Alzheimer's disease (AD) and related tauopathies comprise a large group of neurodegenerative diseases associated with the pathological aggregation of tau protein. While much effort has focused on understanding the function of tau, little is known about the endogenous mechanisms regulating tau metabolism in vivo and how these contribute to disease. Previously, we have shown that the microRNA (miRNA) cluster miR-132/212 is downregulated in tauopathies such as AD. Here, we report that miR-132/212 deficiency in mice leads to increased tau expression, phosphorylation and aggregation. Using reporter assays and cell-based studies, we demonstrate that miR-132 directly targets tau mRNA to regulate its expression. We identified GSK-3β and PP2B as effectors of abnormal tau phosphorylation in vivo. Deletion of miR-132/212 induced tau aggregation in mice expressing endogenous or human mutant tau, an effect associated with autophagy dysfunction. Conversely, treatment of AD mice with miR-132 mimics restored in part memory function and tau metabolism. Finally, miR-132 and miR-212 levels correlated with insoluble tau and cognitive impairment in humans. These findings support a role for miR-132/212 in the regulation of tau pathology in mice and humans and provide new alternatives for therapeutic development.

Muscleblind-like-1 (MBNL1) is a splicing regulatory factor controlling the fetal-to-adult alternative splicing transitions during vertebrate muscle development. Its capture by nuclear CUG expansions is one major cause for type 1 myotonic dystrophy (DM1). Alternative splicing produces MBNL1 isoforms that differ by the presence or absence of the exonic regions 3, 5, and 7. To understand better their respective roles and the consequences of the deregulation of their expression in DM1, here we studied the respective roles of MBNL1 alternative and constitutive exons. By combining genetics, molecular and cellular approaches, we found that (i) the exon 5 and 6 regions are both needed to control the nuclear localization of MBNL1; (ii) the exon 3 region strongly enhances the affinity of MBNL1 for its pre-mRNA target sites; (iii) the exon 3 and 6 regions are both required for the splicing regulatory activity, and this function is not enhanced by an exclusive nuclear localization of MBNL1; and finally (iv) the exon 7 region enhances MBNL1-MBNL1 dimerization properties. Consequently, the abnormally high inclusion of the exon 5 and 7 regions in DM1 is expected to enhance the potential of MBNL1 of being sequestered with nuclear CUG expansions, which provides new insight into DM1 pathophysiology.Splicing of pre-mRNA is a key post-transcriptional step in eukaryotic gene expression. A vast majority of vertebrate pre-mRNAs is alternatively spliced, allowing the production of several protein isoforms from transcripts of a given gene (1). The regulation of alternative splicing plays a major role in cell differentiation and in development and depends on the expression and activity of numerous splicing regulatory factors that are expressed differentially during development, according to the type of tissue. Defects in these alternative-splicing processes can contribute to pathogenesis, as demonstrated for a growing number of diseases, including neuromuscular diseases such as myotonic dystrophy type 1 (DM1) 9 (2, 3). DM1 is an autosomal disorder caused by an unstable CTG repeat expansion in the 3Ј-untranslated region (UTR) of the DMPK gene (4 -6). One of the main etiological hypotheses of DM1 is based on a toxic RNA gain of function, leading to the dysregulation of alternative splicing. Mutant transcripts bearing long-CUG repeats acquire unusual A-form doublestranded RNA structures (7), accumulate in the nucleus, and lead to small ribonucleoprotein inclusions, named foci (8) that sequester RNA-binding proteins such as Muscleblind-like 1 * This work was supported by the Association Française contre les Myopathies Grants 14269 and 15047, the Agence Nationale de Recherche NeuroSplicedeTau BLAN 1114 01, the EURASNET EU Contract FP6, life sciences, genomics and biotechnology for health, the Centre National de la Recherche Scientifique, the Institut National pour la Santé et la Recherche Mé dicale, the French Ministry for Youth, National Education and Research, and the Lorraine Region. The abbreviations used are: DM1, myotonic dystrophy type...

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J. Neurochem. (2008) 104, 1599–1612. Abstract Mitochondrial alterations have been associated with the cytotoxic effect of 6‐hydroxydopamine (6‐OHDA), a widely used toxin to study Parkinson’s disease. In previous work, we have demonstrated that 6‐OHDA increases mitochondrial membrane permeability leading to cytochrome c release, but the precise mechanisms involved in this process remain unknown. Herein we studied the mechanism of increased mitochondrial permeability of SH‐SY5Y neuroblastoma cells in response to 6‐OHDA. Cytochrome c release induced by 6‐OHDA occurred, in both SH‐SY5Y cells and primary cultures, in the absence of mitochondrial swelling or a decrease in mitochondrial calcein fluorescence, suggesting little involvement of the mitochondrial permeability transition pore in this process. In contrast, 6‐OHDA‐induced cell death was associated with a significant translocation of the pro‐apoptotic Bax protein from the cytosol to mitochondria and with a significant induction of the BH3‐only protein PUMA. Experiments in mouse embryonic fibroblasts deficient in Bax or PUMA demonstrated a role for both proteins in 6‐OHDA‐induced apoptosis. Although 6‐OHDA elevated both total and nuclear p53 protein levels, activation of p53 was not essential for subsequent cell death. In contrast, we found that p38 mitogen‐activated protein kinase (MAPK) was activated early during 6‐OHDA‐induced apoptosis, and that treatment with the p38 MAPK inhibitor SKF86002 potently inhibited PUMA induction, green fluorescent protein‐Bax redistribution and apoptosis in response to 6‐OHDA. These data demonstrate a critical involvement of p38 MAPK, PUMA, and Bax in 6‐OHDA‐induced apoptosis.

Alzheimer's disease (AD) is characterized by both amyloid and Tau pathologies. The amyloid component and altered cholesterol metabolism are closely linked, but the relationship between Tau pathology and cholesterol is currently unclear. Brain cholesterol is synthesized in situ and cannot cross the blood-brain barrier: to be exported from the central nervous system into the blood circuit, excess cholesterol must be converted to 24S-hydroxycholesterol by the cholesterol 24-hydroxylase encoded by the CYP46A1 gene. In AD patients, the concentration of 24S-hydroxycholesterol in the plasma and the cerebrospinal fluid are lower than in healthy controls. The THY-Tau22 mouse is a model of AD-like Tau pathology without amyloid pathology. We used this model to investigate the potential association between Tau pathology and CYP46A1 modulation. The amounts of CYP46A1 and 24S-hydroxycholesterol in the hippocampus were lower in THY-Tau22 than control mice. We used an adeno-associated virus (AAV) gene transfer strategy to increase CYP46A1 expression in order to investigate the consequences on THY-Tau22 mouse phenotype. Injection of the AAV-CYP46A1 vector into the hippocampus of THY-Tau22 mice led to CYP46A1 and 24S-hydroxycholesterol content normalization. The cognitive deficits, impaired long-term depression and spine defects that characterize the THY-Tau22 model were completely rescued, whereas Tau hyperphosphorylation and associated gliosis were unaffected. These results argue for a causal link between CYP46A1 protein content and memory impairments that result from Tau pathology. Therefore, CYP46A1 may be a relevant therapeutic target for Tauopathies and especially for AD.

Background: There is a growing interest in the involvement of anesthetic agents in the etiology of postoperative cognitive dysfunction. Recent animal studies suggest that acute anes-

Myotonic dystrophy (DM) of type 1 and 2 (DM1 and DM2) are inherited autosomal dominant diseases caused by dynamic and unstable expanded microsatellite sequences (CTG and CCTG, respectively) in the non-coding regions of the genes DMPK and ZNF9, respectively. These mutations result in the intranuclear accumulation of mutated transcripts and the mis-splicing of numerous transcripts. This so-called RNA gain of toxic function is the main feature of an emerging group of pathologies known as RNAopathies. Interestingly, in addition to these RNA inclusions, called foci, the presence of neurofibrillary tangles (NFT) in patient brains also distinguishes DM as a tauopathy. Tauopathies are a group of nearly 30 neurodegenerative diseases that are characterized by intraneuronal protein aggregates of the microtubule-associated protein Tau (MAPT) in patient brains. Furthermore, a number of neurodegenerative diseases involve the dysregulation of splicing regulating factors and have been characterized as spliceopathies. Thus, myotonic dystrophies are pathologies resulting from the interplay among RNAopathy, spliceopathy, and tauopathy. This review will describe how these processes contribute to neurodegeneration. We will first focus on the tauopathy associated with DM1, including clinical symptoms, brain histology, and molecular mechanisms. We will also discuss the features of DM1 that are shared by other tauopathies and, consequently, might participate in the development of a tauopathy. Moreover, we will discuss the determinants common to both RNAopathies and spliceopathies that could interfere with tau-related neurodegeneration.

A recent genome-wide association meta-analysis for Alzheimer's disease (AD) identified 19 risk loci (in addition to APOE) in which the functional genes are unknown. Using Drosophila, we screened 296 constructs targeting orthologs of 54 candidate risk genes within these loci for their ability to modify Tau neurotoxicity by quantifying the size of >6000 eyes. Besides Drosophila Amph (ortholog of BIN1), which we previously implicated in Tau pathology, we identified p130CAS (CASS4), Eph (EPHA1), Fak (PTK2B) and Rab3-GEF (MADD) as Tau toxicity modulators. Of these, the focal adhesion kinase Fak behaved as a strong Tau toxicity suppressor in both the eye and an independent focal adhesion-related wing blister assay. Accordingly, the human Tau and PTK2B proteins biochemically interacted in vitro and PTK2B co-localized with hyperphosphorylated and oligomeric Tau in progressive pathological stages in the brains of AD patients and transgenic Tau mice. These data indicate that PTK2B acts as an early marker and in vivo modulator of Tau toxicity.