RESUMO
Progranulin is an evolutionarily conserved protein that has been implicated in human neurodevelopmental and neurodegenerative diseases. Human progranulin is comprised of multiple cysteine-rich, biologically active granulin peptides. Granulin peptides accumulate with age and stress, however their functional contributions relative to full-length progranulin remain unclear. To address this, we generated C. elegans strains that produced quantifiable levels of both full-length progranulin/PGRN-1 protein and cleaved granulin peptide. Using these strains, we demonstrated that even in the presence of intact PGRN-1, granulin peptides suppressed the activity of the lysosomal aspartyl protease activity, ASP-3/CTSD. Granulin peptides were also dominant over PGRN-1 in compromising animal fitness as measured by progress through development and stress response. Finally, the degradation of human TDP-43 was impaired when the granulin to PGRN-1 ratio was increased, representing a disease-relevant downstream impact of impaired lysosomal function. In summary, these studies suggest that not only absolute progranulin levels, but also the balance between full-length progranulin and its cleavage products, is important in regulating lysosomal biology. Given its relevance in human disease, this suggests that the processing of progranulin into granulins should be considered as part of disease pathobiology and may represent a site of therapeutic intervention.
Assuntos
Proteínas de Caenorhabditis elegans , Caenorhabditis elegans , Granulinas , Progranulinas , Animais , Humanos , Caenorhabditis elegans/fisiologia , Granulinas/metabolismo , Peptídeos e Proteínas de Sinalização Intercelular , Doenças Neurodegenerativas , Progranulinas/metabolismo , Proteínas de Caenorhabditis elegans/metabolismoRESUMO
Astrocytes respond and contribute to neuroinflammation by adopting inflammatory reactive states. Although recent efforts have characterized the gene expression signatures associated with these reactive states, the cell biology underlying inflammatory reactive astrocyte phenotypes remains under-explored. Here, we used CRISPR-based screening in human iPSC-derived astrocytes to identify mTOR activation a driver of cytokine-induced endolysosomal system remodeling, manifesting as alkalinization of endolysosomal compartments, decreased autophagic flux, and increased exocytosis of certain endolysosomal cargos. Through endolysosomal proteomics, we identified and focused on one such cargo-IL-32, a disease-associated pro-inflammatory cytokine not present in rodents, whose secretion mechanism is not well understood. We found that IL-32 was partially secreted in extracellular vesicles likely to be exosomes. Furthermore, we found that IL-32 was involved in the polarization of inflammatory reactive astrocyte states and was upregulated in astrocytes in multiple sclerosis lesions. We believe that our results advance our understanding of cell biological pathways underlying inflammatory reactive astrocyte phenotypes and identify potential therapeutic targets.
Assuntos
Astrócitos , Exossomos , Interleucinas , Lisossomos , Serina-Treonina Quinases TOR , Astrócitos/metabolismo , Humanos , Exossomos/metabolismo , Serina-Treonina Quinases TOR/metabolismo , Lisossomos/metabolismo , Interleucinas/metabolismo , Endossomos/metabolismo , Células-Tronco Pluripotentes Induzidas/metabolismo , Células Cultivadas , Doenças Neuroinflamatórias/metabolismo , Doenças Neuroinflamatórias/patologia , Inflamação/metabolismo , Inflamação/patologiaRESUMO
Tuberous sclerosis complex (TSC) is a neurogenetic disorder leading to epilepsy, developmental delay, and neurobehavioral dysfunction. The syndrome is caused by pathogenic variants in TSC1 (coding for hamartin) or TSC2 (coding for tuberin). Recently, we reported a progressive frontotemporal dementia-like clinical syndrome in a patient with a mutation in TSC1, but the neuropathological changes seen in adults with TSC with or without dementia have yet to be systematically explored. Here, we examined neuropathological findings in adults with TSC (n = 11) aged 30-58 years and compared them to age-matched patients with epilepsy unrelated to TSC (n = 9) and non-neurological controls (n = 10). In 3 of 11 subjects with TSC, we observed a neurofibrillary tangle-predominant "TSC tauopathy" not seen in epilepsy or non-neurological controls. This tauopathy was observed in the absence of pathological amyloid beta, TDP-43, or alpha-synuclein deposition. The neurofibrillary tangles in TSC tauopathy showed a unique pattern of post-translational modifications, with apparent differences between TSC1 and TSC2 mutation carriers. Tau acetylation (K274, K343) was prominent in both TSC1 and TSC2, whereas tau phosphorylation at a common phospho-epitope (S202) was observed only in TSC2. TSC tauopathy was observed in selected neocortical, limbic, subcortical, and brainstem sites and showed a 3-repeat greater than 4-repeat tau isoform pattern in both TSC1 and TSC2 mutation carriers, but no tangles were immunolabeled with MC1 or p62 antibodies. The findings suggest that individuals with TSC are at risk for a unique tauopathy in mid-life and that tauopathy pathogenesis may involve TSC1, TSC2, and related molecular pathways.
Assuntos
Epilepsia , Tauopatias , Esclerose Tuberosa , Adulto , Humanos , Proteínas Supressoras de Tumor/genética , Esclerose Tuberosa/genética , Esclerose Tuberosa/metabolismo , Peptídeos beta-Amiloides/genética , Mutação/genética , Epilepsia/genética , Tauopatias/genéticaRESUMO
The discovery that heterozygous and homozygous mutations in the gene encoding progranulin are causally linked to frontotemporal dementia and lysosomal storage disease, respectively, reveals previously unrecognized roles of the progranulin protein in regulating lysosome biogenesis and function. Given the importance of lysosomes in cellular homeostasis, it is not surprising that progranulin deficiency has pleiotropic effects on neural circuit development and maintenance, stress response, innate immunity and ageing. This Progress article reviews recent advances in progranulin biology emphasizing its roles in lysosomal function and brain innate immunity, and outlines future avenues of investigation that may lead to new therapeutic approaches for neurodegeneration.
Assuntos
Peptídeos e Proteínas de Sinalização Intercelular/genética , Peptídeos e Proteínas de Sinalização Intercelular/metabolismo , Lisossomos/metabolismo , Doenças Neurodegenerativas/genética , Animais , Humanos , Peptídeos e Proteínas de Sinalização Intercelular/biossíntese , Doenças Neurodegenerativas/metabolismo , ProgranulinasRESUMO
The progressive failure of protein homeostasis is a hallmark of aging and a common feature in neurodegenerative disease. As the enzymes executing the final stages of autophagy, lysosomal proteases are key contributors to the maintenance of protein homeostasis with age. We previously reported that expression of granulin peptides, the cleavage products of the neurodegenerative disease protein progranulin, enhance the accumulation and toxicity of TAR DNA binding protein 43 (TDP-43) in Caenorhabditis elegans (C. elegans). In this study we show that C. elegans granulins are produced in an age- and stress-dependent manner. Granulins localize to the endolysosomal compartment where they impair lysosomal protease expression and activity. Consequently, protein homeostasis is disrupted, promoting the nuclear translocation of the lysosomal transcription factor HLH-30/TFEB, and prompting cells to activate a compensatory transcriptional program. The three C. elegans granulin peptides exhibited distinct but overlapping functional effects in our assays, which may be due to amino acid composition that results in distinct electrostatic and hydrophobicity profiles. Our results support a model in which granulin production modulates a critical transition between the normal, physiological regulation of protease activity and the impairment of lysosomal function that can occur with age and disease.
Assuntos
Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Proteínas de Caenorhabditis elegans/metabolismo , Proteínas de Ligação a DNA/genética , Granulinas/metabolismo , Lisossomos/metabolismo , Doenças Neurodegenerativas/genética , Envelhecimento/genética , Animais , Animais Geneticamente Modificados , Caenorhabditis elegans , Modelos Animais de Doenças , Endopeptidases/metabolismo , Regulação da Expressão Gênica , Granulinas/genética , Humanos , Doenças Neurodegenerativas/patologia , Estresse Fisiológico/genéticaRESUMO
Mutations in the microtubule-associated protein tau (MAPT) underlie multiple neurodegenerative disorders, yet the pathophysiological mechanisms are unclear. A novel variant in MAPT resulting in an alanine to threonine substitution at position 152 (A152T tau) has recently been described as a significant risk factor for both frontotemporal lobar degeneration and Alzheimer's disease. Here we use complementary computational, biochemical, molecular, genetic and imaging approaches in Caenorhabditis elegans and mouse models to interrogate the effects of the A152T variant on tau function. In silico analysis suggests that a threonine at position 152 of tau confers a new phosphorylation site. This finding is borne out by mass spectrometric survey of A152T tau phosphorylation in C. elegans and mouse. Optical pulse-chase experiments of Dendra2-tau demonstrate that A152T tau and phosphomimetic A152E tau exhibit increased diffusion kinetics and the ability to traverse across the axon initial segment more efficiently than wild-type (WT) tau. A C. elegans model of tauopathy reveals that A152T and A152E tau confer patterns of developmental toxicity distinct from WT tau, likely due to differential effects on retrograde axonal transport. These data support a role for phosphorylation of the variant threonine in A152T tau toxicity and suggest a mechanism involving impaired retrograde axonal transport contributing to human neurodegenerative disease.
Assuntos
Alelos , Substituição de Aminoácidos , Variação Genética , Proteínas tau/genética , Proteínas tau/metabolismo , Animais , Animais Geneticamente Modificados , Transporte Axonal , Axônios/metabolismo , Caenorhabditis elegans , Modelos Animais de Doenças , Suscetibilidade a Doenças , Humanos , Camundongos , Mutação , Fosforilação , Ligação Proteica , Vesículas Sinápticas/metabolismo , Tauopatias/etiologia , Tauopatias/metabolismo , Tauopatias/patologiaRESUMO
Tauopathies are neurodegenerative diseases characterized by tau protein pathology in the nervous system. EIF2AK3 (eukaryotic translation initiation factor 2 alpha kinase 3), also known as PERK (protein kinase R-like endoplasmic reticulum kinase), was identified by genome-wide association study as a genetic risk factor in several tauopathies. PERK is a key regulator of the Unfolded Protein Response (UPR), an intracellular signal transduction mechanism that protects cells from endoplasmic reticulum (ER) stress. PERK variants had previously been identified in Wolcott-Rallison Syndrome, a rare autosomal recessive metabolic disorder, and these variants completely abrogated the function of PERK's kinase domain or prevented PERK expression. In contrast, the PERK tauopathy risk variants were distinct from the Wolcott-Rallison variants and introduced missense alterations throughout the PERK protein. The function of PERK tauopathy variants and their effects on neurodegeneration are unknown. Here, we discovered that tauopathy-associated PERK alleles showed reduced signaling activity and increased PERK protein turnover compared to protective PERK alleles. We found that iPSC-derived neurons carrying PERK risk alleles were highly vulnerable to ER stress-induced injury with increased tau pathology. We found that chemical inhibition of PERK in human iPSC-derived neurons also increased neuronal cell death in response to ER stress. Our results indicate that tauopathy-associated PERK alleles are functional hypomorphs during the UPR. We propose that reduced PERK function leads to neurodegeneration by increasing neuronal vulnerability to ER stress-associated damage. In this view, therapies to enhance PERK signaling would benefit at-risk carriers of hypomorphic alleles.
Assuntos
Estresse do Retículo Endoplasmático/genética , Tauopatias/genética , eIF-2 Quinase/genética , Alelos , Animais , Apoptose/genética , Diferenciação Celular/genética , Diabetes Mellitus Tipo 1/genética , Diabetes Mellitus Tipo 1/patologia , Retículo Endoplasmático/genética , Epífises/anormalidades , Epífises/patologia , Fibroblastos/metabolismo , Fibroblastos/patologia , Regulação da Expressão Gênica/genética , Humanos , Camundongos , Mutação de Sentido Incorreto/genética , Degeneração Neural/genética , Degeneração Neural/patologia , Neurônios/metabolismo , Neurônios/patologia , Osteocondrodisplasias/genética , Osteocondrodisplasias/patologia , Polimorfismo de Nucleotídeo Único , Proteólise , Transdução de Sinais/genética , Tauopatias/patologia , Resposta a Proteínas não Dobradas/genéticaRESUMO
The lumenal pH of an organelle is one of its defining characteristics and central to its biological function. Experiments have elucidated many of the key pH regulatory elements and how they vary from compartment-to-compartment, and continuum mathematical models have played an important role in understanding how these elements (proton pumps, counter-ion fluxes, membrane potential, buffering capacity, etc.) work together to achieve specific pH setpoints. While continuum models have proven successful in describing ion regulation at the cellular length scale, it is unknown if they are valid at the subcellular level where volumes are small, ion numbers may fluctuate wildly, and biochemical heterogeneity is large. Here, we create a discrete, stochastic (DS) model of vesicular acidification to answer this question. We used this simplified model to analyze pH measurements of isolated vesicles containing single proton pumps and compared these results to solutions from a continuum, ordinary differential equations (ODE)-based model. Both models predict similar parameter estimates for the mean proton pumping rate, membrane permeability, etc., but, as expected, the ODE model fails to report on the fluctuations in the system. The stochastic model predicts that pH fluctuations decrease during acidification, but noise analysis of single-vesicle data confirms our finding that the experimental noise is dominated by the fluorescent dye, and it reveals no insight into the true noise in the proton fluctuations. Finally, we again use the reduced DS model explore the acidification of large, lysosome-like vesicles to determine how stochastic elements, such as variations in proton-pump copy number and cycling between on and off states, impact the pH setpoint and fluctuations around this setpoint.
Assuntos
Modelos Biológicos , Organelas/metabolismo , Prótons , Soluções Tampão , Biologia Computacional , Simulação por Computador , Corantes Fluorescentes , Concentração de Íons de Hidrogênio , Transporte de Íons , Potenciais da Membrana , Permeabilidade , Bombas de Próton/metabolismo , Processos EstocásticosRESUMO
Progranulin (PGRN) is an evolutionarily conserved glycoprotein associated with several disease states, including neurodegeneration, cancer, and autoimmune disorders. This protein has recently been implicated in the regulation of lysosome function, whereby PGRN may bind to and promote the maturation and activity of the aspartyl protease cathepsin D (proCTSD, inactive precursor; matCTSD, mature, enzymatically active form). As the full-length PGRN protein can be cleaved into smaller peptides, called granulins, we assessed the function of these granulin peptides in binding to proCTSD and stimulating matCTSD enzyme activity in vitro. Here, we report that full-length PGRN and multi-granulin domain peptides bound to proCTSD with low to submicromolar binding affinities. This binding promoted proCTSD destabilization, the magnitude of which was greater for multi-granulin domain peptides than for full-length PGRN. Such destabilization correlated with enhanced matCTSD activity at acidic pH. The presence and function of multi-granulin domain peptides have typically been overlooked in previous studies. This work provides the first in vitro quantification of their binding and activity on proCTSD. Our study highlights the significance of multi-granulin domain peptides in the regulation of proCTSD maturation and enzymatic activity and suggests that attention to PGRN processing will be essential for the future understanding of the molecular mechanisms leading to neurodegenerative disease states with loss-of-function mutations in PGRN.
Assuntos
Catepsina D/metabolismo , Precursores Enzimáticos/metabolismo , Granulinas/metabolismo , Humanos , Ligação Proteica , Conformação Proteica , Estabilidade Proteica , Temperatura de TransiçãoRESUMO
Accurately predicting the underlying neuropathological diagnosis in patients with behavioural variant frontotemporal dementia (bvFTD) poses a daunting challenge for clinicians but will be critical for the success of disease-modifying therapies. We sought to improve pathological prediction by exploring clinicopathological correlations in a large bvFTD cohort. Among 438 patients in whom bvFTD was either the top or an alternative possible clinical diagnosis, 117 had available autopsy data, including 98 with a primary pathological diagnosis of frontotemporal lobar degeneration (FTLD), 15 with Alzheimer's disease, and four with amyotrophic lateral sclerosis who lacked neurodegenerative disease-related pathology outside of the motor system. Patients with FTLD were distributed between FTLD-tau (34 patients: 10 corticobasal degeneration, nine progressive supranuclear palsy, eight Pick's disease, three frontotemporal dementia with parkinsonism associated with chromosome 17, three unclassifiable tauopathy, and one argyrophilic grain disease); FTLD-TDP (55 patients: nine type A including one with motor neuron disease, 27 type B including 21 with motor neuron disease, eight type C with right temporal lobe presentations, and 11 unclassifiable including eight with motor neuron disease), FTLD-FUS (eight patients), and one patient with FTLD-ubiquitin proteasome system positive inclusions (FTLD-UPS) that stained negatively for tau, TDP-43, and FUS. Alzheimer's disease was uncommon (6%) among patients whose only top diagnosis during follow-up was bvFTD. Seventy-nine per cent of FTLD-tau, 86% of FTLD-TDP, and 88% of FTLD-FUS met at least 'possible' bvFTD diagnostic criteria at first presentation. The frequency of the six core bvFTD diagnostic features was similar in FTLD-tau and FTLD-TDP, suggesting that these features alone cannot be used to separate patients by major molecular class. Voxel-based morphometry revealed that nearly all pathological subgroups and even individual patients share atrophy in anterior cingulate, frontoinsula, striatum, and amygdala, indicating that degeneration of these regions is intimately linked to the behavioural syndrome produced by these diverse aetiologies. In addition to these unifying features, symptom profiles also differed among pathological subtypes, suggesting distinct anatomical vulnerabilities and informing a clinician's prediction of pathological diagnosis. Data-driven classification into one of the 10 most common pathological diagnoses was most accurate (up to 60.2%) when using a combination of known predictive factors (genetic mutations, motor features, or striking atrophy patterns) and the results of a discriminant function analysis that incorporated clinical, neuroimaging, and neuropsychological data.
Assuntos
Doença de Alzheimer/patologia , Esclerose Lateral Amiotrófica/patologia , Encéfalo/patologia , Demência Frontotemporal/patologia , Doença de Pick/patologia , Paralisia Supranuclear Progressiva/patologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Doença de Alzheimer/diagnóstico por imagem , Doença de Alzheimer/psicologia , Esclerose Lateral Amiotrófica/diagnóstico por imagem , Esclerose Lateral Amiotrófica/psicologia , Autopsia , Encéfalo/diagnóstico por imagem , Feminino , Demência Frontotemporal/diagnóstico por imagem , Demência Frontotemporal/psicologia , Degeneração Lobar Frontotemporal/diagnóstico por imagem , Degeneração Lobar Frontotemporal/patologia , Degeneração Lobar Frontotemporal/psicologia , Humanos , Imageamento por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Tamanho do Órgão , Doença de Pick/diagnóstico por imagem , Doença de Pick/psicologia , Paralisia Supranuclear Progressiva/diagnóstico por imagem , Paralisia Supranuclear Progressiva/psicologiaRESUMO
Mutations in the human progranulin gene resulting in protein haploinsufficiency cause frontotemporal lobar degeneration with TDP-43 inclusions. Although progress has been made in understanding the normal functions of progranulin and TDP-43, the molecular interactions between these proteins remain unclear. Progranulin is proteolytically processed into granulins, but the role of granulins in the pathogenesis of neurodegenerative disease is unknown. We used a Caenorhabditis elegans model of neuronal TDP-43 proteinopathy to specifically interrogate the contribution of granulins to the neurodegenerative process. Complete loss of the progranulin gene did not worsen TDP-43 toxicity, whereas progranulin heterozygosity did. Interestingly, expression of individual granulins alone had little effect on behavior. In contrast, when granulins were coexpressed with TDP-43, they exacerbated its toxicity in a variety of behaviors including motor coordination. These same granulins increased TDP-43 levels via a post-translational mechanism. We further found that in human neurodegenerative disease subjects, granulin fragments accumulated specifically in diseased regions of brain. To our knowledge, this is the first demonstration of a toxic role for granulin fragments in a neurodegenerative disease model. These studies suggest that presence of cleaved granulins, rather than or in addition to loss of full-length progranulin, may contribute to disease in TDP-43 proteinopathies.
Assuntos
Proteínas de Ligação a DNA/metabolismo , Peptídeos e Proteínas de Sinalização Intercelular/metabolismo , Proteinopatias TDP-43/metabolismo , Animais , Animais Geneticamente Modificados , Caenorhabditis elegans , Modelos Animais de Doenças , Humanos , Immunoblotting , Progranulinas , Reação em Cadeia da Polimerase em Tempo Real , Proteínas de Peixe-Zebra/metabolismoRESUMO
Animals have many ways of protecting themselves against stress; for example, they can induce animal-wide, stress-protective pathways and they can kill damaged cells via apoptosis. We have discovered an unexpected regulatory relationship between these two types of stress responses. We find that C. elegans mutations blocking the normal course of programmed cell death and clearance confer animal-wide resistance to a specific set of environmental stressors; namely, ER, heat and osmotic stress. Remarkably, this pattern of stress resistance is induced by mutations that affect cell death in different ways, including ced-3 (cell death defective) mutations, which block programmed cell death, ced-1 and ced-2 mutations, which prevent the engulfment of dying cells, and progranulin (pgrn-1) mutations, which accelerate the clearance of apoptotic cells. Stress resistance conferred by ced and pgrn-1 mutations is not additive and these mutants share altered patterns of gene expression, suggesting that they may act within the same pathway to achieve stress resistance. Together, our findings demonstrate that programmed cell death effectors influence the degree to which C. elegans tolerates environmental stress. While the mechanism is not entirely clear, it is intriguing that animals lacking the ability to efficiently and correctly remove dying cells should switch to a more global animal-wide system of stress resistance.
Assuntos
Apoptose/genética , Retículo Endoplasmático/genética , Pressão Osmótica , Estresse Fisiológico/genética , Animais , Caenorhabditis elegans/genética , Caenorhabditis elegans/metabolismo , Caenorhabditis elegans/fisiologia , Proteínas de Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/metabolismo , Caspases/genética , Caspases/metabolismo , Retículo Endoplasmático/metabolismo , Humanos , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Mutação , Transdução de Sinais/genéticaRESUMO
Frontotemporal lobar degeneration is a progressive neurodegenerative syndrome that is the second most common cause of early-onset dementia. Mutations in the progranulin gene are a major cause of familial frontotemporal lobar degeneration [Baker M, et al. (2006) Nature 442:916-919 and Cruts M, et al. (2006) Nature 442:920-924]. Although progranulin is involved in wound healing, inflammation, and tumor growth, its role in the nervous system and the mechanism by which insufficient levels result in neurodegeneration are poorly understood [Eriksen and Mackenzie (2008) J Neurochem 104:287-297]. We have characterized the normal function of progranulin in the nematode Caenorhabditis elegans. We found that mutants lacking pgrn-1 appear grossly normal, but exhibit fewer apoptotic cell corpses during development. This reduction in corpse number is not caused by reduced apoptosis, but instead by more rapid clearance of dying cells. Likewise, we found that macrophages cultured from progranulin KO mice displayed enhanced rates of apoptotic-cell phagocytosis. Although most neurodegenerative diseases are thought to be caused by the toxic effects of aggregated proteins, our findings suggest that susceptibility to neurodegeneration may be increased by a change in the kinetics of programmed cell death. We propose that cells that might otherwise recover from damage or injury are destroyed in progranulin mutants, which in turn facilitates disease progression.
Assuntos
Proteínas Reguladoras de Apoptose/genética , Apoptose/genética , Proteínas de Caenorhabditis elegans/genética , Peptídeos e Proteínas de Sinalização Intercelular/genética , Mutação/genética , Doenças Neurodegenerativas/genética , Animais , Proteínas Reguladoras de Apoptose/metabolismo , Caenorhabditis elegans/citologia , Caenorhabditis elegans/embriologia , Caenorhabditis elegans/metabolismo , Proteínas de Caenorhabditis elegans/metabolismo , Embrião não Mamífero/citologia , Embrião não Mamífero/metabolismo , Granulinas , Peptídeos e Proteínas de Sinalização Intercelular/metabolismo , Mucosa Intestinal/metabolismo , Intestinos/citologia , Cinética , Longevidade , Macrófagos/citologia , Macrófagos/metabolismo , Camundongos , Camundongos Knockout , Modelos Biológicos , Neurônios/citologia , Neurônios/metabolismo , Fagocitose , ProgranulinasRESUMO
Frontotemporal degeneration (FTD) is a common cause of dementia for which there are currently no approved therapies. Over the past decade, there has been an explosion of knowledge about the biology and clinical features of FTD that has identified a number of promising therapeutic targets as well as animal models in which to develop drugs. The close association of some forms of FTD with neuropathological accumulation of tau protein or increased neuroinflammation due to progranulin protein deficiency suggests that a drug's success in treating FTD may predict efficacy in more common diseases such as Alzheimer's disease. A variety of regulatory incentives, clinical features of FTD such as rapid disease progression, and relatively pure molecular pathology suggest that there are advantages to developing drugs for FTD as compared with other more common neurodegenerative diseases such as Alzheimer's disease. In March 2011, the Frontotemporal Degeneration Treatment Study Group sponsored a conference entitled "FTD, the Next Therapeutic Frontier," which focused on preclinical aspects of FTD drug development. The goal of the meeting was to promote collaborations between academic researchers and biotechnology and pharmaceutical researchers to accelerate the development of new treatments for FTD. Here we report the key findings from the conference, including the rationale for FTD drug development; epidemiological, genetic, and neuropathological features of FTD; FTD animal models and how best to use them; and examples of successful drug development collaborations in other neurodegenerative diseases.
Assuntos
Modelos Animais de Doenças , Descoberta de Drogas , Degeneração Lobar Frontotemporal/tratamento farmacológico , Fármacos Neuroprotetores/uso terapêutico , Animais , HumanosRESUMO
Frontotemporal degeneration (FTD) encompasses a spectrum of related neurodegenerative disorders with behavioral, language, and motor phenotypes for which there are currently no effective therapies. This is the second of two articles that summarize the presentations and discussions that occurred at two symposia in 2011 sponsored by the Frontotemporal Degeneration Treatment Study Group, a collaborative group of academic and industry researchers that is devoted to developing treatments for FTD. This article discusses the current status of FTD clinical research that is relevant to the conduct of clinical trials, and why FTD research may be an attractive pathway for developing therapies for neurodegenerative disorders. The clinical and molecular features of FTD, including rapid disease progression and relatively pure molecular pathology, suggest that there are advantages to developing drugs for FTD as compared with other dementias. FTD qualifies as orphan indication, providing additional advantages for drug development. Two recent sets of consensus diagnostic criteria will facilitate the identification of patients with FTD, and a variety of neuropsychological, functional, and behavioral scales have been shown to be sensitive to disease progression. Moreover, quantitative neuroimaging measurements demonstrate progressive brain atrophy in FTD at rates that may surpass Alzheimer's disease. Finally, the similarities between FTD and other neurodegenerative diseases with drug development efforts already underway suggest that FTD researchers will be able to draw on this experience to create a road map for FTD drug development. We conclude that FTD research has reached sufficient maturity to pursue clinical development of specific FTD therapies.
Assuntos
Modelos Animais de Doenças , Descoberta de Drogas , Degeneração Lobar Frontotemporal/tratamento farmacológico , Fármacos Neuroprotetores/uso terapêutico , Animais , HumanosRESUMO
BACKGROUND: Autosomal dominant mutations in α-synuclein, TDP-43 and tau are thought to predispose to neurodegeneration by enhancing protein aggregation. While a subset of α-synuclein, TDP-43 and tau mutations has been shown to increase the structural propensity of these proteins toward self-association, rates of aggregation are also highly dependent on protein steady state concentrations, which are in large part regulated by their rates of lysosomal degradation. Previous studies have shown that lysosomal proteases operate precisely and not indiscriminately, cleaving their substrates at very specific linear amino acid sequences. With this knowledge, we hypothesized that certain coding mutations in α-synuclein, TDP-43 and tau may lead to increased protein steady state concentrations and eventual aggregation by an alternative mechanism, that is, through disrupting lysosomal protease cleavage recognition motifs and subsequently conferring protease resistance to these proteins. RESULTS: To test this possibility, we first generated comprehensive proteolysis maps containing all of the potential lysosomal protease cleavage sites for α-synuclein, TDP-43 and tau. In silico analyses of these maps indicated that certain mutations would diminish cathepsin cleavage, a prediction we confirmed utilizing in vitro protease assays. We then validated these findings in cell models and induced neurons, demonstrating that mutant forms of α-synuclein, TDP-43 and tau are degraded less efficiently than wild type despite being imported into lysosomes at similar rates. CONCLUSIONS: Together, this study provides evidence that pathogenic mutations in the N-terminal domain of α-synuclein (G51D, A53T), low complexity domain of TDP-43 (A315T, Q331K, M337V) and R1 and R2 domains of tau (K257T, N279K, S305N) directly impair their own lysosomal degradation, altering protein homeostasis and increasing cellular protein concentrations by extending the degradation half-lives of these proteins. These results also point to novel, shared, alternative mechanism by which different forms of neurodegeneration, including synucleinopathies, TDP-43 proteinopathies and tauopathies, may arise. Importantly, they also provide a roadmap for how the upregulation of particular lysosomal proteases could be targeted as potential therapeutics for human neurodegenerative disease.
Assuntos
Proteínas de Ligação a DNA , Doenças Neurodegenerativas , alfa-Sinucleína , Humanos , alfa-Sinucleína/genética , alfa-Sinucleína/metabolismo , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Meia-Vida , Lisossomos/metabolismo , Mutação/genética , Doenças Neurodegenerativas/metabolismo , Peptídeo Hidrolases/metabolismo , Proteínas tau/genética , Proteínas tau/metabolismoAssuntos
Demência Frontotemporal/genética , Mutação , Transdução de Sinais/fisiologia , Serina-Treonina Quinases TOR/metabolismo , Esclerose Tuberosa/genética , Proteínas Supressoras de Tumor/genética , Demência Frontotemporal/metabolismo , Demência Frontotemporal/patologia , Humanos , Masculino , Pessoa de Meia-Idade , Esclerose Tuberosa/metabolismo , Esclerose Tuberosa/patologia , Proteína 1 do Complexo Esclerose Tuberosa , Proteínas Supressoras de Tumor/metabolismoRESUMO
Lysosomes are intracellular organelles responsible for the degradation of diverse macromolecules in a cell. A highly acidic pH is required for the optimal functioning of lysosomal enzymes. Loss of lysosomal intralumenal acidity can disrupt cellular protein homeostasis and is linked to age-related diseases such as neurodegeneration. Using a new robust lysosomal pH biosensor (FIRE-pHLy), we developed a cell-based fluorescence assay for high-throughput screening (HTS) and applied it to differentiated SH-SY5Y neuroblastoma cells. The goal of this study was twofold: (1) to screen for small molecules that acidify lysosomal pH and (2) to identify molecular targets and pathways that regulate lysosomal pH. We conducted a screen of 1835 bioactive compounds with annotated target information to identify lysosomal pH modulators (both acidifiers and alkalinizers). Forty-five compounds passed the initial hit selection criteria, using a combined analysis approach of population-based and object-based data. Twenty-three compounds were retested in dose-response assays and two compounds, OSI-027 and PP242, were identified as top acidifying hits. Overall, data from this phenotypic HTS screen may be used to explore novel regulatory pathways of lysosomal pH regulation. Additionally, OSI-027 and PP242 may serve as useful tool compounds to enable mechanistic studies of autophagy activation and lysosomal acidification as potential therapeutic pathways for neurodegenerative diseases.
Assuntos
Lisossomos , Doenças Neurodegenerativas , Autofagia/fisiologia , Humanos , Concentração de Íons de Hidrogênio , Lisossomos/metabolismo , Doenças Neurodegenerativas/metabolismo , Neurônios/metabolismoRESUMO
Patient-derived cells hold great promise for precision medicine approaches in human health. Human dermal fibroblasts have been a major source of cells for reprogramming and differentiating into specific cell types for disease modeling. Postmortem human dura mater has been suggested as a primary source of fibroblasts for in vitro modeling of neurodegenerative diseases. Although fibroblast-like cells from human and mouse dura mater have been previously described, their utility for reprogramming and direct differentiation protocols has not been fully established. In this study, cells derived from postmortem dura mater are directly compared to those from dermal biopsies of living subjects. In two instances, we have isolated and compared dermal and dural cell lines from the same subject. Notably, striking differences were observed between cells of dermal and dural origin. Compared to dermal fibroblasts, postmortem dura mater-derived cells demonstrated different morphology, slower growth rates, and a higher rate of karyotype abnormality. Dura mater-derived cells also failed to express fibroblast protein markers. When dermal fibroblasts and dura mater-derived cells from the same subject were compared, they exhibited highly divergent gene expression profiles that suggest dura mater cells originated from a mixed mural lineage. Given their postmortem origin, somatic mutation signatures of dura mater-derived cells were assessed and suggest defective DNA damage repair. This study argues for rigorous karyotyping of postmortem derived cell lines and highlights limitations of postmortem human dura mater-derived cells for modeling normal biology or disease-associated pathobiology.
Assuntos
Dura-Máter , Transcriptoma , Humanos , Animais , Camundongos , Dura-Máter/metabolismo , Dura-Máter/patologia , Diferenciação Celular/genética , Fibroblastos , Células CultivadasRESUMO
Lysosomes are important sites for macromolecular degradation, defined by an acidic lumenal pH of â¼4.5. To better understand lysosomal pH, we designed a novel, genetically encoded, fluorescent protein (FP)-based pH biosensor called Fluorescence Indicator REporting pH in Lysosomes (FIRE-pHLy). This biosensor was targeted to lysosomes with lysosomal-associated membrane protein 1 (LAMP1) and reported lumenal pH between 3.5 and 6.0 with monomeric teal fluorescent protein 1 (mTFP1), a bright cyan pH-sensitive FP variant with a pKa of 4.3. Ratiometric quantification was enabled with cytosolically oriented mCherry using high-content quantitative imaging. We expressed FIRE-pHLy in several cellular models and quantified the alkalinizing response to bafilomycin A1, a specific V-ATPase inhibitor. In summary, we have engineered FIRE-pHLy, a specific, robust, and versatile lysosomal pH biosensor, that has broad applications for investigating pH dynamics in aging- and lysosome-related diseases, as well as in lysosome-based drug discovery.