Cell-state-specific metabolic dependency in hematopoiesis and leukemogenesis.

The balance between oxidative and nonoxidative glucose metabolism is essential for a number of pathophysiological processes. By deleting enzymes that affect aerobic glycolysis with different potencies, we examine how modulating glucose metabolism specifically affects hematopoietic and leukemic cell populations. We find that a deficiency in the M2 pyruvate kinase isoform (PKM2) reduces the levels of metabolic intermediates important for biosynthesis and impairs progenitor function without perturbing hematopoietic stem cells (HSCs), whereas lactate dehydrogenase A (LDHA) deletion significantly inhibits the function of both HSCs and progenitors during hematopoiesis. In contrast, leukemia initiation by transforming alleles putatively affecting either HSCs or progenitors is inhibited in the absence of either PKM2 or LDHA, indicating that the cell-state-specific responses to metabolic manipulation in hematopoiesis do not apply to the setting of leukemia. This finding suggests that fine-tuning the level of glycolysis may be explored therapeutically for treating leukemia while preserving HSC function.

PKM2 isoform-specific deletion reveals a differential requirement for pyruvate kinase in tumor cells.

The pyruvate kinase M2 isoform (PKM2) is expressed in cancer and plays a role in regulating anabolic metabolism. To determine whether PKM2 is required for tumor formation or growth, we generated mice with a conditional allele that abolishes PKM2 expression without disrupting PKM1 expression. PKM2 deletion accelerated mammary tumor formation in a Brca1-loss-driven model of breast cancer. PKM2 null tumors displayed heterogeneous PKM1 expression, with PKM1 found in nonproliferating tumor cells and no detectable pyruvate kinase expression in proliferating cells. This suggests that PKM2 is not necessary for tumor cell proliferation and implies that the inactive state of PKM2 is associated with the proliferating cell population within tumors, whereas nonproliferating tumor cells require active pyruvate kinase. Consistent with these findings, variable PKM2 expression and heterozygous PKM2 mutations are found in human tumors. These data suggest that regulation of PKM2 activity supports the different metabolic requirements of proliferating and nonproliferating tumor cells.

ATP consumption promotes cancer metabolism.

Cancer cells metabolize glucose by aerobic glycolysis, a phenomenon known as the Warburg effect. Fang et al. (2010) show that the endoplasmic reticulum enzyme ENTPD5 promotes ATP consumption and favors aerobic glycolysis. The findings suggest that nutrient uptake in cancer cells is limited by ATP and satisfies energy requirements other than ATP production.

Germline loss of PKM2 promotes metabolic distress and hepatocellular carcinoma.

Alternative splicing of the Pkm gene product generates the PKM1 and PKM2 isoforms of pyruvate kinase (PK), and PKM2 expression is closely linked to embryogenesis, tissue regeneration, and cancer. To interrogate the functional requirement for PKM2 during development and tissue homeostasis, we generated germline PKM2-null mice (Pkm2(-/-)). Unexpectedly, despite being the primary isoform expressed in most wild-type adult tissues, we found that Pkm2(-/-) mice are viable and fertile. Thus, PKM2 is not required for embryonic or postnatal development. Loss of PKM2 leads to compensatory expression of PKM1 in the tissues that normally express PKM2. Strikingly, PKM2 loss leads to spontaneous development of hepatocellular carcinoma (HCC) with high penetrance that is accompanied by progressive changes in systemic metabolism characterized by altered systemic glucose homeostasis, inflammation, and hepatic steatosis. Therefore, in addition to its role in cancer metabolism, PKM2 plays a role in controlling systemic metabolic homeostasis and inflammation, thereby preventing HCC by a non-cell-autonomous mechanism.

Pyruvate kinase isoform expression alters nucleotide synthesis to impact cell proliferation.

Metabolic regulation influences cell proliferation. The influence of pyruvate kinase isoforms on tumor cells has been extensively studied, but whether PKM2 is required for normal cell proliferation is unknown. We examine how PKM2 deletion affects proliferation and metabolism in nontransformed, nonimmortalized PKM2-expressing primary cells. We find that deletion of PKM2 in primary cells results in PKM1 expression and proliferation arrest. PKM1 expression, rather than PKM2 loss, is responsible for this effect, and proliferation arrest cannot be explained by cell differentiation, senescence, death, changes in gene expression, or prevention of cell growth. Instead, PKM1 expression impairs nucleotide production and the ability to synthesize DNA and progress through the cell cycle. Nucleotide biosynthesis is limiting, as proliferation arrest is characterized by severe thymidine depletion, and supplying exogenous thymine rescues both nucleotide levels and cell proliferation. Thus, PKM1 expression promotes a metabolic state that is unable to support DNA synthesis.

Nesting box imager: Contact-free, real-time measurement of activity, surface body temperature, and respiratory rate applied to hibernating mouse models.

Noncontact methods to measure animal activity and physiology are necessary to monitor undisturbed states such as hibernation. Although some noncontact measurement systems are commercially available, they are often incompatible with realistic habitats, which feature freely moving animals in small, cluttered environments. A growing market of single-board computers, microcontrollers, and inexpensive sensors has made it possible to assemble bespoke integrated sensor systems at significantly lower price points. Herein, we describe a custom-built nesting box imager (NBI) that uses a single-board computer (Raspberry Pi) with a passive infrared (IR) motion sensor, silicon charge-coupled device (CCD), and IR camera CCD to monitor the activity, surface body temperature, and respiratory rate of the meadow jumping mouse during hibernation cycles. The data are logged up to 12 samples per minute and postprocessed using custom Matlab scripts. The entire unit can be built at a price point below US$400, which will be drastically reduced as IR (thermal) arrays are integrated into more consumer electronics and become less expensive.

Courtship behavior of the meadow jumping mouse (Zapus hudsonius).

We describe the first recorded observations of courtship behavior of the meadow jumping mouse (Zapus hudsonius) made in wild-caught and captive-reared animals. Male meadow jumping mice performed a series of courtship behaviors upon approach to the female, including rapid fanning of the muzzle with the forelimbs, self-grooming, muzzle fanning, retreat, and eventual mounting attempts. During courtship, female jumping mice may retreat, ignore the courting male, or bat at the male with forelimbs until the male retreats. Active rejection of courting males by the female is suggestive of female mate choice in this species.

Pyruvate kinase: Function, regulation and role in cancer.

Pyruvate kinase is an enzyme that catalyzes the conversion of phosphoenolpyruvate and ADP to pyruvate and ATP in glycolysis and plays a role in regulating cell metabolism. There are four mammalian pyruvate kinase isoforms with unique tissue expression patterns and regulatory properties. The M2 isoform of pyruvate kinase (PKM2) supports anabolic metabolism and is expressed both in cancer and normal tissue. The enzymatic activity of PKM2 is allosterically regulated by both intracellular signaling pathways and metabolites; PKM2 thus integrates signaling and metabolic inputs to modulate glucose metabolism according to the needs of the cell. Recent advances have increased our understanding of metabolic regulation by pyruvate kinase, raised new questions, and suggested the possibility of non-canonical PKM2 functions to regulate gene expression and cell cycle progression via protein-protein interactions and protein kinase activity. Here we review the structure, function, and regulation of pyruvate kinase and discuss how these properties enable regulation of PKM2 for cell proliferation and tumor growth.

Pyruvate kinase M2 activators promote tetramer formation and suppress tumorigenesis.

Cancer cells engage in a metabolic program to enhance biosynthesis and support cell proliferation. The regulatory properties of pyruvate kinase M2 (PKM2) influence altered glucose metabolism in cancer. The interaction of PKM2 with phosphotyrosine-containing proteins inhibits enzyme activity and increases the availability of glycolytic metabolites to support cell proliferation. This suggests that high pyruvate kinase activity may suppress tumor growth. We show that expression of PKM1, the pyruvate kinase isoform with high constitutive activity, or exposure to published small-molecule PKM2 activators inhibits the growth of xenograft tumors. Structural studies reveal that small-molecule activators bind PKM2 at the subunit interaction interface, a site that is distinct from that of the endogenous activator fructose-1,6-bisphosphate (FBP). However, unlike FBP, binding of activators to PKM2 promotes a constitutively active enzyme state that is resistant to inhibition by tyrosine-phosphorylated proteins. These data support the notion that small-molecule activation of PKM2 can interfere with anabolic metabolism.

Fibroblasts as an experimental model system for the study of comparative physiology.

Mechanistic evaluations of processes that underlie organism-level physiology often require reductionist approaches. Dermal fibroblasts offer one such approach. These cells are easily obtained from minimally invasive skin biopsy, making them appropriate for the study of protected and/or logistically challenging species. Cell culture approaches permit extensive and fine-scale sampling regimes as well as gene manipulation techniques that are not feasible in vivo. Fibroblast isolation and culture protocols are outlined here for primary cells, and the benefits and drawbacks of immortalization are discussed. We show examples of physiological metrics that can be used to characterize primary cells (oxygen consumption, translation, proliferation) and readouts that can be informative in understanding cell-level responses to environmental stress (lactate production, heat shock protein induction). Importantly, fibroblasts may display fidelity to whole animal physiological phenotypes, facilitating their study. Fibroblasts from Antarctic Weddell seals show greater resilience to low temperatures and hypoxia exposure than fibroblasts from humans or rats. Fibroblast oxygen consumption rates are not affected by temperature stress in the heat-tolerant camel, whereas similar temperature exposures depress mitochondrial metabolism in fibroblasts from rhinoceros. Finally, dermal fibroblasts from a hibernator, the meadow jumping mouse, better resist experimental cooling than a fibroblast line from the laboratory mouse, with the hibernator demonstrating a greater maintenance of homeostatic processes such as protein translation. These results exemplify the parallels that can be drawn between fibroblast physiology and expectations in vivo, and provide evidence for the power of fibroblasts as a model system to understand comparative physiology and biomedicine.

Pyruvate Kinase M1 Suppresses Development and Progression of Prostate Adenocarcinoma.

SIGNIFICANCE: Differential expression of PKM1 and PKM2 impacts prostate tumorigenesis and suggests a potential therapeutic vulnerability in prostate cancer.

2-Oxo-N-aryl-1,2,3,4-tetrahydroquinoline-6-sulfonamides as activators of the tumor cell specific M2 isoform of pyruvate kinase.

Compared to normal differentiated cells, cancer cells have altered metabolic regulation to support biosynthesis and the expression of the M2 isozyme of pyruvate kinase (PKM2) plays an important role in this anabolic metabolism. While the M1 isoform is a highly active enzyme, the alternatively spliced M2 variant is considerably less active and expressed in tumors. While the exact mechanism by which decreased pyruvate kinase activity contributes to anabolic metabolism remains unclear, it is hypothesized that activation of PKM2 to levels seen with PKM1 may promote a metabolic program that is not conducive to cell proliferation. Here we report the third chemotype in a series of PKM2 activators based on the 2-oxo-N-aryl-1,2,3,4-tetrahydroquinoline-6-sulfonamide scaffold. The synthesis, structure activity relationships, selectivity and notable physiochemical properties are described.

Breeding and hibernation of captive meadow jumping mice (Zapus hudsonius).

Hibernating mammals exhibit unique metabolic and physiological phenotypes that have potential applications in medicine or spaceflight, yet our understanding of the genetic basis and molecular mechanisms of hibernation is limited. The meadow jumping mouse, a small North American hibernator, exhibits traits-including a short generation time-that would facilitate genetic approaches to hibernation research. Here we report the collection, captive breeding, and laboratory hibernation of meadow jumping mice. Captive breeders in our colony produced a statistically significant excess of male offspring and a large number of all-male and all-female litters. We confirmed that short photoperiod induced pre-hibernation fattening, and cold ambient temperature facilitated entry into hibernation. During pre-hibernation fattening, food consumption exhibited non-linear dependence on both body mass and temperature, such that food consumption was greatest in the heaviest animals at the coldest temperatures. Meadow jumping mice exhibited a strong circadian rhythm of nightly activity that was disrupted during the hibernation interval. We conclude that it is possible to study hibernation phenotypes using captive-bred meadow jumping mice in a laboratory setting.

Cancer-associated mutations in human pyruvate kinase M2 impair enzyme activity.

Mammalian pyruvate kinase catalyzes the final step of glycolysis, and its M2 isoform (PKM2) is widely expressed in proliferative tissues. Mutations in PKM2 are found in some human cancers; however, the effects of these mutations on enzyme activity and regulation are unknown. Here, we characterized five cancer-associated PKM2 mutations, occurring at various locations on the enzyme, with respect to substrate kinetics and activation by the allosteric activator fructose-1,6-bisphosphate (FBP). The mutants exhibit reduced maximal velocity, reduced substrate affinity, and/or altered activation by FBP. The kinetic parameters of five additional PKM2 mutants that have been used to study enzyme function or regulation also demonstrate the deleterious effects of mutations on PKM2 function. Our findings indicate that PKM2 is sensitive to many amino acid changes and support the hypothesis that decreased PKM2 activity is selected for in rapidly proliferating cells.

Cutaneous Dermatophilosis in a Meadow Jumping Mouse (Zapus hudsonius).

A laboratory-housed, wild-caught, subadult, male meadow jumping mouse (Zapus hudsonius) presented with extensive scaling of the face, limbs, and tail and severe edema of the paws. Postmortem examination revealed marked distal limb edema with focal digital hematomas and white scales, scabs, and crusts affecting the majority of nonhaired skin. Histopathologic analysis revealed severe, multifocal, chronic-active exudative and proliferative dermatitis characterized by multilaminated crusts covering the epidermis. The epidermis was expanded by hyperkeratosis, acanthosis, and hyperplasia. The superficial dermis contained moderate edema, hemorrhage, and pigmentary incontinence, and was infiltrated by granulocytes and mononuclear cells. The laminated crusts contained numerous branching filaments of gram-positive coccoid bodies arranged in parallel rows, consistent with cutaneous Dermatophilus congolensis infection. This diagnosis was confirmed through bacterial culture and 16S rRNA PCR analysis. In the presented case, factors that might have contributed to disease progression include climatic conditions at the capture site and stress associated with trapping and laboratory housing.

PKM2 is not required for colon cancer initiated by APC loss.

BACKGROUND: Cancer cells express the M2 isoform of the glycolytic enzyme pyruvate kinase (PKM2). PKM2 expression is not required for some cancers, and PKM2 loss can promote cancer progression; however, PKM2 has been reported to be essential in other tumor contexts, including a proposed non-metabolic role in ß-catenin nuclear translocation. PKM2 is expressed in colon cancers where loss of the Apc tumor suppressor results in ß-catenin nuclear translocation and aberrant activation of the canonical Wnt signaling pathway. Whether PKM2 is required in this colon cancer context has not been investigated. RESULTS: Colon tumorigenesis was induced in mice harboring conditional Apc and Pkm2 alleles, and tumor progression was monitored by serial colonoscopy. PKM2 deletion had no effect on overall survival, the number of mice that developed tumors, or the number of tumors that developed per animal. Immunohistochemical analysis demonstrated PKM2 expression in wild-type tumors and the expected loss of PKM2 expression in tumors from Pkm2 conditional mice. Loss of PKM2 resulted in pyruvate kinase M1 expression but had no effect on nuclear ß-catenin staining. These findings are consistent with tumor growth and activated Wnt signaling despite PKM2 loss in this model. We also found a large fraction of human colon cancers had very low or undetectable levels of PKM2 expression. CONCLUSIONS: PKM2 is not required for Apc-deficient colon cancer or for nuclear translocation of ß-catenin in Apc-null tumor cells. These findings suggest that PKM2 expression is not required for colon tumor formation or progression.

Pyruvate kinase M2 activation may protect against the progression of diabetic glomerular pathology and mitochondrial dysfunction.

Diabetic nephropathy (DN) is a major cause of end-stage renal disease, and therapeutic options for preventing its progression are limited. To identify novel therapeutic strategies, we studied protective factors for DN using proteomics on glomeruli from individuals with extreme duration of diabetes (l50 years) without DN and those with histologic signs of DN. Enzymes in the glycolytic, sorbitol, methylglyoxal and mitochondrial pathways were elevated in individuals without DN. In particular, pyruvate kinase M2 (PKM2) expression and activity were upregulated. Mechanistically, we showed that hyperglycemia and diabetes decreased PKM2 tetramer formation and activity by sulfenylation in mouse glomeruli and cultured podocytes. Pkm-knockdown immortalized mouse podocytes had higher levels of toxic glucose metabolites, mitochondrial dysfunction and apoptosis. Podocyte-specific Pkm2-knockout (KO) mice with diabetes developed worse albuminuria and glomerular pathology. Conversely, we found that pharmacological activation of PKM2 by a small-molecule PKM2 activator, TEPP-46, reversed hyperglycemia-induced elevation in toxic glucose metabolites and mitochondrial dysfunction, partially by increasing glycolytic flux and PGC-1α mRNA in cultured podocytes. In intervention studies using DBA2/J and Nos3 (eNos) KO mouse models of diabetes, TEPP-46 treatment reversed metabolic abnormalities, mitochondrial dysfunction and kidney pathology. Thus, PKM2 activation may protect against DN by increasing glucose metabolic flux, inhibiting the production of toxic glucose metabolites and inducing mitochondrial biogenesis to restore mitochondrial function.

Pyruvate kinase M2 regulates Hif-1α activity and IL-1ß induction and is a critical determinant of the warburg effect in LPS-activated macrophages.

Macrophages activated by the TLR4 agonist LPS undergo dramatic changes in their metabolic activity. We here show that LPS induces expression of the key metabolic regulator Pyruvate Kinase M2 (PKM2). Activation of PKM2 using two well-characterized small molecules, DASA-58 and TEPP-46, inhibited LPS-induced Hif-1α and IL-1ß, as well as the expression of a range of other Hif-1α-dependent genes. Activation of PKM2 attenuated an LPS-induced proinflammatory M1 macrophage phenotype while promoting traits typical of an M2 macrophage. We show that LPS-induced PKM2 enters into a complex with Hif-1α, which can directly bind to the IL-1ß promoter, an event that is inhibited by activation of PKM2. Both compounds inhibited LPS-induced glycolytic reprogramming and succinate production. Finally, activation of PKM2 by TEPP-46 in vivo inhibited LPS and Salmonella typhimurium-induced IL-1ß production, while boosting production of IL-10. PKM2 is therefore a critical determinant of macrophage activation by LPS, promoting the inflammatory response.