Der Einfluss des Cannabinoid-Rezeptor 1 auf die Prozessierung des Amyloid-Vorläuferproteins und die autophagosomale Degradation

Die bisher etablierten Therapieansätze der AD durch Acetylcholin-Esterase-Hemmer, NMDA-Antagonisten und Psychopharmaka stellen allein eine Behandlung der Symptome der Patienten dar und können den progressiven Verlauf der Krankheit nur wenig verzögern. Die zur Zeit in klinischen Studien getesteten experimentellen Therapieansätze zielen meist auf das Entfernen der potentiell krankheitsauslösenden Aß-Peptide ab. Dabei lag in der Vergangenheit der Fokus der pharmazeutischen Entwicklung auf der Inhibition der an der amyloidogenen Prozessierung des APP beteiligten Proteasen. Die Weiterentwicklung dieser Therapieansätze mussten auf Grund der schweren Nebenwirkungen in Patienten jedoch vorerst abgebrochen werden. Der CB1 könnte grundsätzlich ein alternatives pharmakologisches Ziel darstellen, da die in dieser Studie erhobenen Daten zeigen, dass es bei Inhibition der Rezeptor-Aktivität zur MAPK-ERK1/2-vermittelten Reduktion der APP-Prozessierung und damit der Aß-Spiegel kommt. Dabei führt die Reduktion der Gliose im Gehirn der APP23/CB1-/--Tiere und die reduzierte APP-Prozessierung schon in jungen Mäusen nicht zur verbesserten kognitiven Fähigkeiten der Tiere im Alter. Die in dieser Studie erhobenen Daten zeigen, dass die CB1-Aktivität auch die nicht-amyloidogene Prozessierung des APP inhibiert. Somit ist die Entwicklung einer Behandlungsstrategie durch die CB1-vermittelte Modulation der APP-Prozessierung kritisch zu sehen, da die als neuroprotektiv angesehene nicht-amyloidogene Prozessierung des APP durch die Inhibition der CB1-Aktivität ebenfalls reduziert wird. Folglich konnte in den APP23/CB1-/--Tieren die reduzierte amyloidogenen Prozessierung des APP nicht ursächlich für den pathologischen Phänotyp sein, weshalb dafür ein alternativer Grund identifiziert werden sollte. Die autophagische/lysosomale Degradation spielt bekanntlich eine Rolle bei der AD-Pathologie und wird zudem auch durch die CB1-Aktivität beeinflusst. Deshalb wurde in dieser Studie der Einfluss des CB1 auf den autophagischen Flux näher analysiert. In einem Zellmodell zeigte sich, dass über die Rezeptor-Aktivität die Bildung autophagischer Vesikel reguliert werden kann. Die lysosomale Aktivität bleibt dabei unbeeinflusst. Zudem ist in diesem Modell die Aktivität des UPS, als zweiter intrazellulärer Protein-Degradationsweg, nicht betroffen. Die Induktion des autophagischen Fluxes über die CB1-Aktivität scheint dabei unabhängig von den beiden kanonischen Autophagie-Regulatoren, des mTOR- und BECLIN1-Komplexes, zu sein. Der genaue Mechanismus über den diese nicht-kanonische CB1-vermittelte Stimulation des autophagischen Fluxes erfolgt bleibt unklar und muss in zukünftigen Studien aufgeklärt werden.Established therapy strategies of Alzheimer's Disease (AD), using acetylcholine-esterase inhibitors, NMDA-antagonists and psychotropic drugs are only targeting the treatment of the patients syndromes. These treatment approaches are able to delay the progression of the disease by merely a few years. Most experimental treatment strategies, which have been evaluated in recent clinical studies are focusing on the elevated clearance of the potentially toxic Aß peptides, whereby the pharmacological development has been concentrated on drugs inhibiting the proteases involved in the amyloidogenic processing of APP. All of these inhibitors, which proceeded up to phase III clinical trials failed at the end, because of severe side effects in patients. Based on the data of this study, one might argue that inhibiting CB1 could be used as an alternative treatment for AD, because the reduction of CB1 activity decreases APP processing and thereby the levels of Aß peptides. However, the reduced gliosis and decreased APP processing in APP23/CB1-/- animals compared to APP23 animals did not correlate with enhanced cognitive abilities, but with a decline in spacial learning. Data raised in this study show, that CB1 is also influencing the non-amyloidogenic processing of APP. Thus, a treatment strategy of AD based on CB1 activity inhibition and thereby the reduction of amyloidogenic APP-processing might be unrewarding as the neuroprotective, non-amyloidogenic processing of APP is decreased at the same time. The reduced amyloidogenic APP-processing in APP23/CB1-/- mice cannot be causative for the detrimental phenotype of those animals. A disturbance in the autophagosomal/lysosomal system might be an alternative explanation for the impact of the CB1 depletion in the genetic background of the APP23 mice. Various scientific reports show, that this degradation system is altered by the pathological changes during AD-progression and some claim that CB1 activity has an influence on lysosomal degradation. Thereby, the possible influence of the CB1 on the autophagic flux was investigated in this study. In the cellular model system utilized, CB1 activity specifically modulated the formation of autophagic vesicles, as the lysosomal activity and the activity of the ubiquitin-proteasom system (UPS) are not altered by CB1 knockdown. Interestingly, the modulation of the autophagic flux by CB1 is independent of the two canonical protein-complexes (mTOR- and BECLIN1-complex) regulating the induction of autophagic vesicle formation. Thus, CB1 modulates the autophagic flux in a non-canonical fashion, whereas the signal-pathway has not been revealed, so far. The precise molecular mechanism connecting CB1 signaling to the induction of autophagic vesicle formation, should be subjected to further investigations in the future

Protein Homeostasis, Aging and Alzheimer’s Disease

Alzheimer’s disease (AD) is one key medical challenge of the aging society and despite a great amount of effort and a huge collection of acquired data on molecular mechanisms that are associated with the onset and progression of this devastating disorder, no causal therapy is in sight. The two main hypotheses of AD, the amyloid cascade hypothesis and the Tau hypothesis, are still in the focus of AD research. With aging as the accepted main risk factor of the most important non familial and late onset sporadic forms of AD, it is now mandatory to discuss more intensively aspects of cellular aging and aging biochemistry and its impact on neurodegeneration. Since aging is accompanied by changes in cellular protein homeostasis and an increasing demand for protein degradation, aspects of protein folding, misfolding, refolding and, importantly, protein degradation need to be linked to AD pathogenesis. This is the purpose of this short review

Target processing in overt serial visual search involves the dorsal attention network: A fixation-based event-related fMRI study

In serial visual search we shift attention successively from location to location in search for the target. Although such search has been investigated using fMRI, overt attention (i.e., eye movements) was usually neglected or discouraged. As a result, it is unclear what happens in the instant when our gaze falls upon a target as compared to a distractor. In the present experiment, we used a multiple target search task that required eye movements and employed an analysis based on fixations as events of interest to investigate differences between target and distractor processing. Twenty young healthy adults indicated the number of targets (0\u20133) among distractors in a 20-item display. Compared to distractor fixations, we found that target fixations gave rise to wide-spread activation in the dorsal attention system, as well as in the visual cortex. Targets that were found later during the search activated the left inferior frontal gyrus and the left supramarginal gyrus more strongly than those that were found earlier. Finally, areas associated with visual and verbal working memory showed increased activation with a larger number of targets in the display.Fonds zur F\uf6rderung der Wissenschaftlichen Forschung P-27824Version of recor

Cannabinoid receptor 1 deficiency in a mouse model of Alzheimer's disease leads to enhanced cognitive impairment despite of a reduction in amyloid deposition

Alzheimer's disease (AD) is characterized by amyloid-beta deposition in amyloid plaques, neurofibrillary tangles, inflammation, neuronal loss, and cognitive deficits. Cannabinoids display neuromodulatory and neuroprotective effects and affect memory acquisition. Here, we studied the impact of cannabinoid receptor type 1 (CB1) deficiency on the development of AD pathology by breeding amyloid precursor protein (APP) Swedish mutant mice (APP23), an AD animal model, with CB1-deficient mice. In addition to the lower body weight of APP23/CB1(-/-) mice, most of these mice died at an age before typical AD-associated changes become apparent. The surviving mice showed a reduced amount of APP and its fragments suggesting a regulatory influence of CB1 on APP processing, which was confirmed by modulating CB1 expression in vitro. Reduced APP levels were accompanied by a reduced plaque load and less inflammation in APP23/CB1(-/-) mice. Nevertheless, compared to APP23 mice with an intact CB1, APP23/CB1(-/-) mice showed impaired learning and memory deficits. These data argue against a direct correlation of amyloid plaque load with cognitive abilities in this AD mouse model lacking CB1. Furthermore, the findings indicate that CB1 deficiency can worsen AD-related cognitive deficits and support a potential role of CB1 as a pharmacologic target

BAG3 proteomic signature under proteostasis stress

The multifunctional HSP70 co-chaperone BAG3 (BCL-2-associated athanogene 3) represents a key player in the quality control of the cellular proteostasis network. In response to stress, BAG3 specifically targets aggregation-prone proteins to the perinuclear aggresome and promotes their degradation via BAG3-mediated selective macroautophagy. To adapt cellular homeostasis to stress, BAG3 modulates and functions in various cellular processes and signaling pathways. Noteworthy, dysfunction and deregulation of BAG3 and its pathway are pathophysiologically linked to myopathies, cancer, and neurodegenerative disorders. Here, we report a BAG3 proteomic signature under proteostasis stress. To elucidate the dynamic and multifunctional action of BAG3 in response to stress, we established BAG3 interactomes under basal and proteostasis stress conditions by employing affinity purification combined with quantitative mass spectrometry. In addition to the identification of novel potential BAG3 interactors, we defined proteins whose interaction with BAG3 was altered upon stress. By functional annotation and protein-protein interaction enrichment analysis of the identified potential BAG3 interactors, we confirmed the multifunctionality of BAG3 and highlighted its crucial role in diverse cellular signaling pathways and processes, ensuring cellular proteostasis and cell viability. These include protein folding and degradation, gene expression, cytoskeleton dynamics (including cell cycle and transport), as well as granulostasis, in particular

RAB3GAP1 and RAB3GAP2 modulate basal and rapamycin-induced autophagy

Macroautophagy is a degradative pathway that sequesters and transports cytosolic cargo in autophagosomes to lysosomes, and its deterioration affects intracellular proteostasis. Membrane dynamics accompanying autophagy are mostly elusive and depend on trafficking processes. RAB GTPase activating proteins (RABGAPs) are important factors for the coordination of cellular vesicle transport systems, and several TBC (TRE2-BUB2-CDC16) domain-containing RABGAPs are associated with autophagy. Employing C. elegans and human primary fibroblasts, we show that RAB3GAP1 and RAB3GAP2, which are components of the TBC domain-free RAB3GAP complex, influence protein aggregation and affect autophagy at basal and rapamycin-induced conditions. Correlating the activity of RAB3GAP1/2 with ATG3 and ATG16L1 and analyzing ATG5 punctate structures, we illustrate that the RAB3GAPs modulate autophagosomal biogenesis. Significant levels of RAB3GAP1/2 colocalize with members of the Atg8 family at lipid droplets, and their autophagy modulatory activity depends on the GTPase-activating activity of RAB3GAP1 but is independent of the RAB GTPase RAB3. Moreover, we analyzed RAB3GAP1/2 in relation to the previously reported suppressive autophagy modulators FEZ1 and FEZ2 and demonstrate that both reciprocally regulate autophagy. In conclusion, we identify RAB3GAP1/2 as novel conserved factors of the autophagy and proteostasis network