Differential expression of genes encoding proteins of the HGF/MET system in insulinomas

Abstract\ud \ud Background\ud Insulinomas are the most common functional pancreatic neuroendocrine tumors, whereas histopathological features do not predict their biological behaviour. In an attempt to better understand the molecular processes involved in the tumorigenesis of islet beta cells, the present study evaluated the expression of genes belonging to the hepatocyte growth factor and its receptor (HGF/MET) system, namely, MET, HGF; HGFAC and ST14 (encode HGF activator and matriptase, respectively, two serine proteases that catalyze conversion of pro-HGF to active HGF); and SPINT1 and SPINT2 (encode serine peptidase inhibitors Kunitz type 1 and type 2, respectively, two inhibitors of HGF activator and of matriptase).\ud \ud \ud Methods\ud Quantitative real-time reverse transcriptase polymerase chain reaction was employed to assess RNA expression of the target genes in 24 sporadic insulinomas: 15 grade 1 (G1), six grade 2 (G2) and three hepatic metastases. Somatic mutations of MET gene were searched by direct sequencing of exons 2, 10, 14, 16, 17 and 19.\ud \ud \ud Results\ud Overexpression of MET was observed in the three hepatic metastases concomitantly with upregulation of the genes encoding HGF and matriptase and downregulation of SPINT1. A positive correlation was observed between MET RNA expression and Ki-67 proliferation index while a negative correlation was detected between SPINT1 expression and the mitotic index. No somatic mutations were found in MET gene.\ud \ud \ud Conclusion\ud The final effect of the increased expression of HGF, its activator (matriptase) and its specific receptor (MET) together with a decreased expression of one potent inhibitor of matriptase (SPINT1) is probably a contribution to tumoral progression and metastatization in insulinomas

Astrocyte Gliotransmission in the Regulation of Systemic Metabolism

Normal brain function highly relies on the appropriate functioning of astrocytes. These glial cells are strategically situated between blood vessels and neurons, provide significant substrate support to neuronal demand, and are sensitive to neuronal activity and energy-related molecules. Astrocytes respond to many metabolic conditions and regulate a wide array of physiological processes, including cerebral vascular remodeling, glucose sensing, feeding, and circadian rhythms for the control of systemic metabolism and behavior-related responses. This regulation ultimately elicits counterregulatory mechanisms in order to couple whole-body energy availability with brain function. Therefore, understanding the role of astrocyte crosstalk with neighboring cells via the release of molecules, e.g., gliotransmitters, into the parenchyma in response to metabolic and neuronal cues is of fundamental relevance to elucidate the distinct roles of these glial cells in the neuroendocrine control of metabolism. Here, we review the mechanisms underlying astrocyte-released gliotransmitters that have been reported to be crucial for maintaining homeostatic regulation of systemic metabolism

Low-glucose sensing in neurons and astrocytes from the nucleus of the tractus solitarius

O cérebro é altamente dependente da glicose para manter o metabolismo celular, e a hipoglicemia cerebral pode comprometer a neurotransmissão e sobrevivência. O núcleo do trato solitário (NTS) é um centro integrativo para o controle da glicemia, e recentes estudos mostram que neurônios e astrócitos do NTS podem responder a alterações da concentração de glicose no ambiente extracelular. No presente estudo, visamos investigar os mecanismos de sensibilidade à baixa glicose extracelular em neurônios e astrócitos do NTS em fatias do tronco encefálico de roedores. Em condições normoglicêmicas, verificamos que a maioria dos neurônios do NTS despolarizam em resposta à baixa glicose extracelular por um mecanismo dependente de voltagem que envolve a abertura de uma corrente catiônica. Adicionalmente, demonstramos que os canais para potássio sensíveis ao ATP (KATP) controlam o potencial de repouso da membrana, e portanto são moduladores significativos da sensibilidade à baixa glicose extracelular em neurônios do NTS. Em astrócitos do NTS, observamos que a diminuição da concentração de glicose extracelular aumenta a frequência de oscilações de cálcio citosólico por um mecanismo dependente da mobilização de cálcio mediada pelo receptor de inositol 1,4,5-trifosfato tipo 2 (IP3R2) em retículos endoplasmáticos. Verificamos também a existência de sinalização astrócito-neurônio por glutamato, a qual pode ser regulada pela concentração de glicose do meio externo. Além disso, demonstramos que uma condição hiperglicêmica compromete a sensibilidade à baixa glicose extracelular em neurônios e astrócitos do NTS, e pode afetar a gliotransmissão. Nossos dados sugerem que a sensibilidade à baixa glicose extracelular em neurônios e astrócitos do NTS pode estar relacionada à deficiência autonômica associada à hipoglicemia.The brain primarily relies on glucose for sustaining cell metabolism, and brain hypoglycemia may compromise neurotransmission and cell survivor. The nucleus tractus solitarius (NTS) is an integrative center for the control of circulating glucose, and recent studies have shown that NTS neurons and astrocytes can respond to glucose concentration changes in the extracellular milieu. Here, we aimed to investigate the low-glucose-sensing mechanisms in NTS neurons and astrocytes from rodent brainstem slices. In normoglycemic conditions (5 mM glucose), we verified that most NTS neurons depolarize in response to a low-glucose challenge (0.5 mM glucose), in a voltage-dependent mechanism involving the opening of a cationic current. Additionally, we demonstrated that ATP-sensitive potassium channels (KATP) control the resting membrane potential, thus notably modulating the low-glucose response in neurons. Regarding the NTS astrocytes, we observed that the reduction of external glucose concentration induces an increase in calcium oscillation frequency in the soma via an inositol 1,4,5-triphosphate type 2 (IP3R2)- dependent calcium release from the endoplasmic reticulum. We also verified the existence of a glutamate-mediated astrocyte-neuron signaling that can be regulated by extracellular glucose levels. Moreover, we showed that a hyperglycemic condition (10 mM glucose) compromises the low-glucose sensitivity in NTS neurons and astrocytes, and can affect gliotransmission. Our data suggest that the low-glucose sensing mechanisms might be related to the hypoglycemia-associated autonomic failur