Calpain upregulation and neuron death in spinal cord of MPTP-induced parkinsonism in mice

Spiral volumetric optoacoustic tomography of reduced oxygen saturation in the spinal cord of M83 mouse model of Parkinson's disease

PURPOSE

Metabolism and bioenergetics in the central nervous system play important roles in the pathophysiology of Parkinson's disease (PD). Here, we employed a multimodal imaging approach to assess oxygenation changes in the spinal cord of the transgenic M83 murine model of PD overexpressing the mutated A53T alpha-synuclein form in comparison with non-transgenic littermates.

METHODS

In vivo spiral volumetric optoacoustic tomography (SVOT) was performed to assess oxygen saturation (sO2) in the spinal cords of M83 mice and non-transgenic littermates. Ex vivo high-field T1-weighted (T1w) magnetic resonance imaging (MRI) at 9.4T was used to assess volumetric alterations in the spinal cord. 3D SVOT analysis and deep learning-based automatic segmentation of T1w MRI data for the mouse spinal cord were developed for quantification. Immunostaining for phosphorylated alpha-synuclein (pS129 α-syn), as well as vascular organization (CD31 and GLUT1), was performed after MRI scan.

RESULTS

In vivo SVOT imaging revealed a lower sO2SVOT in the spinal cord of M83 mice compared to non-transgenic littermates at sub-100 μm spatial resolution. Ex vivo MRI-assisted by in-house developed deep learning-based automatic segmentation (validated by manual analysis) revealed no volumetric atrophy in the spinal cord of M83 mice compared to non-transgenic littermates at 50 μm spatial resolution. The vascular network was not impaired in the spinal cord of M83 mice in the presence of pS129 α-syn accumulation.

CONCLUSION

We developed tools for deep-learning-based analysis for the segmentation of mouse spinal cord structural MRI data, and volumetric analysis of sO2SVOT data. We demonstrated non-invasive high-resolution imaging of reduced sO2SVOT in the absence of volumetric structural changes in the spinal cord of PD M83 mouse model.

Electro-Acupuncture Ameliorated MPTP-Induced Parkinsonism in Mice via TrkB Neurotrophic Signaling

Neurotrophins, such as brain-derived neurotrophic factor (BDNF), have shown promise as neuroprotective agents, indicating their potential in therapeutic strategies for neurodegenerative disease. However, the inherent bioactivity and pharmaceutical limitations of BDNF compromise its clinical efficacy. Research has documented the beneficial effects of electroacupuncture (EA) against neurodegeneration, possibly by BDNF-mediated mechanisms. The present study was designed to clarify whether EA can mount a neuroprotective effect in mice lesioned with MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) via stimulation of the BDNF-TrkB signaling pathway. We found that EA not only ameliorated the motor dysfunction but also restored the dopaminergic neuronal function and upregulated BDNF expression in MPTP-lesioned mice. Interestingly, the TrkB inhibitor K252a abolished the neuroprotective effects of EA. Western blot analyses further demonstrated that EA might recover the level of phospho-Akt, phospho-ERK1/2, and BDNF against MPTP neurotoxicity via reversing the imbalance between TrkB FL and TrkB T1. Taken together, the results of the present study show that EA stimulation can ameliorate MPTP-induced parkinsonism in mice. Such a neuroprotective effect may be partially mediated via restoring TrkB neurotrophic signaling.

SNJ-1945, a calpain inhibitor, protects SH-SY5Y cells against MPP(+) and rotenone

Complex pathophysiology of Parkinson's disease involves multiple CNS cell types. Degeneration in spinal cord neurons alongside brain has been shown to be involved in Parkinson's disease and evidenced in experimental parkinsonism. However, the mechanisms of these degenerative pathways are not well understood. To unravel these mechanisms SH-SY5Y neuroblastoma cells were differentiated into dopaminergic and cholinergic phenotypes, respectively, and used as cell culture model following exposure to two parkinsonian neurotoxicants MPP(+) and rotenone. SNJ-1945, a cell-permeable calpain inhibitor was tested for its neuroprotective efficacy. MPP(+) and rotenone dose-dependently elevated the levels of intracellular free Ca(2+) and induced a concomitant rise in the levels of active calpain. SNJ-1945 pre-treatment significantly protected cell viability and preserved cellular morphology following MPP(+) and rotenone exposure. The neurotoxicants elevated the levels of reactive oxygen species more profoundly in SH-SY5Y cells differentiated into dopaminergic phenotype, and this effect could be attenuated with SNJ-1945 pre-treatment. In contrast, significant levels of inflammatory mediators cyclooxygenase-2 (Cox-2 and cleaved p10 fragment of caspase-1) were up-regulated in the cholinergic phenotype, which could be dose-dependently attenuated by the calpain inhibitor. Overall, SNJ-1945 was efficacious against MPP(+) or rotenone-induced reactive oxygen species generation, inflammatory mediators, and proteolysis. A post-treatment regimen of SNJ-1945 was also examined in cells and partial protection was attained with calpain inhibitor administration 1-3 h after exposure to MPP(+) or rotenone. Taken together, these results indicate that calpain inhibition is a valid target for protection against parkinsonian neurotoxicants, and SNJ-1945 is an efficacious calpain inhibitor in this context. SH-SY5Y cells, differentiated as dopaminergic (TH positive) and cholinergic (ChAT positive), were used as in vitro models for Parkinson's disease. MPP+ and rotenone induced up-regulation of calpain, expression, and activity as a common mechanism of neurodegeneration. SNJ-1945, a novel calpain inhibitor, protected both the cell phenotypes against MPP+ and rotenone.

Transcriptional mechanisms underlying sensitization of peripheral sensory neurons by granulocyte-/granulocyte-macrophage colony stimulating factors

BACKGROUND

Cancer-associated pain is a major cause of poor quality of life in cancer patients and is frequently resistant to conventional therapy. Recent studies indicate that some hematopoietic growth factors, namely granulocyte macrophage colony stimulating factor (GMCSF) and granulocyte colony stimulating factor (GCSF), are abundantly released in the tumor microenvironment and play a key role in regulating tumor-nerve interactions and tumor-associated pain by activating receptors on dorsal root ganglion (DRG) neurons. Moreover, these hematopoietic factors have been highly implicated in postsurgical pain, inflammatory pain and osteoarthritic pain. However, the molecular mechanisms via which G-/GMCSF bring about nociceptive sensitization and elicit pain are not known.

RESULTS

In order to elucidate G-/GMCSF mediated transcriptional changes in the sensory neurons, we performed a comprehensive, genome-wide analysis of changes in the transcriptome of DRG neurons brought about by exposure to GMCSF or GCSF. We present complete information on regulated genes and validated profiling analyses and report novel regulatory networks and interaction maps revealed by detailed bioinformatics analyses. Amongst these, we validate calpain 2, matrix metalloproteinase 9 (MMP9) and a RhoGTPase Rac1 as well as Tumor necrosis factor alpha (TNFα) as transcriptional targets of G-/GMCSF and demonstrate the importance of MMP9 and Rac1 in GMCSF-induced nociceptor sensitization.

CONCLUSION

With integrative approach of bioinformatics, in vivo pharmacology and behavioral analyses, our results not only indicate that transcriptional control by G-/GMCSF signaling regulates a variety of established pain modulators, but also uncover a large number of novel targets, paving the way for translational analyses in the context of pain disorders.

Calpain inhibition protected spinal cord motoneurons against 1-methyl-4-phenylpyridinium ion and rotenone

Parkinson's disease (PD), characterized by selective midbrain nigrostriatal dopaminergic degeneration, is consistently associated with moderate systemic mitochondrial dysfunction. Downstream degeneration of spinal cord has also been suggested in PD, although the mechanisms have not been much investigated. In the present study, two mitochondrial toxicants, 1-methyl-4-phenylpyridinium ion (MPP(+)) and rotenone were tested in ventral spinal cord (VSC 4.1) motoneuronal cells. Cell death was assessed by morphological and biochemical means to discern a lower apoptosis-inducing concentration and lethal concentration of 50% cell death (LC(50)), which were subsequently compared in further cytoprotection experiments. Mitochondrial toxicants dose-dependently induced increase in intracellular free Ca(2+) level, which was conducive for increased expression and activities of Ca(2+)-activated neutral protease calpain and downstream caspase-3. Thus, mitochondrial damage triggered apoptotic mechanisms in spinal cord motoneurons. Inhibition of calpain by calpeptin significantly attenuated damaging effects of MPP(+) and rotenone on motoneurons, especially at low apoptosis-inducing concentrations of toxicants and partly at their LC(50), as demonstrated by absence of DNA ladder formation and decrease in terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells. Cytoprotection by calpeptin was observed with marked decreases in Bax: Bcl-2 ratio and activities of calpain and caspase-3, which affirmed the role of mitochondrial dysfunction and involvement of intrinsic pathway in mediation of apoptosis. These findings strongly suggested that parkinsonian toxicants MPP(+) and rotenone at low doses induced cascade of cell-damaging effects in spinal cord motoneurons, thus, highlighting the possibility of induction of apoptotic mechanisms in these cells, when subjected to mitochondrial stress. Cytoprotection rendered by calpeptin further validated the involvement of calpain in apoptosis and suggested calpain inhibition as a potential neuroprotective strategy.

Tracking extranigral degeneration in animal models of Parkinson's disease: quest for effective therapeutic strategies

Sporadic Parkinson's disease (PD) is now interpreted as a complex nervous system disorder in which the projection neurons are predominantly damaged. Such an interpretation is based on mapping of Lewy body and Lewy neurite pathology. Symptoms of the human disease are much widespread, which span from pre-clinical non-motor symptoms and clinical motor symptoms to cognitive discrepancies often seen in advanced stages. Existing symptomatic treatments further complicate with overt drug-irresponsive symptoms. PD is better understood by assimilation of extranigral degenerative pathways with nigrostriatal degenerative mechanisms. The term 'extranigral' appeared first in the 1990s to more rigorously define the nigral pathology by process of elimination. However, as clinicians progressively identified PD symptoms unresponsive to the gold standard drug l-DOPA, definitions of PD symptoms were redefined. Non-motor symptoms prodromal to motor symptoms just as pre-clinical to clinical, and conjointly emerged the concept of nigral versus extranigral degeneration in PD. While nigrostriatal degeneration is responsible for the neurobiological substrates of extrapyramydal motor features, extranigral degeneration corroborates a vast majority of other changes in discrete central, peripheral, and enteric nervous system nuclei, which together account for global symptoms of the human disease. As an extranigral site, spinal cord degeneration has also been implicated in PD progression. Interconnected to the upper CNS structures with descending and ascending pathways, spinal neurons participate in movement and sensory circuits, controlling movement and reflexes. Several clinical and in vivo studies have demonstrated signs of parkinsonism-related degenerative processes in spinal cord, which led to recent consideration of spinal cord as an area of potential therapeutic target. In a nutshell, this review explores how the existing animal models can actually reflect the human disease in order to facilitate PD research. Evolution of extranigral degeneration studies has been succinctly revisited, followed by a survey on animal models in light of recent findings in clinical PD. Together, it may help to develop effective therapeutic strategies for PD.

Regulation of GSK-3beta by calpain in the 3-nitropropionic acid model

Glycogen synthase kinase-3beta (GSK-3beta) is a crucial component in the cascade of events that culminate in a range of neurodegenerative diseases. It is controlled by several pathways, including calpain-mediated cleavage. Calpain mediates in cell death induced by 3-nitropropionic acid (3-NP), but GSK-3beta regulation has not been demonstrated. Here we studied changes in total GSK-3beta protein levels and GSK-3beta phosphorylation at Ser-9 in this model. The 3-NP treatment induced GSK-3beta truncation. This regulation was dependent on calpain activation, since addition of calpeptin to the medium prevented this cleavage. While calpain inhibition prevented 3-NP-induced neuronal loss, inhibition of GSK-3beta by SB-415286 did not. Furthermore, inhibition of cdk5, a known target of calpain involved in 3-NP-induced cell death, also failed to rescue neurons in our model. Our results point to a new target of calpain and indicate possible cross-talk between calpain and GSK-3beta in the 3-NP toxicity pathway. On the basis of our findings, we propose that calpain may modulate 3-NP-induced neuronal loss.

Pathways of methamphetamine toxicity

Methamphetamine (METH) is a drug of abuse which is neurotoxic for the nigrostriatal system. METH-induced neurodegeneration involves production of reactive oxygen species, triggering autophagic vacuoles within nigral neurons of chronic abusers of METH. In fact, Cu,Zn-superoxide dismutase 1 (SOD1) is a critical protein for the neurotoxic effects of METH on DA neurons. Moreover, mutations in the SOD1 gene cause amyotrophic lateral sclerosis, a dramatic neurodegenerative disorder. In the present paper we demonstrate that in G93A transgenic mice, overexpressing the ALS-linked mutant form of SOD1, surviving motor neurons share common intracellular alterations with METH-exposed DA neurons. We hypothesize that in mutant SOD1 transgenic mice, a defective autophagy might be responsible for the neurotoxic effects seen with in nigral neurons during METH toxicity.

Spinal cord degeneration in C57BL/6N mice following induction of experimental parkinsonism with MPTP

We examined neurodegeneration in spinal cord (SC) and role of such extra-nigral degeneration in MPTP-induced experimental parkinsonism in C57BL/6N mice. HPLC-photodiode array analysis confirmed presence of the active neurotoxin MPP+ in SC after single injection of MPTP (25 mg/kg, i.p.). Mitochondrial enzyme monoamine oxidase-B (MAO-B) responsible for in vivo conversion of MPTP to MPP+ was inhibited in SC by pre-treatment with l-deprenyl, a specific inhibitor of MAO-B. Besides in vitro conversion of MPTP to MPP+ occurred by SC mitochondrial preparation, which was inhibited by l-deprenyl implicating SC as a specific target of MPTP-neurotoxicity. Double immunofluorescent labeling and spectrofluorimetric assay via kynuramine oxidation showed MAO-B expression and activity in SC neurons. Localization of dopamine transporter immunoreactivity in SC along with specific uptake of (3)H-MPP+ by SC synaptosomal preparation further confirmed SC as target of MPTP-neurotoxicity. Compared with control, increased neuronal death on the seventh day in SC of mice injected with MPTP (2 x 25 mg/kg, at 6 h interval) strongly suggested SC degeneration in pre-symptomatic phase of MPTP-induced experimental parkinsonism. Such extra-nigral neurodegeneration in Parkinson's disease indicated novel molecular mechanism preceding nigrostriatal degeneration and suggested designing broad therapeutic intervention for this complex movement disorder.

The parkinsonian neurotoxin rotenone activates calpain and caspase-3 leading to motoneuron degeneration in spinal cord of Lewis rats

Exposure to environmental toxins increases the risk of neurodegenerative diseases including Parkinson's disease (PD). Rotenone is a neurotoxin that has been used to induce experimental Parkinsonism in rats. We used the rotenone model of experimental Parkinsonism to explore a novel aspect of extra-nigral degeneration, the neurodegeneration of spinal cord (SC), in PD. Rotenone administration to male Lewis rats caused significant neuronal cell death in cervical and lumbar SC as compared with control animals. Dying neurons were motoneurons as identified by double immunofluorescent labeling for terminal deoxynucleotidyl transferase, recombinant-mediated dUTP nick-end labeling-positive (TUNEL(+)) cells and choline acetyltransferase (ChAT)-immunoreactivity. Neuronal death was accompanied by abundant astrogliosis and microgliosis as evidenced from glial fibrillary acidic protein (GFAP)-immunoreactivity and OX-42-immunoreactivity, respectively, implicating an inflammatory component during neurodegeneration in SC. However, the integrity of the white matter in SC was not affected by rotenone administration as evidenced from the non co-localization of any TUNEL(+) cells with GFAP-immunoreactivity and myelin basic protein (MBP)-immunoreactivity, the selective markers for astrocytes and oligodendrocytes, respectively. Increased activities of 76 kD active m-calpain and 17/19 kD active caspase-3 further demonstrated involvement of these enzymes in cell death in SC. The finding of ChAT(+) cell death also suggested degeneration of SC motoneurons in rotenone-induced experimental Parkinsonism. Thus, this is the first report of its kind in which the selective vulnerability of a putative parkinsonian target outside of nigrostriatal system has been tested using an environmental toxin to understand the pathophysiology of PD. Moreover, rotenone-induced degeneration of SC motoneuron in this model of experimental Parkinsonism progressed with upregulation of calpain and caspase-3.

Calpain activation in apoptosis of motoneurons in cell culture models of experimental parkinsonism

Parkinson's disease (PD) is a movement disorder characterized by progressive degeneration of primarily the dopaminergic neurons in the substantia nigra (SN). The present study briefly describes our findings to support the hypothesis that there is a possibility of degeneration of spinal cord (SC) motoneurons in course of parkinsonism. In cell culture models of experimental parkinsonism, we examined the degeneration of ventral SC motoneuron cell line (VSC4.1) following exposure to two different toxins, such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and rotenone. Our studies suggested calpain activation in the apoptosis of VSC4.1 motoneurons due to exposure to these parkinsonian toxins. Furthermore, our study showed the toxic effects of the dopaminergic toxin methamphetamine (METH) on VSC4.1 cells. The results strongly implicated a possible role for calpain in the mechanism of motoneuron apoptosis during parkinsonian degeneration, at large. Hence, we examined the neuroprotective efficacy of calpeptin, a specific inhibitor of calpain, in cell culture model of experimental parkinsonism.

Bone marrow-derived microglia contribute to the neuroinflammatory response and express iNOS in the MPTP mouse model of Parkinson's disease

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication in mice results in dopamine neuron degeneration that is alleviated by prevention of microglia cell activation and blockade of iNOS production. However, the role of peripherally derived microglia in this response has not been well characterized. In the present study, we investigated the time course of infiltration and phenotypic differentiation of bone marrow-derived cells (BMDCs) following MPTP treatment in mice, using green fluorescent protein (GFP) bone marrow chimeras. BMDCs were found in the meninges, choroid plexus, blood vessels, and brain parenchyma in both saline and MPTP-treated mice. MPTP stimulated a transient, two-fold increase in the rate of BMDC infiltration into the brain, concomitant with the onset of microglia activation. The majority of BMDCs were microglial in phenotype, as assessed by morphology and expression of the pan-hematopoietic marker CD45 and the microglia marker CD11b. We did not observe BMDCs that expressed neuronal or astroglial markers. Over 90% of bone marrow-derived microglia expressed the inducible form of nitric oxide synthase (iNOS), suggesting that peripherally derived microglia may play a deleterious role in MPTP-induced degeneration.

BimEL up‐regulation potentiates AIF translocation and cell death in response to MPTP

This study attempted to elucidate the signaling mechanism underlying dopaminergic cell death in the MPP+ model for Parkinson's disease. In neuronal-differentiated PC12 cells, through the regulation by activated JNK and c-jun, BimEL expression was markedly increased in response to MPP+ treatment, which led to the cell degeneration. In lieu of Smac translocation as seen in other paradigms, up-regulation of BimEL effected an increase in calpain I activity that, in turn, mediated AIF release from the mitochondria. In support, we found that knocking down BimEL expression resulted in a decrease in calpain I activity, as well as AIF release from the mitochondria and cell death. Finally, inhibition of calpain activity mitigated AIF release from the mitochondria and cell death. Under cell-free conditions, activated purified calpain I could induce the release of AIF from isolated mitochondria without the participation of BimEL or activated JNK, suggesting that AIF release is a direct consequence of calpain I activity. In concert, the results suggest a novel signaling pathway for dopaminergic cell degeneration, in which MPP+ induces the up-regulation of BimEL, which in turn potentiates an elevation in calpain I activity that mediates AIF release and cell death in a caspase-independent manner.

The calpain inhibitor MDL 28170 prevents inflammation-induced neurofilament light chain breakdown in the spinal cord and reduces thermal hyperalgesia

Since long-term hyperexcitability of nociceptive neurons in the spinal cord has been suggested to be caused and maintained by changes of protein expression we assessed protein patterns in lumbar spinal cord during a zymosan induced paw inflammation employing two-dimensional (2D) gel electrophoresis. 2D PAGE revealed a time-dependent breakdown of scaffolding proteins one of which was neurofilament light chain (NFL) protein, which has been previously found to be important for axonal architecture and transport. Nociception induced breakdown of NFL in the spinal cord and dorsal root ganglias was prevented by pretreatment of the animals with a single dose of the specific inhibitor of the protease calpain (MDL-28170) which has been shown to be the primary protease involved in neurofilament degradation in neurodegenerative diseases. Treatment with the calpain inhibitor also provided anti-inflammatory and anti-hyperalgesic effects in the zymosan-induced paw inflammation model irrespective of whether the drug was administered systemically (i.p.) or delivered onto the lumbar spinal cord. This suggests that the activation of calpain is involved in the sensitization of nociceptive neurons what is partly due to neurofilament breakdown but cleavage of other calpain substrates may also be involved. Our results indicate that inhibition of pathological calpain activity may present an interesting novel drug target in the treatment of pain and inflammation.

Immunofluorescent labeling of increased calpain expression and neuronal death in the spinal cord of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice

Parkinson's disease (PD) is a movement disorder characterized by rigidity, tremor, and bradykinesia, originating from degeneration of dopaminergic neurons in the substantia nigra (SN), retrorubral area, and locus ceoruleus (LC). Calpain has been implicated in the pathophysiology of neurodegenerative diseases. Since the spinal cord (SC) and brain are integrally connected and calpain is involved in cell death and mitochondrial dysfunction, we hypothesized that SC neurons are also affected in PD. In order to examine this hypothesis, we examined both brain and SC from mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). To identify cells expressing calpain, double immunofluorescent labeling was performed with antibodies specific for calpain and a cell type (OX-42, GFAP, or NeuN). Combined terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) and double immunofluorescent labeling were used to identify death of specific cells in the central nervous system (CNS). There was an increase in calpain expression in microglia, astrocytes, and neurons in the SC of MPTP-treated mice at 1 and 7 days, as compared to controls. TUNEL-positive neurons in the SC and SN showed apoptotic characteristics. These results demonstrated that neuronal death occurred not only in SN but also in the SC of MPTP-treated mice and has provided evidence for a possible calpain-mediated SC neuronal death in MPTP-induced parkinsonism in mice.

Injury and strain-dependent dopaminergic neuronal degeneration in the substantia nigra of mice after axotomy or MPTP

We studied the effects of axotomy or neurotoxin on the survival of substantia nigra pars compacta (SNpc) neurons in two strains of mice, FVB/N or C57BL/6. Fluoro gold (FG) was injected into both striata of the mice to retrogradely label the nigrostriatal neuronal population. Ten days later, these neurons were axotomized in the medial forebrain bundle (MFB) unilaterally or N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was administered intraperitonealy for 2 days to produce bilateral degeneration. MFB transection or MPTP administration produced a progressive loss of FG-labeled and tyrosine hydroxylase immunolabeled (TH+) neurons in both strains. Relative to control, 72% of SNpc neurons died 4 weeks after axotomy in C57BL/6 mice and 50% died after axotomy in FVB/N mice. MPTP resulted in death of 80% of SNpc neurons in C57BL/6 mice but only 40% in the FVB strain 4 weeks after MPTP administration. In this more sensitive strain, MPTP cell death was associated with positive staining for terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and nuclear condensation. In contrast, no TUNEL staining was detected in SNpc after MPTP in FVB/N mice. Further, while similar kinetics and extent of cell death accompanied axotomy, axotomy-induced cell death was TUNEL negative in both FVB/N and C57BL/6 mice. Double staining for TUNEL and microtubule associated protein 2 confirmed that the majority of the TUNEL positive cells were neurons. These data indicate that genetic factors and the type of lesion play an important role in determining death of dopaminergic neurons after injury.