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Glial pathology and energy metabolism changes in the brain precede symptoms of Parkinson’s disease (PD) and multiple other neurodegenerative diseases. Astrocytes govern and regulate a large part of the energy metabolism in the brain. Prolonged impairment of astrocytic functions could increase the vulnerability of dopaminergic neurons in the substantia nigra (SN). In this model, 40‑50% of dopaminergic neurons were selectively killed, causing transient locomotor disability compensated with time. We also induced death of astrocytes in the SN, simultaneously activating microglia but sparing the dopaminergic neurons. The astrocytes replenished after toxin withdrawal. We studied multiple markers of energy metabolism and mitochondrial oxidative phosphorylation (OxPhos) complex and supercomplex functioning during the early stages of neurodegeneration and compensation in the SN and striatum (STR). Death of astrocytes diminished the capability of the dopaminergic system to compensate for the degeneration of neurons. It caused a local energy deprivation, a shift in the usage of energy substrates, via increased glycogenolysis and glycolysis markers, ketone bodies availability, and fatty acid transport in remaining glial cells. Increased neuronal expression of CPT1c and astrocytic expression of CPT1a suggest adaptation in fatty acid use. On the other hand, lesion of dopaminergic neurons influenced OxPhos system and enhanced its functioning. Microglia activation also plays an important role in the processes of degeneration, compensation, and energy metabolism regulation. Modulation of its activation phenotypes might be beneficial towards the indicated processes. Astrocyte and microglia energetic influence is one of the factors in the neuronal compensatory mechanisms of dopaminergic system and might have a leading role in presymptomatic PD stages.
Parkinson’s Disease (PD) is characterized by an increased production of oxygen free radicals leading to alteration of the cellular constituents and subsequent dopaminergic cell loss within the region of substantia nigra (SN) and ventral tegmental area (VTA). However, it is well known that PD is not only associated with dopaminergic transmission. Involvement of extranigral structures in PD includes the noradrenergic system as well. Post-mortem studies of human brains revealed that neuronal loss associated with PD may proceed and is even greater in the region of locus ceruleus (LC) than SN/ VTA. In PD animal models, the loss of noradrenaline made worse the dopamine nigrostriatal damage and, in opposite, an enhanced noradrenaline level may have a neuroprotective role. The aim of this study was to determine whether genetically evoked, selective loss of noradrenergic neurons may have any long-term, negative impact on the dopaminergic system. We applied the conditional inactivation of the gene encoding transcription factor TIF-IA (essential for the regulation of rRNA synthesis) by the Cre-loxP system to induce the progressive and selective loss of noradrenergic neurons which was achieved by expressing Cre recombinase under dopamine beta-hydroxylase (DBH) promoter. Resulting TIFIADBHCre mice were born at expected rates, viable but showed clear signs of noradrenergic innervations failure e.g. ptosis, reduced locomotor activity, growth retardance and shorten life span. The animals were analyzed at 8 and 12 weeks of age. The selective loss of noradrenergic neurons was confirmed by immunofluorescent staining with the anti-tyrosine hydroxylase (TH) antibody. We observed approx. 90% reduction of TH positive cells in the LC of 8 weeks TIF-IADBHCre mice. The number of TH+ cells was not changed in the region of SN/VTA, neither in 8 nor 12 week old mutants. However, our preliminary data indicate that lack of the noradrenergic transmission may lead to enhanced expression of selected markers associated with neurodegeneration within the region of SN/VTA. Namely, we have found 1.4 fold up-regulation of mRNA encoding for glial fibrillary acidic protein (GFAP) as revealed by quantitative real-time PCR and increased level of oxidative stress shown by immunoblot detection of carbonyl groups by Western Blot in the SN/VTA of 12 weeks TIF-IADBHCre mice compared to control animals. If we provide additional evidences that selective noradrenergic degeneration affects functioning of dopaminergic neurons, TIF-IADBHCre mice may became a valuable, new model for study possible anti-PD treatment at early stages of the disease as dopaminergic neurons in these mice are not directly affected by the mutation. As for today, there are no experimental studies on a possible long-term negative impact of progressive noradrenergic degeneration on other neurotransmitter systems despite of clinically observed concomitant loss of SN/VTA and LC neurons in PD. This study was supported by the grant no 2011/03/B/NZ7/05949 financed by National Science Centre and statutory funds of the Institute of Pharmacology, Polish Academy of Sciences.
Parkinson’s disease (PD) is characterized by an inevitable loss of dopaminergic cells.However, examination of human brain tissues revealed that noradrenergic cell loss in the region of the locus coeruleus (LC) may proceed and may be even greater than dopaminergic degeneration. AIM(S): The aim of this study was to determine whether genetically evoked, selective loss of LC noradrenergic neurons in a progressive manner may negatively influence the dopaminergic system. Our mice models have progressive degeneration of the noradrenergic system, based on deletion of the gene Rrn3 encoding transcription factor TIF-IA, which is essential for the regulation of rRNA synthesis. METHOD(S): First, we applied the conditional inactivation of the Rrn3 by the Cre-loxP system expressing Cre recombinase under DBH promoter. TIF‑IADBHCre mice revealed ptosis, reduced locomotor activity, and a shortened life span associated with enhanced expression of various neurodegenerative markers within the dopaminergic system, including upregulation of micro- and astroglia, pro-inflammatory proteins, and enhanced level of oxidative stress. To limit mutations to the CNS, in a second model a Cre-dependent lentiviral vector carrying the Rrn3 deletion created by the CRISPR/Cas9 system was directly delivered to LC of DBHCre mice. RESULTS: Our construct was first successfully tested in vitro on primary dopamine neurons followed by in vivo stereotactic application. This approach seems to be successful as, in preliminary data, we observed the disintegration of nucleoli in transduced noradrenergic neurons in LC, which is the determinant of the functional impairment of the targeted TIF‑IA. CONCLUSIONS: To-date, there are no experimental studies on possible long-term negative impacts of progressive noradrenergic degeneration on other neurotransmitter systems, despite the clinically observed concomitant loss of SN/VTA and LC neurons in PD. If we provide additional evidence, mice with ongoing neurodegeneration of LC neurons may became a valuable tool for studying the presymptomatic phase of PD.
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