Insulin inhibits AMPK activity and phosphorylates AMPK Ser⁴⁸⁵/⁴⁹¹ through Akt in hepatocytes, myotubes and incubated rat skeletal muscle

Excess Potassium Promotes Autophagy to Maintain the Immunosuppressive Capacity of Myeloid-Derived Suppressor Cells Independent of Arginase 1

Potassium ions (K+) are critical electrolytes that regulate multiple functions in immune cells. Recent studies have shown that the elevated concentration of extracellular potassium in the tumor interstitial fluid limits T cell effector function and suppresses the anti-tumor capacity of tumor-associated macrophages (TAMs). The effect of excess potassium on the biology of myeloid-derived suppressor cells (MDSCs), another important immune cell component of the tumor microenvironment (TME), is unknown. Here, we present data showing that increased concentrations of potassium chloride (KCl), as the source of K+ ions, facilitate autophagy by increasing the expression of the autophagosome marker LC3β. Simultaneously, excess potassium ions significantly decrease the expression of arginase I (Arg I) and inducible nitric oxide synthase (iNOS) without reducing the ability of MDSCs to suppress T cell proliferation. Further investigation reveals that excess K+ ions decrease the expression of the transcription factor C/EBP-β and alter the expression of phosphorylated kinases. While excess K+ ions downregulated the expression levels of phospho-AMPKα (pAMPKα), it increased the levels of pAKT and pERK. Additionally, potassium increased mitochondrial respiration as measured by the oxygen consumption rate (OCR). Interestingly, all these alterations induced by K+ ions were abolished by the autophagy inhibitor 3-methyladenine (3-MA). Our results suggest that hyperosmotic stress caused by excess K+ ions regulate the mitochondrial respiration and signaling pathways in MDSCs to trigger the process of autophagy to support MDSCs' immunosuppressive function by mechanisms independent of Arg I and iNOS. Overall, our in vitro and ex vivo findings offer valuable insights into the adaptations of MDSCs within the K+ ion-rich TME, which has important implications for MDSCs-targeted therapies.

PAK4 phosphorylates and inhibits AMPKα to control glucose uptake

Our recent studies have identified p21-activated kinase 4 (PAK4) as a key regulator of lipid catabolism in the liver and adipose tissue, but its role in glucose homeostasis in skeletal muscle remains to be explored. In this study, we find that PAK4 levels are highly upregulated in the skeletal muscles of diabetic humans and mice. Skeletal muscle-specific Pak4 ablation or administering the PAK4 inhibitor in diet-induced obese mice retains insulin sensitivity, accompanied by AMPK activation and GLUT4 upregulation. We demonstrate that PAK4 promotes insulin resistance by phosphorylating AMPKα2 at Ser491, thereby inhibiting AMPK activity. We additionally show that skeletal muscle-specific expression of a phospho-mimetic mutant AMPKα2S491D impairs glucose tolerance, while the phospho-inactive mutant AMPKα2S491A improves it. In summary, our findings suggest that targeting skeletal muscle PAK4 may offer a therapeutic avenue for type 2 diabetes.

The interaction between 20-hydroxyecdysone and AMPK through PI3K activation in Chinese mitten crab, Eriocheir sinensis

In crustaceans, the steroid hormone 20-hydroxyecdysone (20E) initiates molting, and the molting process is also regulated by energy metabolism. AMPK is an energy sensor and plays a critical role in systemic energy balance. Here, the regulatory mechanism in the interaction between 20E and AMPK was investigated in Chinese mitten crab, Eriocheir sinensis. The results showed that the 20E concentration and the mRNA expression levels of 20E receptors in hepatopancreas were down-regulated post AMPK activator (AICAR) treatment, and were up-regulated after AMPK inhibitor (Compound C) injection in crabs. Besides, the molt-inhibiting hormone (MIH) gene expression in eyestalk showed the opposite patterns in response to the AICAR and Compound C treatment, respectively. Further investigation found that there was a significant reduction in 20E concentration post PI3K inhibitor (LY294002) treatment, and the phosphorylation level of PI3K was increased in hepatopancreas after AMPK inhibitor injection. On the other hand, the positive regulation of PI3K-mediated activation of AMPK was also observed, the phosphorylation levels of AMPKα, AMPKβ and PI3K in hepatopancreas were significantly increased post 20E injection. In addition, the phosphorylation levels of AMPKα and AMPKβ induced by 20E were decreased after the injection of PI3K inhibitor. Taken together, these results suggest that the regulatory cross-talk between 20E and AMPK is likely to act through PI3K pathway in E. sinensis, which appeared to be helpful for a better understanding in molting regulation.

Ethnicity-related differences in mitochondrial regulation by insulin stimulation in diabetes

Mitochondrial dysfunction has long been implicated in the development of insulin resistance, which is a hallmark of type 2 diabetes. However, recent studies reveal ethnicity-related differences in mitochondrial processes, underscoring the need for nuance in studying mitochondrial dysfunction and insulin sensitivity. Furthermore, the higher prevalence of type 2 diabetes among African Americans and individuals of African descent has brought attention to the role of ethnicity in disease susceptibility. In this review, which covers existing literature, genetic studies, and clinical data, we aim to elucidate the complex relationship between mitochondrial alterations and insulin stimulation by considering how mitochondrial dynamics, contact sites, pathways, and metabolomics may be differentially regulated across ethnicities, through mechanisms such as single nucleotide polymorphisms (SNPs). In addition to achieving a better understanding of insulin stimulation, future studies identifying novel regulators of mitochondrial structure and function could provide valuable insights into ethnicity-dependent insulin signaling and personalized care.

Increased regional activity of a pro-autophagy pathway in schizophrenia as a contributor to sex differences in the disease pathology

Based on recent genome-wide association studies, it is theorized that altered regulation of autophagy contributes to the pathophysiology of schizophrenia and bipolar disorder. As activity of autophagy-regulatory pathways is controlled by discrete phosphorylation sites on the relevant proteins, phospho-protein profiling is one of the few approaches available for enabling a quantitative assessment of autophagic activity in the brain. Despite this, a comprehensive phospho-protein assessment in the brains of schizophrenia and bipolar disorder subjects is currently lacking. Using this direction, our broad screening identifies an increase in AMP-activated protein kinase (AMPK)-mediated phospho-activation of the pro-autophagy protein beclin-1 solely in the prefrontal cortex of female, but not male, schizophrenia subjects. Using a reverse translational approach, we surprisingly find that this increase in beclin-1 activity facilitates synapse formation and enhances cognition. These findings are interpreted in the context of human studies demonstrating that female schizophrenia subjects have a lower susceptibility to cognitive dysfunction than males.

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.

Insulin signalling regulates Pink1 mRNA localization via modulation of AMPK activity to support PINK1 function in neurons

Mitochondrial quality control failure is frequently observed in neurodegenerative diseases. The detection of damaged mitochondria by stabilization of PTEN-induced kinase 1 (PINK1) requires transport of Pink1 messenger RNA (mRNA) by tethering it to the mitochondrial surface. Here, we report that inhibition of AMP-activated protein kinase (AMPK) by activation of the insulin signalling cascade prevents Pink1 mRNA binding to mitochondria. Mechanistically, AMPK phosphorylates the RNA anchor complex subunit SYNJ2BP within its PDZ domain, a phosphorylation site that is necessary for its interaction with the RNA-binding protein SYNJ2. Notably, loss of mitochondrial Pink1 mRNA association upon insulin addition is required for PINK1 protein activation and its function as a ubiquitin kinase in the mitophagy pathway, thus placing PINK1 function under metabolic control. Induction of insulin resistance in vitro by the key genetic Alzheimer risk factor apolipoprotein E4 retains Pink1 mRNA at the mitochondria and prevents proper PINK1 activity, especially in neurites. Our results thus identify a metabolic switch controlling Pink1 mRNA localization and PINK1 activity via insulin and AMPK signalling in neurons and propose a mechanistic connection between insulin resistance and mitochondrial dysfunction.

Allium ampeloprasum var. Porrum (Alliaceae) Improves Metabolic and Reproductive Disorders Associated with Polycystic Ovary Syndrome in Wistar Rats

To provide scientific evidence of the efficacy of Allium ampeloprasum against female infertility, the effects of the aqueous extract of the said plant (AE) were evaluated in rats with letrozole-induced polycystic ovary syndrome (PCOS). AE was administered orally to PCOS rats at doses of 192, 384, and 768 mg/kg. The positive control was co-treated with clomiphene citrate (1 mg/kg) and metformin (200 mg/kg). Normal and negative controls received distilled water. The vaginal contents of rats were examined daily under a microscope before (7 days) and during treatment. Treatments were administered orally for 15 days, and then, 6 rats from each group were sacrificed for biochemical and histological analyses. The remaining rats were mated with males of proven fertility for 5 days. The daily examination of vaginal smears allowed the evaluation of fertility index. After parturition, additional fertility parameters were determined. Results showed that in PCOS rats, AE decreased body weight (p < 0.001), abdominal fat weight (p < 0.001), serum levels of LH (p < 0.001), testosterone (p < 0.001), total cholesterol (p < 0.05), and LDL cholesterol (p < 0.01). HDL cholesterol increased and atherogenic indices decreased (p < 0.001). The number of Graafian follicles and corpora lutea increased, while cystic (p < 0.001) and atretic (p < 0.05) follicles decreased. AE also decreased oxidative stress in the ovaries, restored the estrous cycle, induced uterine epithelial cell hypertrophy, and improved fertility. These effects were attributed to phenols, flavonoids, terpenoids, and anthocyanins present in AE. The overall results justify the traditional use of A. ampeloprasum against female infertility and suggest its potential use as a dietary supplement for PCOS patients.

Human anaerobic microbiome: a promising and innovative tool in cancer prevention and treatment by targeting pyruvate metabolism

INTRODUCTION

Even in present-day times, cancer is one of the most fatal diseases. People are overwhelmed by pricey chemotherapy, immunotherapy, and other costly cancer therapies in poor and middle-income countries. Cancer cells grow under anaerobic and hypoxic conditions. Pyruvate is the final product of the anaerobic glycolysis pathway, and many cancer cells utilize pyruvate for their growth and development. The anaerobic microbiome produces many anti-cancer substances that can act as anti-tumor agents and are both feasible and of low cost. There are different mechanisms of action of the anaerobic microbiome, such as the production of short-chain fatty acids (SCFAs), and competition for the anaerobic environment includes the metabolic product pyruvate to form lactic acid for energy.

KEY FINDINGS

In this review, we have summarized the role of the metabolic approach of the anaerobic human microbiome in cancer prevention and treatment by interfering with cancer metabolite pyruvate. SCFAs possess decisive outcomes in condoning almost all the hallmarks of cancer and helping the spread of cancer to other body parts. Studies have demonstrated the impact and significance of using SCFA, which results from anaerobic bacteria, as an anti-cancer agent. Anaerobic bacteria-based cancer therapy has become a promising approach to treat cancer using obligate and facultative anaerobic bacteria because of their ability to penetrate and increase in an acidic hypoxic environment.

SIGNIFICANCE

This review attempts to provide the interconnection of cancer metabolism and anaerobic microbiome metabolism with a focus on pyruvate metabolism to understand and design unique anaerobic microbiota-based therapy for cancer patients.

Metabolic control by AMPK in white adipose tissue

White adipose tissue (WAT) plays an important role in the integration of whole-body metabolism by storing fat and mobilizing triacylglycerol when needed. The released free fatty acids can then be oxidized by other tissues to provide ATP. AMP-activated protein kinase (AMPK) is a key regulator of metabolic pathways, and can be targeted by a new generation of direct, small-molecule activators. AMPK activation in WAT inhibits insulin-stimulated lipogenesis and in some situations also inhibits insulin-stimulated glucose uptake, but AMPK-induced inhibition of β-adrenergic agonist-stimulated lipolysis might need to be re-evaluated in vivo. The lack of dramatic effects of AMPK activation on basal metabolism in WAT could be advantageous when treating type 2 diabetes with pharmacological pan-AMPK activators.

AMPK and the Endocrine Control of Metabolism

Complex multicellular organisms require a coordinated response from multiple tissues to maintain whole-body homeostasis in the face of energetic stressors such as fasting, cold, and exercise. It is also essential that energy is stored efficiently with feeding and the chronic nutrient surplus that occurs with obesity. Mammals have adapted several endocrine signals that regulate metabolism in response to changes in nutrient availability and energy demand. These include hormones altered by fasting and refeeding including insulin, glucagon, glucagon-like peptide-1, catecholamines, ghrelin, and fibroblast growth factor 21; adipokines such as leptin and adiponectin; cell stress-induced cytokines like tumor necrosis factor alpha and growth differentiating factor 15, and lastly exerkines such as interleukin-6 and irisin. Over the last 2 decades, it has become apparent that many of these endocrine factors control metabolism by regulating the activity of the AMPK (adenosine monophosphate-activated protein kinase). AMPK is a master regulator of nutrient homeostasis, phosphorylating over 100 distinct substrates that are critical for controlling autophagy, carbohydrate, fatty acid, cholesterol, and protein metabolism. In this review, we discuss how AMPK integrates endocrine signals to maintain energy balance in response to diverse homeostatic challenges. We also present some considerations with respect to experimental design which should enhance reproducibility and the fidelity of the conclusions.

Phosphorylation of AMPKα at Ser485/491 Is Dependent on Muscle Contraction and Not Muscle-Specific IGF-I Overexpression

Glucose is an important fuel for highly active skeletal muscles. Increased adenosine monophosphate (AMP)/adenosine triphosphate (ATP) ratios during repetitive contractions trigger AMP-activated protein kinase (AMPK), indicated by phosphorylation of AMPKαThr172, which promotes glucose uptake to support heightened energy needs, but it also suppresses anabolic processes. Inhibition of AMPK can occur by protein kinase B (AKT)-mediated phosphorylation of AMPKαSer485/491, releasing its brake on growth. The influence of insulin-like growth factor I (IGF-I) on glucose uptake and its interplay with AMPK activation is not well understood. Thus, the goal of this study was to determine if increased muscle IGF-I altered AMPKα phosphorylation and activity during muscle contraction. Adult male mice harboring the rat Igf1a cDNA regulated by the fast myosin light chain promoter (mIgf1+/+) and wildtype littermates (WT) were used in the study. mIgf1+/+ mice had enhanced glucose tolerance and insulin-stimulated glucose uptake, but similar exercise capacity. Fatiguing stimulations of extensor digitorum longus (EDL) muscles resulted in upregulated AMPKα phosphorylation at both Thr172 and Ser485/491 in WT and mIgf1+/+ muscles. No differences in the phosphorylation response of the downstream AMPK target TBC1D1 were observed, but phosphorylation of raptor was significantly higher only in WT muscles. Further, total raptor content was elevated in mIgf1+/+ muscles. The results show that high muscle IGF-I can enhance glucose uptake under resting conditions; however, in contracting muscle, it is not sufficient to inhibit AMPK activity.

Alterations in skeletal muscle morphology and mechanics in juvenile male Sprague Dawley rats exposed to a high-fat high-sucrose diet

Although once a health concern largely considered in adults, the obesity epidemic is now prevalent in pediatric populations. While detrimental effects on skeletal muscle function have been seen in adulthood, the effects of obesity on skeletal muscle function in childhood is not clearly understood. The purpose of this study was to determine if the consumption of a high-fat high-sucrose (HFS) diet, starting in the post-weaning period, leads to changes in skeletal muscle morphology and mechanics after 14 weeks on the HFS diet. Eighteen 3-week-old male CD-Sprague Dawley rats were randomly assigned to a HFS (C-HFS, n = 10) or standard chow diet (C-CHOW, n = 8). Outcome measures included: weekly energy intake, activity levels, oxygen consumption, body mass, body composition, metabolic profile, serum protein levels, and medial gastrocnemius gene expression, morphology, and mechanics. The main findings from this study were that C-HFS rats: (1) had a greater body mass and percent body fat than control rats; (2) showed early signs of metabolic syndrome; (3) demonstrated potential impairment in muscle remodeling; (4) produced lower relative muscle force; and (5) had a shift in the force-length relationship, indicating that the medial gastrocnemius had shorter muscle fiber lengths compared to those of C-CHOW rats. Based on the results of this study, we conclude that exposure to a HFS diet led to increased body mass, body fat percentage, and early signs of metabolic syndrome, resulting in functional deficits in MG of childhood rats.

Numerous Trigger-like Interactions of Kinases/Protein Phosphatases in Human Skeletal Muscles Can Underlie Transient Processes in Activation of Signaling Pathways during Exercise

Optimizing physical training regimens to increase muscle aerobic capacity requires an understanding of the internal processes that occur during exercise that initiate subsequent adaptation. During exercise, muscle cells undergo a series of metabolic events that trigger downstream signaling pathways and induce the expression of many genes in working muscle fibers. There are a number of studies that show the dependence of changes in the activity of AMP-activated protein kinase (AMPK), one of the mediators of cellular signaling pathways, on the duration and intensity of single exercises. The activity of various AMPK isoforms can change in different directions, increasing for some isoforms and decreasing for others, depending on the intensity and duration of the load. This review summarizes research data on changes in the activity of AMPK, Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), and other components of the signaling pathways in skeletal muscles during exercise. Based on these data, we hypothesize that the observed changes in AMPK activity may be largely related to metabolic and signaling transients rather than exercise intensity per se. Probably, the main events associated with these transients occur at the beginning of the exercise in a time window of about 1-10 min. We hypothesize that these transients may be partly due to putative trigger-like kinase/protein phosphatase interactions regulated by feedback loops. In addition, numerous dynamically changing factors, such as [Ca²⁺], metabolite concentration, and reactive oxygen and nitrogen species (RONS), can shift the switching thresholds and change the states of these triggers, thereby affecting the activity of kinases (in particular, AMPK and CaMKII) and phosphatases. The review considers the putative molecular mechanisms underlying trigger-like interactions. The proposed hypothesis allows for a reinterpretation of the experimental data available in the literature as well as the generation of ideas to optimize future training regimens.

Effect of Obesity on Masticatory Muscle Activity and Rhythmic Jaw Movements Evoked by Electrical Stimulation of Different Cortical Masticatory Areas

This study investigates rhythmic jaw movement (RJM) patterns and masticatory muscle activities during electrical stimulation in two cortical masticatory areas in obese male Zucker rats (OZRs), compared to their counterparts-lean male Zucker rats (LZRs) (seven each). At the age of 10 weeks, electromyographic (EMG) activity of the right anterior digastric muscle (RAD) and masseter muscles, and RJMs were recorded during repetitive intracortical micro-stimulation in the left anterior and posterior parts of the cortical masticatory area (A-area and P-area, respectively). Only P-area-elicited RJMs, which showed a more lateral shift and slower jaw-opening pattern than A-area-elicited RJMs, were affected by obesity. During P-area stimulation, the jaw-opening duration was significantly shorter (p < 0.01) in OZRs (24.3 ms) than LZRs (27.9 ms), the jaw-opening speed was significantly faster (p < 0.05) in OZRs (67.5 mm/s) than LZRs (50.8 mm/s), and the RAD EMG duration was significantly shorter (p < 0.01) in OZRs (5.2 ms) than LZR (6.9 ms). The two groups had no significant difference in the EMG peak-to-peak amplitude and EMG frequency parameters. This study shows that obesity affects the coordinated movement of masticatory components during cortical stimulation. While other factors may be involved, functional change in digastric muscle is partly involved in the mechanism.

Mechanistic insights on impact of Adenosine monophosphate-activated protein kinase (AMPK) mediated signalling pathways on cerebral ischemic injury

Cerebral ischemia is the primary cause of morbidity and mortality worldwide due to the perturbations in the blood supply to the brain. The brain triggers a cascade of complex metabolic and cellular defects in response to ischemic stress. However, due to the disease heterogeneity and complexity, ischemic injury's metabolic and cellular pathologies remain elusive, and the link between various pathological mechanisms is difficult to determine. Efforts to develop effective treatments for these disorders have yielded limited efficacy, with no proper cure available to date. Recent clinical and experimental research indicates that several neuronal diseases commonly coexist with metabolic dysfunction, which may aggravate neurological symptoms. As a result, it stands to a reason that metabolic hormones could be a potential therapeutic target for major NDDs. Moreover, fasting signals also influence the circadian clock, as AMPK phosphorylates and promotes the degradation of the photo-sensing receptor (cryptochrome). Here, the interplay of AMPK signaling between metabolic regulation and neuronal death and its role for pathogenesis and therapeutics has been studied. We have also highlighted a significant signaling pathway, i.e., the adenosine monophosphate-activated protein kinase (AMPK) involved in the relationship between the metabolism and ischemia, which could be used as a target for future studies therapeutics, and review some of the clinical progress in this area.

The ABA/LANCL Hormone/Receptor System in the Control of Glycemia, of Cardiomyocyte Energy Metabolism, and in Neuroprotection: A New Ally in the Treatment of Diabetes Mellitus?

Abscisic acid (ABA), long known as a plant stress hormone, is present and functionally active in organisms other than those pertaining to the land plant kingdom, including cyanobacteria, fungi, algae, protozoan parasites, lower Metazoa, and mammals. The ancient, cross-kingdom role of this stress hormone allows ABA and its signaling pathway to control cell responses to environmental stimuli in diverse organisms such as marine sponges, higher plants, and humans. Recent advances in our knowledge about the physiological role of ABA and of its mammalian receptors in the control of energy metabolism and mitochondrial function in myocytes, adipocytes, and neuronal cells allow us to foresee therapeutic applications for ABA in the fields of pre-diabetes, diabetes, and cardio- and neuro-protection. Vegetal extracts titrated in their ABA content have shown both efficacy and tolerability in preliminary clinical studies. As the prevalence of glucose intolerance, diabetes, and cardiovascular and neurodegenerative diseases is steadily increasing in both industrialized and rapidly developing countries, new and cost-efficient therapeutics to combat these ailments are much needed to ensure disease-free aging for the current and future working generations.

PP2Cα positively regulates neuronal insulin signalling and aggravates neuronal insulin resistance

PP2Cα is one of the newly identified isoforms of metal-dependent protein phosphatases (PPM). The role of this phosphatase in neuronal insulin signalling is completely unknown. In the present study, we show insulin-mediated rapid upregulation of a protein of the insulin signalling cascade, PP2Cα, in mouse N2a cells and human SH-SY5Y cells. By contrast, such PP2Cα upregulation is not observed in insulin-resistant conditions despite insulin stimulation. Here, we report that, under insulin-sensitive and insulin-resistant conditions, the translation of PP2Cα was regulated by insulin through c-Jun N-terminal kinase. PP2Cα in turn dephosphorylated a novel inhibitory site of insulin receptor substrate-1 at Ser522 and AMP-activated protein kinase, hence positively regulating neuronal insulin signalling and insulin resistance.

Current insights in molecular characterization of non-alcoholic fatty liver disease and treatment

There is a continuously rising incidence of non-alcoholic fatty liver disease (NAFLD) around the world, which parallels the increasing incidence of metabolic diseases. NAFLD is a range of liver conditions that contains simple non-alcoholic fatty liver and advanced non-alcoholic steatohepatitis. In serious cases, NAFLD may develop into cirrhosis or even liver cancer. NAFLD has an intense relationship with metabolic syndrome, type 2 diabetes mellitus. It is known that gut microbiota, and functional molecules such as adenosine monophosphate-activated protein kinase JNK, and peroxisome proliferator-activated receptors (PPARs) in progressing and treating NAFLD. Traditionally, the conventional and effective therapeutic strategy is lifestyle intervention. Nowadays, new medicines targeting specific molecules, such as farnesoid X receptor, PPARs, and GLP-1 receptor, have been discovered and shown beneficial effects on patients with NAFLD. In this article, we focus on the molecular mechanisms and therapeutic approaches to NAFLD.

Coordination of the AMPK, Akt, mTOR, and p53 Pathways under Glucose Starvation

Glucose is a direct energy source for eukaryotic cells, and its deficiency elicits complex stress responses and diverse cellular outcomes. Although several signaling pathways involved have been identified, how they coordinately dictate the cell fate remains obscure. We propose a minimal network model for the cellular response to glucose restriction, characterizing the glucose uptake and signaling of the AMPK, Akt, mTOR, and p53 pathways. We demonstrate that in the presence of sufficient growth factors and amino acids, cells may undergo proliferation, senescence, or apoptosis, depending on the extracellular glucose level. AMPK is first activated upon glucose limitation, activating p53 to induce cell-cycle arrest; possibly, cells resume proliferation after timely glucose restoration. For long-term energy stress, cell senescence is maintained by low/intermediate levels of p53 and persistent activation of mTOR and Akt, or cells commit apoptosis when the proteins undergo biphasic dynamics, e.g., p53 switches from intermediate levels to high levels while mTOR and Akt become inactivated in the later phase. The biphasic dynamics of p53 are associated with flipping of two bistable switches. Appropriate mTOR levels are required for optimal cell-fate decision. This work suggests that senescence and apoptosis occur sequentially in glucose-depleted cells, and a theoretical framework is provided for exploring the cellular response to energy stress.

Metabolic Regulation of Mitochondrial Protein Biogenesis from a Neuronal Perspective

Neurons critically depend on mitochondria for ATP production and Ca2+ buffering. They are highly compartmentalized cells and therefore a finely tuned mitochondrial network constantly adapting to the local requirements is necessary. For neuronal maintenance, old or damaged mitochondria need to be degraded, while the functional mitochondrial pool needs to be replenished with freshly synthesized components. Mitochondrial biogenesis is known to be primarily regulated via the PGC-1α-NRF1/2-TFAM pathway at the transcriptional level. However, while transcriptional regulation of mitochondrial genes can change the global mitochondrial content in neurons, it does not explain how a morphologically complex cell such as a neuron adapts to local differences in mitochondrial demand. In this review, we discuss regulatory mechanisms controlling mitochondrial biogenesis thereby making a case for differential regulation at the transcriptional and translational level. In neurons, additional regulation can occur due to the axonal localization of mRNAs encoding mitochondrial proteins. Hitchhiking of mRNAs on organelles including mitochondria as well as contact site formation between mitochondria and endolysosomes are required for local mitochondrial biogenesis in axons linking defects in any of these organelles to the mitochondrial dysfunction seen in various neurological disorders.

Shared pathobiology identifies AMPK as a therapeutic target for obesity and autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common Mendelian kidney disease, affecting approximately one in 1,000 births and accounting for 5% of end-stage kidney disease in developed countries. The pathophysiology of ADPKD is strongly linked to metabolic dysregulation, which may be secondary to defective polycystin function. Overweight and obesity are highly prevalent in patients with ADPKD and constitute an independent risk factor for progression. Recent studies have highlighted reduced AMP-activated protein kinase (AMPK) activity, increased mammalian target of rapamycin (mTOR) signaling, and mitochondrial dysfunction as shared pathobiology between ADPKD and overweight/obesity. Notably, mTOR and AMPK are two diametrically opposed sensors of energy metabolism that regulate cell growth and proliferation. However, treatment with the current generation of mTOR inhibitors is poorly tolerated due to their toxicity, making clinical translation difficult. By contrast, multiple preclinical and clinical studies have shown that pharmacological activation of AMPK provides a promising approach to treat ADPKD. In this narrative review, we summarize the pleiotropic functions of AMPK as a regulator of cellular proliferation, macromolecule metabolism, and mitochondrial biogenesis, and discuss the potential for pharmacological activation of AMPK to treat ADPKD and obesity-related kidney disease.

Effect of arginine supplementation on the production of milk fat in dairy cows

Arginine, one of the conditionally essential AA, has been reported to affect fat synthesis and metabolism in nonruminant animals by influencing adenosine monophosphate activated protein kinase (AMPK) in some organs. In dairy cows, the effect of Arg on milk fat production is not clear, and any potential mechanism that underlies the effect is unknown. We tested the hypothesis that Arg infusion would improve the production of milk fat, and explored possible mechanism that might underlie any effect. We used 6 healthy lactating cows at 20 ± 2 d in milk, in fourth parity, with a body weight of 508 ± 14 kg, body condition score of 3.0 ± 0, and a milk yield of 30.6 ± 1.8 kg/d (mean ± standard deviation). The cows were blocked by days in milk and milk yield and each cow received 3 treatments in a replicated 3 × 3 Latin square design, with each of the experimental periods lasting 7 d with a 14-d washout between each period. The treatments, delivered in random order, were (1) infusion of saline (control); (2) infusion of 0.216 mol/d of l-Arg in saline (Arg); (3) infusion of 0.868 mol/d of l-Ala in saline (the Arg and Ala treatments were iso-nitrogenous) through a jugular vein. On the last day of each experimental period, blood was sampled to measure insulin, nitric oxide, glucose, and nonesterified fatty acid, and the liver and mammary gland were biopsied to measure the expression of genes. Milk yield was recorded, and milk fat percentage was measured daily during each of the experimental periods. The yield and composition of fatty acid (FA) in milk was measured daily on the last 3 d during each of the experimental periods. The data were analyzed using a mixed model with treatment as a fixed factor, and cow, period, and block as random factors. The daily milk yield and milk fat yield when the cows were infused with Arg were 2.2 kg and 76 g, respectively, higher than that in control, and 1.8 kg and 111 g, respectively, higher than that in Ala. When the cows were infused with Arg they had higher concentration and yield of de novo synthesized FA, than when they received the control or Ala infusions, although milk fat percentage, daily feed intake, and the digestibility of nutrients were not affected by treatment. The serum concentration of nitric oxide and insulin were higher during Arg than during control or Ala, with no difference between control and Ala. In the liver, the expression of the genes coding for AMPK (PRKAA1, PRKAB1, and PRKAG1) and genes related to the oxidation of FA were higher during Arg than during control or Ala, whereas in the mammary gland the expression PRKAB1 was lowest, and the expression of genes involved in the synthesis of milk fat were highest, during Arg infusion. The results suggest the intravenous infusion of Arg enhanced the production of milk fat by promoting the de novo synthesis of FA and increasing milk yield.

Liver PP2A-Cα Protects From Parenteral Nutrition-associated Hepatic Steatosis

BACKGROUND & AIMS

Parenteral nutrition (PN) is a lifesaving therapy for patients with intestinal failure. Hepatic steatosis is a potentially fatal complication of long-term PN, but the involved pathological mechanisms are incompletely unclarified. Herein, we identify the role of protein phosphatase 2A (PP2A) in the pathogenesis of parenteral nutrition-associated hepatic steatosis (PNAHS).

METHODS

Proteomic/phosphoproteomic analyses of liver samples from patients with PNAHS were applied to identify the mechanism of PNAHS. Total parenteral nutrition (TPN) mice model, in vivo, and in vitro experiments were used to assess the effect of PP2A-Cα on liver fatty acid metabolism.

RESULTS

Reduced expression of PP2A-Cα (catalytic subunit) enhanced activation of serine/threonine kinase Akt2 and decreased activation of adenosine monophosphate-activated protein kinase (AMPK) were associated with hepatic steatosis in patients with PNAHS. Mice given PN for 14 days developed hepatic steatosis, down-regulation of PP2A-Cα, activation of Akt2, and inhibition of AMPK. Hepatocyte-specific deletion of PP2A-Cα in mice given PN exacerbated Akt2 activation, AMPK inhibition, and hepatic steatosis through an effect on fatty acid degradation, whereas hepatocyte-specific PP2A-Cα overexpression significantly ameliorated hepatic steatosis accompanied with Akt2 suppression and AMPK activation. Additionally, pharmacological activation of Akt2 in mice overexpressing PP2A-Cα led to the aggravation of hepatic steatosis.

CONCLUSIONS

Our findings demonstrate that hepatic PP2A-Cα serves as a protective factor of PNAHS due to ameliorating hepatic steatosis and improving liver function. Our study provides a strong rationale that PP2A-Cα may be involved in the pathogenesis of PNAHS.

The mitochondrial-derived peptide MOTS-c relieves hyperglycemia and insulin resistance in gestational diabetes mellitus

The most common complication during pregnancy, gestational diabetes mellitus (GDM), can cause adverse pregnancy outcomes and result in the mother and infant having a higher risk of developing type 2 diabetes after pregnancy. However, existing therapies for GDM remain scant, with the most common being lifestyle intervention and appropriate insulin treatment. MOTS-c, a mitochondrial-derived peptide, can target skeletal muscle and enhance glucose metabolism. Here, we demonstrate that MOTS-c can be an effective treatment for GDM. A GDM mouse model was established by short term high-fat diet combined with low-dose streptozotocin (STZ) treatment while MOTS-c was administrated daily during pregnancy. GDM symptoms such as blood glucose and insulin levels, glucose and insulin tolerance, as well as reproductive outcomes were investigated. MOTS-c significantly alleviated hyperglycemia, improved insulin sensitivity and glucose tolerance, and reduced birth weight and the death of offspring induced by GDM. Similar to a previous study, MOTS-c also could activate insulin sensitivity in the skeletal muscle of GDM mice and elevate glucose uptake in vitro. In addition, we found that MOTS-c protects pancreatic β-cell from STZ-mediated injury. Taken together, our findings demonstrate that MOTS-c could be a promising strategy for the treatment of GDM.

Factors Influencing AMPK Activation During Cycling Exercise: A Pooled Analysis and Meta-Regression

BACKGROUND

The 5' adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a cellular energy sensor that is activated by increases in the cellular AMP/adenosine diphosphate:adenosine triphosphate (ADP:ATP) ratios and plays a key role in metabolic adaptations to endurance training. The degree of AMPK activation during exercise can be influenced by many factors that impact on cellular energetics, including exercise intensity, exercise duration, muscle glycogen, fitness level, and nutrient availability. However, the relative importance of these factors for inducing AMPK activation remains unclear, and robust relationships between exercise-related variables and indices of AMPK activation have not been established.

OBJECTIVES

The purpose of this analysis was to (1) investigate correlations between factors influencing AMPK activation and the magnitude of change in AMPK activity during cycling exercise, (2) investigate correlations between commonly reported measures of AMPK activation (AMPK-α2 activity, phosphorylated (p)-AMPK, and p-acetyl coenzyme A carboxylase (p-ACC), and (3) formulate linear regression models to determine the most important factors for AMPK activation during exercise.

METHODS

Data were pooled from 89 studies, including 982 participants (93.8% male, maximal oxygen consumption [[Formula: see text]] 51.9 ± 7.8 mL kg^-1 min^-1). Pearson's correlation analysis was performed to determine relationships between effect sizes for each of the primary outcome markers (AMPK-α2 activity, p-AMPK, p-ACC) and factors purported to influence AMPK signaling (muscle glycogen, carbohydrate ingestion, exercise duration and intensity, fitness level, and muscle metabolites). General linear mixed-effect models were used to examine which factors influenced AMPK activation.

RESULTS

Significant correlations (r = 0.19-0.55, p < .05) with AMPK activity were found between end-exercise muscle glycogen, exercise intensity, and muscle metabolites phosphocreatine, creatine, and free ADP. All markers of AMPK activation were significantly correlated, with the strongest relationship between AMPK-α2 activity and p-AMPK (r = 0.56, p < 0.001). The most important predictors of AMPK activation were the muscle metabolites and exercise intensity.

CONCLUSION

Muscle glycogen, fitness level, exercise intensity, and exercise duration each influence AMPK activity during exercise when all other factors are held constant. However, disrupting cellular energy charge is the most influential factor for AMPK activation during endurance exercise.

Mangosteen xanthone γ-mangostin exerts lowering blood glucose effect with potentiating insulin sensitivity through the mediation of AMPK/PPARγ

Diabetes mellitus (DM) is concomitant with significant morbidity and mortality and its prevalence is accumulative in worldwide. The conventional antidiabetic agents are known to mitigate the symptoms of diabetes; however, they may also cause side and adverse effects. There is an imperative necessity to conduct preclinical and clinical trials for the discovery of alternative therapeutic agents that can overcome the drawbacks of current synthetic antidiabetic drugs. This study aimed to investigate the efficacy of lowering blood glucose and underlined mechanism of γ-mangostin, mangosteen (Garcinia mangostana) xanthones. The results showed γ-Mangostin had a antihyperglycemic ability in short (2 h)- and long-term (28 days) administrations to diet-induced diabetic mice. The long-term administration of γ-mangostin attenuated fasting blood glucose of diabetic mice and exhibited no hepatotoxicity and nephrotoxicity. Moreover, AMPK, PPARγ, α-amylase, and α-glucosidase were found to be the potential targets for simulating binds with γ-mangostin after molecular docking. To validate the docking results, the inhibitory potency of γ-mangostin againstα-amylase/α-glucosidase was higher than Acarbose via enzymatic assay. Interestingly, an allosteric relationship between γ-mangostin and insulin was also found in the glucose uptake of VSMC, FL83B, C2C12, and 3T3-L1 cells. Taken together, the results showed that γ-mangostin exerts anti-hyperglycemic activity through promoting glucose uptake and reducing saccharide digestion by inhibition of α-amylase/α-glucosidase with insulin sensitization, suggesting that γ-mangostin could be a new clue for drug discovery and development to treat diabetes.

Serum- and glucocorticoid-induced kinase drives hepatic insulin resistance by directly inhibiting AMP-activated protein kinase

A hallmark of type 2 diabetes (T2D) is hepatic resistance to insulin's glucose-lowering effects. The serum- and glucocorticoid-regulated family of protein kinases (SGK) is activated downstream of mechanistic target of rapamycin complex 2 (mTORC2) in response to insulin in parallel to AKT. Surprisingly, despite an identical substrate recognition motif to AKT, which drives insulin sensitivity, pathological accumulation of SGK1 drives insulin resistance. Liver-specific Sgk1-knockout (Sgk1Lko) mice display improved glucose tolerance and insulin sensitivity and are protected from hepatic steatosis when fed a high-fat diet. Sgk1 promotes insulin resistance by inactivating AMP-activated protein kinase (AMPK) via phosphorylation on inhibitory site AMPKαSer485/491. We demonstrate that SGK1 is dominant among SGK family kinases in regulation of insulin sensitivity, as Sgk1, Sgk2, and Sgk3 triple-knockout mice have similar increases in hepatic insulin sensitivity. In aggregate, these data suggest that targeting hepatic SGK1 may have therapeutic potential in T2D.

Neurobiological Opportunities in Diabetic Polyneuropathy

This review highlights a selection of potential translational directions for the treatment of diabetic polyneuropathy (DPN) currently irreversible and without approved interventions beyond pain management. The list does not include all diabetic targets that have been generated over several decades of research but focuses on newer work. The emphasis is firstly on approaches that support the viability and growth of peripheral neurons and their ability to withstand a barrage of diabetic alterations. We include a section describing Schwann cell targets and finally how mitochondrial damage has been a common element in discussing neuropathic damage. Most of the molecules and pathways described here have not yet reached clinical trials, but many trials have been negative to date. Nonetheless, these failures clear the pathway for new thoughts over reversing DPN.

A Systematic Review of the Biological Effects of Cordycepin

We conducted a systematic review of the literature on the effects of cordycepin on cell survival and proliferation, inflammation, signal transduction and animal models. A total of 1204 publications on cordycepin were found by the cut-off date of 1 February 2021. After application of the exclusion criteria, 791 papers remained. These were read and data on the chosen subjects were extracted. We found 192 papers on the effects of cordycepin on cell survival and proliferation and calculated a median inhibitory concentration (IC50) of 135 µM. Cordycepin consistently repressed cell migration (26 papers) and cellular inflammation (53 papers). Evaluation of 76 papers on signal transduction indicated consistently reduced PI3K/mTOR/AKT and ERK signalling and activation of AMPK. In contrast, the effects of cordycepin on the p38 and Jun kinases were variable, as were the effects on cell cycle arrest (53 papers), suggesting these are cell-specific responses. The examination of 150 animal studies indicated that purified cordycepin has many potential therapeutic effects, including the reduction of tumour growth (37 papers), repression of pain and inflammation (9 papers), protecting brain function (11 papers), improvement of respiratory and cardiac conditions (8 and 19 papers) and amelioration of metabolic disorders (8 papers). Nearly all these data are consistent with cordycepin mediating its therapeutic effects through activating AMPK, inhibiting PI3K/mTOR/AKT and repressing the inflammatory response. We conclude that cordycepin has excellent potential as a lead for drug development, especially for age-related diseases. In addition, we discuss the remaining issues around the mechanism of action, toxicity and biodistribution of cordycepin.

Insulin signaling in health and disease

The molecular mechanisms of cellular insulin action have been the focus of much investigation since the discovery of the hormone 100 years ago. Insulin action is impaired in metabolic syndrome, a condition known as insulin resistance. The actions of the hormone are initiated by binding to its receptor on the surface of target cells. The receptor is an α2β2 heterodimer that binds to insulin with high affinity, resulting in the activation of its tyrosine kinase activity. Once activated, the receptor can phosphorylate a number of intracellular substrates that initiate discrete signaling pathways. The tyrosine phosphorylation of some substrates activates phosphatidylinositol-3-kinase (PI3K), which produces polyphosphoinositides that interact with protein kinases, leading to activation of the kinase Akt. Phosphorylation of Shc leads to activation of the Ras/MAP kinase pathway. Phosphorylation of SH2B2 and of Cbl initiates activation of G proteins such as TC10. Activation of Akt and other protein kinases produces phosphorylation of a variety of substrates, including transcription factors, GTPase-activating proteins, and other kinases that control key metabolic events. Among the cellular processes controlled by insulin are vesicle trafficking, activities of metabolic enzymes, transcriptional factors, and degradation of insulin itself. Together these complex processes are coordinated to ensure glucose homeostasis.

A spotlight on underlying the mechanism of AMPK in diabetes complications

OBJECTIVE

Type 2 diabetes (T2D) is one of the centenarian metabolic disorders and is considered as a stellar and leading health issue worldwide. According to the International Diabetes Federation (IDF) Diabetes Atlas and National Diabetes Statistics, the number of diabetic patients will increase at an exponential rate from 463 to 700 million by the year 2045. Thus, there is a great need for therapies targeting functions that can help in maintaining the homeostasis of glucose levels and improving insulin sensitivity. 5' adenosine monophosphate-activated protein kinase (AMPK) activation, by various direct and indirect factors, might help to overcome the hurdles (like insulin resistance) associated with the conventional approach.

MATERIALS AND RESULTS

A thorough review and analysis was conducted using various database including MEDLINE and EMBASE databases, with Google scholar using various keywords. This extensive review concluded that various drugs (plant-based, synthetic indirect/direct activators) are available, showing tremendous potential in maintaining the homeostasis of glucose and lipid metabolism, without causing insulin resistance, and improving insulin sensitivity. Moreover, these drugs have an effect against diabetes and are therapeutically beneficial in the treatment of diabetes-associated complications (neuropathy and nephropathy) via mechanism involving inhibition of nuclear translocation of SMAD4 (SMAD family member) expression and association with peripheral nociceptive neurons mediated by AMPK.

CONCLUSION

From the available information, it may be concluded that various indirect/direct activators show tremendous potential in maintaining the homeostasis of glucose and lipid metabolism, without resulting in insulin resistance, and may improve insulin sensitivity, as well. Therefore, in a nut shell, it may be concluded that the regulation of APMK functions by various direct/indirect activators may bring promising results. These activators may emerge as a novel therapy in diabetes and its associated complications.

Galactose-NlGr11 inhibits AMPK phosphorylation by activating the PI3K-AKT-PKF-ATP signaling cascade via insulin receptor and Gβγ

As ligands of the sugar gustatory receptors, sugars have been known to activate the insulin/insulin-like growth factor signaling pathway; however, the precise pathways that are activated by the sugar-bound gustatory receptors in insects remain unclear. In this study, we aimed to investigate the signaling cascades activated by NlGr11, a sugar gustatory receptor in the brown planthopper Nilaparvata lugens (Stål), and its ligand. Galactose-bound NlGr11 (galactose-NlGr11) activated the -phosphatidylinositol 3-kinase (PI3K)-AKT signaling cascade via insulin receptor (InR) and Gβγ in vitro. In addition, galactose-NlGr11 inhibited the adenosine monophosphate-activated protein kinase (AMPK) phosphorylation by activating the AKT-phosphofructokinase (PFK)-ATP signaling cascade in vitro. Importantly, the InR-PI3K-AKT-PFK-AKT signaling cascade was activated and the AMPK phosphorylation was inhibited after feeding the brown planthoppers with galactose solution. Collectively, these findings confirm that NlGr11 can inhibit AMPK phosphorylation by activating the PI3K-AKT-PFK-ATP signaling cascades via both InR and Gβγ when bound to galactose. Thus, our study provides novel insights into the signaling pathways regulated by the sugar gustatory receptors in insects.

Metformin Actions on the Liver: Protection Mechanisms Emerging in Hepatocytes and Immune Cells against NASH-Related HCC

Nonalcoholic fatty liver disease (NAFLD) is strongly linked to the global epidemic of obesity and type 2 diabetes mellitus (T2DM). Notably, NAFLD can progress from the mildest form of simple steatosis to nonalcoholic steatohepatitis (NASH) that increases the risk for hepatocellular carcinoma (HCC), which is a malignancy with a dismal prognosis and rising incidence in the United States and other developed counties, possibly due to the epidemic of NAFLD. Metformin, the first-line drug for T2DM, has been suggested to reduce risks for several types of cancers including HCC and protect against NASH-related HCC, as revealed by epidemical studies on humans and preclinical studies on animal models. This review focuses on the pathogenesis of NASH-related HCC and the mechanisms by which metformin inhibits the initiation and progression of NASH-related HCC. Since the functional role of immune cells in liver homeostasis and pathogenesis is increasingly appreciated in developing anti-cancer therapies on liver malignancies, we discuss both the traditional targets of metformin in hepatocytes and the recently defined effects of metformin on immune cells.

Autoregulation of insulin receptor signaling through MFGE8 and the αvβ5 integrin

The role of integrins, in particular αv integrins, in regulating insulin resistance is incompletely understood. We have previously shown that the αvβ5 integrin ligand milk fat globule epidermal growth factor like 8 (MFGE8) regulates cellular uptake of fatty acids. In this work, we evaluated the impact of MFGE8 on glucose homeostasis. We show that acute blockade of the MFGE8/β5 pathway enhances while acute augmentation dampens insulin-stimulated glucose uptake. Moreover, we find that insulin itself induces cell-surface enrichment of MFGE8 in skeletal muscle, which then promotes interaction between the αvβ5 integrin and the insulin receptor leading to dampening of skeletal-muscle insulin receptor signaling. Blockade of the MFGE8/β5 pathway also enhances hepatic insulin sensitivity. Our work identifies an autoregulatory mechanism by which insulin-stimulated signaling through its cognate receptor is terminated through up-regulation of MFGE8 and its consequent interaction with the αvβ5 integrin, thereby establishing a pathway that can potentially be targeted to improve insulin sensitivity.

Insulin on the brain: The role of central insulin signalling in energy and glucose homeostasis

Insulin signals to the brain where it coordinates multiple physiological processes underlying energy and glucose homeostasis. This review explores where and how insulin interacts within the brain parenchyma, how brain insulin signalling functions to coordinate energy and glucose homeostasis and how this contributes to the pathogenesis of metabolic disease.

Untangling the effect of insulin action on brain mitochondria and metabolism

The regulation of energy homeostasis is controlled by the brain and, besides requiring high amounts of energy, it relies on functional insulin/insulin-like growth factor (IGF)-1 signalling in the central nervous system. This energy is mainly provided by mitochondria in form of ATP. Thus, there is an intricate interplay between mitochondrial function and insulin/IGF-1 action to enable functional brain signalling and, accordingly, propagate a healthy metabolism. To adapt to different nutritional conditions, the brain is able to sense the current energy status via mitochondrial and insulin signalling-dependent pathways and exerts an appropriate metabolic response. However, regional, cell type and receptor-specific consequences of this interaction occur and are linked to diverse outcomes such as altered nutrient sensing, body weight regulation or even cognitive function. Impairments of this cross-talk can lead to obesity and glucose intolerance and are linked to neurodegenerative diseases, yet they also induce a self-sustainable, dysfunctional 'metabolic triangle' characterised by insulin resistance, mitochondrial dysfunction and inflammation in the brain. The identification of causal factors deteriorating insulin action, mitochondrial function and concomitantly a signature of metabolic stress in the brain is of utter importance to offer novel mechanistic insights into development of the continuously rising prevalence of non-communicable diseases such as type 2 diabetes and neurodegeneration. This review aims to determine the effect of insulin action on brain mitochondrial function and energy metabolism. It precisely outlines the interaction and differences between insulin action, insulin-like growth factor (IGF)-1 signalling and mitochondrial function; distinguishes between causality and association; and reveals its consequences for metabolism and cognition. We hypothesise that an improvement of at least one signalling pathway can overcome the vicious cycle of a self-perpetuating metabolic dysfunction in the brain present in metabolic and neurodegenerative diseases.

Adipose-specific knockout of Protein Kinase D1 suppresses de novo lipogenesis in mice via SREBP1c-dependent signaling

Having healthy adipose tissue is essential for metabolic health, as excessive adipose tissue in the body can cause its dysregulation and driving chronic metabolic diseases. Protein kinase D1 (PKD1) is considered to be a key kinase in signal transduction, which regulates multiple cellular functions, but its physiological functions in adipose are still not fully understood. This study aimed at elucidating the function of adipocyte PKD1 on lipogenesis. From RNA-Sequencing data, we found that the fatty acid biosynthesis pathway in white adipose tissue lacking PKD1 was significantly affected. Critical rate-limiting enzymes for de novo lipogenesis in adipocytes, such as FASN, ACCα, and SCD1, were significantly repressed after deleting PKD1 in vivo and in vitro. Further studies revealed that blockade of PKD1 significantly increased phosphorylation of SREBP1c at serine 372 site. Co-immunoprecipitation analysis showed that PKD1 interacts with SREBP1c in vitro and in vivo. Importantly, overexpression of SREBP1c reversed the inhibition of FASN and ACCα expression caused by PKD1 silencing. Together, adipocyte PKD1 promotes de novo lipogenesis via SREBP1c-dependent manner in visceral white adipose tissue and might provide a new target for the development of anti-obesity therapies.

Protein kinase A negatively regulates VEGF-induced AMPK activation by phosphorylating CaMKK2 at serine 495

Activation of AMP-activated protein kinase (AMPK) in endothelial cells by vascular endothelial growth factor (VEGF) via the Ca2+/calmodulin-dependent protein kinase kinase 2 (CaMKK2) represents a pro-angiogenic pathway, whose regulation and function is incompletely understood. This study investigates whether the VEGF/AMPK pathway is regulated by cAMP-mediated signalling. We show that cAMP elevation in endothelial cells by forskolin, an activator of the adenylate cyclase, and/or 3-isobutyl-1-methylxanthine (IBMX), an inhibitor of phosphodiesterases, triggers protein kinase A (PKA)-mediated phosphorylation of CaMKK2 (serine residues S495, S511) and AMPK (S487). Phosphorylation of CaMKK2 by PKA led to an inhibition of its activity as measured in CaMKK2 immunoprecipitates of forskolin/IBMX-treated cells. This inhibition was linked to phosphorylation of S495, since it was not seen in cells expressing a non-phosphorylatable CaMKK2 S495C mutant. Phosphorylation of S511 alone in these cells was not able to inhibit CaMKK2 activity. Moreover, phosphorylation of AMPK at S487 was not sufficient to inhibit VEGF-induced AMPK activation in cells, in which PKA-mediated CaMKK2 inhibition was prevented by expression of the CaMKK2 S495C mutant. cAMP elevation in endothelial cells reduced basal and VEGF-induced acetyl-CoA carboxylase (ACC) phosphorylation at S79 even if AMPK was not inhibited. Together, this study reveals a novel regulatory mechanism of VEGF-induced AMPK activation by cAMP/PKA, which may explain, in part, inhibitory effects of PKA on angiogenic sprouting and play a role in balancing pro- and anti-angiogenic mechanisms in order to ensure functional angiogenesis.

Rosemary extract activates AMPK, inhibits mTOR and attenuates the high glucose and high insulin-induced muscle cell insulin resistance

Impaired action of insulin in skeletal muscle, termed insulin resistance, leads to increased blood glucose levels resulting in compensatory increase in insulin levels. The elevated blood glucose and insulin levels exacerbate insulin resistance and contribute to the pathogenesis of type 2 diabetes mellitus. In previous studies we found attenuation of free fatty acid-induced muscle cell insulin resistance by rosemary extract (RE). In the present study we investigated the effects of RE on high glucose (HG) and high insulin (HI)-induced muscle cell insulin resistance. Exposure of L6 myotubes to 25 mmol/L glucose and 100 nmol/L insulin for 24 h, to mimic hyperglycemia and hyperinsulinemia, abolished the acute insulin-stimulated glucose uptake, increased the serine phosphorylation of IRS-1 and the phosphorylation/activation of mTOR and p70S6K. Treatment with RE significantly improved the insulin-stimulated glucose uptake and increased the acute insulin-stimulated tyrosine phosphorylation while reducing the HG+HI-induced serine phosphorylation of IRS-1 and phosphorylation of mTOR and p70S6K. Additionally, treatment with RE significantly increased the phosphorylation of AMPK, its downstream effector ACC and the plasma membrane GLUT4 levels. Our data indicate a potential of RE to counteract muscle cell insulin resistance and more studies are required to investigate its effectiveness in vivo. Novelty: RE phosphorylated muscle cell AMPK and ACC under both normal and HG+HI conditions. The HG+HI-induced serine phosphorylation of IRS-1 and activation of mTOR and p70S6K were attenuated by RE. RE restored the insulin-stimulated glucose uptake by enhancing GLUT4 glucose transporter translocation to plasma membrane.

Caloric Intake in Renal Patients: Repercussions on Mineral Metabolism

The aim of this paper is to review current knowledge about how calorie intake influences mineral metabolism focussing on four aspects of major interest for the renal patient: (a) phosphate (P) handling, (b) fibroblast growth factor 23 (FGF23) and calcitriol synthesis and secretion, (c) metabolic bone disease, and (d) vascular calcification (VC). Caloric intake has been shown to modulate P balance in experimental models: high caloric intake promotes P retention, while caloric restriction decreases plasma P concentrations. Synthesis and secretion of the phosphaturic hormone FGF23 is directly influenced by energy intake; a direct correlation between caloric intake and FGF23 plasma concentrations has been shown in animals and humans. Moreover, in vitro, energy availability has been demonstrated to regulate FGF23 synthesis through mechanisms in which the molecular target of rapamycin (mTOR) signalling pathway is involved. Plasma calcitriol concentrations are inversely proportional to caloric intake due to modulation by FGF23 of the enzymes implicated in vitamin D metabolism. The effect of caloric intake on bone is controversial. High caloric intake has been reported to increase bone mass, but the associated changes in adipokines and cytokines may as well be deleterious for bone. Low caloric intake tends to reduce bone mass but also may provide indirect (through modulation of inflammation and insulin regulation) beneficial effects on bone. Finally, while VC has been shown to be exacerbated by diets with high caloric content, the opposite has not been demonstrated with low calorie intake. In conclusion, although prospective studies in humans are needed, when planning caloric intake for a renal patient, it is important to take into consideration the associated changes in mineral metabolism.

Andrographolide, an Anti-Inflammatory Multitarget Drug: All Roads Lead to Cellular Metabolism

Andrographolide is a labdane diterpene and the main active ingredient isolated from the herb Andrographis paniculata. Andrographolide possesses diverse biological effects including anti-inflammatory, antioxidant, and antineoplastic properties. Clinical studies have demonstrated that andrographolide could be useful in therapy for a wide range of diseases such as osteoarthritis, upper respiratory diseases, and multiple sclerosis. Several targets are described for andrographolide, including the interference of transcription factors NF-κB, AP-1, and HIF-1 and signaling pathways such as PI3K/Akt, MAPK, and JAK/STAT. In addition, an increase in the Nrf2 (nuclear factor erythroid 2–related factor 2) signaling pathway also supports its antioxidant and anti-inflammatory properties. However, this scenario could be more complex since recent evidence suggests that andrographolide targets can modulate glucose metabolism. The metabolic effect of andrographolide might be the key to explaining the diverse therapeutic effects described in preclinical and clinical studies. This review discusses some of the most recent evidence about the anti-inflammatory and metabolic effects of andrographolide.

Critical Role for AMPK in Metabolic Disease-Induced Chronic Kidney Disease

Chronic kidney disease (CKD) is prevalent in 9.1% of the global population and is a significant public health problem associated with increased morbidity and mortality. CKD is associated with highly prevalent physiological and metabolic disturbances such as hypertension, obesity, insulin resistance, cardiovascular disease, and aging, which are also risk factors for CKD pathogenesis and progression. Podocytes and proximal tubular cells of the kidney strongly express AMP-activated protein kinase (AMPK). AMPK plays essential roles in glucose and lipid metabolism, cell survival, growth, and inflammation. Thus, metabolic disease-induced renal diseases like obesity-related and diabetic chronic kidney disease demonstrate dysregulated AMPK in the kidney. Activating AMPK ameliorates the pathological and phenotypical features of both diseases. As a metabolic sensor, AMPK regulates active tubular transport and helps renal cells to survive low energy states. AMPK also exerts a key role in mitochondrial homeostasis and is known to regulate autophagy in mammalian cells. While the nutrient-sensing role of AMPK is critical in determining the fate of renal cells, the role of AMPK in kidney autophagy and mitochondrial quality control leading to pathology in metabolic disease-related CKD is not very clear and needs further investigation. This review highlights the crucial role of AMPK in renal cell dysfunction associated with metabolic diseases and aims to expand therapeutic strategies by understanding the molecular and cellular processes underlying CKD.

Intranasal Insulin Increases Synaptic Protein Expression and Prevents Anesthesia-Induced Cognitive Deficits Through mTOR-eEF2 Pathway

General anesthesia increases the risk for cognitive impairment and Alzheimer's disease (AD) in vulnerable individuals such as the elderly. We previously reported that prior administration of insulin through intranasal delivery can prevent the anesthesia-induced cognitive impairment and biochemical changes in the brain. However, little is known about the underlying molecular mechanisms. Here, we report that general anesthesia resulted in downregulation of mammalian/mechanistic target of rapamycin (mTOR) and eukaryotic elongation factor 2 (eEF2) in the brain along with reduction of presynaptic proteins and brain-derived neurotrophic factor and cognitive impairment in aged mice. Prior administration of intranasal insulin prevented these anesthesia-induced changes. These results suggest the involvement of the mTOR-eEF2 signaling pathway in the anesthesia-induced brain changes and cognitive impairment and in the prevention of these changes with insulin. Correlation analyses and the use of eEF2 kinase inhibitor further support our conclusions. These studies shed light on the molecular mechanism by which anesthesia and insulin could act on synaptic proteins and cognitive function.

Microbial Imidazole Propionate Affects Responses to Metformin through p38γ-Dependent Inhibitory AMPK Phosphorylation

Metformin is the first-line therapy for type 2 diabetes, but there are large inter-individual variations in responses to this drug. Its mechanism of action is not fully understood, but activation of AMP-activated protein kinase (AMPK) and changes in the gut microbiota appear to be important. The inhibitory role of microbial metabolites on metformin action has not previously been investigated. Here, we show that concentrations of the microbial metabolite imidazole propionate are higher in subjects with type 2 diabetes taking metformin who have high blood glucose. We also show that metformin-induced glucose lowering is not observed in mice pretreated with imidazole propionate. Furthermore, we demonstrate that imidazole propionate inhibits AMPK activity by inducing inhibitory AMPK phosphorylation, which is dependent on imidazole propionate-induced basal Akt activation. Finally, we identify imidazole propionate-activated p38γ as a novel kinase for Akt and demonstrate that p38γ kinase activity mediates the inhibitory action of imidazole propionate on metformin.

The Potential Roles of Ghrelin in Metabolic Syndrome and Secondary Symptoms of Alzheimer's Disease

Although the major causative factors of Alzheimer's disease (AD) are the accumulation of amyloid β and hyperphosphorylated tau, AD can also be caused by metabolic dysfunction. The major clinical symptom of AD is cognitive dysfunction. However, AD is also accompanied by various secondary symptoms such as depression, sleep-wake disturbances, and abnormal eating behaviors. Interestingly, the orexigenic hormone ghrelin has been suggested to have beneficial effects on AD-related metabolic syndrome and secondary symptoms. Ghrelin improves lipid distribution and alters insulin sensitivity, effects that are hypothesized to delay the progression of AD. Furthermore, ghrelin can relieve depression by enhancing the secretion of hormones such as serotonin, noradrenaline, and orexin. Moreover, ghrelin can upregulate the expression of neurotrophic factors such as brain-derived neurotrophic factor and modulate the release of proinflammatory cytokines such as tumor necrosis factor α and interleukin 1β. Ghrelin alleviates sleep-wake disturbances by increasing the levels of melatonin, melanin-concentrating hormone. Ghrelin reduces the risk of abnormal eating behaviors by increasing neuropeptide Y and γ-aminobutyric acid. In addition, ghrelin increases food intake by inhibiting fatty acid biosynthesis. However, despite the numerous studies on the role of ghrelin in the AD-related pathology and metabolic disorders, there are only a few studies that investigate the effects of ghrelin on secondary symptoms associated with AD. In this mini review, our purpose is to provide the insights of future study by organizing the previous studies for the role of ghrelin in AD-related pathology and metabolic disorders.

The leaf aqueous extract of Myrianthus arboreus P. Beauv. (Cecropiaceae) improved letrozole-induced polycystic ovarian syndrome associated conditions and infertility in female Wistar rats

BACKGROUND

Myrianthus arboreus P. Beauv. (Cecropiaceae) is a medicinal plant used to treat female infertility. The aqueous extract of M. arboreus leaves was found to improve the fertility of healthy female Wistar rats. In the present study, we proposed evaluating the effects of such an extract on an animal model of infertility caused by polycystic ovary syndrome (PCOS), in order to bring scientific evidence to the curative action of this plant against female infertility.

METHODS

Following a 21-day administration (gavage) of letrozole (1 mg/kg), animals with PCOS, indicated by overweight and an estrous cycle blocked in the diestrus phase, were co-treated with letrozole (1 mg/kg) and the aqueous extract of M. arboreus leaves at doses of 20, 110 and 200 mg/kg. The positive control received clomiphene citrate (1 mg/kg) and metformin (200 mg/kg). The negative control received distilled water. Each group of animals was made up of 10 female rats. Vaginal smear was examined 7 days before and during co-treatments. Co-treatments were orally administered for 30 consecutive days and 5 animals per group were sacrificed thereafter for biochemical and histological analyses. The 5 remaining animals in each group were crossbred with males of proven fertility for 5 consecutive days. The daily examination of vaginal smears allowed evaluating fertility index. Following parturition, gestation rate was calculated.

RESULTS

The aqueous extract of M. arboreus leaves reversed letrozole effects by decreasing body weight, abdominal fat accumulation, and serum levels of LH and testosterone (p < 0.001). Ovarian dynamic was improved and the number of tertiary, Graafian follicles (p < 0.001) and corpus luteum increased while that of cystic (p < 0.001) and atretic follicles (p < 0.01) decreased. These effects were associated with increased serum levels of estradiol, decreased ovarian oxidative stress, the resumption of the estrous cycle, the hypertrophy of uterine epithelial cells and increased fertility index and gestation rate.

CONCLUSIONS

These results justify at least in part, the traditional use of M. arboreus against female infertility and suggest that this plant could be a promising alternative treatment to improve symptoms associated with different PCOS phenotypes.

Exercise and dietary intervention ameliorate high-fat diet-induced NAFLD and liver aging by inducing lipophagy

Exercise and dietary intervention are currently available strategies to treat nonalcoholic fatty liver disease (NAFLD), while the underlying mechanism remains controversial. Emerging evidence shows that lipophagy is involved in the inhibition of the lipid droplets accumulation. However, it is still unclear if exercise and dietary intervention improve NAFLD through regulating lipophagy, and how exercise of skeletal muscle can modulate lipid metabolism in liver. Moreover, NAFLD is associated with aging, and little is known about the effect of lipid accumulation on aging process. Here in vivo and in vitro models, we found that exercise and dietary intervention reduced lipid droplets formation, decreased hepatic triglyceride in the liver induced by high-fat diet. Exercise and dietary intervention enhanced the lipophagy by activating AMPK/ULK1 and inhibiting Akt/mTOR/ULK1 pathways respectively. Furthermore, exercise stimulated FGF21 production in the muscle, followed by secretion to the circulation to promote the lipophagy in the liver via an AMPK-dependent pathway. Importantly, for the first time, we demonstrated that lipid accumulation exacerbated liver aging, which was ameliorated by exercise and dietary intervention through inducing lipophagy. Our findings suggested a new mechanism of exercise and dietary intervention to improve NAFLD through promoting lipophagy. The study also provided evidence to support that muscle exercise is beneficial to other metabolic organs such as liver. The FGF21-mediated AMPK dependent lipophagy might be a potential drug target for NAFLD and aging caused by lipid metabolic dysfunction.

Proteome and Phosphoproteome Analysis of Brown Adipocytes Reveals That RICTOR Loss Dampens Global Insulin/AKT Signaling

Stimulating brown adipose tissue (BAT) activity represents a promising therapy for overcoming metabolic diseases. mTORC2 is important for regulating BAT metabolism, but its downstream targets have not been fully characterized. In this study, we apply proteomics and phosphoproteomics to investigate the downstream effectors of mTORC2 in brown adipocytes. We compare wild-type controls to isogenic cells with an induced knockout of the mTORC2 subunit RICTOR (Rictor-iKO) by stimulating each with insulin for a 30-min time course. In Rictor-iKO cells, we identify decreases to the abundance of glycolytic and de novo lipogenesis enzymes, and increases to mitochondrial proteins as well as a set of proteins known to increase upon interferon stimulation. We also observe significant differences to basal phosphorylation because of chronic RICTOR loss including decreased phosphorylation of the lipid droplet protein perilipin-1 in Rictor-iKO cells, suggesting that RICTOR could be involved with regulating basal lipolysis or droplet dynamics. Finally, we observe mild dampening of acute insulin signaling response in Rictor-iKO cells, and a subset of AKT substrates exhibiting statistically significant dependence on RICTOR.