Effects of glucose and insulin on glucokinase activity in rat hypothalamus

Abstract

In an attempt to study the role of glucokinase (GK) and the effects of glucose and peptides on GK gene expression and on the activity of this enzyme in the hypothalamus, we used two kinds of biological models: hypothalamic GT1-7 cells and rat hypothalamic slices. The expression of the GK gene in GT1-7 cells was reduced by insulin (INS) and was not modified by different glucose concentrations, while GK enzyme activities were significantly reduced by the different peptides. Interestingly, a distinctive pattern of GK activities between the ventromedial hypothalamus (VMH) and lateral hypothalamus (LH) were found, with higher enzyme activities in the VMH as the glucose concentrations rose, while LH enzyme activities decreased at 2 . 8 and 20 mM glucose, the latter effect being prevented by incubation with INS. These effects were produced only by D-glucose and the modifications found were due to GK, but not to other hexokinases. In addition, GK activities in the VMH and the LH were reduced by glucagonlike peptide 1, leptin, orexin B, INS, and neuropeptide Y (NPY), but this effect was only statistically significant for NPY in LH. Our results indicate that the effects of both glucose and peptides occur on GK enzyme activities rather than on GK gene transcription. Moreover, the effects of glucose and INS on GK activity suggest that in the brain GK behaves in a manner opposite to that in the liver, which might facilitate its role in glucose sensing. Finally, hypothalamic slices seem to offer a good physiological model to discriminate the effects between different areas.

Glucokinase as a Glucose Sensor in Hypothalamus - Regulation by Orexigenic and Anorexigenic Peptides

“…These findings could reflect a different type of behavior for the GE and GI neurons located in the VMH and the LH, when challenged by different concentrations of glucose. This would be in agreement with the tendency of GK activity to increase with rises in glucose in the range of 0.5-20 mM that was reported in the VMH (Sanz et al, 2007), while neurons in LH were not excited by the higher concentrations of glucose but by lower concentrations of this hexose, as happens with GK activities (Sanz et al, 2007). The observed changes in GK activity in response to glucose in certain hypothalamic areas suggest that such activity would not only be tissue-specific but also even cell-specific in defined brain areas.…”

“…The effects of orexigenic and anorexigenic peptides and glucose on GK gene expression were tested (Sanz et al, 2007) in GT1-7 immortalized hypothalamic neurons, which are glucose-sensing cells able to respond to glucose deprivation or high-glucose levels, as well as having intrinsic GK activity. Neither the promoter activity of the GK gene in transfected GT1-7 cells nor the endogenous GK gene expression were modified by the action of different concentrations of glucose or GLP-1, leptin, or NPY in the extracellular space.…”

“…In fact, slices of developing brain tissue can be grown for several weeks as so called organotypic slice cultures (Noraberg et al, 2005), but also adult rats have been used. In this sense our group have used short-term hypothalamic slices cultures, obtained from adult rat, to test the effect of different peptides on the gene expression and enzymatic activity in the VMH and LH areas (Sanz et al, 2007;Sanz et al, 2008). Thus, the hypothalamic organotypic cultures are a useful model for the study of the physiological effect of some peptides on specific hypothalamic nuclei, which could be dissected after the treatment and analyzed by enzymatic, molecular, biochemical or histological procedures.…”

Signaling and biological effects of glucagon-like peptide 1 on the differentiation of mesenchymal stem cells from human bone marrow

“…The hMSCs, cultured under undifferentiated or differentiating conditions, were harvested, and RT-PCR was performed as described previously (36). Total RNA was isolated with Trizol Reagent (Invitrogen, Carlsbad, CA), and reverse transcription (RT; Applied Biosystems, Foster City, CA) was performed with 1 g of total RNA to obtain 20 l of cDNA.…”

Location, location, location: the CNS sites of leptin action dictate its regulation of homeostatic and hedonic pathways

“…8,9 VMH neurons express glucokinase, an important component of the glucose-sensing machinery, and the VMH acts as a major sensor of brain glucose levels. 10 Leptin treatment of the VMH promotes increased glucose uptake in peripheral tissues, though it is not clear whether this effect is mediated by direct connections with the sympathetic nervous system or through modulation of other hypothalamic neurons that project to the periphery. 11 Indeed, VMH neurons, potentially including VMH LepRb neurons, project to and activate POMC neurons in the dorsolateral ARC, and the modulation of these as well as other circuits likely contributes to the effects of leptin action in the VMH.…”