Marina P. Sánchez

Perinatal lethality of microtubule-associated protein 1B-deficient mice expressing alternative isoforms of the protein at low levels.

Microtubule-associated protein 1B (MAP1B) has been implicated in axogenesis in cultured cells. To gain insight into the functions that MAP1B plays in vivo, we analyzed a strain of Map1B mutant mice generated by a gene trapping approach. Homozygous mice die on the first day after birth, probably due to a severe abnormal development of the nervous system. They present alterations in the structure of several brain regions. The normal Map1B gene yields different protein isoforms from alternatively spliced transcripts. The smaller isoforms were present in wild type, hetero-, and homozygous mice, but their expression was higher in the mutants than in the wild-type. Moreover, trace amounts of MAP1B protein were also observed in Map1B homozygous mutants, indicating an alternative splicing around the gene trap insertion. Thus, the Map1B gene trapped mutation reported in this work did not generated a null mutant, but a mouse with a drastic deficiency in MAP1B expression. Analyses of these mice indicate the presence of several neural defects and suggest the participation of MAP1B in neuronal migration.

Lafora bodies and neurological defects in malin-deficient mice correlate with impaired autophagy

Lafora disease (LD), a fatal neurodegenerative disorder characterized by the presence of intracellular inclusions called Lafora bodies (LBs), is caused by loss-of-function mutations in laforin or malin. Previous studies suggested a role of these proteins in the regulation of glycogen biosynthesis, in glycogen dephosphorylation and in the modulation of the intracellular proteolytic systems. However, the contribution of each of these processes to LD pathogenesis is unclear. We have generated a malin-deficient (Epm2b-/-) mouse with a phenotype similar to that of LD patients. By 3-6 months of age, Epm2b-/- mice present neurological and behavioral abnormalities that correlate with a massive presence of LBs in the cortex, hippocampus and cerebellum. Sixteen-day-old Epm2b-/- mice, without detectable LBs, show an impairment of macroautophagy (hereafter called autophagy), which remains compromised in adult animals. These data demonstrate similarities between the Epm2a-/- and Epm2b-/- mice that provide further insights into LD pathogenesis. They illustrate that the dysfunction of autophagy is a consequence of the lack of laforin-malin complexes and a common feature of both mouse models of LD. Because this dysfunction precedes other pathological manifestations, we propose that decreased autophagy plays a primary role in the formation of LBs and it is critical in LD pathogenesis.

Steele-Richardson-Olszewski syndrome in a patient with a single C212Y mutation in the parkin protein.

Steele‐Richardson‐Olszewski syndrome (SROS) is a neurodegenerative disorder of unknown aetiology, most frequently sporadic. Familial cases of SROS have been described. An intronic polymorphism of the tau gene is associated with sporadic SROS and mutations of the tau gene are present in atypical cases of SROS. The role of tau has been excluded in other families with pathology proven SROS, suggesting that this syndrome may have multiple causes. An 82‐year‐old patient, father of 3 children with autosomal recessive juvenile parkinsonism due to combined heterozygous mutations of the parkin gene, developed clinical features of SROS 2 years before death. The diagnosis was confirmed by pathology. He carried the C212Y mutation of the parkin gene and was homozygous for the A0 polymorphism and for the H1 haplotype. The role of parkin in the processing of tau is discussed.

Effects of cinnarizine, a calcium antagonist that produces human parkinsonism, in parkin knock out mice

Cinnarizine, a calcium antagonist that produces parkinsonism in humans, induces behavioural changes such as alopecia, buco-lingual dyskinesia and reduction of motor activity in female parkin knock out (PK-KO) mice but not in wild-type (WT) controls. PK-KO mice have high striatal dopamine levels and increased dopamine metabolism in spite of low reduced tyrosine hydroxylase protein. Cinnarizine, which blocks dopamine receptors and increases dopamine release, further increased dopamine metabolism. PK-KO mice increased GSH levels as a compensatory mechanism against enhanced free radical production related to acceleration of dopamine turnover. Neuronal markers, such as beta-tubulin slightly increased in PK-KO and furthermore with cinnarizine. Astroglial markers were decreased in PK-KO mice, and this effect was potentiated by cinnarizine, suggesting abnormal glia in these animals. Microglia was hyperactivated in PK-KO midbrain, suggesting inflammation in these animals. Proapoptotic proteins were increased by cinnarizine and, to a lesser extent, in PK-KO mice. Our data indicate that mutation of parkin is a risk factor for drug-induced parkinsonism.

Progressive supranuclear palsy and tau hyperphosphorylation in a patient with a C212Y parkin mutation

Autosomal recessive-juvenile parkinsonism (AR-JP) is one of the most common forms of familial Parkinsons disease (PD) and is related to mutations in the Park-2 gene, encoding for a protein ligase of ubiquitin, parkin. Different mutations located along the parkin gene have been observed in different AR-JP affected families, possibly interfering with the normal function of parkin and the proteasome system. Two cases of patients with AR-JP have been recently described presenting different homo- and heterozygous parkin mutations and limited tau pathology. We report here the case of a patient with clinical and pathological findings compatible with progressive supranuclear palsy (PSP), carrier of a single, heterozygous mutation of the parkin gene, and homozygous for the H1/H1 haplotype in the tau gene. Abnormal tau hyperphosphorylation has been observed in our patient brain samples, suggesting that a partial deficit of parkin, a protein with ubiquitin-ligase function, may trigger tau pathology in individuals with molecular genetic risk factors.

Hyperexcitability and epileptic seizures in a model of frontotemporal dementia

Epileptic seizures are more common in patients with Alzheimer disease than in the general elderly population. Abnormal forms of hyperphosphorylated tau accumulate in Alzheimer disease and other tauopathies. Aggregates of tau are also found in patients with epilepsy and in experimental models of epilepsy. We report here the analysis of epileptic activity and neuropathological correlates of a transgenic line over-expressing human mutant tau, a model of frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17). The FTDP-17 model displays spontaneous epileptic activity and seizures with spike-wave complexes in the EEG, and a higher sensitivity to the GABAA receptor antagonist pentylenetetrazol (PTZ) when compared to age-matched controls, showing a notably increased seizure length and a shorter latency to develop severe seizures. FTDP-17 human tau mutants also display lower convulsive thresholds and higher lethality after PTZ injections. Astrocytosis and activated microglia are prominent in the hippocampus and other brain regions of young FTDP-17 mice where the human mutant tau transgene is expressed, before the appearance of hyperphosphorylated tau aggregates in these structures. FTDP-17 human mutant tau over-expression produces epilepsy and increased GABAA receptor-mediated hyperexcitability in the absence of Aβ pathology. Although aggregates of hyperphosphorylated tau have been observed in patients with epilepsy and in different chemically and electrically generated models of epilepsy, the FTDP-17 tau mutant analyzed here is the first model of genetically modified tau that presents with epilepsy. This model may represent a valuable tool to assay novel treatments in order to reduce tau pathology, a potential factor which may be involved in the development of epileptic seizures in dementia and other neurodegenerative diseases.

Park2-Null/Tau Transgenic Mice Reveal a Functional Relationship between Parkin and Tau

Mutations, haplotypes, and polymorphisms of tau and Park-2 genes constitute risk factors for developing tauopathies. In order to analyze the possible relationship between parkin and tau we generated a double-mutant mouse deficient for Park-2 expression and overexpressing a mutant tau protein (hTauVLW). Mice develop normally, although the median survival rate is considerably reduced with respect to wild type (45%). Aggregates of phosphorylated tau in neurons and reactive gliosis are quite abundant in cortex and hippocampus of these mice. Moreover, while in young transgenic mice the hTauVLW immunostained transgene product is observed in both cell bodies and dendrites, the hTauVLW mutant protein is only detected in the neuronal cell bodies when Park-2 gene is additionally deleted. Moreover, DNA fragmentation was detected by the TUNEL method, and cerebral atrophy is also present in these regions. The levels of phosphorylated tau and Hsp70 are increased in the double-mutant mice, while CHIP expression in hippocampus is lower when the Park-2 gene is deleted. Thus, the combination of Park-2 gene deletion with hTauVLW transgene overexpression in mice produces serious neuropathological effects, which reflect the existence of some relationship between both proteins.

Pharmacological Interventions to Ameliorate Neuropathological Symptoms in a Mouse Model of Lafora Disease.

Lafora disease (LD, OMIM 254780) is a rare fatal neurodegenerative disorder that usually occurs during childhood with generalized tonic-clonic seizures, myoclonus, absences, drop attacks, or visual seizures. Unfortunately, at present, available treatments are only palliatives and no curative drugs are available yet. The hallmark of the disease is the accumulation of insoluble polyglucosan inclusions, called Lafora bodies (LBs), within the neurons but also in heart, muscle, and liver cells. Mouse models lacking functional EPM2A or EPM2B genes (the two major loci related to the disease) recapitulate the Lafora disease phenotype: they accumulate polyglucosan inclusions, show signs of neurodegeneration, and have a dysregulation of protein clearance and endoplasmic reticulum stress response. In this study, we have subjected a mouse model of LD (Epm2b−/−) to different pharmacological interventions aimed to alleviate protein clearance and endoplasmic reticulum stress. We have used two chemical chaperones, trehalose and 4-phenylbutyric acid. In addition, we have used metformin, an activator of AMP-activated protein kinase (AMPK), as it has a recognized neuroprotective role in other neurodegenerative diseases. Here, we show that treatment with 4-phenylbutyric acid or metformin decreases the accumulation of Lafora bodies and polyubiquitin protein aggregates in the brain of treated animals. 4-Phenylbutyric acid and metformin also diminish neurodegeneration (measured in terms of neuronal loss and reactive gliosis) and ameliorate neuropsychological tests of Epm2b−/− mice. As these compounds have good safety records and are already approved for clinical uses on different neurological pathologies, we think that the translation of our results to the clinical practice could be straightforward.

Laforin and malin deletions in mice produce similar neurologic impairments.

Abstract Lafora disease is a progressive myoclonus epilepsy caused by mutations in the EPM2A gene encoding laforin or in the EPM2B gene encoding malin. It is characterized by the presence of polyglucosan intracellular inclusion bodies (Lafora bodies) in brain and other tissues. Targeted disruption of Epm2a or Epm2b genes in mice produced widespread neuronal degeneration and accumulation of Lafora bodies in neuronal and nonneuronal tissues. Here we analyzed the neurologic alterations produced by disruption of the laforin gene in Epm2a−/− mice and compared them to those in malin-deficient mice. Both Epm2a−/− and Epm2b−/− mice showed altered motor activity, impaired motor coordination, abnormal hind limb clasping, and episodic memory deficits. Epm2a−/− mice also had tonic-clonic seizures, whereas both Epm2a−/− and Epm2b−/− mice had spontaneous single spikes, spike-wave, polyspikes, and polyspike-wave complexes with correlated myoclonic jerks. Neurologic alterations observed in the mutants were comparable and correlated with the accumulation of abundant Lafora bodies in the cerebral cortex, the hippocampus, the basal ganglia, the cerebellum, and the brainstem, suggesting that these inclusions could cause cognitive and behavioral deterioration. Thus, both Epm2a−/− and Epm2b−/− mice exhibit many pathologic aspects seen in patients with Lafora disease and may be valuable for the study of this disorder.

Sodium selenate treatment improves symptoms and seizure susceptibility in a malin-deficient mouse model of Lafora disease

To search for new therapies aimed at ameliorating the neurologic symptoms and epilepsy developing in patients with Lafora disease.