RESUMEN
Parkinson's disease (PD) is characterized by the pathological accumulation of α-synuclein (α-syn) and loss of dopaminergic neurons in the substantia nigra. Aging is a significant risk factor for PD. The accumulation of senescent glial cells in the aged brain contributes to PD progression by inducing chronic neuroinflammatory processes. However, although the insufficient degradation of α-syn aggregates results in PD deterioration, the possible alteration in the ability of α-syn clearance in senescent glia has received little attention. In this study, we investigated how aging and glial senescence affect the capacity of α-syn clearance. We found that following the intra-striatal injection of human α-syn (hu-α-syn) preformed fibril, hu-α-syn pathology persisted more in aged mice compared with younger mice and that aged microglia exhibited greater accumulation of hu-α-syn than younger microglia. Moreover, in vitro assay revealed that the clearance of hu-α-syn was primarily dependent on the autophagy-lysosome system rather than on the ubiquitin-proteasome system and that the capacity of hu-α-syn clearance was diminished in senescent glia because of autophagy-lysosome system dysfunction. Overall, this study provides new insights into the role of senescent glia in PD pathogenesis.
RESUMEN
Severed CNS axons fail to regenerate in adult mammals and there are no effective regenerative strategies to treat patients with CNS injuries. Several genes, including phosphatase and tensin homolog (PTEN) and Krüppel-like factors, regulate intrinsic growth capacity of mature neurons. The Lin28 gene is essential for cell development and pluripotency in worms and mammals. In this study, we evaluated the role of Lin28a in regulating regenerative capacity of diverse populations of CNS neurons in adult mammals. Using a neuron-specific Thy1 promoter, we generated transgenic mice that overexpress Lin28a protein in multiple populations of projection neurons, including corticospinal tracts and retinal ganglion cells. We demonstrate that upregulation of Lin28a in transgenic mice induces significant long distance regeneration of both corticospinal axons and the optic nerve in adult mice. Importantly, overexpression of Lin28a by post-injury treatment with adeno-associated virus type 2 (AAV2) vector stimulates dramatic regeneration of descending spinal tracts and optic nerve axons after lesions. Upregulation of Lin28a also enhances activity of the Akt signaling pathway in mature CNS neurons. Therefore, Lin28a is critical for regulating growth capacity of multiple CNS neurons and may become an important molecular target for treating CNS injuries.
Asunto(s)
Axones/metabolismo , Regeneración Nerviosa/genética , Nervio Óptico/metabolismo , Proteínas de Unión al ARN/genética , Traumatismos de la Médula Espinal/etiología , Traumatismos de la Médula Espinal/metabolismo , Animales , Corteza Cerebral/metabolismo , Dependovirus/genética , Modelos Animales de Enfermedad , Técnicas de Transferencia de Gen , Terapia Genética , Vectores Genéticos/genética , Ratones , Ratones Transgénicos , Neurogénesis , Neuronas/metabolismo , Nervio Óptico/patología , Regiones Promotoras Genéticas , Células Ganglionares de la Retina/metabolismo , Transducción de Señal , Traumatismos de la Médula Espinal/patología , Traumatismos de la Médula Espinal/terapiaRESUMEN
Modulation of immune activation using immunotherapy has attracted considerable attention for many years as a potential therapeutic intervention for several inflammation-associated neurodegenerative diseases. However, the efficacy of single-target immunotherapy intervention has shown limited or no efficacy in alleviating disease burden and restoring functional capacity. Marked immune system activation and neuroinflammation are important features and prodromal signs in polyQ repeat disorders and α-synucleinopathies. This review describes the current status and future directions of immunotherapies in proteinopathy-induced neurodegeneration with emphasis on preclinical and clinical efficacies of several anti-inflammatory compounds and antibody-based therapies for the treatment of Huntington's disease and α-synucleinopathies. The review concludes with how disease modification and functional restoration could be achieved by using targeted multimodality therapy to target multiple factors.
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Enfermedad de Huntington/tratamiento farmacológico , Enfermedad de Huntington/inmunología , Factores Inmunológicos/uso terapéutico , Sinucleinopatías/tratamiento farmacológico , Sinucleinopatías/inmunología , Humanos , Inmunoterapia , Inflamación , Enfermedades NeurodegenerativasRESUMEN
Liver kinase B1 (LKB1), a downstream effector of cyclic AMP (cAMP)/PKA and phosphatidylinositol 3-kinase (PI3K) pathways, is a determinant for migration and differentiation of many cells, but its role in CNS axon regeneration is unknown. Therefore, LKB1 was overexpressed in sensorimotor cortex of adult mice five days after mid-thoracic spinal cord injury, using an AAV2 vector. Regeneration of corticospinal axons was dramatically enhanced. Next, systemic injection of a mutant-AAV9 vector was used to upregulate LKB1 specifically in neurons. This promoted long-distance regeneration of injured corticospinal fibers into caudal spinal cord in adult mice and regrowth of descending serotonergic and tyrosine hydroxylase immunoreactive axons. Either intracortical or systemic viral delivery of LKB1 significantly improved recovery of locomotor functions in adult mice with spinal cord injury. Moreover, we demonstrated that LKB1 used AMPKα, NUAK1, and ERK as the downstream effectors in the cortex of adult mice. Thus, LKB1 may be a critical factor for enhancing the growth capacity of mature neurons and may be an important molecular target in the treatment of CNS injuries.
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Axones/fisiología , Regeneración Nerviosa/fisiología , Proteínas Serina-Treonina Quinasas/metabolismo , Traumatismos de la Médula Espinal/terapia , Proteínas Quinasas Activadas por AMP , Animales , Axones/metabolismo , Modelos Animales de Enfermedad , Neurogénesis/fisiología , Fosfatidilinositol 3-Quinasas/genética , Fosfatidilinositol 3-Quinasas/metabolismo , Proteínas Serina-Treonina Quinasas/genética , Recuperación de la Función/fisiología , Traumatismos de la Médula Espinal/metabolismoRESUMEN
Abnormal accumulation of the microtubule-associated protein tau is thought to cause neuronal cell death in a group of age-associated neurodegenerative disorders. Tau is phosphorylated at multiple sites in diseased brains, and phosphorylation of tau at Ser262 initiates tau accumulation and toxicity. In this study, we sought to identify novel factors that affect the metabolism and toxicity of tau phosphorylated at Ser262 (pSer262-tau). A biased screen using a Drosophila model of tau toxicity revealed that knockdown of S6K, the Drosophila homolog of p70S6K1, increased the level of pSer262-tau and enhanced tau toxicity. S6K can be activated by the insulin signaling, however, unlike knockdown of S6K, knockdown of insulin receptor or insulin receptor substrate nonselectively decreased total tau levels via autophagy. Importantly, activation of S6K significantly suppressed tau-mediated axon degeneration, whereas manipulation of either the insulin signaling pathway or autophagy did not. Our results suggest that activation of S6K may be an effective therapeutic strategy for selectively decreasing the levels of toxic tau species and suppressing neurodegeneration.
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Proteínas de Drosophila/metabolismo , Tauopatías/metabolismo , Proteínas tau/metabolismo , Animales , Animales Modificados Genéticamente , Autofagia , Modelos Animales de Enfermedad , Drosophila melanogaster , Fosforilación , Transducción de SeñalRESUMEN
Adult mammalian peripheral neurons have an intrinsic regrowth capacity in response to axonal injury. The induction of calcium ion (Ca2+) oscillations at an injured site is critical for the regulation of regenerative responses. In polarized neurons, distal axonal segments contain a well-developed endoplasmic reticulum (ER) network that is responsible for Ca2+ homeostasis. Although these characteristics implicate the relevance among injury-induced Ca2+ dynamics, axonal ER-derived signaling, and regenerative responses propagated along the axons, the details are not fully understood. In the present study, we found that Ca2+ release from the axonal ER was accelerated in response to injury. Additionally, axonal injury-dependent Ca2+ release from the ER activated unfolded protein response (UPR) signaling at injured sites. Inhibition of axonal UPR signaling led to fragmentation of the axonal ER and disrupted growth cone formation, suggesting that activation of axonal UPR branches following axonal injury promotes regeneration via regulation of ER reconstruction and formation of growth cones. Our studies revealed that local activation of axonal UPR signaling by injury-induced Ca2+ release from the ER is critical for regeneration. These findings provide a new concept for the link between injury-induced signaling at a distant location and regulation of organelle and cytoskeletal formation in the orchestration of axonal regeneration.
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Axones/metabolismo , Retículo Endoplásmico/metabolismo , Regeneración Nerviosa/fisiología , Traumatismos de los Nervios Periféricos/metabolismo , Respuesta de Proteína Desplegada/fisiología , Animales , Axones/patología , Calcio/metabolismo , Cationes Bivalentes/metabolismo , Células Cultivadas , Estrés del Retículo Endoplásmico/fisiología , Femenino , Ganglios Espinales/metabolismo , Ganglios Espinales/patología , Masculino , Proteínas de la Membrana/antagonistas & inhibidores , Proteínas de la Membrana/metabolismo , Ratones Endogámicos ICR , Traumatismos de los Nervios Periféricos/patología , Proteínas Serina-Treonina Quinasas/antagonistas & inhibidores , Proteínas Serina-Treonina Quinasas/metabolismo , Proteína Serina-Treonina Quinasas de Interacción con Receptores/antagonistas & inhibidores , Proteína Serina-Treonina Quinasas de Interacción con Receptores/metabolismo , Nervio Ciático/lesiones , Nervio Ciático/metabolismo , Nervio Ciático/patología , eIF-2 Quinasa/antagonistas & inhibidores , eIF-2 Quinasa/metabolismoRESUMEN
Tyrosine phosphorylation is a common means of regulating protein functions and signal transduction in multiple cells. Protein tyrosine phosphatases (PTPs) are a large family of signaling enzymes that remove phosphate groups from tyrosine residues of target proteins and change their functions. Among them, receptor-type PTPs (RPTPs) exhibit a distinct spatial pattern of expression and play essential roles in regulating neurite outgrowth, axon guidance, and synaptic organization in developmental nervous system. Some RPTPs function as essential receptors for chondroitin sulfate proteoglycans that inhibit axon regeneration following CNS injury. Interestingly, certain RPTPs are also important to regulate functions of immune cells and development of autoimmune diseases. PTPσ, a RPTP in the LAR subfamily, is expressed in various immune cells and regulates their differentiation, production of various cytokines and immune responses. In this review, we highlight the physiological and pathological significance of PTPσ and related molecules in both nervous and immune systems.
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Sistema Inmunológico/enzimología , Sistema Nervioso/enzimología , Proteínas Tirosina Fosfatasas/metabolismo , Animales , Proteoglicanos Tipo Condroitín Sulfato/metabolismo , Citocinas/metabolismo , Humanos , FosforilaciónRESUMEN
We identified 37 ubiquitin ligases containing RING-finger and transmembrane domains. Of these, we found that RNF183 is abundantly expressed in the kidney. RNF183 predominantly localizes to the endoplasmic reticulum (ER), Golgi, and lysosome. We identified Sec16A, which is involved in coat protein complex II vesicle formation, as an RNF183-interacting protein. RNF183 colocalized with Sec16A and interacted through the central conserved domain (CCD) of Sec16A. Although Sec16A is not a substrate for RNF183, RNF183 was more rapidly degraded by the ER-associated degradation (ERAD) in the absence of Sec16A. Sec16A also stabilized the interacting ubiquitin ligase RNF152, which localizes to the lysosome and has structural similarity with RNF183. These results suggest that Sec16A appears to regulate the protein stability and localization of lysosomal ubiquitin ligases.
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Vesículas Cubiertas por Proteínas de Revestimiento/metabolismo , Ubiquitina-Proteína Ligasas/metabolismo , Proteínas de Transporte Vesicular/fisiología , Retículo Endoplásmico/metabolismo , Aparato de Golgi/metabolismo , Humanos , Lisosomas/metabolismoRESUMEN
Unfolded protein response (UPR) has roles not only in resolving the accumulation of unfolded proteins owing to endoplasmic reticulum (ER) stress, but also in regulation of cellular physiological functions. ER stress transducers providing the branches of UPR signaling are known to localize in distal dendritic ER of neurons. These reports suggest that local activation of UPR branches may produce integrated outputs for distant communication, and allow regulation of local events in highly polarized neurons. Here, we demonstrated that synaptic activity- and brain-derived neurotrophic factor (BDNF)-dependent local activation of UPR signaling could be associated with dendritic functions through retrograde signal propagation by using murine neuroblastoma cell line, Neuro-2A and primary cultured hippocampal neurons derived from postnatal day 0 litter C57BL/6 mice. ER stress transducer, inositol-requiring kinase 1 (IRE1), was activated at postsynapses in response to excitatory synaptic activation. Activated dendritic IRE1 accelerated accumulation of the downstream transcription factor, x-box-binding protein 1 (XBP1), in the nucleus. Interestingly, excitatory synaptic activation-dependent up-regulation of XBP1 directly facilitated transcriptional activation of BDNF. BDNF in turn drove its own expression via IRE1-XBP1 pathway in a protein kinase A-dependent manner. Exogenous treatment with BDNF promoted extension and branching of dendrites through the protein kinase A-IRE1-XBP1 cascade. Taken together, our findings indicate novel mechanisms for communication between soma and distal sites of polarized neurons that are coordinated by local activation of IRE1-XBP1 signaling. Synaptic activity- and BDNF-dependent distinct activation of dendritic IRE1-XBP1 cascade drives BDNF expression in cell soma and may be involved in dendritic extension. Cover Image for this issue: doi. 10.1111/jnc.14159.
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Factor Neurotrófico Derivado del Encéfalo/biosíntesis , Neuronas/metabolismo , Respuesta de Proteína Desplegada , Animales , Factor Neurotrófico Derivado del Encéfalo/genética , Línea Celular Tumoral , Núcleo Celular/metabolismo , Proteínas Quinasas Dependientes de AMP Cíclico/fisiología , Dendritas/metabolismo , Retículo Endoplásmico/metabolismo , Ácido Glutámico/farmacología , Hipocampo/citología , Proteínas de la Membrana/biosíntesis , Proteínas de la Membrana/genética , Ratones , Ratones Endogámicos C57BL , Neuroblastoma , Proteínas Serina-Treonina Quinasas/biosíntesis , Proteínas Serina-Treonina Quinasas/genética , Transducción de Señal/fisiología , Sinapsis/fisiología , Proteína 1 de Unión a la X-Box/metabolismoRESUMEN
Abnormal deposition of the microtubule-associated protein tau is a common pathological feature of multiple neurodegenerative diseases, including Alzheimer's disease (AD), and plays critical roles in their pathogenesis. Disruption of calcium homeostasis and the downstream kinase Ca2+/calmodulin-dependent protein kinase II (CaMKII) coincides with pathological phosphorylation of tau in AD brains. However, it remains unclear whether and how dysregulation of CaMKII affects tau toxicity. Using a Drosophila model, we found that CaMKII promotes neurodegeneration caused by tau phosphorylated at the AD-associated sites Ser262/356. Overexpression of CaMKII promoted, while RNA-mediated knockdown of CaMKII and inhibition of CaMKII activity by expression of an inhibitory peptide suppressed, tau-mediated neurodegeneration. Blocking tau phosphorylation at Ser262/356 by alanine substitutions suppressed promotion of tau toxicity by CaMKII, suggesting that tau phosphorylation at these sites is required for this phenomenon. However, neither knockdown nor overexpression of CaMKII affected tau phosphorylation levels at Ser262/356, suggesting that CaMKII is not directly involved in tau phosphorylation at Ser262/356 in this model. These results suggest that a pathological cascade of events, including elevated levels of tau phosphorylated at Ser262/356 and aberrant activation of CaMKII, work in concert to promote tau-mediated neurodegeneration.
Asunto(s)
Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/metabolismo , Drosophila melanogaster/genética , Degeneración Nerviosa/genética , Degeneración Nerviosa/metabolismo , Proteínas tau/metabolismo , Secuencia de Aminoácidos , Animales , Animales Modificados Genéticamente , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/genética , Citosol , Femenino , Microtúbulos/fisiología , Fosforilación , Transporte de ProteínasRESUMEN
Secretory and membrane proteins are synthesized in ribosomes, then mature in the endoplasmic reticulum (ER), but if ER function is impaired, immature defective proteins accumulate in the ER. This situation is called ER stress: in response, a defensive mechanism called the unfolded protein response (UPR) is activated in cells to reduce the defective proteins. During the UPR, the ER transmembrane sensor molecules inositol-requiring enzyme 1 (IRE1), activating transcription factor 6 (ATF6), and RNA-dependent protein kinase (PKR)-like ER kinase (PERK) are activated, stress signals are transduced to the outside of the ER, and various cell responses, including gene induction, occur. In ER-associated degradation (ERAD), one type of UPR, defective proteins are eventually expelled from the ER and degraded in the cytoplasm through the ubiquitin proteasome system. Since ER stress has been reported to have relationships with neurodegenerative diseases, diabetes, metabolic syndromes, and cancer, it is the focus of increased attention from the perspectives of elucidating pathogenic mechanisms, and in the development of therapeutics.
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Estrés del Retículo Endoplásmico/efectos de los fármacos , Estrés del Retículo Endoplásmico/fisiología , Retículo Endoplásmico/metabolismo , Animales , Enfermedad , Retículo Endoplásmico/efectos de los fármacos , Degradación Asociada con el Retículo Endoplásmico , Humanos , Respuesta de Proteína Desplegada/efectos de los fármacosRESUMEN
Protein tyrosine phosphatases (PTPs) play essential roles in regulating signaling events in multiple cells by tyrosine dephosphorylation. One of them, PTPσ, appears important in regulating function of plasmacytoid dendritic cells (pDC). Here we report that PTPσ deletion in knockout mice and inhibition with a selective antagonist peptide exacerbated symptoms of experimental autoimmune encephalomyelitis (EAE) by enhancing axon and myelin damage in the spinal cord. PTPσ-/- mice displayed pro-inflammatory profiles in the spinal cord and lymphoid organs following MOG peptide immunization. PTPσ deletion promoted a pro-inflammatory phenotype in conventional DCs and directly regulated differentiation of CD4+ T cells. It also facilitated infiltration of T lymphocytes, activation of macrophages in the CNS and development of EAE. Therefore, PTPσ is a key negative regulator in EAE initiation and progression, which acts by regulating functions of DCs, T cells, and other immune cells. PTPσ may become an important molecular target for treating autoimmune disorders.
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Encefalomielitis Autoinmune Experimental/inmunología , Proteínas Tirosina Fosfatasas Clase 2 Similares a Receptores/metabolismo , Proteínas Tirosina Fosfatasas Clase 2 Similares a Receptores/fisiología , Animales , Diferenciación Celular , Citocinas/metabolismo , Células Dendríticas/metabolismo , Encefalomielitis Autoinmune Experimental/metabolismo , Encefalomielitis Autoinmune Experimental/fisiopatología , Activación de Linfocitos , Macrófagos/inmunología , Ratones , Ratones Endogámicos BALB C , Ratones Noqueados , Vaina de Mielina/metabolismo , Glicoproteína Mielina-Oligodendrócito/inmunología , Médula Espinal/metabolismo , Linfocitos T/inmunologíaRESUMEN
Receptor protein tyrosine phosphatase σ (PTPσ) and its subfamily member LAR act as transmembrane receptors that mediate growth inhibition of chondroitin sulfate proteoglycans (CSPGs). Inhibition of either receptor increases axon growth into and beyond scar tissues after CNS injury. However, it is unclear why neurons express two similar CSPG receptors, nor whether they use the same or different intracellular pathways. We have now studied the signaling pathways of these two receptors using N2A cells and primary neurons derived from knockout mice. We demonstrate that both receptors share certain signaling pathways (RhoA, Akt and Erk), but also use distinct signals to mediate CSPG actions. Activation of PTPσ by CSPGs selectively inactivated CRMP2, APC, S6 kinase and CREB. By contrast LAR activation inactivated PKCζ, cofilin and LKB1. For the first time, we propose a model of the signaling pathways downstream of these two CSPG receptors. We also demonstrate that deleting both receptors exhibits additive enhancement of axon growth in adult neuronal cultures in vitro. Our findings elucidate the novel downstream pathways of CSPGs and suggest potential synergy of blocking their two PTP receptors.
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Proteoglicanos Tipo Condroitín Sulfato/metabolismo , Sistema de Señalización de MAP Quinasas/fisiología , Neuronas/metabolismo , Proteínas Quinasas/metabolismo , Proteínas Tirosina Fosfatasas Clase 5 Similares a Receptores/metabolismo , Animales , Línea Celular , Proteoglicanos Tipo Condroitín Sulfato/genética , Ratones , Neuronas/citología , Proteínas Quinasas/genética , Proteínas Tirosina Fosfatasas Clase 5 Similares a Receptores/genéticaRESUMEN
Abnormal phosphorylation of the microtubule-associated protein tau is observed in many neurodegenerative diseases, including Alzheimer's disease (AD). AD-related phosphorylation of two tau residues, Ser262 and Ser356, by PAR-1/MARK stabilizes tau in the initial phase of mismetabolism, leading to subsequent phosphorylation events, accumulation, and toxicity. However, the relative contribution of phosphorylation at each of these sites to tau stabilization has not yet been elucidated. In a Drosophila model of human tau toxicity, we found that tau was phosphorylated at Ser262, but not at Ser356, and that blocking Ser262 phosphorylation decreased total tau levels. By contrast, when PAR-1 was co-overexpressed with tau, tau was hyperphosphorylated at both Ser262 and Ser356. Under these conditions, the protein levels of tau were significantly elevated, and prevention of tau phosphorylation at both residues was necessary to completely suppress this elevation. These results suggest that tau phosphorylation at Ser262 plays the predominant role in tau stabilization when PAR-1/MARK activity is normal, whereas Ser356 phosphorylation begins to contribute to this process when PAR-1/MARK activity is abnormally elevated, as in diseased brains.
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Enfermedad de Alzheimer/metabolismo , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/metabolismo , Glucógeno Sintasa Quinasa 3/metabolismo , Fosfoserina/metabolismo , Proteínas tau/metabolismo , Enfermedad de Alzheimer/patología , Sustitución de Aminoácidos , Animales , Modelos Animales de Enfermedad , Humanos , Fosforilación , Estabilidad ProteicaRESUMEN
Cell ablation is a powerful tool for studying cell lineage and/or function; however, current cell-ablation models have limitations. Intermedilysin (ILY), a cytolytic pore-forming toxin that is secreted by Streptococcus intermedius, lyses human cells exclusively by binding to the human complement regulator CD59 (hCD59), but does not react with CD59 from nonprimates. Here, we took advantage of this feature of ILY and developed a model of conditional and targeted cell ablation by generating floxed STOP-CD59 knockin mice (ihCD59), in which expression of human CD59 only occurs after Cre-mediated recombination. The administration of ILY to ihCD59+ mice crossed with various Cre-driver lines resulted in the rapid and specific ablation of immune, epithelial, or neural cells without off-target effects. ILY had a large pharmacological window, which allowed us to perform dose-dependent studies. Finally, the ILY/ihCD59-mediated cell-ablation method was tested in several disease models to study immune cell functionalities, hepatocyte and/or biliary epithelial damage and regeneration, and neural cell damage. Together, the results of this study demonstrate the utility of the ihCD59 mouse model for studying the effects of cell ablation in specific organ systems in a variety of developmental and disease states.
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Bacteriocinas/administración & dosificación , Antígenos CD59/fisiología , Animales , Astrocitos/efectos de los fármacos , Astrocitos/inmunología , Astrocitos/patología , Bacteriocinas/toxicidad , Antígenos CD59/genética , Técnicas de Sustitución del Gen , Hemólisis/genética , Hemólisis/fisiología , Hepatitis Animal/etiología , Hepatitis Animal/genética , Hepatitis Animal/inmunología , Hepatocitos/efectos de los fármacos , Hepatocitos/inmunología , Hepatocitos/patología , Humanos , Integrasas , Depleción Linfocítica , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Linfocitos T/efectos de los fármacos , Linfocitos T/inmunología , Linfocitos T/patologíaRESUMEN
Abnormal accumulation of the microtubule-interacting protein tau is associated with neurodegenerative diseases including Alzheimer's disease (AD). ß-amyloid (Aß) lies upstream of abnormal tau behavior, including detachment from microtubules, phosphorylation at several disease-specific sites, and self-aggregation into toxic tau species in AD brains. To prevent the cascade of events leading to neurodegeneration in AD, it is essential to elucidate the mechanisms underlying the initial events of tau mismetabolism. Currently, however, these mechanisms remain unclear. In this study, using transgenic Drosophila co-expressing human tau and Aß, we found that tau phosphorylation at AD-related Ser262/356 stabilized microtubule-unbound tau in the early phase of tau mismetabolism, leading to neurodegeneration. Aß increased the level of tau detached from microtubules, independent of the phosphorylation status at GSK3-targeted SP/TP sites. Such mislocalized tau proteins, especially the less phosphorylated species, were stabilized by phosphorylation at Ser262/356 via PAR-1/MARK. Levels of Ser262 phosphorylation were increased by Aß42, and blocking this stabilization of tau suppressed Aß42-mediated augmentation of tau toxicity and an increase in the levels of tau phosphorylation at the SP/TP site Thr231, suggesting that this process may be involved in AD pathogenesis. In contrast to PAR-1/MARK, blocking tau phosphorylation at SP/TP sites by knockdown of Sgg/GSK3 did not reduce tau levels, suppress tau mislocalization to the cytosol, or diminish Aß-mediated augmentation of tau toxicity. These results suggest that stabilization of microtubule-unbound tau by phosphorylation at Ser262/356 via the PAR-1/MARK may act in the initial steps of tau mismetabolism in AD pathogenesis, and that such tau species may represent a potential therapeutic target for AD.
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Enfermedad de Alzheimer/genética , Péptidos beta-Amiloides/genética , Glucógeno Sintasa Quinasa 3/genética , Receptor PAR-1/genética , Proteínas tau/genética , Enfermedad de Alzheimer/metabolismo , Enfermedad de Alzheimer/patología , Péptidos beta-Amiloides/metabolismo , Animales , Animales Modificados Genéticamente , Modelos Animales de Enfermedad , Drosophila/genética , Drosophila/metabolismo , Glucógeno Sintasa Quinasa 3/metabolismo , Glucógeno Sintasa Quinasa 3 beta , Hipocampo/metabolismo , Hipocampo/patología , Humanos , Microtúbulos/metabolismo , Microtúbulos/patología , Neuronas/metabolismo , Neuronas/patología , Fosforilación , Receptor PAR-1/metabolismo , Tubulina (Proteína)/genética , Tubulina (Proteína)/metabolismo , Proteínas tau/metabolismoRESUMEN
The intrinsic growth ability of all the neurons declines during development although some may grow better than others. Numerous intracellular signaling proteins and transcription factors have been shown to regulate the intrinsic growth capacity in mature neurons. Among them, PI3 kinase/Akt pathway is important for controlling axon elongation. As a negative regulator of this pathway, the tumor suppressor phosphatase and tensin homolog (PTEN) appears critical to control the regenerative ability of young and adult neurons. This review will focus on recent research progress in axon regeneration and neural repair by PTEN inhibition and therapeutic potential of blocking this phosphatase for neurological disorders. Inhibition of PTEN by deletion in conditional knockout mice, knockdown by short-hairpin RNA, or blockade by pharmacological approaches, including administration of selective PTEN antagonist peptides, stimulates various degrees of axon regrowth in juvenile or adult rodents with central nervous system injuries. Importantly, post-injury PTEN suppression could enhance axonal growth and functional recovery in adult central nervous system after injury.
RESUMEN
Identification of substances with specific toxicity for carcinoma cells promises to facilitate the development of cancer chemotherapeutics that cause minimal side effects. Here, we show that knockdown of the farnesoid X receptor (FXR) effectively suppresses the proliferation of human hepatocellular carcinoma cell lines HepG2 and HLE accompanied by elevated expression of cyclin-dependent kinase (CDK) inhibitor p16/INK4a and p21/Cip1 proteins. On the other hand, the growth of the primary human hepatocyte-derived cell line Fa2N-4 is not affected by the treatment with FXR siRNA irrespective of marked increases in the mRNAs of p16/INK4a and p21/Cip1. Surprisingly, the expression levels of p16/INK and p21/Cip1 proteins are left unchanged in Fa2N-4 cells that are subjected to the FXR siRNA treatment. Since the expression levels of these CDK inhibitor proteins in FXR-knockdown Fa2N-4 cells were elevated in the presence of proteasomal inhibitor MG132, these CDK inhibitors may be subjected to the proteasomal degradation, thereby counteracting the increased expression of their cognate mRNAs, therefore similar levels of p16 and p21 proteins were observed in control and FXR-knockdown Fa2N-4 cells. These results suggest that FXR-knockdown is effective for inhibiting the proliferation of hepatocellular carcinoma cells, not interfering with the regulatory mechanism of normal hepatocyte growth.
Asunto(s)
Carcinoma Hepatocelular/genética , Carcinoma Hepatocelular/patología , Proliferación Celular/genética , Técnicas de Silenciamiento del Gen , Hepatocitos/citología , Neoplasias Hepáticas/genética , Neoplasias Hepáticas/patología , Receptores Citoplasmáticos y Nucleares/genética , Receptores Citoplasmáticos y Nucleares/fisiología , Inhibidor p16 de la Quinasa Dependiente de Ciclina/genética , Inhibidor p16 de la Quinasa Dependiente de Ciclina/metabolismo , Inhibidor p21 de las Quinasas Dependientes de la Ciclina/genética , Inhibidor p21 de las Quinasas Dependientes de la Ciclina/metabolismo , Expresión Génica , Células Hep G2 , Humanos , Leupeptinas , Complejo de la Endopetidasa Proteasomal/metabolismo , ARN Mensajero , ARN Interferente PequeñoRESUMEN
Astrogliosis is a defense response of the CNS to minimize primary damage and to repair injured tissues, but it ultimately generates harmful effects by upregulating inhibitory molecules to suppress neuronal elongation and forming potent barriers to axon regeneration. Chondroitin sulfate proteoglycans (CSPGs) are highly expressed by reactive scars and are potent contributors to the non-permissive environment in mature CNS. Surmounting strong inhibition by CSPG-rich scar is an important therapeutic goal for achieving functional recovery after CNS injuries. Currently, enzymatic digestion of CSPGs with locally applied chondroitinase ABC is the main in vivo approach to overcome scar inhibition, but several disadvantages may prevent using this bacterial enzyme as a therapeutic option for patients. A better understanding of molecular mechanisms underlying CSPG function may facilitate development of new effective therapies to overcome scar-mediated inhibition. Previous studies support that CSPGs act by non-specifically hindering the binding of matrix molecules to their cell surface receptors through steric interactions, but two members of the leukocyte common antigen related (LAR) phosphatase subfamily, protein tyrosine phosphatase σ and LAR, are functional receptors that bind CSPGs with high affinity and mediate CSPG inhibition. CSPGs may also act by binding two receptors for myelin-associated growth inhibitors, Nogo receptors 1 and 3. Thus, CSPGs inhibit axon growth through multiple mechanisms, making them especially potent and difficult therapeutic targets. Identification of CSPG receptors is not only important for understanding the scar-mediated growth suppression, but also for developing novel and selective therapies to promote axon sprouting and/or regeneration after CNS injuries. This article is part of a Special Issue entitled SI: Spinal cord injury.