RESUMO
Synaptic loss is an early event in the penumbra area after an ischemic stroke. Promoting synaptic preservation in this area would likely improve functional neurological recovery. We aimed to detect proteins involved in endogenous protection mechanisms of synapses in the penumbra after stroke and to analyse potential beneficial effects of these candidates for a prospective stroke treatment. For this, we performed Liquid Chromatography coupled to Mass Spectrometry (LC-MS)-based proteomics of synaptosomes isolated from the ipsilateral hemispheres of mice subjected to experimental stroke at different time points (24 h, 4 and 7 days) and compared them to sham-operated mice. Proteomic analyses indicated that, among the differentially expressed proteins between the two groups, cystatin C (CysC) was significantly increased at 24 h and 4 days following stroke, before returning to steady-state levels at 7 days, thus indicating a potential transient and intrinsic rescue mechanism attempt of neurons. When CysC was applied to primary neuronal cultures subjected to an in vitro model of ischemic damage, this treatment significantly improved the preservation of synaptic structures. Notably, similar effects were observed when CysC was loaded into brain-derived extracellular vesicles (BDEVs). Finally, when CysC contained in BDEVs was administered intracerebroventricularly to stroked mice, it significantly increased the expression of synaptic markers such as SNAP25, Homer-1, and NCAM in the penumbra area compared to the group supplied with empty BDEVs. Thus, we show that CysC-loaded BDEVs promote synaptic protection after ischemic damage in vitro and in vivo, opening the possibility of a therapeutic use in stroke patients.
Assuntos
Isquemia Encefálica , Encéfalo , Cistatina C , Vesículas Extracelulares , Camundongos Endogâmicos C57BL , Sinapses , Animais , Vesículas Extracelulares/metabolismo , Vesículas Extracelulares/transplante , Cistatina C/metabolismo , Sinapses/metabolismo , Camundongos , Masculino , Isquemia Encefálica/metabolismo , Isquemia Encefálica/patologia , Encéfalo/metabolismo , Encéfalo/patologia , Proteômica/métodos , Sinaptossomos/metabolismo , Neurônios/metabolismo , Acidente Vascular Cerebral/metabolismo , Acidente Vascular Cerebral/patologia , Acidente Vascular Cerebral/terapia , Células Cultivadas , Modelos Animais de DoençasRESUMO
The prion protein (PrP) is a broadly expressed glycoprotein linked with a multitude of (suggested) biological and pathological implications. Some of these roles seem to be due to constitutively generated proteolytic fragments of the protein. Among them is a soluble PrP form, which is released from the surface of neurons and other cell types by action of the metalloprotease ADAM10 in a process termed 'shedding'. The latter aspect is the focus of this review, which aims to provide a comprehensive overview on (i) the relevance of proteolytic processing in regulating cellular PrP functions, (ii) currently described involvement of shed PrP in neurodegenerative diseases (including prion diseases and Alzheimer's disease), (iii) shed PrP's expected roles in intercellular communication in many more (patho)physiological conditions (such as stroke, cancer or immune responses), (iv) and the need for improved research tools in respective (future) studies. Deeper mechanistic insight into roles played by PrP shedding and its resulting fragment may pave the way for improved diagnostics and future therapeutic approaches in diseases of the brain and beyond.
Assuntos
Doenças Priônicas , Príons , Humanos , Proteínas Priônicas/metabolismo , Proteína ADAM10/metabolismo , Príons/metabolismo , Doenças Priônicas/metabolismo , Doenças Priônicas/patologia , Encéfalo/metabolismo , Proteínas de Membrana/metabolismo , Secretases da Proteína Precursora do Amiloide/metabolismoRESUMO
Nemaline myopathies (NEMs) are genetically and clinically heterogenous. Biallelic or monoallelic variants in TNNT1, encoding slow skeletal troponin T1 (TnT1), cause NEM. We report a 2-year-old patient and his mother carrying the heterozygous TNNT1 variant c.194A>C/p.(Asp65Ala) that occurred de novo in the mother. Both had muscle hypotrophy and muscle weakness. Muscle pathology in the proband's mother revealed slow twitch type 1 fiber hypotrophy and fast twitch type 2 fiber hypertrophy that was confirmed by a reduced ratio of slow skeletal myosin to fast skeletal myosin type 2a. Reverse transcription polymerase chain reaction and immunoblotting data demonstrated increased levels of high-molecular-weight TnT1 isoforms in skeletal muscle of the proband's mother that were also observed in some controls. In an overexpression system, complex formation of TnT1-D65A with tropomyosin 3 (TPM3) was enhanced. The previously reported TnT1-E104V and TnT1-L96P mutants showed reduced or no co-immunoprecipitation with TPM3. Our studies support pathogenicity of the TNNT1 p.(Asp65Ala) variant.
Assuntos
Miopatias da Nemalina , Pré-Escolar , Humanos , Músculo Esquelético/patologia , Mutação , Miopatias da Nemalina/patologia , Isoformas de Proteínas/genética , Troponina T/genéticaRESUMO
ß-Site amyloid precursor protein (APP) cleaving enzyme-1 (BACE1) is the major described ß-secretase to generate Aß peptides in Alzheimer's disease (AD). However, all therapeutic attempts to block BACE1 activity and to improve AD symptoms have so far failed. A potential candidate for alternative Aß peptides generation is the metalloproteinase meprin ß, which cleaves APP predominantly at alanine in p2 and in this study we can detect an increased meprin ß expression in AD brain. Here, we report the generation of the transgenic APP/lon mouse model of AD lacking the functional Mep1b gene (APP/lon × Mep1b-/-). We examined levels of canonical and truncated Aß species using urea-SDS-PAGE, ELISA and immunohistochemistry in brains of APP/lon mouse × Mep1b-/-. Additionally, we investigated the cognitive abilities of these mice during the Morris water maze task. Aß1-40 and 1-42 levels are reduced in APP/lon mice when meprin ß is absent. Immunohistochemical staining of mouse brain sections revealed that N-terminally truncated Aß2-x peptide deposition is decreased in APP/lon × Mep1b-/- mice. Importantly, loss of meprin ß improved cognitive abilities and rescued learning behavior impairments in APP/lon mice. These observations indicate an important role of meprin ß within the amyloidogenic pathway and Aß production in vivo.
Assuntos
Doença de Alzheimer/metabolismo , Doença de Alzheimer/patologia , Peptídeos beta-Amiloides/metabolismo , Encéfalo/metabolismo , Aprendizagem , Transtornos da Memória/patologia , Metaloendopeptidases/deficiência , Idoso , Secretases da Proteína Precursora do Amiloide/metabolismo , Animais , Astrócitos/metabolismo , Encéfalo/patologia , Cruzamentos Genéticos , Modelos Animais de Doenças , Feminino , Proteína Glial Fibrilar Ácida/metabolismo , Humanos , Masculino , Metaloendopeptidases/metabolismo , Camundongos Knockout , Peptídeos/metabolismo , Processamento de Proteína Pós-TraducionalRESUMO
Despite existing knowledge about the role of the A Disintegrin and Metalloproteinase 10 (ADAM10) as the α-secretase involved in the non-amyloidogenic processing of the amyloid precursor protein (APP) and Notch signalling we have only limited information about its regulation. In this study, we have identified ADAM10 interactors using a split ubiquitin yeast two hybrid approach. Tetraspanin 3 (Tspan3), which is highly expressed in the murine brain and elevated in brains of Alzheimer´s disease (AD) patients, was identified and confirmed to bind ADAM10 by co-immunoprecipitation experiments in mammalian cells in complex with APP and the γ-secretase protease presenilin. Tspan3 expression increased the cell surface levels of its interacting partners and was mainly localized in early and late endosomes. In contrast to the previously described ADAM10-binding tetraspanins, Tspan3 did not affect the endoplasmic reticulum to plasma membrane transport of ADAM10. Heterologous Tspan3 expression significantly increased the appearance of carboxy-terminal cleavage products of ADAM10 and APP, whereas N-cadherin ectodomain shedding appeared unaffected. Inhibiting the endocytosis of Tspan3 by mutating a critical cytoplasmic tyrosine-based internalization motif led to increased surface expression of APP and ADAM10. After its downregulation in neuroblastoma cells and in brains of Tspan3-deficient mice, ADAM10 and APP levels appeared unaltered possibly due to a compensatory increase in the expression of Tspans 5 and 7, respectively. In conclusion, our data suggest that Tspan3 acts in concert with other tetraspanins as a stabilizing factor of active ADAM10, APP and the γ-secretase complex at the plasma membrane and within the endocytic pathway.
Assuntos
Proteína ADAM10/genética , Secretases da Proteína Precursora do Amiloide/genética , Precursor de Proteína beta-Amiloide/genética , Endossomos/metabolismo , Proteínas de Membrana/genética , Presenilinas/genética , Tetraspaninas/genética , Proteína ADAM10/metabolismo , Secretases da Proteína Precursora do Amiloide/metabolismo , Precursor de Proteína beta-Amiloide/metabolismo , Animais , Encéfalo/metabolismo , Química Encefálica , Caderinas/genética , Caderinas/metabolismo , Linhagem Celular Tumoral , Membrana Celular/metabolismo , Endocitose , Endossomos/química , Regulação da Expressão Gênica , Células HEK293 , Humanos , Proteínas de Membrana/metabolismo , Camundongos , Proteínas do Tecido Nervoso/genética , Proteínas do Tecido Nervoso/metabolismo , Neurônios/citologia , Neurônios/metabolismo , Presenilinas/metabolismo , Ligação Proteica , Transporte Proteico , Receptores Notch/genética , Receptores Notch/metabolismo , Transdução de Sinais , Tetraspaninas/metabolismo , Técnicas do Sistema de Duplo-HíbridoRESUMO
Alzheimer's disease is a common neurodegenerative, progressive, and fatal disorder. Generation and deposition of amyloid beta (Aß) peptides associate with its pathogenesis and small soluble Aß oligomers show the most pronounced neurotoxic effects and correlate with disease initiation and progression. Recent findings showed that Aß oligomers bind to the cellular prion protein (PrP(C) ) eliciting neurotoxic effects. The role of exosomes, small extracellular vesicles of endosomal origin, in Alzheimer's disease is only poorly understood. Besides serving as disease biomarkers they may promote Aß plaque formation, decrease Aß-mediated synaptotoxicity, and enhance Aß clearance. Here, we explore how exosomal PrP(C) connects to protective functions attributed to exosomes in Alzheimer's disease. To achieve this, we generated a mouse neuroblastoma PrP(C) knockout cell line using transcription activator-like effector nucleases. Using these, as well as SH-SY5Y human neuroblastoma cells, we show that PrP(C) is highly enriched on exosomes and that exosomes bind amyloid beta via PrP(C) . Exosomes showed highest binding affinity for dimeric, pentameric, and oligomeric Aß species. Thioflavin T assays revealed that exosomal PrP(C) accelerates fibrillization of amyloid beta, thereby reducing neurotoxic effects imparted by oligomeric Aß. Our study provides further evidence for a protective role of exosomes in Aß-mediated neurodegeneration and highlights the importance of exosomal PrP(C) in molecular mechanisms of Alzheimer's disease. We show that the prion protein (PrP(C) ) on exosomes captures neurotoxic species of amyloid beta (Aß) promoting its fibrillization. Our study provides evidence for a protective role of exosomes in Alzheimer`s disease and suggests that, depending on its membrane topology, PrP(C) holds a dual function: when expressed at the neuronal surface it acts as receptor for Aß leading to neurotoxic signaling, whereas it detoxifies Aß when present on exosomes. This provides further support for key roles of PrP(C) in Alzheimer's disease.
Assuntos
Peptídeos beta-Amiloides/metabolismo , Amiloide/metabolismo , Exossomos/fisiologia , Proteínas PrPC/fisiologia , Doença de Alzheimer/metabolismo , Peptídeos beta-Amiloides/toxicidade , Animais , Linhagem Celular Tumoral , Técnicas de Inativação de Genes , Camundongos , Proteínas de Neoplasias/metabolismo , Neuroblastoma/patologia , Fragmentos de Peptídeos/metabolismo , Fragmentos de Peptídeos/toxicidade , Solubilidade , TransfecçãoRESUMO
Proteolytic activation of the fusion protein of the highly pathogenic Nipah virus (NiV F) is a prerequisite for the production of infectious particles and for virus spread via cell-to-cell fusion. Unlike other paramyxoviral fusion proteins, functional NiV F activation requires endocytosis and pH-dependent cleavage at a monobasic cleavage site by endosomal proteases. Using prototype Vero cells, cathepsin L was previously identified to be a cleavage enzyme. Compared to Vero cells, MDCK cells showed substantially higher F cleavage rates in both NiV-infected and NiV F-transfected cells. Surprisingly, this could not be explained either by an increased F endocytosis rate or by elevated cathepsin L activities. On the contrary, MDCK cells did not display any detectable cathepsin L activity. Though we could confirm cathepsin L to be responsible for F activation in Vero cells, inhibitor studies revealed that in MDCK cells, cathepsin B was required for F-protein cleavage and productive replication of pathogenic NiV. Supporting the idea of an efficient F cleavage in early and recycling endosomes of MDCK cells, endocytosed F proteins and cathepsin B colocalized markedly with the endosomal marker proteins early endosomal antigen 1 (EEA-1), Rab4, and Rab11, while NiV F trafficking through late endosomal compartments was not needed for F activation. In summary, this study shows for the first time that endosomal cathepsin B can play a functional role in the activation of highly pathogenic NiV.