Suppression of the JAK/STAT Pathway Inhibits Neuroinflammation in the Line 61-PFF Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is characterized by neuroinflammation, progressive loss of dopaminergic neurons, and accumulation of a-synuclein (a-Syn) into insoluble aggregates called Lewy pathology. The Line 61 a-Syn mouse is an established preclinical model of PD; Thy-1 is used to promote human a-Syn expression, and features of sporadic PD develop at 9-18 months of age. To accelerate the PD phenotypes, we injected sonicated human a-Syn preformed fibrils (PFFs) into the striatum, which produced phospho-Syn (p-a-Syn) inclusions in the substantia nigra pars compacta and significantly increased MHC Class II-positive immune cells. Additionally, there was enhanced infiltration and activation of innate and adaptive immune cells in the midbrain. We then used this new model, Line 61-PFF, to investigate the effect of inhibiting the JAK/STAT signaling pathway, which is critical for regulation of innate and adaptive immune responses. After administration of the JAK1/2 inhibitor AZD1480, immunofluorescence staining showed a significant decrease in p-a-Syn inclusions and MHC Class II expression. Flow cytometry showed reduced infiltration of CD4 + T-cells, CD8 + T-cells, CD19 + B-cells, dendritic cells, macrophages, and endogenous microglia into the midbrain. Importantly, single-cell RNA-Sequencing analysis of CD45 + cells from the midbrain identified 9 microglia clusters, 5 monocyte/macrophage (MM) clusters, and 5 T-cell (T) clusters, in which potentially pathogenic MM4 and T3 clusters were associated with neuroinflammatory responses in Line 61-PFF mice. AZD1480 treatment reduced cell numbers and cluster-specific expression of the antigen-presentation genes H2-Eb1 , H2-Aa , H2-Ab1 , and Cd74 in the MM4 cluster and proinflammatory genes such as Tnf , Il1b , C1qa , and C1qc in the T3 cluster. Together, these results indicate that inhibiting the JAK/STAT pathway suppresses the activation and infiltration of innate and adaptive cells, reducing neuroinflammation in the Line 61-PFF mouse model.

Neuromelanin as a nidus for neurodegeneration

This scientific commentary refers to ‘Neuromelanin accumulation drives endogenous synucleinopathy in non-human primates’ by Chocarro et al. (https://doi.org/10.1093/brain/awad331).

Alpha-synuclein in Parkinson's disease and other synucleinopathies: from overt neurodegeneration back to early synaptic dysfunction

Although the discovery of the critical role of α-synuclein (α-syn) in the pathogenesis of Parkinson's disease (PD) is now twenty-five years old, it still represents a milestone in PD research. Abnormal forms of α-syn trigger selective and progressive neuronal death through mitochondrial impairment, lysosomal dysfunction, and alteration of calcium homeostasis not only in PD but also in other α-syn-related neurodegenerative disorders such as dementia with Lewy bodies, multiple system atrophy, pure autonomic failure, and REM sleep behavior disorder. Furthermore, α-syn-dependent early synaptic and plastic alterations and the underlying mechanisms preceding overt neurodegeneration have attracted great interest. In particular, the presence of early inflammation in experimental models and PD patients, occurring before deposition and spreading of α-syn, suggests a mechanistic link between inflammation and synaptic dysfunction. The knowledge of these early mechanisms is of seminal importance to support the research on reliable biomarkers to precociously identify the disease and possible disease-modifying therapies targeting α-syn. In this review, we will discuss these critical issues, providing a state of the art of the role of this protein in early PD and other synucleinopathies.

Multiplicity of α-Synuclein Aggregated Species and Their Possible Roles in Disease

α-Synuclein amyloid aggregation is a defining molecular feature of Parkinson's disease, Lewy body dementia, and multiple system atrophy, but can also be found in other neurodegenerative disorders such as Alzheimer's disease. The process of α-synuclein aggregation can be initiated through alternative nucleation mechanisms and dominated by different secondary processes giving rise to multiple amyloid polymorphs and intermediate species. Some aggregated species have more inherent abilities to induce cellular stress and toxicity, while others seem to be more potent in propagating neurodegeneration. The preference for particular types of polymorphs depends on the solution conditions and the cellular microenvironment that the protein encounters, which is likely related to the distinct cellular locations of α-synuclein inclusions in different synucleinopathies, and the existence of disease-specific amyloid polymorphs. In this review, we discuss our current understanding on the nature and structure of the various types of α-synuclein aggregated species and their possible roles in pathology. Precisely defining these distinct α-synuclein species will contribute to understanding the molecular origins of these disorders, developing accurate diagnoses, and designing effective therapeutic interventions for these highly debilitating neurodegenerative diseases.

Neuronal vulnerability in Parkinson disease: Should the focus be on axons and synaptic terminals?

While current effective therapies are available for the symptomatic control of PD, treatments to halt the progressive neurodegeneration still do not exist. Loss of dopamine neurons in the SNc and dopamine terminals in the striatum drive the motor features of PD. Multiple lines of research point to several pathways which may contribute to dopaminergic neurodegeneration. These pathways include extensive axonal arborization, mitochondrial dysfunction, dopamine's biochemical properties, abnormal protein accumulation of α-synuclein, defective autophagy and lysosomal degradation, and synaptic impairment. Thus, understanding the essential features and mechanisms of dopaminergic neuronal vulnerability is a major scientific challenge and highlights an outstanding need for fostering effective therapies against neurodegeneration in PD. This article, which arose from the Movement Disorders 2018 Conference, discusses and reviews the possible mechanisms underlying neuronal vulnerability and potential therapeutic approaches in PD. © 2019 International Parkinson and Movement Disorder Society.

Prion-like propagation of pathology in Parkinson disease

Over 100 years ago, Lewy bodies and Lewy neurites were defined as a pathologic hallmark of Parkinson disease. Eighty years later, α-synuclein was found to be the primary component of these inclusions. Emerging evidence suggests that α-synuclein pathology propagates across interconnected networks throughout the nervous system in a prion-like manner. Pathologic α-synuclein seeds aggregation of native α-synuclein, resulting in the formation of insoluble inclusions. These seeds can propagate within the neuron and to interconnected neurons, resulting in the spread of pathology throughout the brain. Here, we discuss how the findings that α-synuclein pathology spreads throughout the nervous system has revolutionized our understanding about Parkinson disease pathogenesis and resulted in the development of novel therapeutic strategies to halt disease progression.

Trehalose does not improve neuronal survival on exposure to alpha-synuclein pre-formed fibrils

Parkinson's disease is a debilitating neurodegenerative disorder that is pathologically characterized by intracellular inclusions comprised primarily of alpha-synuclein (αSyn) that can also be transmitted from neuron to neuron. Several lines of evidence suggest that these inclusions cause neurodegeneration. Thus exploring strategies to improve neuronal survival in neurons with αSyn aggregates is critical. Previously, exposure to αSyn pre-formed fibrils (PFFs) has been shown to induce aggregation of endogenous αSyn resulting in cell death that is exacerbated by either starvation or inhibition of mTOR by rapamycin, both of which are able to induce autophagy, an intracellular protein degradation pathway. Since mTOR inhibition may also inhibit protein synthesis and starvation itself can be detrimental to neuronal survival, we investigated the effects of autophagy induction on neurons with αSyn inclusions by a starvation and mTOR-independent autophagy induction mechanism. We exposed mouse primary cortical neurons to PFFs to induce inclusion formation in the presence and absence of the disaccharide trehalose, which has been proposed to induce autophagy and stimulate lysosomal biogenesis. As expected, we observed that on exposure to PFFs, there was increased abundance of pS129-αSyn aggregates and cell death. Trehalose alone increased LC3-II levels, consistent with increased autophagosome levels that remained elevated with PFF exposure. Interestingly, trehalose alone increased cell viability over a 14-d time course. Trehalose was also able to restore cell viability to control levels, but PFFs still exhibited toxic effects on the cells. These data provide essential information regarding effects of trehalose on αSyn accumulation and neuronal survival on exposure to PFF.

Transforming Growth Factor Beta (TGF-β) Is a Muscle Biomarker of Disease Progression in ALS and Correlates with Smad Expression

We recently identified Smads1, 5 and 8 as muscle biomarkers in human ALS. In the ALS mouse, these markers are elevated and track disease progression. Smads are signal transducers and become activated upon receptor engagement of ligands from the TGF-β superfamily. Here, we sought to characterize ligands linked to activation of Smads in ALS muscle and their role as biomarkers of disease progression. RNA sequencing data of ALS muscle samples were mined for TGF-β superfamily ligands. Candidate targets were validated by qRT-PCR in a large cohort of human ALS muscle biopsy samples and in the G93A SOD1 mouse. Protein expression was evaluated by Western blot, ELISA and immunohistochemistry. C2C12 muscle cells were used to assess Smad activation and induction. TGF-β1, 2 and 3 mRNAs were increased in ALS muscle samples compared to controls and correlated with muscle strength and Smads1, 2, 5 and 8. In the G93A SOD1 mouse, the temporal pattern of TGF-β expression paralleled the Smads and increased with disease progression. TGF-β1 immunoreactivity was detected in mononuclear cells surrounding muscle fibers in ALS samples. In muscle cells, TGF-β ligands were capable of activating Smads. In conclusion, TGF-β1, 2 and 3 are novel biomarkers of ALS in skeletal muscle. Their correlation with weakness in human ALS and their progressive increase with advancing disease in the ALS mouse suggest that they, as with the Smads, can track disease progression. These ligands are capable of upregulating and activating Smads and thus may contribute to the Smad signaling pathway in ALS muscle.

Reduction of synaptojanin 1 accelerates Aβ clearance and attenuates cognitive deterioration in an Alzheimer mouse model

Recent studies link synaptojanin 1 (synj1), the main phosphoinositol (4,5)-biphosphate phosphatase (PI(4,5)P2-degrading enzyme) in the brain and synapses, to Alzheimer disease. Here we report a novel mechanism by which synj1 reversely regulates cellular clearance of amyloid-β (Aβ). Genetic down-regulation of synj1 reduces both extracellular and intracellular Aβ levels in N2a cells stably expressing the Swedish mutant of amyloid precursor protein (APP). Moreover, synj1 haploinsufficiency in an Alzheimer disease transgenic mouse model expressing the Swedish mutant APP and the presenilin-1 mutant ΔE9 reduces amyloid plaque load, as well as Aβ40 and Aβ42 levels in hippocampus of 9-month-old animals. Reduced expression of synj1 attenuates cognitive deficits in these transgenic mice. However, reduction of synj1 does not affect levels of full-length APP and the C-terminal fragment, suggesting that Aβ generation by β- and γ-secretase cleavage is not affected. Instead, synj1 knockdown increases Aβ uptake and cellular degradation through accelerated delivery to lysosomes. These effects are partially dependent upon elevated PI(4,5)P2 with synj1 down-regulation. In summary, our data suggest a novel mechanism by which reduction of a PI(4,5)P2-degrading enzyme, synj1, improves amyloid-induced neuropathology and behavior deficits through accelerating cellular Aβ clearance.

Role of dynamin, synaptojanin, and endophilin in podocyte foot processes

Podocytes are specialized cells that play an integral role in the renal glomerular filtration barrier via their foot processes. The foot processes form a highly organized structure, the disruption of which causes nephrotic syndrome. Interestingly, several similarities have been observed between mechanisms that govern podocyte organization and mechanisms that mediate neuronal synapse development. Dynamin, synaptojanin, and endophilin are functional partners in synaptic vesicle recycling via interconnected actions in clathrin-mediated endocytosis and actin dynamics in neurons. A role of dynamin in the maintenance of the kidney filtration barrier via an action on the actin cytoskeleton of podocytes was suggested. Here we used a conditional double-KO of dynamin 1 (Dnm1) and Dnm2 in mouse podocytes to confirm dynamin's role in podocyte foot process maintenance. In addition, we demonstrated that while synaptojanin 1 (Synj1) KO mice and endophilin 1 (Sh3gl2), endophilin 2 (Sh3gl1), and endophilin 3 (Sh3gl3) triple-KO mice had grossly normal embryonic development, these mutants failed to establish a normal filtration barrier and exhibited severe proteinuria due to abnormal podocyte foot process formation. These results strongly implicate a protein network that functions at the interface between endocytosis and actin at neuronal synapses in the formation and maintenance of the kidney glomerular filtration barrier.

Pharmacological rescue of mitochondrial deficits in iPSC-derived neural cells from patients with familial Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disorder caused by genetic and environmental factors that results in degeneration of the nigrostriatal dopaminergic pathway in the brain. We analyzed neural cells generated from induced pluripotent stem cells (iPSCs) derived from PD patients and presymptomatic individuals carrying mutations in the PINK1 (PTEN-induced putative kinase 1) and LRRK2 (leucine-rich repeat kinase 2) genes, and compared them to those of healthy control subjects. We measured several aspects of mitochondrial responses in the iPSC-derived neural cells including production of reactive oxygen species, mitochondrial respiration, proton leakage, and intraneuronal movement of mitochondria. Cellular vulnerability associated with mitochondrial dysfunction in iPSC-derived neural cells from familial PD patients and at-risk individuals could be rescued with coenzyme Q(10), rapamycin, or the LRRK2 kinase inhibitor GW5074. Analysis of mitochondrial responses in iPSC-derived neural cells from PD patients carrying different mutations provides insight into convergence of cellular disease mechanisms between different familial forms of PD and highlights the importance of oxidative stress and mitochondrial dysfunction in this neurodegenerative disease.

Constitutive activated Cdc42-associated kinase (Ack) phosphorylation at arrested endocytic clathrin-coated pits of cells that lack dynamin

In cells in which clathrin-mediated endocytosis is arrested before fission by depleting dynamin, the major change in tyrosine phosphorylation is the increased phosphorylation/activation of Ack, a tyrosine kinase. Our finding reveals a link between the progression of clathrin-coated pits to endocytic vesicles and an activation-deactivation cycle of Ack.

Clathrin-mediated endocytosis is a fundamental cellular process conserved from yeast to mammals and is an important endocytic route for the internalization of many specific cargos, including activated growth factor receptors. Here we examined changes in tyrosine phosphorylation, a representative output of growth factor receptor signaling, in cells in which endocytic clathrin-coated pits are frozen at a deeply invaginated state, that is, cells that lack dynamin (fibroblasts from dynamin 1, dynamin 2 double conditional knockout mice). The major change observed in these cells relative to wild-type cells was an increase in the phosphorylation state, and thus activation, of activated Cdc42-associated kinase (Ack), a nonreceptor tyrosine kinase. Ack is concentrated at clathrin-coated pits, and binds clathrin heavy chain via two clathrin boxes. RNA interference–based approaches and pharmacological manipulations further demonstrated that the phosphorylation of Ack requires both clathrin assembly into endocytic clathrin-coated pits and active Cdc42. These findings reveal a link between progression of clathrin-coated pits to endocytic vesicles and an activation–deactivation cycle of Ack.

The beta- and gamma-isoforms of type I PIP5K regulate distinct stages of Ca2+ signaling in mast cells

Crosslinking of IgE receptors by antigen initiates Ca2+ mobilization in mast cells by activating phospholipase-C gamma-mediated hydrolysis of phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P2]. The resulting inositol 1,4,5-trisphosphate-mediated Ca2+ release from the endoplasmic reticulum (ER) activates store-operated Ca2+ entry, which is necessary for exocytotic release of inflammatory mediators. To investigate roles for PtdIns(4,5)P2-synthesizing isozymes of the type I phosphatidylinositol 4-phosphate 5-kinase family (PIP5K-I) in mast cell signaling, we compared the ectopic expression of wild-type and catalytically inactive PIP5K-I beta in RBL-2H3 mast cells. Surprisingly, both antigen and thapsigargin-stimulated Ca2+ influx were reduced by overexpression of active PIP5K-I beta, whereas antigen-stimulated Ca2+ release from ER stores was unaffected. Consistent with these results, Ca2+ entry stimulated by antigen or thapsigargin was enhanced by expression of a plasma-membrane-associated inositol polyphosphate 5'-phosphatase, whereas antigen-stimulated Ca2+ release from stores was reduced. To investigate the role of PIP5K-I gamma in antigen-stimulated Ca2+ mobilization, we used bone-marrow-derived mast cells from PIP5K-I gamma(-/-) mice. Antigen-stimulated Ca2+ release from ER stores was substantially reduced in the absence of PIP5K-I gamma, but thapsigargin-mediated Ca2+ entry was unaffected. In summary, PIP5K-I gamma positively regulates antigen-stimulated Ca2+ release from ER stores, whereas PIP5K-I beta negatively regulates store-operated Ca2+ entry, suggesting that these different PIP5K-I isoforms synthesize functionally distinct pools of PtdIns(4,5)P2 at the plasma membrane.

Wnt3a-mediated formation of phosphatidylinositol 4,5-bisphosphate regulates LRP6 phosphorylation

The canonical Wnt-beta-catenin signaling pathway is initiated by inducing phosphorylation of one of the Wnt receptors, low-density lipoprotein receptor-related protein 6 (LRP6), at threonine residue 1479 (Thr1479) and serine residue 1490 (Ser1490). By screening a human kinase small interfering RNA library, we identified phosphatidylinositol 4-kinase type II alpha and phosphatidylinositol-4-phosphate 5-kinase type I (PIP5KI) as required for Wnt3a-induced LRP6 phosphorylation at Ser1490 in mammalian cells and confirmed that these kinases are important for Wnt signaling in Xenopus embryos. Wnt3a stimulates the formation of phosphatidylinositol 4,5-bisphosphates [PtdIns (4,5)P2] through frizzled and dishevelled, the latter of which directly interacted with and activated PIP5KI. In turn, PtdIns (4,5)P2 regulated phosphorylation of LRP6 at Thr1479 and Ser1490. Therefore, our study reveals a signaling mechanism for Wnt to regulate LRP6 phosphorylation.

Arf family GTPases: roles in membrane traffic and microtubule dynamics

Database mining and phylogenetic analysis of the Arf (ADP-ribosylation factor) superfamily revealed the presence in mammals of at least 22 members, including the six Arfs, two Sars and 14 Arl (Arf-like) proteins. At least six Arf family members were found in very early eukaryotes, including orthologues of Arf, Sar, Arl2, Arl3, Arl6 and Arl8. While roles for Arfs in membrane traffic are well known, those for most of the Arls remain unknown. Depletion in cells of the most closely related human Arf proteins, Arf1-Arf5, reveals specificities among their cellular roles and suggests that they may function in pairs at different steps in endocytic and secretory membrane traffic. In addition, recent results from a number of laboratories suggest that several of the Arl proteins may be involved in different aspects of microtubule-dependent functions. Thus, a second major role for Arf family GTPases, that of regulating microtubules, is emerging. Because membrane traffic is often dependent upon movement of vesicles along microtubules this raises the possibility that these two fundamental functions of Arf family members, regulation of vesicle traffic and microtubule dynamics, diverged from one function of Arfs in the earliest cells that has continued to branch and allow additional levels of regulation.