Immunofluorescence and histochemical methods for neural M1 pyruvate kinase localization

A metabolic switch in brain: glucose and lactate metabolism modulation by ascorbic acid

In this review, we discuss a novel function of ascorbic acid in brain energetics. It has been proposed that during glutamatergic synaptic activity neurons preferably consume lactate released from glia. The key to this energetic coupling is the metabolic activation that occurs in astrocytes by glutamate and an increase in extracellular [K(+)]. Neurons are cells well equipped to consume glucose because they express glucose transporters and glycolytic and tricarboxylic acid cycle enzymes. Moreover, neuronal cells express monocarboxylate transporters and lactate dehydrogenase isoenzyme 1, which is inhibited by pyruvate. As glycolysis produces an increase in pyruvate concentration and a decrease in NAD(+)/NADH, lactate and glucose consumption are not viable at the same time. In this context, we discuss ascorbic acid participation as a metabolic switch modulating neuronal metabolism between rest and activation periods. Ascorbic acid is highly concentrated in CNS. Glutamate stimulates ascorbic acid release from astrocytes. Ascorbic acid entry into neurons and within the cell can inhibit glucose consumption and stimulate lactate transport. For this switch to occur, an ascorbic acid flow is necessary between astrocytes and neurons, which is driven by neural activity and is part of vitamin C recycling. Here, we review the role of glucose and lactate as metabolic substrates and the modulation of neuronal metabolism by ascorbic acid.

Is Melanoma a stem cell tumor? Identification of neurogenic proteins in trans-differentiated cells

Background

Although several genes and proteins have been implicated in the development of melanomas, the molecular mechanisms involved in the development of these tumors are not well understood. To gain a better understanding of the relationship between the cell growth, tumorigenesis and differentiation, we have studied a highly malignant cat melanoma cell line that trans-differentiates into neuronal cells after exposure to a feline endogenous retrovirus RD114.

Methods

To define the repertoire of proteins responsible for the phenotypic differences between melanoma and its counterpart trans-differentiated neuronal cells we have applied proteomics technology and compared protein profiles of the two cell types and identified differentially expressed proteins by 2D-gel electrophoresis, image analyses and mass spectrometry.

Results

The melanoma and trans-differentiated neuronal cells could be distinguished by the presence of distinct sets of proteins in each. Although approximately 60–70% of the expressed proteins were shared between the two cell types, twelve proteins were induced de novo after infection of melanoma cells with RD114 virus in vitro. Expression of these proteins in trans-differentiated cells was significantly associated with concomitant down regulation of growth promoting proteins and up-regulation of neurogenic proteins (p = < 0.001). Based on their physiologic properties, >95% proteins expressed in trans-differentiated cells could be associated with the development, differentiation and regulation of nervous system cells.

Conclusion

Our results indicate that the cat melanoma cells have the ability to differentiate into distinct neuronal cell types and they express proteins that are essential for self-renewal. Since melanocytes arise from the neural crest of the embryo, we conclude that this melanoma arose from embryonic precursor stem cells. This model system provides a unique opportunity to identify domains of interactions between the expressed proteins that halt the tumorigenic potential of melanoma cells and drive them toward neurogenerative pathways involved in early neurogenesis. A better understanding of these proteins in a well-coordinated signaling network would also help in developing novel approaches for suppression of highly malignant tumors that arise from stem-like embryonic cells.

Trifluoperazine activates and releases latent ATP-generating enzymes associated with the synaptic plasma membrane

Neurone-specific enolase (NSE) and the brain form of creatine phosphokinase (CPK-BB) were previously found to be present in rat synaptosomal plasma membranes (SPM) using two-dimensional gel (2-D gel) and peptide analysis; enzymatic activities of these and of pyruvate kinase (PK), all involved in ATP generation, were shown to be "cryptic" unless the SPM were treated with Triton X-100. We now show that enzymatic activation also occurs when the SPM are treated with trifluoperazine (TFP). TFP activation occurred even when the enzymes were membrane associated, showing that solubilization was not responsible for "unmasking" the enzyme activities. When TFP treatment was performed at alkaline instead of neutral pH, NSE and CPK-BB were released as well as PK, nonneuronal enolase, and aldolase which were identified by 2-D gel and tryptic peptide analysis. Other proteins released included calmodulin, actin, and the 70-kilodalton heat-shock cognate protein. Tubulin, synapsin I, and a 35-kilodalton basic protein were largely unaffected. The latter was identified as the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase on the basis of 2-D gel and peptide analyses and subsequent partial sequencing of a rat brain cDNA coding for the same protein. TFP treatment is thus useful for activating latent enzymes as well as for distinguishing enzymes that have a different disposition on the membrane.

Monoclonal antibody to aldolase C: a selective marker for Purkinje cells in the human cerebellum

A monoclonal antibody to the glycolytic enzyme aldolase C was used in an immunoperoxidase technique on unfixed and formalin-fixed paraffin-embedded tissues from the human central nervous system (CNS) and other tissues. No staining outside the CNS was detected. In the central nervous system the antibody gave a selective and intense staining of Purkinje cell perikarya, axons and dendrites in both fixed and unfixed tissues. In the human fetal brain, positive staining of Purkinje cells was seen from 35-36 weeks' gestation onwards. This coincides with the conversion of Purkinje cells to a tetraploid state, and may reflect increased glycolytic activity accompanying the rapid dendritic growth at this stage of development. Preliminary investigations on a variety of disease states suggest that this antibody may be useful in studies of ischaemic damage, congenital abnormalities and degenerative conditions affecting the cerebellum.

Insulin dependence of M2 pyruvate kinase in primary culture of human liver

In the basal state, the presence of L pyruvate kinase (LPK) was constantly observed in primary human liver cell cultures initiated from explants, when cells were examined by immunofluorescence and double labelling. After short-term insulin incubation, M pyruvate kinase (MPK) appeared. Therefore, both LPK and MPK were located in the same cells. We previously obtained the same results in isolated rat hepatocytes in which we demonstrated that short-term regulation of M2PK by insulin was a function of dose and/or incubation time. The present work established that similar conditions govern the regulation of this isozyme in vitro in human hepatocytes.