Subunit Of AMP-activated Protein Kinase Research Articles

Plant-Derived Flavonoids as AMPK Activators: Unveiling Their Potential in Type 2 Diabetes Management through Mechanistic Insights, Docking Studies, and Pharmacokinetics

Type 2 diabetes mellitus (T2DM) remains a significant global health issue, marked by insulin resistance and disrupted glucose metabolism. AMP-activated protein kinase (AMPK) serves as a key regulator of cellular energy balance, playing a crucial role in enhancing insulin sensitivity, promoting glucose uptake, and reducing glucose production in the liver. Recently, there has been growing interest in plant-derived flavonoids as natural activators of AMPK, offering a promising complementary approach to conventional diabetes treatments. This review delves into ten flavonoids identified as AMPK activators, including baicalein, dihydromyricetin, bavachin, 7-O-MA, derrone, and alpinumisoflavone. Their activation mechanisms are explored, which include both direct binding to the AMPK complex and indirect pathways involving upstream signaling. Through molecular docking studies, the binding affinities and interaction profiles of these flavonoids with AMPK are assessed, revealing varying levels of activation potential. Notably, baicalein and dihydromyricetin showed strong binding to the α1 subunit of AMPK, indicating high potential for robust activation. Additionally, this review provides a thorough analysis of the pharmacokinetic properties and drug-likeness of these flavonoids using the SwissADME tool, focusing on aspects such as ADME (Absorption, Distribution, Metabolism, and Excretion). While the overall profiles of these compounds are promising, issues like solubility and possible drug–drug interactions are areas that need further refinement. In summary, plant-derived flavonoids emerge as a promising avenue for developing new natural therapies for T2DM. Moving forward, research should aim at optimizing these compounds for clinical application, elucidating their specific mechanisms of AMPK activation, and confirming their efficacy in T2DM treatment. This review highlights the potential of flavonoids as safer and more holistic alternatives or adjuncts to current diabetes therapies.

How mass spectrometry can be exploited to study AMPK.

AMP-activated protein kinase (AMPK) is a key regulator of metabolism and a recognised target for the treatment of metabolic diseases such as Type 2 diabetes (T2D). Here, we review how mass spectrometry (MS) can be used to study short-term control by AMPK via protein phosphorylation and long-term control due to changes in protein expression. We discuss how MS can quantify AMPK subunit levels in tissues from different species. We propose hydrogen-deuterium exchange (HDX)-MS to investigate molecular mechanisms of AMPK activation and thermoproteomic profiling (TPP) to assess off-target effects of pharmacological AMPK activators/inhibitors. Lastly, because large MS data sets are generated, we consider different approaches that can be used for their interpretation.

Discovery of Oral AMP-Activated Protein Kinase Activators for Treating Hyperlipidemia.

Activation of AMP-activated protein kinase (AMPK) is proposed to alleviate hyperlipidemia. With cordycepin and N6-(2-hydroxyethyl) adenosine (HEA) as lead compounds, a series of adenosine-based derivatives were designed, synthesized, and evaluated on activation of AMPK. Finally, compound V1 was identified as a potent AMPK activator with the lipid-lowering effect. Molecular docking and circular dichroism indicated that V1 exerted its activity by binding to the γ subunit of AMPK. V1 markedly decreased the serum low-density lipoprotein cholesterol levels in C57BL/6 mice, golden hamsters, and rhesus monkeys. V1 was selected as the clinical compound and concluded Phase 1 clinical trials. A single dose of V1 (2000 mg) increased AMPK activation in human erythrocytes after 5 and 12 h of treatment. RNA sequencing data suggested that V1 downregulated expression of genes involved in regulation of apoptotic process, lipid metabolism, endoplasmic reticulum stress, and inflammatory response in liver by activating AMPK.

The α subunit of AMP-activated protein kinase is critical for the metabolic success and tachyzoite proliferation of Toxoplasma gondii.

Toxoplasma gondii is a zoonotic parasite infecting humans and nearly all warm-blooded animals. Successful parasitism in diverse hosts at various developmental stages requires the parasites to fine tune their metabolism according to environmental cues and the parasite's needs. By manipulating the β and γ subunits, we have previously shown that AMP-activated protein kinase (AMPK) has critical roles in regulating the metabolic and developmental programmes. However, the biological functions of the α catalytic subunit have not been established. T. gondii encodes a canonical AMPKα, as well as a KIN kinase whose kinase domain has high sequence similarities to those of classic AMPKα proteins. Here, we found that TgKIN is dispensable for tachyzoite growth, whereas TgAMPKα is essential. Depletion of TgAMPKα expression resulted in decreased ATP levels and reduced metabolic flux in glycolysis and the tricarboxylic acid cycle, confirming that TgAMPK is involved in metabolic regulation and energy homeostasis in the parasite. Sequential truncations at the C-terminus found an α-helix that is key for the function of TgAMPKα. The amino acid sequences of this α-helix are not conserved among various AMPKα proteins, likely because it is involved in interactions with TgAMPKβ, which only have limited sequence similarities to AMPKβ in other eukaryotes. The essential role of the less conserved C-terminus of TgAMPKα provides opportunities for parasite specific drug designs targeting TgAMPKα.

Shear Stress and the AMP-Activated Protein Kinase Independently Protect the Vascular Endothelium from Palmitate Lipotoxicity.

Saturated free fatty acids are thought to play a critical role in metabolic disorders associated with obesity, insulin resistance, type 2 diabetes (T2D), and their vascular complications via effects on the vascular endothelium. The most abundant saturated free fatty acid, palmitate, exerts lipotoxic effects on the vascular endothelium, eventually leading to cell death. Shear stress activates the endothelial AMP-activated protein kinase (AMPK), a cellular energy sensor, and protects endothelial cells from lipotoxicity, however their relationship is uncertain. Here, we used isoform-specific shRNA-mediated silencing of AMPK to explore its involvement in the long-term protection of macrovascular human umbilical vein endothelial cells (HUVECs) against palmitate lipotoxicity and to relate it to the effects of shear stress. We demonstrated that it is the α1 catalytic subunit of AMPK that is critical for HUVEC protection under static conditions, whereas AMPK-α2 autocompensated a substantial loss of AMPK-α1, but failed to protect the cells from palmitate. Shear stress equally protected the wild type HUVECs and those lacking either α1, or α2, or both AMPK-α isoforms; however, the protective effect of AMPK reappeared after returning to static conditions. Moreover, in human adipose microvascular endothelial cells isolated from obese diabetic individuals, shear stress was a strong protector from palmitate lipotoxicity, thus highlighting the importance of circulation that is often obstructed in obesity/T2D. Altogether, these results indicate that AMPK is important for vascular endothelial cell protection against lipotoxicity in the static environment, however it may be dispensable for persistent and more effective protection exerted by shear stress.

Empagliflozin ameliorates diabetic cardiomyopathy probably via activating AMPK/PGC-1α and inhibiting the RhoA/ROCK pathway.

Diabetic cardiomyopathy (DCM) increases the risk of hospitalization for heart failure (HF) and mortality in patients with diabetes mellitus. However, no specific therapy to delay the progression of DCM has been identified. Mitochondrial dysfunction, oxidative stress, inflammation, and calcium handling imbalance play a crucial role in the pathological processes of DCM, ultimately leading to cardiomyocyte apoptosis and cardiac dysfunctions. Empagliflozin, a novel glucose-lowering agent, has been confirmed to reduce the risk of hospitalization for HF in diabetic patients. Nevertheless, the molecular mechanisms by which this agent provides cardioprotection remain unclear. To investigate the effects of empagliflozin on high glucose (HG)-induced oxidative stress and cardiomyocyte apoptosis and the underlying molecular mechanism. Twelve-week-old db/db mice and primary cardiomyocytes from neonatal rats stimulated with HG (30 mmol/L) were separately employed as in vivo and in vitro models. Echocardiography was used to evaluate cardiac function. Flow cytometry and TdT-mediated dUTP-biotin nick end labeling staining were used to assess apoptosis in myocardial cells. Mitochondrial function was assessed by cellular ATP levels and changes in mitochondrial membrane potential. Furthermore, intracellular reactive oxygen species production and superoxide dismutase activity were analyzed. Real-time quantitative PCR was used to analyze Bax and Bcl-2 mRNA expression. Western blot analysis was used to measure the phosphorylation of AMP-activated protein kinase (AMPK) and myosin phosphatase target subunit 1 (MYPT1), as well as the peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) and active caspase-3 protein levels. In the in vivo experiment, db/db mice developed DCM. However, the treatment of db/db mice with empagliflozin (10 mg/kg/d) for 8 wk substantially enhanced cardiac function and significantly reduced myocardial apoptosis, accompanied by an increase in the phosphorylation of AMPK and PGC-1α protein levels, as well as a decrease in the phosphorylation of MYPT1 in the heart. In the in vitro experiment, the findings indicate that treatment of cardiomyocytes with empagliflozin (10 μM) or fasudil (FA) (a ROCK inhibitor, 100 μM) or overexpression of PGC-1α significantly attenuated HG-induced mitochondrial injury, oxidative stress, and cardiomyocyte apoptosis. However, the above effects were partly reversed by the addition of compound C (CC). In cells exposed to HG, empagliflozin treatment increased the protein levels of p-AMPK and PGC-1α protein while decreasing phosphorylated MYPT1 levels, and these changes were mitigated by the addition of CC. Adding FA and overexpressing PGC-1α in cells exposed to HG substantially increased PGC-1α protein levels. In addition, no sodium-glucose cotransporter (SGLT)2 protein expression was detected in cardiomyocytes. Empagliflozin partially achieves anti-oxidative stress and anti-apoptotic effects on cardiomyocytes under HG conditions by activating AMPK/PGC-1α and suppressing of the RhoA/ROCK pathway independent of SGLT2.

Stress-Induced AMPK Interactome Analysis Reveals Novel Protein-Protein Interactions Associated with Chromatin Remodeling and Transcription Machinery in Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is a leading cause of cancer-related death among children, adolescents and young adults. Survival rates for relapsed/refractory ALL remain dismal. We have previously reported that ALL cells are vulnerable to energy/metabolic stress conditions following AMP-activated protein kinase (AMPK) activation, leading to cell death. AMPK is the master metabolic regulator, and our lab and others have reported it interacts with chromatin-associated proteins to epigenetically regulate gene expression in response to energy/metabolic stress. To identify genome-wide genes regulated by direct association of AMPK to chromatin in response to energy/metabolic stress, we previously used ChIP-seq and RNA-seq in Bp-ALL (KASUMI-2) and T-ALL (KE-37) cells treated with or without glucose or AICAR, a well-known AMPK activator, and found that (i) AMPK interacts with components of the transcription machinery including the TATA-Box Binding Protein Associated Factor (TAF) and RNA polymerase II, (ii) AMPKα2 was enriched for genes involved in histone H3-K4 methylation, protein localization, Notch signaling, and mRNA destabilization, (iii) AMPKa2 was recruited to promoter regions of the epigenetic regulators KMT2A and SETD1A, and (iv) the mRNA expression of KMT2A and SETD1A genes was upregulated in KASUMI-2 cells treated with AICAR. To further investigate AMPK's involvement in epigenetic mechanisms in response to energy/metabolic stress, we performed a comprehensive interactome analysis using TurboID-based proximity labeling proteomics. AMPK is a highly conserved heterotrimeric kinase complex composed of catalytic α-subunit (α1 or α2) and regulatory β (β1 or β2) and γ (γ1, γ2, or γ3) subunits. We generated HEK293T cells stably expressing TurboID fused to the AMPKα1, AMPKα2, AMPKβ1 or AMPKγ1 (which are the most abundant AMPK subunits expressed in ALL cells), and these stable cell lines were treated with the potent allosteric AMPK activator PF-06409577 for 1 hr, to mimic the cell's rapid response to energy/metabolic stress. Following characterization of these stable cell lines and small-scale optimization experiments, treated samples and controls were submitted to mass spectrometry analysis. Proteomics data analysis identified novel AMPK's protein-protein interactions (PPI) which were altered (enhanced or reduced) following PF-06409577 treatment. Among PPI altered by PF-06409577 treatment, 148 were enhanced and 144 reduced for AMPKα1, 169 enhanced and 172 reduced for AMPKα2, 250 enhanced and 188 reduced for AMPKβ1 and 289 enhanced and 153 reduced for AMPKγ1. For proteomics data visualization we used Cytoscape software. The GO analysis of proteins interacting with AMPKα1β1γ1 and/or AMPKα2β1γ1 heterotrimeric complexes in cells treated with PF-06409577 showed that energy/metabolic stress enhances their interaction with proteins involved in gene expression, cellular metabolic processes, chromatin organization, DNA repair, histone modifications, etc.. Using the STRING database, we performed MCL clustering analysis and uncovered a major cluster of known epigenetic regulators (e.g., histone modifiers such as KDM6A, HDAC2, SETD2, KMT2A and SETD1A etc.) and components of the transcription machinery (such as NELFE, POLR2A etc.) that interacted with AMPK under stress-induced conditions. These data support our previous findings uncovered by ChIP-seq and RNA-seq analysis. Consequently, our findings further validate an epigenetic role for AMPK via interactions with putative members of chromatin-associated and transcription machinery complexes and chromatin modifying enzymes that allow ALL cells to respond to conditions of energy/metabolic stress. To our knowledge, this is the first report describing the AMPK interactome in pediatric ALL. Further elucidation of the uncovered protein-protein interactions may lead to potential epigenetic-based targeted therapies to overcome therapeutic resistance in relapse/refractory ALL and other hematological malignancies.

Regulation of AMP-Activated Protein Kinase (AMPK) Subunit Expression at the Transcriptional Level by the Neutral Amino Acid Transporter SNAT2

AMP-Activated Protein Kinase (AMPK) is a key enzyme that maintains cellular energy homeostasis. AMPK promotes catabolic pathways and inhibits anabolic pathways under low-energy conditions, such as glucose deprivation. SLC38A2/SNAT2 is an amino acid transporter that imports a wide range of neutral amino acids, including glutamine and alanine. The expression of SNAT2 is down regulated in patients with metabolic diseases such as obesity, nonalcoholic steatohepatitis, and hepatocellular carcinoma. Here, we demonstrate that SNAT2 is required for LKB1-mediated activation of AMPK. Depletion of SNAT2 results in diminished activation of AMPK under conditions of glucose or serum starvation, while the induction of SNAT2 expression augments AMPK activation. SNAT2 overexpression-mediated induction of AMPK activation is abrogated by LKB1 depletion but not by CaMKK2 or TAK1 depletion. Interestingly, the mRNA levels of AMPKβ2 are comparably reduced by SNAT2 depletion, indicating regulation of AMPKβ2 at the transcriptional level. AMPKβ1 mRNA levels are also reduced to a lesser extent. Consistently, SNAT2 depletion leads to a marked reduction in AMPK-mediated autophagy induction, as evidenced by reduced conversion to LC3 II and LC3 puncta formation under nutrient-deprived conditions. Given that AMPK activation plays a pivotal role in nutrient sensing and the subsequent cellular response to low-energy levels and various stress conditions, we provide another level of regulatory mechanism for AMPK-mediated cellular energy homeostasis.

Adenosine monophosphate-activated protein kinase is elevated in human cachectic muscle and prevents cancer-induced metabolic dysfunction in mice.

Metabolic dysfunction and cachexia are associated with poor cancer prognosis. With no pharmacological treatments, it is crucial to define the molecular mechanisms causing cancer-induced metabolic dysfunction and cachexia. Adenosine monophosphate-activated protein kinase (AMPK) connects metabolic and muscle mass regulation. As AMPK could be a potential treatment target, it is important to determine the function for AMPK in cancer-associated metabolic dysfunction and cachexia. We therefore established AMPK's roles in cancer-associated metabolic dysfunction, insulin resistance and cachexia. In vastus lateralis muscle biopsies from n=26 patients with non-small cell lung cancer (NSCLC), AMPK signalling and protein content were examined by immunoblotting. To determine the role of muscle AMPK, male mice overexpressing a dominant-negative AMPKα2 (kinase-dead [KiDe]) specifically in striated muscle were inoculated with Lewis lung carcinoma (LLC) cells (wild type [WT]: n=27, WT+LLC: n=34, mAMPK-KiDe: n=23, mAMPK-KiDe+LLC: n=38). Moreover, male LLC-tumour-bearing mice were treated with (n=10)/without (n=9) 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) to activate AMPK for 13days. Littermate mice were used as controls. Metabolic phenotyping of mice was performed via indirect calorimetry, body composition analyses, glucose and insulin tolerance tests, tissue-specific 2-[3H]deoxy-d-glucose (2-DG) uptake and immunoblotting. Patients with NSCLC presented increased muscle protein content of AMPK subunits α1, α2, β2, γ1 and γ3 ranging from +27% to +79% compared with control subjects. In patients with NSCLC, AMPK subunit protein content correlated with weight loss (α1, α2, β2 and γ1), fat-free mass (α1, β2 and γ1) and fat mass (α1 and γ1). Tumour-bearing mAMPK-KiDe mice presented increased fat loss and glucose and insulin intolerance. LLC in mAMPK-KiDe mice displayed lower insulin-stimulated 2-DG uptake in skeletal muscle (quadriceps: -35%, soleus: -49%, extensor digitorum longus: -48%) and the heart (-29%) than that in non-tumour-bearing mice. In skeletal muscle, mAMPK-KiDe abrogated the tumour-induced increase in insulin-stimulated TBC1D4thr642 phosphorylation. The protein content of TBC1D4 (+26%), pyruvate dehydrogenase (PDH; +94%), PDH kinases (+45% to +100%) and glycogen synthase (+48%) was increased in skeletal muscle of tumour-bearing mice in an AMPK-dependent manner. Lastly, chronic AICAR treatment elevated hexokinase II protein content and normalized phosphorylation of p70S6Kthr389 (mTORC1 substrate) and ACCser212 (AMPK substrate) and rescued cancer-induced insulin intolerance. Protein contents of AMPK subunits were upregulated in skeletal muscle of patients with NSCLC. AMPK activation seemed protectively inferred by AMPK-deficient mice developing metabolic dysfunction in response to cancer, including AMPK-dependent regulation of multiple proteins crucial for glucose metabolism. These observations highlight the potential for targeting AMPK to counter cancer-associated metabolic dysfunction and possibly cachexia.

Loss of AMPKα2 promotes melanoma tumor growth and brain metastasis

AMP-activated protein kinase (AMPK) is a critical cellular energy sensor at the interface of metabolism and cancer. However, the role of AMPK in carcinogenesis remains unclear. Here, through analysis of the TCGA melanoma dataset, we found that PRKAA2 gene that encodes the α2 subunit of AMPK is mutated in ∼9% of cutaneous melanomas, and these mutations tend to co-occur with NF1 mutations. Knockout of AMPKα2 promoted anchorage-independent growth of NF1-mutant melanoma cells, whereas ectopic expression of AMPKα2 inhibited their growth in soft agar assays. Moreover, loss of AMPKα2 accelerated tumor growth of NF1-mutant melanoma and enhanced their brain metastasis in immune-deficient mice. Our findings support that AMPKα2 serves as a tumor suppressor in NF1-mutant melanoma and suggest that AMPK could be a therapeutic target for treating melanoma brain metastasis.

PROTECTIVE EFFECTS OF HUMANIN-G IN HEMORRHAGIC SHOCK IN FEMALE MICE VIA AMPKα1-INDEPENDENT MECHANISMS.

Introduction: Despite therapeutic advances in hemorrhagic shock, mortality from multiple organ failure remains high. We previously showed that the α1 subunit of AMP-activated protein kinase (AMPK), a crucial regulator of mitochondrial function, exerts a protective role in hemorrhagic shock. Humanin is a mitochondrial peptide with cytoprotective properties against cellular stress. Here, we investigated whether AMPKα1 influences systemic levels of endogenous humanin in hemorrhagic shock and whether treatment with the synthetic analog humanin-G affords beneficial effects. Methods: AMPKα1 wild-type (WT) and knockout (KO) female mice were subjected to hemorrhagic shock followed by resuscitation with blood and lactated Ringer's solution. In short-term studies, mice were treated with humanin-G or vehicle and sacrificed at 3 h after resuscitation; in survival studies, mice were treated with PEGylated humanin-G and monitored for 7 days. Results: Compared with the vehicle WT group, KO mice exhibited severe hypotension, cardiac mitochondrial damage, and higher plasma levels of Th17 cytokines but had similar lung injury and similar plasma elevation of endogenous humanin. Treatment with humanin-G improved lung injury, mean arterial blood pressure, and survival in both WT and KO mice, without affecting systemic cytokine or humanin levels. Humanin-G also ameliorated cardiac mitochondrial damage and increased adenosine triphosphate levels in KO mice. Beneficial effects of humanin-G were associated with lung cytoplasmic and nuclear activation of the signal transducer and activator of transcription-3 (STAT3) in AMPKα1-independent manner with marginal or no effects on mitochondrial STAT3 and complex I subunit GRIM-19. Conclusions: Our data indicate that circulating levels of humanin increase during hemorrhagic shock in AMPKα1-independent fashion as a defense mechanism to counteract metabolic derangement and that administration of humanin-G affords beneficial effects through STAT3 activation even in the absence of a functional AMPKα1.

Integrative Analysis of the AMPK subunits in Colorectal Adeno Carcinoma.

The 5-adenosine monophosphate (AMP)-activated protein kinase (AMPK) is an emerging cancer treatment and therapeutic target. Due to the enzyme's complexity and dual nature, it is a confounding target in the treatment strategy. The study aimed to conduct an integrative analysis of the seven subunits and twelve isoforms of AMPK, which is not reported so far in colorectal adenocarcinoma patients. The web-based tools UALCAN, Timer 2.0, KM Plotter, cBioPortal, COSMIC, and STRING were used to investigate the differential expression of AMPK subunits, protein-level Expression, promoter methylation status, survival analyses, Enrichment analysis, and protein-protein interaction. The mRNA expression of AMPK subunits are upregulated in Colorectal Adeno Carcinoma (COAD), while the protein expression is comparatively reduced in colon tumors. The protein-level expression of α2 and β2 is decreased significantly in COAD patients. The γ3 subunit in colon tumor is hypermethylated. The study also reports that Liver Kinase B1 mutation in 7% of CRC patients, which might be the reason for downregulation of the gene and the protein expression of AMPK subunits in COAD. The Overall analysis of the subunits affirms that AMPK expression is beneficial in cancer.

Isoform-specific effects of neuronal repression of the AMPK catalytic subunit on cognitive function in aged mice.

AMP-activated protein kinase (AMPK) functions as a molecular sensor that plays a critical role in maintaining cellular energy homeostasis. Dysregulation of the AMPK signaling has been linked to synaptic failure and cognitive impairments. Our recent study demonstrates abnormally increased AMPK activity in the hippocampus of aged mice. The kinase catalytic subunit of AMPK exists in two isoforms α1 and α2, and their specific roles in aging-related cognitive deficits are unknown. Taking advantage of the unique transgenic mice (AMPKα1/α2 cKO) recently developed by our group, we investigated how isoform-specific suppression of the neuronal AMPKα may contribute to the regulation of cognitive and synaptic function associated with aging. We found that aging-related impairment of long-term object recognition memory was improved with suppression of AMPKα1 but not AMPKα2 isoform. Moreover, aging-related spatial memory deficits were unaltered with suppression of either AMPKα isoform. Biochemical experiments showed that the phosphorylation levels of the eukaryotic initiation factor 2 α subunit (eIF2α) were specifically decreased in the hippocampus of the AMPKα1 cKO mice. We further performed large-scale unbiased proteomics analysis and revealed identities of proteins whose expression is differentially regulated with AMPKα isoform suppression. These novel findings may provide insights into the roles of AMPK signaling pathway in cognitive aging.

Energy sensor AMPK gamma regulates translation via phosphatase PPP6C independent of AMPK alpha

Maintenance of energy level to drive movements and material exchange with the environment is a basic principle of life. AMP-activated protein kinase (AMPK) senses energy level and is a major regulator of cellular energy responses. The gamma subunit of AMPK senses elevated ratio of AMP to ATP and allosterically activates the alpha catalytic subunit to phosphorylate downstream effectors. Here, we report that knockout of AMPKγ, but not AMPKα, suppressed phosphorylation of eukaryotic translation elongation factor 2 (eEF2) induced by energy starvation. We identified PPP6C as an AMPKγ-regulated phosphatase of eEF2. AMP-bound AMPKγ sequesters PPP6C, thereby blocking dephosphorylation of eEF2 and thus inhibiting translation elongation to preserve energy and to promote cell survival. Further phosphoproteomic analysis identified additional targets of PPP6C regulated by energy stress in an AMPKγ-dependent manner. Thus, AMPKγ senses cellular energy availability to regulate not only AMPKα kinase, but also PPP6C phosphatase and possibly other effectors.

Differential expression of AMPK subunit isoforms in subcutaneous adipose tissue of post-mortem subjects with BMI>25kg/m2

AMP-activated protein kinase (AMPK) is a heterotrimeric complex that is made up of α-, β- and γ- subunits isoforms making up various isomers. AMPK has been shown to improve catabolic ATP-generating pathways, making it a promising therapeutic target. Studies have shown that different AMPK isomers are predominant in different tissues. However, determination of the predominant isomer in adipose tissue remains obscure. The goal of this study is to identify the AMPK isomers present in human subcutaneous adipose tissues comparing between lean and overweight/obese subjects. Total RNA from post-mortem subcutaneous adipose tissue was extracted and its quantity and integrity were evaluated using a bioanalyzer before being reverse transcribed to cDNA. Then, by using SYBR-green as a fluorophore detection, quantitative real-time PCR was performed. The relative expression of each target gene was calculated using the comparative 2-∆∆Ct method, and the expression levels of target genes were normalized to that of GAPDH, RPLP0, and HPRT1. Mean differences of AMPK subunits mRNA level for both lean and overweight/obese subjects were determined by Mann-Whitney for two-sample comparisons using SPSS 26.0 (SPSS Inc., USA). This study revealed that in overweight/obese subjects, the gene expression of α1-AMPK was upregulated (2.5-fold) whilst α2-AMPK was downregulated (0.5-fold) when compared to lean controls (p=0.044). There were no differences observed between the β and γ subunits in both lean and overweight/obese subjects. Findings from this study suggests that α1- and α2-AMPK gene expression plays an important role in overweight/obese subjects. Future studies to explore the AMPK gene expressions in visceral adipose tissue and among underweight subjects would further close this knowledge gap.

The Inhibition of Zinc Excitotoxicity and AMPK Phosphorylation by a Novel Zinc Chelator, 2G11, Ameliorates Neuronal Death Induced by Global Cerebral Ischemia.

AMP-activated protein kinase (AMPK) is necessary for maintaining a positive energy balance and essential cellular processes such as glycolysis, gene transcription, glucose uptake, and several other biological functions. However, brain injury-induced energy and metabolic stressors, such as cerebral ischemia, increase AMPK phosphorylation. Phosphorylated AMPK contributes to excitotoxicity, oxidative, and metabolic problems. Furthermore, brain disease-induced release of zinc from synaptic vesicles contributes to neuronal damage via mechanisms including ROS production, apoptotic cell death, and DNA damage. For this reason, we hypothesized that regulating zinc accumulation and AMPK phosphorylation is critical for protection against global cerebral ischemia (GCI). Through virtual screening based on the structure of AMPK subunit alpha 2, we identified a novel compound, 2G11. In this study, we verified that 2G11 administration has neuroprotective effects via the blocking of zinc translocation and AMPK phosphorylation after GCI. As a result, we demonstrated that 2G11 protected hippocampal neurons against GCI and OGD/R-derived cellular damage. In conclusion, we propose that AMPK inhibition and zinc chelation by 2G11 may be a promising tool for preventing GCI-induced hippocampal neuronal death.

CircPRKAA1 activates a Ku80/Ku70/SREBP-1 axis driving de novo fatty acid synthesis in cancer cells.

Many metabolism-related genes undergo alternative splicing to generate circular RNAs, but their functions remain poorly understood. Here we report that circPRKAA1, a circular RNA (circRNA) derived from the α1 subunit of AMP-activated protein kinase (AMPK), fulfills a fundamental role in maintaining lipid homeostasis. circPRKAA1 expression facilitates fatty acid synthesis and promotes lipid storage through two coordinated functions. First, circPRKAA1 promotes a tetrameric complex between the Ku80/Ku70 heterodimer and the mature form of sterol regulatory element-binding protein 1 (mSREBP-1) to enhance the stability of mSREBP-1. Second, circPRKAA1 selectively binds to the promoters of the ACC1, ACLY, SCD1, and FASN genes to recruit mSREBP-1, upregulating their transcription and increasing fatty acid synthesis to promote cancer growth. circPRKAA1 biogenesis is negatively regulated by AMPK activity, with lower AMPK activation in hepatocellular carcinoma tissue frequently associated with elevated circPRKAA1 expression. This work identifies circPRKAA1 as an integral element of AMPK-regulated reprogramming of lipid metabolism in cancer cells.

Left ventricular non-compaction cardiomyopathy associated with the PRKAG2 mutation

Left ventricular non-compaction cardiomyopathy (LVNC) is one of the most common inherited cardiovascular diseases. The genetic backgrounds of most LVNC patients are not fully understood. We collected clinical data, family histories, and blood samples and performed genetic analysis using next-generation sequencing (NGS) from a Chinese family of 15 subjects. Clinically LVNC affected subjects showed marked cardiac phenotype heterogeneity. We found that these subjects with LVNC carried a missense heterozygous genetic mutation c.905G>A (p.R302Q) in γ2 subunit of AMP-activated protein kinase (PRKAG2) gene through NGS. Individuals without this mutation showed no symptoms or cardiac structural abnormalities related to LVNC. One subject was the victim of sudden cardiac death. To sum up, PRKAG2 mutation c.905G>A (p.R302Q) caused familial LVNC. Our results described a potentially pathogenic mutation associated with LVNC, which may further extend the spectrum of LVNC phenotypes related to PRKAG2 gene mutations.

The beta subunit of AMP-activated protein kinase is critical for cell cycle progression and parasite development in Toxoplasma gondii.

Toxoplasma gondii is a widespread eukaryotic pathogen that causes life-threatening diseases in humans and diverse animals. It has a complex life cycle with multiple developmental stages, which are timely adjusted according to growth conditions. But the regulatory mechanisms are largely unknown. Here we show that the AMP-activated protein kinase (AMPK), a key regulator of energy homeostasis in eukaryotes, plays crucial roles in controlling the cell cycle progression and bradyzoite development in Toxoplasma. Deleting the β regulatory subunit of AMPK in the type II strain ME49 caused massive DNA damage and increased spontaneous conversion to bradyzoites (parasites at chronic infection stage), leading to severe growth arrest and reduced virulence of the parasites. Under alkaline stress, all Δampkβ mutants converted to a bradyzoite-like state but the cell division pattern was significantly impaired, resulting in compromised parasite viability. Moreover, we found that phosphorylation of the catalytic subunit AMPKα was greatly increased in alkaline stressed parasites, whereas AMPKβ deletion mutants failed to do so. Phosphoproteomics found that many proteins with predicted roles in cell cycle and cell division regulation were differentially phosphorylated after AMPKβ deletion, under both normal and alkaline stress conditions. Together, these results suggest that the parasite AMPK has critical roles in safeguarding cell cycle progression, and guiding the proper exist of the cell cycle to form mature bradyzoites when the parasites are stressed. Consistent with this model, growth of parasites was not significantly altered when AMPKβ was deleted in a strain that was naturally reluctant to bradyzoite development.

AMPKβ isoform expression patterns in various adipocyte models and in relation to body mass index.

AMP-activated protein kinase (AMPK) activation is considered a useful strategy for the treatment of type 2 diabetes (T2D). It is unclear whether the expression and/or activity of AMPK in adipocytes is dysregulated in obesity. Also, the expression/activity pattern of AMPKβ isoforms, which are targets for AMPK activators, in adipocytes remains elusive. In this study we show that the two AMPKβ isoforms make roughly equal contributions to AMPK activity in primary human and mouse adipocytes, whereas in cultured 3T3-L1 adipocytes of mouse origin and in primary rat adipocytes, β1-associated activity clearly dominates. Additionally, we found that obesity is not associated with changes in AMPK subunit expression or kinase activity in adipocytes isolated from subcutaneous adipose tissue from individuals with various BMI.