The Parkinson's Disease Composite of Executive Functioning: A Measure for Detecting Cognitive Decline in Clinical Trials.

BACKGROUND AND OBJECTIVES: Executive functioning is one of the first domains to be impaired in Parkinson disease (PD), and the majority of patients with PD eventually develop dementia. Thus, developing a cognitive endpoint measure specifically assessing executive functioning is critical for PD clinical trials. The objective of this study was to develop a cognitive composite measure that is sensitive to decline in executive functioning for use in PD clinical trials. METHODS: We used cross-sectional and longitudinal follow-up data from PD participants enrolled in the PD Cognitive Genetics Consortium, a multicenter setting focused on PD. All PD participants with Trail Making Test, Digit Symbol, Letter-Number Sequencing, Semantic Fluency, and Phonemic Fluency neuropsychological data collected from March 2010 to February 2020 were included. Baseline executive functioning data were used to create the Parkinson's Disease Composite of Executive Functioning (PaCEF) through confirmatory factor analysis. We examined the changes in the PaCEF over time, how well baseline PaCEF predicts time to cognitive progression, and the required sample size estimates for PD clinical trials. PaCEF results were compared with the Montreal Cognitive Assessment (MoCA), individual tests forming the PaCEF, and tests of visuospatial, language, and memory functioning. RESULTS: A total of 841 participants (251 no cognitive impairment [NCI], 480 mild cognitive impairment [MCI], and 110 dementia) with baseline data were included, of which the mean (SD) age was 67.1 (8.9) years and 270 were women (32%). Five hundred forty five PD participants had longitudinal neuropsychological data spanning 9 years (mean [SD] 4.5 [2.2] years) and were included in analyses examining cognitive decline. A 1-factor model of executive functioning with excellent fit (comparative fit index = 0.993, Tucker-Lewis index = 0.989, and root mean square error of approximation = 0.044) was used to calculate the PaCEF. The average annual change in PaCEF ranged from 0.246 points per year for PD-NCI participants who remained cognitively unimpaired to -0.821 points per year for PD-MCI participants who progressed to dementia. For PD-MCI, baseline PaCEF, but not baseline MoCA, significantly predicted time to dementia. Sample size estimates were 69%-73% smaller for PD-NCI trials and 16%-19% smaller for PD-MCI trials when using the PaCEF rather than MoCA as the endpoint. DISCUSSION: The PaCEF is a sensitive measure of executive functioning decline in PD and will be especially beneficial for PD clinical trials.

Poly(ADP-ribose) mediates bioenergetic defects and redox imbalance in neurons following oxygen and glucose deprivation.

PARP-1 over-activation results in cell death via excessive PAR generation in different cell types, including neurons following brain ischemia. Glycolysis, mitochondrial function, and redox balance are key cellular processes altered in brain ischemia. Studies show that PAR generated after PARP-1 over-activation can bind hexokinase-1 (HK-1) and result in glycolytic defects and subsequent mitochondrial dysfunction. HK-1 is the neuronal hexokinase and catalyzes the first reaction of glycolysis, converting glucose to glucose-6-phosphate (G6P), a common substrate for glycolysis, and the pentose phosphate pathway (PPP). PPP is critical in maintaining NADPH and GSH levels via G6P dehydrogenase activity. Therefore, defects in HK-1 will not only decrease cellular bioenergetics but will also cause redox imbalance due to the depletion of GSH. In brain ischemia, whether PAR-mediated inhibition of HK-1 results in bioenergetics defects and redox imbalance is not known. We used oxygen-glucose deprivation (OGD) in mouse cortical neurons to mimic brain ischemia in neuronal cultures and observed that PARP-1 activation via PAR formation alters glycolysis, mitochondrial function, and redox homeostasis in neurons. We used pharmacological inhibition of PARP-1 and adenoviral-mediated overexpression of wild-type HK-1 (wtHK-1) and PAR-binding mutant HK-1 (pbmHK-1). Our data show that PAR inhibition or overexpression of HK-1 significantly improves glycolysis, mitochondrial function, redox homeostasis, and cell survival in mouse cortical neurons exposed to OGD. These results suggest that PAR binding and inhibition of HK-1 during OGD drive bioenergetic defects in neurons due to inhibition of glycolysis and impairment of mitochondrial function.

PARIS undergoes liquid-liquid phase separation and poly(ADP-ribose)-mediated solidification.

ZNF746 was identified as parkin-interacting substrate (PARIS). Investigating its pathophysiological properties, we find that PARIS undergoes liquid-liquid phase separation (LLPS) and amorphous solid formation. The N-terminal low complexity domain 1 (LCD1) of PARIS is required for LLPS, whereas the C-terminal prion-like domain (PrLD) drives the transition from liquid to solid phase. In addition, we observe that poly(ADP-ribose) (PAR) strongly binds to the C-terminus of PARIS near the PrLD, accelerating its LLPS and solidification. N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced PAR formation leads to PARIS oligomerization in human iPSC-derived dopaminergic neurons that is prevented by the PARP inhibitor, ABT-888. Furthermore, SDS-resistant PARIS species are observed in the substantia nigra (SN) of aged mice overexpressing wild-type PARIS, but not with a PAR binding-deficient PARIS mutant. PARIS solidification is also found in the SN of mice injected with preformed fibrils of α-synuclein (α-syn PFF) and adult mice with a conditional knockout (KO) of parkin, but not if α-syn PFF is injected into mice deficient for PARP1. Herein, we demonstrate that PARIS undergoes LLPS and PAR-mediated solidification in models of Parkinson's disease.

Atp7b-dependent choroid plexus dysfunction causes transient copper deficit and metabolic changes in the developing mouse brain.

Copper (Cu) has a multifaceted role in brain development, function, and metabolism. Two homologous Cu transporters, Atp7a (Menkes disease protein) and Atp7b (Wilson disease protein), maintain Cu homeostasis in the tissue. Atp7a mediates Cu entry into the brain and activates Cu-dependent enzymes, whereas the role of Atp7b is less clear. We show that during postnatal development Atp7b is necessary for normal morphology and function of choroid plexus (ChPl). Inactivation of Atp7b causes reorganization of ChPl' cytoskeleton and cell-cell contacts, loss of Slc31a1 from the apical membrane, and a decrease in the length and number of microvilli and cilia. In ChPl lacking Atp7b, Atp7a is upregulated but remains intracellular, which limits Cu transport into the brain and results in significant Cu deficit, which is reversed only in older animals. Cu deficiency is associated with down-regulation of Atp7a in locus coeruleus and catecholamine imbalance, despite normal expression of dopamine-ß-hydroxylase. In addition, there are notable changes in the brain lipidome, which can be attributed to inhibition of diacylglyceride-to-phosphatidylethanolamine conversion. These results identify the new role for Atp7b in developing brain and identify metabolic changes that could be exacerbated by Cu chelation therapy.

The c-Abl inhibitor IkT-148009 suppresses neurodegeneration in mouse models of heritable and sporadic Parkinson's disease.

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease of the central nervous system, with an estimated 5,000,000 cases worldwide. PD pathology is characterized by the accumulation of misfolded α-synuclein, which is thought to play a critical role in the pathogenesis of the disease. Animal models of PD suggest that activation of Abelson tyrosine kinase (c-Abl) plays an essential role in the initiation and progression of α-synuclein pathology and initiates processes leading to degeneration of dopaminergic and nondopaminergic neurons. Given the potential role of c-Abl in PD, a c-Abl inhibitor library was developed to identify orally bioavailable c-Abl inhibitors capable of crossing the blood-brain barrier based on predefined characteristics, leading to the discovery of IkT-148009. IkT-148009, a brain-penetrant c-Abl inhibitor with a favorable toxicology profile, was analyzed for therapeutic potential in animal models of slowly progressive, α-synuclein-dependent PD. In mouse models of both inherited and sporadic PD, IkT-148009 suppressed c-Abl activation to baseline and substantially protected dopaminergic neurons from degeneration when administered therapeutically by once daily oral gavage beginning 4 weeks after disease initiation. Recovery of motor function in PD mice occurred within 8 weeks of initiating treatment concomitantly with a reduction in α-synuclein pathology in the mouse brain. These findings suggest that IkT-148009 may have potential as a disease-modifying therapy in PD.

α-Synuclein pathology disrupts mitochondrial function in dopaminergic and cholinergic neurons at-risk in Parkinson's disease.

Background: Pathological accumulation of aggregated α-synuclein (aSYN) is a common feature of Parkinson's disease (PD). However, the mechanisms by which intracellular aSYN pathology contributes to dysfunction and degeneration of neurons in the brain are still unclear. A potentially relevant target of aSYN is the mitochondrion. To test this hypothesis, genetic and physiological methods were used to monitor mitochondrial function in substantia nigra pars compacta (SNc) dopaminergic and pedunculopontine nucleus (PPN) cholinergic neurons after stereotaxic injection of aSYN pre-formed fibrils (PFFs) into the mouse brain. Methods: aSYN PPFs were stereotaxically injected into the SNc or PPN of mice. Twelve weeks later, mice were studied using a combination of approaches, including immunocytochemical analysis, cell- type specific transcriptomic profiling, electron microscopy, electrophysiology and two-photon-laser- scanning microscopy of genetically encoded sensors for bioenergetic and redox status. Results: In addition to inducing a significant neuronal loss, SNc injection of PFFs induced the formation of intracellular, phosphorylated aSYN aggregates selectively in dopaminergic neurons. In these neurons, PFF-exposure decreased mitochondrial gene expression, reduced the number of mitochondria, increased oxidant stress, and profoundly disrupted mitochondrial adenosine triphosphate production. Consistent with an aSYN-induced bioenergetic deficit, the autonomous spiking of dopaminergic neurons slowed or stopped. PFFs also up-regulated lysosomal gene expression and increased lysosomal abundance, leading to the formation of Lewy-like inclusions. Similar changes were observed in PPN cholinergic neurons following aSYN PFF exposure. Conclusions: Taken together, our findings suggest that disruption of mitochondrial function, and the subsequent bioenergetic deficit, is a proximal step in the cascade of events induced by aSYN pathology leading to dysfunction and degeneration of neurons at-risk in PD.

Poly(ADP-ribose) promotes toxicity of C9ORF72 arginine-rich dipeptide repeat proteins.

Arginine-rich dipeptide repeat proteins (R-DPRs), abnormal translational products of a GGGGCC hexanucleotide repeat expansion in C9ORF72, play a critical role in C9ORF72-related amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), the most common genetic form of the disorders (c9ALS/FTD). R-DPRs form liquid condensates in vitro, induce stress granule formation in cultured cells, aggregate, and sometimes coaggregate with TDP-43 in postmortem tissue from patients with c9ALS/FTD. However, how these processes are regulated is unclear. Here, we show that loss of poly(ADP-ribose) (PAR) suppresses neurodegeneration in c9ALS/FTD fly models and neurons differentiated from patient-derived induced pluripotent stem cells. Mechanistically, PAR induces R-DPR condensation and promotes R-DPR-induced stress granule formation and TDP-43 aggregation. Moreover, PAR associates with insoluble R-DPR and TDP-43 in postmortem tissue from patients. These findings identified PAR as a promoter of R-DPR toxicity and thus a potential target for treating c9ALS/FTD.

Amelioration of pathologic α-synuclein-induced Parkinson's disease by irisin.

Physical activity provides clinical benefit in Parkinson's disease (PD). Irisin is an exercise-induced polypeptide secreted by skeletal muscle that crosses the blood-brain barrier and mediates certain effects of exercise. Here, we show that irisin prevents pathologic α-synuclein (α-syn)-induced neurodegeneration in the α-syn preformed fibril (PFF) mouse model of sporadic PD. Intravenous delivery of irisin via viral vectors following the stereotaxic intrastriatal injection of α-syn PFF cause a reduction in the formation of pathologic α-syn and prevented the loss of dopamine neurons and lowering of striatal dopamine. Irisin also substantially reduced the α-syn PFF-induced motor deficits as assessed behaviorally by the pole and grip strength test. Recombinant sustained irisin treatment of primary cortical neurons attenuated α-syn PFF toxicity by reducing the formation of phosphorylated serine 129 of α-syn and neuronal cell death. Tandem mass spectrometry and biochemical analysis revealed that irisin reduced pathologic α-syn by enhancing endolysosomal degradation of pathologic α-syn. Our findings highlight the potential for therapeutic disease modification of irisin in PD.

Deubiquitinase CYLD acts as a negative regulator of dopamine neuron survival in Parkinson's disease.

Mutations in PINK1 and parkin highlight the mitochondrial axis of Parkinson's disease (PD) pathogenesis. PINK1/parkin regulation of the transcriptional repressor PARIS bears direct relevance to dopamine neuron survival through augmentation of PGC-1α-dependent mitochondrial biogenesis. Notably, knockout of PARIS attenuates dopaminergic neurodegeneration in mouse models, indicating that interventions that prevent dopaminergic accumulation of PARIS could have therapeutic potential in PD. To this end, we have identified the deubiquitinase cylindromatosis (CYLD) to be a regulator of PARIS protein stability and proteasomal degradation via the PINK1/parkin pathway. Knockdown of CYLD in multiple models of PINK1 or parkin inactivation attenuates PARIS accumulation by modulating its ubiquitination levels and relieving its repressive effect on PGC-1α to promote mitochondrial biogenesis. Together, our studies identify CYLD as a negative regulator of dopamine neuron survival, and inhibition of CYLD may potentially be beneficial in PD by lowering PARIS levels and promoting mitochondrial biogenesis.

Interleukin-6 triggers toxic neuronal iron sequestration in response to pathological α-synuclein.

α-synuclein (α-syn) aggregation and accumulation drive neurodegeneration in Parkinson's disease (PD). The substantia nigra of patients with PD contains excess iron, yet the underlying mechanism accounting for this iron accumulation is unclear. Here, we show that misfolded α-syn activates microglia, which release interleukin 6 (IL-6). IL-6, via its trans-signaling pathway, induces changes in the neuronal iron transcriptome that promote ferrous iron uptake and decrease cellular iron export via a pathway we term the cellular iron sequestration response, or CISR. The brains of patients with PD exhibit molecular signatures of the IL-6-mediated CISR. Genetic deletion of IL-6, or treatment with the iron chelator deferiprone, reduces pathological α-syn toxicity in a mouse model of sporadic PD. These data suggest that IL-6-induced CISR leads to toxic neuronal iron accumulation, contributing to synuclein-induced neurodegeneration.

ADP-ribosyltransferases, an update on function and nomenclature.

ADP-ribosylation, a modification of proteins, nucleic acids, and metabolites, confers broad functions, including roles in stress responses elicited, for example, by DNA damage and viral infection and is involved in intra- and extracellular signaling, chromatin and transcriptional regulation, protein biosynthesis, and cell death. ADP-ribosylation is catalyzed by ADP-ribosyltransferases (ARTs), which transfer ADP-ribose from NAD+ onto substrates. The modification, which occurs as mono- or poly-ADP-ribosylation, is reversible due to the action of different ADP-ribosylhydrolases. Importantly, inhibitors of ARTs are approved or are being developed for clinical use. Moreover, ADP-ribosylhydrolases are being assessed as therapeutic targets, foremost as antiviral drugs and for oncological indications. Due to the development of novel reagents and major technological advances that allow the study of ADP-ribosylation in unprecedented detail, an increasing number of cellular processes and pathways are being identified that are regulated by ADP-ribosylation. In addition, characterization of biochemical and structural aspects of the ARTs and their catalytic activities have expanded our understanding of this protein family. This increased knowledge requires that a common nomenclature be used to describe the relevant enzymes. Therefore, in this viewpoint, we propose an updated and broadly supported nomenclature for mammalian ARTs that will facilitate future discussions when addressing the biochemistry and biology of ADP-ribosylation. This is combined with a brief description of the main functions of mammalian ARTs to illustrate the increasing diversity of mono- and poly-ADP-ribose mediated cellular processes.

Integrative genome-wide analysis of dopaminergic neuron-specific PARIS expression in Drosophila dissects recognition of multiple PPAR-γ associated gene regulation.

The transcriptional repressor called parkin interacting substrate (PARIS; ZNF746) was initially identified as a novel co-substrate of parkin and PINK1 that leads to Parkinson's disease (PD) by disrupting mitochondrial biogenesis through peroxisome proliferator-activated receptor gamma (PPARγ) coactivator -1α (PGC-1α) suppression. Since its initial discovery, growing evidence has linked PARIS to defective mitochondrial biogenesis observed in PD pathogenesis. Yet, dopaminergic (DA) neuron-specific mechanistic underpinnings and genome-wide PARIS binding landscape has not been explored. We employed conditional translating ribosome affinity purification (TRAP) followed by RNA sequencing (TRAP-seq) for transcriptome profiling of DA neurons in transgenic Drosophila lines expressing human PARIS wild type (WT) or mutant (C571A). We also generated genome-wide maps of PARIS occupancy using ChIP-seq in human SH-SY5Y cells. The results demonstrated that PPARγ functions as a master regulator of PARIS-induced molecular changes at the transcriptome level, confirming that PARIS acts primarily on PGC-1α to lead to neurodegeneration in PD. Moreover, we identified that PARIS actively modulates expression of PPARγ target genes by physically binding to the promoter regions. Together, our work revealed how PARIS drives adverse effects on modulation of PPAR-γ associated gene clusters in DA neurons.

USP39 promotes non-homologous end-joining repair by poly(ADP-ribose)-induced liquid demixing.

Mutual crosstalk among poly(ADP-ribose) (PAR), activated PAR polymerase 1 (PARP1) metabolites, and DNA repair machinery has emerged as a key regulatory mechanism of the DNA damage response (DDR). However, there is no conclusive evidence of how PAR precisely controls DDR. Herein, six deubiquitinating enzymes (DUBs) associated with PAR-coupled DDR were identified, and the role of USP39, an inactive DUB involved in spliceosome assembly, was characterized. USP39 rapidly localizes to DNA lesions in a PAR-dependent manner, where it regulates non-homologous end-joining (NHEJ) via a tripartite RG motif located in the N-terminus comprising 46 amino acids (N46). Furthermore, USP39 acts as a molecular trigger for liquid demixing in a PAR-coupled N46-dependent manner, thereby directly interacting with the XRCC4/LIG4 complex during NHEJ. In parallel, the USP39-associated spliceosome complex controls homologous recombination repair in a PAR-independent manner. These findings provide mechanistic insights into how PAR chains precisely control DNA repair processes in the DDR.

Parkin interacting substrate phosphorylation by c-Abl drives dopaminergic neurodegeneration.

Aberrant activation of the non-receptor kinase c-Abl is implicated in the development of pathogenic hallmarks of Parkinson's disease, such as α-synuclein aggregation and progressive neuronal loss. c-Abl-mediated phosphorylation and inhibition of parkin ligase function lead to accumulation of parkin interacting substrate (PARIS) that mediates α-synuclein pathology-initiated dopaminergic neurodegeneration. Here we show that, in addition to PARIS accumulation, c-Abl phosphorylation of PARIS is required for PARIS-induced cytotoxicity. c-Abl-mediated phosphorylation of PARIS at Y137 (within the Krüppel-associated box domain) drives its association with KAP1 and the repression of genes with diverse functions in pathways such as chromatin remodelling and p53-dependent cell death. One phosphorylation-dependent PARIS target, MDM4 (a p53 inhibitor that associates with MDM2; also known as MDMX), is transcriptionally repressed in a histone deacetylase-dependent manner via PARIS binding to insulin response sequence motifs within the MDM4 promoter. Virally induced PARIS transgenic mice develop c-Abl activity-dependent Parkinson's disease features such as motor deficits, dopaminergic neuron loss and neuroinflammation. PARIS expression in the midbrain resulted in c-Abl activation, PARIS phosphorylation, MDM4 repression and p53 activation, all of which are blocked by the c-Abl inhibitor nilotinib. Importantly, we also observed aberrant c-Abl activation and PARIS phosphorylation along with PARIS accumulation in the midbrain of adult parkin knockout mice, implicating c-Abl in recessive Parkinson's disease. Inhibition of c-Abl or PARIS phosphorylation by nilotinib or Y137F-PARIS expression in adult parkin knockout mice blocked MDM4 repression and p53 activation, preventing motor deficits and dopaminergic neurodegeneration. Finally, we found correlative increases in PARIS phosphorylation, MDM4 repression and p53 activation in post-mortem Parkinson's disease brains, pointing to clinical relevance of the c-Abl-PARIS-MDM4-p53 pathway. Taken together, our results describe a novel mechanism of epigenetic regulation of dopaminergic degeneration downstream of pathological c-Abl activation in Parkinson's disease. Since c-Abl activation has been shown in sporadic Parkinson's disease, PARIS phosphorylation might serve as both a useful biomarker and a potential therapeutic target to regulate neuronal loss in Parkinson's disease.

Mechanistic basis for receptor-mediated pathological α-synuclein fibril cell-to-cell transmission in Parkinson's disease.

The spread of pathological α-synuclein (α-syn) is a crucial event in the progression of Parkinson's disease (PD). Cell surface receptors such as lymphocyte activation gene 3 (LAG3) and amyloid precursor-like protein 1 (APLP1) can preferentially bind α-syn in the amyloid over monomeric state to initiate cell-to-cell transmission. However, the molecular mechanism underlying this selective binding is unknown. Here, we perform an array of biophysical experiments and reveal that LAG3 D1 and APLP1 E1 domains commonly use an alkaline surface to bind the acidic C terminus, especially residues 118 to 140, of α-syn. The formation of amyloid fibrils not only can disrupt the intramolecular interactions between the C terminus and the amyloid-forming core of α-syn but can also condense the C terminus on fibril surface, which remarkably increase the binding affinity of α-syn to the receptors. Based on this mechanism, we find that phosphorylation at serine 129 (pS129), a hallmark modification of pathological α-syn, can further enhance the interaction between α-syn fibrils and the receptors. This finding is further confirmed by the higher efficiency of pS129 fibrils in cellular internalization, seeding, and inducing PD-like α-syn pathology in transgenic mice. Our work illuminates the mechanistic understanding on the spread of pathological α-syn and provides structural information for therapeutic targeting on the interaction of α-syn fibrils and receptors as a potential treatment for PD.

Targeting Parthanatos in Ischemic Stroke.

Parthanatos is a cell death signaling pathway in which excessive oxidative damage to DNA leads to over-activation of poly(ADP-ribose) polymerase (PARP). PARP then generates the formation of large poly(ADP-ribose) polymers that induce the release of apoptosis-inducing factor from the outer mitochondrial membrane. In the cytosol, apoptosis-inducing factor forms a complex with macrophage migration inhibitory factor that translocates into the nucleus where it degrades DNA and produces cell death. In a review of the literature, we identified 24 publications from 13 laboratories that support a role for parthanatos in young male mice and rats subjected to transient and permanent middle cerebral artery occlusion (MCAO). Investigators base their conclusions on the use of nine different PARP inhibitors (19 studies) or PARP1-null mice (7 studies). Several studies indicate a therapeutic window of 4-6 h after MCAO. In young female rats, two studies using two different PARP inhibitors from two labs support a role for parthanatos, whereas two studies from one lab do not support a role in young female PARP1-null mice. In addition to parthanatos, a body of literature indicates that PARP inhibitors can reduce neuroinflammation by interfering with NF-κB transcription, suppressing matrix metaloproteinase-9 release, and limiting blood-brain barrier damage and hemorrhagic transformation. Overall, most of the literature strongly supports the scientific premise that a PARP inhibitor is neuroprotective, even when most did not report behavior outcomes or address the issue of randomization and treatment concealment. Several third-generation PARP inhibitors entered clinical oncology trials without major adverse effects and could be repurposed for stroke. Evaluation in aged animals or animals with comorbidities will be important before moving into clinical stroke trials.

LRRK2 Modulates the Exocyst Complex Assembly by Interacting with Sec8.

Mutations in LRRK2 play a critical role in both familial and sporadic Parkinson's disease (PD). Up to date, the role of LRRK2 in PD onset and progression remains largely unknown. However, experimental evidence highlights a critical role of LRRK2 in the control of vesicle trafficking, likely by Rab phosphorylation, that in turn may regulate different aspects of neuronal physiology. Here we show that LRRK2 interacts with Sec8, one of eight subunits of the exocyst complex. The exocyst complex is an evolutionarily conserved multisubunit protein complex mainly involved in tethering secretory vesicles to the plasma membrane and implicated in the regulation of multiple biological processes modulated by vesicle trafficking. Interestingly, Rabs and exocyst complex belong to the same protein network. Our experimental evidence indicates that LRRK2 kinase activity or the presence of the LRRK2 kinase domain regulate the assembly of exocyst subunits and that the over-expression of Sec8 significantly rescues the LRRK2 G2019S mutant pathological effect. Our findings strongly suggest an interesting molecular mechanism by which LRRK2 could modulate vesicle trafficking and may have important implications to decode the complex role that LRRK2 plays in neuronal physiology.

AMPA Receptor Surface Expression Is Regulated by S-Nitrosylation of Thorase and Transnitrosylation of NSF.

The regulation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) trafficking affects multiple brain functions, such as learning and memory. We have previously shown that Thorase plays an important role in the internalization of AMPARs from the synaptic membrane. Here, we show that N-methyl-d-aspartate receptor (NMDAR) activation leads to increased S-nitrosylation of Thorase and N-ethylmaleimide-sensitive factor (NSF). S-nitrosylation of Thorase stabilizes Thorase-AMPAR complexes and enhances the internalization of AMPAR and interaction with protein-interacting C kinase 1 (PICK1). S-nitrosylated NSF is dependent on the S-nitrosylation of Thorase via trans-nitrosylation, which modulates the surface insertion of AMPARs. In the presence of the S-nitrosylation-deficient C137L Thorase mutant, AMPAR trafficking, long-term potentiation, and long-term depression are impaired. Overall, our data suggest that both S-nitrosylation and interactions of Thorase and NSF/PICK1 are required to modulate AMPAR-mediated synaptic plasticity. This study provides critical information that elucidates the mechanism underlying Thorase and NSF-mediated trafficking of AMPAR complexes.

Poly (ADP-ribose) (PAR)-dependent cell death in neurodegenerative diseases.

Disruption of cellular functions with aging-induced accumulation of neuronal stressors causes cell death which is a common feature of neurodegenerative diseases. Studies in a variety of neurodegenerative disease models demonstrate that poly (ADP-ribose) (PAR)-dependent cell death, also named parthanatos, is responsible for neuronal loss in neurological diseases, such as Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD) and amyotrophic lateral sclerosis (ALS). Parthanatos has distinct features that differ from caspase-dependent apoptosis, necrosis or autophagic cell death. Parthanatos can be triggered by the accumulation of PAR due to overactivation of PAR polymerase-1 (PARP-1). Excess PAR, induces the mitochondrial release apoptosis-inducing factor (AIF), which binds to macrophage migration inhibitory factor (MIF) carrying MIF into the nucleus where it cleaves genomic DNA into large fragments. In this review, we will discuss the molecular mechanisms of parthanatos and their role in neurodegenerative diseases. Furthermore, we will discuss promising therapeutic interventions within the pathological PAR signaling cascade that could be designed to halt the progression of neurodegeneration.

Integration of Human Induced Pluripotent Stem Cell (hiPSC)-Derived Neurons into Rat Brain Circuits.

Human neuron transplantation offers novel opportunities for modeling human neurologic diseases and potentially replacement therapies. However, the complex structure of the human cerebral cortex, which is organized in six layers with tightly interconnected excitatory and inhibitory neuronal networks, presents significant challenges for in vivo transplantation techniques to obtain a balanced, functional and homeostatically stable neuronal network. Here, we present a protocol to introduce human induced pluripotent stem cell (hiPSC)-derived neural progenitors to rat brains. Using this approach, hiPSC-derived neurons structurally integrate into the rat forebrain, exhibit electrophysiological characteristics, including firing, excitatory and inhibitory synaptic activity, and establish neuronal connectivity with the host circuitry.