Autophagy is a conserved pathway that delivers cytoplasmic contents to the lysosome for degradation. Here we consider its roles in neuronal health and disease. We review evidence from mouse knockout studies demonstrating the normal functions of autophagy as a protective factor against neurodegeneration associated with intracytoplasmic aggregate-prone protein accumulation as well as other roles, including in neuronal stem cell differentiation. We then describe how autophagy may be affected in a range of neurodegenerative diseases. Finally, we describe how autophagy upregulation may be a therapeutic strategy in a wide range of neurodegenerative conditions and consider possible pathways and druggable targets that may be suitable for this objective.

We used primary cultures of cortical neurons to examine the relationship between ␤-amyloid toxicity and hyperphosphorylation of the tau protein, the biochemical substrate for neurofibrillary tangles of Alzheimer's brain. Exposure of the cultures to ␤-amyloid peptide (␤AP) induced the expression of the secreted glycoprotein Dickkopf-1 (DKK1). DKK1 negatively modulates the canonical Wnt signaling pathway, thus activating the tau-phosphorylating enzyme glycogen synthase kinase-3␤. DKK1 was induced at late times after ␤AP exposure, and its expression was dependent on the tumor suppressing protein p53. The antisense induced knock-down of DKK1 attenuated neuronal apoptosis but nearly abolished the increase in tau phosphorylation in ␤AP-treated neurons. DKK1 was also expressed by degenerating neurons in the brain from Alzheimer's patients, where it colocalized with neurofibrillary tangles and distrophic neurites. We conclude that induction of DKK1 contributes to the pathological cascade triggered by ␤-amyloid and is critically involved in the process of tau phosphorylation.

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The Wilms tumor suppressor gene WTI is implicated in the ontogeny of genito-urinary abnormalities, including Denys-Drash syndrome and Wilms tumor of the kidney. WTI encodes Kruppel-type zinc finger proteins that can regulate the expression of several growth-related genes, apparently by binding to specific DNA sites located within 5' untranslated leader regions as well as 5' promoter sequences.Both WT1 and a closely related early growth response factor, EGR1, can bind the same DNA sequences from the mouse gene encoding insulin-like growth factor 2 (Igf-2). We report that WT1, but not EGR1, can bind specific Igf-2 exonic RNA sequences, and that the zinc fingers are required for this interaction. WT1 zinc finger 1, which is not represented in EGR1, plays a more significant role in RNA binding than zinc finger 4, which does have a counterpart in EGRI. Furthermore, the normal subnuclear localization of WT1 proteins is shown to be RNase, but not DNase, sensitive. Therefore, WT1 might, like the Kruppel-type zinc finger protein TFIIIA, regulate gene expression by both transcriptional and posttranscriptional mechanisms.The tumor suppressor gene, WT1, was identified by positional cloning at chromosome llpl3 on the basis of predisposition to Wilms tumor of the kidney (1, 2). Mutation of WT1 has been associated with abnormalities of the genito-urinary tract, in both humans (reviewed in refs. 3 and 4) and rodents (5, 6), establishing a clear developmental role for the Kruppel-type zinc finger proteins it encodes. Alternative splicing of WTJ results in the production of four variant WT1 proteins that differ by the presence or absence of 17 amino acids, encoded by exon 5, and 3 amino acids (lysine, threonine, and serine; KTS), encoded at the 3' terminus of exon 9 (7). All of the WT1 proteins contain four zinc fingers, which mediate binding to specific DNA sequences, and zinc fingers 2, 3, and 4 are highly homologous with the three zinc fingers of the early growth response factor EGR1 (1, 2, 8, 9). The KTS insertion occurs in the conserved linker region between zinc fingers 3 and 4, such that WT1 variants lacking these three amino acids (WT1-KTS) resemble EGR1 more closely than those in which they are present (WT1 +KTS). Consistent with this is the observation that WT1-KTS binds DNA sequences that resemble the EGR1 consensus-binding site (5'-GCGGGGGCG-3'), whereas WT1+KTS binds more disparate sequences (8-13). In transient transfection assays WT1 can regulate the expression of several growth-related genes containing these motifs (e.g., refs. 14-20), and usually acts as a repressor of these genes. WT1 has thus been described as a transcription factor.We were prompted to examine the possibility of a posttranscriptional regulatory role for WT1 by a number of observations. For maximum effect on at least some of its target genes, WT1-binding sites must be present both upstream and downstream of transcript initiation' sites (14,17,18,21,22). Functional WT1-binding sites are present within 5' untranslated leader sequences of s...

J. Neurochem. (2010) 112, 1539–1551. Abstract To investigate the role of the Wnt inhibitor Dickkopf‐1 (DKK‐1) in the pathophysiology of neurodegenerative diseases, we analysed DKK‐1 expression and localization in transgenic mouse models expressing familial Alzheimer’s disease mutations and a frontotemporal dementia mutation. A significant increase of DKK‐1 expression was found in the diseased brain areas of all transgenic lines, where it co‐localized with hyperphosphorylated tau‐bearing neurons. In TgCRND8 mice, DKK‐1 immunoreactivity was detected in neurons surrounding amyloid deposits and within the choline acetyltransferase‐positive neurons of the basal forebrain. Active glycogen synthase kinase‐3 (GSK‐3) was found to co‐localize with DKK‐1 and phospho‐tau staining. Downstream to GSK‐3, a significant reduction in β‐catenin translocation to the nucleus, indicative of impaired Wnt signaling functions, was found as well. Cumulatively, our findings indicate that DKK‐1 expression is associated with events that lead to neuronal death in neurodegenerative diseases and support a role for DKK‐1 as a key mediator of neurodegeneration with therapeutic potential.

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.

L-Acetylcarnitine (LAC, 100 mg/kg, s.c.), a drug commonly used for the treatment of painful neuropathies, substantially reduced mechanical allodynia in rats subjected to monolateral chronic constriction injury (CCI) of the sciatic nerve and also attenuated acute thermal pain in intact rats. In both cases, induction of analgesia required repeated injections of LAC, suggesting that the drug induces plastic changes within the nociceptive pathway. In both CCI-and sham-operated rats, a 24-day treatment with LAC increased the expression of metabotropic glutamate (mGlu) receptors 2 and 3 in the lumbar segment of the spinal cord, without changing the expression of mGlu1a or -5 receptors. A similar up-regulation of mGlu2/3 receptors was detected in the dorsal horns and dorsal root ganglia of intact rats treated with LAC for 5-7 days, a time sufficient for the induction of thermal analgesia. Immunohistochemical analysis showed that LAC treatment enhanced mGlu2/3 immunoreactivity in the inner part of lamina II and in laminae III and IV of the spinal cord. An increased mGlu2/3 receptor expression was also observed in the cerebral cortex but not in the hippocampus or cerebellum of LAC-treated animals.Reverse transcription-polymerase chain reaction combined with Northern blot analysis showed that repeated LAC injections selectively induced mGlu2 mRNA in the dorsal horns and cerebral cortex (but not in the hippocampus). mGlu3 mRNA levels did not change in any brain region of LAC-treated animals. To examine whether the selective up-regulation of mGlu2 receptors had any role in LAC-induced analgesia, we have used the novel compound LY 341495, which is a potent and systemically active mGlu2/3 receptor antagonist. LAC-induced analgesia was largely reduced 45 to 75 min after a single injection of LY 341495 (1 mg/kg, i.p.) in both CCI rats tested for mechanical allodynia and intact rats tested for thermal pain. We conclude that LAC produces analgesia against chronic pain produced not only by peripheral nerve injury but also by acute pain in intact animals and that LACinduced analgesia is associated with and causally related to a selective up-regulation of mGlu2 receptors. This offers the first example of a selective induction of mGlu2 receptors and discloses a novel mechanism for drug-induced analgesia.Neuropathic pain is characterized by spontaneous pain, allodynia, hyperalgesia, and pain summation and is a hallmark of neuropathies caused by traumatic injury, diabetes, and viral infections. An enhanced sensitivity of dorsal horn neurons to sensory stimulation (a phenomenon referred as "central sensitization") is commonly recognized as one of the mechanisms underlying chronic pain. In animal models of neuropathic pain, a sustained release of glutamate and peptides induces long-term potentiation at the synapses between primary afferent fibers and second-order neurons in the dorsal horns (reviewed by Sandkuhler, 2000). Induction of longterm potentiation requires the simultaneous activation of neurokinin receptors, NMDA recepto...

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.