Hierarchical activation of compartmentalized pools of AMPK depends on severity of nutrient or energy stress

Glucosylated cholesterol accumulates in atherosclerotic lesions and impacts macrophage immune response

Atherosclerosis can be described as a local acquired lysosomal storage disorder (LSD), resulting from the build-up of undegraded material in lysosomes. Atherosclerotic foam cells accumulate cholesterol (Chol) and glycosphingolipids (GSLs) within lysosomes. This constitutes the ideal milieu for the formation of a side product of lysosomal storage: glucosylated cholesterol (GlcChol), previously found in several LSDs. Using LC-MS/MS, we demonstrated that GlcChol is abundant in atherosclerotic lesions. Patients suffering from cardiovascular diseases presented unaltered plasma GlcChol levels but slightly elevated GlcChol/Chol ratios. Furthermore, we mimicked GlcChol formation in vitro by exposing macrophages (Mφ) to a pro-atherogenic oxidized cholesteryl ester, an atherosclerosis foam cell model. Additionally, Mφ exposed to GlcChol exhibited an enlarged and multinucleated phenotype. These Mφ present signs of decreased proliferation and reduced pro-inflammatory capacity. Mechanistically the process seems to be associated with the activation of the AMPK signalling pathway and the cyclin-dependent kinase inhibitor 1 (CDKN1A/p21), in response to DNA damage inflicted by reactive oxygen species (ROS). At the organelle level, exposure to GlcChol impacted the lysosomal compartment, resulting in the activation of the mTOR signalling pathway and lysosomal biogenesis mediated by the transcription factor EB (TFEB). This suggests that high concentrations of GlcChol impact cellular homeostasis. In contrast, under this threshold GlcChol formation most likely represents a relatively innocuous compensatory mechanism to cope with Chol and GSL build-up within lesions. Our findings demonstrate that glycosidase-mediated lipid modifications may play a role in the aetiology of genetic and acquired LSDs, warranting further investigation.

The non-canonical Smoothened-AMPK axis regulates Smaug1 biomolecular condensates

Biomolecular condensates (BMCs) emerge as important players in RNA regulation. The RNA-binding protein Smaug forms cytosolic BMCs in mammals, insects and yeasts and affects mitochondrial function and/or responses to nutrient deprivation. Here, we found that the non-canonical activation of the Smoothened (SMO)-AMPK pathway, which is known to affect energy metabolism, triggers the immediate disassembly of BMCs formed by a number of human and rodent Smaug orthologs, whereas processing bodies remain rather unaltered. A non-phosphorylatable SMO mutant abrogated the effect, involving SMO phosphorylation in human (h)Smaug1 (also known as SAMD4A) BMCs regulation. Three mechanistically different SMO ligands, namely SAG, GSA-10 and cyclopamine, elicited a similar response, which was blocked upon AMPK pharmacological inhibition. Polysome disassembly by puromycin halted Smaug1 BMC dissolution, thus suggesting that unbound transcripts became translationally active. Single-molecule fluorescent in situ hybridization illustrated the release of UQCRC1 mRNA. Finally, Smaug1 is a phosphoprotein bound by 14-3-3 proteins, and the competitive inhibitor difopein blocked the response to non-canonical SMO stimulation. We propose that the regulated condensation and dispersion of Smaug1 BMCs generate translational changes that contribute to metabolic regulation downstream of the non-canonical SMO-AMPK axis.

Energy metabolism in health and diseases

Energy metabolism is indispensable for sustaining physiological functions in living organisms and assumes a pivotal role across physiological and pathological conditions. This review provides an extensive overview of advancements in energy metabolism research, elucidating critical pathways such as glycolysis, oxidative phosphorylation, fatty acid metabolism, and amino acid metabolism, along with their intricate regulatory mechanisms. The homeostatic balance of these processes is crucial; however, in pathological states such as neurodegenerative diseases, autoimmune disorders, and cancer, extensive metabolic reprogramming occurs, resulting in impaired glucose metabolism and mitochondrial dysfunction, which accelerate disease progression. Recent investigations into key regulatory pathways, including mechanistic target of rapamycin, sirtuins, and adenosine monophosphate-activated protein kinase, have considerably deepened our understanding of metabolic dysregulation and opened new avenues for therapeutic innovation. Emerging technologies, such as fluorescent probes, nano-biomaterials, and metabolomic analyses, promise substantial improvements in diagnostic precision. This review critically examines recent advancements and ongoing challenges in metabolism research, emphasizing its potential for precision diagnostics and personalized therapeutic interventions. Future studies should prioritize unraveling the regulatory mechanisms of energy metabolism and the dynamics of intercellular energy interactions. Integrating cutting-edge gene-editing technologies and multi-omics approaches, the development of multi-target pharmaceuticals in synergy with existing therapies such as immunotherapy and dietary interventions could enhance therapeutic efficacy. Personalized metabolic analysis is indispensable for crafting tailored treatment protocols, ultimately providing more accurate medical solutions for patients. This review aims to deepen the understanding and improve the application of energy metabolism to drive innovative diagnostic and therapeutic strategies.

Biguanides antithetically regulate tumor properties by the dose-dependent mitochondrial reprogramming-driven c-Src pathway

The biguanide metformin attenuates mitochondrial oxidation and is proposed as an anti-cancer therapy. However, recent clinical studies suggest increased proliferation and fatty acid β-oxidation (FAO) in a subgroup of patients with breast cancer (BC) after metformin therapy. Considering that FAO can activate Src kinase in aggressive triple-negative BC (TNBC), we postulate that low-dose biguanide-driven AMPK-ACC-FAO signaling may activate the Src pathway in TNBC. The low bioavailability of metformin in TNBC xenografts mimics metformin's in vitro low-dose effect. Pharmacological or genetic inhibition of FAO significantly enhances the anti-tumor properties of biguanides. Lower doses of biguanides induce and higher doses suppress Src signaling. Dasatinib and metformin synergistically inhibit TNBC patient-derived xenograft growth, but not in high-fat diet-fed mice. This combination also suppresses TNBC metastatic progression. A combination of biguanides with Src inhibitors provides synergy to target metastatic TNBC suffering with limited treatment options.

Autophagy induced by metabolic processes leads to solid tumor cell metastatic dormancy and recurrence

A crucial cellular mechanism that has a complex impact on the biology of cancer, particularly in solid tumors, is autophagy. This review explores how metabolic processes trigger autophagy, which helps metastatic tumor cells go dormant and recur. During metastasis, tumor cells frequently encounter severe stressors, such as low oxygen levels and nutritional deprivation, which causes them to activate autophagy as a survival tactic. This process allows cancer stem cells (CSCs) to withstand severe conditions while also preserving their features. After years of dormancy, dormant disseminated tumor cells (DTCs) may reappear as aggressive metastatic cancers. The capacity of autophagy to promote resistance to treatments and avoid immune detection is intimately related to this phenomenon. According to recent research, autophagy promotes processes, such as the epithelial-to-mesenchymal transition (EMT) and helps build a pre-metastatic niche, which makes treatment strategies more challenging. Autophagy may be a promising therapeutic target because of its dual function as a tumor suppressor in early-stage cancer and a survival promoter in advanced stages. To effectively treat metastatic diseases, it is crucial to comprehend how metabolic processes interact with autophagy and affect tumor behavior. In order to find novel therapeutic approaches that can interfere with these processes and improve patient outcomes, this study highlights the critical need for additional investigation into the mechanisms by which autophagy controls tumor dormancy and recurrence.

Methods to Determine Lysosomal AMPK Activation

Recent studies have revealed that AMP-activated protein kinase (AMPK) can be activated in a non-canonical, AMP- and ADP-independent manner on the lysosome surface in response to low glucose. This novel mode of activation requires the participation of the glycolytic enzyme aldolase, which acts as a sensor of falling levels of the glucose metabolite fructose-1,6-bisphosphate (FBP). The FBP-unoccupied aldolase blocks the V subfamily of transient receptor potential (TRPV) cation channel to generate a local low calcium environment, under which conditions the inhibited TRPVs contact the lysosome-localized vacuolar ATPase (v-ATPase). This in turn triggers the translocation of AXIN and the associated liver kinase B1 (LKB1) to the lysosomal surface to activate AMPK thereon. Interestingly, such a lysosomal AMPK activating pathway has now been demonstrated to be shared by both the anti-diabetic drug metformin and the anti-tumor/inflammation drug mannose. Here, we describe the experimental conditions and procedures for distinguishing if a certain activation of AMPK is mediated by the lysosomal pathway. We will update the previously described methods for determining AXIN lysosomal translocation and the AMP:ATP and ADP:ATP ratios that are used for differentiating the lysosomal pathway from the canonical, AMP-dependent pathway [1, 2]. We also describe how to determine the lysosomal pH and the inhibition of TRPV activity that are prerequisite for triggering the lysosomal pathway during sensing of low glucose.

Higher AMPK activation in mouse oxidative compared with glycolytic muscle does not correlate with LKB1 or CaMKKβ expression

AMP-activated protein kinase (AMPK) is an energy-sensing serine/threonine kinase involved in metabolic regulation. It is phosphorylated by the upstream liver kinase B1 (LKB1) or calcium/calmodulin-dependent kinase kinase 2 (CaMKKβ). In cultured cells, AMPK activation correlates with LKB1 activity. The phosphorylation activates AMPK, shifting metabolism toward catabolism and promoting mitogenesis. In muscles, inactivity reduces AMPK activation, shifting the phenotype of oxidative muscles toward a more glycolytic profile. Here, we compared the basal level of AMPK activation in glycolytic and oxidative muscles and analyzed whether this relates to LKB1 or CaMKKβ. Using Western blotting, we assessed AMPK expression and phosphorylation in soleus, gastrocnemius (GAST), extensor digitorum longus (EDL), and heart from C57BL6J mice. We also assessed LKB1 and CaMKKβ expression, and CaMKKβ activity in tissue homogenates. AMPK activation was higher in oxidative (soleus and heart) than in glycolytic muscles (gastrocnemius and EDL). This correlated with AMPK α1-isoform expression, but not LKB1 and CaMKKβ. LKB1 expression was sex dependent and lower in male than female muscles. CaMKKβ expression was very low in skeletal muscles and did not phosphorylate AMPK in muscle lysates. The higher AMPK activation in oxidative muscles is in line with the fact that activated AMPK maintains an oxidative phenotype. However, this could not be explained by LKB1 and CaMKKβ. These results suggest that the regulation of AMPK activation is more complex in muscle than in cultured cells. As AMPK has been proposed as a therapeutic target for several diseases, future research should consider AMPK isoform expression and localization, and energetic compartmentalization.NEW & NOTEWORTHY It is important to understand how AMP-activated kinase, AMPK, is regulated, as it is a potential therapeutic target for several diseases. AMPK is activated by liver kinase B1, LKB1, and calcium/calmodulin-dependent kinase kinase 2, CaMKKβ. In cultured cells, AMPK activation correlates with LKB1 expression. In contrast, we show that AMPK-activation was higher in oxidative than glycolytic muscle, without correlating with LKB1 or CaMKKβ expression. Thus, AMPK regulation is more complex in highly compartmentalized muscle cells.

Lipid droplet formation induced by icaritin derivative IC2 promotes a combination strategy for cancer therapy

BACKGROUND

Lipid metabolism is crucial in cancer progression. Lipid droplets (LDs) generated in cancer cells can act as protective mechanisms through alleviating lipotoxicity under stress conditions. We previously developed IC2 from the Chinese medicine icaritin as an inhibitor of stearoyl-CoA desaturase 1 (SCD1). IC2 has been shown to disrupt lipid metabolism and inhibits cancer cell proliferation. However, the impact of IC2 on intracellular LDs and the potential of targeting LD formation for combination cancer therapy remain unexplored.

METHODS

LD formation in cancer cells was analyzed with oil red O or BODIPY staining by microscopy. LD quantification was normalized to the cell number. IC2-induced cellular responses were revealed by transcriptional analysis, real-time PCR, and immunoblotting. Mitochondrial functions were assessed by measuring ATP production and oxygen consumption. The lipid source for LD formation was studied using lipid transporter inhibitors or lipid deprivation. The effect of inhibiting LD formation on IC2's anti-tumor effects was evaluated using MTT assays and apoptosis assays, which was subsequently validated in an in vivo xenografted tumor model.

RESULTS

IC2 exerted anti-tumor effects, resulting in LD formation in various cancer cells. LD formation stimulated by IC2 was independent of extracellular lipid sources and did not result from increased de novo fatty acid (FA) synthesis within the cancer cells. Transcriptional analysis indicated that IC2 disturbed mitochondrial functions, which was confirmed by impaired mitochondrial membrane potential (MMP) and reduced capacity for ATP production and oxygen consumption. Moreover, IC2 treatment led to a greater accumulation of lipids in LDs outside the mitochondria compared with the control group. IC2 inhibited the proliferation of PC3 cells and promoted the apoptosis of the cancer cells. These effects were further enhanced after inhibiting the diacylglycerol acyltransferase 1 (DGAT1), a key intracellular enzyme involved in LD formation. In PC3-xenografted mice, the DGAT1 inhibitor augmented the IC2-induced reduction in tumor growth by modulating LD formation.

CONCLUSION

LD formation is a feedback response to IC2's anti-tumor effects, which compromises the anti-tumor actions. IC2's anti-tumor efficacy can be enhanced by combining it with inhibitors targeting LD formation. This strategy may be extended to other anti-tumor agents that regulate lipid metabolism.

Lithocholic acid binds TULP3 to activate sirtuins and AMPK to slow down ageing

Lithocholic acid (LCA) is accumulated in mammals during calorie restriction and it can activate AMP-activated protein kinase (AMPK) to slow down ageing1. However, the molecular details of how LCA activates AMPK and induces these biological effects are unclear. Here we show that LCA enhances the activity of sirtuins to deacetylate and subsequently inhibit vacuolar H+-ATPase (v-ATPase), which leads to AMPK activation through the lysosomal glucose-sensing pathway. Proteomics analyses of proteins that co-immunoprecipitated with sirtuin 1 (SIRT1) identified TUB-like protein 3 (TULP3), a sirtuin-interacting protein2, as a LCA receptor. In detail, LCA-bound TULP3 allosterically activates sirtuins, which then deacetylate the V1E1 subunit of v-ATPase on residues K52, K99 and K191. Muscle-specific expression of a V1E1 mutant (3KR), which mimics the deacetylated state, strongly activates AMPK and rejuvenates muscles in aged mice. In nematodes and flies, LCA depends on the TULP3 homologues tub-1 and ktub, respectively, to activate AMPK and extend lifespan and healthspan. Our study demonstrates that activation of the TULP3-sirtuin-v-ATPase-AMPK pathway by LCA reproduces the benefits of calorie restriction.

Lithocholic acid phenocopies anti-ageing effects of calorie restriction

Calorie restriction (CR) is a dietary intervention used to promote health and longevity1,2. CR causes various metabolic changes in both the production and the circulation of metabolites1; however, it remains unclear which altered metabolites account for the physiological benefits of CR. Here we use metabolomics to analyse metabolites that exhibit changes in abundance during CR and perform subsequent functional validation. We show that lithocholic acid (LCA) is one of the metabolites that alone can recapitulate the effects of CR in mice. These effects include activation of AMP-activated protein kinase (AMPK), enhancement of muscle regeneration and rejuvenation of grip strength and running capacity. LCA also activates AMPK and induces life-extending and health-extending effects in Caenorhabditis elegans and Drosophila melanogaster. As C. elegans and D. melanogaster are not able to synthesize LCA, these results indicate that these animals are able to transmit the signalling effects of LCA once administered. Knockout of AMPK abrogates LCA-induced phenotypes in all the three animal models. Together, we identify that administration of the CR-mediated upregulated metabolite LCA alone can confer anti-ageing benefits to metazoans in an AMPK-dependent manner.

Astragaloside IV intervenes multi-regulatory cell death forms against doxorubicin-induced cardiotoxicity by regulating AMPKα2 pathway

The clinical use of doxorubicin has been severely limited by doxorubicin-induced cardiotoxicity (DIC). Its mechanism is extremely complex and involves reactive oxygen species overgeneration, DNA damage, and aberrant inflammatory activity, which also involves multi-regulatory cell death mechanisms, including apoptosis, autophagy, and pyroptosis. These mechanisms overlap and crosstalk, resulting in the poor intervention of DIC injury. Astragaloside IV (Ast) has polybioactivity and mitigates DIC damage; however, the underlying mechanisms remain unknown. This study aimed to investigate whether Ast pretreatment (Ast-pre) could protect the myocardium against DIC damage and the underlying mechanisms. In particular, the relationship between Ast-pre, AMPKα2 activity, autophagy, apoptosis, and pyroptosis was explored. Firstly, DIC injury models were established using neonatal rat cardiomyocytes (NRCMs) and mice. And then the effects of adaptive autophagy, anti-pyroptosis and anti-apoptosis of Ast-pre were detected using multi-relevant indexes in NRCMs. Further, how does Ast-pre in AMPKα2 phosphorylation was explored. Finally, these results were validated by DIC injury in mice. Ast-pre, similar to disulfiram (pyroptosis inhibitor), effectively alleviated the inflammatory response, inhibited oxidative and energy stress, prevented mitochondrial dysfunction, and protected the myocardium resisting DIC damage, as demonstrated using multi-indexes. The protection of Ast-pre to DIC damage was almostly canceled by paclitaxel (pyroptosis inducer), 3-methyladenine (autophagy inhibitor), and pAD/AMPKα2-shRNA or compound C (AMPK inhibitor) to varying degrees. In conclusion, Ast-pre could upregulate and activate AMPKα2, enhance adaptive autophagy, and improve energy metabolism and mitochondrial function, thereby alleviate DIC-induced pyroptosis and apoptosis in NRCMs and mice.

Rab2A-mediated Golgi-lipid droplet interactions support very-low-density lipoprotein secretion in hepatocytes

Lipid droplets (LDs) serve as crucial hubs for lipid trafficking and metabolic regulation through their numerous interactions with various organelles. While the interplay between LDs and the Golgi apparatus has been recognized, their roles and underlying mechanisms remain poorly understood. Here, we reveal the role of Ras-related protein Rab-2A (Rab2A) in mediating LD-Golgi interactions, thereby contributing to very-low-density lipoprotein (VLDL) lipidation and secretion in hepatocytes. Mechanistically, our findings identify a selective interaction between Golgi-localized Rab2A and 17-beta-hydroxysteroid dehydrogenase 13 (HSD17B13) protein residing on LDs. This complex facilitates dynamic organelle communication between the Golgi apparatus and LDs, thus contributing to lipid transfer from LDs to the Golgi apparatus for VLDL2 lipidation and secretion. Attenuation of Rab2A activity via AMP-activated protein kinase (AMPK) suppresses the Rab2A-HSD17B13 complex formation, impairing LD-Golgi interactions and subsequent VLDL secretion. Furthermore, genetic inhibition of Rab2A and HSD17B13 in the liver reduces the serum triglyceride and cholesterol levels. Collectively, this study provides a new perspective on the interactions between the Golgi apparatus and LDs.

Dihydrolipoamide S-acetyltransferase activation alleviates diabetic kidney disease via AMPK-autophagy axis and mitochondrial protection

Diabetic kidney disease (DKD), a severe complication of diabetes marked by deregulated glucose metabolism, remains enigmatic in its pathogenesis. Herein, we delved into the functional role of Dihydrolipoamide S-acetyltransferase (DLAT), a pivotal E2 component of the pyruvate dehydrogenase complex (PDC), in the context of DKD. Our findings revealed a downregulation of DLAT in the kidneys of diabetic patients, correlating inversely with kidney function. Parallel downregulation was observed in both high-fat diet/streptozotocin (HFD/STZ) and db/db mouse models, as well as in human proximal tubular epithelial cells (HK-2) cultured under hyperglycemic conditions. To further elucidate the role of endogenous DLAT in DKD, we employed genetic ablation of Dlat in mouse models. Dlat haploinsufficient mice exhibited exacerbated renal dysfunction, structural damage, fibrosis, and mitochondrial dysfunction under DKD conditions. Consistent with these findings, modulation of DLAT expression in HK-2 cells highlighted its influence on fibrosis, with overexpression attenuating Fibronectin and Collagen I levels, while downregulation exacerbated fibrosis. Mechanistically, we discovered that DLAT activates mitochondria autophagy through the Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) signaling pathway, thereby mitigating mitochondrial dysfunction associated with DKD progression. Inhibition of AMPK abrogated the protective effects of DLAT against mitochondrial dysfunction and DKD. Notably, we identified Hyperforin (HPF), a phytochemical, as a potential therapeutic agent. HPF activates DLAT and AMPK, subsequently ameliorating renal dysfunction, injuries, and fibrosis in both in vivo and in vitro models. In summary, our study underscores the pivotal role of DLAT and AMPK in kidney health and highlights the therapeutic potential of HPF in treating DKD.

Mitochondrial structure and function: A new direction for the targeted treatment of chronic liver disease with Chinese herbal medicine

ETHNOPHARMACOLOGICAL RELEVANCE

Excessive fat accumulation, biological clock dysregulation, viral infections, and sustained inflammatory responses can lead to liver inflammation, fibrosis, and cancer, thus promoting the development of chronic liver disease. A comprehensive understanding of the etiological factors leading to chronic liver disease and the intrinsic mechanisms influencing its onset and progression can aid in identifying potential targets for targeted therapy. Mitochondria, as key organelles that maintain the metabolic homeostasis of the liver, provide an important foundation for exploring therapeutic targets for chronic liver disease. Recent studies have shown that active ingredients in herbal medicines and their natural products can modulate chronic liver disease by influencing the structure and function of mitochondria. Therefore, studying how Chinese herbs target mitochondrial structure and function to treat chronic liver diseases is of great significance.

AIM OF THE STUDY

Investigating the prospects of herbal medicine the Lens of chronic liver disease based on mitochondrial structure and function.

MATERIALS AND METHODS

A computerized search of PubMed was conducted using the keywords "mitochondrial structure", "mitochondrial function", "mitochondria and chronic liver disease", "botanicals, mitochondria and chronic liver disease".Data from the Web of Science and Science Direct databases were also included. The research findings regarding herbal medicines targeting mitochondrial structure and function for the treatment of chronic liver disease are summarized.

RESULTS

A computerized search of PubMed using the keywords "mitochondrial structure", "mitochondrial function", "mitochondria and chronic liver disease", "phytopharmaceuticals, mitochondria, and chronic liver disease", as well as the Web of Science and Science Direct databases was conducted to summarize information on studies of mitochondrial structure- and function-based Chinese herbal medicines for the treatment of chronic liver disease and to suggest that the effects of herbal medicines on mitochondrial division and fusion.The study suggested that there is much room for research on the influence of Chinese herbs on mitochondrial division and fusion.

CONCLUSIONS

Targeting mitochondrial structure and function is crucial for herbal medicine to combat chronic liver disease.

A Spatiotemporally Controlled and Mitochondria-Targeted Prodrug of Hydrogen Sulfide Enables Mild Mitochondrial Uncoupling for the Prevention of Lipid Deposition

Mild mitochondrial uncoupling offers therapeutic benefits for various diseases like obesity by regulating cellular energy metabolism. However, effective chemical intervention tools for inducing mild mitochondria-targeted uncoupling are limited. Herein, we have developed a mitochondria-targeted H2S prodrug M1 with a unique property of on-demand photoactivated generation of H2S accompanied by self-reporting fluorescence for real-time tracking. Upon photoirradiation, M1 decomposes in mitochondria to generate H2S and a turn-on fluorescent coumarin derivative for the visualization and quantification of H2S. M1 is confirmed to induce reactive oxygen species (ROS)-dependent mild mitochondrial uncoupling, activating mitochondria-associated adenosine monophosphate-activated protein kinase (AMPK) to suppress palmitic acid (PA)-induced lipid deposition in hepatocytes. The uncoupling functions induced by M1 are strictly controlled in mitochondria, representing a fresh strategy to prevent lipid deposition and improve metabolic syndrome by increasing cellular energy expenditure.

Spatiotemporal control of kinases and the biomolecular tools to trace activity

The delicate balance of cell physiology is implicitly tied to the expression and activation of proteins. Post-translational modifications offer a tool to dynamically switch protein activity on and off to orchestrate a wide range of protein-protein interactions to tune signal transduction during cellular homeostasis and pathological responses. There is a growing acknowledgment that subcellular locations of kinases define the spatial network of potential scaffolds, adaptors, and substrates. These highly ordered and localized biomolecular microdomains confer a spatially distinct bias in the outcomes of kinase activity. Furthermore, they may hold essential clues to the underlying mechanisms that promote disease. Developing tools to dissect the spatiotemporal activation of kinases is critical to reveal these mechanisms and promote the development of spatially targeted kinase inhibitors. Here, we discuss the spatial regulation of kinases, the tools used to detect their activity, and their potential impact on human health.

Compartmentalization in cardiomyocytes modulates creatine kinase and adenylate kinase activities

Intracellular molecules are transported by motor proteins or move by diffusion resulting from random molecular motion. Cardiomyocytes are packed with structures that are crucial for function, but also confine the diffusional spaces, providing cells with a means to control diffusion. They form compartments in which local concentrations are different from the overall, average concentrations. For example, calcium and cyclic AMP are highly compartmentalized, allowing these versatile second messengers to send different signals depending on their location. In energetic compartmentalization, the ratios of AMP and ADP to ATP are different from the average ratios. This is important for the performance of ATPases fuelling cardiac excitation-contraction coupling and mechanical work. A recent study suggested that compartmentalization modulates the activity of creatine kinase and adenylate kinase in situ. This could have implications for energetic signaling through, for example, AMP-activated kinase. It highlights the importance of taking compartmentalization into account in our interpretation of cellular physiology and developing methods to assess local concentrations of AMP and ADP to enhance our understanding of compartmentalization in different cell types.

Carnosol suppresses cardiomyocyte hypertrophy via promoting the activation of AMPK pathway

Pathological cardiac hypertrophy is associated with adverse cardiovascular events and can gradually lead to heart failure, arrhythmia, and even sudden death. However, the current development of treatment strategies has been unsatisfactory. Therefore, it is of great significance to find new and effective drugs for the treatment of myocardial hypertrophy. We found that carnosol can inhibit myocardial hypertrophy induced by PE stimulation, and the effect is very significant at 5 μM. Moreover, we demonstrated that 50 mg/kg of carnosol protect against cardiac hypertrophy and fibrosis induced by TAC surgery in mice. Mechanically, we proved that the inhibitory effect of carnosol on cardiac hypertrophy depends on its regulation on the phosphorylation activation of AMPK. In conclusion, our study suggested that carnosol may be a novel drug component for the treatment of pathological cardiac hypertrophy.

AMPK targets PDZD8 to trigger carbon source shift from glucose to glutamine

The shift of carbon utilization from primarily glucose to other nutrients is a fundamental metabolic adaptation to cope with decreased blood glucose levels and the consequent decline in glucose oxidation. AMP-activated protein kinase (AMPK) plays crucial roles in this metabolic adaptation. However, the underlying mechanism is not fully understood. Here, we show that PDZ domain containing 8 (PDZD8), which we identify as a new substrate of AMPK activated in low glucose, is required for the low glucose-promoted glutaminolysis. AMPK phosphorylates PDZD8 at threonine 527 (T527) and promotes the interaction of PDZD8 with and activation of glutaminase 1 (GLS1), a rate-limiting enzyme of glutaminolysis. In vivo, the AMPK-PDZD8-GLS1 axis is required for the enhancement of glutaminolysis as tested in the skeletal muscle tissues, which occurs earlier than the increase in fatty acid utilization during fasting. The enhanced glutaminolysis is also observed in macrophages in low glucose or under acute lipopolysaccharide (LPS) treatment. Consistent with a requirement of heightened glutaminolysis, the PDZD8-T527A mutation dampens the secretion of pro-inflammatory cytokines in macrophages in mice treated with LPS. Together, we have revealed an AMPK-PDZD8-GLS1 axis that promotes glutaminolysis ahead of increased fatty acid utilization under glucose shortage.

Metformin promotes anti-tumor immunity in STK11 mutant NSCLC through AXIN1-dependent upregulation of multiple nucleotide metabolites

Background

Metformin has pleiotropic effects beyond glucose reduction, including tumor inhibition and immune regulation. It enhanced the anti-tumor effects of programmed cell death protein 1 (PD-1) inhibitors in serine/threonine kinase 11 (STK11) mutant non-small cell lung cancer (NSCLC) through an axis inhibition protein 1 (AXIN1)-dependent manner. However, the alterations of tumor metabolism and metabolites upon metformin administration remain unclear.

Methods

We performed untargeted metabolomics using liquid chromatography (LC)-mass spectrometry (MS)/MS system and conducted cell experiments to verify the results of bioinformatics analysis.

Results

According to the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database, most metabolites were annotated into metabolism, including nucleotide metabolism. Next, the differentially expressed metabolites in H460 (refers to H460 cells), H460_met (refers to metformin-treated H460 cells), and H460_KO_met (refers to metformin-treated Axin1 -/- H460 cells) were distributed into six clusters based on expression patterns. The clusters with a reversed expression pattern upon metformin treatment were selected for further analysis. We screened out metabolic pathways through KEGG pathway enrichment analysis and found that multiple nucleotide metabolites enriched in this pathway were upregulated. Furthermore, these metabolites enhanced the cytotoxicity of activated T cells on H460 cells in vitro and can activate the stimulator of the interferon genes (STING) pathway independently of AXIN1.

Conclusion

Relying on AXIN1, metformin upregulated multiple nucleotide metabolites which promoted STING signaling and the killing of activated T cells in STK11 mutant NSCLC, indicating a potential immunotherapeutic strategy for STK11 mutant NSCLC.

Alpha lipoic acid diminishes migration and invasion in hepatocellular carcinoma cells through an AMPK-p53 axis

Hepatocellular carcinoma (HCC) associated with viral or metabolic liver diseases is a growing cancer without effective therapy. AMPK is downregulated in HCC and its activation diminishes tumor growth. Alpha lipoic acid (ALA), an indirect AMPK activator that inhibits hepatic steatosis, shows antitumor effects in different cancers. We aimed to study its putative action in liver-cancer derived cell lines through AMPK signaling. We performed cytometric studies for apoptosis and cell cycle, and 2D and 3D migration analysis in HepG2/C3A and Hep3B cells. ALA led to significant inhibition of cell migration/invasion only in HepG2/C3A cells. We showed that these effects depended on AMPK, and ALA also increased the levels and nuclear compartmentalization of the AMPK target p53. The anti-invasive effect of ALA was abrogated in stable-silenced (shTP53) versus isogenic-TP53 HepG2/C3A cells. Furthermore, ALA inhibited epithelial-mesenchymal transition (EMT) in control HepG2/C3A but not in shTP53 nor in Hep3B cells. Besides, we spotted that in patients from the HCC-TCGA dataset some EMT genes showed different expression patterns or survival depending on TP53. ALA emerges as a potent activator of AMPK-p53 axis in HCC cells, and it decreases migration/invasion by reducing EMT which could mitigate the disease in wild-type TP53 patients.

MLKL promotes hepatocarcinogenesis through inhibition of AMPK-mediated autophagy

The pseudokinase mixed lineage kinase domain-like (MLKL) is an essential component of the activation of the necroptotic pathway. Emerging evidence suggests that MLKL plays a key role in liver disease. However, how MLKL contributes to hepatocarcinogenesis has not been fully elucidated. Herein, we report that MLKL is upregulated in a diethylnitrosamine (DEN)-induced murine HCC model and is associated with human hepatocellular carcinomas. Hepatocyte-specific MLKL knockout suppresses the progression of hepatocarcinogenesis. Conversely, MLKL overexpression aggravates the initiation and progression of DEN-induced HCC. Mechanistic study reveals that deletion of MLKL significantly increases the activation of autophagy, thereby protecting against hepatocarcinogenesis. MLKL directly interacts with AMPKα1 and inhibits its activity independent of its necroptotic function. Mechanistically, MLKL serves as a bridging molecule between AMPKα1 and protein phosphatase 1B (PPM1B), thus enhancing the dephosphorylation of AMPKα1. Consistently, MLKL expression correlates negatively with AMPKα1 phosphorylation in HCC patients. Taken together, our findings highlight MLKL as a novel AMPK gatekeeper that plays key roles in inhibiting autophagy and driving hepatocarcinogenesis, suggesting that the MLKL-AMPKα1 axis is a potential therapeutic target for HCC.

Fine-tuning AMPK in physiology and disease using point-mutant mouse models

AMP-activated protein kinase (AMPK) is an evolutionarily conserved serine/threonine kinase that monitors the cellular energy status to adapt it to the fluctuating nutritional and environmental conditions in an organism. AMPK plays an integral part in a wide array of physiological processes, such as cell growth, autophagy and mitochondrial function, and is implicated in diverse diseases, including cancer, metabolic disorders, cardiovascular diseases and neurodegenerative diseases. AMPK orchestrates many different physiological outcomes by phosphorylating a broad range of downstream substrates. However, the importance of AMPK-mediated regulation of these substrates in vivo remains an ongoing area of investigation to better understand its precise role in cellular and metabolic homeostasis. Here, we provide a comprehensive overview of our understanding of the kinase function of AMPK in vivo, as uncovered from mouse models that harbor phosphorylation mutations in AMPK substrates. We discuss some of the inherent limitations of these mouse models, highlight the broader implications of these studies for understanding human health and disease, and explore the valuable insights gained that could inform future therapeutic strategies for the treatment of metabolic and non-metabolic disorders.

Specific regulation of epigenome landscape by metabolic enzymes and metabolites

Metabolism includes anabolism and catabolism, which play an essential role in many biological processes. Chromatin modifications are post-translational modifications of histones and nucleic acids that play important roles in regulating chromatin-associated processes such as gene transcription. There is a tight connection between metabolism and chromatin modifications. Many metabolic enzymes and metabolites coordinate cellular activities with alterations in nutrient availability by regulating gene expression through epigenetic mechanisms such as DNA methylation and histone modifications. The dysregulation of gene expression by metabolism and epigenetic modifications may lead to diseases such as diabetes and cancer. Recent studies reveal that metabolic enzymes and metabolites specifically regulate chromatin modifications, including modification types, modification residues and chromatin regions. This specific regulation has been implicated in the development of human diseases, yet the underlying mechanisms are only beginning to be uncovered. In this review, we summarise recent studies of the molecular mechanisms underlying the metabolic regulation of histone and DNA modifications and discuss how they contribute to pathogenesis. We also describe recent developments in technologies used to address the key questions in this field. We hope this will inspire further in-depth investigations of the specific regulatory mechanisms involved, and most importantly will shed lights on the development of more effective disease therapies.

Potential application of traditional Chinese medicine in age-related macular degeneration-focusing on mitophagy

Retinal pigment epithelial cell and neuroretinal damage in age-related macular degeneration (AMD) can lead to serious visual impairments and blindness. Studies have shown that mitophagy, a highly specialized cellular degradation system, is implicated in the pathogenesis of AMD. Mitophagy selectively eliminates impaired or non-functioning mitochondria via several pathways, such as the phosphatase and tensin homolog-induced kinase 1/Parkin, BCL2-interacting protein 3 and NIP3-like protein X, FUN14 domain-containing 1, and AMP-activated protein kinase pathways. This has a major impact on the maintenance of mitochondrial homeostasis. Therefore, the regulation of mitophagy could be a promising therapeutic strategy for AMD. Traditional Chinese medicine (TCM) uses natural products that could potentially prevent and treat various diseases, such as AMD. This review aims to summarize recent findings on mitophagy regulation pathways and the latest progress in AMD treatment targeting mitophagy, emphasizing methods involving TCM.

YAP upregulates AMPKα1 to induce cancer cell senescence

Yes-associated protein (YAP)-a major effector protein of the Hippo pathway- regulates cell proliferation, differentiation, apoptosis, and senescence. Amp-activated protein kinase (AMPK) is a key sensor that monitors cellular nutrient supply and energy status. Although YAP and AMPK are considered to regulate cellular senescence, it is still unclear whether AMPK is involved in YAP-regulated cellular senescence. Here, we found that YAP promoted AMPKα1 aggregation and localization around mitochondria by co-transfecting CFP-YAP and YFP-AMPKα1 plasmids. Subsequent live cell fluorescence resonance energy transfer (FRET) assay did not exhibit direct interaction between YAP and AMPKα1. FRET, Co-immunoprecipitation, and western blot experiments revealed that YAP directly bound to TEAD, enhancing the expression of AMPKα1 and p-AMPKα. Treatment with verteporfin inhibited YAP's binding to TEAD and reversed the elevated expression of AMPKα1 in the cells overexpressing CFP-YAP. Verteporfin also reduced the proportion of AMPKα1 puncta in the cells co-expressing CFP-YAP and YFP-AMPKα1. In addition, the AMPKα1 puncta were demonstrated to inhibit cell viability, autophagy, and proliferation, and ultimately promote cell senescence. In conclusion, YAP binds to TEAD to upregulate AMPKα1 and promotes the formation of AMPKα1 puncta around mitochondria under the condition of co-expression of CFP-YAP and YFP-AMPKα1, in which AMPKα1 puncta lead to cellular senescence.

Mitochondrial Kinase Signaling for Cardioprotection

Myocardial ischemia/reperfusion injury is reduced by cardioprotective adaptations such as local or remote ischemic conditioning. The cardioprotective stimuli activate signaling cascades, which converge on mitochondria and maintain the function of the organelles, which is critical for cell survival. The signaling cascades include not only extracellular molecules that activate sarcolemmal receptor-dependent or -independent protein kinases that signal at the plasma membrane or in the cytosol, but also involve kinases, which are located to or within mitochondria, phosphorylate mitochondrial target proteins, and thereby modify, e.g., respiration, the generation of reactive oxygen species, calcium handling, mitochondrial dynamics, mitophagy, or apoptosis. In the present review, we give a personal and opinionated overview of selected protein kinases, localized to/within myocardial mitochondria, and summarize the available data on their role in myocardial ischemia/reperfusion injury and protection from it. We highlight the regulation of mitochondrial function by these mitochondrial protein kinases.

Sestrin2 can alleviate endoplasmic reticulum stress to improve traumatic brain injury by activating AMPK/mTORC1 signaling pathway

Traumatic brain injury (TBI), as a serious central nervous system disease, can result in severe neurological dysfunction or even disability and death of patients. The early and effective intervention of secondary brain injury can improve the prognosis of TBI. Endoplasmic reticulum (ER) stress is one of the main reasons to recover TBI. ER stress inhibition may be beneficial in treating TBI. Sestrin2 is a crucial regulator of ER stress, and its activation can significantly improve TBI. In this paper, we analyze the biological function of sestrin2, the latest findings on ER stress, and the relationship between ER stress and TBI. We elucidate the relationship of sestrin2 inhibiting ER stress via activating the AMP-activated protein kinase (AMPK)/mammalian target of rapamycin complex 1 (MTORC1) signaling. Finally, we elaborate on the possible role of sestrin2 in TBI and explain how its activation potentially improves TBI.

TBC1D23 mediates Golgi-specific LKB1 signaling

Liver kinase B1 (LKB1), an evolutionarily conserved serine/threonine kinase, is a master regulator of the AMPK subfamily and controls cellular events such as polarity, proliferation, and energy homeostasis. Functions and mechanisms of the LKB1-AMPK axis at specific subcellular compartments, such as lysosome and mitochondria, have been established. AMPK is known to be activated at the Golgi; however, functions and regulatory mechanisms of the LKB1-AMPK axis at the Golgi apparatus remain elusive. Here, we show that TBC1D23, a Golgi-localized protein that is frequently mutated in the neurodevelopment disorder pontocerebellar hypoplasia (PCH), is specifically required for the LKB1 signaling at the Golgi. TBC1D23 directly interacts with LKB1 and recruits LKB1 to Golgi, promoting Golgi-specific activation of AMPK upon energy stress. Notably, Golgi-targeted expression of LKB1 rescues TBC1D23 deficiency in zebrafish models. Furthermore, the loss of LKB1 causes neurodevelopmental abnormalities in zebrafish, which partially recapitulates defects in TBC1D23-deficient zebrafish, and LKB1 sustains normal neuronal development via TBC1D23 interaction. Our study uncovers a regulatory mechanism of the LKB1 signaling, and reveals that a disrupted Golgi-LKB1 signaling underlies the pathogenesis of PCH.

The scaffold protein AXIN1: gene ontology, signal network, and physiological function

AXIN1, has been initially identified as a prominent antagonist within the WNT/β-catenin signaling pathway, and subsequently unveiled its integral involvement across a diverse spectrum of signaling cascades. These encompass the WNT/β-catenin, Hippo, TGFβ, AMPK, mTOR, MAPK, and antioxidant signaling pathways. The versatile engagement of AXIN1 underscores its pivotal role in the modulation of developmental biological signaling, maintenance of metabolic homeostasis, and coordination of cellular stress responses. The multifaceted functionalities of AXIN1 render it as a compelling candidate for targeted intervention in the realms of degenerative pathologies, systemic metabolic disorders, cancer therapeutics, and anti-aging strategies. This review provides an intricate exploration of the mechanisms governing mammalian AXIN1 gene expression and protein turnover since its initial discovery, while also elucidating its significance in the regulation of signaling pathways, tissue development, and carcinogenesis. Furthermore, we have introduced the innovative concept of the AXIN1-Associated Phosphokinase Complex (AAPC), where the scaffold protein AXIN1 assumes a pivotal role in orchestrating site-specific phosphorylation modifications through interactions with various phosphokinases and their respective substrates.

Research Progress on the Mechanism of Milk Fat Synthesis in Cows and the Effect of Conjugated Linoleic Acid on Milk Fat Metabolism and Its Underlying Mechanism: A Review

Milk fat synthesis in cows mainly includes the synthesis of short- and medium-chain fatty acids, the uptake, transport, and activation of long-chain fatty acids (LCFAs), the synthesis of triglycerides, and the synthesis of the genes, transcription factors, and signaling pathways involved. Although the various stages of milk fat synthesis have been outlined in previous research, only partial processes have been revealed. CLA consists of an aggregation of positional and geometric isomers of linoleic fatty acid, and the accumulated evidence suggests that the two isomers of the active forms of CLA (cis-9, trans-11 conjugated linoleic acid and trans-10, cis-12 conjugated linoleic acid, abbreviated as c9, t11-CLA and t10, c12-CLA) can reduce the fat content in milk by regulating lipogenesis, fatty acid (FA) uptake, oxidation, and fat synthesis. However, the mechanism through which CLA inhibits milk fat synthesis is unique, with most studies focusing only on the effects of CLA on one of the genes, transcription factors, or signaling pathways involved. In this study, we summarized the structure and function of classic genes and pathways (mTOR, SREBP, AMPK, and PPARG) and new genes or pathways (THRSP, METTL3, ELOVL, and LPIN1) involved in each stage of milk fat synthesis and demonstrated the interactions between genes and pathways. We also examined the effects of other substances (melanin, nicotinic acid, SA, etc.). Furthermore, we evaluated the influence of β-sitosterol, sodium butyrate, Met arginine, and Camellia oleifera Abel on milk fat synthesis to improve the mechanism of milk fat synthesis in cows and provide a mechanistic reference for the use of CLA in inhibiting milk fat biosynthesis.

Molecular complexity of mammary glands development: a review of lactogenic differentiation in epithelial cells

The mammary gland is a dynamic organ with various physiological processes like cellular proliferation, differentiation, and apoptosis during the pregnancy-lactation-involution cycle. It is essential to understand the molecular changes during the lactogenic differentiation of mammary epithelial cells (MECs, the milk-synthesizing cells). The MECs are organized as luminal milk-secreting cells and basal myoepithelial cells (responsible for milk ejection by contraction) that form the alveoli. The branching morphogenesis and lactogenic differentiation of the MECs prepare the gland for lactation. This process is governed by many molecular mediators including hormones, growth factors, cytokines, miRNAs, regulatory proteins, etc. Interestingly, various signalling pathways guide lactation and understanding these molecular transitions from pregnancy to lactation will help researchers design further research. Manipulation of genes responsible for milk synthesis and secretion will promote augmentation of milk yield in dairy animals. Identifying protein signatures of lactation will help develop strategies for persistent lactation and shortening the dry period in farm animals. The present review article discusses in details the physiological and molecular changes occurring during lactogenic differentiation of MECs and the associated hormones, regulatory proteins, miRNAs, and signalling pathways. An in-depth knowledge of the molecular events will aid in developing engineered cellular models for studies related to mammary gland diseases of humans and animals.

Glycolysis maintains AMPK activation in sorafenib-induced Warburg effect

Hepatocellular carcinoma (HCC) is the second deadly cancer in the world and still lacks curative treatment. Aerobic glycolysis, or Warburg effect, is a major resistance mechanism induced by first-line treatment of HCC, sorafenib, and is regulated by the master regulator of metabolism, AMPK. Activation of AMPK is required for resistance; however, activation dynamics of AMPK and its regulation is rarely studied. Engineering cells to express an AMPK activity biosensor, we monitor AMPK activation in single HCC cells in a high throughput manner during sorafenib-induced drug resistance. Sorafenib induces transient activation of AMPK, duration of which is dependent on glucose. Inhibiting glycolysis shortens AMPK activation; whereas increasing glycolysis increases its activation duration. Our data highlight that activation duration of AMPK is important for cancer evasion of therapeutic treatment and glycolysis is a key regulator of activation duration of AMPK.

Low glucose metabolite 3-phosphoglycerate switches PHGDH from serine synthesis to p53 activation to control cell fate

Glycolytic intermediary metabolites such as fructose-1,6-bisphosphate can serve as signals, controlling metabolic states beyond energy metabolism. However, whether glycolytic metabolites also play a role in controlling cell fate remains unexplored. Here, we find that low levels of glycolytic metabolite 3-phosphoglycerate (3-PGA) can switch phosphoglycerate dehydrogenase (PHGDH) from cataplerosis serine synthesis to pro-apoptotic activation of p53. PHGDH is a p53-binding protein, and when unoccupied by 3-PGA interacts with the scaffold protein AXIN in complex with the kinase HIPK2, both of which are also p53-binding proteins. This leads to the formation of a multivalent p53-binding complex that allows HIPK2 to specifically phosphorylate p53-Ser46 and thereby promote apoptosis. Furthermore, we show that PHGDH mutants (R135W and V261M) that are constitutively bound to 3-PGA abolish p53 activation even under low glucose conditions, while the mutants (T57A and T78A) unable to bind 3-PGA cause constitutive p53 activation and apoptosis in hepatocellular carcinoma (HCC) cells, even in the presence of high glucose. In vivo, PHGDH-T57A induces apoptosis and inhibits the growth of diethylnitrosamine-induced mouse HCC, whereas PHGDH-R135W prevents apoptosis and promotes HCC growth, and knockout of Trp53 abolishes these effects above. Importantly, caloric restriction that lowers whole-body glucose levels can impede HCC growth dependent on PHGDH. Together, these results unveil a mechanism by which glucose availability autonomously controls p53 activity, providing a new paradigm of cell fate control by metabolic substrate availability.

Pretreatment with Kahweol Attenuates Sepsis-Induced Acute Lung Injury via Improving Mitochondrial Homeostasis in a CaMKKII/AMPK-Dependent Pathway

SCOPE

It is well-established that dysregulated mitochondrial homeostasis in macrophages leads to inflammation, oxidative stress, and tissue damage, which are essential in the pathogenesis of sepsis-induced acute lung injury (ALI). Kahweol, a natural diterpene extracted from coffee beans, reportedly possesses anti-inflammatory and mitochondrial protective properties. Herein, the study investigates whether Kahweol can alleviate sepsis-induced ALI and explore the underlying mechanisms.

METHODS AND RESULTS

C57BL/6J mice are intraperitoneally injected with lipopolysaccharide (LPS) for 12 h to induce ALI. Pretreatment with kahweol by gavage for 5 days significantly alleviates lung pathological injury, inflammation, and oxidative stress, accompanied by shifting the dynamic process of mitochondria from fission to fusion, enhancing mitophagy, and activating AMPK. To investigate the underlying molecular mechanisms, differentiated THP-1 cells are cultured in a medium containing Kahweol for 12 h prior to LPS exposure, yielding consistent findings with the in vivo results. Moreover, AMPK inhibitors abrogate the above effects, indicating Kahweol acts in an AMPK-dependent manner. Furthermore, the study explores how Kahweol activates AMPK and finds that this process is mediated by CamKK II.

CONCLUSION

Pretreatment with Kahweol attenuates sepsis-induced acute lung injury via improving mitochondrial homeostasis in a CaMKKII/AMPK-dependent pathway and may be a potential candidate to prevent sepsis-induced ALI.

Metabolic switch from glycogen to lipid in the liver maintains glucose homeostasis in neonatal mice

Neonates strive to acquire energy when the continuous transplacental nutrient supply ceases at birth, whereas milk consumption takes hours to start. Using murine models, we report the metabolic switches in the first days of life, with an unexpected discovery of glucose as the universal fuel essential for neonatal life. Blood glucose quickly drops as soon as birth, but immediately rebounds even before suckling and maintains stable afterward. Meanwhile, neonatal liver undergoes drastic metabolic changes, from extensive glycogenolysis before suckling to dramatically induced fatty acid oxidation (FAO) and gluconeogenesis after milk suckling. Unexpectedly, blocking hepatic glycogenolysis only caused a transient hypoglycemia before milk suckling without causing lethality. Limiting lipid supply in milk (low-fat milk, [LFM]) using Cidea-/- mice, however, led to a chronic and severe hypoglycemia and consequently claimed neonatal lives. While fat replenishment rescued LFM-caused neonatal lethality, the rescue effects were abolished by blocking FAO or gluconeogenesis, pointing to a funneling of lipids and downstream metabolites into glucose as the essential fuel. Finally, glucose administration also rescued LFM-caused neonatal lethality, independent on FAO or gluconeogenesis. Therefore, our results show that the liver works as an energy conversion center to maintain blood glucose homeostasis in neonates, providing theoretical basis for managing infant hypoglycemia.

The involvement of AMP-activated protein kinase α in regulating glycolysis in Yesso scallop Patinopecten yessoensis under high temperature stress

AMP-activated protein kinase α subunit (AMPKα), the central regulatory molecule of energy metabolism, plays an important role in maintaining energy homeostasis and helping cells to resist the influence of various adverse factors. In the present study, an AMPKα was identified from Yesso scallop Patinopecten yessoensis (PyAMPKα). The open reading frame (ORF) of PyAMPKα was of 1599 bp encoding a putative polypeptide of 533 amino acid residues with a typical KD domain, a α-AID domain and a α-CTD domain. The deduced amino acid sequence of PyAMPKα shared 59.89-74.78% identities with AMPKαs from other species. The mRNA transcripts of PyAMPKα were found to be expressed in haemocytes and all the examined tissues, including gill, mantle, gonad, adductor muscle and hepatopancreas, with the highest expression level in adductor muscle. PyAMPKα was mainly located in cytoplasm of scallop haemocytes. At 3 h after high temperature stress treatment (25 °C), the mRNA transcripts of PyAMPKα, the phosphorylation level of PyAMPKα at Thr170 and the lactic acid (LD) content in adductor muscle all increased significantly, while the glycogen content decreased significantly. The activity of pyruvate kinase (PyPK) and the relative mRNA expression level of phosphofructokinase (PyPFK) were significantly up-regulated at 3 h after high temperature stress treatment (25 °C). Furthermore, the PyAMPKα activator AICAR could effectively upregulate the phosphorylation level of PyAMPKα, and increase activities of PyPFK and pyruvate kinase (PyPK). Meanwhile the glycogen content also declined under AICAR treatment. These results collectively suggested that PyAMPKα was involved in the high temperature stress response of scallops by enhancing glycolysis pathway of glycogen. These results would be helpful for understanding the functions of PyAMPKα in maintaining energy homeostasis under high temperature stress in scallops.

The Beneficial and Adverse Effects of Autophagic Response to Caloric Restriction and Fasting

Each cell is equipped with a conserved housekeeping mechanism, known as autophagy, to recycle exhausted materials and dispose of injured organelles via lysosomal degradation. Autophagy is an early-stage cellular response to stress stimuli in both physiological and pathological situations. It is thought that the promotion of autophagy flux prevents host cells from subsequent injuries by removing damaged organelles and misfolded proteins. As a correlate, the modulation of autophagy is suggested as a therapeutic approach in diverse pathological conditions. Accumulated evidence suggests that intermittent fasting or calorie restriction can lead to the induction of adaptive autophagy and increase longevity of eukaryotic cells. However, prolonged calorie restriction with excessive autophagy response is harmful and can stimulate a type II autophagic cell death. Despite the existence of a close relationship between calorie deprivation and autophagic response in different cell types, the precise molecular mechanisms associated with this phenomenon remain unclear. Here, we aimed to highlight the possible effects of prolonged and short-term calorie restriction on autophagic response and cell homeostasis.

AMPKα1 Deficiency in Astrocytes from a Rat Model of ALS Is Associated with an Altered Metabolic Resilience

Alterations in the activity of the regulator of cell metabolism AMP-activated protein kinase (AMPK) have been reported in motor neurons from patients and animal models of amyotrophic lateral sclerosis (ALS). Considering the key role played by astrocytes in modulating energy metabolism in the nervous system and their compromised support towards neurons in ALS, we examined whether a putative alteration in AMPK expression/activity impacted astrocytic functions such as their metabolic plasticity and glutamate handling capacity. We found a reduced expression of AMPK mRNA in primary cultures of astrocytes derived from transgenic rats carrying an ALS-associated mutated superoxide dismutase (hSOD1G93A). The activation of AMPK after glucose deprivation was reduced in hSOD1G93A astrocytes compared to non-transgenic. This was accompanied by a lower increase in ATP levels and increased vulnerability to this insult, although the ATP production rate did not differ between the two cell types. Furthermore, soliciting the activity of glutamate transporters was found to induce similar AMPK activity in these cells. However, manipulation of AMPK activity did not influence glutamate transport. Together, these results suggest that the altered AMPK responsiveness in ALS might be context dependent and may compromise the metabolic adaptation of astrocytes in response to specific cellular stress.

Hierarchical inhibition of mTORC1 by glucose starvation-triggered AXIN lysosomal translocation and by AMPK

When glucose is replete, mammalian/mechanistic target of rapamycin complex 1 (mTORC1) is active and anchored to the lysosomal surface via the two GTPases, Ras-related GTPase (RAG) and Ras homolog enriched in brain (Rheb), which are regulated by Ragulator and tuberous sclerosis complex 2 (TSC2), respectively. When glucose is low, aldolase senses low fructose-1,6-bisphosphate level and promotes the translocation of AXIN-liver kinase B1 (LKB1) to the lysosomal surface, which leads to the activation of AMP-activated protein kinase (AMPK) and the inhibition of RAGs, sundering mTORC1 from the lysosome and causing its inactivation. AMPK can also inactivate mTORC1 by phosphorylating Raptor and TSC2. However, the hierarchy of AXIN- and AMPK-mediated inhibition of mTORC1 remains poorly defined. Here, we show that AXIN translocation does not require AMPK expression or activity. In glucose starvation conditions, knockout of AXIN extended the half-life of mTORC1 inhibition from 15 to 60 min, whereas knockout of AMPK only extended it to 30 min. RAGBGTP (constitutively active RAGB) almost entirely blocked the lysosomal dissociation and inhibition of mTORC1 under glucose starvation, but it did not inhibit AMPK, indicating that under these conditions, it is AXIN lysosomal translocation that inhibits mTORC1, and it does so via inhibition of RAGs. 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), a mimetic of AMP, which activates both cytosolic AMPK and lysosomal AMPK, fully inhibited mTORC1 even when it is stably anchored to the lysosome by RAGBGTP, whereas glucose starvation mildly inhibited such anchored mTORC1. Together, we demonstrate that the lysosomal translocation of AXIN plays a primary role in glucose starvation-triggered inhibition of mTORC1 by inhibiting RAGs, and that AMPK activity inhibits mTORC1 through phosphorylating Raptor and TSC2, especially under severe stress.

WSSV exploits AMPK to activate mTORC2 signaling for proliferation by enhancing aerobic glycolysis

AMPK plays significant roles in the modulation of metabolic reprogramming and viral infection. However, the detailed mechanism by which AMPK affects viral infection is unclear. The present study aims to determine how AMPK influences white spot syndrome virus (WSSV) infection in shrimp (Marsupenaeus japonicus). Here, we find that AMPK expression and phosphorylation are significantly upregulated in WSSV-infected shrimp. WSSV replication decreases remarkably after knockdown of Ampkα and the shrimp survival rate of AMPK-inhibitor injection shrimp increases significantly, suggesting that AMPK is beneficial for WSSV proliferation. Mechanistically, WSSV infection increases intracellular Ca2+ level, and activates CaMKK, which result in AMPK phosphorylation and partial nuclear translocation. AMPK directly activates mTORC2-AKT signaling pathway to phosphorylate key enzymes of glycolysis in the cytosol and promotes expression of Hif1α to mediate transcription of key glycolytic enzyme genes, both of which lead to increased glycolysis to provide energy for WSSV proliferation. Our findings reveal a novel mechanism by which WSSV exploits the host CaMKK-AMPK-mTORC2 pathway for its proliferation, and suggest that AMPK might be a target for WSSV control in shrimp aquaculture.

Trigonochinene E promotes lysosomal biogenesis and enhances autophagy via TFEB/TFE3 in human degenerative NP cells against oxidative stress

BACKGROUND

Macroautophagy (henceforth autophagy) is the major form of autophagy, which delivers intracellular cargo to lysosomes for degradation. Considerable research has revealed that the impairment of lysosomal biogenesis and autophagic flux exacerbates the development of autophagy-related diseases. Therefore, reparative medicines restoring lysosomal biogenesis and autophagic flux in cells may have therapeutic potential against the increasing prevalence of these diseases.

PURPOSE

The aim of the present study was thus to explore the effect of trigonochinene E (TE), an aromatic tetranorditerpene isolated from Trigonostemon flavidus, on lysosomal biogenesis and autophagy and to elucidate the potential underlying mechanism.

METHODS

Four human cell lines, HepG2, nucleus pulposus (NP), HeLa and HEK293 cells were applied in this study. The cytotoxicity of TE was evaluated by MTT assay. Lysosomal biogenesis and autophagic flux induced by 40 μM TE were analyzed using gene transfer techniques, western blotting, real-time PCR and confocal microscopy. Immunofluorescence, immunoblotting and pharmacological inhibitors/activators were applied to determine the changes in the protein expression levels in mTOR, PKC, PERK, and IRE1α signaling pathways.

RESULTS

Our results showed that TE promotes lysosomal biogenesis and autophagic flux by activating the transcription factors of lysosomes, transcription factor EB (TFEB) and transcription factor E3 (TFE3). Mechanistically, TE induces TFEB and TFE3 nuclear translocation through an mTOR/PKC/ROS-independent and endoplasmic reticulum (ER) stress-mediated pathway. The PERK and IRE1α branches of ER stress are crucial for TE-induced autophagy and lysosomal biogenesis. Whereas TE activated PERK, which mediated calcineurin dephosphorylation of TFEB/TFE3, IRE1α was activated and led to inactivation of STAT3, which further enhanced autophagy and lysosomal biogenesis. Functionally, knockdown of TFEB or TFE3 impairs TE-induced lysosomal biogenesis and autophagic flux. Furthermore, TE-induced autophagy protects NP cells from oxidative stress to ameliorate intervertebral disc degeneration (IVDD).

CONCLUSIONS

Here, our study showed that TE can induce TFEB/TFE3-dependent lysosomal biogenesis and autophagy via the PERK-calcineurin axis and IRE1α-STAT3 axis. Unlike other agents regulating lysosomal biogenesis and autophagy, TE showed limited cytotoxicity, thereby providing a new direction for therapeutic opportunities to use TE to treat diseases with impaired autophagy-lysosomal pathways, including IVDD.

Rapid metabolic reprogramming mediated by the AMP-activated protein kinase during the lytic cycle of Toxoplasma gondii

The ubiquitous pathogen Toxoplasma gondii has a complex lifestyle with different metabolic activities at different stages that are intimately linked to the parasitic environments. Here we identified the eukaryotic regulator of cellular homeostasis AMP-activated protein kinase (AMPK) in Toxoplasma and discovered its role in metabolic programming during parasite's lytic cycle. The catalytic subunit AMPKα is quickly phosphorylated after the release of intracellular parasites to extracellular environments, driving energy-producing catabolism to power parasite motility and invasion into host cells. Once inside host cells, AMPKα phosphorylation is reduced to basal level to promote a balance between energy production and biomass synthesis, allowing robust parasite replication. AMPKγ depletion abolishes AMPKα phosphorylation and suppresses parasite growth, which can be partially rescued by overexpressing wildtype AMPKα but not the phosphorylation mutants. Thus, through the cyclic reprogramming by AMPK, the parasites' metabolic needs at each stage are satisfied and the lytic cycle progresses robustly.

TRAF3: A novel regulator of mitochondrial physiology and metabolic pathways in B lymphocytes

Mitochondria, the organelle critical for cell survival and metabolism, are exploited by cancer cells and provide an important therapeutic target in cancers. Mitochondria dynamically undergo fission and fusion to maintain their diverse functions. Proteins controlling mitochondrial fission and fusion have been recognized as essential regulators of mitochondrial functions, mitochondrial quality control, and cell survival. In a recent proteomic study, we identified the key mitochondrial fission factor, MFF, as a new interacting protein of TRAF3, a known tumor suppressor of multiple myeloma and other B cell malignancies. This interaction recruits the majority of cytoplasmic TRAF3 to mitochondria, allowing TRAF3 to regulate mitochondrial morphology, mitochondrial functions, and mitochondria-dependent apoptosis in resting B lymphocytes. Interestingly, recent transcriptomic, metabolic and lipidomic studies have revealed that TRAF3 also vitally regulates multiple metabolic pathways in B cells, including phospholipid metabolism, glucose metabolism, and ribonucleotide metabolism. Thus, TRAF3 emerges as a novel regulator of mitochondrial physiology and metabolic pathways in B lymphocytes and B cell malignancies. Here we review current knowledge in this area and discuss relevant clinical implications.

Compartmentalization, a key mechanism controlling the multitasking role of the SnRK1 complex

SNF1-related protein kinase 1 (SnRK1), the plant ortholog of mammalian AMP-activated protein kinase/fungal (yeast) Sucrose Non-Fermenting 1 (AMPK/SNF1), plays a central role in metabolic responses to reduced energy levels in response to nutritional and environmental stresses. SnRK1 functions as a heterotrimeric complex composed of a catalytic α- and regulatory β- and βγ-subunits. SnRK1 is a multitasking protein involved in regulating various cellular functions, including growth, autophagy, stress response, stomatal development, pollen maturation, hormone signaling, and gene expression. However, little is known about the mechanism whereby SnRK1 ensures differential execution of downstream functions. Compartmentalization has been recently proposed as a new key mechanism for regulating SnRK1 signaling in response to stimuli. In this review, we discuss the multitasking role of SnRK1 signaling associated with different subcellular compartments.

AMPK-dependent phosphorylation of MTFR1L regulates mitochondrial morphology

Mitochondria are dynamic organelles that undergo membrane remodeling events in response to metabolic alterations to generate an adequate mitochondrial network. Here, we investigated the function of mitochondrial fission regulator 1-like protein (MTFR1L), an uncharacterized protein that has been identified in phosphoproteomic screens as a potential AMP-activated protein kinase (AMPK) substrate. We showed that MTFR1L is an outer mitochondrial membrane-localized protein modulating mitochondrial morphology. Loss of MTFR1L led to mitochondrial elongation associated with increased mitochondrial fusion events and levels of the mitochondrial fusion protein, optic atrophy 1. Mechanistically, we show that MTFR1L is phosphorylated by AMPK, which thereby controls the function of MTFR1L in regulating mitochondrial morphology both in mammalian cell lines and in murine cortical neurons in vivo. Furthermore, we demonstrate that MTFR1L is required for stress-induced AMPK-dependent mitochondrial fragmentation. Together, these findings identify MTFR1L as a critical mitochondrial protein transducing AMPK-dependent metabolic changes through regulation of mitochondrial dynamics.