Jens Pahnke

Prevalence of Fabry disease in patients with cryptogenic stroke: a prospective study

BACKGROUNDnStrokes are an important cause of morbidity and mortality in young adults. However, in most cases the cause of the stroke remains unclear. Anderson-Fabry disease is an X-linked recessive lysosomal storage disease resulting from deficient alpha-galactosidase and causes an endothelial vasculopathy followed by cerebral ischaemia. To determine the importance of Fabry disease in young people with stroke, we measured the frequency of unrecognised Fabry disease in a cohort of acute stroke patients.nnnMETHODSnBetween February, 2001, and December, 2004, 721 German adults aged 18 to 55 years suffering from acute cryptogenic stroke were screened for Fabry disease. The plasma alpha-galactosidase activity in men was measured followed by sequencing of the entire alpha-GAL gene in those with low enzyme activity. By contrast, the entire alpha-GAL gene was genetically screened for mutations in women even if enzyme activity was normal.nnnFINDINGSn21 of 432 (4.9%) male stroke patients and seven of 289 (2.4%) women had a biologically significant mutation within the alpha-GAL gene. The mean age at onset of symptomatic cerebrovascular disease was 38.4 years (SD 13.0) in the male stroke patients and 40.3 years (13.1) in the female group. The higher frequency of infarctions in the vertebrobasilar area correlated with more pronounced changes in the vertebrobasilar vessels like dolichoectatic pathology (42.9%vs 6.8%).nnnINTERPRETATIONnWe have shown a high frequency of Fabry disease in a cohort of patients with cryptogenic stroke, which corresponds to about 1.2% in young stroke patients. Fabry disease must be considered in all cases of unexplained stroke in young patients, especially in those with the combination of infarction in the vertebrobasilar artery system and proteinuria.

Lethal recessive myelin toxicity of prion protein lacking its central domain

PrPC‐deficient mice expressing prion protein variants with large amino‐proximal deletions (termed PrPΔF) suffer from neurodegeneration, which is rescued by full‐length PrPC. We now report that expression of PrPΔCD, a PrP variant lacking 40 central residues (94–134), induces a rapidly progressive, lethal phenotype with extensive central and peripheral myelin degeneration. This phenotype was rescued dose‐dependently by coexpression of full‐length PrPC or PrPC lacking all octarepeats. Expression of a PrPC variant lacking eight residues (114–121) was innocuous in the presence or absence of full‐length PrPC, yet enhanced the toxicity of PrPΔCD and diminished that of PrPΔF. Therefore, deletion of the entire central domain generates a strong recessive‐negative mutant of PrPC, whereas removal of residues 114–121 creates a partial agonist with context‐dependent action. These findings suggest that myelin integrity is maintained by a constitutively active neurotrophic protein complex involving PrPC, whose effector domain encompasses residues 94–134.

An impaired neocortical Ih is associated with enhanced excitability and absence epilepsy.

Neuronal subthreshold excitability and firing behaviour are markedly influenced by the activation and deactivation of the somato‐dendritic hyperpolarization‐activated cation current (Ih). Here, we evaluated possible contributions of Ih to hyperexcitability in an animal model of absence seizures (WAG/Rij rats). We investigated pyramidal neurons of the somatosensory neocortex, the site of generation of spike–wave discharges. Ih‐mediated functions in neurons from WAG/Rij rats, Wistar rats (sharing the same genetic background with WAG/Rij, but less epilepsy‐prone) and ACI rats (an inbred strain, virtually free of seizures) were compared. We complemented whole‐cell recordings from layeru20032–3 pyramidal neurons with immunohistochemistry, Western blot and RT‐PCR analysis of the h‐channel subunits HCN1–4. The fast component of Ih activation in WAG/Rij neurons was significantly reduced (50% reduction in the h‐current density) and four times slower than in neurons from nonepileptic Wistar or ACI rats. The results showing decreases in currents corresponded to a 34% reduction in HCN1 protein in the WAG/Rij compared to the Wistar neocortex, but HCN1 mRNA showed stable expression. The other three Ih subunit mRNAs and proteins (HCN2–4) were not affected. The alterations in Ih magnitude and kinetics of gating in WAG/Rij neurons may contribute to augmented excitatory postsynaptic potentials, the increase in their temporal summation and the facilitation of burst firing of these neurons because each of these effects could be mimicked by the selective Ih antagonist ZDu20037288. We suggest that the deficit in Ih‐mediated functions may contribute to the development and onset of spontaneously occurring hyperexcitability in a rat model of absence seizures.

Alzheimer's disease and blood-brain barrier function - Why have anti-β-amyloid therapies failed to prevent dementia progression?

Proteopathies of the brain are defined by abnormal, disease-inducing protein deposition that leads to functional abrogation and death of neurons. Immunization trials targeting the removal of amyloid-beta plaques in Alzheimers disease have so far failed to stop the progression of dementia, despite autopsy findings of reduced plaque load. Here, we summarize current knowledge of the relationship between AD pathology and blood-brain barrier function, and propose that the activation of the excretion function of the blood-brain barrier might help to achieve better results in trials targeting the dissolution of cerebral amyloid-beta aggregates. We further discuss a possible role of oligomers in limiting the efficacy of immunotherapy.

The proteasomal subunit S6 ATPase is a novel synphilin-1 interacting protein—implications for Parkinson’s disease

Synphilin‐1 is linked to Parkinsons disease (PD), based on its role as an alpha‐synuclein (PARK1)‐interacting protein and substrate of the ubiquitin E3 ligase Parkin (PARK2) and because of its presence in Lewy bodies (LB) in brains of PD patients. We found that overexpression of synphilin‐1 in cells leads to the formation of ubiquitinated cytoplasmic inclusions supporting a derangement of the ubiquitin‐proteasome system in PD. We report here a novel specific interaction of synphilin‐1 with the regulatory proteasomal protein S6 ATPase (tbp7). Functional characterization of this interaction on a cellular level revealed colocalization of S6 and synphilin‐1 in aggresome‐like intracytoplasmic inclusions. Overexpression of synphilin‐1 and S6 in cells caused reduced proteasomal activity associated with a significant increase in inclusion formation compared to cells expressing syn‐philin‐1 alone. Steady‐state levels of synphilin‐1 in cells were not altered after cotransfection of S6 and colocal‐ization of synphilin‐1‐positive inclusions with lysosomal markers suggests the presence of an alternative lysosomal degradation pathway. Subsequent immunohistochemical studies in brains of PD patients identified S6 ATPase as a component of LB. This is the first study investigating the physiological role of synphilin‐1 in the ubiquitin protea‐some system. Our data suggest a direct interaction of synphilin‐1 with the regulatory complex of the protea‐some modulating proteasomal function.—Marx F. P., Soehn, A. S., Berg, D., Melle, C., Schiesling, C., Lang, M., Kautzmann, S., Strauss, K. M., Franck, T., Engelender, S., Pahnke, J., Dawson, S., von Eggeling F., Schulz, J. B., Riess, O., Krüger R. The proteasomal subunit S6 ATPase is a novel synphilin‐1 interacting protein—implications for Parkinsons disease. FASEB J. 21, 1759–1767 (2007)

Uptake of 18F-Fluorocholine, 18F-FET, and 18F-FDG in C6 Gliomas and Correlation with 131I-SIP(L19), a Marker of Angiogenesis

Targeting extracellular structures that are involved in angiogenic processes, such as the extra domain B of fibronectin, is a promising approach for the diagnosis of solid tumors. The aim of this study was to determine uptake of the 18F-labeled PET tracers 18F-fluorocholine (N,N-dimethyl-N-18F-fluoromethyl-2-hydroxyethylammonium), 18F-fluoro-ethyl-l-tyrosine (FET), and 18F-FDG in C6 gliomas of the rat and to correlate it with uptake of the anti–extra domain B antibody 131I-SIP(L19) as a marker of neoangiogenesis. Methods: C6 gliomas were orthotopically induced in 17 rats. Uptake of all tracers was measured using quantitative autoradiography, and uptake of 18F-fluorocholine, 18F-FET, and 18F-FDG was correlated with uptake of 131I-SIP(L19) on a pixelwise basis. Results: The mean 131I-SIP(L19), 18F-fluorocholine, 18F-FET, and 18F-FDG standardized uptake values in the tumor and the contralateral normal cortex (in parentheses) were 0.31 ± 0.22 (not detectable), 2.00 ± 0.53 (0.49 ± 0.07), 3.67 ± 0.36 (1.42 ± 0.22), and 7.23 ± 1.22 (3.64 ± 0.51), respectively. The 131I-SIP(L19) uptake pattern correlated best with 18F-fluorocholine uptake (ż = 0.80, averaged ż-transformed Pearson correlation coefficient) and 18F-FET uptake (ż = 0.79) and least with 18F-FDG (ż = 0.37). Conclusion: One day after intravenous injection, 131I-SIP(L19) displayed a very high tumor-to-cortex ratio, which may be used in the diagnostic work-up of brain tumor patients. Of the 3 investigated 18F tracers, 18F-fluorocholine and 18F-FET correlated better with the pattern of 131I-SIP(L19) uptake than did 18F-FDG. Whether this means that 18F-fluorocholine and 18F-FET are better suited than 18F-FDG to monitor antiangiogenic therapy should be investigated in future studies.

McLeod phenotype associated with a XK missense mutation without hematologic, neuromuscular, or cerebral involvement

BACKGROUND: The X‐linked McLeod neuroacanthocytosis syndrome is a multisystem disorder with hematologic, neuromuscular, and central nervous system (CNS) manifestations. All carriers of the McLeod blood group phenotype examined so far had at least subclinical signs of systemic involvement.

Alzheimer’s and ABC transporters — new opportunities for diagnostics and treatment

Much has been said about the increasing number of demented patients and the main risk factor age. Frustratingly, we do not know the precise pattern and all modulating factors that provoke the pathologic changes in the brains of affected elderly. We have to diagnose early to be able to stop the progression of diseases that irreversibly destroy brain substance. Familiar AD cases have mislead some researchers for almost 20 years, which has unfortunately narrowed the scientific understanding and has, thus, lead to insufficient funding of independent approaches. Therefore, basic researchers hardly have been able to develop causative treatments and clinicians still do not have access to prognostic and early diagnostic tools. During the recent years it became clear that insufficient Aβ export, physiologically facilitated by the ABC transporter superfamily at the brains barriers, plays a fundamental role in disease initiation and progression. Furthermore, export mechanisms that are deficient in affected elderly are new targets for activation and, thus, treatment, but ideally also for prevention. In sporadic AD disturbed clearance of β-amyloid from the brain is so far the most important factor for its accumulation in the parenchyma and vessel walls. Here, we review findings about the contribution of ABC transporters and of the perivascular drainage/glymphatic system on β-amyloid clearance. We highlight their potential value for innovative early diagnostics using PET and describe recently described, effective ABC transporter-targeting agents as potential causative treatment for neurodegenerative proteopathies/dementias.

Development of Alzheimer-disease neuroimaging-biomarkers using mouse models with amyloid-precursor protein-transgene expression

There are important recent developments in Alzheimers disease (AD) translational research, especially with respect to the imaging of amyloid pathology in vivo using MRI and PET technologies. Here we exploit the most widely used transgenic mouse models of amyloid pathology in order to relate the imaging findings to our knowledge about the histopathological phenotype of these models. The development of new diagnostic criteria of AD necessitates the use of biological markers to diagnose AD even in the absence of overt dementia or early symptomatic mild cognitive impairment. The validity of the diagnosis will depend on the availability of an in vivo marker to reflect underlying neurobiological changes of AD. Transgenic models with essential features of AD pathology and mechanisms provide a test setting for the development and evaluation of new biological imaging markers. Among the best established imaging markers of amyloid pathology in transgenic animals are high-field MRI of brain atrophy, proton spectroscopy of neurochemical changes, high-field MRI of amyloid plaque load, and in vivo plaque imaging using radio-labelled ligands with PET. We discuss the implications of the findings as well as the methodological limitations and the specific requirements of these technologies. We furthermore outline future directions of transgene-imaging research. Transgene imaging is an emerging area of translational research that implies strong multi- and interdisciplinary collaborations. It will become ever more valuable with the introduction of new diagnostic standards and novel treatment approaches which will require valid and reliable biological markers to improve the diagnosis and early treatment of AD patients.

Deep brain stimulation in a rat model modulates TH, CaMKIIa and Homer1 gene expression

High‐frequency stimulation (HFS) of subthalamic nucleus (STN) is a therapy for late‐stage Parkinsons disease. Its mechanisms of action are not yet fully understood. In the present study, gene expression analyses were performed in a rat model of Parkinsons disease, i.e. striatal 6‐hydroxydopamine (6‐OHDA) lesion. Using microarrays, gene expression was analysed in 1‐mm‐thick sagittal brain slices, including basal ganglia of five groups of male Wistar rats. These were unmanipulated rats (group A), unlesioned rats with implanted electrode but without stimulation (group B), unlesioned, stimulated rats (group C), 6‐OHDA‐lesioned rats with implanted electrode but without stimulation (group D), and finally 6‐OHDA‐lesioned and stimulated rats (group E). A statistically significant downregulation of tyrosine hydroxylase (TH) mRNA expression induced by 6‐OHDA lesion and an HFS‐induced TH upregulation in 6‐OHDA‐lesioned rats could be detected. It could be hypothesized that the HFS‐induced upregulation of TH is the result of neuronal STN modulation and mediated via projections from STN to substantia nigra pars compacta. Furthermore, a downregulation of calcium/calmodulin‐dependent protein kinase type IIA and Homer1 was observed. This downregulation could result in a reduced sensitivity towards glutamate in basal ganglia downstream of STN.