Small molecule C381 targets the lysosome to reduce inflammation and ameliorate disease in models of neurodegeneration

Proteostasis and lysosomal repair deficits in transdifferentiated neurons of Alzheimer's disease

Ageing is the most prominent risk factor for Alzheimer's disease (AD). However, the cellular mechanisms linking neuronal proteostasis decline to the characteristic aberrant protein deposits in the brains of patients with AD remain elusive. Here we develop transdifferentiated neurons (tNeurons) from human dermal fibroblasts as a neuronal model that retains ageing hallmarks and exhibits AD-linked vulnerabilities. Remarkably, AD tNeurons accumulate proteotoxic deposits, including phospho-tau and amyloid β, resembling those in APP mouse brains and the brains of patients with AD. Quantitative tNeuron proteomics identify ageing- and AD-linked deficits in proteostasis and organelle homeostasis, most notably in endosome-lysosomal components. Lysosomal deficits in aged tNeurons, including constitutive lysosomal damage and ESCRT-mediated lysosomal repair defects, are exacerbated in AD tNeurons and linked to inflammatory cytokine secretion and cell death. Providing support for the centrality of lysosomal deficits in AD, compounds ameliorating lysosomal function reduce amyloid β deposits and cytokine secretion. Thus, the tNeuron model system reveals impaired lysosomal homeostasis as an early event of ageing and AD.

MHC-I upregulation by macbecin II in the solid tumors potentiates the effect of active immunotherapy

We aimed to restore MHC-I expression on the surface of solid tumors including breast cancer and melanoma cells to regain sensitivity to immunotherapy and suppress metastatic progression. We screened a natural compound library and identified macbecin II as a reagent that upregulates MHC-I expression and induces antigen-dependent cell death in pre-invasive and invasive breast cancer models. Furthermore, we employed active immunotherapy using engineered small extracellular vesicles from dendritic cells (DCs) as a tumor vaccine (IL2-ep13nsEV) in combination with macbecin II for personalized breast cancer treatment. We found that macbecin II induced MHC-I-dependent antigen presentation and that IL2-ep13nsEV synergized with macbecin II inducing cell death, reducing metastasis, and boosting immune cell infiltration. In addition, macbecin II potentiated the effects of anti-PD-1 immunotherapy in suppressing tumor growth and metastasis. Mechanistically, macbecin II upregulated MHC-I expression post-translationally by rescuing it from lysosomal degradation. Our findings revealed a strong efficacy of macbecin II in regulating MHC-I expression and following antigen-dependent cell death. Therefore, combining active immunotherapies and macbecin II represents an effective strategy to prevent growth and progression of solid tumors including breast cancer and melanoma.

Immune cell metabolic dysfunction in Parkinson's disease

Parkinson's disease (PD) is a multi-system disorder characterized histopathologically by degeneration of dopaminergic neurons in the substantia nigra pars compacta. While the etiology of PD remains multifactorial and complex, growing evidence suggests that cellular metabolic dysfunction is a critical driver of neuronal death. Defects in cellular metabolism related to energy production, oxidative stress, metabolic organelle health, and protein homeostasis have been reported in both neurons and immune cells in PD. We propose that these factors act synergistically in immune cells to drive aberrant inflammation in both the CNS and the periphery in PD, contributing to a hostile inflammatory environment which renders certain subsets of neurons vulnerable to degeneration. This review highlights the overlap between established neuronal metabolic deficits in PD with emerging findings in central and peripheral immune cells. By discussing the rapidly expanding literature on immunometabolic dysfunction in PD, we aim to draw attention to potential biomarkers and facilitate future development of immunomodulatory strategies to prevent or delay the progression of PD.

Activating autophagy to eliminate toxic protein aggregates with small molecules in neurodegenerative diseases

Neurodegenerative diseases (NDs), such as Alzheimer disease, Parkinson disease, Huntington disease, amyotrophic lateral sclerosis, and frontotemporal dementia, are well known to pose formidable challenges for their treatment due to their intricate pathogenesis and substantial variability among patients, including differences in environmental exposures and genetic predispositions. One of the defining characteristics of NDs is widely reported to be the buildup of misfolded proteins. For example, Alzheimer disease is marked by amyloid beta and hyperphosphorylated Tau aggregates, whereas Parkinson disease exhibits α-synuclein aggregates. Amyotrophic lateral sclerosis and frontotemporal dementia exhibit TAR DNA-binding protein 43, superoxide dismutase 1, and fused-in sarcoma protein aggregates, and Huntington disease involves mutant huntingtin and polyglutamine aggregates. These misfolded proteins are the key biomarkers of NDs and also serve as potential therapeutic targets, as they can be addressed through autophagy, a process that removes excess cellular inclusions to maintain homeostasis. Various forms of autophagy, including macroautophagy, chaperone-mediated autophagy, and microautophagy, hold a promise in eliminating toxic proteins implicated in NDs. In this review, we focus on elucidating the regulatory connections between autophagy and toxic proteins in NDs, summarizing the cause of the aggregates, exploring their impact on autophagy mechanisms, and discussing how autophagy can regulate toxic protein aggregation. Moreover, we underscore the activation of autophagy as a potential therapeutic strategy across different NDs and small molecules capable of activating autophagy pathways, such as rapamycin targeting the mTOR pathway to clear α-synuclein and Sertraline targeting the AMPK/mTOR/RPS6KB1 pathway to clear Tau, to further illustrate their potential in NDs' therapeutic intervention. Together, these findings would provide new insights into current research trends and propose small-molecule drugs targeting autophagy as promising potential strategies for the future ND therapies. SIGNIFICANCE STATEMENT: This review provides an in-depth overview of the potential of activating autophagy to eliminate toxic protein aggregates in the treatment of neurodegenerative diseases. It also elucidates the fascinating interrelationships between toxic proteins and the process of autophagy of "chasing and escaping" phenomenon. Moreover, the review further discusses the progress utilizing small molecules to activate autophagy to improve the efficacy of therapies for neurodegenerative diseases by removing toxic protein aggregates.

Lysosomal acidification impairment in astrocyte-mediated neuroinflammation

Astrocytes are a major cell type in the central nervous system (CNS) that play a key role in regulating homeostatic functions, responding to injuries, and maintaining the blood-brain barrier. Astrocytes also regulate neuronal functions and survival by modulating myelination and degradation of pathological toxic protein aggregates. Astrocytes have recently been proposed to possess both autophagic activity and active phagocytic capability which largely depend on sufficiently acidified lysosomes for complete degradation of cellular cargos. Defective lysosomal acidification in astrocytes impairs their autophagic and phagocytic functions, resulting in the accumulation of cellular debris, excessive myelin and lipids, and toxic protein aggregates, which ultimately contributes to the propagation of neuroinflammation and neurodegenerative pathology. Restoration of lysosomal acidification in impaired astrocytes represent new neuroprotective strategy and therapeutic direction. In this review, we summarize pathogenic factors, including neuroinflammatory signaling, metabolic stressors, myelin and lipid mediated toxicity, and toxic protein aggregates, that contribute to lysosomal acidification impairment and associated autophagic and phagocytic dysfunction in astrocytes. We discuss the role of lysosomal acidification dysfunction in astrocyte-mediated neuroinflammation primarily in the context of neurodegenerative diseases along with other brain injuries. We then highlight re-acidification of impaired lysosomes as a therapeutic strategy to restore autophagic and phagocytic functions as well as lysosomal degradative capacity in astrocytes. We conclude by providing future perspectives on the role of astrocytes as phagocytes and their crosstalk with other CNS cells to impart neurodegenerative or neuroprotective effects.

Neuronal constitutive endolysosomal perforations enable α-synuclein aggregation by internalized PFFs

Endocytosis, required for the uptake of receptors and their ligands, can also introduce pathological aggregates such as α-synuclein (α-syn) in Parkinson's Disease. We show here the unexpected presence of intrinsically perforated endolysosomes in neurons, suggesting involvement in the genesis of toxic α-syn aggregates induced by internalized preformed fibrils (PFFs). Aggregation of endogenous α-syn in late endosomes and lysosomes of human iPSC-derived neurons (iNs), seeded by internalized α-syn PFFs, caused the death of the iNs but not of the parental iPSCs and non-neuronal cells. Live-cell imaging of iNs showed constitutive perforations in ∼5% of their endolysosomes. These perforations, identified by 3D electron microscopy in iNs and CA1 pyramidal neurons and absent in non-neuronal cells, may facilitate cytosolic access of endogenous α-syn to PFFs in the lumen of endolysosomes, triggering aggregation. Inhibiting the PIKfyve phosphoinositol kinase reduced α-syn aggregation and associated iN death, even with ongoing PFF endolysosomal entry, suggesting that maintaining endolysosomal integrity might afford a therapeutic strategy to counteract synucleinopathies.

Nanomaterials-mediated lysosomal regulation: a robust protein-clearance approach for the treatment of Alzheimer's disease

Alzheimer's disease is a debilitating, progressive neurodegenerative disorder characterized by the progressive accumulation of abnormal proteins, including amyloid plaques and intracellular tau tangles, primarily within the brain. Lysosomes, crucial intracellular organelles responsible for protein degradation, play a key role in maintaining cellular homeostasis. Some studies have suggested a link between the dysregulation of the lysosomal system and pathogenesis of neurodegenerative diseases, including Alzheimer's disease. Restoring the normal physiological function of lysosomes hold the potential to reduce the pathological burden and improve the symptoms of Alzheimer's disease. Currently, the efficacy of drugs in treating Alzheimer's disease is limited, with major challenges in drug delivery efficiency and targeting. Recently, nanomaterials have gained widespread use in Alzheimer's disease drug research owing to their favorable physical and chemical properties. This review aims to provide a comprehensive overview of recent advances in using nanomaterials (polymeric nanomaterials, nanoemulsions, and carbon-based nanomaterials) to enhance lysosomal function in treating Alzheimer's disease. This review also explores new concepts and potential therapeutic strategies for Alzheimer's disease through the integration of nanomaterials and modulation of lysosomal function. In conclusion, this review emphasizes the potential of nanomaterials in modulating lysosomal function to improve the pathological features of Alzheimer's disease. The application of nanotechnology to the development of Alzheimer's disease drugs brings new ideas and approaches for future treatment of this disease.

Dysfunctional β-cell autophagy induces β-cell stress and enhances islet immunogenicity

Background

Type 1 Diabetes (T1D) is caused by a combination of genetic and environmental factors that trigger autoimmune-mediated destruction of pancreatic β-cells. Defects in β-cell stress response pathways such as autophagy may play an important role in activating and/or exacerbating the immune response in disease development. Previously, we discovered that β-cell autophagy is impaired prior to the onset of T1D, implicating this pathway in T1D pathogenesis.

Aims

To assess the role of autophagy in β-cell health and survival, and whether defects in autophagy render islets more immunogenic.

Methods

We knocked out the critical autophagy enzyme, ATG7, in the β-cells of mice (ATG7Δβ-cell) then monitored blood glucose, performed glucose tolerance tests, and evaluated bulk islet mRNA and protein. We also assessed MHC-I expression and presence of CD45+ immune cells in ATG7Δβ-cell islets and evaluated how impaired autophagy affects EndoC-βH1 HLA-I expression under basal and IFNα stimulated conditions. Lastly, we co-cultured ATG7Δβ-cell islet cells with diabetogenic BDC2.5 helper T cells and evaluated T cell activation.

Results

We found that all ATG7Δβ-cell mice developed diabetes between 11-15 weeks of age. Gene ontology analysis revealed a significant upregulation of pathways involved in inflammatory processes, response to ER stress, and the ER-associated degradation pathway. Interestingly, we also observed upregulation of proteins involved in MHC-I presentation, suggesting that defective β-cell autophagy may alter the immunopeptidome, or antigen repertoire, and enhance β-cell immune visibility. In support of this hypothesis, we observed increased MHC-I expression and CD45+ immune cells in ATG7Δβ-cell islets. We also demonstrate that HLA-I is upregulated in EndoC β-cells when autophagic degradation is inhibited. This effect was observed under both basal and IFNα stimulated conditions. Conversely, a stimulator of lysosome acidification/function, C381, decreased HLA-I expression. Lastly, we showed that in the presence of islet cells with defective autophagy, there is enhanced BDC2.5 T cell activation.

Conclusions

Our findings demonstrate that β-cell autophagy is critical to cell survival/function. Defective β-cell autophagy induces ER stress, alters pathways of antigen production, and enhances MHC-I/HLA-I presentation to surveilling immune cells. Overall, our results suggest that defects in autophagy make β-cells more susceptible to immune attack and destruction.

Multimodal Blood-Based Biomarker Panel Reveals Altered Lysosomal Ionic Content in Alzheimer's Disease

Lysosomal storage disorders (LSDs) and adult neurodegenerative disorders like Alzheimer's disease (AD) share various clinical and pathophysiological features. LSDs are characterized by impaired lysosomal activity caused by mutations in key proteins and enzymes. While lysosomal dysfunction is also linked to AD pathogenesis, its precise role in disease onset or progression remains unclear. Lysosomal ionic homeostasis is recognized as a key feature of many LSDs, but it has not been clinically linked with AD pathology. Thus, investigating whether this regulation is disrupted in AD is important, as it could lead to new therapeutic targets and biomarkers for this multifactorial disease. Here, using two-ion mapping (2-IM) technology, we quantitatively profiled lysosomal pH and Ca2+ in blood-derived monocytes from AD patients and age-matched controls and correlated lysosome ionicity with age and key markers of AD pathology, namely, amyloid deposits, tauopathy, neurodegeneration, and inflammation. Together, the data show that the ionic milieu of lysosomes is dysregulated in monocytes of AD patients and correlates with key plasma biomarkers of AD. Using a machine learning model based on the above parameters, we describe a proof-of-concept combinatorial biomarker platform that accurately distinguishes between patients with AD and control participants with an area under the curve of >96%. Our study introduces a convenient, noninvasive platform with the potential to diagnose Alzheimer's disease based on fluid, cellular, and molecular biomarkers. Further, these findings highlight the potential for investigating therapeutic mechanisms capable of restoring lysosome ionic homeostasis to ameliorate AD.

Proteostasis and lysosomal repair deficits in transdifferentiated neurons of Alzheimer's disease

Aging is the most prominent risk factor for Alzheimer's disease (AD). However, the cellular mechanisms linking neuronal proteostasis decline to the characteristic aberrant protein deposits in AD brains remain elusive. Here, we develop transdifferentiated neurons (tNeurons) from human dermal fibroblasts as a neuronal model that retains aging hallmarks and exhibits AD-linked vulnerabilities. Remarkably, AD tNeurons accumulate proteotoxic deposits, including phospho-Tau and Aβ, resembling those in AD patient and APP mouse brains. Quantitative tNeuron proteomics identify aging and AD-linked deficits in proteostasis and organelle homeostasis, most notably in endosome-lysosomal components. Lysosomal deficits in aged tNeurons, including constitutive lysosomal damage and ESCRT-mediated lysosomal repair defects, are exacerbated in AD tNeurons and linked to inflammatory cytokine secretion and cell death. Supporting lysosomal deficits' centrality in AD, compounds ameliorating lysosomal function reduce Aβ deposits and cytokine secretion. Thus, the tNeuron model system reveals impaired lysosomal homeostasis as an early event of aging and AD.

Development and Application of a BODIPY Carbazole Derivative Probe for Lysosomal Imaging: Insights into Lysosomal Dynamics and Dysfunction in Inflammation-Related Diseases

Inflammation is crucial in neurodegenerative and chronic diseases, including Alzheimer disease (AD) and liver fibrosis. To gain a deeper understanding of lysosomal functions in cellular physiology and disease mechanisms, we developed a carbazole-based BODIPY lysosomal probe, designated LysoI. This probe specifically targets lysosomes within 15 min and exhibits a Stokes shift of approximately 180 nm, enabling continuous incubation for up to 5 h without the need for washing steps. Interestingly, LysoI remained effective for long-term imaging, even up to 24 h poststaining. Despite varying pH values and conditions, such as autophagy, apoptosis, and inflammation, it consistently provides excellent lysosomal imaging. Notably, inflammation disrupts lysosomal morphology and motility, as evidenced by an increased size, a decrease in number, and a reduction in movement speed, as observed with LysoI. Furthermore, lysosomal rupture and impaired clearance may exacerbate inflammation and contribute to cellular apoptosis. These findings suggest that lysosomal dysfunction is closely associated with disease progression; therefore, protection and repair targeting lysosomes may offer promising strategies for treating inflammation-related diseases.

Ammonia-induced lysosomal and mitochondrial damage causes cell death of effector CD8+ T cells

Ammonia is thought to be a cytotoxin and its increase in the blood impairs cell function. However, whether and how this toxin triggers cell death under pathophysiological conditions remains unclear. Here we show that ammonia induces a distinct form of cell death in effector T cells. We found that rapidly proliferating T cells use glutaminolysis to release ammonia in the mitochondria, which is then translocated to and stored in the lysosomes. Excessive ammonia accumulation increases lysosomal pH and results in the termination of lysosomal ammonia storage and ammonia reflux into mitochondria, leading to mitochondrial damage and cell death, which is characterized by lysosomal alkalization, mitochondrial swelling and impaired autophagic flux. Inhibition of glutaminolysis or blocking lysosomal alkalization prevents ammonia-induced T cell death and improves T cell-based antitumour immunotherapy. These findings identify a distinct form of cell death that differs from previously known mechanisms.

TGF-β Signaling in Microglia: A Key Regulator of Development, Homeostasis and Reactivity

Microglia, the resident immune cells of the central nervous system (CNS), are crucial for normal brain development and function. They become reactive in response to brain injury and disease, a process known as microglial reactivity. This reactivity, along with microglial homeostasis, is tightly regulated by the local microenvironment and interactions with surrounding cells. The TGF-β signaling pathway plays an essential role in this regulation. Recent genetic studies employing microglia-specific manipulation of the TGF-β signaling pathway have shed light on its significance in microglial development, homeostasis and reactivity. This review provides an updated overview of how TGF-β signaling modulates microglial function and reactivity, contributing to our understanding of microglial biology in health and disease.

Small Molecule Drug C381 Attenuates Brain Vascular Damage Following Repetitive Mild Traumatic Injury

Traumatic brain injury (TBI) remains a significant public health concern, with no effective therapeutic interventions to ameliorate the enduring consequences. The prevailing understanding of TBI pathophysiology indicates a central role for vascular dysfunction. Transforming growth factor-β (TGF-β) is a multifunctional cytokine crucial for vascular development. Aberrant TGF-β signaling is implicated in vascular pathologies associated with various neurological conditions. We recently developed a novel small molecule drug, C381, a TGF-β activator with the ability to restore lysosomal function. Here we used a mouse model of repetitive mild TBI (mTBI) to examine whether C381 would attenuate vascular injury. We first employed RNA-seq analysis to investigate the gene expression patterns associated with mTBI and evaluated the therapeutic potential of C381 in mitigating these changes. Our results demonstrate distinct mTBI-related gene expression signatures, prominently implicating pathways related to vascular integrity and endothelial function. Notably, treatment with C381 reversed these mTBI-induced gene expression changes. Immunohistochemical analysis further corroborated these findings, revealing that C381 treatment attenuated vascular damage in mTBI-affected brain tissue. These findings strongly support the potential clinical usefulness of C381 as a novel therapeutic intervention for mTBI.

Azobenzene-based liposomes with nanomechanical action for cytosolic chemotherapeutic drug delivery

The stimuli-responsive nano-carriers are at the forefront of research in nanotechnology and materials science. These advanced systems are designed to alter their physicochemical properties upon exposure to specific stimuli, enabling controllable and targeted delivery of therapeutic agents. Nevertheless, limited endosomal escape reduces the drug bioavailability in clinical use. We herein report azobenzene (Azo)-based liposomes, prepared by co-assembling the photoisomerizable cationic Azo lipids and helper lipids, which achieve controllable doxorubicin (Dox) release and enhanced cytosolic transport upon light irradiation. Azo lipids undergo reversible isomerization between cis-isomers and trans-isomer when received UV and visible (Vis) light irradiation, causing liposomal membrane permeability changes for controlled drug release. Moreover, the nanomechanical action created by the isomerization of Azo lipids promotes the endosomal escape of the liposomes. DSPC-Azo liposomes, with minimal Dox leakage, showed significant tumor cell killing upon irradiation. For in vivo study, we co-encapsulated the upconverting nanoparticles (UCNPs), which can convert the near-infrared (NIR) light into UV/Vis emissions, facilitating Azo units activation. UCNP/Dox-loaded DSPC-Azo liposomes inhibited tumor growth under NIR irradiation in a 4T1 tumor-bearing mouse model.

The Art of Finding the Right Drug Target: Emerging Methods and Strategies

Drug targets are specific molecules in biological tissues and body fluids that interact with drugs. Drug target discovery is a key component of drug discovery and is essential for the development of new drugs in areas such as cancer therapy and precision medicine. Traditional in vitro or in vivo target discovery methods are time-consuming and labor-intensive, limiting the pace of drug discovery. With the development of modern discovery methods, the discovery and application of various emerging technologies have greatly improved the efficiency of drug discovery, shortened the cycle time, and reduced the cost. This review provides a comprehensive overview of various emerging drug target discovery strategies, including computer-assisted approaches, drug affinity response target stability, multiomics analysis, gene editing, and nonsense-mediated mRNA degradation, and discusses the effectiveness and limitations of the various approaches, as well as their application in real cases. Through the review of the aforementioned contents, a general overview of the development of novel drug targets and disease treatment strategies will be provided, and a theoretical basis will be provided for those who are engaged in pharmaceutical science research. SIGNIFICANCE STATEMENT: Target-based drug discovery has been the main approach to drug discovery in the pharmaceutical industry for the past three decades. Traditional drug target discovery methods based on in vivo or in vitro validation are time-consuming and costly, greatly limiting the development of new drugs. Therefore, the development and selection of new methods in the drug target discovery process is crucial.

Stigmasterol Activates the mTOR Signaling Pathway by Inhibiting ORP5 Ubiquitination to Promote Milk Synthesis in Bovine Mammary Epithelial Cells

Stigmasterol (ST), a phytosterol found in food, has various biological activities. However, the effect of ST on milk synthesis in dairy cows remains unclear. Therefore, bovine primary mammary epithelial cells (BMECs) were isolated, cultured, and treated with ST to determine the effect of ST on milk synthesis. The study revealed that 10 μM ST significantly increased milk synthesis in BMECs by activating the mammalian target of rapamycin (mTOR) signaling pathway. Further investigation revealed that this activation depends on the regulatory role of oxysterol binding protein 5 (ORP5). ST induces the translocation of ORP5 from the cytoplasm to the lysosome, interacts with the mTOR, recruits mTOR to target the lysosomal surface, and promotes the activation of the mTOR signaling pathway. Moreover, ST was found to increase ORP5 protein levels by inhibiting its degradation via the ubiquitin-proteasome pathway. Specifically, the E3 ubiquitin ligase membrane-associated cycle-CH-type finger 4 (MARCH4) promotes the ubiquitination and subsequent degradation of ORP5. ST mitigates the interaction between MARCH4 and ORP5, thereby enhancing the structural stability of ORP5 and reducing its ubiquitination. In summary, ST stabilizes ORP5 by inhibiting the interaction between MARCH4 and ORP5, thereby activating mTOR signaling pathway and enhancing milk synthesis.

Comprehensive Overview of Alzheimer's Disease: Etiological Insights and Degradation Strategies

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder and affects millions of individuals globally. AD is associated with cognitive decline and memory loss that worsens with aging. A statistical report using U.S. data on AD estimates that approximately 6.9 million individuals suffer from AD, a number projected to surge to 13.8 million by 2060. Thus, there is a critical imperative to pinpoint and address AD and its hallmark tau protein aggregation early to prevent and manage its debilitating effects. Amyloid-β and tau proteins are primarily associated with the formation of plaques and neurofibril tangles in the brain. Current research efforts focus on degrading amyloid-β and tau or inhibiting their synthesis, particularly targeting APP processing and tau hyperphosphorylation, aiming to develop effective clinical interventions. However, navigating this intricate landscape requires ongoing studies and clinical trials to develop treatments that truly make a difference. Genome-wide association studies (GWASs) across various cohorts identified 40 loci and over 300 genes associated with AD. Despite this wealth of genetic data, much remains to be understood about the functions of these genes and their role in the disease process, prompting continued investigation. By delving deeper into these genetic associations, novel targets such as kinases, proteases, cytokines, and degradation pathways, offer new directions for drug discovery and therapeutic intervention in AD. This review delves into the intricate biological pathways disrupted in AD and identifies how genetic variations within these pathways could serve as potential targets for drug discovery and treatment strategies. Through a comprehensive understanding of the molecular underpinnings of AD, researchers aim to pave the way for more effective therapies that can alleviate the burden of this devastating disease.

Human tNeurons reveal aging-linked proteostasis deficits driving Alzheimer's phenotypes

Aging is a prominent risk factor for Alzheimer's disease (AD), but the cellular mechanisms underlying neuronal phenotypes remain elusive. Both accumulation of amyloid plaques and neurofibrillary tangles in the brain1 and age-linked organelle deficits2-7 are proposed as causes of AD phenotypes but the relationship between these events is unclear. Here, we address this question using a transdifferentiated neuron (tNeuron) model directly from human dermal fibroblasts. Patient-derived tNeurons retain aging hallmarks and exhibit AD-linked deficits. Quantitative tNeuron proteomic analyses identify aging and AD-linked deficits in proteostasis and organelle homeostasis, particularly affecting endosome-lysosomal components. The proteostasis and lysosomal homeostasis deficits in aged tNeurons are exacerbated in sporadic and familial AD tNeurons, promoting constitutive lysosomal damage and defects in ESCRT-mediated repair. We find deficits in neuronal lysosomal homeostasis lead to inflammatory cytokine secretion, cell death and spontaneous development of Aß and phospho-Tau deposits. These proteotoxic inclusions co-localize with lysosomes and damage markers and resemble inclusions in brain tissue from AD patients and APP-transgenic mice. Supporting the centrality of lysosomal deficits driving AD phenotypes, lysosome-function enhancing compounds reduce AD-associated cytokine secretion and Aβ deposits. We conclude that proteostasis and organelle deficits are upstream initiating factors leading to neuronal aging and AD phenotypes.

Progranulin haploinsufficiency mediates cytoplasmic TDP-43 aggregation with lysosomal abnormalities in human microglia

BACKGROUND

Progranulin (PGRN) haploinsufficiency due to progranulin gene (GRN) variants can cause frontotemporal dementia (FTD) with aberrant TAR DNA-binding protein 43 (TDP-43) accumulation. Despite microglial burden with TDP-43-related pathophysiology, direct microglial TDP-43 pathology has not been clarified yet, only emphasized in neuronal pathology. Thus, the objective of this study was to investigate TDP-43 pathology in microglia of patients with PGRN haploinsufficiency.

METHODS

To design a human microglial cell model with PGRN haploinsufficiency, monocyte-derived microglia (iMGs) were generated from FTD-GRN patients carrying pathogenic or likely pathogenic variants (p.M1? and p.W147*) and three healthy controls.

RESULTS

iMGs from FTD-GRN patients with PGRN deficiency exhibited severe neuroinflammation phenotype and failure to maintain their homeostatic molecular signatures, along with impaired phagocytosis. In FTD-GRN patients-derived iMGs, significant cytoplasmic TDP-43 aggregation and accumulation of lipid droplets with profound lysosomal abnormalities were observed. These pathomechanisms were mediated by complement C1q activation and upregulation of pro-inflammatory cytokines.

CONCLUSIONS

Our study provides considerable cellular and molecular evidence that loss-of-function variants of GRN in human microglia can cause microglial dysfunction with abnormal TDP-43 aggregation induced by inflammatory milieu as well as the impaired lysosome. Elucidating the role of microglial TDP-43 pathology in intensifying neuroinflammation in individuals with FTD due to PGRN deficiency and examining consequential effects on microglial dysfunction might yield novel insights into the mechanisms underlying FTD and neurodegenerative disorders.

Constitutive Endolysosomal Perforation in Neurons allows Induction of α-Synuclein Aggregation by Internalized Pre-Formed Fibrils

The endocytic pathway is both an essential route of molecular uptake in cells and a potential entry point for pathology-inducing cargo. The cell-to-cell spread of cytotoxic aggregates, such as those of α-synuclein (α-syn) in Parkinson's Disease (PD), exemplifies this duality. Here we used a human iPSC-derived induced neuronal model (iNs) prone to death mediated by aggregation in late endosomes and lysosomes of endogenous α-syn, seeded by internalized pre-formed fibrils of α-syn (PFFs). This PFF-mediated death was not observed with parental iPSCs or other non-neuronal cells. Using live-cell optical microscopy to visualize the read out of biosensors reporting endo-lysosome wounding, we discovered that up to about 10% of late endosomes and lysosomes in iNs exhibited spontaneous constitutive perforations, regardless of the presence of internalized PFFs. This wounding, absent in parental iPSCs and non-neuronal cells, corresponded to partial damage by nanopores in the limiting membranes of a subset of endolysosomes directly observed by volumetric focused ion beam scanning electron microscopy (FIB-SEM) in iNs and in CA1 pyramidal neurons from mouse brain, and not found in iPSCs or in other non-neuronal cells in culture or in mouse liver and skin. We suggest that the compromised limiting membranes in iNs and neurons in general are the primary conduit for cytosolic α-syn to access PFFs entrapped within endo-lysosomal lumens, initiating PFF-mediated α-syn aggregation. Significantly, eradicating the intrinsic endolysosomal perforations in iNs by inhibiting the endosomal Phosphatidylinositol-3-Phosphate/Phosphatidylinositol 5-Kinase (PIKfyve kinase) using Apilimod or Vacuolin-1 markedly reduced PFF-induced α-syn aggregation, despite PFFs continuing to enter the endolysosomal compartment. Crucially, this intervention also diminished iN death associated with PFF incubation. Our results reveal the surprising presence of intrinsically perforated endo-lysosomes in neurons, underscoring their crucial early involvement in the genesis of toxic α-syn aggregates induced by internalized PFFs. This discovery offers a basis for employing PIKfyve kinase inhibition as a potential therapeutic strategy to counteract synucleinopathies.

Nanomechanical action opens endo-lysosomal compartments

Endo-lysosomal escape is a highly inefficient process, which is a bottleneck for intracellular delivery of biologics, including proteins and nucleic acids. Herein, we demonstrate the design of a lipid-based nanoscale molecular machine, which achieves efficient cytosolic transport of biologics by destabilizing endo-lysosomal compartments through nanomechanical action upon light irradiation. We fabricate lipid-based nanoscale molecular machines, which are designed to perform mechanical movement by consuming photons, by co-assembling azobenzene lipidoids with helper lipids. We show that lipid-based nanoscale molecular machines adhere onto the endo-lysosomal membrane after entering cells. We demonstrate that continuous rotation-inversion movement of Azo lipidoids triggered by ultraviolet/visible irradiation results in the destabilization of the membranes, thereby transporting cargoes, such as mRNAs and Cre proteins, to the cytoplasm. We find that the efficiency of cytosolic transport is improved about 2.1-fold, compared to conventional intracellular delivery systems. Finally, we show that lipid-based nanoscale molecular machines are competent for cytosolic transport of tumour antigens into dendritic cells, which induce robust antitumour activity in a melanoma mouse model.

Glycosphingolipids are linked to elevated neurotransmission and neurodegeneration in a Drosophila model of Niemann Pick type C

The lipid storage disease Niemann Pick type C (NPC) causes neurodegeneration owing primarily to loss of NPC1. Here, we employed a Drosophila model to test links between glycosphingolipids, neurotransmission and neurodegeneration. We found that Npc1a nulls had elevated neurotransmission at the glutamatergic neuromuscular junction (NMJ), which was phenocopied in brainiac (brn) mutants, impairing mannosyl glucosylceramide (MacCer) glycosylation. Npc1a; brn double mutants had the same elevated synaptic transmission, suggesting that Npc1a and brn function within the same pathway. Glucosylceramide (GlcCer) synthase inhibition with miglustat prevented elevated neurotransmission in Npc1a and brn mutants, further suggesting epistasis. Synaptic MacCer did not accumulate in the NPC model, but GlcCer levels were increased, suggesting that GlcCer is responsible for the elevated synaptic transmission. Null Npc1a mutants had heightened neurodegeneration, but no significant motor neuron or glial cell death, indicating that dying cells are interneurons and that elevated neurotransmission precedes neurodegeneration. Glycosphingolipid synthesis mutants also had greatly heightened neurodegeneration, with similar neurodegeneration in Npc1a; brn double mutants, again suggesting that Npc1a and brn function in the same pathway. These findings indicate causal links between glycosphingolipid-dependent neurotransmission and neurodegeneration in this NPC disease model.

Cogs in the autophagic machine-equipped to combat dementia-prone neurodegenerative diseases

Neurodegenerative diseases are often characterized by hydrophobic inclusion bodies, and it may be the case that the aggregate-prone proteins that comprise these inclusion bodies are in fact the cause of neurotoxicity. Indeed, the appearance of protein aggregates leads to a proteostatic imbalance that causes various interruptions in physiological cellular processes, including lysosomal and mitochondrial dysfunction, as well as break down in calcium homeostasis. Oftentimes the approach to counteract proteotoxicity is taken to merely upregulate autophagy, measured by an increase in autophagosomes, without a deeper assessment of contributors toward effective turnover through autophagy. There are various ways in which autophagy is regulated ranging from the mammalian target of rapamycin (mTOR) to acetylation status of proteins. Healthy mitochondria and the intracellular energetic charge they preserve are key for the acidification status of lysosomes and thus ensuring effective clearance of components through the autophagy pathway. Both mitochondria and lysosomes have been shown to bear functional protein complexes that aid in the regulation of autophagy. Indeed, it may be the case that minimizing the proteins associated with the respective neurodegenerative pathology may be of greater importance than addressing molecularly their resulting inclusion bodies. It is in this context that this review will dissect the autophagy signaling pathway, its control and the manner in which it is molecularly and functionally connected with the mitochondrial and lysosomal system, as well as provide a summary of the role of autophagy dysfunction in driving neurodegenerative disease as a means to better position the potential of rapamycin-mediated bioactivities to control autophagy favorably.

Lysosomal acidification dysfunction in microglia: an emerging pathogenic mechanism of neuroinflammation and neurodegeneration

Microglia are the resident innate immune cells in the brain with a major role in orchestrating immune responses. They also provide a frontline of host defense in the central nervous system (CNS) through their active phagocytic capability. Being a professional phagocyte, microglia participate in phagocytic and autophagic clearance of cellular waste and debris as well as toxic protein aggregates, which relies on optimal lysosomal acidification and function. Defective microglial lysosomal acidification leads to impaired phagocytic and autophagic functions which result in the perpetuation of neuroinflammation and progression of neurodegeneration. Reacidification of impaired lysosomes in microglia has been shown to reverse neurodegenerative pathology in Alzheimer's disease. In this review, we summarize key factors and mechanisms contributing to lysosomal acidification impairment and the associated phagocytic and autophagic dysfunction in microglia, and how these defects contribute to neuroinflammation and neurodegeneration. We further discuss techniques to monitor lysosomal pH and therapeutic agents that can reacidify impaired lysosomes in microglia under disease conditions. Finally, we propose future directions to investigate the role of microglial lysosomal acidification in lysosome-mitochondria crosstalk and in neuron-glia interaction for more comprehensive understanding of its broader CNS physiological and pathological implications.

Propranolol reduces the accumulation of cytotoxic aggregates in C9orf72-ALS/FTD in vitro models

Mutations in the C9orf72 gene are the most common cause of familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The pathogenetic mechanisms linked to this gene are a direct consequence of an aberrant intronic expansion of a GGGGCC hexanucleotide located between the 1a and 1b non-coding exons, which can be transcribed to form cytotoxic RNA foci or even translated into aggregation-prone dipeptide repeat proteins. Importantly, the abnormal length of these repeats affects also the expression levels of C9orf72 itself, which suggests haploinsufficiency as additional pathomechanism. Thus, it appears that both toxic gain of function and loss of function are distinct but still coexistent features contributing to the insurgence of the disease in case of C9orf72 mutations. In this study, we aimed at identifying a strategy to address both aspects of the C9orf72-related pathobiochemistry and provide proof-of-principle information for a better understanding of the mechanisms leading to neuronal loss. By using primary neurons overexpressing toxic poly(GA), the most abundant protein product of the GGGGCC repeats, we found that the antiarrhythmic drug propranolol could efficiently reduce the accumulation of aberrant aggregates and increase the survival of C9orf72-related cultures. Interestingly, the improved catabolism appeared to not depend on major degradative pathways such as autophagy and the proteasome. By analyzing the proteome of poly(GA)-expressing neurons after exposure to propranolol, we found that the drug increased lysosomal degradation through a mechanism directly involving C9orf72 protein, whose levels were increased after treatment. Further confirmation of the beneficial effect of the beta blocker on aggregates' accumulation and survival of hiPSC-derived C9orf72-mutant motoneurons strengthened the finding that addressing both facets of C9orf72 pathology might represent a valid strategy for the treatment of these ALS/FTD cases.

Defective lysosomal acidification: a new prognostic marker and therapeutic target for neurodegenerative diseases

Lysosomal acidification dysfunction has been implicated as a key driving factor in the pathogenesis of neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. Multiple genetic factors have been linked to lysosomal de-acidification through impairing the vacuolar-type ATPase and ion channels on the organelle membrane. Similar lysosomal abnormalities are also present in sporadic forms of neurodegeneration, although the underlying pathogenic mechanisms are unclear and remain to be investigated. Importantly, recent studies have revealed early occurrence of lysosomal acidification impairment before the onset of neurodegeneration and late-stage pathology. However, there is a lack of methods for organelle pH monitoring in vivo and a dearth of lysosome-acidifying therapeutic agents. Here, we summarize and present evidence for the notion of defective lysosomal acidification as an early indicator of neurodegeneration and urge the critical need for technological advancement in developing tools for lysosomal pH monitoring and detection both in vivo and for clinical applications. We further discuss current preclinical pharmacological agents that modulate lysosomal acidification, including small molecules and nanomedicine, and their potential clinical translation into lysosome-targeting therapies. Both timely detection of lysosomal dysfunction and development of therapeutics that restore lysosomal function represent paradigm shifts in targeting neurodegenerative diseases.

Trigonochinene E promotes lysosomal biogenesis and enhances autophagy via TFEB/TFE3 in human degenerative NP cells against oxidative stress

BACKGROUND

Macroautophagy (henceforth autophagy) is the major form of autophagy, which delivers intracellular cargo to lysosomes for degradation. Considerable research has revealed that the impairment of lysosomal biogenesis and autophagic flux exacerbates the development of autophagy-related diseases. Therefore, reparative medicines restoring lysosomal biogenesis and autophagic flux in cells may have therapeutic potential against the increasing prevalence of these diseases.

PURPOSE

The aim of the present study was thus to explore the effect of trigonochinene E (TE), an aromatic tetranorditerpene isolated from Trigonostemon flavidus, on lysosomal biogenesis and autophagy and to elucidate the potential underlying mechanism.

METHODS

Four human cell lines, HepG2, nucleus pulposus (NP), HeLa and HEK293 cells were applied in this study. The cytotoxicity of TE was evaluated by MTT assay. Lysosomal biogenesis and autophagic flux induced by 40 μM TE were analyzed using gene transfer techniques, western blotting, real-time PCR and confocal microscopy. Immunofluorescence, immunoblotting and pharmacological inhibitors/activators were applied to determine the changes in the protein expression levels in mTOR, PKC, PERK, and IRE1α signaling pathways.

RESULTS

Our results showed that TE promotes lysosomal biogenesis and autophagic flux by activating the transcription factors of lysosomes, transcription factor EB (TFEB) and transcription factor E3 (TFE3). Mechanistically, TE induces TFEB and TFE3 nuclear translocation through an mTOR/PKC/ROS-independent and endoplasmic reticulum (ER) stress-mediated pathway. The PERK and IRE1α branches of ER stress are crucial for TE-induced autophagy and lysosomal biogenesis. Whereas TE activated PERK, which mediated calcineurin dephosphorylation of TFEB/TFE3, IRE1α was activated and led to inactivation of STAT3, which further enhanced autophagy and lysosomal biogenesis. Functionally, knockdown of TFEB or TFE3 impairs TE-induced lysosomal biogenesis and autophagic flux. Furthermore, TE-induced autophagy protects NP cells from oxidative stress to ameliorate intervertebral disc degeneration (IVDD).

CONCLUSIONS

Here, our study showed that TE can induce TFEB/TFE3-dependent lysosomal biogenesis and autophagy via the PERK-calcineurin axis and IRE1α-STAT3 axis. Unlike other agents regulating lysosomal biogenesis and autophagy, TE showed limited cytotoxicity, thereby providing a new direction for therapeutic opportunities to use TE to treat diseases with impaired autophagy-lysosomal pathways, including IVDD.

Lysosomal functions of progranulin and implications for treatment of frontotemporal dementia

Loss-of-function heterozygous mutations in GRN, the gene encoding progranulin (PGRN), were identified in patients with frontotemporal lobar degeneration (FTLD) almost two decades ago and are generally linked to reduced PGRN protein expression levels. Although initial characterization of PGRN function primarily focused on its role in extracellular signaling as a secreted protein, more recent studies revealed critical roles of PGRN in regulating lysosome function, including proteolysis and lipid degradation, consistent with its lysosomal localization. Emerging from these studies is the notion that PGRN regulates glucocerebrosidase activity via direct chaperone activities and via interaction with prosaposin (i.e., a key regulator of lysosomal sphingolipid-metabolizing enzymes), as well as with the anionic phospholipid bis(monoacylglycero)phosphate. This emerging lysosomal biology of PGRN identified novel and promising opportunities in therapeutic discovery as well as biomarker development.

Role of Ubiquitin-Proteasome and Autophagy-Lysosome Pathways in α-Synuclein Aggregate Clearance

Synuclein aggregation in neuronal cells is the primary underlying cause of synucleinopathies. Changes in gene expression patterns, structural modifications, and altered interactions with other cellular proteins often trigger aggregation of α-synuclein, which accumulates as oligomers or fibrils in Lewy bodies. Although fibrillar forms of α-synuclein are primarily considered pathological, recent studies have revealed that even the intermediate states of aggregates are neurotoxic, complicating the development of therapeutic interventions. Autophagy and ubiquitin-proteasome pathways play a significant role in maintaining the soluble levels of α-synuclein inside cells; however, the heterogeneous nature of the aggregates presents a significant bottleneck to its degradation by these cellular pathways. With studies focused on identifying the proteins that modulate synuclein aggregation and clearance, detailed mechanistic insights are emerging about the individual and synergistic effects of these degradation pathways in regulating soluble α-synuclein levels. In this article, we discuss the impact of α-synuclein aggregation on autophagy-lysosome and ubiquitin-proteasome pathways and the therapeutic strategies that target various aspects of synuclein aggregation or degradation via these pathways. Additionally, we also highlight the natural and synthetic compounds that have shown promise in alleviating the cellular damage caused due to synuclein aggregation.

TGF-β as a Key Modulator of Astrocyte Reactivity: Disease Relevance and Therapeutic Implications

Astrocytes are essential for normal brain development and functioning. They respond to brain injury and disease through a process referred to as reactive astrogliosis, where the reactivity is highly heterogenous and context-dependent. Reactive astrocytes are active contributors to brain pathology and can exert beneficial, detrimental, or mixed effects following brain insults. Transforming growth factor-β (TGF-β) has been identified as one of the key factors regulating astrocyte reactivity. The genetic and pharmacological manipulation of the TGF-β signaling pathway in animal models of central nervous system (CNS) injury and disease alters pathological and functional outcomes. This review aims to provide recent understanding regarding astrocyte reactivity and TGF-β signaling in brain injury, aging, and neurodegeneration. Further, it explores how TGF-β signaling modulates astrocyte reactivity and function in the context of CNS disease and injury.