SLP-2 interacts with Parkin in mitochondria and prevents mitochondrial dysfunction in Parkin-deficient human iPSC-derived neurons and Drosophila.

BackgroundLoss-of-function mutations in the PRKN gene, encoding Parkin, are the most common cause of autosomal recessive Parkinson’s disease (PD). We have previously identified mitochondrial Stomatin-like protein 2 (SLP-2), which functions in the assembly of respiratory chain proteins, as a Parkin-binding protein. Selective knockdown of either Parkin or SLP-2 led to reduced mitochondrial and neuronal function in neuronal cells and Drosophila, where a double knockdown led to a further worsening of Parkin-deficiency phenotypes. Here, we investigated the minimal Parkin region involved in the Parkin-SLP-2 interaction and explored the ability of Parkin-fragments and peptides from this minimal region to restore mitochondrial function.MethodsIn fibroblasts, human induced pluripotent stem cell (hiPSC)-derived neurons, and neuroblastoma cells the interaction between Parkin and SLP-2 was investigated, and the Parkin domain responsible for the binding to SLP-2 was mapped. High resolution respirometry, immunofluorescence analysis and live imaging were used to analyze mitochondrial function.ResultsUsing a proximity ligation assay, we quantitatively assessed the Parkin-SLP-2 interaction in skin fibroblasts and hiPSC-derived neurons. When PD-associated PRKN mutations were present, we detected a significantly reduced interaction between the two proteins. We found a preferential binding of SLP-2 to the N-terminal part of Parkin, with a highest affinity for the RING0 domain. Computational modeling based on the crystal structure of Parkin protein predicted several potential binding sites for SLP-2 within the Parkin RING0 domain. Amongst these, three binding sites were observed to overlap with natural PD-causing missense mutations, which we demonstrated interfere substantially with the binding of Parkin to SLP-2. Finally, delivery of the isolated Parkin RING0 domain and a Parkin mini-peptide, conjugated to cell-permeant and mitochondrial transporters, rescued compromised mitochondrial function in Parkin-deficient neuroblastoma cells and hiPSC-derived neurons with endogenous, disease causing PRKN mutations.ConclusionsThese findings place further emphasis on the importance of the protein–protein interaction between Parkin and SLP-2 for the maintenance of optimal mitochondrial function. The possibility of restoring an abolished binding to SLP-2 by delivering the Parkin RING0 domain or the Parkin mini-peptide involved in this specific protein–protein interaction into cells might represent a novel organelle-specific therapeutic approach for correcting mitochondrial dysfunction in Parkin-linked PD.

Identifying potential genes driving ferroptosis in the substantia nigra and dopaminergic neurons in Parkinson's disease.

Delayed Dominant-Negative TNF Gene Therapy Halts Progressive Loss of Nigral Dopaminergic Neurons in a Rat Model of Parkinson's Disease

Synapsin III alterations in Parkinson's disease

The loss of nigral dopaminergic (DA) neurons in idiopathic Parkinson's disease (PD) is believed to result from interactions between genetic susceptibility and environmental factors. Evidence that inflammatory processes modulate PD risk comes from prospective studies that suggest that higher plasma concentrations of a number of proinflammatory cytokines correlate with an increased risk of developing PD and chronic nonsteroidal anti-inflammatory drug regimens reduce the incidence of PD. Although loss-of-function mutations in the parkin gene cause early-onset familial PD, Parkin-deficient (parkin-/-) mice do not display nigrostriatal pathway degeneration, suggesting that a genetic factor is not sufficient, and an environmental trigger may be needed to cause nigral DA neuron loss. To test the hypothesis that parkin-/- mice require an inflammatory stimulus to develop nigral DA neuron loss, low-dose lipopolysaccaride (LPS) was administered intraperitoneally for prolonged periods. Quantitative real-time PCR and immunofluorescence labeling of inflammatory markers indicated that this systemic LPS treatment regimen triggered persistent neuroinflammation in wild-type and parkin-/- mice. Although inflammatory and oxidative stress responses to the inflammation regimen did not differ significantly between the two genotypes, only parkin-/- mice displayed subtle fine-motor deficits and selective loss of DA neurons in substantia nigra. Therefore, our studies suggest that loss of Parkin function increases the vulnerability of nigral DA neurons to inflammation-related degeneration. This new model of nigral DA neuron loss may enable identification of early biomarkers of degeneration and aid in preclinical screening efforts to identify compounds that can halt or delay the progressive degeneration of the nigrostriatal pathway.

Parkinson's disease (PD), characterized by dopaminergic neuron loss, still lacks disease-modifying therapies due to incompletely understood mechanisms. Guanylate-binding proteins (GBPs) are well-known immune regulators, but their roles in PD are largely unknown. In this study, we identify GBP2 as a critical driver of PD pathogenesis by impairing mitophagy. We found that GBP2 was significantly upregulated in the substantia nigra of PD patients, and in both MPTP-induced and A53T transgenic mouse models, as well as in MPP+-treated or A53T α-synuclein-overexpressing SH-SY5Y cells. Both in vivo and in vitro, genetic knockdown of GBP2 robustly alleviated the MPTP/MPP+-induced motor deficits, dopaminergic neuron loss, and apoptosis. Mechanistically, PD-related stress promotes GBP2 geranylgeranylation, driving its mitochondrial accumulation. At mitochondria, GBP2 directly binds the mitophagy receptor NIX via its large GTPase domain and targets it for ubiquitin-proteasomal degradation, thereby suppressing NIX-mediated mitophagy. Accordingly, GBP2 knockdown enhanced mitophagy, improved mitochondrial homeostasis, and protected against neuronal apoptosis. The neuroprotective effects of GBP2 knockdown were abolished by either pharmacological inhibition of mitophagy or genetic knockdown of NIX, indicating a linear pathway. Importantly, therapeutically targeting geranylgeranylation with GGTI298 significantly attenuated MPTP-induced neurotoxicity. Our study unveils a novel, druggable axis in PD pathogenesis where GBP2 disrupts mitochondrial quality control. Targeting GBP2 geranylgeranylation with GGTI298 presents a promising therapeutic strategy.

Parkinson’s disease (PD) is caused by the loss of dopaminergic (DA) neurons in the midbrain substantia nigra (SN). Neuroinflammation, which is marked by microglial activation, plays a very important role in the pathogenesis of PD. Pro-inflammatory mediators produced by activated microglia could damage DA neurons. Hence, the inhibition of microglial activation may provide a new approach for treating PD. Galangin has been shown to inhibit inflammation in a variety of diseases, but not PD. In this study, we aimed to investigate the anti-inflammatory effect of galangin and the underlying mechanisms in Lipopolysaccharide (LPS) induced PD models. We first examined the protective effect of galangin in the LPS-induced PD rat model. Specifically, we investigated the effects on motor dysfunction, microglial activation, and the loss of DA neurons. Then, galangin was used to detect the impact on the inflammatory responses and inflammatory signaling pathways in LPS-induced BV-2 cells. The in vivo results showed that galangin dose-dependently attenuates the activation of microglia, the loss of DA neurons, and motor dysfunction. In vitro, galangin markedly inhibited LPS-induced expression of tumor necrosis factor α (TNF-α), interleukin-6 (IL-6) and interleukin-1β (IL-1β), cyclooxygenase 2 (COX-2), and induced nitric oxide synthase (iNOS) via associating with the phosphorylation of c-JUN N-terminal Kinase (JNK), p38, protein kinase B (AKT), and nuclear factor κB (NF-κB) p65. Collectively, the results indicated that galangin has a role in protecting DA neurons by inhibiting microglial activation.

BackgroundParkinson’s disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic (DA) neurons in the substantia nigra (SN). Microglia-mediated neuroinflammation has been largely considered one of main factors to the PD pathology. MicroRNA-218-5p (miR-218-5p) is a microRNA that plays a role in neurodevelopment and function, while its potential function in PD and neuroinflammation remains unclear.MethodsWe explore the involvement of miR-218-5p in the PD in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model. The miR-218-5p agomir used for overexpression was delivered into the substantia nigra (SN) by bilateral stereotaxic infusions. The loss of dopaminergic (DA) neurons and microglial inflammation in the SN was determined using Western blotting and immunofluorescence. Motor function was assessed using the rotarod test. RNA sequencing (RNA-seq) was performed to explore the pathways regulated by miR-218-5p. The target genes of miR-218-5p were predicted using TargetScan and confirmed using dual luciferase reporter assays. The effects of miR-218-5p on microglial inflammation and related pathways were verified in murine microglia-like BV2 cells. To stimulate BV2 cells, SH-SY5Y cells were treated with 1-methyl-4-phenylpyridinium (MPP+) and the conditioned media (CM) were collected.ResultsMiR-218-5p expression was reduced in both the SN of MPTP-induced mice and MPP+-treated BV2 cells. MiR-218-5p overexpression significantly alleviated MPTP-induced microglial inflammation, loss of DA neurons, and motor dysfunction. RNA sequence and gene set enrichment analysis showed that type I interferon (IFN-I) pathways were upregulated in MPTP-induced mice, while this upregulation was reversed by miR-218-5p overexpression. A luciferase reporter assay verified that Ddx41 was a target gene of miR-218-5p. In vitro, miR-218-5p overexpression or Ddx41 knockdown inhibited the IFN-I response and expression of inflammatory cytokines in BV2 cells stimulated with MPP+-CM.ConclusionsMiR-218-5p suppresses microglia-mediated neuroinflammation and preserves DA neurons via Ddx41/IFN-I. Hence, miR-218-5p-Ddx41 is a promising therapeutic target for PD.

Clinical symptoms in Parkinson's disease do not appear until almost total depletion of dopamine has occurred in the striatum, suggesting the existence of compensatory mechanisms to offset the loss of nigrostriatal dopaminergic neurons. This compensation has been attributed mainly to an increased turnover of dopamine in the remaining dopaminergic neurons. Besides this biochemical phenomenon intrinsic to dopaminergic neurons, we tested whether morphological changes in the nerve afferents to the dopaminergic neurons could participate in these compensatory mechanisms. The afferents to the dendrites of dopaminergic neurons were analyzed ultrastructurally in the substantia nigra of parkinsonian patients and matched controls, using simultaneous histochemical detection of acetylcholine-like cation and tyrosine hydroxylase. The size of acetylcholine-like cation-containing terminals in contact with dopaminergic dendrites increased significantly by 38% in the substantia nigra of parkinsonian patients; whereas their number per section of dopaminergic dendrite showed an increase of 60%, although not reaching statistical significance. The number of the terminals devoid of acetylcholine-like cation per section of dopaminergic dendrite decreased significantly by 52% in the substantia nigra of parkinsonian patients. These results suggest (1) a plasticity of excitatory cholinergic neurons targeting nigral dopaminergic neurons and (2) an involution of noncholinergic nerve terminals, mostly originating from inhibitory nigral, pallidal, and striatal GABAergic neurons. The findings provide evidence of a capacity for neuronal plasticity in the elderly human brain, even in the presence of neurodegenerative disorders.

Parkinson's disease (PD) involves the progressive loss of dopaminergic (DA) neurons within the substantia nigra (SN) region of the midbrain, although the precise molecular processes driving this degeneration are still not fully understood. This research investigates the expression patterns of genes associated with mitochondrial function in the SN and DA neurons of individuals with PD, aimed at uncovering new potential therapeutic targets. Two independent expression array datasets, GSE7621 and GSE8397 (GPL-96), retrieved from the GEO database, were analyzed to identify mitochondria-related genes that are differentially expressed in the SN of PD patients. Gene Ontology and pathway enrichment analyses were also performed to gain insight into the molecular mechanisms involved. To validate our findings, we utilized an additional dataset, GSE49036. We also examined the altered expression of these mitochondrial-related genes in DA neurons using RNA-seq data from GSE169755, which includes DA neurons isolated from the SN of both PD patients and healthy controls. Finally, the proposed hypothesis was tested experimentally using an in vitro model of PD. This integrative analysis across multiple datasets reveals previously unrecognized mitochondrial gene candidates implicated in PD pathogenesis and highlights their potential as targets for therapeutic intervention.

Diaminodiphenyl sulfone–induced parkin ameliorates age-dependent dopaminergic neuronal loss

Mitochondrial network structure is controlled by the dynamical processes of fusion and fission, which merge and split mitochondrial tubes into structures including branches and loops. To investigate the impact of mitochondrial network dynamics and structure on the spread of proteins and other molecules through mitochondrial networks, we used stochastic simulations of two distinct quantitative models that each included mitochondrial fusion and fission, and particle diffusion via the network. Better-connected mitochondrial networks and networks with faster dynamics exhibit more rapid particle spread on the network, with little further improvement once a network has become well connected. As fragmented networks gradually become better connected, particle spread either steadily improves until the networks become well connected for slow-diffusing particles or plateaus for fast-diffusing particles. We compared model mitochondrial networks with both end-to-end and end-to-side fusion, which form branches, to nonbranching model networks that lack end-to-side fusion. To achieve the optimum (most rapid) spread that occurs on well-connected branching networks, nonbranching networks require much faster fusion and fission dynamics. Thus, the process of end-to-side fusion, which creates branches in mitochondrial networks, enables rapid spread of particles on the network with relatively slow fusion and fission dynamics. This modeling of protein spread on mitochondrial networks builds toward mechanistic understanding of how mitochondrial structure and dynamics regulate mitochondrial function. Published by the American Physical Society 2024

Compound mutations and homozygous loss of function of the parkin gene causes juvenile and early onset, autosomal recessive parkinsonism. Pathologically, the disease is associated with loss of dopaminergic neurons in the substantia nigra pars compacta and locus ceruleus, usually without Lewy body pathology. Hemizygous families have been described that may harbor mutations outside of the open reading frame. The parkin gene promoter has yet to be characterized, and therein, mutations in hemizygous families may plausibly be identified. To identify the promoter of the parkin gene, the transcription start site was defined by a combination of primer extension and 5' RACE. Five kilobases of DNA 5' to the parkin start codon were directly sequenced from a BAC containing parkin exon 1 and evaluated for promoter motifs. The parkin promoter lacks TATA or CAAT boxes and appears to share homology to the alpha-synuclein promoter. Deletion constructs demonstrated core promoter activity and tissue specific enhancing regions in HEK-293T and SH-SY5Y cells.

Mutations, duplication and triplication of α-synuclein genes are linked to familial Parkinson’s disease (PD), and aggregation of α-synuclein (α-syn) in Lewy bodies (LB) is involved in the pathogenesis of the disease. The targeted overexpression of α-syn in the substantia nigra (SN) mediated by viral vectors may provide a better alternative to recapitulate the neurodegenerative features of PD. Therefore, we overexpressed human wild-type α-syn using rAAV2/1 vectors in the bilateral SN of mouse and examined the effects for up to 12 weeks. Delivery of rAAV-2/1-α-syn caused significant nigrostriatal degeneration including appearance of dystrophic striatal neurites, loss of nigral dopaminergic (DA) neurons and dissolving nigral neuron bodies in a time-dependent manner. In addition, the α-syn overexpressed mice also developed significant deficits in motor function at 12 weeks when the loss of DA neurons exceeded a threshold of 50%. To investigate the sensitivity to neurotoxins in mice overexpressing α-syn, we performed an MPTP treatment with the subacute regimen 8 weeks after rAAV injection. The impact of the combined genetic and environmental insults on DA neuronal loss, striatal dopamine depletion, dopamine turnover and motor dysfunction was markedly greater than that of either alone. Moreover, we observed increased phosphorylation (S129), accumulation and nuclear distribution of α-syn after the combined insults. In summary, these results reveal that the overexpressed α-syn induces progressive nigrostriatal degeneration and increases the susceptibility of DA neurons to MPTP. Therefore, the targeted overexpression of α-syn and the combination with environmental toxins may provide valuable models for understanding PD pathogenesis and developing related therapies.

Parkinson's disease (PD) is a progressive neurodegenerative disorder marked by dopaminergic (DA) neuron loss and neuroinflammation. Current therapies fail to halt disease progression, which underscores the need for new treatments. This study investigated the neuroprotective effects and mechanisms of Gastrodia elata polysaccharide (GEP) in MPTP-induced PD mice. GEP was administered for two weeks, and motor function was assessed using behavioral tests. Immunohistochemical and Western Blot analyses evaluated DA neuron survival, microglial activation, and NLRP3 inflammasome components. GEP-medicated serum (GMS) was applied to SH-SY5Y neuroblastoma cells exposed to neuroinflammatory conditions, and metabolomic analysis identified key metabolites. GEP improved motor function, reduced DA neuron loss, and increased tyrosine hydroxylase expression. It suppressed microglial activation, decreased NLRP3 inflammasome components, and lowered pro-inflammatory cytokines (IL-1β, IL-6, TNF-α). GMS reduced ROS levels, enhanced mitochondrial membrane potential, and promoted autophagy in SH-SY5Y cells. Metabolomic analysis revealed elevated dopamine levels in GMS, linked to NLRP3 inflammasome inhibition, and reduced neuroinflammation. GMS also activated the PINK1/Parkin pathway to promote mitochondrial autophagy and prevent apoptosis. GEP alleviates PD symptoms by targeting neuroinflammation, mitochondrial dysfunction, and dopamine regulation, which highlights its potential as a therapeutic candidate. Further research is needed to explore its long-term efficacy and clinical applications.