Golgi fragmentation in Alzheimer's disease

Involvement of the choroid plexus in Alzheimer's disease pathophysiology: findings from mouse and human proteomic studies

BACKGROUND

Structural and functional changes of the choroid plexus (ChP) have been reported in Alzheimer's disease (AD). Nonetheless, the role of the ChP in the pathogenesis of AD remains largely unknown. We aim to unravel the relation between ChP functioning and core AD pathogenesis using a unique proteomic approach in mice and humans.

METHODS

We used an APP knock-in mouse model, APPNL-G-F, exhibiting amyloid pathology, to study the association between AD brain pathology and protein changes in mouse ChP tissue and CSF using liquid chromatography mass spectrometry. Mouse proteomes were investigated at the age of 7 weeks (n = 5) and 40 weeks (n = 5). Results were compared with previously published human AD CSF proteomic data (n = 496) to identify key proteins and pathways associated with ChP changes in AD.

RESULTS

ChP tissue proteome was dysregulated in APPNL-G-F mice relative to wild-type mice at both 7 and 40 weeks. At both ages, ChP tissue proteomic changes were associated with epithelial cells, mitochondria, protein modification, extracellular matrix and lipids. Nonetheless, some ChP tissue proteomic changes were different across the disease trajectory; pathways related to lysosomal function, endocytosis, protein formation, actin and complement were uniquely dysregulated at 7 weeks, while pathways associated with nervous system, immune system, protein degradation and vascular system were uniquely dysregulated at 40 weeks. CSF proteomics in both mice and humans showed similar ChP-related dysregulated pathways.

CONCLUSIONS

Together, our findings support the hypothesis of ChP dysfunction in AD. These ChP changes were related to amyloid pathology. Therefore, the ChP could become a novel promising therapeutic target for AD.

GolpHCat (TMEM87A), a unique voltage-dependent cation channel in Golgi apparatus, contributes to Golgi-pH maintenance and hippocampus-dependent memory

Impaired ion channels regulating Golgi pH lead to structural alterations in the Golgi apparatus, such as fragmentation, which is found, along with cognitive impairment, in Alzheimer's disease. However, the causal relationship between altered Golgi structure and cognitive impairment remains elusive due to the lack of understanding of ion channels in the Golgi apparatus of brain cells. Here, we identify that a transmembrane protein TMEM87A, renamed Golgi-pH-regulating cation channel (GolpHCat), expressed in astrocytes and neurons that contributes to hippocampus-dependent memory. We find that GolpHCat displays unique voltage-dependent currents, which is potently inhibited by gluconate. Additionally, we gain structural insights into the ion conduction through GolpHCat at the molecular level by determining three high-resolution cryogenic-electron microscopy structures of human GolpHCat. GolpHCat-knockout mice show fragmented Golgi morphology and altered protein glycosylation and functions in the hippocampus, leading to impaired spatial memory. These findings suggest a molecular target for Golgi-related diseases and cognitive impairment.

General toxicity and screening of reproductive and developmental toxicity following bioaccumulation of oral-dosed perfluorooctanoic acid: Loss of the Golgi apparatus

Despite its widespread use as a stabilizer across various industries over the past several decades, the health effects of chronic exposure to PFOA are still unclear. We administered PFOA by oral gavage (0, 12.5, 50, and 200 μg/day/mouse, eight groups) to male and female mice for six months. Body weight gain decreased with dose accompanied by increased liver weight, and PFOA altered liver damage-related-blood biochemical indicators and induced pathological lesions, including hepatocellular hypertrophy, cholangiofibrosis, and centrilobular hepatocellular vacuolation. Loss of the Golgi apparatus, formation of lamellar body-like structures, and lipid accumulation were observed in the liver of PFOA-treated mice. We also cohabited five pairs of male and female mice for the last ten days of administration, dosed PFOA to dam up to 28 days after birth, and investigated effects on reproduction and development. The survival rate of pups and the sex ratio of surviving mice decreased significantly at the highest dose. PFOA tissue concentration increased with the dose in the parent mice's liver and the pups' blood and brain. Taken together, we suggest that PFOA primarily affects the liver and reproduction system and that disturbance in lipid metabolism and Golgi's structural stability may be involved in PFOA-induced toxicity.

Long-term ketogenic diet causes hyperlipidemia, liver dysfunction, and glucose intolerance from impaired insulin trafficking and secretion in mice

A ketogenic diet (KD) is a very low-carbohydrate, very high-fat diet proposed to treat obesity and type 2 diabetes. While KD grows in popularity, its effects on metabolic health are understudied. Here we show that, in male and female mice, while KD protects against weight gain and induces weight loss, over long-term, mice develop hyperlipidemia, hepatic steatosis, and severe glucose intolerance. Unlike high fat diet-fed mice, KD mice are not insulin resistant and have low levels of insulin. Hyperglycemic clamp and ex vivo GSIS revealed cell-autonomous and whole-body impairments in insulin secretion. Major ER/Golgi stress and disrupted ER-Golgi protein trafficking was indicated by transcriptomic profiling of KD islets and confirmed by electron micrographs showing a dilated Golgi network likely responsible for impaired insulin granule trafficking and secretion. Overall, our results suggest long-term KD leads to multiple aberrations of metabolic parameters that caution its systematic use as a health promoting dietary intervention.

Upregulation of the secretory pathway Ca2+/Mn2+-ATPase isoform 1 in LPS-stimulated microglia and its involvement in Mn2+-induced Golgi fragmentation

Microglia play an important protective role in the healthy nervous tissue, being able to react to a variety of stimuli that induce different intracellular cascades for specific tasks. Ca2+ signaling can modulate these pathways, and we recently reported that microglial functions depend on the endoplasmic reticulum as a Ca2+ store, which involves the Ca2+ transporter SERCA2b. Here, we investigated whether microglial functions may also rely on the Golgi, another intracellular Ca2+ store that depends on the secretory pathway Ca2+/Mn2+-transport ATPase isoform 1 (SPCA1). We found upregulation of SPCA1 upon lipopolysaccharide stimulation of microglia BV2 cells and primary microglia, where alterations of the Golgi ribbon were also observed. Silencing and overexpression experiments revealed that SPCA1 affects cell morphology, Golgi apparatus integrity, and phagocytic functions. Since SPCA1 is also an efficient Mn2+ transporter and considering that Mn2+ excess causes manganism in the brain, we addressed the role of microglial SPCA1 in Mn2+ toxicity. Our results revealed a clear effect of Mn2+ excess on the viability and morphology of microglia. Subcellular analysis showed Golgi fragmentation and subsequent alteration of SPCA1 distribution from early stages of toxicity. Removal of Mn2+ by washing improved the culture viability, although it did not effectively reverse Golgi fragmentation. Interestingly, pretreatment with curcumin maintained microglia cultures viable, prevented Mn2+-induced Golgi fragmentation, and preserved SPCA Ca2+-dependent activity, suggesting curcumin as a potential protective agent against Mn2+-induced Golgi alterations in microglia.

Early signs of neurodegenerative diseases: Possible mechanisms and targets for Golgi stress

The Golgi apparatus plays a crucial role in mediating the modification, transport, and sorting of intracellular proteins and lipids. The morphological changes occurring in the Golgi apparatus are exceptionally important for maintaining its function. When exposed to external pressure or environmental stimulation, the Golgi apparatus undergoes adaptive changes in both structure and function, which are known as Golgi stress. Although certain signal pathway responses or post-translational modifications have been observed following Golgi stress, further research is needed to comprehensively summarize and understand the related mechanisms. Currently, there is evidence linking Golgi stress to neurodegenerative diseases; however, the role of Golgi stress in the progression of neurodegenerative diseases such as Alzheimer's disease remains largely unexplored. This review focuses on the structural and functional alterations of the Golgi apparatus during stress, elucidating potential mechanisms underlying the involvement of Golgi stress in regulating immunity, autophagy, and metabolic processes. Additionally, it highlights the pivotal role of Golgi stress as an early signaling event implicated in the pathogenesis and progression of neurodegenerative diseases. Furthermore, this study summarizes prospective targets that can be therapeutically exploited to mitigate neurodegenerative diseases by targeting Golgi stress. These findings provide a theoretical foundation for identifying novel breakthroughs in preventing and treating neurodegenerative diseases.

Dynamic movement of the Golgi unit and its glycosylation enzyme zones

Knowledge on the distribution and dynamics of glycosylation enzymes in the Golgi is essential for better understanding this modification. Here, using a combination of CRISPR/Cas9 knockin technology and super-resolution microscopy, we show that the Golgi complex is assembled by a number of small 'Golgi units' that have 1-3 μm in diameter. Each Golgi unit contains small domains of glycosylation enzymes which we call 'zones'. The zones of N- and O-glycosylation enzymes are colocalised. However, they are less colocalised with the zones of a glycosaminoglycan synthesizing enzyme. Golgi units change shapes dynamically and the zones of glycosylation enzymes rapidly move near the rim of the unit. Photobleaching analysis indicates that a glycosaminoglycan synthesizing enzyme moves between units. Depletion of giantin dissociates units and prevents the movement of glycosaminoglycan synthesizing enzymes, which leads to insufficient glycosaminoglycan synthesis. Thus, we show the structure-function relationship of the Golgi and its implications in human pathogenesis.

New approaches for challenging therapeutic targets

Despite successes with new drug approvals over the past two decades through conventional drug development approaches, many human diseases remain intractable to current therapeutic interventions. Possible barriers may be that the complexity of the target, and disease biology, are impervious to such conventional drug development approaches. The US National Institutes of Health hosted a workshop with the goal of identifying challenges and opportunities with alternative modalities for developing treatments across diseases associated with historically undruggable targets. This report highlights key issues discussed during the workshop that, if addressed, could expand the pool of therapeutic approaches for treating various diseases.

Cellular Organelle-Related Transcriptomic Profile Abnormalities in Neuronopathic Types of Mucopolysaccharidosis: A Comparison with Other Neurodegenerative Diseases

Mucopolysaccharidoses (MPS) are a group of diseases caused by mutations in genes encoding lysosomal enzymes that catalyze reactions of glycosaminoglycan (GAG) degradation. As a result, GAGs accumulate in lysosomes, impairing the proper functioning of entire cells and tissues. There are 14 types/subtypes of MPS, which are differentiated by the kind(s) of accumulated GAG(s) and the type of a non-functional lysosomal enzyme. Some of these types (severe forms of MPS types I and II, MPS III, and MPS VII) are characterized by extensive central nervous system disorders. The aim of this work was to identify, using transcriptomic methods, organelle-related genes whose expression levels are changed in neuronopathic types of MPS compared to healthy cells while remaining unchanged in non-neuronopathic types of MPS. The study was conducted with fibroblast lines derived from patients with neuronopathic and non-neuronopathic types of MPS and control (healthy) fibroblasts. Transcriptomic analysis has identified genes related to cellular organelles whose expression is altered. Then, using fluorescence and electron microscopy, we assessed the morphology of selected structures. Our analyses indicated that the genes whose expression is affected in neuronopathic MPS are often associated with the structures or functions of the cell nucleus, endoplasmic reticulum, or Golgi apparatus. Electron microscopic studies confirmed disruptions in the structures of these organelles. Special attention was paid to up-regulated genes, such as PDIA3 and MFGE8, and down-regulated genes, such as ARL6IP6, ABHD5, PDE4DIP, YIPF5, and CLDN11. Of particular interest is also the GM130 (GOLGA2) gene, which encodes golgin A2, which revealed an increased expression in neuronopathic MPS types. We propose to consider the levels of mRNAs of these genes as candidates for biomarkers of neurodegeneration in MPS. These genes may also become potential targets for therapies under development for neurological disorders associated with MPS and candidates for markers of the effectiveness of these therapies. Although fibroblasts rather than nerve cells were used in this study, it is worth noting that potential genetic markers characteristic solely of neurons would be impractical in testing patients, contrary to somatic cells that can be relatively easily obtained from assessed persons.

Quantification of golgi dispersal and classification using machine learning models

The Golgi body is a critical organelle in eukaryotic cells responsible for processing and modifying proteins and lipids. Under certain conditions, such as stress, disease, or ageing, the Golgi structure alters. Therefore, understanding the mechanisms that regulate Golgi dispersion has significant research contributions to identifying disease. However, there is a lack of tools to quantify the Golgi dispersion datasets. In this paper, we aim to automate the process of quantification of Golgi dispersion and use extracted features to classify dispersed Golgi images from undispersed Golgi images using machine learning models. First, we collected confocal microscopy images of transiently transfected HeLa cells expressing Galactose-1-phosphate uridylyltransferase (GALT)- green fluorescent protein (GFP) to quantify Golgi dispersal and classification. For the quantification, we introduced automated image processing and segmentation by applying mean and Gaussian filters. Then we used Otsu thresholding on preprocessed images and watershed segmentation to refine the segmentation of dispersed Golgi particles. In the case of classification, we extracted features from the Golgi dispersal images and classified them into empty vector (EV) versus CARP1 ring mutant (CARP1 RM) and empty vector (EV) versus CARP1 wildtype (CARP1 WT) classes. Our approach used machine-learning models, including logistic regression, decision tree, random forest, Naive Bayes, k-Nearest Neighbor (KNN), and gradient boosting for dispersed Golgi image classification. The experiment results show that our quantification technique on Golgi dispersal images reached 65% classification accuracy when the system uses a gradient boosting classifier for EV vs. CARP1 WT classification. Furthermore, our approach achieved 65% classification accuracy using a random forest classifier for EV vs. CARP1 RM classification.

Ultrastructural Abnormalities in Induced Pluripotent Stem Cell-Derived Neural Stem Cells and Neurons of Two Cohen Syndrome Patients

Cohen syndrome is an autosomal recessive disorder caused by VPS13B (COH1) gene mutations. This syndrome is significantly underdiagnosed and is characterized by intellectual disability, microcephaly, autistic symptoms, hypotension, myopia, retinal dystrophy, neutropenia, and obesity. VPS13B regulates intracellular membrane transport and supports the Golgi apparatus structure, which is critical for neuron formation. We generated induced pluripotent stem cells from two patients with pronounced manifestations of Cohen syndrome and differentiated them into neural stem cells and neurons. Using transmission electron microscopy, we documented multiple new ultrastructural changes associated with Cohen syndrome in the neuronal cells. We discovered considerable disturbances in the structure of some organelles: Golgi apparatus fragmentation and swelling, endoplasmic reticulum structural reorganization, mitochondrial defects, and the accumulation of large autophagosomes with undigested contents. These abnormalities underline the ultrastructural similarity of Cohen syndrome to many neurodegenerative diseases. The cell models that we developed based on patient-specific induced pluripotent stem cells can serve to uncover not only neurodegenerative processes, but the causes of intellectual disability in general.

Unraveling the Multifaceted Role of the Golgi Apparatus: Insights into Neuronal Plasticity, Development, Neurogenesis, Alzheimer's Disease, and SARS-CoV-2 Interactions

This article critically evaluates the multifunctional role of the Golgi apparatus within neurological paradigms. We succinctly highlight its influence on neuronal plasticity, development, and the vital trafficking and sorting mechanisms for proteins and lipids. The discourse further navigates to its regulatory prominence in neurogenesis and its implications in Alzheimer's Disease pathogenesis. The emerging nexus between the Golgi apparatus and SARS-CoV-2 underscores its potential in viral replication processes. This consolidation accentuates the Golgi apparatus's centrality in neurobiology and its intersections with both neurodegenerative and viral pathologies. In essence, understanding the Golgi's multifaceted functions harbors profound implications for future therapeutic innovations in neurological and viral afflictions.

GOLPH3 promotes endotoxemia-induced liver and kidney injury through Golgi stress-mediated apoptosis and inflammatory response

Sepsis is a serious clinical condition characterized by a systemic inflammatory response, a leading cause of acute liver and kidney injury, and is associated with a high morbidity and mortality. Understanding the molecular mechanisms underlying the acute liver and kidney injury is crucial for developing an effective therapy. Golgi apparatus plays important roles and has various substrates mediating cellular stress responses. Golgi phosphoprotein 3 (GOLPH3), linking Golgi membranes to the cytoskeleton, has been identified as an important oncogenic regulator; however, its role in endotoxemia-induced acute liver and kidney injury remains elusive. Here, we found that upregulation of GOLPH3 was associated with endotoxemia-induced acute liver and kidney injury. Lipopolysaccharide (LPS) treatment increased Golgi stress and fragmentation, and associated pro-inflammatory mediator (Tnfα, IL-6, and IL-1β) production in vivo and in vitro. Interestingly, the downregulation of GOLPH3 significantly decreased LPS-induced Golgi stress and pro-inflammatory mediators (Tnfα, IL-6, Mcp1, and Nos2), and reversed apoptotic cell deaths in LPS-treated hepatocytes and renal tubular cells. GOLPH3 knockdown also reduced inflammatory response in LPS-treated macrophages. The AKT/NF-kB signaling pathway was suppressed in GOLPH3 knockdown, which may be associated with a reduction of inflammatory response and apoptosis and the recovery of Golgi morphology and function. Taken together, GOLPH3 plays a crucial role in the development and progression of acute liver and kidney injury by promoting Golgi stress and increasing inflammatory response and apoptosis, suggesting GOLPH3 as a potential therapeutic target for endotoxemia-induced tissue injury.

Ubiquitin-mediated degradation at the Golgi apparatus

The Golgi apparatus is an essential organelle of the secretory pathway in eukaryotic cells. It processes secretory and transmembrane proteins and orchestrates their transport to other endomembrane compartments or the plasma membrane. The Golgi apparatus thereby shapes the cell surface, controlling cell polarity, cell-cell communication, and immune signaling. The cytosolic face of the Golgi hosts and regulates signaling cascades, impacting most notably the DNA damage response and mitosis. These essential functions strongly depend on Golgi protein homeostasis and Golgi integrity. Golgi fragmentation and consequent malfunction is associated with neurodegenerative diseases and certain cancer types. Recent studies provide first insight into the critical role of ubiquitin signaling in maintaining Golgi integrity and in Golgi protein quality control. Similar to well described pathways at the endoplasmic reticulum, ubiquitin-dependent degradation of non-native proteins prevents the accumulation of toxic protein aggregates at the Golgi. Moreover, ubiquitination regulates Golgi structural rearrangements in response to cellular stress. Advances in elucidating ubiquitination and degradation events at the Golgi are starting to paint a picture of the molecular machinery underlying Golgi (protein) homeostasis.

The metal ion hypothesis of Alzheimer's disease and the anti-neuroinflammatory effect of metal chelators

Alzheimer's disease (AD), characterized by the β-amyloid protein (Aβ) deposition and tau hyperphosphorylation, is the most common dementia with uncertain etiology. The clinical trials of Aβ monoclonal antibody drugs have almost failed, giving rise to great attention on the other etiologic hypothesis regarding AD such as metal ions dysmetabolism and chronic neuroinflammation. Mounting evidence revealed that the metal ions (iron, copper, and zinc) were dysregulated in the susceptible brain regions of AD patients, which was highly associated with Aβ deposition, tau hyperphosphorylation, neuronal loss, as well as neuroinflammation. Further studies uncovered that iron, copper and zinc could not only enhance the production of Aβ but also directly bind to Aβ and tau to promote their aggregations. In addition, the accumulation of iron and copper could respectively promote ferroptosis and cuproptosis. Therefore, the metal ion chelators were recognized as promising agents for treating AD. This review comprehensively summarized the effects of metal ions on the Aβ dynamics and tau phosphorylation in the progression of AD. Furthermore, taking chronic neuroinflammation contributes to the progression of AD, we also provided a summary of the mechanisms concerning metal ions on neuroinflammation and highlighted the metal ion chelators may be potential agents to alleviate neuroinflammation under the condition of AD. Nevertheless, more investigations regarding metal ions on neuroinflammation should be taken into practice, and the effects of metal ion chelators on neuroinflammation should gain more attention. Running title: Metal chelators against neuroinflammation.

Golgi fragmentation - One of the earliest organelle phenotypes in Alzheimer's disease neurons

Alzheimer's disease (AD) is the most common cause of dementia, with no current cure. Consequently, alternative approaches focusing on early pathological events in specific neuronal populations, besides targeting the well-studied amyloid beta (Aβ) accumulations and Tau tangles, are needed. In this study, we have investigated disease phenotypes specific to glutamatergic forebrain neurons and mapped the timeline of their occurrence, by implementing familial and sporadic human induced pluripotent stem cell models as well as the 5xFAD mouse model. We recapitulated characteristic late AD phenotypes, such as increased Aβ secretion and Tau hyperphosphorylation, as well as previously well documented mitochondrial and synaptic deficits. Intriguingly, we identified Golgi fragmentation as one of the earliest AD phenotypes, indicating potential impairments in protein processing and post-translational modifications. Computational analysis of RNA sequencing data revealed differentially expressed genes involved in glycosylation and glycan patterns, whilst total glycan profiling revealed minor glycosylation differences. This indicates general robustness of glycosylation besides the observed fragmented morphology. Importantly, we identified that genetic variants in Sortilin-related receptor 1 (SORL1) associated with AD could aggravate the Golgi fragmentation and subsequent glycosylation changes. In summary, we identified Golgi fragmentation as one of the earliest disease phenotypes in AD neurons in various in vivo and in vitro complementary disease models, which can be exacerbated via additional risk variants in SORL1.

Analysis of Golgi Morphology Using Immunofluorescence and CellProfiler Software

The architecture of the Golgi apparatus in mammalian cells changes dynamically in response to internal and external cues and may be permanently altered in disease states. Here, we present a method to quantify changes in Golgi morphology using immunofluorescence and confocal microscopy followed by CellProfiler software analysis. This method will assist researchers in evaluating alterations in the Golgi complex morphology of cultured cells under a variety of different experimental conditions.

Analysis of Golgi Protein Acetylation Using In Vitro Assays and Parallel Reaction Monitoring Mass Spectrometry

Acetylation is one of the most abundant post-translational protein modifications that regulates all cellular compartments ranging from chromatin to cytoskeleton and Golgi. The dynamic acetylation of the Golgi stacking protein GRASP55 was shown to regulate Golgi reassembly after mitosis. Here we provide a detailed protocol for the analysis of Golgi acetylation including in vitro assays to detect protein acetylation and mass spectrometry analysis to identify specific acetylation sites and their relative abundance.

New insights into the role of the Golgi apparatus in the pathogenesis and therapeutics of human diseases

The Golgi apparatus is an essential cellular organelle that mediates homeostatic functions, including vesicle trafficking and the post-translational modification of macromolecules. Its unique stacked structure and dynamic functions are tightly regulated, and several Golgi proteins play key roles in the functioning of unconventional protein secretory pathways triggered by cellular stress responses. Recently, an increasing number of studies have implicated defects in Golgi functioning in human diseases such as cancer, neurodegenerative, and immunological disorders. Understanding the extraordinary characteristics of Golgi proteins is important for elucidating its associated intracellular signaling mechanisms and has important ramifications for human health. Therefore, analyzing the mechanisms by which the Golgi participates in disease pathogenesis may be useful for developing novel therapeutic strategies. This review articulates the structural features and abnormalities of the Golgi apparatus reported in various diseases and the suspected mechanisms underlying the Golgi-associated pathologies. Furthermore, we review the potential therapeutic strategies based on Golgi function.

Adaptor-Specific Antibody Fragment Inhibitors for the Intracellular Modulation of p97 (VCP) Protein-Protein Interactions

Protein-protein interactions (PPIs) form complex networks to drive cellular signaling and cellular functions. Precise modulation of a target PPI helps explain the role of the PPI in cellular events and possesses therapeutic potential. For example, valosin-containing protein (VCP/p97) is a hub protein that interacts with more than 30 adaptor proteins involved in various cellular functions. However, the role of each p97 PPI during the relevant cellular event is underexplored. The development of small-molecule PPI modulators remains challenging due to a lack of grooves and pockets in the relatively large PPI interface and the fact that a common binding groove in p97 binds to multiple adaptors. Here, we report an antibody fragment-based modulator for the PPI between p97 and its adaptor protein NSFL1C (p47). We engineered these antibody modulators by phage display against the p97-interacting domain of p47 and minimizing binding to other p97 adaptors. The selected antibody fragment modulators specifically disrupt the intracellular p97/p47 interaction. The potential of this antibody platform to develop PPI inhibitors in therapeutic applications was demonstrated through the inhibition of Golgi reassembly, which requires the p97/p47 interaction. This study presents a unique approach to modulate specific intracellular PPIs using engineered antibody fragments, demonstrating a method to dissect the function of a PPI within a convoluted PPI network.

A Method for Bridging Population-Specific Genotypes to Detect Gene Modules Associated with Alzheimer's Disease

BACKGROUND

Genome-wide association studies have successfully identified variants associated with multiple conditions. However, generalizing discoveries across diverse populations remains challenging due to large variations in genetic composition. Methods that perform gene expression imputation have attempted to address the transferability of gene discoveries across populations, but with limited success.

METHODS

Here, we introduce a pipeline that combines gene expression imputation with gene module discovery, including a dense gene module search and a gene set variation analysis, to address the transferability issue. Our method feeds association probabilities of imputed gene expression with a selected phenotype into tissue-specific gene-module discovery over protein interaction networks to create higher-level gene modules.

RESULTS

We demonstrate our method's utility in three case-control studies of Alzheimer's disease (AD) for three different race/ethnic populations (Whites, African descent and Hispanics). We discovered 182 AD-associated genes from gene modules shared between these populations, highlighting new gene modules associated with AD.

CONCLUSIONS

Our innovative framework has the potential to identify robust discoveries across populations based on gene modules, as demonstrated in AD.

Golgi stress induces upregulation of the ER-Golgi SNARE Syntaxin-5, altered βAPP processing, and Caspase-3-dependent apoptosis in NG108-15 cells

The involvement of secretory pathways and Golgi dysfunction in neuronal cells during Alzheimer's disease progression is poorly understood. Our previous overexpression and knockdown studies revealed that the intracellular protein level of Syntaxin-5, an endoplasmic reticulum-Golgi soluble N-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE), modulates beta-amyloid precursor protein processing in neuronal cells. We recently showed that changes in endogenous Syntaxin-5 protein expression occur under stress induction. Syntaxin-5 was upregulated by endoplasmic reticulum stress but was degraded by Caspase-3 during apoptosis in neuronal cells. In addition, we showed that sustained endoplasmic reticulum stress promotes Caspase-3-dependent apoptosis during the later phase of the endoplasmic reticulum stress response in NG108-15 cells. In this study, to elucidate the consequences of secretory pathway dysfunction in beta-amyloid precursor protein processing that lead to neuronal cell death, we examined the effect of various stresses on endoplasmic reticulum-Golgi SNARE expression and beta-amyloid precursor protein processing. By using compounds to disrupt Golgi function, we show that Golgi stress promotes upregulation of the endoplasmic reticulum-Golgi SNARE Syntaxin-5, and prolonged stress causes Caspase-3-dependent apoptosis. Golgi stress induced intracellular beta-amyloid precursor protein accumulation and a concomitant decrease in total amyloid-beta production. We also examined the protective effect of the chemical chaperone 4-phenylbutylate on changes in amyloid-beta production and the activation of Caspase-3 induced by endoplasmic reticulum and Golgi stress. The compound alleviated the increase in the amyloid-beta 1-42/amyloid-beta 1-40 ratio induced by endoplasmic reticulum and Golgi stress. Furthermore, 4-phenylbutylate could rescue Caspase-3-dependent apoptosis induced by prolonged organelle stress. These results suggest that organelle stress originating from the endoplasmic reticulum and Golgi has a substantial impact on the amyloidogenic processing of beta-amyloid precursor protein and Caspase-3-dependent apoptosis, leading to neuronal cell death.

The Golgi complex: An organelle that determines urothelial cell biology in health and disease

The Golgi complex undergoes considerable structural remodeling during differentiation of urothelial cells in vivo and in vitro. It is known that in a healthy bladder the differentiation from the basal to the superficial cell layer leads to the formation of the tightest barrier in our body, i.e., the blood–urine barrier. In this process, urothelial cells start expressing tight junctional proteins, apical membrane lipids, surface glycans, and integral membrane proteins, the uroplakins (UPs). The latter are the most abundant membrane proteins in the apical plasma membrane of differentiated superficial urothelial cells (UCs) and, in addition to well-developed tight junctions, contribute to the permeability barrier by their structural organization and by hindering endocytosis from the apical plasma membrane. By studying the transport of UPs, we were able to demonstrate their differentiation-dependent effect on the Golgi architecture. Although fragmentation of the Golgi complex is known to be associated with mitosis and apoptosis, we found that the process of Golgi fragmentation is required for delivery of certain specific urothelial differentiation cargoes to the plasma membrane as well as for cell–cell communication. In this review, we will discuss the currently known contribution of the Golgi complex to the formation of the blood–urine barrier in normal UCs and how it may be involved in the loss of the blood–urine barrier in cancer. Some open questions related to the Golgi complex in the urothelium will be highlighted.

PRRSV Infection Induces Gasdermin D-Driven Pyroptosis of Porcine Alveolar Macrophages through NLRP3 Inflammasome Activation

For more than 3 decades, mounting evidence has associated porcine reproductive and respiratory syndrome virus (PRRSV) infection with late-term abortions and stillbirths in sows and respiratory disease in piglets, causing enormous economic losses to the global swine industry. However, to date, the underlying mechanisms of PRRSV-triggered cell death have not been well clarified, especially in the pulmonary inflammatory injury characterized by the massive release of pro-inflammatory factors. Here, we demonstrated that PRRSV infection triggered gasdermin D-mediated host pyroptosis in vitro and in vivo. Mechanistically, PRRSV infection triggered disassembly of the trans-Golgi network (TGN); the dispersed TGN then acted as a scaffold for NLRP3 activation through phosphatidylinositol-4-phosphate. In addition, PRRSV replication-transcription complex (RTC) formation stimulated TGN dispersion and pyroptotic cell death. Furthermore, our results indicated that TMEM41B, an endoplasmic reticulum (ER)-resident host protein, functioned as a crucial host factor in the formation of PRRSV RTC, which is surrounded by the intermediate filament network. Collectively, these findings uncover new insights into clinical features as previously unrecognized mechanisms for PRRSV-induced pathological effects, which may be conducive to providing treatment options for PRRSV-associated diseases and may be conserved during infection by other highly pathogenic viruses. IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the pathogens responsible for major economic losses in the global swine industry. Characterizing the detailed process by which PRRSV induces cell death pathways will help us better understand viral pathogenesis and provide implications for therapeutic intervention against PRRSV. Here, we showed that PRRSV infection induces GSDMD-driven host pyroptosis and IL-1β secretion through NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome activation in vitro and in vivo. Furthermore, the molecular mechanisms of PRRSV-induced NLRP3 inflammasome activation and pyroptosis are elucidated here. The dispersed trans-Golgi network (TGN) induced by PRRSV serves as a scaffold for NLRP3 aggregation into multiple puncta via phosphatidylinositol 4-phosphate (PtdIns4P). Moreover, the formation of PRRSV replication-transcription complex is essential for TGN dispersion and host pyroptosis. This research advances our understanding of the PRRSV-mediated inflammatory response and cell death pathways, paving the way for the development of effective treatments for PRRSV diseases.

The key roles of organelles and ferroptosis in Alzheimer's disease

Alzheimer's disease (AD), an age-related neurodegenerative disease, is a striking global health problem. Ferroptosis is a newly discovered form of cell death characterized by iron-dependent lipid peroxidation products and the accumulation of lethal reactive oxygen species. Strict regulation of iron metabolism is essential to ensure neuronal homeostasis. Excess and deficiency of iron are both associated with neurodegeneration. Studies have shown that oxidative stress caused by cerebral iron metabolism disorders in the body is involved in the process of AD, ferroptosis may play an important role in the pathogenesis of AD, and regulating ferroptosis is expected to be a new direction for the treatment of AD. Various organelles are closely related to ferroptosis: mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosome are involved in the regulation of ferroptosis from the aspects of iron metabolism and redox imbalance. In this review, the relationship between AD and the dysfunction of organelles (including mitochondria, endoplasmic reticulum, lysosome, and Golgi apparatus) and the role of organelles in ferroptosis of AD were reviewed to provide insights for understanding the relationship between organelles and ferroptosis in AD and the treatment of AD.

Coenzyme Q10 effects in neurological diseases

Coenzyme Q10 (CoQ10), a lipophilic substituted benzoquinone, is present in animal and plant cells. It is endogenously synthetized in every cell and involved in a variety of cellular processes. CoQ10 is an obligatory component of the respiratory chain in inner mitochondrial membrane. In addition, the presence of CoQ10 in all cellular membranes and in blood. It is the only endogenous lipid antioxidant. Moreover, it is an essential factor for uncoupling protein and controls the permeability transition pore in mitochondria. It also participates in extramitochondrial electron transport and controls membrane physicochemical properties. CoQ10 effects on gene expression might affect the overall metabolism. Primary changes in the energetic and antioxidant functions can explain its remedial effects. CoQ10 supplementation is safe and well-tolerated, even at high doses. CoQ10 does not cause any serious adverse effects in humans or experimental animals. New preparations of CoQ10 that are less hydrophobic and structural derivatives, like idebenone and MitoQ, are being developed to increase absorption and tissue distribution. The review aims to summarize clinical and experimental effects of CoQ10 supplementations in some neurological diseases such as migraine, Parkinson´s disease, Huntington´s disease, Alzheimer´s disease, amyotrophic lateral sclerosis, Friedreich´s ataxia or multiple sclerosis. Cardiovascular hypertension was included because of its central mechanisms controlling blood pressure in the brainstem rostral ventrolateral medulla and hypothalamic paraventricular nucleus. In conclusion, it seems reasonable to recommend CoQ10 as adjunct to conventional therapy in some cases. However, sometimes CoQ10 supplementations are more efficient in animal models of diseases than in human patients (e.g. Parkinson´s disease) or rather vague (e.g. Friedreich´s ataxia or amyotrophic lateral sclerosis).

The Role of GM130 in Nervous System Diseases

Golgi matrix protein 130 (GM130) is a Golgi-shaping protein located on the cis surface of the Golgi apparatus (GA). It is one of the most studied Golgin proteins so far. Its biological functions are involved in many aspects of life processes, including mitosis, autophagy, apoptosis, cell polarity, and directed migration at the cellular level, as well as intracellular lipid and protein transport, microtubule formation and assembly, lysosome function maintenance, and glycosylation modification. Mutation inactivation or loss of expression of GM130 has been detected in patients with different diseases. GM130 plays an important role in the development of the nervous system, but the studies on it are limited. This article reviewed the current research progress of GM130 in nervous system diseases. It summarized the physiological functions of GM130 in the occurrence and development of Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), microcephaly (MCPH), sepsis associated encephalopathy (SAE), and Ataxia, aiming to provide ideas for the further study of GM130 in nervous system disease detection and treatment.

Soft materials as biological and artificial membranes

The past few decades have seen emerging growth in the field of soft materials for synthetic biology. This review focuses on soft materials involved in biological and artificial membranes. The biological membranes discussed here are mainly those involved in the structure and function of cells and organelles. As building blocks in medicine, non-native membranes including nanocarriers (NCs), especially liposomes and DQAsomes, and polymeric membranes for scaffolds are constructed from amphiphilic combinations of lipids, proteins, and carbohydrates. Artificial membranes can be prepared using synthetic, soft materials and molecules and then incorporated into structures through self-organization to form micelles or niosomes. The modification of artificial membranes can be realized using traditional chemical methods such as click reactions to target the delivery of NCs and control the release of therapeutics. The biomembrane, a lamellar structure inlaid with ion channels, receptors, lipid rafts, enzymes, and other functional units, separates cells and organelles from the environment. An active domain inserted into the membrane and organelles for energy conversion and cellular communication can target disease by changing the membrane's composition, structure, and fluidity and affecting the on/off status of the membrane gates. The biological membrane targets analyzing pathological mechanisms and curing complex diseases, which inspires us to create NCs with artificial membranes.

The GTPase Arf1 Is a Determinant of Yeast Vps13 Localization to the Golgi Apparatus

VPS13 proteins are evolutionarily conserved. Mutations in the four human genes (VPS13A-D) encoding VPS13A-D proteins are linked to developmental or neurodegenerative diseases. The relationship between the specific localization of individual VPS13 proteins, their molecular functions, and the pathology of these diseases is unknown. Here we used a yeast model to establish the determinants of Vps13's interaction with the membranes of Golgi apparatus. We analyzed the different phenotypes of the arf1-3 arf2Δ vps13∆ strain, with reduced activity of the Arf1 GTPase, the master regulator of Golgi function and entirely devoid of Vps13. Our analysis led us to propose that Vps13 and Arf1 proteins cooperate at the Golgi apparatus. We showed that Vps13 binds to the Arf1 GTPase through its C-terminal Pleckstrin homology (PH)-like domain. This domain also interacts with phosphoinositol 4,5-bisphosphate as it was bound to liposomes enriched with this lipid. The homologous domain of VPS13A exhibited the same behavior. Furthermore, a fusion of the PH-like domain of Vps13 to green fluorescent protein was localized to Golgi structures in an Arf1-dependent manner. These results suggest that the PH-like domains and Arf1 are determinants of the localization of VPS13 proteins to the Golgi apparatus in yeast and humans.

Signaling Overlap between the Golgi Stress Response and Cysteine Metabolism in Huntington's Disease

Huntington's disease (HD) is caused by expansion of polyglutamine repeats in the protein huntingtin, which affects the corpus striatum of the brain. The polyglutamine repeats in mutant huntingtin cause its aggregation and elicit toxicity by affecting several cellular processes, which include dysregulated organellar stress responses. The Golgi apparatus not only plays key roles in the transport, processing, and targeting of proteins, but also functions as a sensor of stress, signaling through the Golgi stress response. Unlike the endoplasmic reticulum (ER) stress response, the Golgi stress response is relatively unexplored. This review focuses on the molecular mechanisms underlying the Golgi stress response and its intersection with cysteine metabolism in HD.

Alzheimer's Disease: A Molecular View of β-Amyloid Induced Morbific Events

Amyloid-β (Aβ) is a dynamic peptide of Alzheimer’s disease (AD) which accelerates the disease progression. At the cell membrane and cell compartments, the amyloid precursor protein (APP) undergoes amyloidogenic cleavage by β- and γ-secretases and engenders the Aβ. In addition, externally produced Aβ gets inside the cells by receptors mediated internalization. An elevated amount of Aβ yields spontaneous aggregation which causes organelles impairment. Aβ stimulates the hyperphosphorylation of tau protein via acceleration by several kinases. Aβ travels to the mitochondria and interacts with its functional complexes, which impairs the mitochondrial function leading to the activation of apoptotic signaling cascade. Aβ disrupts the Ca²⁺ and protein homeostasis of the endoplasmic reticulum (ER) and Golgi complex (GC) that promotes the organelle stress and inhibits its stress recovery machinery such as unfolded protein response (UPR) and ER-associated degradation (ERAD). At lysosome, Aβ precedes autophagy dysfunction upon interacting with autophagy molecules. Interestingly, Aβ act as a transcription regulator as well as inhibits telomerase activity. Both Aβ and p-tau interaction with neuronal and glial receptors elevate the inflammatory molecules and persuade inflammation. Here, we have expounded the Aβ mediated events in the cells and its cosmopolitan role on neurodegeneration, and the current clinical status of anti-amyloid therapy.

Amyloid β production along the neuronal secretory pathway: Dangerous liaisons in the Golgi?

β-amyloid peptides (Aβ) are generated in intracellular compartments of neurons and secreted to form cytotoxic fibrils and plaques. Dysfunctional membrane trafficking contributes to aberrant Aβ production and Alzheimer's disease. Endosomes represent one of the major sites for Aβ production and recently the Golgi has re-emerged also as a major location for amyloid precursor protein (APP) processing and Aβ production. Based on recent findings, here we propose that APP processing in the Golgi is finely tuned by segregating newly-synthesised APP and the β-secretase BACE1 within the Golgi and into distinct trans-Golgi network transport pathways. We hypothesise that there are multiple mechanisms responsible for segregating APP and BACE1 during transit through the Golgi, and that perturbation in Golgi morphology associated with Alzheimer's disease, and or changes in cholesterol metabolism associated with Alzheimer's disease risk factors, may lead to a loss of partitioning and enhanced Aβ production.

PsGRASP, a Golgi Reassembly Stacking Protein in Phytophthora sojae, Is Required for Mycelial Growth, Stress Responses, and Plant Infection

Golgi reassembly stacking proteins (GRASPs) play important roles in Golgi structure formation, ER stress response, and unconventional secretion in eukaryotic cells. However, GRASP functions in oomycetes haven’t been adequately characterized. Here, we report the identification and functional analysis of PsGRASP, a GRASP-encoding gene from the soybean-infecting oomycete Phytophthora sojae. Transcriptional profiling showed that PsGRASP expression is up-regulated at the infection stages. PsGRASP knockout mutants were created using the CRISPR/Cas9 system. These mutants exhibited impaired vegetative growth, zoospore release and virulence. PsGRASP was involved ER stress responses and altered laccase activity. Our work suggests that PsGRASP is crucial for P. sojae development and pathogenicity.

The glyco-redox interplay: Principles and consequences on the role of reactive oxygen species during protein glycosylation

Reactive oxygen species (ROS) carry out prime physiological roles as intracellular signaling agents, yet pathologically high concentrations of ROS cause irreversible damage to biomolecules, alter cellular programs and contribute to various diseases. While decades of intensive research have identified redox-related patterns and signaling pathways, very few addressed how the glycosylation machinery senses and responds to oxidative stress. A common trait among ROS and glycans residing on glycoconjugates is that they are both highly dynamic, as they are quickly fine-tuned in response to stressors such as inflammation, cancer and infectious diseases. On this account, the delicate balance of the redox potential, which is tightly regulated by dozens of enzymes including NOXs, and the mitochondrial electron transport chain as well as the fluidity of glycan biosynthesis resulting from the cooperation of glycosyltransferases, glycosidases, and nucleotide sugar transporters, is paramount to cell survival. Here, we review the broad spectrum of the interplay between redox changes and glycosylation with respect to their principle consequences on human physiology.

Reimagining dots and dashes: Visualizing structure and function of organelles for high-content imaging analysis

Organelles are responsible for biochemical and cellular processes that sustain life and their dysfunction causes diseases from cancer to neurodegeneration. While researchers are continuing to appreciate new roles of organelles in disease, the rapid development of specifically targeted fluorescent probes that report on the structure and function of organelles will be critical to accelerate drug discovery. Here, we highlight four organelles that collectively exemplify the progression of phenotypic discovery, starting with mitochondria, where many functional probes have been described, then continuing with lysosomes and Golgi and concluding with nascently described membraneless organelles. We introduce emerging probe designs to explore organelle-specific morphology and dynamics and highlight recent case studies using high-content analysis to stimulate further development of probes and approaches for organellar high-throughput screening.

The role of the Golgi apparatus in disease (Review)

The Golgi apparatus is known to underpin many important cellular homeostatic functions, including trafficking, sorting and modifications of proteins or lipids. These functions are dysregulated in neurodegenerative diseases, cancer, infectious diseases and cardiovascular diseases, and the number of disease-related genes associated with Golgi apparatus is on the increase. Recently, many studies have suggested that the mutations in the genes encoding Golgi resident proteins can trigger the occurrence of diseases. By summarizing the pathogenesis of these genetic diseases, it was found that most of these diseases have defects in membrane trafficking. Such defects typically result in mislocalization of proteins, impaired glycosylation of proteins, and the accumulation of undegraded proteins. In the present review, we aim to understand the patterns of mutations in the genes encoding Golgi resident proteins and decipher the interplay between Golgi resident proteins and membrane trafficking pathway in cells. Furthermore, the detection of Golgi resident protein in human serum samples has the potential to be used as a diagnostic tool for diseases, and its central role in membrane trafficking pathways provides possible targets for disease therapy. Thus, we also introduced the clinical value of Golgi apparatus in the present review.

Implications of Glycosylation in Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia, affecting millions of people worldwide, and no cure is currently available. The major pathological hallmarks of AD are considered to be amyloid beta plaques and neurofibrillary tangles, generated by respectively APP processing and Tau phosphorylation. Recent evidence imply that glycosylation of these proteins, and a number of other AD-related molecules is altered in AD, suggesting a potential implication of this process in disease pathology. In this review we summarize the understanding of glycans in AD pathogenesis, and discuss how glycobiology can contribute to early diagnosis and treatment of AD, serving as potential biomarkers and therapeutic targets. Furthermore, we look into the potential link between the emerging topic neuroinflammation and glycosylation, combining two interesting, and until recent years, understudied topics in the scope of AD. Lastly, we discuss how new model platforms such as induced pluripotent stem cells can be exploited and contribute to a better understanding of a rather unexplored area in AD.

Parkinson's Disease Master Regulators on Substantia Nigra and Frontal Cortex and Their Use for Drug Repositioning

Parkinson's disease (PD) is among the most prevalent neurodegenerative diseases. Available evidences support the view of PD as a complex disease, being the outcome of interactions between genetic and environmental factors. In face of diagnosis and therapy challenges, and the elusive PD etiology, the use of alternative methodological approaches for the elucidation of the disease pathophysiological mechanisms and proposal of novel potential therapeutic interventions has become increasingly necessary. In the present study, we first reconstructed the transcriptional regulatory networks (TN), centered on transcription factors (TF), of two brain regions affected in PD, the substantia nigra pars compacta (SNc) and the frontal cortex (FCtx). Then, we used case-control studies data from these regions to identify TFs working as master regulators (MR) of the disease, based on region-specific TNs. Twenty-nine regulatory units enriched with differentially expressed genes were identified for the SNc, and twenty for the FCtx, all of which were considered MR candidates for PD. Three consensus MR candidates were found for SNc and FCtx, namely ATF2, SLC30A9, and ZFP69B. In order to search for novel potential therapeutic interventions, we used these consensus MR candidate signatures as input to the Connectivity Map (CMap), a computational drug repositioning webtool. This analysis resulted in the identification of four drugs that reverse the expression pattern of all three MR consensus simultaneously, benperidol, harmaline, tubocurarine chloride, and vorinostat, thus suggested as novel potential PD therapeutic interventions.

Hydrogen peroxide induces Arl1 degradation and impairs Golgi-mediated trafficking

Reactive oxygen species (ROS)-induced oxidative stress has been associated with diseases such as amyotrophic lateral sclerosis, stroke, and cancer. While the effect of ROS on mitochondria and endoplasmic reticulum (ER) has been well documented, its consequence on the Golgi apparatus is less well understood. In this study, we characterized the Golgi structure and function in HeLa cells after exposure to hydrogen peroxide (H2O2), a reagent commonly used to introduce ROS to cells. Treatment of cells with 1 mM H2O2 for 10 min resulted in the degradation of Arl1 and dissociation of GRIP domain-containing proteins Golgin-97 and Golgin-245 from the trans-Golgi. This effect could be rescued by treatment of cells with a ROS scavenger N-acetyl cysteine or protease inhibitors. Structurally, H2O2 treatment reduced the number of cisternal membranes per Golgi stack, suggesting a loss of trans-Golgi cisternae. Functionally, H2O2 treatment inhibited both anterograde and retrograde protein transport, consistent with the loss of membrane tethers on the trans-Golgi cisternae. This study revealed membrane tethers at the trans-Golgi as novel specific targets of ROS in cells.

Dual Eigen-modules of Cis-Element Regulation Profiles and Selection of Cognition-Language Eigen-direction along Evolution in Hominidae

To understand the genomic basis accounting for the phenotypic differences between human and apes, we compare the matrices consisting of the cis-element frequencies in the proximal regulatory regions of their genomes. One such frequency matrix is represented by a robust singular value decomposition. For each singular value, the negative and positive ends of the sorted motif eigenvector correspond to the dual ends of the sorted gene eigenvector, respectively, comprising a dual eigen-module defined by cis-regulatory element frequencies (CREF). The CREF eigen-modules at levels 1, 2, 3, and 6 are highly conserved across humans, chimpanzees, and orangutans. The key biological processes embedded in the top three CREF eigen-modules are reproduction versus embryogenesis, fetal maturation versus immune system, and stress responses versus mitosis. Although the divergence at the nucleotide level between the chimpanzee and human genome was small, their cis-element frequency matrices crossed a singularity point, at which the fourth and fifth singular values were identical. The CREF eigen-modules corresponding to the fourth and fifth singular values were reorganized along the evolution from apes to human. Interestingly, the fourth sorted gene eigenvector encodes the phenotypes unique to human such as long-term memory, language development, and social behavior. The number of motifs present on Alu elements increases substantially at the fourth level. The motif analysis together with the cases of human-specific Alu insertions suggests that mutations related to Alu elements play a critical role in the evolution of the human-phenotypic gene eigenvector.

Selective fragmentation of the trans-Golgi apparatus by Rickettsia rickettsii

Fragmentation of the Golgi apparatus is observed during a number of physiological processes including mitosis and apoptosis, but also occurs in pathological states such as neurodegenerative diseases and some infectious diseases. Here we show that highly virulent strains of Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever, induce selective fragmentation of the trans-Golgi network (TGN) soon after infection of host cells by secretion of the effector protein Rickettsial Ankyrin Repeat Protein 2 (RARP2). Remarkably, this fragmentation is pronounced for the trans-Golgi network but the cis-Golgi remains largely intact and appropriately localized. Thus R. rickettsii targets specifically the TGN and not the entire Golgi apparatus. Dispersal of the TGN is mediated by the secreted effector protein RARP2, a recently identified type IV secreted effector that is a member of the clan CD cysteine proteases. Site-directed mutagenesis of a predicted cysteine protease active site in RARP2 prevents TGN disruption. General protein transport to the cell surface is severely impacted in cells infected with virulent strains of R. rickettsii. These findings suggest a novel manipulation of cellular organization by an obligate intracellular bacterium to determine interactions with the host cell.

Physiological and Pathological Roles of Cdk5: Potential Directions for Therapeutic Targeting in Neurodegenerative Disease

Cyclin-dependent kinase 5 (Cdk5) is a proline-directed serine (ser)/threonine (Thr) kinase that has been demonstrated to be one of the most functionally diverse kinases within neurons. Cdk5 is regulated via binding with its neuron-specific regulatory subunits, p35 or p39. Cdk5-p35 activity is critical for a variety of developmental and cellular processes in the brain, including neuron migration, memory formation, microtubule regulation, and cell cycle suppression. Aberrant activation of Cdk5 via the truncated p35 byproduct, p25, is implicated in the pathogenesis of several neurodegenerative diseases. The present review highlights the importance of Cdk5 activity and function in the brain and demonstrates how deregulation of Cdk5 can contribute to the development of neurodegenerative conditions such as Alzheimer's and Parkinson's disease. Additionally, we cover past drug discovery attempts at inhibiting Cdk5-p25 activity and discuss which types of targeting strategies may prove to be the most successful moving forward.

Cytosolic Ca2+ Modulates Golgi Structure Through PKCα-Mediated GRASP55 Phosphorylation

It has been well documented that the ER responds to cellular stresses through the unfolded protein response (UPR), but it is unknown how the Golgi responds to similar stresses. In this study, we treated HeLa cells with ER stress inducers, thapsigargin (TG), tunicamycin (Tm), and dithiothreitol (DTT), and found that only TG treatment resulted in Golgi fragmentation. TG induced Golgi fragmentation at a low dose and short time when UPR was undetectable, indicating that Golgi fragmentation occurs independently of ER stress. Further experiments demonstrated that TG induces Golgi fragmentation through elevating intracellular Ca²⁺ and protein kinase Cα (PKCα) activity, which phosphorylates the Golgi stacking protein GRASP55. Significantly, activation of PKCα with other activating or inflammatory agents, including phorbol 12-myristate 13-acetate and histamine, modulates Golgi structure in a similar fashion. Hence, our study revealed a novel mechanism through which increased cytosolic Ca²⁺ modulates Golgi structure and function.

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Thapsigargin (TG) treatment leads to Golgi fragmentation independent of ER stress

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TG induces Golgi fragmentation through elevated cytosolic Ca²⁺

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TG-induced cytosolic Ca²⁺ spikes activate PKCα that phosphorylates GRASP55

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Histamine modulates the Golgi structure and function by a similar mechanism

Association Between Atg5-independent Alternative Autophagy and Neurodegenerative Diseases

Autophagy is a cellular process that degrades intracellular components, including misfolded proteins and damaged organelles. Many neurodegenerative diseases are considered to progress via the accumulation of misfolded proteins and damaged organelles; therefore, autophagy functions in regulating disease severity. There are at least two types of autophagy (canonical autophagy and alternative autophagy), and canonical autophagy has been applied to therapeutic strategies against various types of neurodegenerative diseases. In contrast, the role of alternative autophagy has not yet been clarified, but it is speculated to be involved in the pathogenesis of various neurodegenerative diseases, including Alzheimer's disease.

The prospective role of mesenchymal stem cells exosomes on circumvallate taste buds in induced Alzheimer's disease of ovariectomized albino rats: (Light and transmission electron microscopic study)

OBJECTIVE

To elucidate the effect of Alzheimer's disease on the structure of circumvallate papilla taste buds and the possible role of exosomes on the taste buds in Alzheimer's disease.

DESIGN

Forty two ovariectomized female adult albino rats were utilized and divided into: Group I: received vehicle. Group II: received aluminum chloride to induce Alzheimer's disease. Group III: after the induction of Alzheimer's disease, each rat received single dose of exosomes then left for 4 weeks. The circumvallate papillae were prepared for examination by light and transmission electron microscope.

STATISTICAL ANALYSIS

histomorphometric data were statistically analyzed.

RESULTS

Histological examination of circumvallate papilla in Group I showed normal histological features. Group II revealed distorted features. Group III illustrated nearly normal histological features of circumvallate. Silver impregnation results showed apparently great number of heavily impregnated glossopharyngeal nerve fibers in both Groups I & III but markedly decreased in Group II. Synaptophysin-immunoreactivity was strong in Group I, mild in Group II and moderate in Group III. The ultra-structural examination of taste bud cells revealed normal features in Group I, distorted features in Group II and almost normal features in Group III. Statistically highest mean of Synaptophysin-immunoreactivity area% was for Group I, followed by Group III, and the least value was for Group II.

CONCLUSIONS

Alzheimer's disease has degenerative effects. Bone marrow mesenchymal stem cell (BM-MSC)-derived exosomes have the ability to improve the destructive changes induced by Alzheimer's disease.

A New Look at the Functional Organization of the Golgi Ribbon

A characteristic feature of vertebrate cells is a Golgi ribbon consisting of multiple cisternal stacks connected into a single-copy organelle next to the centrosome. Despite numerous studies, the mechanisms that link the stacks together and the functional significance of ribbon formation remain poorly understood. Nevertheless, these questions are of considerable interest, since there is increasing evidence that Golgi fragmentation – the unlinking of the stacks in the ribbon – is intimately connected not only to normal physiological processes, such as cell division and migration, but also to pathological states, including neurodegeneration and cancer. Challenging a commonly held view that ribbon architecture involves the formation of homotypic tubular bridges between the Golgi stacks, we present an alternative model, based on direct interaction between the biosynthetic (pre-Golgi) and endocytic (post-Golgi) membrane networks and their connection with the centrosome. We propose that the central domains of these permanent pre- and post-Golgi networks function together in the biogenesis and maintenance of the more transient Golgi stacks, and thereby establish “linker compartments” that dynamically join the stacks together. This model provides insight into the reversible fragmentation of the Golgi ribbon that takes place in dividing and migrating cells and its regulation along a cell surface – Golgi – centrosome axis. Moreover, it helps to understand transport pathways that either traverse or bypass the Golgi stacks and the positioning of the Golgi apparatus in differentiated neuronal, epithelial, and muscle cells.

Form and function of the Golgi apparatus: scaffolds, cytoskeleton and signalling

In addition to the classical functions of the Golgi in membrane transport and glycosylation, the Golgi apparatus of mammalian cells is now recognised to contribute to the regulation of a range of cellular processes, including mitosis, DNA repair, stress responses, autophagy, apoptosis and inflammation. These processes are often mediated, either directly or indirectly, by membrane scaffold molecules, such as golgins and GRASPs which are located on Golgi membranes. In many cases, these scaffold molecules also link the actin and microtubule cytoskeleton and influence Golgi morphology. An emerging theme is a strong relationship between the morphology of the Golgi and regulation of a variety of signalling pathways. Here, we review the molecular regulation of the morphology of the Golgi, especially the role of the golgins and other scaffolds in the interaction with the microtubule and actin networks. In addition, we discuss the impact of the modulation of the Golgi ribbon in various diseases, such as neurodegeneration and cancer, to the pathology of disease.

The N-Glycosylation Processing Potential of the Mammalian Golgi Apparatus

Heterogeneity is an inherent feature of the glycosylation process. Mammalian cells often produce a variety of glycan structures on separate molecules of the same protein, known as glycoforms. This heterogeneity is not random but is controlled by the organization of the glycosylation machinery in the Golgi cisternae. In this work, we use a computational model of the N-glycosylation process to probe how the organization of the glycosylation machinery into different cisternae drives N-glycan biosynthesis toward differing degrees of heterogeneity. Using this model, we demonstrate the N-glycosylation potential and limits of the mammalian Golgi apparatus, for example how the number of cisternae limits the goal of achieving near homogeneity for N-glycans. The production of specific glycoforms guided by this computational study could pave the way for “glycoform engineering,” which will find uses in the functional investigation of glycans, the modulation of glycan-mediated physiological functions, and in biotechnology.

New Insights Into the Golgi Stacking Proteins

The Golgi stacking proteins, GRASP55 and GRASP65, are best known for their roles in Golgi structure formation. These peripheral Golgi proteins form trans-oligomers that hold the flat cisternal membranes into stacks. Depletion of both GRASP proteins in cells disrupts the Golgi stack structure, increases protein trafficking, but impairs accurate glycosylation, and sorting. Golgi unstacking by GRASPs depletion also reduces cell adhesion and migration in an integrin-dependent manner. In addition to Golgi structure formation and regulation of cellular activities, GRASPs, in particular GRASP55, have recently drawn attention in their roles in autophagy, and unconventional secretion. In autophagy, GRASP55 senses the energy level by O-GlcNAcylation, which regulates GRASP55 translocation from the Golgi to the autophagosome-lysosome interface, where it interacts with LC3 and LAMP2 to facilitate autophagosome-lysosome fusion. This newly discovered function of GRASP55 in autophagy may help explain its role in the stress-induced, autophagosome-dependent unconventional secretion. In this review, we summarize the emerging functions of the GRASP proteins, focusing on their roles in cell adhesion and migration, autophagy, unconventional secretion, as well as on novel GRASP-interacting proteins.