Role of axonal transport in neurodegenerative diseases

Decreasing ganglioside synthesis delays motor and cognitive symptom onset in Spg11 knockout mice

Biallelic variants in the SPG11 gene account for the most common form of autosomal recessive hereditary spastic paraplegia characterized by motor and cognitive impairment, with currently no therapeutic option. We previously observed in a Spg11 knockout mouse that neurodegeneration is associated with accumulation of gangliosides in lysosomes. To test whether a substrate reduction therapy could be a therapeutic option, we downregulated the key enzyme involved in ganglioside biosynthesis using an AAV-PHP.eB viral vector expressing a miRNA targeting St3gal5. Downregulation of St3gal5 in Spg11 knockout mice prevented the accumulation of gangliosides, delayed the onset of motor and cognitive symptoms, and prevented the upregulation of serum levels of neurofilament light chain, a biomarker widely used in neurodegenerative diseases. Importantly, similar results were observed when Spg11 knockout mice were administrated venglustat, a pharmacological inhibitor of glucosylceramide synthase expected to decrease ganglioside synthesis. Downregulation of St3gal5 or venglustat administration in Spg11 knockout mice strongly decreased the formation of axonal spheroids, previously associated with impaired trafficking. Venglustat had similar effect on cultured human SPG11 neurons. In conclusion, this work identifies the first disease-modifying therapeutic strategy in SPG11, and provides data supporting its relevance for therapeutic testing in SPG11 patients.

Current neuroprotective therapies and future prospects for motor neuron disease

Four medications with neuroprotective disease-modifying effects are now in use for motor neuron disease (MND). With FDA approvals for tofersen, relyvrio and edaravone in just the past year, 2022 ended a quarter of a century when riluzole was the sole such drug to offer to patients. The acceleration of approvals may mean we are witnessing the beginning of a step-change in how MND can be treated. Improvements in understanding underlying disease biology has led to more therapies being developed to target specific and multiple disease mechanisms. Consideration for how the pipeline of new therapeutic agents coming through in clinical and preclinical development can be more effectively evaluated with biomarkers, advances in patient stratification and clinical trial design pave the way for more successful translation for this archetypal complex neurodegenerative disease. While it must be cautioned that only slowed rates of progression have so far been demonstrated, pre-empting rapid neurodegeneration by using neurofilament biomarkers to signal when to treat, as is currently being trialled with tofersen, may be more effective for patients with known genetic predisposition to MND. Early intervention with personalized medicines could mean that for some patients at least, in future we may be able to substantially treat what is considered by many to be one of the most distressing diseases in medicine.

Compartmental Differences in the Retinal Ganglion Cell Mitochondrial Proteome

Among neurons, retinal ganglion cells (RGCs) are uniquely sensitive to mitochondrial dysfunction. The RGC is highly polarized, with a somatodendritic compartment in the inner retina and an axonal compartment projecting to targets in the brain. The drastically dissimilar functions of these compartments implies that mitochondria face different bioenergetic and other physiological demands. We hypothesized that compartmental differences in mitochondrial biology would be reflected by disparities in mitochondrial protein composition. Here, we describe a protocol to isolate intact mitochondria separately from mouse RGC somatodendritic and axonal compartments by immunoprecipitating labeled mitochondria from RGC MitoTag mice. Using mass spectrometry, 471 and 357 proteins were identified in RGC somatodendritic and axonal mitochondrial immunoprecipitates, respectively. We identified 10 mitochondrial proteins exclusively in the somatodendritic compartment and 19 enriched ≥2-fold there, while 3 proteins were exclusively identified and 18 enriched in the axonal compartment. Our observation of compartment-specific enrichment of mitochondrial proteins was validated through immunofluorescence analysis of the localization and relative abundance of superoxide dismutase ( SOD2 ), sideroflexin-3 ( SFXN3 ) and trifunctional enzyme subunit alpha ( HADHA ) in retina and optic nerve specimens. The identified compartmental differences in RGC mitochondrial composition may provide promising leads for uncovering physiologically relevant pathways amenable to therapeutic intervention for optic neuropathies.

Short-distance vesicle transport via phase separation

In addition to long-distance molecular motor-mediated transport, cellular vesicles also need to be moved at short distances with defined directions to meet functional needs in subcellular compartments but with unknown mechanisms. Such short-distance vesicle transport does not involve molecular motors. Here, we demonstrate, using synaptic vesicle (SV) transport as a paradigm, that phase separation of synaptic proteins with vesicles can facilitate regulated, directional vesicle transport between different presynaptic bouton sub-compartments. Specifically, a large coiled-coil scaffold protein Piccolo, in response to Ca2+ and via its C2A domain-mediated Ca2+ sensing, can extract SVs from the synapsin-clustered reserve pool condensate and deposit the extracted SVs onto the surface of the active zone protein condensate. We further show that the Trk-fused gene, TFG, also participates in COPII vesicle trafficking from ER to the ER-Golgi intermediate compartment via phase separation. Thus, phase separation may play a general role in short-distance, directional vesicle transport in cells.

Modulation of neural gene networks by estradiol in old rhesus macaque females

The postmenopausal decrease in circulating estradiol (E2) levels has been shown to contribute to several adverse physiological and psychiatric effects. To elucidate the molecular effects of E2 on the brain, we examined differential gene expression and DNA methylation (DNAm) patterns in the nonhuman primate brain following ovariectomy (Ov) and subsequent subcutaneous bioidentical E2 chronic treatment. We identified several dysregulated molecular networks, including MAPK signaling and dopaminergic synapse response, that are associated with ovariectomy and shared across two different brain areas, the occipital cortex (OC) and prefrontal cortex (PFC). The finding that hypomethylation (p = 1.6 × 10-51) and upregulation (p = 3.8 × 10-3) of UBE2M across both brain regions provide strong evidence for molecular differences in the brain induced by E2 depletion. Additionally, differential expression (p = 1.9 × 10-4; interaction p = 3.5 × 10-2) of LTBR in the PFC provides further support for the role E2 plays in the brain, by demonstrating that the regulation of some genes that are altered by ovariectomy may also be modulated by Ov followed by hormone replacement therapy (HRT). These results present real opportunities to understand the specific biological mechanisms that are altered with depleted E2. Given E2's potential role in cognitive decline and neuroinflammation, our findings could lead to the discovery of novel therapeutics to slow cognitive decline. Together, this work represents a major step toward understanding molecular changes in the brain that are caused by ovariectomy and how E2 treatment may revert or protect against the negative neuro-related consequences caused by a depletion in estrogen as women approach menopause.

Endoplasmic reticulum stress and its role in various neurodegenerative diseases

The Endoplasmic reticulum (ER), a critical cellular organelle, maintains cellular homeostasis by regulating calcium levels and orchestrating essential functions such as protein synthesis, folding, and lipid production. A pivotal aspect of ER function is its role in protein quality control. When misfolded proteins accumulate within the ER due to factors like protein folding chaperone dysfunction, toxicity, oxidative stress, or inflammation, it triggers the Unfolded protein response (UPR). The UPR involves the activation of chaperones like calnexin, calreticulin, glucose-regulating protein 78 (GRP78), and Glucose-regulating protein 94 (GRP94), along with oxidoreductases like protein disulphide isomerases (PDIs). Cells employ the Endoplasmic reticulum-associated degradation (ERAD) mechanism to counteract protein misfolding. ERAD disruption causes the detachment of GRP78 from transmembrane proteins, initiating a cascade involving Inositol-requiring kinase/endoribonuclease 1 (IRE1), Activating transcription factor 6 (ATF6), and Protein kinase RNA-like endoplasmic reticulum kinase (PERK) pathways. The accumulation and deposition of misfolded proteins within the cell are hallmarks of numerous neurodegenerative diseases. These aberrant proteins disrupt normal neuronal signalling and contribute to impaired cellular homeostasis, including oxidative stress and compromised protein degradation pathways. In essence, ER stress is defined as the cellular response to the accumulation of misfolded proteins in the endoplasmic reticulum, encompassing a series of signalling pathways and molecular events that aim to restore cellular homeostasis. This comprehensive review explores ER stress and its profound implications for the pathogenesis and progression of neurodegenerative diseases.

Rab11 suppresses neuronal stress signaling by localizing Dual leucine zipper kinase to axon terminals for protein turnover

Dual Leucine Zipper Kinase (DLK) mediates multiple neuronal stress responses, and its expression levels are constantly suppressed to prevent excessive stress signaling. We found that Wallenda (Wnd), the Drosophila ortholog of DLK, is highly enriched in the axon terminals of Drosophila sensory neurons in vivo and that this subcellular localization is necessary for Highwire-mediated Wnd protein turnover under normal conditions. Our structure-function analysis found that Wnd palmitoylation is essential for its axon terminal localization. Palmitoylation-defective Wnd accumulated in neuronal cell bodies, exhibited dramatically increased protein expression levels, and triggered excessive neuronal stress responses. Defective intracellular transport is implicated in neurodegenerative conditions. Comprehensive dominant-negative Rab protein screening identified Rab11 as an essential factor for Wnd localization in axon terminals. Consequently, Rab11 loss-of-function increased the protein levels of Wnd and induced neuronal stress responses. Inhibiting Wnd activity significantly ameliorated neuronal loss and c-Jun N-terminal kinase signaling triggered by Rab11 loss-of-function. Taken together, these suggest that DLK proteins are constantly transported to axon terminals by Rab11 for protein turnover. Our study demonstrates how subcellular protein localization is coupled to protein turnover for neuronal stress signaling.

Highlights

Wnd is highly enriched in axon terminals.Wnd protein turnover by Hiw is restricted in the axon terminals.Protein palmitoylation of Wnd and Rab11 activity is essential for Wnd axonal localization. Rab11 mutations and defective Wnd palmitoylation impair Wnd protein turnover leading to increased Wnd protein levels and neuronal loss. Inhibiting Wnd activity mitigates neuronal stress response caused by Rab11 loss-of-function.

Silica Nanoparticles Disclose a Detailed Neurodegeneration Profile throughout the Life Span of a Model Organism

The incidence of age-related neurodegenerative diseases is rising globally. However, the temporal sequence of neurodegeneration throughout adult life is poorly understood. To identify the starting points and schedule of neurodegenerative events, serotonergic and dopaminergic neurons were monitored in the model organism C. elegans, which has a life span of 2-3 weeks. Neural morphology was examined from young to old nematodes that were exposed to silica nanoparticles. Young nematodes showed phenotypes such as dendritic beading of serotonergic and dopaminergic neurons that are normally not seen until late life. During aging, neurodegeneration spreads from specifically susceptible ADF and PDE neurons in young C. elegans to other more resilient neurons, such as dopaminergic CEP in middle-aged worms. Investigation of neurodegenerative hallmarks and animal behavior revealed a temporal correlation with the acceleration of neuromuscular defects, such as internal hatch in 2-day-old C. elegans. Transcriptomics and proteomics of young worms exposed to nano silica showed a change in gene expression concerning the gene ontology groups serotonergic and dopaminergic signaling as well as neuropeptide signaling. Consistent with this, reporter strains for nlp-3, nlp-14 and nlp-21 confirmed premature degeneration of the serotonergic neuron HSN and other neurons in young C. elegans. The results identify young nematodes as a vulnerable age group for nano silica-induced neural defects with a significantly reduced health span. Neurodegeneration of specific neurons impairs signaling by classical neurotransmitters as well as neuropeptides and compromises related neuromuscular behaviors in critical phases of life, such as the reproductive phase.

Modulation of neural gene networks by estradiol in old rhesus macaque females

The postmenopausal decrease in circulating estradiol (E2) levels has been shown to contribute to several adverse physiological and psychiatric effects. To elucidate the molecular effects of E2 on the brain, we examined differential gene expression and DNA methylation (DNAm) patterns in the nonhuman primate brain following ovariectomy (Ov) and subsequent E2 treatment. We identified several dysregulated molecular networks, including MAPK signaling and dopaminergic synapse response, that are associated with ovariectomy and shared across two different brain areas, the occipital cortex (OC) and prefrontal cortex (PFC). The finding that hypomethylation (p=1.6×10-51) and upregulation (p=3.8×10-3) of UBE2M across both brain regions, provide strong evidence for molecular differences in the brain induced by E2 depletion. Additionally, differential expression (p=1.9×10-4; interaction p=3.5×10-2) of LTBR in the PFC, provides further support for the role E2 plays in the brain, by demonstrating that the regulation of some genes that are altered by ovariectomy may also be modulated by Ov followed by hormone replacement therapy (HRT). These results present real opportunities to understand the specific biological mechanisms that are altered with depleted E2. Given E2's potential role in cognitive decline and neuroinflammation, our findings could lead to the discovery of novel therapeutics to slow cognitive decline. Together, this work represents a major step towards understanding molecular changes in the brain that are caused by ovariectomy and how E2 treatment may revert or protect against the negative neuro-related consequences caused by a depletion in estrogen as women approach menopause.

Kif15 deficiency contributes to depression-like behavior in mice

Neuropsychiatric disorders have a high incidence worldwide. Kinesins, a family of microtubule-based molecular motor proteins, play essential roles in intracellular and axonal transport. Variants of kinesins have been found to be related to many diseases, including neurodevelopmental/neurodegenerative disorders. Kinesin-12 (also known as Kif15) was previously found to affect the frequency of both directional microtubule transports. However, whether Kif15 deficiency impacts mood in mice is yet to be investigated. In this study, we used the CRISPR/Cas9 method to obtain Kif15-/- mice. In behavioral tests, Kif15-/- female mice exhibited prominent depressive characteristics. Further studies showed that the expression of BDNF was significantly decreased in the frontal cortex, corpus callosum, and hippocampus of Kif15-/- mice, along with the upregulation of Interleukin-6 and Interleukin-1β in the corpus callosum. In addition, the expression patterns of AnkG were notably changed in the developing brain of Kif15-/- mice. Based on our previous studies, we suggested that this appearance of altered AnkG was due to the maladjustment of the microtubule patterns induced by Kif15 deficiency. The distribution of PSD95 in neurites notably decreased after cultured neurons treated with the Kif15 inhibitor, but total PSD95 protein level was not impacted, which revealed that Kif15 may contribute to PSD95 transportation. This study suggested that Kif15 may serve as a potential target for future depression studies.

Loss of the extracellular matrix protein Perlecan disrupts axonal and synaptic stability during Drosophila development

Heparan sulfate proteoglycans (HSPGs) form essential components of the extracellular matrix (ECM) and basement membrane (BM) and have both structural and signaling roles. Perlecan is a secreted ECM-localized HSPG that contributes to tissue integrity and cell-cell communication. Although a core component of the ECM, the role of Perlecan in neuronal structure and function is less understood. Here, we identify a role for Drosophila Perlecan in the maintenance of larval motoneuron axonal and synaptic stability. Loss of Perlecan causes alterations in the axonal cytoskeleton, followed by axonal breakage and synaptic retraction of neuromuscular junctions. These phenotypes are not prevented by blocking Wallerian degeneration and are independent of Perlecan's role in Wingless signaling. Expression of Perlecan solely in motoneurons cannot rescue synaptic retraction phenotypes. Similarly, removing Perlecan specifically from neurons, glia, or muscle does not cause synaptic retraction, indicating the protein is secreted from multiple cell types and functions non-cell autonomously. Within the peripheral nervous system, Perlecan predominantly localizes to the neural lamella, a specialized ECM surrounding nerve bundles. Indeed, the neural lamella is disrupted in the absence of Perlecan, with axons occasionally exiting their usual boundary in the nerve bundle. In addition, entire nerve bundles degenerate in a temporally coordinated manner across individual hemi-segments throughout larval development. These observations indicate disruption of neural lamella ECM function triggers axonal destabilization and synaptic retraction of motoneurons, revealing a role for Perlecan in axonal and synaptic integrity during nervous system development.

Amyotrophic lateral sclerosis: a neurodegenerative disorder poised for successful therapeutic translation

Amyotrophic lateral sclerosis (ALS) is a devastating disease caused by degeneration of motor neurons. As with all major neurodegenerative disorders, development of disease-modifying therapies has proven challenging for multiple reasons. Nevertheless, ALS is one of the few neurodegenerative diseases for which disease-modifying therapies are approved. Significant discoveries and advances have been made in ALS preclinical models, genetics, pathology, biomarkers, imaging and clinical readouts over the last 10-15 years. At the same time, novel therapeutic paradigms are being applied in areas of high unmet medical need, including neurodegenerative disorders. These developments have evolved our knowledge base, allowing identification of targeted candidate therapies for ALS with diverse mechanisms of action. In this Review, we discuss how this advanced knowledge, aligned with new approaches, can enable effective translation of therapeutic agents from preclinical studies through to clinical benefit for patients with ALS. We anticipate that this approach in ALS will also positively impact the field of drug discovery for neurodegenerative disorders more broadly.

The Mobility of Neurofilaments in Mature Myelinated Axons of Adult Mice

Studies in cultured neurons have shown that neurofilaments are cargoes of axonal transport that move rapidly but intermittently along microtubule tracks. However, the extent to which axonal neurofilaments move in vivo has been controversial. Some researchers have proposed that most axonally transported neurofilaments are deposited into a persistently stationary network and that only a small proportion of axonal neurofilaments are transported in mature axons. Here we use the fluorescence photoactivation pulse-escape technique to test this hypothesis in intact peripheral nerves of adult male hThy1-paGFP-NFM mice, which express low levels of mouse neurofilament protein M tagged with photoactivatable GFP. Neurofilaments were photoactivated in short segments of large, myelinated axons, and the mobility of these fluorescently tagged polymers was determined by analyzing the kinetics of their departure. Our results show that >80% of the fluorescence departed the window within 3 h after activation, indicating a highly mobile neurofilament population. The movement was blocked by glycolytic inhibitors, confirming that it was an active transport process. Thus, we find no evidence for a substantial stationary neurofilament population. By extrapolation of the decay kinetics, we predict that 99% of the neurofilaments would have exited the activation window after 10 h. These data support a dynamic view of the neuronal cytoskeleton in which neurofilaments cycle repeatedly between moving and pausing states throughout their journey along the axon, even in mature myelinated axons. The filaments spend a large proportion of their time pausing, but on a timescale of hours, most of them move.

Digest it all: the lysosomal turnover of cytoplasmic aggregates

Aggrephagy describes the selective lysosomal transport and turnover of cytoplasmic protein aggregates by macro-autophagy. In this process, protein aggregates and conglomerates are polyubiquitinated and then sequestered by autophagosomes. Soluble selective autophagy receptors (SARs) are central to aggrephagy and physically bind to both ubiquitin and the autophagy machinery, thus linking the cargo to the forming autophagosomal membrane. Because the accumulation of protein aggregates is associated with cytotoxicity in several diseases, a better molecular understanding of aggrephagy might provide a conceptual framework to develop therapeutic strategies aimed at delaying the onset of these pathologies by preventing the buildup of potentially toxic aggregates. We review recent advances in our knowledge about the mechanism of aggrephagy.

Huntingtin-associated protein 1-associated intracellular trafficking in neurodegenerative diseases

Huntingtin-associated protein 1 (HAP1), the first identified HTT-binding partner, is highly expressed in the central nervous system, and has been found to associated with neurological diseases. Mounting evidence suggests that HAP1 functions as a component of cargo-motor molecules to bind various proteins and participates in intracellular trafficking. It is known that the failure of intracellular transport is a key contributor to the progression of neurodegenerative disorders (NDs) including Alzheimer's disease (AD), Huntington's disease (HD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), spinal and bulbar muscular atrophy (SBMA) and spinocerebellar ataxia (SCA). The link between HAP1 and various NDs is supported by growing evidence. This review aims to provide a comprehensive overview of the intracellular trafficking function of HAP1 and its involvement in NDs.

Axonal transport deficits in the pathogenesis of diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is a chronic and prevalent metabolic disease that gravely endangers human health and seriously affects the quality of life of hyperglycemic patients. More seriously, it can lead to amputation and neuropathic pain, imposing a severe financial burden on patients and the healthcare system. Even with strict glycemic control or pancreas transplantation, peripheral nerve damage is difficult to reverse. Most current treatment options for DPN can only treat the symptoms but not the underlying mechanism. Patients with long-term diabetes mellitus (DM) develop axonal transport dysfunction, which could be an important factor in causing or exacerbating DPN. This review explores the underlying mechanisms that may be related to axonal transport impairment and cytoskeletal changes caused by DM, and the relevance of the latter with the occurrence and progression of DPN, including nerve fiber loss, diminished nerve conduction velocity, and impaired nerve regeneration, and also predicts possible therapeutic strategies. Understanding the mechanisms of diabetic neuronal injury is essential to prevent the deterioration of DPN and to develop new therapeutic strategies. Timely and effective improvement of axonal transport impairment is particularly critical for the treatment of peripheral neuropathies.

Evaluation of the Hematological and Serum Biochemistry Parameters in the Pre-Symptomatic and Symptomatic Stages of ALS Disease to Support Early Diagnosis and Prognosis

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease. Since there are no pathognomonic tests for ALS prognoses; clinical diagnoses of the disease take time and are usually difficult. Prognostic biomarkers are urgently needed for rapid and effective ALS prognoses. Male albino rats were divided into ten groups based on age: 0 (40-45 days old), A (70-75 days old), B (90-95 days old), C (110-115 days old), and D (130-135 days old). Each group was divided into two subgroups according to its mutation status: wild type (SOD1^WT) or mutated (SOD1^G93A). Serum biochemistry and hematological parameters were measured in 90 rats to evaluate possible biomarkers for faster ALS diagnoses and prognoses. Weight loss, cholesterol, creatinine, glucose, total bilirubin (TBIL), blood urine nitrogen (BUN), c-peptide, glucagon, PYY, white blood cell (WBC), lymphocyte (LYM), monocyte (MID), granulocyte (GRAN), red cell distribution width with standard deviation (RDW-SD), red cell distribution width with the coefficient of variation (RDW-CV), platelet (PLT), mean platelet volume (MPV), platelet distribution width (PDW), and procalcitonin (PCT) levels were changed in the SOD1^G93A rats compared to the SOD1^WT rats independently from aging. For the first time in the literature, we showed promising hematological and serum biochemistry parameters in the pre-symptomatic and symptomatic stages of ALS by eliminating the effects of aging. Our results can be used for early diagnoses and prognoses of ALS, improving the quality of life and survival time of ALS patients.

Mitochondrial Dysfunction and Pharmacodynamics of Mitofusin Activation in Murine Charcot-Marie-Tooth Disease Type 2A

Mitofusin (MFN) 1 and MFN2 are dynamin GTPase family mitochondrial proteins that mediate mitochondrial fusion requiring MFN conformational shifts, formation of macromolecular complexes on and between mitochondria, and GTP hydrolysis. Damaging MFN2 mutations cause an untreatable, largely pediatric progressive peripheral neuropathy, Charcot-Marie-Tooth (CMT) disease type 2A. We used small molecule allosteric mitofusin activators that promote MFN conformations favoring fusion to interrogate the effects of MFN2 conformation and GTPase activity on MFN2-mediated mitochondrial fusion and motility in vitro. We translated these findings in vivo by defining dose-dependent pharmacodynamic and disease-modifying effects of mitofusin activators in murine CMT2A. MFN2 catalytic GTPase activity and MFN2 conformational switching are essential for mitochondrial fusion, but the two processes are separate and dissociable. We report the first concentration-response relationships for mitofusin activators to stimulate mitochondrial transport through CMT2A neuronal axons, which is similar to their stimulation of mitochondrial fusion. In CMT2A mice, intermittent (daily short acting) and sustained (twice daily long acting) mitofusin activation were equally effective in reversing neuromuscular degeneration. Moreover, acute dose-dependent pharmacodynamic effects of mitofusin activators on mitochondrial transport through CMT2A neuronal axons anticipated those for long-term reversal of neurodegenerative phenotypes. A crossover study showed that CMT2A neuronal deficits recurred after mitofusin activators are discontinued, and revealed that CMT2A can be ameliorated by mitofusin activation even in old (>74 week) mice. These data add to our understanding of mitochondrial dysfunction induced by a CMT2A MFN2 GTPase mutation and provide additional information supporting the approach of pharmacological mitofusin activation in CMT2A. SIGNIFICANCE: This study interrogated the roles of MFN2 catalytic activity and allosteric activation on impaired mitochondrial fusion and neuronal transport as they impact an untreatable peripheral neuropathy caused by MFN2 mutations, Charcot-Marie-Tooth disease type 2A. The results mechanistically link mitochondrial fusion and motility to the relaxed MFN2 protein conformation and correction of mitochondrial abnormalities to in vivo reversal of neurodegeneration in murine CMT2A.

Decreasing pdzd8-mediated mito-ER contacts improves organismal fitness and mitigates Aβ42 toxicity

Mitochondria-ER contact sites (MERCs) orchestrate many important cellular functions including regulating mitochondrial quality control through mitophagy and mediating mitochondrial calcium uptake. Here, we identify and functionally characterize the Drosophila ortholog of the recently identified mammalian MERC protein, Pdzd8. We find that reducing pdzd8-mediated MERCs in neurons slows age-associated decline in locomotor activity and increases lifespan in Drosophila. The protective effects of pdzd8 knockdown in neurons correlate with an increase in mitophagy, suggesting that increased mitochondrial turnover may support healthy aging of neurons. In contrast, increasing MERCs by expressing a constitutive, synthetic ER-mitochondria tether disrupts mitochondrial transport and synapse formation, accelerates age-related decline in locomotion, and reduces lifespan. Although depletion of pdzd8 prolongs the survival of flies fed with mitochondrial toxins, it is also sufficient to rescue locomotor defects of a fly model of Alzheimer's disease expressing Amyloid β₄₂ (Aβ₄₂). Together, our results provide the first in vivo evidence that MERCs mediated by the tethering protein pdzd8 play a critical role in the regulation of mitochondrial quality control and neuronal homeostasis.

Reduction of kinesin I heavy chain decreases tau hyperphosphorylation, aggregation, and memory impairment in Alzheimer's disease and tauopathy models

Many neurodegenerative diseases, such as Alzheimer's disease (AD) and frontotemporal dementia with Parkinsonism linked to chromosome 17, are characterized by tau pathology. Numerous motor proteins, many of which are involved in synaptic transmission, mediate transport in neurons. Dysfunction in motor protein-mediated neuronal transport mechanisms occurs in several neurodegenerative disorders but remains understudied in AD. Kinesins are the most important molecular motor proteins required for microtubule-dependent transport in neurons, and kinesin-1 is crucial for neuronal transport among all kinesins. Although kinesin-1 is required for normal neuronal functions, the dysfunction of these motor domains leading to neurodegenerative diseases is not fully understood. Here, we reported that the kinesin-I heavy chain (KIF5B), a key molecular motor protein, is involved in tau homeostasis in AD cells and animal models. We found that the levels of KIF5B in P301S tau mice are high. We also found that the knockdown and knockout (KO) of KIFf5B significantly decreased the tau stability, and overexpression of KIF5B in KIF5B-KO cells significantly increased the expression of phosphorylated and total tau levels. This suggested that KIF5B might prevent tau accumulation. By conducting experiments on P301S tau mice, we showed that partially reducing KIF5B levels can reduce hyperphosphorylation of the human tau protein, formation of insoluble aggregates, and memory impairment. Collectively, our results suggested that decreasing KIF5B levels is sufficient to prevent and/or slow down abnormal tau behavior of AD and other tauopathies.

Decreased anterograde transport coupled with sustained retrograde transport contributes to reduced axonal mitochondrial density in tauopathy neurons

Mitochondria are essential organelle required for neuronal homeostasis. Mitochondria supply ATP and buffer calcium at synaptic terminals. However, the complex structural geometry of neurons poses a unique challenge in transporting mitochondria to synaptic terminals. Kinesin motors supply mitochondria to the axonal compartments, while cytoplasmic dynein is required for retrograde transport. Despite the importance of presynaptic mitochondria, how and whether axonal mitochondrial transport and distribution are altered in tauopathy neurons remain poorly studied. In the current study, we have shown that anterograde transport of mitochondria is reduced in P301L neurons, while there is no change in the retrograde transport. Consistently, axonal mitochondrial abundance is reduced in P301L neurons. We further studied the possible role of two opposing motor proteins on mitochondrial transport and found that mitochondrial association of kinesin is decreased significantly in P301L cells. Interestingly, fitting our experimental data into mathematical equations suggested a possible rise in dynein activity to maintain retrograde flux in P301L cells. Our data indicate that decreased kinesin-mediated transport coupled with sustained retrograde transport might reduce axonal mitochondria in tauopathy neurons, thus contributing to the synaptic deficits in Alzheimer’s disease (AD) and other tauopathies.

Evaluation of the mechanism of action of albendazole on adult rat lungworm (Angiostrongyluscantonensis)

Albendazole is considered the anthelmintic of choice for the management of rat lungworm disease (neuroangiostrongyliasis), due to its broad spectrum of nematocidal activity and its ability to cross the blood-brain barrier. Albendazole binds to β-tubulin, preventing its polymerization into microtubules, thereby corrupting the cascade of cell division at metaphase, which ultimately leads to the death of individual cells and eventually the death of the parasite. Inhibition of microtubule formation will also hinder the axoplasmic transport system, affecting the neuronal activities of the parasite. While this mechanism has been explicated in other parasitic and non-parasitic nematodes, it has never been evaluated in Angiostrongylus cantonensis. This study evaluates the antimitotic effects of albendazole sulphoxide (active metabolite) on the microtubules of adult A. cantonensis using the tubulin polymerization assay and measures its effects on worm viability using the colorimetric MTT assay. Three different concentrations of albendazole (62.5 μM, 250 μΜ, and 1 mM) were evaluated. We saw a statistically significant dose-dependent reduction in the band intensity of polymerized tubulins (or microtubules) (P = 0.019), suggesting that albendazole imparts its antimitotic effect in a dose-dependent manner. Similarly, our MTT assay showed a dose-dependent decrease in formazan intensity (proportional to cell viability), suggesting that the rate of nematocidal activity of albendazole is also proportional to its concentration. In compiling the results from both these experiments, a correlation between the microtubule assembly and worm viability is evident.

Biological effects of inhaled crude oil vapor V. Altered biogenic amine neurotransmitters and neural protein expression

Workers in the oil and gas industry are at risk for exposure to a number of physical and chemical hazards at the workplace. Chemical hazard risks include inhalation of crude oil or its volatile components. While several studies have investigated the neurotoxic effects of volatile hydrocarbons, in general, there is a paucity of studies assessing the neurotoxicity of crude oil vapor (COV). Consequent to the 2010 Deepwater Horizon (DWH) oil spill, there is growing concern about the short- and long-term health effects of exposure to COV. NIOSH surveys suggested that the DWH oil spill cleanup workers experienced neurological symptoms, including depression and mood disorders, but the health effects apart from oil dispersants were difficult to discern. To investigate the potential neurological risks of COV, male Sprague-Dawley rats were exposed by whole-body inhalation to COV (300 ppm; Macondo surrogate crude oil) following an acute (6 h/d × 1 d) or sub-chronic (6 h/d × 4 d/wk. × 4 wks) exposure regimen. At 1, 28 or 90 d post-exposure, norepinephrine (NE), epinephrine (EPI), dopamine (DA) and serotonin (5-HT) were evaluated as neurotransmitter imbalances are associated with psychosocial-, motor- and cognitive- disorders. Sub-chronic COV exposure caused significant reductions in NE, EPI and DA in the dopaminergic brain regions, striatum (STR) and midbrain (MB), and a large increase in 5-HT in the STR. Further, sub-chronic exposure to COV caused upregulation of synaptic and Parkinson's disease-related proteins in the STR and MB. Whether such effects will lead to neurodegenerative outcomes remain to be investigated.

Kinesin-3 motors are fine-tuned at the molecular level to endow distinct mechanical outputs

BACKGROUND

Kinesin-3 family motors drive diverse cellular processes and have significant clinical importance. The ATPase cycle is integral to the processive motility of kinesin motors to drive long-distance intracellular transport. Our previous work has demonstrated that kinesin-3 motors are fast and superprocessive with high microtubule affinity. However, chemomechanics of these motors remain poorly understood.

RESULTS

We purified kinesin-3 motors using the Sf9-baculovirus expression system and demonstrated that their motility properties are on par with the motors expressed in mammalian cells. Using biochemical analysis, we show for the first time that kinesin-3 motors exhibited high ATP turnover rates, which is 1.3- to threefold higher compared to the well-studied kinesin-1 motor. Remarkably, these ATPase rates correlate to their stepping rate, suggesting a tight coupling between chemical and mechanical cycles. Intriguingly, kinesin-3 velocities (KIF1A > KIF13A > KIF13B > KIF16B) show an inverse correlation with their microtubule-binding affinities (KIF1A < KIF13A < KIF13B < KIF16B). We demonstrate that this differential microtubule-binding affinity is largely contributed by the positively charged residues in loop8 of the kinesin-3 motor domain. Furthermore, microtubule gliding and cellular expression studies displayed significant microtubule bending that is influenced by the positively charged insert in the motor domain, K-loop, a hallmark of kinesin-3 family.

CONCLUSIONS

Together, we propose that a fine balance between the rate of ATP hydrolysis and microtubule affinity endows kinesin-3 motors with distinct mechanical outputs. The K-loop, a positively charged insert in the loop12 of the kinesin-3 motor domain promotes microtubule bending, an interesting phenomenon often observed in cells, which requires further investigation to understand its cellular and physiological significance.

Crucial Roles of Ubiquitin Carboxy-Terminal Hydrolase L1 in Motor Neuronal Health by Drosophila Model

Aims: Ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) plays an important role in the ubiquitin-proteasome system and is distributed mostly in the brain. Previous studies have shown that mutated forms or reduction of UCH-L1 are related to neurodegenerative disorders, but the mechanisms of pathogenesis are still not well understood. To study its roles in motor neuronal health, we utilized the Drosophila model in which dUCH, a homolog of human UCH-L1, was specifically knocked down in motor neurons. Results: The reduction of Drosophila ubiquitin carboxyl-terminal hydrolase (dUCH) in motor neurons induced excessive reactive oxygen species production and multiple aging-like phenotypes, including locomotive defects, muscle degeneration, enhanced apoptosis, and shortened longevity. In addition, there is a decrease in the density of the synaptic active zone and glutamate receptor area at the neuromuscular junction. Interestingly, all these defects were rescued by vitamin C treatment, suggesting a close association with oxidative stress. Strikingly, the knockdown of dUCH at motor neurons exhibited aberrant morphology and function of mitochondria, such as mitochondrial DNA (mtDNA) depletion, an increase in mitochondrial size, and overexpression of antioxidant enzymes. Innovation: This research indicates a new, possible pathogenesis of dUCH deficiency in the ventral nerve cord and peripheral nervous systems, which starts with abnormal mitochondria, leading to oxidative stress and accumulation aging-like defects in general. Conclusion: Taken together, by using the Drosophila model, our findings strongly emphasize how the UCH-L1 shortage affects motor neurons and further demonstrate the crucial roles of UCH-L1 in neuronal health. Antioxid. Redox Signal. 37, 257-273.

Defective axonal transport of endo-lysosomes and dense core vesicles in a Drosophila model of C9-ALS/FTD

A GGGGCC (G₄ C₂ ) repeat expansion in the C9orf72 gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Although disruptions in axonal transport are implicated in the pathogenesis of multiple neurodegenerative diseases, the underlying mechanisms causing these defects remain unclear. Here, we performed live imaging of Drosophila motor neurons expressing expanded G₄ C₂ repeats in third-instar larvae and investigated the axonal transport of multiple organelles in vivo. Expression of expanded G₄ C₂ repeats causes an increase in static axonal lysosomes, while it impairs trafficking of late endosomes (LEs) and dense core vesicles (DCVs). Surprisingly, however, axonal transport of mitochondria is unaffected in motor axons expressing expanded G₄ C₂ repeats. Thus, our data indicate that expanded G₄ C₂ repeat expression differentially impacts axonal transport of vesicular organelles and mitochondria in Drosophila models of C9orf72-associated ALS/FTD. This article is protected by copyright. All rights reserved.

Ethnomedicinal plants used for the treatment of neurodegenerative diseases in Himachal Pradesh, India in Western Himalaya

ETHNOPHARMACOLOGICAL RELEVANCE

Medicinal plants are considered as a healthcare resource and widely used by rural people in their traditional medicine system for curing neurodegenerative diseases. Neurodegenerative diseases refer to incurable and debilitating conditions that result in progressive degeneration/death of nerve cells or neurons in the human brain. This review is mainly focused on the usage of different ethnomedicinal plants in the treatment of different neurodegenerative diseases in Himachal Pradesh. Study reveals total of 73 ethnomedicinal plants, which are used for treating different neurological disorders in different areas of Himachal Pradesh. The data is compiled from the different sources that described the detailed information of plants in tabular form and highlights the significance of different phytochemicals on neuroprotective function. The present study also provides the scientific data and clinical (in-vivo and in-vitro) studies in support of ethnomedicinal use.

AIM OF THE STUDY

This review aims to provide information of ethnomedicinal plants which are used for the treatment of neurodegenerative diseases in Himachal Pradesh.

MATERIALS AND METHODS

Information on the use of ethnomedicinal plants to treat various neurological disorders has been gathered from a variety of sources, including various types of literature, books, and relevant publications in Google Scholar, Research Gate, Science Direct, Scopus, and Pub Med, among others. The collected data is tabulated, including the botanical names of plants, mode of use and the disease for which it is used for curing, etc. RESULTS: There are 73 ethnomedicinal plants that are used to cure various neurological disorders, with the most plants being used to treat epilepsy problem in Himachal Pradesh.

CONCLUSION

Numerous phytochemicals and extracts from diverse plants were found to have a protective effect against neurodegenerative diseases. Antioxidant activity is known to exist in a variety of herbal plants. The most common bioactive antioxidant chemicals having their significant impacts include flavonoids, flavones, coumarins, lignans, isoflavones, catechins, anthocyanins, and isocatechins.

The Role of Spastin in Axon Biology

Neurons are highly polarized cells with elaborate shapes that allow them to perform their function. In neurons, microtubule organization—length, density, and dynamics—are essential for the establishment of polarity, growth, and transport. A mounting body of evidence shows that modulation of the microtubule cytoskeleton by microtubule-associated proteins fine tunes key aspects of neuronal cell biology. In this respect, microtubule severing enzymes—spastin, katanin and fidgetin—a group of microtubule-associated proteins that bind to and generate internal breaks in the microtubule lattice, are emerging as key modulators of the microtubule cytoskeleton in different model systems. In this review, we provide an integrative view on the latest research demonstrating the key role of spastin in neurons, specifically in the context of axonal cell biology. We focus on the function of spastin in the regulation of microtubule organization, and axonal transport, that underlie its importance in the intricate control of axon growth, branching and regeneration.

Programming axonal mitochondrial maintenance and bioenergetics in neurodegeneration and regeneration

Mitochondria generate ATP essential for neuronal growth, function, and regeneration. Due to their polarized structures, neurons face exceptional challenges to deliver mitochondria to and maintain energy homeostasis throughout long axons and terminal branches where energy is in high demand. Chronic mitochondrial dysfunction accompanied by bioenergetic failure is a pathological hallmark of major neurodegenerative diseases. Brain injury triggers acute mitochondrial damage and a local energy crisis that accelerates neuron death. Thus, mitochondrial maintenance defects and axonal energy deficits emerge as central problems in neurodegenerative disorders and brain injury. Recent studies have started to uncover the intrinsic mechanisms that neurons adopt to maintain (or reprogram) axonal mitochondrial density and integrity, and their bioenergetic capacity, upon sensing energy stress. In this review, we discuss recent advances in how neurons maintain a healthy pool of axonal mitochondria, as well as potential therapeutic strategies that target bioenergetic restoration to power neuronal survival, function, and regeneration.

BAG2 prevents Tau hyperphosphorylation and increases p62/SQSTM1 in cell models of neurodegeneration

BACKGROUND

Protein aggregates are pathological hallmarks of many neurodegenerative diseases, however the physiopathological role of these aggregates is not fully understood. Protein quality control has a pivotal role for protein homeostasis and depends on specific chaperones. The co-chaperone BAG2 can target phosphorylated Tau for degradation by an ubiquitin-independent pathway, although its possible role in autophagy was not yet elucidated. In view of this, the aim of the present study was to investigate the association among protein aggregation, autophagy and BAG2 levels in cultured cells from hippocampus and locus coeruleus as well as in SH-SY5Y cell line upon different protein aggregation scenarios induced by rotenone, which is a flavonoid used as pesticide and triggers neurodegeneration.

METHODS AND RESULTS

The present study showed that rotenone exposure at 0.3 nM for 48 h impaired autophagy prior to Tau phosphorylation at Ser199/202 in hippocampus but not in locus coeruleus cells, suggesting that distinct neuron cells respond differently to rotenone toxicity. Rotenone induced Tau phosphorylation at Ser199/202, together with a decrease in the endogenous BAG2 protein levels in SH-SY5Y and hippocampus cell culture, which indicates that rotenone and Tau hyperphosphorylation can affect this co-chaperone. Finally, it has been shown that BAG2 overexpression, increased p62/SQSTM1 levels in cells from hippocampus and locus coeruleus, stimulated LC3II recycling as well as prevented the raise of phosphorylated Tau at Ser199/202 in hippocampus.

CONCLUSIONS

Results demonstrate a possible role for BAG2 in degradation pathways of specific substrates and its importance for the study of cellular aspects of neurodegenerative diseases.

Electrochemical Aptasensors for Parkinson's Disease Biomarkers Detection

BACKGROUND

Biomarkers are characteristic molecules that can be measured as indicators of biological process status or condition, exhibiting special relevance in Parkinson's Disease (PD). This disease is a chronic neurodegenerative disorder very difficult to study given the site of pathology and due to a clinical phenotype that fluctuates over time. Currently there is no definitive diagnostic test, thus clinicians hope that the detection of crucial biomarkers will help to the symptomatic and presymptomatic diagnostics and providing surrogate endpoints to demonstrate the clinical efficacy of new treatments.

METHODS

Electrochemical aptasensors are excellent analytical tools that are used in the detection of PD biomarkers, as they are portable, easy to use, and perform real-time analysis.

RESULTS

In this review, we discuss the most important clinical biomarkers for PD, highlighting their physiological role and function in the disease. Herein, we review for the first time innovative aptasensors for the detection of current potential PD biomarkers based on electrochemical techniques and discuss future alternatives, including ideal analytical platforms for point-of-care diagnostics.

CONCLUSION

These new tools will be critical not only in the discovery of sensitive, specific, and reliable biomarkers of preclinical PD, but also in the development of tests that can assist in the early detection and differential diagnosis of parkinsonian disorders and in monitoring disease progression. Various methods for fixing aptamers onto the sensor surfaces, enabling quantitative and specific PD biomarker detection present in synthetic and clinical samples, will also be discussed.

An adult-stage transcriptional program for survival of serotonergic connectivity

Neurons must function for decades of life, but how these non-dividing cells are preserved is poorly understood. Using mouse serotonin (5-HT) neurons as a model, we report an adult-stage transcriptional program specialized to ensure the preservation of neuronal connectivity. We uncover a switch in Lmx1b and Pet1 transcription factor function from controlling embryonic axonal growth to sustaining a transcriptomic signature of 5-HT connectivity comprising functionally diverse synaptic and axonal genes. Adult-stage deficiency of Lmx1b and Pet1 causes slowly progressing degeneration of 5-HT synapses and axons, increased susceptibility of 5-HT axons to neurotoxic injury, and abnormal stress responses. Axon degeneration occurs in a die back pattern and is accompanied by accumulation of α-synuclein and amyloid precursor protein in spheroids and mitochondrial fragmentation without cell body loss. Our findings suggest that neuronal connectivity is transcriptionally protected by maintenance of connectivity transcriptomes; progressive decay of such transcriptomes may contribute to age-related diseases of brain circuitry.

Analysis of multi-omics data on the relationship between epigenetic changes and nervous system disorders caused by exposure to environmentally harmful substances

Environmentally hazardous substances and exposure to these can cause various diseases. Volatile organic compounds can easily evaporate into the atmosphere, thereby exerting toxic effects through either the skin or respiratory tract exposures. Toluene, a neurotoxin, has been widely used in various industries. However, it has a detrimental effect on the nervous system (such as hallucinations or memory impairment), while data on the mechanism underlaying its harmful effects remain limited. Therefore, this study investigates the effect of toluene on the nervous system via epigenetic and genetic changes of toluene-exposed individuals. We identified significant epigenetic changes and confirmed that the affected abnormally expressed genes negatively influenced the nervous system. In particular, we confirmed that the miR-15 family, upregulated by toluene, downregulated ABL2, which could affect the R as signaling pathway resulting in neuronal structural abnormalities. Our study suggests that miR-15a-5p, miR-15b-5p, miR-16-5p, miR-301a-3p, and lncRNA NEAT1 may represent effective epigenomic markers associated with neurodegenerative diseases caused by toluene.

NAD+-dependent mechanism of pathological axon degeneration

Pathological axon degeneration is broadly observed in neurodegenerative diseases. This unique process of axonal pathology could directly interfere with the normal functions of neurocircuitries and contribute to the onset of clinical symptoms in patients. It has been increasingly recognized that functional preservation of axonal structures is an indispensable part of therapeutic strategies for treating neurological disorders. In the past decades, the research field has witnessed significant breakthroughs in understanding the stereotyped self-destruction of axons upon neurodegenerative insults, which is distinct from all the known types of programmed cell death. In particular, the novel NAD+-dependent mechanism involving the WLDs, NMNAT2, and SARM1 proteins has emerged. This review summarizes the landmark discoveries elucidating the molecular pathway of pathological axon degeneration and highlights the evolving concept that neurodegeneration would be intrinsically linked to NAD+ and energy metabolism.

Predicting Mitochondrial Dynamic Behavior in Genetically Defined Neurodegenerative Diseases

Mitochondrial dynamics encompass mitochondrial fusion, fission, and movement. Mitochondrial fission and fusion are seemingly ubiquitous, whereas mitochondrial movement is especially important for organelle transport through neuronal axons. Here, we review the roles of different mitochondrial dynamic processes in mitochondrial quantity and quality control, emphasizing their impact on the neurological system in Charcot–Marie–Tooth disease type 2A, amyotrophic lateral sclerosis, Friedrich’s ataxia, dominant optic atrophy, and Alzheimer’s, Huntington’s, and Parkinson’s diseases. In addition to mechanisms and concepts, we explore in detail different technical approaches for measuring mitochondrial dynamic dysfunction in vitro, describe how results from tissue culture studies may be applied to a better understanding of mitochondrial dysdynamism in human neurodegenerative diseases, and suggest how this experimental platform can be used to evaluate candidate therapeutics in different diseases or in individual patients sharing the same clinical diagnosis.

Modeling material transport regulation and traffic jam in neurons using PDE-constrained optimization

The intracellular transport process plays an important role in delivering essential materials throughout branched geometries of neurons for their survival and function. Many neurodegenerative diseases have been associated with the disruption of transport. Therefore, it is essential to study how neurons control the transport process to localize materials to necessary locations. Here, we develop a novel optimization model to simulate the traffic regulation mechanism of material transport in complex geometries of neurons. The transport is controlled to avoid traffic jam of materials by minimizing a pre-defined objective function. The optimization subjects to a set of partial differential equation (PDE) constraints that describe the material transport process based on a macroscopic molecular-motor-assisted transport model of intracellular particles. The proposed PDE-constrained optimization model is solved in complex tree structures by using isogeometric analysis (IGA). Different simulation parameters are used to introduce traffic jams and study how neurons handle the transport issue. Specifically, we successfully model and explain the traffic jam caused by reduced number of microtubules (MTs) and MT swirls. In summary, our model effectively simulates the material transport process in healthy neurons and also explains the formation of a traffic jam in abnormal neurons. Our results demonstrate that both geometry and MT structure play important roles in achieving an optimal transport process in neuron.

SARM1 Depletion Slows Axon Degeneration in a CNS Model of Neurotropic Viral Infection

Zika virus (ZIKV) is a neurotropic flavivirus recently linked to congenital ZIKV syndrome in children and encephalitis and Guillain-Barré syndrome in adults. Neurotropic viruses often use axons to traffic to neuronal or glial cell somas where they either remain latent or replicate and proceed to infect new cells. Consequently, it has been suggested that axon degeneration could represent an evolutionarily conserved mechanism to limit viral spread. Whilst it is not known if ZIKV transits in axons, we previously reported that ZIKV infection of glial cells in a murine spinal cord-derived cell culture model of the CNS is associated with a profound loss of neuronal cell processes. This, despite that postmitotic neurons are relatively refractory to infection and death. Here, we tested the hypothesis that ZIKV-associated degeneration of neuronal processes is dependent on activation of Sterile alpha and armadillo motif-containing protein 1 (SARM1), an NADase that acts as a central executioner in a conserved axon degeneration pathway. To test this, we infected wild type and Sarm1 homozygous or heterozygous null cell cultures with ZIKV and examined NAD⁺ levels as well as the survival of neurons and their processes. Unexpectedly, ZIKV infection led to a rapid SARM1-independent reduction in NAD⁺. Nonetheless, the subsequent profound loss of neuronal cell processes was SARM1-dependent and was preceded by early changes in the appearance of β-tubulin III staining. Together, these data identify a role for SARM1 in the pathogenesis of ZIKV infection, which may reflect SARM1's conserved prodegenerative function, independent of its NADase activity.

Caspase-cleaved tau is senescence-associated and induces a toxic gain of function by putting a brake on axonal transport

The microtubule-associated protein tau plays a central role in tauopathies such as Alzheimer's disease (AD). The exact molecular mechanisms underlying tau toxicity are unclear, but aging is irrefutably the biggest risk factor. This raises the question of how cellular senescence affects the function of tau as a microtubule regulator. Here we report that the proportion of tau that is proteolytically cleaved at the caspase-3 site (TauC3) doubles in the hippocampus of senescent mice. TauC3 is also elevated in AD patients. Through quantitative live-cell imaging, we show that TauC3 has a drastically reduced dynamics of its microtubule interaction. Single-molecule tracking of tau confirmed that TauC3 has a longer residence time on axonal microtubules. The reduced dynamics of the TauC3-microtubule interaction correlated with a decreased transport of mitochondria, a reduced processivity of APP-vesicle transport and an induction of region-specific dendritic atrophy in CA1 neurons of the hippocampus. The microtubule-targeting drug Epothilone D normalized the interaction of TauC3 with microtubules and modulated the transport of APP-vesicles dependent on the presence of overexpressed human tau. The results indicate a novel toxic gain of function, in which a post-translational modification of tau changes the dynamics of the tau-microtubule interaction and thus leads to axonal transport defects and neuronal degeneration. The data also introduce microtubule-targeting drugs as pharmacological modifiers of the tau-microtubule interaction with the potential to restore the physiological interaction of pathologically altered tau with microtubules.

Pathophysiology of neurodegenerative diseases: An interplay among axonal transport failure, oxidative stress, and inflammation?

Neurodegenerative diseases (NDs) are heterogeneous neurological disorders characterized by a progressive loss of selected neuronal populations. A significant risk factor for most NDs is aging. Considering the constant increase in life expectancy, NDs represent a global public health burden. Axonal transport (AT) is a central cellular process underlying the generation and maintenance of neuronal architecture and connectivity. Deficits in AT appear to be a common thread for most, if not all, NDs. Neuroinflammation has been notoriously difficult to define in relation to NDs. Inflammation is a complex multifactorial process in the CNS, which varies depending on the disease stage. Several lines of evidence suggest that AT defect, axonopathy and neuroinflammation are tightly interlaced. However, whether these impairments play a causative role in NDs or are merely a downstream effect of neuronal degeneration remains unsettled. We still lack reliable information on the temporal relationship between these pathogenic mechanisms, although several findings suggest that they may occur early during ND pathophysiology. This article will review the latest evidence emerging on whether the interplay between AT perturbations and some aspects of CNS inflammation can participate in ND etiology, analyze their potential as therapeutic targets, and the urge to identify early surrogate biomarkers.

Simulation of a sudden drop-off in distal dense core vesicle concentration in Drosophila type II motoneuron terminals

Recent experimental observations have shown evidence of an unexpected sudden drop-off in the dense core vesicles (DCVs) content at the ends of certain types of axon endings. This article seeks to determine whether these observations may be explained without modifying the parameters characterizing the ability of distal en passant boutons to capture and accumulate DCVs. We developed a mathematical model that is based on the conservation of captured and transiting DCVs in boutons. The model consists of 77 ordinary differential equations and is solved using a standard Matlab solver. We hypothesize that the drop in DCV content in distal boutons is due to an insufficient supply of anterogradely moving DCVs coming from the soma. As anterogradely moving DCVs are captured (and eventually destroyed) in more proximal boutons on their way to the end of the terminal, the fluxes of anterogradely moving DCVs between the boutons become increasingly smaller, and the most distal boutons are left without DCVs. We tested this hypothesis by modifying the flux of DCVs entering the terminal and found that the number of most distal boutons left unfilled increases if the DCV flux entering the terminal is decreased. The number of anterogradely moving DCVs in the axon can be increased either by the release of a portion of captured DCVs into the anterograde component or by an increase of the anterograde DCV flux into the terminal. This increase could lead to having enough anterogradely moving DCVs such that they could reach the most distal bouton and then turn around by changing molecular motors that propel them. The model suggests that this could result in an increased concentration of resident DCVs in distal boutons beginning with bouton 2 (the most distal is bouton 1). This is because in distal boutons, DCVs have a larger chance to be captured from the transiting state as they pass the boutons moving anterogradely and then again as they pass the same boutons moving retrogradely.

Potential Role of Growth Factors Controlled Release in Achieving Enhanced Neuronal Trans-differentiation from Mesenchymal Stem Cells for Neural Tissue Repair and Regeneration

With an increase in the incidence of neurodegenerative diseases, a need to replace incapable conventional methods has arisen. To overcome this burden, stem cells therapy has emerged as an efficient treatment option. Endeavours to accomplish this have paved the path to neural regeneration through efficient neuronal transdifferentiation. Despite their potential, the use of stem cells still entails several limitations, such as low differentiation efficiency and difficulties in guiding differentiation. The process of neural differentiation through the stem cells is achieved through the use of chemical inducers or growth factors and their direct introduction reduces their bioavailability in the system. To address these limitations, neural regeneration ventures require growth factors to be effectively implemented on stem cells in order to produce functional neuronal precursor cells. An efficient technique to achieve it is through the delivery of growth factors via microcarriers for their sustained release. It ensures the presence of commensurable concentration even at later stages of neuronal transdifferentiation. Nanofibers and nanoparticles, along with liposomes and such, have been used to implement this. The interaction between such carriers and the growth factors is mainly electrostatic. Such interaction enables them to form a stable assembly through immobilisation of the growth factor either onto their surfaces or within the core of their structures. The rate of sustained release depends upon the release kinetics associated with the polymeric structure employed and its interaction with the encapsulated growth factor. The sustained release ensures that the stem cells immerse under the effect of the growth factors for a prolonged period, ultimately aiding in the formation of cells showing ample characteristics of neuron precursors. This review analyses the various carriers that have been employed for the release of growth factors in an orderly fashion and their constituents, along with the advantages and the limitations they pose in delivering the growth factors for facilitating the process of neuronal transdifferentiation.

Diverse midbrain dopaminergic neuron subtypes and implications for complex clinical symptoms of Parkinson's disease

Parkinson’s disease (PD), the most common degenerative movement disorder, is clinically manifested with various motor and non-motor symptoms. Degeneration of midbrain substantia nigra pas compacta (SNc) dopaminergic neurons (DANs) is generally attributed to the motor syndrome. The underlying neuronal mechanisms of non-motor syndrome are largely unexplored. Besides SNc, midbrain ventral tegmental area (VTA) DANs also produce and release dopamine and modulate movement, reward, motivation, and memory. Degeneration of VTA DANs also occurs in postmortem brains of PD patients, implying an involvement of VTA DANs in PD-associated non-motor symptoms. However, it remains to be established that there is a distinct segregation of different SNc and VTA DAN subtypes in regulating different motor and non-motor functions, and that different DAN subpopulations are differentially affected by normal ageing or PD. Traditionally, the distinction among different DAN subtypes was mainly based on the location of cell bodies and axon terminals. With the recent advance of single cell RNA sequencing technology, DANs can be readily classified based on unique gene expression profiles. A combination of specific anatomic and molecular markers shows great promise to facilitate the identification of DAN subpopulations corresponding to different behavior modules under normal and disease conditions. In this review, we first summarize the recent progress in characterizing genetically, anatomically, and functionally diverse midbrain DAN subtypes. Then, we provide perspectives on how the preclinical research on the connectivity and functionality of DAN subpopulations improves our current understanding of cell-type and circuit specific mechanisms of the disease, which could be critically informative for designing new mechanistic treatments.

Mitochondrial Miro GTPases coordinate mitochondrial and peroxisomal dynamics

Mitochondria and peroxisomes are highly dynamic, multifunctional organelles. Both perform key roles for cellular physiology and homoeostasis by mediating bioenergetics, biosynthesis, and/or signalling. To support cellular function, they must be properly distributed, of proper size, and be able to interact with other organelles. Accumulating evidence suggests that the small atypical GTPase Miro provides a central signalling node to coordinate mitochondrial as well as peroxisomal dynamics. In this review, I summarize our current understanding of Miro-dependent functions and molecular mechanisms underlying the proper distribution, size and function of mitochondria and peroxisomes.

Myxobacteria as a Source of New Bioactive Compounds: A Perspective Study

Myxobacteria are unicellular, Gram-negative, soil-dwelling, gliding bacteria that belong to class δ-proteobacteria and order Myxococcales. They grow and proliferate by transverse fission under normal conditions, but form fruiting bodies which contain myxospores during unfavorable conditions. In view of the escalating problem of antibiotic resistance among disease-causing pathogens, it becomes mandatory to search for new antibiotics effective against such pathogens from natural sources. Among the different approaches, Myxobacteria, having a rich armor of secondary metabolites, preferably derivatives of polyketide synthases (PKSs) along with non-ribosomal peptide synthases (NRPSs) and their hybrids, are currently being explored as producers of new antibiotics. The Myxobacterial species are functionally characterized to assess their ability to produce antibacterial, antifungal, anticancer, antimalarial, immunosuppressive, cytotoxic and antioxidative bioactive compounds. In our study, we have found their compounds to be effective against a wide range of pathogens associated with the concurrence of different infectious diseases.

A novel orally active HDAC6 inhibitor T-518 shows a therapeutic potential for Alzheimer's disease and tauopathy in mice

Accumulation of tau protein is a key pathology of age-related neurodegenerative diseases such as Alzheimer's disease and progressive supranuclear palsy. Those diseases are collectively termed tauopathies. Tau pathology is associated with axonal degeneration because tau binds to microtubules (MTs), a component of axon and regulates their stability. The acetylation state of MTs contributes to stability and histone deacetylase 6 (HDAC6) is a major regulator of MT acetylation status, suggesting that pharmacological HDAC6 inhibition could improve axonal function and may slow the progression of tauopathy. Here we characterize N-[(1R,2R)-2-{3-[5-(difluoromethyl)-1,3,4-oxadiazol-2-yl]-5-oxo-5H,6H,7H-pyrrolo[3,4-b]pyridin-6-yl}cyclohexyl]-2,2,3,3,3-pentafluoropropanamide (T-518), a novel, potent, highly selective HDAC6 inhibitor with clinically favorable pharmacodynamics. T-518 shows potent inhibitory activity against HDAC6 and superior selectivity over other HDACs compared with the known HDAC6 inhibitors in the enzyme and cellular assays. T-518 showed brain penetration in an oral dose and blocked HDAC6-dependent tubulin deacetylation at Lys40 in mouse hippocampus. A 2-week treatment restored impaired axonal transport and novel object recognition in the P301S tau Tg mouse, tauopathy model, while a 3-month treatment also decreased RIPA-insoluble tau accumulation. Pharmaceutical inhibition of HDAC6 is a potential therapeutic strategy for tauopathy, and T-518 is a particularly promising drug candidate.

Risk Factors for Retinal Ganglion Cell Distress in Glaucoma and Neuroprotective Potential Intervention

Retinal ganglion cells (RGCs) are a population of neurons of the central nervous system (CNS) extending with their soma to the inner retina and with their axons to the optic nerve. Glaucoma represents a group of neurodegenerative diseases where the slow progressive death of RGCs results in a permanent loss of vision. To date, although Intra Ocular Pressure (IOP) is considered the main therapeutic target, the precise mechanisms by which RGCs die in glaucoma have not yet been clarified. In fact, Primary Open Angle Glaucoma (POAG), which is the most common glaucoma form, also occurs without elevated IOP. This present review provides a summary of some pathological conditions, i.e., axonal transport blockade, glutamate excitotoxicity and changes in pro-inflammatory cytokines along the RGC projection, all involved in the glaucoma cascade. Moreover, neuro-protective therapeutic approaches, which aim to improve RGC degeneration, have also been taken into consideration.

A Novel NAD Signaling Mechanism in Axon Degeneration and its Relationship to Innate Immunity

Axon degeneration represents a pathological feature of many neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease where axons die before the neuronal soma, and axonopathies, such as Charcot-Marie-Tooth disease and hereditary spastic paraplegia. Over the last two decades, it has slowly emerged that a central signaling pathway forms the basis of this process in many circumstances. This is an axonal NAD-related signaling mechanism mainly regulated by the two key proteins with opposing roles: the NAD-synthesizing enzyme NMNAT2, and SARM1, a protein with NADase and related activities. The crosstalk between the axon survival factor NMNAT2 and pro-degenerative factor SARM1 has been extensively characterized and plays an essential role in maintaining the axon integrity. This pathway can be activated in necroptosis and in genetic, toxic or metabolic disorders, physical injury and neuroinflammation, all leading to axon pathology. SARM1 is also known to be involved in regulating innate immunity, potentially linking axon degeneration to the response to pathogens and intercellular signaling. Understanding this NAD-related signaling mechanism enhances our understanding of the process of axon degeneration and enables a path to the development of drugs for a wide range of neurodegenerative diseases.

Deep learning of material transport in complex neurite networks

Neurons exhibit complex geometry in their branched networks of neurites which is essential to the function of individual neuron but also brings challenges to transport a wide variety of essential materials throughout their neurite networks for their survival and function. While numerical methods like isogeometric analysis (IGA) have been used for modeling the material transport process via solving partial differential equations (PDEs), they require long computation time and huge computation resources to ensure accurate geometry representation and solution, thus limit their biomedical application. Here we present a graph neural network (GNN)-based deep learning model to learn the IGA-based material transport simulation and provide fast material concentration prediction within neurite networks of any topology. Given input boundary conditions and geometry configurations, the well-trained model can predict the dynamical concentration change during the transport process with an average error less than 10% and [Formula: see text] times faster compared to IGA simulations. The effectiveness of the proposed model is demonstrated within several complex neurite networks.

Mechanistic insights and perspectives involved in neuroprotective action of quercetin

Neurodegenerative diseases (NDDs) are the primary cause of disabilities in the elderly people. Growing evidence indicates that oxidative stress, mitochondrial dysfunction, neuroinflammation and apoptosis are associated with aging and the basis of most neurodegenerative disorders. Quercetin is a flavonoid with significant pharmacological effects and promising therapeutic potential. It is widely distributed among plants and typically found in daily diets mainly in fruits and vegetables. It shows a number of biological properties connected to its antioxidant activity. Neuroprotection by quercetin has been reported in many in vitro as well as in in vivo studies. However, the exact mechanism of action is still mystery and similarly there are a number of hypothesis exploring the mechanism of neuroprotection. Quercetin enhances neuronal longevity and neurogenesis by modulating and inhibiting wide number of pathways. This review assesses the food sources of quercetin, its pharmacokinetic profile, structure activity relationship and its pathophysiological role in various NDDs and it also provides a synopsis of the literature exploring the relationship between quercetin and various downstream signalling pathways modulated by quercetin for neuroprotection for eg. nuclear factor erythroid 2-related factor 2 (Nrf2), Paraoxonase-2 (PON2), c-Jun N-terminal kinase (JNK), Tumour Necrosis Factor alpha (TNF-α), Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha (PGC-1α), Sirtuins, Mitogen-activated protein kinases (MAPKs) signalling cascades, CREB (Cyclic AMP response element binding protein) and Phosphoinositide 3- kinase(PI3K/Akt). Therefore, the aim of the present review was to elaborate on the cellular and molecular mechanisms of the quercetin involved in the protection against NDDs.