Novel antiadipogenic effect of menadione in 3T3-L1 cells.

Inhibition of adipocyte differentiation can be used as a strategy for preventing adipose tissue expansion and, consequently, for obesity management. Since reactive oxygen species (ROS) have emerged as key modulators of adipogenesis, the effect of menadione (a synthetic form of vitamin K known to induce the increase of intracellular ROS) on 3T3-L1 preadipocyte differentiation was studied. Menadione (15 µM) increased ROS and lipid peroxidation, generating mild oxidative stress without affecting cell viability. Menadione drastically inhibited adipogenesis, accompanied by decreased intracellular lipid accumulation and diminished expression of the lipo/adipogenic markers peroxisome proliferator-activated receptor (PPAR)γ, fatty acid synthase (FAS), CCAAT/enhancer-binding protein (C/EBP) α, fatty acid binding protein (FABP) 4, and perilipin. Menadione treatment also increased lipolysis, as indicated by augmented glycerol release and reinforced by the increased expression of hormone-sensitive lipase (HSL). Additionally, menadione increased the inhibitory phosphorylation of acetyl-CoA-carboxylase (ACC), which results in the inhibition of fatty acid synthesis. As a consequence, triglyceride content was decreased. Menadione also inhibited the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. Further, treatment with increased concentration of insulin, a potent physiological activator of the PI3K/Akt pathway, rescued the normal level of expression of PPARγ, the master regulator of adipogenesis, and overcame the restraining effect of menadione on the differentiation capacity of 3T3-L1 preadipocytes. Our study reveals novel antiadipogenic action for menadione, which is, at least in part, mediated by the PI3K/Akt pathway signaling and raises its potential as a therapeutic agent in the treatment or prevention of adiposity.

Phosphoinositides: Two-Path Signaling in Neuronal Response to Oligomeric Amyloid ß Peptide.

We have previously demonstrated that oligomeric amyloid ß peptide (oAß) together with iron overload generates synaptic injury and activation of several signaling cascades. In this work, we characterized hippocampal neuronal response to oAß. HT22 neurons exposed to 500 nM oAß showed neither increased lipid peroxidation nor altered mitochondrial function. In addition, biophysical studies showed that oAß did not perturb the lipid order of the membrane. Interestingly, although no neuronal damage could be demonstrated, oAß was found to trigger bifurcated phosphoinositide-dependent signaling in the neuron, on one hand, the phosphorylation of insulin receptor, the phosphatidylinositol 3-kinase (PI3K)-dependent activation of Akt, its translocation to the nucleus and the concomitant phosphorylation, inactivation, and nuclear exclusion of the transcription factor Forkhead Box O3a (FoxO3a), and on the other, phosphoinositide-phospholipase C (PI-PLC)-dependent extracellular signal-regulated kinase 1/2 (ERK1/2) activation. Pharmacological manipulation of the signaling cascades was used in order to better characterize the role of oAß-activated signals, and mitochondrial function was determined as a measure of neuronal viability. The inhibition of PI3K, PI-PLC, and general phosphoinositide metabolism impaired neuronal mitochondrial function. Furthermore, increased oAß-induced cell death was observed in the presence of phosphoinositide metabolism inhibition. Our results allow us to conclude that oAß triggers the activation of phosphoinositide-dependent signaling, which results in the subsequent activation of neuroprotective mechanisms that could be involved in the determination of neuronal fate.