Faculty Bibliography

We report that neuronal overexpression of the endogenous inhibitor of calpains, calpastatin (CAST), in a mouse model of human Alzheimer's disease (AD) beta-amyloidosis, the APP23 mouse, reduces beta-amyloid (Abeta) pathology and Abeta levels when comparing aged, double transgenic (tg) APP23/CAST with APP23 mice. Concurrent with Abeta plaque deposition, aged APP23/CAST mice show a decrease in the steady-state brain levels of the amyloid precursor protein (APP) and APP C-terminal fragments (CTFs) when compared with APP23 mice. This CAST-dependent decrease in APP metabolite levels was not observed in single tg CAST mice expressing endogenous APP or in younger, Abeta plaque predepositing APP23/CAST mice. We also determined that the CAST-mediated inhibition of calpain activity in the brain is greater in the CAST mice with Abeta pathology than in non-APP tg mice, as demonstrated by a decrease in calpain-mediated cytoskeleton protein cleavage. Moreover, aged APP23/CAST mice have reduced extracellular signal-regulated kinase 1/2 (ERK1/2) activity and tau phosphorylation when compared with APP23 mice. In summary, in vivo calpain inhibition mediated by CAST transgene expression reduces Abeta pathology in APP23 mice, with our findings further suggesting that APP metabolism is modified by CAST overexpression as the mice develop Abeta pathology. Our results indicate that the calpain system in neurons is more responsive to CAST inhibition under conditions of Abeta pathology, suggesting that in the disease state neurons may be more sensitive to the therapeutic use of calpain inhibitors.

Familial partial epilepsy with variable foci (FPEVF) is an autosomal dominant form of partial epilepsy characterized by the presence of epileptic seizures originating from different cerebral lobes in different members of the same family. Linkage to chromosomes 22q12 and 2q36 has been reported, although only six families have been published. We studied a new FPEVF family including nine affected individuals. The phenotype in this family was similar to that previously described and consisted of nocturnal and daytime seizures with semiology suggesting a frontal lobe origin. A video-EEG (electroencephalography) recording of the proband's seizures is presented and revealed hyperkinetic seizures of frontal lobe origin preceded by left frontal spikes. We excluded linkage to chromosome 2q36 and found a suggestion of linkage to chromosome 22q12 with a lod score of 2.64 (h = 0) for marker D22S689.

The metabolism of the amyloid precursor protein (APP) and tau are central to the pathobiology of Alzheimer's disease (AD). We have examined the in vivo turnover of APP, secreted APP (sAPP), Abeta and tau in the wild-type and Tg2576 mouse brain using cycloheximide to block protein synthesis. In spite of overexpression of APP in the Tg2576 mouse, APP is rapidly degraded, similar to the rapid turnover of the endogenous protein in the wild-type mouse. sAPP is cleared from the brain more slowly, particularly in the Tg2576 model where the half-life of both the endogenous murine and transgene-derived human sAPP is nearly doubled compared to wild-type mice. The important Abeta degrading enzymes neprilysin and IDE were found to be highly stable in the brain, and soluble Abeta40 and Abeta42 levels in both wild-type and Tg2576 mice rapidly declined following the depletion of APP. The cytoskeletal-associated protein tau was found to be highly stable in both wild-type and Tg2576 mice. Our findings unexpectedly show that of these various AD-relevant protein metabolites, sAPP turnover in the brain is the most different when comparing a wild-type mouse and a beta-amyloid depositing, APP overexpressing transgenic model. Given the neurotrophic roles attributed to sAPP, the enhanced stability of sAPP in the beta-amyloid depositing Tg2576 mice may represent a neuroprotective response

Individuals with Down syndrome develop beta-amyloid deposition characteristic of early-onset Alzheimer's disease (AD) in mid-life, presumably because of an extra copy of the chromosome 21-located amyloid precursor protein (App) gene. App mRNA and APP metabolite levels were assessed in the brains of Ts65Dn mice, a mouse model of Down syndrome, using quantitative PCR, western blot analysis, immunoprecipitation, and ELISAs. In spite of the additional App gene copy, App mRNA, APP holoprotein, and all APP metabolite levels in the brains of 4-month-old trisomic mice were not increased compared with the levels seen in diploid littermate controls. However starting at 10 months of age, brain APP levels were increased proportional to the App gene dosage imbalance reflecting increased App message levels in Ts65Dn mice. Similar to APP levels, soluble amino-terminal fragments of APP (sAPPalpha and sAPPbeta) were increased in Ts65Dn mice compared with diploid mice at 12 months but not at 4 months of age. Brain levels of both Abeta40 and Abeta42 were not increased in Ts65Dn mice compared with diploid mice at all ages examined. Therefore, multiple mechanisms contribute to the regulation towards diploid levels of APP metabolites in the Ts65Dn mouse brain

Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE; MIM 600513) has been associated with mutations in the genes coding for the alfa-4 (CHRNA4), beta-2 (CHRNB2), and alpha-2 (CHRNA2) subunits of the neuronal nicotinic acetylcholine receptor (nAChR) and for the corticotropin-releasing hormone (CRH). A four-generation ADNFLE family with six affected members was identified. All affected members presented the clinical characteristics of ADNFLE. Interictal awake and sleep EEG recordings showed no epileptiform abnormalities. Ictal video-EEG recordings showed focal seizures with frontal lobe semiology. Mutation analysis of the CHRNB2 gene revealed a c.859G>A transition (Val287Met) within the second transmembrane domain, identical to that previously described in a Scottish ADNFLE family. To our knowledge, this is the third family reported presenting a mutation in CHRNB2. The clinical phenotype appears similar to that described with mutations in CHRNA4, suggesting that mutations in these two subunits lead to similar functional alterations of the nAChR.

BACKGROUND: Lafora disease (LD; progressive myoclonus epilepsy type 2; EPM2) is an autosomal recessive disorder caused by mutations in the EPM2A and EPM2B genes. LD is characterized by the presence of strongly PAS-positive intracellular inclusions (Lafora bodies) in several tissues. Glycogen storage disease type IV (GSD-IV; Andersen disease) is an autosomal recessive disorder characterized by cirrhosis leading to severe liver failure. GSD-IV has been associated with mutations in the glycogen branching enzyme gene (GBE). Histopathologic changes of the liver in both diseases show an identical appearance, although cirrhosis has never been described in patients with LD. We report a LD family in which the proband presented severe liver failure at onset of the disease. METHODS: Clinical histories, physical and neurologic examination, laboratory tests, EEGs, MRI of the brain, and liver or axillary skin biopsies were performed in the two affected siblings. The diagnosis was confirmed by molecular genetic analysis of the EPM2A, EPM2B, and GBE genes and loci. RESULTS: During the first decade of life, abnormalities in liver function tests were detected in the two affected siblings. The proband's liver dysfunction was severe enough to require liver transplantation. Subsequently, both sibs developed LD. Mutation analysis of EPM2A revealed a homozygous Arg241stop mutation in both patients. CONCLUSIONS: This is the first description of severe hepatic dysfunction as the initial clinical manifestation of LD. The phenotypic differences between the two affected siblings suggest that modifier genes must condition clinical expression of the disease outside the CNS.

BACKGROUND: The Ehlers-Danlos syndrome (EDS) comprises a group of hereditary connective tissue disorders. Periventricular nodular heterotopia (PNH) is a human neuronal migration disorder characterised by seizures and conglomerates of neural cells around the lateral ventricles of the brain, caused by FLNA mutations. FLNA encodes filamin A, an actin binding protein involved in cytoskeletal organisation. The amino-terminal actin binding domain (ABD) of filamins contains two tandem calponin homology domains, CHD1 and CHD2. OBJECTIVE: To report clinical and genetic analyses in a Spanish family affected by a connective tissue disorder suggestive of EDS type III and PNH. METHODS: A clinical and molecular study was undertaken in the three affected women. Clinical histories, physical and neurological examinations, brain magnetic resonance imaging studies, and skin biopsies were done. Genetic analysis of the FLNA gene was undertaken by direct sequencing and restriction fragment length polymorphism analysis. RESULTS: Mutation analysis of the FLNA gene resulted in the identification of a novel mutation in exon 3 (c.383C-->T) segregating with the combination of both syndromes. This mutation results in a substitution of an alanine residue (A128V) in CHD1. CONCLUSIONS: The findings suggest that the Ala128Val mutation causes the dual EDS-PNH phenotype. This association constitutes a new variant within the EDS spectrum. This is the first description of a familial EDS-PNH association with a mutation in FLNA.