metabolic diseases, through multiple signaling pathways. Recent studies open a new direction for AMPK research and demonstrate that AMPK is a critical player in the pathogenesis of cholestatic liver injury and plays paradoxical roles in the regulation of different pathological processes, including the disruption of bile acid homeostasis and the regulation of hepatic polarity, inflammation and fibrosis. In the present review, we summarize recent findings that implicate AMPK-mediated signaling pathways in the pathogenesis of cholestatic liver injury. These findings provide novel insight regarding the potential use of AMPK as a therapeutic target for the treatment of cholestatic liver injury.