Distinct mechanisms of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine resistance revealed by transcriptome mapping in mouse striatum

Oligodendrocytes drive neuroinflammation and neurodegeneration in Parkinson's disease via the prosaposin-GPR37-IL-6 axis

Parkinson's disease (PD) is a common neurodegenerative disease and is difficult to treat due to its elusive mechanisms. Recent studies have identified a striking association between oligodendrocytes and PD progression, yet how oligodendrocytes regulate the pathogenesis of PD is still unknown. Here, we show that G-protein-coupled receptor 37 (GPR37) is upregulated in oligodendrocytes of the substantia nigra and that prosaposin (PSAP) secretion is increased in parkinsonian mice. The released PSAP can induce interleukin (IL)-6 upregulation and secretion from oligodendrocytes via a GPR37-dependent pathway, resulting in enhanced neuroinflammation, dopamine neuron degeneration, and behavioral deficits. GPR37 deficiency in oligodendrocytes prevents neurodegeneration in multiple PD models. Finally, the hallmarks of the PSAP-GPR37-IL-6 axis are observed in patients with PD. Thus, our results reveal that dopaminergic neurons interact with oligodendrocytes via secreted PSAP, and our findings identify the PSAP-GPR37-IL-6 axis as a driver of PD pathogenesis and a potential therapeutic target that might alleviate PD progression in patients.

Inhibition of mitochondrial transcription by the neurotoxin MPP. Exp Cell Res 2023;425:113536. [PMID: 36858342 DOI: 10.1016/j.yexcr.2023.113536] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The neurotoxin MPP⁺ triggers cell death of dopamine neurons and induces Parkinson's disease symptoms in mice and men, but the immediate transcriptional response to this neurotoxin has not been studied. We therefore treated human SH-SY5Y cells with a low dose (0.1 mM) of MPP⁺ and measured the effect on nascent transcription by precision run-on sequencing (PRO-seq). We found that transcription of the mitochondrial genome was significantly reduced already after 30 min, whereas nuclear gene transcription was unaffected. Inhibition of respiratory complex I by MPP⁺ led to reduced ATP production, that may explain the diminished activity of mitochondrial RNA polymerase. Our results show that MPP⁺ has a direct effect on mitochondrial function and transcription, and that other gene expression or epigenetic changes induced by this neurotoxin are secondary effects that reflect a cellular adaptation program.

Voltage-Gated Proton Channel Hv1 Regulates Neuroinflammation and Dopaminergic Neurodegeneration in Parkinson's Disease Models

Although the precise mechanisms for neurodegeneration in Parkinson's disease (PD) are unknown, evidence suggests that neuroinflammation is a critical factor in the pathogenic process. Here, we sought to determine whether the voltage-gated proton channel, Hv1 (HVCN1), which is expressed in microglia and regulates NADPH oxidase, is associated with dopaminergic neurodegeneration. We utilized data mining to evaluate the mRNA expression of HVCN1 in the brains of PD patients and controls and uncovered increased expression of the gene encoding Hv1, HVCN1, in the brains of PD patients compared to controls, specifically in male PD patients. In an acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 4 × 16 mg/kg) mouse model of PD, Hvcn1 gene expression was increased 2-fold in the striatum. MPTP administration to wild-type (WT) mice resulted in a ~65% loss of tyrosine hydroxylase positive neurons (TH+) in the substantia nigra (SN), while a ~39% loss was observed in Hv1 knockout (KO) mice. Comparable neuroprotective effects of Hv1 deficiency were found in a repeated-dose LPS model. Neuroprotection was associated with decreased pro-inflammatory cytokine levels and pro-oxidant factors in both neurotoxicant animal models. These in vivo results were confirmed in primary microglial cultures, with LPS treatment increasing Hvcn1 mRNA levels and Hv1 KO microglia failing to exhibit the LPS-mediated inflammatory response. Conditioned media from Hv1 KO microglia treated with LPS resulted in an attenuated loss of cultured dopamine neuron cell viability compared to WT microglia. Taken together, these data suggest that Hv1 is upregulated and mediates microglial pro-inflammatory cytokine production in parkinsonian models and therefore represents a novel target for neuroprotection.

The glycoprotein GPNMB attenuates astrocyte inflammatory responses through the CD44 receptor

BACKGROUND

Neuroinflammation is one of the hallmarks of neurodegenerative diseases, such as Parkinson's disease (PD). Activation of glial cells, including microglia and astrocytes, is a characteristic of the inflammatory response. Glycoprotein non-metastatic melanoma protein B (GPNMB) is a transmembrane glycoprotein that releases a soluble signaling peptide when cleaved by ADAM10 or other extracellular proteases. GPNMB has demonstrated a neuroprotective role in animal models of ALS and ischemia. However, the mechanism of this protection has not been well established. CD44 is a receptor expressed on astrocytes that can bind GPNMB, and CD44 activation has been demonstrated to reduce NFκB activation and subsequent inflammatory responses in macrophages. GPNMB signaling has not been investigated in models of PD or specifically in astrocytes. More recently, genetic studies have linked polymorphisms in GPNMB with risk for PD. Therefore, it is important to understand the role this signaling protein plays in PD.

METHODS

We used data mining techniques to evaluate mRNA expression of GPNMB and its receptor CD44 in the substantia nigra of PD and control brains. Immunofluorescence and qPCR techniques were used to assess GPNMB and CD44 levels in mice treated with MPTP. In vitro experiments utilized the immortalized mouse astrocyte cell line IMA2.1 and purified primary mouse astrocytes. The effects of recombinant GPNMB on cytokine-induced astrocyte activation was determined by qPCR, immunofluorescence, and measurement of nitric oxide and reactive oxygen production.

RESULTS

Increased GPNMB and CD44 expression was observed in the substantia nigra of human PD brains and in GFAP-positive astrocytes in an animal model of PD. GPNMB treatment attenuated cytokine-induced levels of inducible nitric oxide synthase, nitric oxide, reactive oxygen species, and the inflammatory cytokine IL-6 in an astrocyte cell line and primary mouse astrocytes. Using primary mouse astrocytes from CD44 knockout mice, we found that the anti-inflammatory effects of GPNMB are CD44-mediated.

CONCLUSIONS

These results demonstrate that GPNMB may exert its neuroprotective effect through reducing astrocyte-mediated neuroinflammation in a CD44-dependent manner, providing novel mechanistic insight into the neuroprotective properties of GPNMB.

Folding Underlies Bidirectional Role of GPR37/Pael-R in Parkinson Disease

Since conformational flexibility, which is required for the function of a protein, comes at the expense of structural stability, many proteins, including G-protein-coupled receptors (GPCRs), are under constant risk of misfolding and aggregation. In this regard GPR37 (also named PAEL-R and ETBR-LP-1) takes a prominent role, particularly in relation to Parkinson disease (PD). GPR37 is a substrate for parkin and accumulates abnormally in autosomal recessive juvenile parkinsonism, contributing to endoplasmic reticulum stress and death of dopaminergic neurons. GPR37 also constitutes a core structure of Lewy bodies, demonstrating a more general involvement in PD pathology. However, if folded and matured properly, GPR37 seems to be neuroprotective. Moreover, GPR37 modulates functionality of the dopamine transporter and the dopamine D2 receptor and stimulates dopamine neurotransmission. Here we review the multiple roles of GPR37 with relevance to potential disease modification and symptomatic therapies of PD and highlight unsolved issues in this field.

Regulation of striatal astrocytic receptor for advanced glycation end-products variants in an early stage of experimental Parkinson's disease

Convincing evidence indicates that advanced glycation end-products and danger-associated protein S100B play a role in Parkinson's disease (PD). These agents operate through the receptor for advanced glycation end-products (RAGE), which displays distinct isoforms playing protective/deleterious effects. However, the nature of RAGE variants has been overlooked in PD studies. Hence, we attempted to characterize RAGE regulation in early stages of PD striatal pathology. A neurotoxin-based rodent model of PD was used in this study, through administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to C57BL/6 mice. Animals were killed 6 h post-MPTP to assess S100B/RAGE contents (RT-qPCR, ELISA) and RAGE isoform density (WB) and cellular distribution (immunohistochemistry). Dopaminergic and gliotic status were also mapped (HPLC-ED, WB, immunohistochemistry). At this preliminary stage of MPTP-induced PD in mice, RAGE inhibitory isoforms were increased whereas full-length RAGE was not affected. This putative cytoprotective RAGE phenotype paired an inflammatory and pro-oxidant setting fueling DAergic denervation. Increased RAGE inhibitory variants occur in astrocytes showing higher S100B density but no overt signs of hypertrophy or NF-κB activation, a canonical effector of RAGE. These findings expand our understanding of the toxic effect of MPTP on striatum and offer first in vivo evidence of RAGE being a responder in early stages of astrogliosis dynamics, supporting a protective rather tissue-destructive phenotype of RAGE in the initial phase of PD degeneration. These data lay the groundwork for future studies on the relevance of astrocytic RAGE in DAergic neuroprotection strategies. We report increased antagonistic RAGE variants paralleling S100B up-regulation in early stages of MPTP-induced astrogliosis dynamics . We propose that selective RAGE regulation reflects a self-protective mechanism to maintain low levels of RAGE ligands , preventing long-term inflammation and oxidative stress arising from sustained ligands/flRAGE activation . Understanding loss of RAGE protective response to stress may provide new therapeutic options to halt or slow down dopaminergic axonopathy and, ultimately, neuronal death .

Gene dysregulation is restored in the Parkinson's disease MPTP neurotoxic mice model upon treatment of the therapeutic drug Cu(II)(atsm)

The administration of MPTP selectively targets the dopaminergic system resulting in Parkinsonism-like symptoms and is commonly used as a mice model of Parkinson’s disease. We previously demonstrated that the neuroprotective compound Cu^II(atsm) rescues nigral cell loss and improves dopamine metabolism in the MPTP model. The mechanism of action of Cu^II(atsm) needs to be further defined to understand how the compound promotes neuronal survival. Whole genome transcriptomic profiling has become a popular method to examine the relationship between gene expression and function. Substantia nigra samples from MPTP-lesioned mice were evaluated using whole transcriptome sequencing to investigate the genes altered upon Cu^II(atsm) treatment. We identified 143 genes affected by MPTP lesioning that are associated with biological processes related to brain and cognitive development, dopamine synthesis and perturbed synaptic neurotransmission. Upon Cu^II(atsm) treatment, the expression of 40 genes involved in promoting dopamine synthesis, calcium signaling and synaptic plasticity were restored which were validated by qRT-PCR. The study provides the first detailed whole transcriptomic analysis of pathways involved in MPTP-induced Parkinsonism. In addition, we identify key therapeutic pathways targeted by a potentially new class of neuroprotective agents which may provide therapeutic benefits for other neurodegenerative disorders.

Neuroprotective effects of alkaloids from Piper longum in a MPTP-induced mouse model of Parkinson's disease

CONTEXT

Alkaloids of Piper longum L. (Piperaceae) (PLA) include piperine and piperlonguminine. Piper longum and piperine have multiple biological properties including antioxidant activity.

OBJECTIVE

The present study investigated the neuroprotective effects of PLA in a MPTP-induced mouse model of Parkinson's disease.

MATERIALS AND METHODS

PLA was prepared by extracting the dry seed of P. longum using 85% ethanol. Adult male C57BL/6 mice were divided into eight groups of 12 rats each. Experimental and control groups received an equivalent volume of saline, 0.5% CMC-Na, and 0.1% Tween 80, treated groups received oral PLA (30, 60, and 120 mg/kg), other groups treated with piperine (60 mg/kg) or Madopar (50 mg/kg). The PLA prevention group (PLA-Pr) administrated PLA (120 mg/kg) for 1 week before MPTP challenged. Except for the PLA-Pr group, others were treated for seven consecutive weeks. Parkinson's disease was induced by injecting MPTP intraperitoneally (25 mg/kg) twice weekly for five consecutive weeks. Dopaminerigic (DA) neurons and their metabolism were detected by UFLC-MS/MS. Tyrosine hydroxylase (TH)-immunohistochemistry assay and Western blotting were performed. The antioxidant enzymatic levels were determined by kit-based assays.

RESULTS

The LD50 value of PLA was determined at 1509 mg/kg of body weight. PLA (60 mg/kg) can significantly increase total movement time and distance (p < 0.05), increase levels of DA (p < 0.05) and DOPAC (p <  .05), increase glutathione (GSH) level and superoxide dismutase (SOD) activity (p < 0.05), and decrease the lipid peroxidation of malondiadehycle (MDA) (p < 0.05) in PLA-treated groups as compared with the control group.

DISCUSSION AND CONCLUSION

Our results indicate that PLA possesses neuroprotective effects and has ameliorative properties in dopaminergic neurons.

Validity of the MPTP-Treated Mouse as a Model for Parkinson's Disease

Parkinson's disease (PD) is characterized by dopaminergic (DA) neuron death in the substantia nigra (SN) and subsequent striatal adaptations. Mice treated with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine (MPTP) are widely used as a model for PD. To assess the validity of the MPTP mouse model for PD pathogenesis, we here identify the biological processes that are dysregulated in both human PD and MPTP-treated mice. Gene enrichment analysis of published differentially expressed messenger RNAs (mRNAs) in the SN of PD patients and MPTP-treated mice revealed an enrichment of gene categories related to motor dysfunction and neurodegeneration. In the PD striatum, a similar enrichment was found, whereas in the striatum of MPTP mice, acute processes linked to epilepsy were selectively enriched shortly following MPTP treatment. More importantly, we integrated the proteins encoded by the differentially expressed mRNAs into molecular landscapes showing PD pathogenesis-implicated processes only in the SN, including vesicular trafficking, exocytosis, mitochondrial apoptosis, and DA neuron-specific transcription, but not in the striatum. We conclude that the current use of the MPTP mouse as a model for studying the molecular processes in PD pathogenesis is more valid for SN than striatal mechanisms in PD. This novel insight has important practical implications for future studies using this model to investigate PD pathogenesis and evaluate the efficacy of new treatments.

Transcriptional and metabolic adaptation of human neurons to the mitochondrial toxicant MPP(+)

Assessment of the network of toxicity pathways by Omics technologies and bioinformatic data processing paves the road toward a new toxicology for the twenty-first century. Especially, the upstream network of responses, taking place in toxicant-treated cells before a point of no return is reached, is still little explored. We studied the effects of the model neurotoxicant 1-methyl-4-phenylpyridinium (MPP⁺) by a combined metabolomics (mass spectrometry) and transcriptomics (microarrays and deep sequencing) approach to provide unbiased data on earliest cellular adaptations to stress. Neural precursor cells (LUHMES) were differentiated to homogeneous cultures of fully postmitotic human dopaminergic neurons, and then exposed to the mitochondrial respiratory chain inhibitor MPP⁺ (5 μM). At 18–24 h after treatment, intracellular ATP and mitochondrial integrity were still close to control levels, but pronounced transcriptome and metabolome changes were seen. Data on altered glucose flux, depletion of phosphocreatine and oxidative stress (e.g., methionine sulfoxide formation) confirmed the validity of the approach. New findings were related to nuclear paraspeckle depletion, as well as an early activation of branches of the transsulfuration pathway to increase glutathione. Bioinformatic analysis of our data identified the transcription factor ATF-4 as an upstream regulator of early responses. Findings on this signaling pathway and on adaptive increases of glutathione production were confirmed biochemically. Metabolic and transcriptional profiling contributed complementary information on multiple primary and secondary changes that contribute to the cellular response to MPP⁺. Thus, combined ‘Omics' analysis is a new unbiased approach to unravel earliest metabolic changes, whose balance decides on the final cell fate.

Rodent models and contemporary molecular techniques: notable feats yet incomplete explanations of Parkinson's disease pathogenesis

Rodent models and molecular tools, mainly omics and RNA interference, have been rigorously used to decode the intangible etiology and pathogenesis of Parkinson's disease (PD). Although convention of contemporary molecular techniques and multiple rodent models paved imperative leads in deciphering the role of putative causative factors and sequential events leading to PD, complete and clear-cut mechanisms of pathogenesis are still hard to pin down. The current article reviews the implications and pros and cons of rodent models and molecular tools in understanding the molecular and cellular bases of PD pathogenesis based on the existing literature. Probable rationales for short of comprehensive leads and future possibilities in spite of the extensive applications of molecular tools and rodent models have also been discussed.

Long-lasting transcriptional refractoriness triggered by a single exposure to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine

Parkinson's disease (PD) is a progressive neurodegenerative disorder whose etiology is thought to have environmental (toxin) and genetic contributions. The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine (MPTP) induces pathological features of PD including loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and striatal dopamine (DA) depletion. We previously described the striatal transcriptional response following acute MPTP administration in MPTP-sensitive C57BL/6J mice. We identified three distinct phases: early (5h), intermediate (24h) and late (72h) and reported that the intermediate and late responses were absent in MPTP-resistant Swiss-Webster (SWR) mice. Here we show that C57BL/6J mice pre-treated with a single 40 mg/kg dose of MPTP and treated 9 days later with 4×20 mg/kg MPTP, display a striatal transcriptional response similar to that of MPTP-resistant SWR mice, i.e. a robust acute response but no intermediate or late response. Transcriptional refractoriness is dependent upon the dose of the priming challenge with as little as 10mg/kg MPTP being effective and can persist for more than 28 days. Priming of SWR mice has no effect on their response to subsequent challenge with MPTP. We also report that paraquat, another free radical producer, also elicits striatal transcriptional alterations but these are largely distinct from those triggered by MPTP. Paraquat-induced changes are also refractory to priming with paraquat. However neither paraquat nor MPTP elicits cross-attenuation. Thus exposure to specific toxins triggers distinct transcriptional responses in striatum that are influenced by prior exposure to the same toxin. The prolonged refractory period described here for MPTP could explain at the molecular level the reported discrepancies between different MPTP administration regimens and may have implications for our understanding of the relationship between environmental toxin exposure and PD.

Regulation of the Bcas1 and Baiap3 transcripts in the subthalamic nucleus in mice recovering from MPTP toxicity

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) exposure leads to significant and irreversible damage to dopaminergic neurons in both mice and humans. While MPTP exposure in humans causes permanent symptoms of Parkinson's disease, MPTP treated mice will recover behaviorally over a 3-week period. This mouse specific recovery might be linked to transcriptional changes in the basal ganglia enabling mice to maintain normal motor function in spite of low striatal dopamine levels. Laser microdissection was used to isolate the subthalamic nucleus from mice 7 and 28 days following MPTP exposure. High quality RNA was recovered and expressional analysis was performed on whole mouse genome microarrays. Identified regulated transcripts were validated in a separate batch of animals using quantitative PCR. Two transcripts with a significant regulation from days 7 to 28 in the MPTP treated groups, were identified: the brain specific angiogenesis inhibitor associated protein 3 (Baiap3) and the breast carcinoma amplified sequence 1 (Bcas1). Further studies of the molecular pathways involving these two transcripts may uncover processes in the subthalamic nucleus associated with the behavioral recovery observed after MPTP exposure.

Neuroprotective changes of striatal degeneration-related gene expression by acupuncture in an MPTP mouse model of Parkinsonism: microarray analysis

Acupuncture at acupoints GB34 and LR3 has been reported to inhibit nigrostriatal degeneration in Parkinsonism models, yet the genes related to this preventive effect of acupuncture on the nigrostriatal dopaminergic system remain elusive. This study investigated gene expression profile changes in the striatal region of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinsonism models after acupuncture at the acupoints GB34 and LR3 using a whole transcript genechip microarray (Affymetrix genechip mouse gene 1.0 ST array). It was confirmed that acupuncture at these acupoints could inhibit the decrease of tyrosine hydroxylase and dopamine transporter in the nigrostriatal region of the MPTP model while acupuncture at the non-acupoints could not counteract this decrease. Genechip gene array analysis (fold change cutoff 1.3 and P < 0.05) showed that 12 of the 69 probes up-regulated in MPTP when compared to the control were down-regulated by acupuncture at the acupoints. Of these 12 probes, 11 probes (nine annotated genes) were exclusively down-regulated by acupuncture only at the acupoints; the Gfral gene was excluded because it was commonly down-regulated by acupuncture at both the acupoints and the non-acupoints. In addition, 28 of the 189 probes down-regulated in MPTP when compared to the control were up-regulated by acupuncture at the acupoints. Of these 28 probes, 19 probes (seven annotated genes) were exclusively up-regulated by acupuncture only at the acupoints while nine probes were commonly up-regulated by acupuncture at both the acupoints and the non-acupoints. The regulation patterns of representative genes in real-time RT-PCR correlated with those of the genes in the microarray. These results suggest that the 30 probes (16 annotated genes), which are affected by MPTP and acupuncture only at the acupoints, are responsible for exerting in the striatal regions the inhibitory effect of acupuncture at the acupoints on MPTP-induced striatal degeneration.

Gene expression profiling in progressively MPTP-lesioned macaques reveals molecular pathways associated with sporadic Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disease characterized by progressive loss of midbrain dopaminergic neurons. To gain an insight into the mechanisms underlying the progression of PD, gene expression analysis was performed using two different brain regions, the substantia nigra pars compacta (SN) and the striatum (STR), of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned monkey model of PD. 230 genes were differentially expressed in the MPTP-treated SN compared to control, whereas 452 genes showed altered expression in the MPTP-treated STR, implying that MPTP elicits more damages in the striatal gene expression than in the SN. Comparative data analysis of the transcription profiles on the PD patients and MPTP monkey models, and pathway analysis indicated several signaling pathways as possible routes to MPTP-induced neurodegeneration. Interestingly, the networks which associated with cytoskeletal stability, ubiquitin-proteasome system (UPS) and Wnt signaling gained prominence in our study. Further transcriptional regulatory network analysis suggested the association of the neuronal repressor REST (RE1-silencing transcription factor; NRSF) and androgen receptor with the dysregulation of the striatal genes. Our study suggests the possibility that the dysfunction of multi-network signaling may induce abnormalities in a diverse range of biological processes, such as synaptic function, cytoskeletal stability, survival and differentiation.

Induction of macroautophagy by overexpression of the Parkinson's disease-associated GPR37 receptor

The orphan G-protein-coupled receptor 37 (GPR37) is a substrate of parkin, and its insoluble aggregates accumulate in brain tissue samples of Parkinson's disease patients, including Lewy bodies and neurites. Parkin activates the clearance of the unfolded receptor, while the overexpression of GPR37, in the absence of parkin, can lead to unfolded protein-induced cell death. We found that overexpression of the human GPR37 receptor in HEK293 cells and consequent activation of an endoplasmic reticulum (ER) stress response had effects comparable to starvation, in inducing the cellular autophagic pathway. Treatment with specific modulators provided further evidence for the autophagic clearance of the overexpressed GPR37 protein, in detergent-soluble and -insoluble fractions, as confirmed by the conversion of the microtubule-associated protein 1, light chain 3 (LC3)-I marker to its LC3-II isoform. Furthermore, Gpr37-null mutant mice displayed consistent alterations of ER stress and autophagic pathway markers in brain tissue samples. These findings show that GPR37 overexpression per se can induce cellular autophagy, which may prevent the selective degeneration of GPR37-expressing neurons, as reported for Parkinson's and related neurodegenerative diseases.