Fractalkine signaling and Tau hyper-phosphorylation are associated with autophagic alterations in lentiviral Tau and Aβ1-42 gene transfer models

Pharmacotherapies for the Treatment of Progressive Supranuclear Palsy: A Narrative Review

Progressive supranuclear palsy (PSP) is a neurodegenerative disorder resulting from the deposition of misfolded and neurotoxic forms of tau protein in specific areas of the midbrain, basal ganglia, and cortex. It is one of the most representative forms of tauopathy. PSP presents in several different phenotypic variations and is often accompanied by the development of concurrent neurodegenerative disorders. PSP is universally fatal, and effective disease-modifying therapies for PSP have not yet been identified. Several tau-targeting treatment modalities, including vaccines, monoclonal antibodies, and microtubule-stabilizing agents, have been investigated and have had no efficacy. The need to treat PSP and other tauopathies is critical, and many clinical trials investigating tau-targeted treatments are underway. In this review, the PubMed database was queried to collect information about preclinical and clinical research on PSP treatment. Additionally, the US National Library of Medicine's ClinicalTrials.gov website was queried to identify past and ongoing clinical trials relevant to PSP treatment. This narrative review summarizes our findings regarding these reports, which include potential disease-modifying drug trials, modifiable risk factor management, and symptom treatments.

The possible protective role of melatonin versus garlic on monosodium Glutamate-induced changes in rat cerebellar cortex: histological, immunohistochemical and electron microscope study

Monosodium glutamate (MSG) is widely used as a flavor enhancer. Melatonin and garlic are well known as antioxidant. The present study was performed to evaluate the microscopic changes in the cerebellar cortex of rats after the administration of MSG and the possible protective effect of melatonin versus garlic on those changes. The rats were divided into four main groups. Group I (control group). Group II received MSG (4 mg/ g/day). Group III received MSG+ melatonin (10 mg/kg bw/day). Group IV received MSG+garlic (300 mg/kg bw/day). Immunohistochemical staining for glial fibrillary acidic protein (GFAP) was done as a marker for astrocyte demonstration. Morphometric study was done to assess the mean number and diameter of Purkinje cells, the number of astrocytes and the percentage area of positive GFAP immune stain. MSG group demonstrated congested blood vessels, vacuolations in the molecular layer, and Purkinje cells appeared irregular with nuclear degeneration. Granule cells appeared shrunken with darkly stained nuclei. The immunohistochemical stain for GFAP was less than expected in the three layers of the cerebellar cortex. Purkinje cells and granule cells appeared irregular in shape with dark small heterochromatic nuclei. The myelinated nerve fibers showed splitting and loss of the lamellar structure of their myelin sheath. Melatonin group showed that the cerebellar cortex was nearly similar to that of control group. Garlic treated group showed partial improvement. In conclusion, melatonin and garlic could partially protect against MSG induced changes and the protective effect of melatonin was better than garlic.

Slingshot homolog-1 mediates the secretion of small extracellular vesicles containing misfolded proteins by regulating autophagy cargo receptors and actin dynamics

Increasing evidence indicates that the accumulation misfolded proteins in Alzheimer's disease (AD) arises from clearance defects in the autophagy-lysosome pathway. Misfolded proteins such as Aβ and tau are secreted in small extracellular vesicles (i.e., exosomes) and are propagated from cell to cell in part through secreted small extracellular vesicles (sEVs). Recent studies suggest that autophagic activity and exosome secretion are coregulated events, and multiple autophagy-related proteins are found in sEVs, including the cargo receptors Sqstm1/p62 and optineurin. However, whether and how autophagy cargo receptors per se regulate the secretion of sEVs is unknown. Moreover, despite the prominent role of actin dynamics in secretory vesicle release, its role in EV secretion is unknown. In this study, we leveraged the dual axes of Slingshot Homolog-1 (SSH1), which inhibits Sqstm1/p62-mediated autophagy and activates cofilin-mediated actin dynamics, to study the regulation of sEV secretion. Here we show that cargo receptors Sqstm1/p62 and optineurin inhibit sEV secretion, an activity that requires their ability to bind ubiquitinated cargo. Conversely, SSH1 increases sEV secretion by dephosphorylating Sqstm1/p62 at pSer403, the phospho-residue that allows Sqstm1/p62 to bind ubiquitinated cargo. In addition, increasing actin dynamics through the SSH1-cofilin activation pathway also increases sEV secretion, which is mimicked by latrunculin B treatment. Finally, Aβ42 oligomers and mutant tau increase sEV secretion and are physically associated with secreted sEVs. These findings suggest that increasing cargo receptor engagement with autophagic cargo and reducing actin dynamics (i.e., SSH1 inhibition) represents an attractive strategy to promote misfolded protein degradation while reducing sEV-mediated cell to cell spread of pathology.

Targeting microglial autophagic degradation in NLRP3 inflammasome-mediated neurodegenerative diseases

Neuroinflammation is considered as a detrimental factor in neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), etc. Nucleotide-binding oligomerization domain-, leucine-rich repeat- and pyrin domain-containing 3 (NLRP3), the most well-studied inflammasome, is abundantly expressed in microglia and has gained considerable attention. Misfolded proteins are characterized as the common hallmarks of neurodegenerative diseases due to not only their induced neuronal toxicity but also their effects in over-activating microglia and the NLRP3 inflammasome. The activated NLRP3 inflammasome aggravates the pathology and accelerates the progression of neurodegenerative diseases. Emerging evidence indicates that microglial autophagy plays an important role in the maintenance of brain homeostasis and the negative regulation of NLRP3 inflammasome-mediated neuroinflammation. The excessive activation of NLRP3 inflammasome impairs microglial autophagy and further aggravates the pathogenesis of neurodegenerative diseases. In this review article, we summarize and discuss the NLRP3 inflammasome and its specific inhibitors in microglia. The crucial role of microglial autophagy and its inducers in the removal of misfolded proteins, the clearance of damaged mitochondria and reactive oxygen species (ROS), and the degradation of the NLRP3 inflammasome or its components in neurodegenerative diseases are summarized. Understanding the underlying mechanisms behind the sex differences in NLRP3 inflammasome-mediated neurodegenerative diseases will help researchers to develop more targeted therapies and increase our diagnostic and prognostic abilities. In addition, the superiority of the combined use of microglial autophagy inducers with the specific inhibitors of the NLRP3 inflammasome in the inhibition of NLRP3 inflammasome-mediated neuroinflammation requires further preclinical and clinical validations in the future.

SSH1 impedes SQSTM1/p62 flux and MAPT/Tau clearance independent of CFL (cofilin) activation

Accumulation of toxic protein assemblies and damaged mitochondria are key features of neurodegenerative diseases, which arise in large part from clearance defects in the Macroautophagy/autophagy-lysosome system. The autophagy cargo receptor SQSTM1/p62 plays a major role in the clearance of ubiquitinated cargo through Ser403 phosphorylation by multiple kinases. However, no phosphatase is known to physiologically dephosphorylate SQSTM1 on this activating residue. RNAi-mediated knockdown and overexpression experiments using genetically encoded fluorescent reporters and defined mutant constructs in cell lines, primary neurons, and brains show that SSH1, the canonical CFL (cofilin) phosphatase, mediates the dephosphorylation of phospho-Ser403-SQSTM1, thereby impairing SQSTM1 flux and phospho-MAPT/tau clearance. The inhibitory action of SSH1 on SQSTM1 is fully dependent on SQSTM1 Ser403 phosphorylation status and is separable from SSH1-mediated CFL activation. These findings reveal a unique action of SSH1 on SQSTM1 independent of CFL and implicate an inhibitory role of SSH1 in SQSTM1-mediated clearance of autophagic cargo, including phospho-MAPT/tau. Abbreviations: AAV: adeno-associated virus; Aβ42_O: amyloid β1-42 oligomers; AD: Alzheimer disease; CA3: cornu Ammonis 3; CSNK2/CK2: casein kinase 2; FCCP: 2-[2-[4-(trifluoromethoxy)phenyl]hydrazinylidene]-propanedinitrile; FTLD: frontotemporal lobar degeneration; GFP: green fluorescent protein; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; SQSTM1/p62: sequestosome-1; PLA: proximity ligation assay; RFP: red fluorescent protein; RIPA: radioimmunoprecipitation assay; shRNA: short hairpin RNA; siRNA: small interfering RNA; Ser403: Serine403; SSH1: slingshot protein phosphatase 1; TBK1: TANK-binding kinase 1; ULK: unc-51 like kinase 1.

Dynamic changes of autophagic flux induced by Abeta in the brain of postmortem Alzheimer's disease patients, animal models and cell models

Autophagy has been reported to play a dual "double-edged sword" role in the occurrence and development of Alzheimer’s disease (AD). To assess the relationship between AD and autophagy, the dynamic changes of autophagic flux in the brain of postmortem AD patients, animal models and cell models were studied. The results showed that autophagosomes (APs) accumulation and expression of lysosomal markers were decreased in the brains of AD patients. In the brain of APP/PS1 double transgenic mice, APs did not accumulate before the formation of SPs but accumulated along with the deposition of SPs, as well as the level of lysosomal markers cathepsin B and Lamp1 protein decreased significantly. In the brains of APP/PS1/LC3 triple - transgenic mice, the number of APs increased with age, but the number of ALs did not increase accordingly. The activation of autophagy is mainly due to the increase in Aβ rather than the overexpression of mutated APP gene. However, both the treatment with exogenous Aβ_25-35 and the mutation of the endogenous APP gene blocked the fusion of APs with lysosomes and decreased lysosomal functioning in AD model cells, which may be the main mechanism of autophagy dysregulation in AD.

MAPT/Tau accumulation represses autophagy flux by disrupting IST1-regulated ESCRT-III complex formation: a vicious cycle in Alzheimer neurodegeneration

Macroautophagy/autophagy deficit induces intracellular MAPT/tau accumulation, the hallmark pathology in Alzheimer disease (AD) and other tauopathies; however, the reverse role of MAPT accumulation in autophagy and neurodegeneration is not clear. Here, we found that overexpression of human wild-type full-length MAPT, which models MAPT pathologies as seen in sporadic AD patients, induced autophagy deficits via repression of autophagosome-lysosome fusion leading to significantly increased LC3 (microtubule-associated protein 1 light chain 3)-II and SQSTM1/p62 (sequestosome 1) protein levels with autophagosome accumulation. At the molecular level, intracellular MAPT aggregation inhibited expression of IST1 (IST1 factor associated with ESCRT-III), a positive modulator for the formation of ESCRT (the Endosomal Sorting Complex Required for Transport) complex that is required for autophagosome-lysosome fusion. Upregulating IST1 in human MAPT transgenic mice attenuated autophagy deficit with reduced MAPT aggregation and ameliorated synaptic plasticity and cognitive functions, while downregulating IST1 per se induced autophagy deficit with impaired synapse and cognitive function in naïve mice. IST1 can facilitate association of CHMP2B (charged multivesicular body protein 2B) and CHMP4B/SNF7-2 to form ESCRT-III complex, while lack of IST1 impeded the complex formation. Finally, we demonstrate that MAPT accumulation suppresses IST1 transcription with the mechanisms involving the ANP32A-regulated mask of histone acetylation. Our findings suggest that the AD-like MAPT accumulation can repress autophagosome-lysosome fusion by deregulating ANP32A-INHAT-IST1-ESCRT-III pathway, which also reveals a vicious cycle of MAPT accumulation and autophagy deficit in the chronic course of AD neurodegeneration.Abbreviations: AAV: adeno-associated virus; Aβ: β-amyloid; aCSF: artificial cerebrospinal fluid; AD: Alzheimer disease; ANP32A: acidic nuclear phosphoprotein 32 family member A; ATG: autophagy related; AVs: autophagic vacuoles; CEBPB: CCAAT enhancer binding protein beta; CHMP: charged multivesicular body protein; DMEM: Dulbecco's modified eagle's medium; EBSS: Earle's balanced salt solution; EGFR: epidermal growth factor receptor; ESCRT: endosomal sorting complex required for transport; fEPSPs: field excitatory postsynaptic potentials; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GSK3B: glycogen synthase kinase 3 beta; HAT: histone acetyl transferase; HDAC: histone deacetylase; INHAT: inhibitor of histone acetyl transferase; IST1: IST1 factor associated with ESCRT-III; LAMP2: lysosomal associated membrane protein 2; LTP: long-term potentiation; MAP1LC3: microtubule associated protein 1 light chain 3; MAPT/tau: microtubule associated protein tau; MVB: multivesicular bodies; MWM: Morris water maze; PBS: phosphate-buffered saline solution; RAB7: member RAS oncogene family; SNAREs: soluble N-ethylmaleimide-sensitive factor attachment protein receptors; SQSTM1/p62: sequestosome 1.

Axonal Degeneration in Tauopathies: Disease Relevance and Underlying Mechanisms

Tauopathies are a diverse group of diseases featuring progressive dying-back neurodegeneration of specific neuronal populations in association with accumulation of abnormal forms of the microtubule-associated protein tau. It is well-established that the clinical symptoms characteristic of tauopathies correlate with deficits in synaptic function and neuritic connectivity early in the course of disease, but mechanisms underlying these critical pathogenic events are not fully understood. Biochemical in vitro evidence fueled the widespread notion that microtubule stabilization represents tau's primary biological role and that the marked atrophy of neurites observed in tauopathies results from loss of microtubule stability. However, this notion contrasts with the mild phenotype associated with tau deletion. Instead, an analysis of cellular hallmarks common to different tauopathies, including aberrant patterns of protein phosphorylation and early degeneration of axons, suggests that alterations in kinase-based signaling pathways and deficits in axonal transport (AT) associated with such alterations contribute to the loss of neuronal connectivity triggered by pathogenic forms of tau. Here, we review a body of literature providing evidence that axonal pathology represents an early and common pathogenic event among human tauopathies. Observations of axonal degeneration in animal models of specific tauopathies are discussed and similarities to human disease highlighted. Finally, we discuss potential mechanistic pathways other than microtubule destabilization by which disease-related forms of tau may promote axonopathy.

The role of autophagy in modulation of neuroinflammation in microglia

Microglia have multiple functions in regulating homeostasis in the central nervous system (CNS), and microglial inflammation is thought to play a role in the etiology of the neurodegenerative diseases. When endogenous or exogenous stimuli trigger disorders in microenvironmental homeostasis in CNS, microglia critically determine the fate of other neural cells. Recently, it was reported that autophagy might influence inflammation and activation of microglia. Though the interaction between autophagy and macrophages has been reported and reviewed in length, the role of autophagy in microglia has yet to be reviewed. Herein, we will highlight recent advances on the emerging role of autophagy in microglia, focusing on the regulation of autophagy during microglial inflammation, and the possible mechanism involved.

Gene Therapy Models of Alzheimer's Disease and Other Dementias

Dementias are among the most common neurological disorders, and Alzheimer's disease (AD) is the most common cause of dementia worldwide. AD remains a looming health crisis despite great efforts to learn the mechanisms surrounding the neuron dysfunction and neurodegeneration that accompanies AD primarily in the medial temporal lobe. In addition to AD, a group of diseases known as frontotemporal dementias (FTDs) are degenerative diseases involving atrophy and degeneration in the frontal and temporal lobe regions. Importantly, AD and a number of FTDs are collectively known as tauopathies due to the abundant accumulation of pathological tau inclusions in the brain. The precise role tau plays in disease pathogenesis remains an area of strong research focus. A critical component to effectively study any human disease is the availability of models that recapitulate key features of the disease. Accordingly, a number of animal models are currently being pursued to fill the current gaps in our knowledge of the causes of dementias and to develop effective therapeutics. Recent developments in gene therapy-based approaches, particularly in recombinant adeno-associated viruses (rAAVs), have provided new tools to study AD and other related neurodegenerative disorders. Additionally, gene therapy approaches have emerged as an intriguing possibility for treating these diseases in humans. This chapter explores the current state of rAAV models of AD and other dementias, discuss recent efforts to improve these models, and describe current and future possibilities in the use of rAAVs and other viruses in treatments of disease.

Neuronal Cx3cr1 Deficiency Protects against Amyloid β-Induced Neurotoxicity

Cx3cr1, the receptor for the chemokine Cx3cl1 (fractalkine), has been implicated in the progression and severity of Alzheimer's disease-like pathology in mice, but the underlying mechanisms remain unclear. A complicating factor is that Cx3cr1 has been demonstrated in both neurons and microglia. Here, we have dissected the differences between neuronal and microglial Cx3cr1, specifically by comparing direct amyloid-β-induced toxicity in cultured, mature, microglia-depleted hippocampal neurons from wild-type and Cx3cr1-/- mice. Wild-type neurons expressed both Cx3cl1 and Cx3cr1 and released Cx3cl1 in response to amyloid-β. Knockout of neuronal Cx3cr1 abated amyloid-β-induced lactate dehydrogenase release. Furthermore, amyloid-β differentially induced depression of pre- and postsynaptic components of miniature excitatory postsynaptic currents, in a peptide conformation-dependent manner. Knockout of neuronal Cx3cr1 abated effects of both amyloid-β conformational states, which were differentiable by aggregation kinetics and peptide morphology. We obtained similar results after both acute and chronic treatment of cultured neurons with the Cx3cr1 antagonist F1. Thus, neuronal Cx3cr1 may impact Alzheimer's disease-like pathology by modulating conformational state-dependent amyloid-β-induced synaptotoxicity.

Tau deletion impairs intracellular β-amyloid-42 clearance and leads to more extracellular plaque deposition in gene transfer models

Background

Tau is an axonal protein that binds to and regulates microtubule function. Hyper-phosphorylation of Tau reduces its binding to microtubules and it is associated with β-amyloid deposition in Alzheimer’s disease. Paradoxically, Tau reduction may prevent β-amyloid pathology, raising the possibility that Tau mediates intracellular Aβ clearance. The current studies investigated the role of Tau in autophagic and proteasomal intracellular Aβ1-42 clearance and the subsequent effect on plaque deposition.

Results

Tau deletion impaired Aβ clearance via autophagy, but not the proteasome, while introduction of wild type human Tau into Tau^−/− mice partially restored autophagic clearance of Aβ1-42, suggesting that exogenous Tau expression can support autophagic Aβ1-42 clearance. Tau deletion impaired autophagic flux and resulted in Aβ1-42 accumulation in pre-lysosomal autophagic vacuoles, affecting Aβ1-42 deposition into the lysosome. This autophagic defect was associated with decreased intracellular Aβ1-42 and increased plaque load in Tau^−/− mice, which displayed less cell death. Nilotinib, an Abl tyrosine kinase inhibitor that promotes autophagic clearance mechanisms, reduced Aβ1-42 only when exogenous human Tau was expressed in Tau^−/− mice.

Conclusions

These studies demonstrate that Tau deletion affects intracellular Aβ1-42 clearance, leading to extracellular plaque.

Electronic supplementary material

The online version of this article (doi:10.1186/1750-1326-9-46) contains supplementary material, which is available to authorized users.

Tyrosine Kinase Inhibition Regulates Early Systemic Immune Changes and Modulates the Neuroimmune Response in α-Synucleinopathy

Objectives

Neuro-inflammation is common in α-Synucleinopathies and Tauopathies; and evidence suggests a link between the tyrosine kinase Abl and neurodegeneration. Abl upregulates α-Synuclein and promotes Tau hyper-phosphorylation (p-Tau), while Abl inhibitors facilitate autophagic clearance.

Methods

A model of α-Synucleinopathy harboring human mutant A53T α-Synuclein and exhibits concomitant increase in murine p-Tau was used to determine the immunological response to Abl inhibition.

Results

Age-dependent alterations of brain immunity, including loss of IL-10 and decreased levels of IL-2 and IL-3 were observed in old A53T mice. Brain CCL2 and CCL5 were decreased, but CX3CL1 remained constantly elevated. Young A53T mice exhibited differential systemic and central immune profiles in parallel with increased blood markers of adaptive immunity, suggesting an early systemic immune response. Tyrosine kinase inhibitors (TKIs), including nilotinib and bosutinib reduced brain and peripheral α-Synuclein and p-Tau and modulated blood immunological responses. TKIs did not affect brain IL-10, but they changed the levels of all measured blood immune markers, except CX3CL1. TKIs altered microglia morphology and reduced the number of astrocyte and dendritic cells, suggesting beneficial regulation of microglia.

Conclusions

These data indicate that tyrosine kinase inhibition affects neuro-inflammation via early changes of the peripheral immune profile, leading to modulation of the neuro-immune response to α-Synuclein and p-Tau.