Insulin stimulates expression of the pyruvate kinase M gene in 3T3-L1 adipocytes

The Role of PKM2 in Metabolic Reprogramming: Insights into the Regulatory Roles of Non-Coding RNAs

Pyruvate kinase is a key regulator in glycolysis through the conversion of phosphoenolpyruvate (PEP) into pyruvate. Pyruvate kinase exists in various isoforms that can exhibit diverse biological functions and outcomes. The pyruvate kinase isoenzyme type M2 (PKM2) controls cell progression and survival through the regulation of key signaling pathways. In cancer cells, the dimer form of PKM2 predominates and plays an integral role in cancer metabolism. This predominance of the inactive dimeric form promotes the accumulation of phosphometabolites, allowing cancer cells to engage in high levels of synthetic processing to enhance their proliferative capacity. PKM2 has been recognized for its role in regulating gene expression and transcription factors critical for health and disease. This role enables PKM2 to exert profound regulatory effects that promote cancer cell metabolism, proliferation, and migration. In addition to its role in cancer, PKM2 regulates aspects essential to cellular homeostasis in non-cancer tissues and, in some cases, promotes tissue-specific pathways in health and diseases. In pursuit of understanding the diverse tissue-specific roles of PKM2, investigations targeting tissues such as the kidney, liver, adipose, and pancreas have been conducted. Findings from these studies enhance our understanding of PKM2 functions in various diseases beyond cancer. Therefore, there is substantial interest in PKM2 modulation as a potential therapeutic target for the treatment of multiple conditions. Indeed, a vast plethora of research has focused on identifying therapeutic strategies for targeting PKM2. Recently, targeting PKM2 through its regulatory microRNAs, long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs) has gathered increasing interest. Thus, the goal of this review is to highlight recent advancements in PKM2 research, with a focus on PKM2 regulatory microRNAs and lncRNAs and their subsequent physiological significance.

Proteomic identification of aerobic glycolysis as a potential metabolic target for methylglyoxal in adipocytes

Obesity is often accompanied by metabolic changes in adipocytes that are closely associated with metabolic disease. Although high sugar consumption contributes to obesity, it may also directly affect adipocytes by increasing the rate of glycolysis and formation of the glycolytic by-product methylglyoxal (MG). MG is a reactive dicarbonyl that irreversibly damages proteins and other cellular components. Although the accumulation of MG is clinically associated with hyperglycemia and diabetic complications, a better understanding of how proteins are regulated by MG is needed to evaluate its role in the pathogenesis of metabolic disease. Because adipocytes rely heavily on glycolysis for glucose disposal, we hypothesized that prolonged MG treatment at nontoxic concentrations would impact the landscape of proteins involved in glucose metabolism. To test this hypothesis, we treated 3T3-L1 adipocytes with MG (100 μmol/L) and used comparative proteomics to assess the effects. We identified 25 differentially expressed proteins in adipocytes treated with MG compared to the control. Our results suggested that MG induced metabolic changes typically associated with aerobic glycolysis, including a lowered expression of proteins involved in oxidative metabolism and increased expression of the glycolytic enzymes L-lactate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase. The detection of increased lactate secreted into the culture media of adipocytes treated with MG further supported these findings, as did gene expression analysis. In summary, these results indicate MG as a metabolic contributor to aerobic glycolysis in adipocytes, a potential adaptive response to increased glucose flux which over time could lead to permanent metabolic changes.

Berberine Promotes Beige Adipogenic Signatures of 3T3-L1 Cells by Regulating Post-transcriptional Events

Induced brown adipocytes (also referred to as beige cells) execute thermogenesis, as do the classical adipocytes by consuming stored lipids, being related to metabolic homeostasis. Treatment of phytochemicals, including berberine (BBR), was reported to induce conversion from white adipocytes to beige cells. In this study, results of microRNA (miRNA)-seq analyses revealed a decrease in miR-92a, of which the transcription is driven by the c13orf25 promoter in BBR-treated 3T3-L1 cells. BBR treatment manipulated the expressions of SP1 and MYC, in turn, reducing the activity of the c13orf25 promoter. A decrease in miR-92a led to an increase in RNA-binding motif protein 4a (RBM4a) expression, which facilitated the beige adipogenesis. Overexpression of miR-92a or depletion of RBM4a reversely interfered with the impact of BBR treatment on the beige adipogenic signatures, gene expressions, and splicing events in 3T3-L1 cells. Our findings demonstrated that BBR treatment enhanced beige adipogenesis of 3T3-L1 cells through transcription-coupled post-transcriptional regulation.

Metabolic regulation of T cell development by Sin1-mTORC2 is mediated by pyruvate kinase M2

Glucose metabolism plays a key role in thymocyte development. The mammalian target of rapamycin complex 2 (mTORC2) is a critical regulator of cell growth and metabolism, but its role in early thymocyte development and metabolism has not been fully studied. We show here that genetic ablation of Sin1, an essential component of mTORC2, in T lineage cells results in severely impaired thymocyte development at the CD4-CD8- double negative (DN) stages but not at the CD4+CD8+ double positive (DP) or later stages. Notably, Sin1-deficient DN thymocytes show markedly reduced proliferation and glycolysis. Importantly, we discover that the M2 isoform of pyruvate kinase (PKM2) is a novel and crucial Sin1 effector in promoting DN thymocyte development and metabolism. At the molecular level, we show that Sin1-mTORC2 controls PKM2 expression through an AKT-dependent PPAR-γ nuclear translocation. Together, our study unravels a novel mTORC2-PPAR-γ-PKM2 pathway in immune-metabolic regulation of early thymocyte development.

Posttranslational Modifications of Pyruvate Kinase M2: Tweaks that Benefit Cancer

Cancer cells rewire metabolism to meet biosynthetic and energetic demands. The characteristic increase in glycolysis, i.e., Warburg effect, now considered as a hallmark, supports cancer in various ways. To attain such metabolic reshuffle, cancer cells preferentially re-express the M2 isoform of pyruvate kinase (PKM2, M2-PK) and alter its quaternary structure to generate less-active PKM2 dimers. The relatively inactive dimers cause the accumulation of glycolytic intermediates that are redirected into anabolic pathways. In addition, dimeric PKM2 also benefits cancer cells through various non-glycolytic moonlight functions, such as gene transcription, protein kinase activity, and redox balance. A large body of data have shown that several distinct posttranslation modifications (PTMs) regulate PKM2 in a way that benefits cancer growth, e.g., formation of PKM2 dimers. This review discusses the recent advancements in our understanding of various PTMs and the benefits they impart to the sustenance of cancer. Understanding the PTMs in PKM2 is crucial to assess their therapeutic potential and to design novel anticancer strategies.

PROTECTIVE EFFECT OF CAMEL MILK AS ANTI-DIABETIC SUPPLEMENT: BIOCHEMICAL, MOLECULAR AND IMMUNOHISTOCHEMICAL STUDY

Background:

Diabetes is a serious disease affects human health. Diabetes in advanced stages is accompanied by general weakness and alteration in fats and carbohydrates metabolism. Recently there are some scientific trends about the usage of camel milk (CM) in the treatment of diabetes and its associated alterations. CM contains vital active particles with insulin like action that cure diabetes and its complications but how these effects occur, still unclear.

Materials and Methods:

Seventy-five adult male rats of the albino type divided into five equal groups. Group 1 served as a negative control (C). Group 2 was supplemented with camel milk (CM). Diabetes was induced in the remaining groups (3, 4 and 5). Group 3 served as positive diabetic control (D). Group 4 served as diabetic and administered metformin (D+MET). Group 5 served as diabetes and supplemented with camel milk (D+CM). Camel milk was supplemented for two consecutive months. Serum glucose, leptin, insulin, liver, kidney, antioxidants, MDA and lipid profiles were assayed. Tissues from liver and adipose tissues were examined using RT-PCR analysis for the changes in mRNA expression of genes of carbohydrates and lipid metabolism. Pancreas and liver were used for immunohistochemical examination using specific antibodies.

Results:

Camel milk supplementation ameliorated serum biochemical measurements that altered after diabetes induction. CM supplementation up-regulated mRNA expression of IRS-2, PK, and FASN genes, while down-regulated the expression of CPT-1 to control mRNA expression level. CM did not affect the expression of PEPCK gene. On the other hand, metformin failed to reduce the expression of CPT-1 compared to camel milk administered rats. Immunohistochemical findings revealed that CM administration restored the immunostaining reactivity of insulin and GLUT-4 in the pancreas of diabetic rats.

Conclusion:

CM administration is of medical importance and helps physicians in the treatment of diabetes mellitus.

RBM4a-regulated splicing cascade modulates the differentiation and metabolic activities of brown adipocytes

RNA-binding motif protein 4a (RBM4a) reportedly reprograms splicing profiles of the insulin receptor (IR) and myocyte enhancer factor 2C (MEF2C) genes, facilitating the differentiation of brown adipocytes. Using an RNA-sequencing analysis, we first compared the gene expressing profiles between wild-type and RBM4a^−/− brown adipocytes. The ablation of RBM4a led to increases in the PTBP1, PTBP2 (nPTB), and Nova1 proteins, whereas elevated RBM4a reduced the expression of PTBP1 and PTBP2 proteins in brown adipocytes through an alternative splicing-coupled nonsense-mediated decay mechanism. Subsequently, RBM4a indirectly shortened the half-life of the Nova1 transcript which was comparatively stable in the presence of PTBP2. RBM4a diminished the influence of PTBP2 in adipogenic development by reprogramming the splicing profiles of the FGFR2 and PKM genes. These results constitute a mechanistic understanding of the RBM4a-modulated splicing cascade during the brown adipogenesis.

Pyruvate kinase M2 and cancer: an updated assessment

Cancer cells are characterized by high glycolytic rates to support energy regeneration and anabolic metabolism, along with the expression of pyruvate kinase isoenzyme M2 (PKM2). The latter catalyzes the last step of glycolysis and reprograms the glycolytic flux to feed the special metabolic demands of proliferating cells. Besides, PKM2 has moonlight functions, such as gene transcription, favoring cancer. Accumulating evidence suggests a critical role played by the low-activity-dimeric PKM2 in tumor progression, supported by the identification of mutations which result in the down-regulation of its activity and tumorigenesis in a nude mouse model. This review discusses PKM2 regulation and the benefits it confers to cancer cells. Further, conflicting views on PKM2's role in cancer, its therapeutic relevance and future directions in the field are also discussed.

Insulin enhances metabolic capacities of cancer cells by dual regulation of glycolytic enzyme pyruvate kinase M2

Background

Insulin is tightly associated with cancer progression; however, mechanistic insights into such observations are poorly understood. Recent studies show that metabolic transformation is critical to cancer cell proliferation. Here, we attempt to understand the role of insulin in promotion of cancer metabolism. To this end, the role of insulin in regulating glycolytic enzyme pyruvate kinase M2 (PKM2) was examined.

Results

We observed that insulin up-regulated PKM2 expression, through PI3K/mTOR mediated HIF1α induction, but significantly reduced PKM2 activity independent of this pathway. Drop in PKM2 activity was attributed to subunit dissociation leading to formation of low activity PKM2 oligomers, as assessed by density gradient centrifugation. However, tyrosine 105 phosphorylation of PKM2, known for inhibiting PKM2 activity, remained unaffected on insulin treatment. Interestingly, insulin-induced ROS was found responsible for PKM2 activity reduction. The observed changes in PKM2 status led to augmented cancer metabolism. Insulin-induced PKM2 up-regulation resulted in enhanced aerobic glycolysis as confirmed by PKM2 knockdown studies. Further, PKM2 activity reduction led to characteristic pooling of glycolytic intermediates and increased accumulation of NADPH; suggesting diversion of glucose flux towards macromolecular synthesis, necessary for cancer cell growth.

Conclusion

The study identifies new PKM2-mediated effects of insulin on cancer metabolism, thus, advancing the understanding of insulin’s role in cancer.

Rocking cell metabolism: revised functions of the key glycolytic regulator PKM2 in cancer

Cancer cell metabolism is exemplified by high glucose consumption and lactate production. Pyruvate kinase (PK), which catalyzes the final step of glycolysis, has emerged as a potential regulator of this metabolic phenotype. The M2 isoform of PK (PKM2) is highly expressed in cancer cells. However, the mechanisms by which PKM2 coordinates high energy requirements with high anabolic activities to support cancer cell proliferation are still not completely understood. Current research has elucidated novel regulatory mechanisms for PKM2, contributing to its important role in cancer. This review summarizes the current understanding and explores future directions in the field, highlighting controversies regarding the activity and specificity of PKM2 in cancer. In light of this knowledge, the potential therapeutic implications and strategies are critically discussed.

Skin fibroblasts as a tool for identifying the risk of nephropathy in the type 1 diabetic population

Human fibroblasts in culture have been employed as an in vitro system to investigate some pathophysiological mechanisms of diabetes mellitus also associated with the development of diabetic nephropathy. In fact, there is increasing evidence that genetic factors either convey the risk of, or protect from, diabetic nephropathy and that the expression profiles and/or the behaviour of the cultured skin fibroblasts from type 1 diabetic patients could reflect these genetic influences. On the other hand, alterations could be attributable not only to changes in DNA sequence, but also to epigenetic factors. Our aim is to make a critical overview of the studies involving primary cultures of skin fibroblasts as tools to investigate the pathophysiology of diabetic nephropathy performed until now in this area. Cultured skin fibroblasts could be useful not only for the identification of patients at risk of developing diabetic renal disease, but also for a better understanding of the complex multifactorial mechanisms leading to the long-term complications in diabetes.

Insulin resistance and metabolic hepatocarcinogenesis with parent-of-origin effects in A×B mice

Insulin resistance is a defining feature of metabolic syndrome and type 2 diabetes mellitus but also may occur independently of these conditions. Nonalcoholic fatty liver disease (NAFLD), the hepatic manifestation of these disorders, increases the risk of hepatocellular carcinoma (HCC). However, mechanisms linking hyperinsulinemia to NAFLD and HCC require clarification. We describe a novel model of primary insulin resistance and HCC with strong parent-of-origin effects. Male AB6F1 (A/JCr dam × C57BL/6 sire) but not B6AF1 (B6 dam × A/J sire) mice developed spontaneous insulin resistance, NAFLD, and HCC without obesity or diabetes. A survey of mitochondrial, imprinted, and sex-linked traits revealed modest associations with X-linked genes. However, a diet-induced obesity study, including B6.A chromosome substitution-strain (consomic) mice, showed no segregation by sex chromosome. Thus, parent-of-origin effects were specified within the autosomal genome. Next, we interrogated mechanisms of insulin-associated hepatocarcinogenesis. Steatotic hepatocytes exhibited adipogenic transition characterized by vacuolar metaplasia and up-regulation of vimentin, adipsin, fatty acid translocase (CD36), peroxisome proliferator-activated receptor-γ, and related products. This profile was largely recapitulated in insulin-supplemented primary mouse hepatocyte cultures. Importantly, pyruvate kinase M2, a fetal anabolic enzyme implicated in the Warburg effect, was activated by insulin in vivo and in vitro. Thus, our study reveals parent-of-origin effects in heritable insulin resistance, implicating adipogenic transition with acquired anabolic metabolism in the progression from NAFLD to HCC.

Silencing of pkm2 increases the efficacy of docetaxel in human lung cancer xenografts in mice

Tumor aerobic glycolysis, or the Warburg effect, plays important roles in tumor survival, growth, and metastasis. Pyruvate kinase isoenzyme M2 (PKM2) is a key enzyme that regulates aerobic glycolysis in tumor cells. Recent research has shown that PKM2 can be used as a tumor marker for diagnosis and, in particular, as a potential target for cancer therapy. We investigated the effects of combining shRNA targeting PKM2 and docetaxel on human A549 lung carcinoma cells both in vivo and in vitro. We observed that the shRNA can significantly downregulate the expression level of PKM2. The decrease of PKM2 resulted in a decrease in ATP synthesis, which caused intracellular accumulation of docetaxel. Furthermore, the combination of pshRNA-pkm2 and docetaxel inhibited tumor growth and promoted more cancer cell apoptosis both in vivo and in vitro. Our findings suggest that targeting tumor glycolysis can increase the efficacy of chemotherapy. In particular, the targeting of PKM2 could, to some extent, be a new way of reversing chemotherapy resistance to cancer therapy.

Glycolytic enzyme expression and pyruvate kinase activity in cultured fibroblasts from type 1 diabetic patients with and without nephropathy

Since type 1 diabetes mellitus (T1DM) patients with nephropathy (DN+) are insulin-resistant, we aimed to identify (new) potential molecular sites involved in the alterations of glucose metabolism in these patients. We examined the expression of glycolytic enzymes in cultured fibroblasts from T1DM(DN+) patients as compared to those from T1DM patients without nephropathy (DN-) and from controls. Pyruvate kinase (PK) activity was also determined. Human skin fibroblasts were grown in normal glucose (6 mM). RNAs and proteins were analyzed, respectively, using cRNA microarray and two-dimensional electrophoresis followed by identification with mass spectrometry. PK activity was measured using a spectrophotometric assay. As compared to controls, increases in the gene expression of hexokinase, phosphoglucomutase, phosphofructokinase, aldolase and triosephosphate isomerase were found in T1DM(DN+) patients, but not in T1DM(DN-) patients. In T1DM(DN+) patients, the protein analysis showed an altered expression of three glycolytic enzymes: triosophosphate isomerase, enolase and PK. In addition, PK activity in fibroblasts from T1DM(DN+) patients was lower than that in T1DM(DN-) and in controls. In conclusion, this study reports novel alterations of enzymes involved in glucose metabolism that may be associated with the pathophysiology of insulin resistance and of renal damage in T1DM(DN+) patients.

Signature patterns revealed by microarray analyses of mice infected with influenza virus A and Streptococcus pneumoniae

We used cDNA microarrays to identify differentially expressed genes in mice in response to infections with influenza virus A/PR/8/34 (H1N1) and Streptococcus pneumoniae. Expression microarray analysis showed up-regulation and down-regulation of many genes involved in the defense, inflammatory response and intracellular signaling pathways including chemokine, apoptosis, MAPK, Notch, Jak-STAT, T-cell receptor and complement and coagulation cascades. We have revealed signature patterns of gene expression in mice infected with two different classes of pathogens: influenza virus A and S. pneumoniae. Quantitative real-time RT-PCR results confirmed microarray results for most of the genes tested. These studies document clear differences in gene expression profiles between mice infected with influenza virus A and S. pneumoniae. Identification of genes that are differentially expressed after respiratory infections can provide insights into the mechanisms by which the host interacts with different pathogens, useful information about stage of diseases and selection of suitable targets for early diagnosis and treatments. The advantage of this novel approach is that the detection of pathogens is based on the differences in host gene expression profiles in response to different pathogens instead of detecting pathogens directly.