No abstract

The use of neural progenitor cells (NPCs) is limited by the incomplete knowledge of the extracellular signals regulating their proliferation and survival. We report that cultured mouse NPCs express functional mGlu3 and mGlu5 metabotropic glutamate receptors. Pharmacological blockade of both receptors reduced NPC proliferation and survival, whereas activation of mGlu5 receptors substantially enhanced cell proliferation. Adult mice lacking mGlu5 receptors or treated with mGlu5 or mGlu3 receptor antagonists showed a dramatic reduction in the number of dividing neuroprogenitors present in the subventricular zone and in the dentate gyrus of the hippocampus. These data disclose a novel function of mGlu receptors and offer new potential strategies for the optimization of cell replacement therapy in neurodegenerative disorders.

Methamphetamine (METH) is abused worldwide, and it represents a threat for public health. METH exposure induces a variety of detrimental effects. In fact, METH produces a number of oxidative species, which lead to lipid peroxidation, protein misfolding, and nuclear damage. Cell clearing pathways such as ubiquitin-proteasome (UP) and autophagy (ATG) are involved in METH-induced oxidative damage. Although these pathways were traditionally considered to operate as separate metabolic systems, recent studies demonstrate their interconnection at the functional and biochemical level. Very recently, the convergence between UP and ATG was evidenced within a single organelle named autophagoproteasome (APP), which is suppressed by mTOR activation. In the present research study, the occurrence of APP during METH toxicity was analyzed. In fact, coimmunoprecipitation indicates a binding between LC3 and P20S particles, which also recruit p62 and alpha-synuclein. The amount of METH-induced toxicity correlates with APP levels. Specific markers for ATG and UP, such as LC3 and P20S in the cytosol, and within METH-induced vacuoles, were measured at different doses and time intervals following METH administration either alone or combined with mTOR modulators. Western blotting, coimmunoprecipitation, light microscopy, confocal microscopy, plain transmission electron microscopy, and immunogold staining were used to document the effects of mTOR modulation on METH toxicity and the merging of UP with ATG markers within APPs. METH-induced cell death is prevented by mTOR inhibition, while it is worsened by mTOR activation, which correlates with the amount of autophagoproteasomes. The present data, which apply to METH toxicity, are also relevant to provide a novel insight into cell clearing pathways to counteract several kinds of oxidative damage.

Expression of Dickkopf-1 (Dkk-1), a secreted protein that negatively modulates the Wnt pathway, was induced in the hippocampus of gerbils and rats subjected to transient global cerebral ischemia as well as in cultured cortical neurons challenged with an excitotoxic pulse. In ischemic animals, the temporal and regional pattern of Dkk-1 expression correlated with the profile of neuronal death, as assessed by Nissl staining and Dkk-1 immunostaining in adjacent hippocampal sections. Treatment of ischemic animals with either Dkk-1 antisense oligonucleotides or lithium ions (which rescue the Wnt pathway acting downstream of the Dkk-1 blockade) protected vulnerable hippocampal neurons against ischemic damage. The same treatments protected cultured cortical neurons against NMDA toxicity. We conclude that induction of Dkk-1 with the ensuing inhibition of the canonical Wnt signaling pathway is required for the development of ischemic and excitotoxic neuronal death.

Summary:  Inhibition of the Wnt pathway by the secreted glycoprotein, Dickkopf‐1 (Dkk‐1) has been related to processes of excitotoxic and ischemic neuronal death. We now report that Dkk‐1 is induced in neurons of the rat olfactory cortex and hippocampus degenerating in response to seizures produced by systemic injection of kainate (12 mg/kg, i.p.). There was a tight correlation between Dkk‐1 expression and neuronal death in both regions, as shown by the different expression profiles in animals classified as “high” and “low” responders to kainate. For example, no induction of Dkk‐1 was detected in the hippocampus of low responder rats, in which seizures did not cause neuronal loss. Induction of Dkk‐1 always anticipated neuronal death and was associated with a reduction in nuclear levels of β‐catenin, which reflects an ongoing inhibition of the canonical Wnt pathway. Intracerebroventricular injections of Dkk‐1 antisense oligonucleotides (12 nmol/2 μL) substantially reduced kainate‐induced neuronal damage, as did a pretreatment with lithium ions (1 mEq/kg, i.p.), which rescue the Wnt pathway by acting downstream of the Dkk‐1 blockade. Taken collectively, these data suggest that an early inhibition of the Wnt pathway by Dkk‐1 contributes to neuronal damage associated with temporal lobe epilepsy. We also examined Dkk‐1 expression in the hippocampus of epileptic patients and their controls. A strong Dkk‐1 immunolabeling was found in six bioptic samples and in one autoptic sample from patients with mesial temporal lobe epilepsy associated with hippocampal sclerosis. Dkk‐1 expression was undetectable or very low in autoptic samples from nonepileptic patients or in bioptic samples from patients with complex partial seizures without neuronal loss and/or reactive gliosis in the hippocampus. Our data raise the attractive possibility that drugs able to rescue the canonical Wnt pathway, such as Dkk‐1 antagonists or inhibitors of glycogen synthase kinase‐3β, reduce the development of hippocampal sclerosis in patients with temporal lobe epilepsy.