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[spa] Se ha observado en nuestro grupo de investigación que tanto las células 3T3L1 como el tejido adiposo blanco in vivo son capaces de liberar, a partir de la glucosa, grandes cantidades de lactato en condiciones aeróbicas y glicerol en mayor cantidad que la que puede justificarse por lipólisis. Para investigar por qué los adipocitos actúan principalmente de manera glucolítica produciendo fragmentos de 3C sin verse afectados por la hipoxia desarrollamos la metodología necesaria aplicada a cultivos primarios. Puesto que el tejido adiposo blanco está compuesto por otros tipos celulares, comprobamos también si la hipoxia afecta de la misma manera a las células de la fracción estromal del tejido. El tejido responde a señales que el organismo produce como hormonas, por ello nos propusimos estudiar en adipocitos y en la fracción estromal, la modulación del metabolismo provocada por la insulina y la respuesta innata del tejido, es decir sin ningún estimulo externo más que el de la glucosa. Los resultados obtenidos señalan que el tejido adiposo blanco tiene una actividad metabólica elevada en términos relativos ya que a pesar de su escasa cantidad de masa “viva” (sólo el 1,3% del total), las células adiposas producen y liberan grandes cantidades de fragmentos de 3C. En los adipocitos, el lactato es producido a partir de la glucosa, independientemente de la presencia de oxígeno e insulina, para ser exportado a otras células y utilizado como fuente de energía. Esta idea se ve reforzada por el hecho que a concentraciones más elevadas de glucosa se produce más cantidad de lactato. Sin embargo, aunque las células de la fracción estromal también producen gran cantidad de lactato, este proceso no se ve influenciado por las concentraciones de glucosa. Por otra parte, el glicerol es producido solo por los adipocitos, siendo regulado por la insulina y constante en el tiempo. No obstante, al inicio el glicerol proviene de la vía glucolítica cuando la concentración de glucosa es elevada, pero cuando esta es baja proviene de la lipolisis. A las 48 h su origen cambia a glucolítico-lipolítico, excepto a 3,5mM de glucosa. Mientras que los ácidos grasos libres se reciclan para formar triacilgliceroles, muy poca glucosa 14C es incorporada, lo que indica una lipogénesis limitada. Sin embargo, la insulina promueve esta lipogénesis, aunque al mismo tiempo limita, al inicio, la incorporación de glicerol-3P para la síntesis de triacilgliceroles. La coexistencia de estos dos procesos, lipogénico y glucolítico a la vez, es probablemente una consecuencia para evitar la acumulación del exceso de energía, como un mecanismo de defensa contra la “glucolipotoxicidad” y una manera de suministrar energía en forma de fragmentos de 3C, fácilmente utilizable por otros tejidos., [eng] Our research group has observed that both 3T3L1 cells and white adipose tissue in vivo are able to release, from glucose, large amounts of lactate under aerobic conditions and glycerol in greater quantity than which can be justified by lipolysis. To study why adipocytes, act mainly in a glycolytic manner producing 3C fragments without being affected by hypoxia, we developed the necessary methodology applied to primary cultures. Since white adipose tissue is composed by other cell types, we also check whether hypoxia affects the stromal fraction cells in the same way. White adipose tissue responds to signals produced by the body as hormones, so we decided to study in adipocytes and the stromal fraction, how insulin can affect the adipocytes metabolism and their innate response, that is without any external stimulus. The results indicate that white adipose tissue has a high metabolic activity in relative terms since, despite its small amount of "living" mass (only 1.3% of the total), adipose cells produce and release large amounts of 3C fragments. In adipocytes, lactate is produced from glucose, independently of the presence of oxygen and insulin, to be exported to other cells and used as an energy source. This idea is reinforced by the fact that at higher concentrations of glucose, more lactate is produced. However, although the stromal fraction cells also produce large amounts of lactate, this process is not influenced by glucose concentrations. On the other hand, glycerol is produced only by adipocytes, being regulated by insulin and constant over time. However, initially glycerol comes from the glycolytic pathway, when the glucose concentration is high, but when it is low it comes from lipolysis. At 48 h, its origin changes to glycolytic-lipolytic, except at 3.5 mM glucose. While free fatty acids are recycled to form triacyclglycerols, very little 14C glucose is incorporated over time, indicating limited lipogenesis. But when insulin is added, this lipogenesis is promoted, even though at the same time the hormone limits, at the beginning, the incorporation of glycerol-3P for the synthesis of triacylglycerols. The coexistence of these two processes, lipogenic and glycolytic simultaneously, is probably a consequence to prevent the accumulation of energy excess as a defense mechanism against "glycolipotoxicity", and a way to supply easily usable energy by other tissues in the form of 3C fragments.

White adipose tissue (WAT) produces large amounts of lactate and glycerol from glucose. We used mature epididymal adipocytes to analyse the relative importance of glycolytic versus lipogenic glycerol in adipocytes devoid of external stimuli. Cells were incubated (24/48 h) with 7/14 mM glucose; half of the wells contained 14C-glucose. We analysed glucose label fate, medium metabolites, and the expression of key genes coding for proteins controlling glycerol metabolism. The effects of initial glucose levels were small, but time of incubation increased cell activity and modified its metabolic focus. The massive efflux of lactate was uniform with time and unrelated to glucose concentration; however, glycerol-3P synthesis was higher in the second day of incubation, being largely incorporated into the glycerides-glycerol fraction. Glycerophosphatase expression was not affected by incubation. The stimulation of glycerogenic enzymes’ expression was mirrored in lipases. The result was a shift from medium glycolytic to lipolytic glycerol released as a consequence of increased triacylglycerol turnover, in which most fatty acids were recycled. Production of glycerol seems to be an important primary function of adipocytes, maintained both by glycerogenesis and acyl-glycerol turnover. Production of 3C fragments may also contribute to convert excess glucose into smaller, more readily usable, 3C metabolites.