The loss of body weight control is a critical public health problem. Our research group addresses this issue by studying the brain controls food intake and energy expenditure. In particular, we have been analyzing various aspects of the mechanism to detect and respond to glucose (glucosensing) in particular areas of the hypothalamus.

Tanycytes and glucodetection

The ventromedial hypothalamus (VMH) is involved in regulating feeding and satiety behaviors through their capacity to detect changes in glucose concentrations. VMH neurons release neuropeptides that control food intake and are contacted in apposition with highly elongated ependymal glial cells known as tanycytes. We have shown that tanycytes respond to glucose with the increase of intracellular calcium, which depends on glycolysis and not on oxidative phosphorylation. In this mechanism, the enzyme glucokinase has an important role, currently, we are studying the regulation of this enzyme by nuclear compartmentalization and the effect of inhibition of specific tanycyte proteins on the feeding behavior.

Neuron-glia interaction

As well as other important physiological and pathophysiological events, we have postulated that the hypothalamic glucosensing is carried out by a glia-neuron interaction. Our localization results of monocarboxylate transporters (MCTs) in the basal hypothalamus support the existence of a glia-neuron communication. We have shown that cultured tanycytes release ATP and lactate, which can be incorporated into the orexigenic and anorexigenic neurons. Currently, we evaluated if the expression of neuropeptides could be affected once inhibited MCTs, specifically in tanycytes. We are exploring whether the endocannabinoid system and ketogenesis might modulate glia-neuron interaction.

Stem cells

Dentin generation from stem cell, derived from dental pulp. BMP participation in odontoblastic differentiation in vitro.

In vitro studies

We use transport techniques to assess incorporation and release of glucose or lactate, microscopy of cell live to evaluate calcium waves and pH changes in response to glucose and its metabolites in culture of hypothalamic glia and neurons.

In situ studies

We use brain and different tissues for immunolocalization assays using multiple labeling and spectral confocal microscopy.

Ex vivo studies

In sliced of hypothalamus we analyzing calcium waves and electrophysiological recording using transgenic mice (POMC-EGFP).

In vivo studies

We have developed adenovirus that allows to inhibit or overexpress specifical proteins in the tanycytes through injection into the third ventricle. Lentivirus are commonly used to affect the expression of neuronal proteins. In these models we evaluate expression of neuropeptides that controls food intake and changes in the frequency of feeding.

Quiñones M, Cofre J, Benítez J, García D, Romero N, González A, Carvajal N, García-Robles MA, López V, Schenk G, Uribe E. (2015). Insight on the interaction of an agmatinase-like protein with Mn(2+) activator ions. J Inorg Biochem. 145:65-9.
Agmatinase is an enzyme that catalyzes the hydrolysis of agmatine, a compound that is associated with numerous functions in the brain of mammalian organisms such as neurotransmitter, anticonvulsant, antinociceptive, anxiolytic and antidepressant-like actions.

Elizondo-Vega R, Barahona MJ, Oyarce K, Cortes-Campos C, Carril C, García-Robles MA. (2015). The Role of Tanycytes in Hypothalamic Glucosensing. J Cell Molec Med. 20(10):1-12
Tanycytes are elongated hypothalamic glial cells that cover the basal walls of the third ventricle; their apical regions contact the cerebrospinal fluid (CSF), and their processes reach hypothalamic neuronal nuclei that control the energy status of an organism.

Salgado M, Tarifeño-Saldivia E, Ordenes P, Millán C, Yañez MJ, Llanos P, Villagra M, Elizondo-Vega R, Martínez F, Nualart F, Uribe E, García-Robles MA. 2014. Dynamic localization of glucokinase and its regulatory protein in hypothalamic tanycytes. PLoS One.9(4):e94035. doi: 10.1371/ journal.pone.0094035
Glucokinase (GK), the hexokinase involved in glucose sensing in pancreatic β cells, is also expressed in hypothalamic tanycytes, which cover the ventricular walls of the basal hypothalamus and are implicated in an indirect control of neuronal activity by glucose.

Salazar K, Cerda G, Martínez F, Sarmiento JM, González C, Rodríguez F, García-Robles M, Tapia JC, Cifuentes M, Nualart F. 2014. SVCT2 transporter expression is post-natally induced in cortical neurons and its function is regulated by its short isoform. J Neurochem. 130(5):693-706. doi: 10.1111/jnc.12793.
Different studies have demonstrated the importance of micronutrients, such as vitamins, for normal adult brain function and development.

Rodríguez FS, Salazar KA, Jara NA, García-Robles MA, Pérez F, Ferrada LE, Martínez F, Nualart F. 2013. Superoxide’dependent uptake of vitamin C in human glioma cells. J Neurochem. 127(6):793-804. doi: 10.1111/jnc.12365J .
Glioblastomas are lethal brain tumors that resist current cytostatic therapies.

Cortes-Campos C, Elizondo R, Carril C, Martinez F, Boric K, Nualart F, Garcia-Robles MA. (2013). MCT2 expression and lactate influx in anorexigenic and orexigenic neurons of the arcuate nucleus (ISI) PLoS One. 2013 Apr 26;8(4):e62532.doi: 10.1371/journal.pone.
Hypothalamic neurons of the arcuate nucleus control food intake, releasing orexigenic and anorexigenic neuropeptides in response to changes in glucose concentration.

Montoya F, Martínez F, García-Robles M, Balmaceda-Aguilera C, Koch X, Rodríguez F, Silva-Álvarez C, Salazar K, Ulloa V, Nualart F. Clinical and experimental approaches to knee cartilage lesion repair and mesenchymal stem cell chondrocyte differentiation.
Cartilage has poor regeneration capacity due to the scarcity of endogenous stem cells, its low metabolic activity and the avascular environment.

Nualart F, Castro T, Low M, Henríquez JP, Oyarce K, Cisternas P, García A, Yáñez AJ, Bertinat R, Montecinos VP, García-Robles MA. (2013). Dynamic expression of the sodium-vitamin C co-transporters, SVCT1 and SVCT2, during perinatal kidney development. Histochem Cell Biol. 139(2):233-47.
Isoform 1 of the sodium-vitamin C co-transporter (SVCT1) is expressed in the apical membrane of proximal tubule epithelial cells in adult human and mouse kidneys.

García-Robles MA, Elizondo R, Cortés-Campos C, Martínez F, Nualart F. Brain monitoring of glucose homeostasis. Neuron-glia interactions. (2012). Biomedical Research 3(1):29-39 2012 (Cielo)

Nualart F, Salazar K, Oyarce K, Cisternas P, Jara N, Silva-Álvarez C, Pastor P, Martínez F, García A, García-Robles MA, Tapia JC. (2013). Typical and atypical stem cells in the brain, vitamin C effect and neuropathology Biol Res. 45(3):243-56.
Stem cells are considered a valuable cellular resource for tissue replacement therapies in most brain disorders.

Balmaceda-Aguilera C, Cortés-Campos C, Cifuentes M, Peruzzo B, Mack L, Tapia JC, Oyarce K, García MA, Nualart F. (2012). Glucose transporter 1 and monocarboxylate transporters 1, 2, and 4 localization within the glial cells of shark blood-brain-barriers. PLoS One. 7(2):e32409. doi: 10.1371/journal.pone.0032409.
The ventromedial hypothalamus is involved in regulating feeding and satiety behavior, and its neurons interact with specialized ependymal-glial cells, termed tanycytes.

Orellana JA, Sáez PJ, Cortés-Campos C, Elizondo RJ, Shoji KF, Contreras-Duarte S, Figueroa V, Velarde V, Jiang JX, Nualart F, Sáez JC, García MA. (2012) Glucose increases intracellular free Ca(2+) in tanycytes via ATP released through connexin 43 hemichannels. Glia. 60(1):53-68. doi: 10.1002/glia.21246.
The ventromedial hypothalamus is involved in regulating feeding and satiety behavior, and its neurons interact with specialized ependymal-glial cells, termed tanycytes.

Nuñez-Parra A, Cortes-Campos C, Bacigalupo J, García MA, Nualart F, Reyes JG. (2011). Expression and distribution of facilitative glucose (GLUTs) and monocarboxylate/H+ (MCTs) transporters in rat olfactory epithelia. Chem Senses. 36(9):771-80. doi: 10.1093/chemse/bjr052.
Cell-to-cell metabolic interactions are crucial for the functioning of the nervous system and depend on the differential expression of glucosetransporters (GLUTs) and monocarboxylate transporters (MCTs).

Cifuentes M*, García MA*, Arrabal PM, Martínez F, Yañez MJ, Jara N, Weil B, Domínguez D, Medina RA, Nualart F. (2011). Insulin regulates GLUT1-mediated glucose transport in MG-63 human osteosarcoma cells. J Cell Physiol. 226(6):1425-32 DOI: 10.1002/jcp.22668 * equal contribution
Metabolic interaction via lactate between glial cells and neurons has been proposed as one of the mechanisms involved in hypothalamic glucosensing.

Cortés-Campos C, Elizondo R, Llanos P, Uranga RM, Nualart F, García MA. (2011). MCT expression and lactate influx/efflux in tanycytes involved in glia-neuron metabolic interaction. PLoS One. 6(1):e16411. doi: 10.1093/chemse/bjr052. Epub 2011 Jun 15
Metabolic interaction via lactate between glial cells and neurons has been proposed as one of the mechanisms involved in hypothalamic glucosensing. We have postulated that hypothalamic glial cells, also known as tanycytes, produce lactate by glycolytic metabolism of glucose.

Mella C, Martínez F, García MA, Nualart F, Castro V, Bustos P, Carvajal N, Uribe E. (2010). Expression and localization of an agmatinase-like protein in the rat brain. Histochem Cell Biol. 134(2):137-44. doi: 10.1007/s00418-010-0720-z
Agmatinase catalyzes the hydrolysis of agmatine into putrescine and urea, and agmatine (decarboxylated L: -arginine) plays several roles in mammalian tissues, including neurotransmitter/neuromodulatory actions in the brain.

Millán C, Martínez F, Cortés-Campos C, Lizama I, Yañez MJ, Llanos P, Reinicke K, Rodríguez F, Peruzzo B, Nualart F, García MA. (2010). Glial glucokinase expression in adult and post-natal development of the hypothalamic region. ASN Neuro. 2(3):e00035. doi: 10.1042/AN20090059.
It has recently been proposed that hypothalamic glial cells sense glucose levels and release lactate as a signal to activate adjacent neurons.

Mella A, Martinez F, Garcia MA, Nualart F, Bustos P, Carvajal N, Uribe A. (2010). Expression and localization of a agmatinase-like protein in the rat brain. Histochemistry and Cell Biology 134(2):137-44
Agmatinase catalyzes the hydrolysis of agmatine into putrescine and urea, and agmatine (decarboxylated L: -arginine) plays several roles in mammalian tissues, including neurotransmitter/neuromodulatory actions in the brain.

Mella A, Martinez F, Garcia MA, Nualart F, Bustos P, Carvajal N, Uribe A. (2010). Expression and localization of a agmatinase-like protein in the rat brain. Histochemistry and Cell Biology 134(2):137-44
Agmatinase catalyzes the hydrolysis of agmatine into putrescine and urea, and agmatine (decarboxylated L: -arginine) plays several roles in mammalian tissues, including neurotransmitter/neuromodulatory actions in the brain.

Nualart F, García MA, Medina R, Owen G. (2009). Glucose transporters in sex steroid hormone related cancer. Current Vascular Pharmacology 7: 534-548.
Cancer cells, as with most mammalian cells, depend on a continuous supply of glucose; not only as a precursor of glycoproteins, triglycerides and glycogen, but also as an important source of energy.

Caprile T, Salazar C, Astuya A, Cisternas P, Montecinos H, Millán C, García MA, Nualart F. (2009). The Na+-dependent L-ascorbic acid transporter SVCT2 expressed in brain stem cells, neurons and neuroblastoma cells is inhibited by flavonoids. Journal of Neurochemistry 108: 563-577.
Ascorbic acid (AA) is best known for its role as an essential nutrient in humans and other species1.

Godoy A, Salazar K, Figueroa C, Smith GJ, García MA, Nualart F. (2009). Nutricional channels in breast cancer. Journal and Cellular Molecular Medicine 12(6): 1-12.
Breast cancers increase glucose uptake by increasing expression of the facilitative glucose transporters (GLUTs), mainly GLUT1.

Castro T, Low M, Salazar K, Montecinos H, Cifuentes M, Yáñez AJ, Slebe JC, Figueroa CD, Reinicke K, García MA, Henríquez JP, Nualart F. (2008) Differential distribution of the Sodium-vitamin C cotransporter-1 along the proximal tubule of the mouse and human kidney. Kidney International 74(10):1278-86.
Vitamin C is reabsorbed from the renal lumen by one isoform of sodium-vitamin C co-transporters that mediate high affinity sodium-dependent L-ascorbic acid transport.

Meneses AM, Medina RA, Kato S, Pinto M, Jaque MP, Lizama I, García MA, Nualart F, Owen GI. 2008. Regulation of GLUT3 and glucose uptake by the cAMP signalling pathway in the breast cancer cell line ZR-75. J Cell Physiol. 214(1):110-6. PubMed PMID: 17559076.
Increased glucose uptake as a principal energy source is a requirement for the continued survival of tumour cells.

Castro MA, Pozo M, Cortés C, García MA, Concha II, Nualart F. Intracellular ascorbic acid inhibits transport of glucose by neurons, but not by astrocytes. J Neurochem. 2007 Aug;102(3):773-82. PubMed PMID: 17630983. Castro MA, Pozo. It has been demonstrated that glutamatergic activity induces ascorbic acid (AA) depletion in astrocytes.

Godoy A, Ulloa V, Rodríguez F, Reinicke K, Yañez AJ, García MA, Medina RA, Carrasco M, Barberis S, Castro T, Martínez F, Koch X, Vera JC, Poblete MT, Figueroa CD, Peruzzo B, Pérez F, Nualart F. 2006. Differential subcellular distributionof glucose transporters GLUT1-6 and GLUT9 in human cancer: ultrastructurallocalization of GLUT1 and GLUT5 in breast tumor tissues. J Cell Physiol207(3):614-27. PubMed PMID: 16523487.
It has been proposed that the enhanced metabolic activity of tumor cells is accompanied by an increased expression of facilitative hexose transporters(GLUTs).

Astuya A, Caprile T, Castro M, Salazar K, García M, Reinicke K, Rodríguez F, Vera JC, Millán C, Ulloa V, Low M, Martínez F, Nualart F. Vitamin C uptake and recycling among normal and tumor cells from the central nervous system. J. Neurosci Res. 79(1-2):146-56. PubMed PMID:15578707.
Specialized cells transport vitamin C in its reduced form using sodium-dependent cotransporters (SVCT1 and SVCT2)0.

García MA, Salazar K, Millán C, Rodríguez F, Montecinos H, Caprile T, Silva C, Cortes C, Reinicke K, Vera JC, Aguayo LG, Olate J, Molina B, Nualart F. Sodium vitamin C cotransporter SVCT2 is expressed in hypothalamic glial cells. Glia. 2005 Apr 1;50(1):32-47. PubMed PMID: 15625716.
Kinetic analysis of vitamin C uptake demonstrated that different specialized cells take up ascorbic acid through sodium-vitamin C cotransporters.

Yáñez AJ, Bertinat R, Spichiger C, Carcamo JG, García M, Concha II, Nualart F, Slebe JC. 2005. Novel expression of liver FBPase in Langerhans islets of human and rat pancreas. J Cell Physiol. 205(1):19-24. PubMed PMID: 15965961.
Several reports have indicated the absence of gluconeogenic enzymes in pancreatic islet cells.

Silva-Alvarez C, Carrasco M, Balmaceda-Aguilera C, Pastor P, García MA, Reinicke K, Aguayo L, Molina B, Cifuentes M, Medina R, Nualart F. 2005. Ependymal cell differentiation and GLUT1 expression is a synchronous process in the ventricular wall. Neurochem Res. 30(10):1227-36.
Ependymal cells appear to be totally differentiated during the first 3 weeks in the mouse brain.

Medina RA, Meneses AM, Vera JC, Gúzman C, Nualart F, Rodriguez F, Garcia M, Kato S, Espinoza N, Monsó C, Carvajal A, Pinto M, Owen GI. 2004. Differential regulation of glucose transporter expression by estrogen and progesterone in Ishikawa endometrial cancer cells. J Endocrinol. 182(3):467-78.
Estrogen replacement therapy and other unopposed estrogen treatments increase the incidence of endometrial abnormalities, including cancer.

Verleysdonk S, Hirschner W, Wellard J, Rapp M, Garcia M, Nualart F, Hamprecht B. 2004. Regulation by insulin and insulin-like growth factor of 2-deoxyglucose uptake in primary ependymal cell cultures. Neurochem Res. 29(1):127-34.
Ependymal cells have been reported to express the facilitative glucose carriers GLUT1, GLUT2, and GLUT4, as well as glucokinase.

Medina RA, Meneses AM, Vera JC, Guzman C, Nualart F, Astuya A, García MA, Kato S, Carvajal A, Pinto M, Owen GI. 2003. Estrogen and progesterone up-regulateglucose transporter expression in ZR-75-1 human breast cancer cells. Endocrinology. 144(10):4527-35 Breast cancer incidence increases in women receiving combined estrogen and progesterone therapy.

García M, Millán C, Balmaceda-Aguilera C, Castro T, Pastor P, Montecinos H, Reinicke K, Zúñiga F, Vera JC, Oñate SA, Nualart F. 2003. Hypothalamic ependymal-glial cells express the glucose transporter GLUT2, a protein involved in glucose sensing. J Neurochem. Aug;86(3):709-24. PubMed PMID: 12859684.
The GLUT2 glucose transporter and the K-ATP-sensitive potassium channels have been implicated as an integral part of the glucose-sensingmechanism in the pancreatic islet beta cells.

Klattenhoff C, Montecino M, Soto X, Guzmán L, Romo X, García MA, Mellstrom B, Naranjo JR, Hinrichs MV, Olate J. 2003. Human brain synembryn interacts with Gsalpha and Gqalpha and is translocated to the plasma membrane in response to isoproterenol and carbachol. J Cell Physiol. 195(2):151-7.
Heterotrimeric G-proteins transduce signals from heptahelical transmembrane receptors to different effector systems, regulating diverse complex intracellular pathways and functions.

Garcia MA, Carrasco M, Godoy A, Reinicke K, Montecinos VP, Aguayo LG, Tapia JC, Vera JC, Nualart F. 2001. Elevated expression of glucose transporter-1 in hypothalamic ependymal cells not involved in the formation of the brain-cerebrospinal fluid barrier. J Cell Biochem. 80(4):491-50.
Glucose transporters play an essential role in the acquisition of glucose by the brain.