Biomedical subjects

Katrin Beyer

Publications and source records attributed to Katrin Beyer.

7 recordsLinked to original sources

PubMed2006

Low alpha-synuclein 126 mRNA levels in dementia with Lewy bodies and Alzheimer disease.

Alpha-synuclein, a main component of Lewy bodies in synucleinopathies and senile plaques in Alzheimer disease, is centrally involved in neurodegeneration. Three different isoforms (alpha-synuclein 112, 126, and 140) resulting from alternative splicing have been described so far. The present study explores alpha-synuclein 126 mRNA expression levels in the prefrontal cortex of six patients with dementia with Lewy bodies, eight patients with Lewy body variant of Alzheimer disease, eight patients with Alzheimer disease, and 10 controls. Relative alpha-synuclein 126 expression levels were determined by real-time polymerase chain reaction with competimer technology. Alpha-synuclein 126 mRNA expression was markedly decreased in the three dementias in comparison with controls, suggesting an important role of this alpha-synuclein isoform in the normal brain.

Aged↗

PubMed2006

Alpha-synuclein structure, posttranslational modification and alternative splicing as aggregation enhancers.

Alpha-synuclein aggregation is thought to be a key event in the pathogenesis of synucleinopathies. Although different alpha-synuclein alterations and modifications have been proposed to be responsible for early aggregation steps, the mechanisms underlying these events remain unclarified. Alpha-synuclein is a small protein localized to synaptic terminals and its intrinsic structure has been claimed to be an important factor for self-oligomerization and self-aggregation. Alpha-synuclein expression studies in cell cultures have demonstrated that posttranslational modifications, such as phosphorylation, oxidation, and sumoylation, are primarily involved in alpha-synuclein aggregation. Furthermore, in the last few years accumulating evidence has pointed to alternative splicing as a crucial mechanism in the development of neurodegenerative disorders. At least three different alpha-synuclein isoforms have been described as products of alternative splicing. Two of these isoforms (alpha-synuclein 112 and alpha-synuclein 126) are shorter proteins with probably altered functions and aggregation propensity. The present review attempts to summarize the data so far available on alpha-synuclein structure, posttranslational modifications, and alternative splicing as possible enhancers of aggregation.

Alternative Splicing↗

PubMed2004

Upregulation of amyloid precursor protein isoforms containing Kunitz protease inhibitor in dementia with Lewy bodies.

Amyloid precursor protein (APP) is involved in the accumulation of alpha-synuclein, the main component of Lewy bodies. It is currently unknown, however, whether any of the APP isoforms is instrumental in alpha-synuclein deposition in dementia with Lewy bodies (DLB). Using real-time RT-PCR, we have studied relative mRNA expression levels of APP isoforms in frozen postmortem frontal cortices of DLB patients, Alzheimer disease (AD) patients, and control subjects. Of the three main APP isoforms, the two with a Kunitz protease inhibitory (KPI) motif (APP770 and APP751) were found to be specifically overexpressed in the frontal cortices of DLB patients when compared with controls and AD patients. These findings suggest a specific role of APP isoforms containing Kunitz protease inhibitor in DLB pathogenesis.

Aged↗

PubMed2004

Autocrine and paracrine calcium signaling by the CD38/NAD+/cyclic ADP-ribose system.

CD38, a multifunctional enzyme, generates two potent Ca2+-releasing signal metabolites, cyclic ADP-ribose (cADPR) and NAADP+, thereby upmodulating many important Ca2+-mediated cell functions. A topological paradox has long been recognized, as CD38 is an ectoenzyme, or an intravesicularly located enzyme in subcellular membrane vesicles, therefore apparently shielded from its substrate NAD+. Moreover, cADPR generated by CD38 should be unavailable to its target Ca2+ stores, the ryanodine receptors (RyR). We have solved this paradox by identifying some NAD+ and cADPR transmembrane transporters, whose interplay mediates a hitherto-unrecognized subcellular and intercellular trafficking of nucleotides that enhances intracellular Ca2+ ([Ca2+]i). Connexin 43 (Cx43) hemichannels mediate an equilibrative transport of NAD+ from the cytosol to the active site of CD38 (either ectocellular or intravesicular). Subsequent translocation of in situ-generated cADPR to reach the RyR is performed, (i) by CD38 itself (concentrative) or (ii) by nucleoside transporters (NT) (one equilibrative and three concentrative). Besides this autocrine mechanism, the same transporters also mediate intercellular (paracrine) trafficking. Thus, Cx43+ and CD38+ cells can provide cADPR to neighboring RyR+ parenchymal cells and enhance their [Ca2+]i levels and Ca2+-dependent functions accordingly. Examples of cADPR-responsive cells via paracrine processes include (i) smooth myocytes, (ii) 3T3 murine fibroblasts, (iii) hippocampal neurons, and (iv) human hemopoietic stem cells.

3T3 Cells↗

PubMed2004

Cystathionine beta synthase as a risk factor for Alzheimer disease.

One of the known risk factors for developing Alzheimer disease (AD) is hyperhomocysteinemia. The latter may result from mutations of the genes coding for three key enzymes involved in homocysteine metabolism (methylenetetrahydrofolate reductase [MTHFR], methionine synthase [MS], and cystathionine beta-synthase [CBS]). Although MTHFR and MS polymorphisms have been shown to be positively associated with AD in some populations, the relationship of the CBS gene with AD remains undefined. In order to evaluate whether AD is associated with CBS gene changes leading to decreased CBS activity and homocysteine accumulation, we genotyped the CBS 844ins68 mutation and VNTR polymorphisms of the CBS gene in 206 AD patients and 186 age-matched controls. A slight increase in both 844ins68 mutation and VNTR allele 19 frequencies was detected in the whole AD patient group, compared with controls. The division of AD patients and controls into three age-at-onset/age dependent subgroups (<65 years, 65-74 years, > 75 years) revealed that the 844ins68 mutation and VNTR allele 19 are independent risk factors for AD development in subjects aged 75 years or more.

Age of Onset↗

PubMed2003

Methionine synthase polymorphism is a risk factor for Alzheimer disease.

Alzheimer disease (AD) patients show increased plasma levels of homocysteine, whose conversion to methionine is catalyzed by methionine synthase (MS). Although altered MS activity may result from the MS A2756G polymorphism, the latter's possible associ-ation with AD remains unexplored. To assess whether the MS A2756G polymorphism holds any influence on AD risk, we have analyzed 172 AD patients and 166 controls. We have also investigated whether the MS-A or MS-G allele interacts with the APOE4 allele. Our results indicate that association with the MS-AA genotype is an APOE4 allele-independent risk factor for AD. These findings provide novel evidence implicating genetic enzymatic alterations of homocysteine metabolic pathways in the pathogenesis of AD.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗

PubMed2002

The Th1/E47cs-G apolipoprotein E (APOE) promoter allele is a risk factor for Alzheimer disease of very later onset.

Several polymorphisms in the apolipoprotein E (APOE) promoter region have been recently described. Of interest, APOE gene expression is increased in association with the -491AT polymorphism T-allele and decreased in relation to the Th1/E47cs polymorphism G-allele. In the present study we have investigated both polymorphisms in a series of 183 Alzheimer disease (AD) patients and 169 controls divided into age at onset/age dependent subgroups and the data obtained have been corrected for the presence of both expression-changing alleles in APOE homozygous individuals. Subsequently, the associations among APOE promoter polymorphisms, APOE4, and AD were assessed by chi-square and logistic regression analyses. Significantly, patients whose age at onset of AD was 80 years or more showed an association between the Th1/E47cs-G allele and AD that was independent of the APOE4 allele.

Age of Onset↗