Proteasomal degradation of tyrosine hydroxylase and neurodegeneration

Initial Molecular Mechanisms of the Pathogenesis of Parkinson's Disease in a Mouse Neurotoxic Model of the Earliest Preclinical Stage of This Disease

Studying the initial molecular mechanisms of the pathogenesis of Parkinson's disease (PD), primarily in the nigrostriatal dopaminergic system, is one of the priorities in neurology. Of particular interest is elucidating these mechanisms in the preclinical stage of PD, which lasts decades before diagnosis and is therefore not available for study in patients. Therefore, our main goal was to study the initial molecular mechanisms of the pathogenesis of PD in the striatum, the key center for dopamine regulation in motor function, in a mouse model of the earliest preclinical stage of PD, from 1 to 24 h after the administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). It was shown that the content of tyrosine hydroxylase (TH), the first enzyme in dopamine synthesis, does not change within 6 h after the administration of MPTP, but decreases after 24 h. In turn, TH activity increases after 1 h, decreases after 3 h, remains at the control level after 6 h, and decreases 24 h after the administration of MPTP. The concentration of dopamine in the striatum gradually decreases after MPTP administration, despite a decrease in its degradation. The identified initial molecular mechanisms of PD pathogenesis are considered as potential targets for the development of preventive neuroprotective treatment.

Synergistic effect of electric stimulation and mesenchymal stem cells against Parkinson's disease

Electroconvulsive therapy (ECT) has known beneficial effects on the core motor symptoms of Parkinson's disease (PD), likely through induction of dopamine release and sensitivity of dopamine receptors. Mesenchymal stem cells (MSCs) can salvage loss of dopamine in PD through their differentiation into dopaminergic neurons. However, it is not known if combined ECT and MSC transplantation may have a synergistic effect against PD. Here, we showed that ECT significantly increased the differentiation of the transplanted MSCs into dopaminergic neurons in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of PD. On the other hand, transplantation of MSCs significantly increased dopamine levels after ECT. Co-application of ECT and MSC transplantation generated a synergistic effect through increases in dopamine and decreases in pro-inflammatory cytokines, resulting in significantly attenuated defect in stepping test and rotational behavior in MPTP-mice. Together, our data suggest that combined ECT and MSC transplantation can be a valuable treatment of PD.

Epigenetic Control of Rho-Associated Protein Kinase 2 in Neurodegeneration

Upregulation of Rho-associated protein kinase 2 (ROCK2) hallmarks the progression of neurodegenerative diseases. However, the molecular mechanisms underlying the regulation of ROCK2 expression are not clear and thus addressed in the current study. We generated a subacute model of Parkinson's disease in mice with a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) method. The MPTP model was validated by impaired rotational behavior of the mice upon apomorphine exposure, astrocytic activation, and reduction in tyrosine-hydroxylase-positive neurons in the mouse striatum. Moreover, MPTP induced increases in ROCK2 protein but not in ROCK2 mRNA. Further analysis showed that MPTP inhibited the expression of microRNA-291 (miR-291), which suppressed ROCK2 mRNA via 3'-UTR-binding in neuronal cells to increase ROCK2 protein. Intracranial injection of miR-291 four days before MPTP alleviated the impaired rotational behavior of the mice upon apomorphine exposure, MPTP-induced astrocytic activation, and the reduction in tyrosine-hydroxylase-positive neurons in the mouse striatum. Together, these data suggest that miR-291 has a protective role in neurodegeneration, likely through regulation of ROCK2.

Iron Oxide Nanoparticles Affects Behaviour and Monoamine Levels in Mice

Iron oxide (Fe₂O₃) nanoparticles (NPs) attract the attention of clinicians for its unique magnetic and paramagnetic properties, which are exclusively used in neurodiagnostics and therapeutics among the other biomedical applications. Despite numerous research findings has already proved neurotoxicity of Fe₂O₃-NPs, factors affecting neurobehaviour has not been elucidated. In this study, mice were exposed to Fe₂O₃-NPs (25 and 50 mg/kg body weight) by oral intubation daily for 30 days. It was observed that Fe₂O₃-NPs remarkably impair motor coordination and memory. In the treated brain regions, mitochondrial damage, depleted energy level and decreased ATPase (Mg²⁺, Ca²⁺ and Na⁺/K⁺) activities were observed. Disturbed ion homeostasis and axonal demyelination in the treated brain regions contributes to poor motor coordination. Increased intracellular calcium ([Ca²⁺]_i) and decreased expression of growth associated protein 43 (GAP43) impairs vesicular exocytosis could result in insufficient signal between neurons. In addition, levels of dopamine (DA), norepinephrine (NE) and epinephrine (EP) were found to be altered in the subjected brain regions in correspondence to the expression of monoamine oxidases (MAO). Along with all these factors, over expression of glial fibrillary acidic protein (GFAP) confirms the neuronal damage, suggesting the evidences for behavioural changes.

Diagnosis and management of Neuromyelitis Optica Spectrum Disorder (NMOSD) in Iran: A consensus guideline and recommendations

Neuromyelitis Optica Spectrum Disorder (NMOSD) is a relapsing neuro inflammatory disease of the central nervous system that typically presents with optic neuritis or myelitis and may cause severe disability. The diagnostic criteria have been updated and several immunosuppressive agents have been demonstrated to prevent acute exacerbations. As the disease rarely develops in a progressive course, management of acute attacks and proper prevention of exacerbations may change the long term out-come and prevent future disability. Consensus recommendations and guidelines will help the physicians to improve their practice and unify the treatment approaches in different communities. In order to develop a national consensus and recommendations for the diagnosis and management of NMOSD in Iran, a group of neurologists with long term experience in management of NMOSD were gathered to develop this consensus based on available national and international data. The primary draft was prepared and discussed to suggest the most appropriate treatment for these patients. We propose strategies for early diagnosis and treatment for prevention of relapses and minimizing consequences of attacks as a primary therapeutic goal. Attacks are currently treated with intravenous corticosteroids and, in refractory cases, with plasma exchange. All participants agreed on preventive treatment with currently available immunosuppressive agents such as azothioprin, rituximab and mycofenolate mofetil based on previous positive data in NMOSD in order to reduce attack frequency. The current consensus reviews the previous data and provides the clinicians with practical recommendations and advices for the diagnosis and management of NMOSD based on scientific data and clinical experience.

Catecholaminergic-to-cholinergic transition of sympathetic nerve fibers is stimulated under healthy but not under inflammatory arthritic conditions

OBJECTIVE

Density of sympathetic nerve fibers decreases in inflamed arthritic tissue tested by immunoreactivity towards tyrosine-hydroxylase (TH, catecholaminergic key enzyme). Since sympathetic nerve fibers may change phenotype from catecholaminergic to cholinergic (example: sweat glands), loss of nerve fibers may relate to undetectable TH. We aimed to investigate possible catecholaminergic-to-cholinergic transition of sympathetic nerve fibers in synovial tissue of animals with arthritis, and patients with rheumatoid arthritis (RA) and osteoarthritis (OA), and we wanted to find a possible transition factor.

METHODS

Nerve fibers were detected by immunofluorescence towards TH (catecholaminergic) and vesicular acetylcholine transporter (cholinergic). Co-culture experiments with sympathetic ganglia and lymphocytes or osteoclast progenitors were designed to find stimulators of catecholaminergic-to-cholinergic transition (including gene expression profiling).

RESULTS

In mouse joints, an increased density of cholinergic relative to catecholaminergic nerve fibers appeared towards day 35 after immunization, but most nerve fibers were located in healthy joint-adjacent skin or muscle and almost none in inflamed synovial tissue. In humans, cholinergic fibers are more prevalent in OA synovial tissue than in RA. Co-culture of sympathetic ganglia with osteoclast progenitors obtained from healthy but not from arthritic animals induced catecholaminergic-to-cholinergic transition. Osteoclast mRNA microarray data indicated that leukemia inhibitory factor (LIF) is a candidate transition factor, which was confirmed in ganglia experiments, particularly, in the presence of progesterone.

CONCLUSION

In humans and mice, catecholaminergic-to-cholinergic sympathetic transition happens in less inflamed tissue but not in inflamed arthritic tissue. Under healthy conditions, presence of cholinergic sympathetic nerve fibers may support the cholinergic anti-inflammatory influence recently described.

Anti-inflammatory effects of cell-based therapy with tyrosine hydroxylase-positive catecholaminergic cells in experimental arthritis

OBJECTIVES

Studies in rheumatoid arthritis (RA), osteoarthritis (OA) and mice with arthritis demonstrated tyrosine hydroxylase-positive (TH(+)) cells in arthritic synovium and parallel loss of sympathetic nerve fibres. The exact function of TH(+) cells and mode of TH induction are not known.

METHODS

Synovial cells of RA/OA were isolated and cultured under normoxic/hypoxic conditions with/without stimulating enzyme cofactors of TH and inhibitors of TH. We studied TH expression and release of cytokines/catecholamines. In vivo function was tested by cell therapy with TH(+) neuronal precursor cells (TH(+) neuronal cells) in DBA/1 mice with collagen type II-induced arthritis (CIA).

RESULTS

Compared with normoxic conditions, hypoxia increased TH protein expression and catecholamine synthesis and decreased release of tumour necrosis factor (TNF) in OA/RA synovial cells. This inhibitory effect on TNF was reversed by TH inhibition with α-methyl-para-tyrosine (αMPT), which was particularly evident under hypoxic conditions. Incubation with specific TH cofactors (tetrahydrobiopterin and Fe(2+)) increased hypoxia-induced inhibition of TNF, which was also reversed by αMPT. To address a possible clinical role of TH(+) cells, murine TH(+) neuronal cells were generated from mesenchymal stem cells. TH(+) neuronal cells exhibited a typical catecholaminergic phenotype. Adoptive transfer of TH(+) neuronal cells markedly reduced CIA in mice, and 6-hydroxydopamine, which depletes TH(+) cells, reversed this effect.

CONCLUSIONS

The anti-inflammatory effect of TH(+) neuronal cells on experimental arthritis has been presented for the first time. In RA/OA, TH(+) synovial cells have TH-dependent anti-inflammatory capacities, which are augmented under hypoxia. Using generated TH(+) neuronal cells might open new avenues for cell-based therapy.