Role of inflammation in 6- hydroxydopamine model of Parkinson’s disease and its modulation by Peroxisome Proliferator Activated receptor gamma (PPAR-γ) agonist as a neuroprotective strategy

Parkinson’s disease is an age related progressive neurodegenerative disorder affecting ~2% of the population over the age of 65. The aetiology of Parkinson’s disease is not fully understood and treatment limited. Hence, the goal of ongoing research is to understand and target the mechanisms underlying the disease process to halt or slow down its progression. Parkinson’s disease is pathologically characterised by the loss of dopaminergic neurons in the substantial nigra that leads to the loss of innervation to the striatum, subsequently leading to the motor complications observed in Parkinson’s sufferers. Recent clinical and experimental evidence suggests that inflammation, characterised by over activation of the brain’s resident immune cells such as microglia/macrophages, play a detrimental role in Parkinson’s pathology. This project, for the first time aims to explore the time course of microglial activation in association with dopaminergic neuronal cell death in the substantia nigra utilising the 6-hydroxy dopamine rat model of Parkinson’s. The dynamics of morphological, immunophenotypic and phagocytic properties of activated microglia in the substantia nigra was assessed immunohistochemically. In addition we explored the cellular events between activated microglia and degenerating neurons in this model that had not been previously well defined. The role of matrix metalloproteinases as signalling molecules that activate microglia were also studied. Finally the significance of local microglial activation in the substantia nigra was elucidated by modulation of the microglial response via activation of the gamma subtype of peroxisome proliferator activated receptors. This project provided evidence that microglial activation preceded dopaminergic neuronal cell death in the substantia nigra and inhibition of microglial response serves as a neuroprotective strategy in Parkinson’s disease

Loss of locus coeruleus noradrenergic neurons alters the inflammatory response to LPS in substantia nigra but does not affect nigral cell loss

This is the accepted version of the following article: Mahmoud M. Iravani, Mona Sadeghian, Sarah Rose and Peter Jenner, “Loss of locus coeruleus noradrenergic neurons alters the inflammatory response to LPS in substantia nigra but does not affect nigral cell loss”, Journal of Neural Transmission, Vol. 121(12): 1493-1505, first published online 30 April 2014. The version of record is available online via doi: 10.1007/s00702-014-1223-1. © Springer-Verlag Wien 2014In Parkinson's disease (PD), destruction of noradrenergic neurons in the locus coeruleus (LC) may precede damage to nigral cells and subsequently exaggerate dopaminergic cell loss. We examine if destruction of the locus coeruleus with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) alters dopaminergic cell loss in substantia nigra (SN) initiated by lipopolysaccharide (LPS) in the rat through an effect on glial cell activation. In rats, a single intraperitoneal dose of DSP-4 administered 8 days previously, caused a marked loss of tyrosine hydroxylase positive neurons in LC but no change in dopaminergic cell number in SN. Unilateral nigral LPS administration resulted in marked dopaminergic cell death with reactive microgliosis associated with enhanced p47 phox in OX-6 and OX-42 positive microglia. There was proliferation of inducible nitric oxide synthase (iNOS)-positive cells, formation of 3-nitrotyrosine (3-NT) and proliferation of astrocytes that expressed glial cell line-derived neurotrophic factor (GDNF). Following combined DSP-4 treatment and subsequent administration of LPS, unexpectedly, no further loss of tyrosine hydroxylase (TH)-immunoreactivity (-ir) occurred in the SN compared to the effects of LPS alone. However, there was a marked alteration in the morphology of microglial cell and a reduction of 3-NT- and iNOS-ir was evident. Expression of p47 phox was downregulated in microglia but up-regulated in TH-ir neurons. No further change in GFAP-ir was observed compared to that produced by DSP-4 alone or LPS alone, but the expression of GDNF was markedly reduced. This study suggests that in contrast to previous reports, prior LC damage does not influence subsequent nigral dopaminergic cell degeneration induced by LPS. Rather it appears to attenuate the microglial response thought to contribute to disease progression in PD.Peer reviewedFinal Accepted Versio

Assessment of Mitochondrial Dysfunction in Experimental Autoimmune Encephalomyelitis (EAE) Models of Multiple Sclerosis.

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) that involves the autoreactive T-cell attack on axonal myelin sheath. Lesions or plaques formed as a result of repeated damage and repair mechanisms lead to impaired relay of electrical impulses along the nerve, manifesting as clinical symptoms of MS. Evidence from studies in experimental autoimmune encephalomyelitis (EAE) models of MS strongly suggests that mitochondrial dysfunction presents at the onset of disease and throughout the disease course. The aim of this study was to determine if mitochondrial dysfunction occurs before clinical symptoms arise, and whether this is confined to the CNS. EAE was induced in C57B/L6 mice, and citrate synthase and mitochondrial respiratory chain (MRC) complex I-IV activities were assayed at presymptomatic (3 or 10 days post first immunisation (3 or 10 DPI)) and asymptomatic (17 days post first immunisation (17 DPI) time-points in central nervous system (CNS; spinal cord) and peripheral (liver and jaw muscle) tissues. Samples from animals immunised with myelin oligodendrocyte glycoprotein (MOG) as EAE models were compared with control animals immunised with adjuvant (ADJ) only. Significant changes in MOG compared to control ADJ animals in MRC complex I activity occurred only at presymptomatic stages, with an increase in the spinal cord at 10 DPI (87.9%), an increase at 3 DPI (25.6%) and decrease at 10 DPI (22.3%) in the jaw muscle, and an increase in the liver at 10 DPI (71.5%). MRC complex II/III activity changes occurred at presymptomatic and the asymptomatic stages of the disease, with a decrease occurring in the spinal cord at 3 DPI (87.6%) and an increase at 17 DPI (36.7%), increase in the jaw muscle at 10 DPI (25.4%), and an increase at 3 DPI (75.2%) and decrease at 17 DPI (95.7%) in the liver. Citrate synthase activity was also significantly decreased at 10 DPI (27.3%) in the liver. No significant changes were observed in complex IV across all three tissues assayed. Our findings reveal evidence that mitochondrial dysfunction is present at the asymptomatic stages in the EAE model of MS, and that the changes in MRC enzyme activities are tissue-specific and are not confined to the CNS

Global burden of 288 causes of death and life expectancy decomposition in 204 countries and territories and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

BACKGROUND Regular, detailed reporting on population health by underlying cause of death is fundamental for public health decision making. Cause-specific estimates of mortality and the subsequent effects on life expectancy worldwide are valuable metrics to gauge progress in reducing mortality rates. These estimates are particularly important following large-scale mortality spikes, such as the COVID-19 pandemic. When systematically analysed, mortality rates and life expectancy allow comparisons of the consequences of causes of death globally and over time, providing a nuanced understanding of the effect of these causes on global populations. METHODS The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 cause-of-death analysis estimated mortality and years of life lost (YLLs) from 288 causes of death by age-sex-location-year in 204 countries and territories and 811 subnational locations for each year from 1990 until 2021. The analysis used 56 604 data sources, including data from vital registration and verbal autopsy as well as surveys, censuses, surveillance systems, and cancer registries, among others. As with previous GBD rounds, cause-specific death rates for most causes were estimated using the Cause of Death Ensemble model-a modelling tool developed for GBD to assess the out-of-sample predictive validity of different statistical models and covariate permutations and combine those results to produce cause-specific mortality estimates-with alternative strategies adapted to model causes with insufficient data, substantial changes in reporting over the study period, or unusual epidemiology. YLLs were computed as the product of the number of deaths for each cause-age-sex-location-year and the standard life expectancy at each age. As part of the modelling process, uncertainty intervals (UIs) were generated using the 2·5th and 97·5th percentiles from a 1000-draw distribution for each metric. We decomposed life expectancy by cause of death, location, and year to show cause-specific effects on life expectancy from 1990 to 2021. We also used the coefficient of variation and the fraction of population affected by 90% of deaths to highlight concentrations of mortality. Findings are reported in counts and age-standardised rates. Methodological improvements for cause-of-death estimates in GBD 2021 include the expansion of under-5-years age group to include four new age groups, enhanced methods to account for stochastic variation of sparse data, and the inclusion of COVID-19 and other pandemic-related mortality-which includes excess mortality associated with the pandemic, excluding COVID-19, lower respiratory infections, measles, malaria, and pertussis. For this analysis, 199 new country-years of vital registration cause-of-death data, 5 country-years of surveillance data, 21 country-years of verbal autopsy data, and 94 country-years of other data types were added to those used in previous GBD rounds. FINDINGS The leading causes of age-standardised deaths globally were the same in 2019 as they were in 1990; in descending order, these were, ischaemic heart disease, stroke, chronic obstructive pulmonary disease, and lower respiratory infections. In 2021, however, COVID-19 replaced stroke as the second-leading age-standardised cause of death, with 94·0 deaths (95% UI 89·2-100·0) per 100 000 population. The COVID-19 pandemic shifted the rankings of the leading five causes, lowering stroke to the third-leading and chronic obstructive pulmonary disease to the fourth-leading position. In 2021, the highest age-standardised death rates from COVID-19 occurred in sub-Saharan Africa (271·0 deaths [250·1-290·7] per 100 000 population) and Latin America and the Caribbean (195·4 deaths [182·1-211·4] per 100 000 population). The lowest age-standardised death rates from COVID-19 were in the high-income super-region (48·1 deaths [47·4-48·8] per 100 000 population) and southeast Asia, east Asia, and Oceania (23·2 deaths [16·3-37·2] per 100 000 population). Globally, life expectancy steadily improved between 1990 and 2019 for 18 of the 22 investigated causes. Decomposition of global and regional life expectancy showed the positive effect that reductions in deaths from enteric infections, lower respiratory infections, stroke, and neonatal deaths, among others have contributed to improved survival over the study period. However, a net reduction of 1·6 years occurred in global life expectancy between 2019 and 2021, primarily due to increased death rates from COVID-19 and other pandemic-related mortality. Life expectancy was highly variable between super-regions over the study period, with southeast Asia, east Asia, and Oceania gaining 8·3 years (6·7-9·9) overall, while having the smallest reduction in life expectancy due to COVID-19 (0·4 years). The largest reduction in life expectancy due to COVID-19 occurred in Latin America and the Caribbean (3·6 years). Additionally, 53 of the 288 causes of death were highly concentrated in locations with less than 50% of the global population as of 2021, and these causes of death became progressively more concentrated since 1990, when only 44 causes showed this pattern. The concentration phenomenon is discussed heuristically with respect to enteric and lower respiratory infections, malaria, HIV/AIDS, neonatal disorders, tuberculosis, and measles. INTERPRETATION Long-standing gains in life expectancy and reductions in many of the leading causes of death have been disrupted by the COVID-19 pandemic, the adverse effects of which were spread unevenly among populations. Despite the pandemic, there has been continued progress in combatting several notable causes of death, leading to improved global life expectancy over the study period. Each of the seven GBD super-regions showed an overall improvement from 1990 and 2021, obscuring the negative effect in the years of the pandemic. Additionally, our findings regarding regional variation in causes of death driving increases in life expectancy hold clear policy utility. Analyses of shifting mortality trends reveal that several causes, once widespread globally, are now increasingly concentrated geographically. These changes in mortality concentration, alongside further investigation of changing risks, interventions, and relevant policy, present an important opportunity to deepen our understanding of mortality-reduction strategies. Examining patterns in mortality concentration might reveal areas where successful public health interventions have been implemented. Translating these successes to locations where certain causes of death remain entrenched can inform policies that work to improve life expectancy for people everywhere. FUNDING Bill & Melinda Gates Foundation

Demyelination models in the spinal cord

Disruption of axonal conduction within the central nervous system has obvious, negative consequences on numerous functions, including the ability to execute movement successfully. One important cause of axonal conduction deficits is primary demyelination, that is, the loss of the myelin sheaths but sparing of the axons which they surround. Such demyelination leads to conduction deficits ranging from action potential slowing and loss of transmission fidelity, to conduction block, and this latter, most severe consequence is almost inevitably the first consequence of the loss of a whole internode(s) of myelin. Several methods have been developed to induce primary demyelination in the spinal cord and some of the more common of these will be discussed in this chapter. © 2011 Springer Science+Business Media, LLC

Lipopolysaccharide-induced nigral inflammation leads to increased IL-1β tissue content and expression of astrocytic glial cell line-derived neurotrophic factor.

Reactive gliosis and inflammatory change is a key component of nigral dopaminergic cell death in Parkinson's disease (PD). Astrocyte derived glial cell line-derived neurotrophic factor (GDNF) promotes the survival and growth of dopaminergic neurones and it protects against or reverses nigral degeneration induced by 6-OHDA and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in rodents and primates. But the effect of increased levels of pro-inflammatory cytokines on the release of GDNF is unknown. This study examined the relationship between release of tumour necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) and the expression of GDNF in rats following nigral lipopolysaccharide (LPS) administration. Acute nigral administration of LPS led to marked elevation of IL-1 beta but insignificant INF-cs tissue content and to a prominent expression of GDNF immunoreactivity in astrocytes but not microglia. The results suggest that inflammation is not only involved in neuronal loss but could promote neuronal survival through increased release of GDNF following up-regulation of IL-1 beta. (C) 2012 Elsevier Ireland Ltd. All rights reserved.Peer reviewe

The acute and the long-term effects of nigral lipopolysaccharide administration on dopaminergic dysfunction and glial cell activation

Sustained reactive microgliosis may contribute to the progressive degeneration of nigral dopaminergic neurons in Parkinson's disease (PD), in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) exposed human and in non-human primates. However, the temporal relationship between glial cell activation and nigral cell death is relatively unexplored. Consequently, the effects of acute (24 h) and chronic (30 days) glial cell activation induced by unilateral supranigral lipopolysaccharide (LPS) administration were studied in rats. At 24 h, LPS administration caused a marked reduction in the number of tyrosine hydroxylase-immunoreactive (TH-ir) neurons in the substantia nigra (SN) but striatal TH-ir was unaffected. By 30 days, the loss of TH-positive neurons in the LPS-treated nigra was no greater than at 24 h although a heterogeneous loss of striatal TH-ir was present. The loss of nigrostriatal neurons was of functional significance, as at 30 days, LPS-treated rats exhibited ipsiversive circling in response to (+)-amphetamine administration. At 24 h, there was a moderate increase in glial fibrillary acidic protein (GFAP)-ir astrocytes in the SN but a marked elevation of p47phox positive OX-42-ir microglia, and intense inducible nitric oxide synthase (iNOS)-ir and 3-nitrotyrosine (3-NT)-ir was present. However, by 30 days the morphology of OX-42-ir microglia returned to a resting state, the numbers were greatly reduced and no 3-NT-ir was present. At 30 days, GFAP-ir astrocytes were markedly increased in number and iNOS-ir was present in fibrillar astrocyte-like cells. This study shows that acute glial activation leading to dopaminergic neuron degeneration is an acute short-lasting response that does not itself perpetuate cell death or lead to prolonged microglial activation.Peer reviewe

Continuous subcutaneous infusion of pramipexole protects against lipopolysaccharide-induced dopaminergic cell death without affecting the inflammatory response

The D2/D3 dopamine receptor agonist pramipexole, protects against toxin-induced dopaminergic neuronal destruction but its mechanism of action is unknown. Inflammation following glial cell activation contributes to cell death in Parkinson's disease and we now report on the effects of acute or chronic administration of pramipexole on lipopolysaccharide (LPS) induced inflammation and nigral dopaminergic cell death in the rat. At 48 h and 30 days following supranigral administration of LPS, approximately 70% of tyrosine hydroxylase (TH) immunoreactive (-ir) cells in substantia nigra had degenerated with a corresponding loss of TH-ir terminals in the striatum. In rats acutely treated with pramipexole (2 x 1 mg/k; s.c.) 48 h following LPS application, there was no difference in the number of TH-ir cells or terminals compared to LPS-treated Fats receiving vehicle. However, the continuous Subcutaneous infusion of pramipexole for 7 days prior to LPS and 21 days subsequently, produced a marked preservation of both TH-ir cells and terminals. At 48 h or 30 days, LPS induced an up-regulation of ubiquitin-ir within the nigral TH-ir neurons, which was reduced by pramipexole treatment. Thirty days following supranigral LPS administration (9 days after the end of infusion), (+)-amphetamine (5 mg/kg, i.p.) caused robust ipsiversive rotation. In rats treated with LPS but receiving continuous subcutaneous administration of pramipexole, (+)-amphetamine-induced rotation was markedly reduced. LPS-induced increase in the levels of inflammatory markers, were not affected by either acute administration or Continuous infusion of pramipexole. Continuous infusion of pramipexole protected dopaminergic neurones against inflammation induced degeneration but without modification of the inflammatory response. (C) 2008 Elsevier Inc. All rights reserved.Peer reviewe

Impulse Conduction Increases Mitochondrial Transport in Adult Mammalian Peripheral Nerves <i>In Vivo</i>

<div><p>Matching energy supply and demand is critical in the bioenergetic homeostasis of all cells. This is a special problem in neurons where high levels of energy expenditure may occur at sites remote from the cell body, given the remarkable length of axons and enormous variability of impulse activity over time. Positioning mitochondria at areas with high energy requirements is an essential solution to this problem, but it is not known how this is related to impulse conduction <i>in vivo</i>. Therefore, to study mitochondrial trafficking along resting and electrically active adult axons <i>in vivo</i>, confocal imaging of saphenous nerves in anaesthetised mice was combined with electrical and pharmacological stimulation of myelinated and unmyelinated axons, respectively. We show that low frequency activity induced by electrical stimulation significantly increases anterograde and retrograde mitochondrial traffic in comparison with silent axons. Higher frequency conduction within a physiological range (50 Hz) dramatically further increased anterograde, but not retrograde, mitochondrial traffic, by rapidly increasing the number of mobile mitochondria and gradually increasing their velocity. Similarly, topical application of capsaicin to skin innervated by the saphenous nerve increased mitochondrial traffic in both myelinated and unmyelinated axons. In addition, stationary mitochondria in axons conducting at higher frequency become shorter, thus supplying additional mitochondria to the trafficking population, presumably through enhanced fission. Mitochondria recruited to the mobile population do not accumulate near Nodes of Ranvier, but continue to travel anterogradely. This pattern of mitochondrial redistribution suggests that the peripheral terminals of sensory axons represent sites of particularly high metabolic demand during physiological high frequency conduction. As the majority of mitochondrial biogenesis occurs at the cell body, increased anterograde mitochondrial traffic may represent a mechanism that ensures a uniform increase in mitochondrial density along the length of axons during high impulse load, supporting the increased metabolic demand imposed by sustained conduction.</p></div

Higher frequency (50 Hz) conduction is associated with shortening of stationary, and an increase in distance between stationary mitochondria.

<p>(A) The total number of stationary mitochondrial profiles did not change significantly in response to impulse conduction (<i>p</i>>0.05, Kruskal-Wallis test with Dunn's multiple comparison test). (B) Average length of stationary mitochondria was significantly lower in axons conducting impulses at 50 Hz (<i>n</i> = 366, <i>p</i><0.01), or at 1 Hz following 50 Hz (<i>n</i> = 231, <i>p</i><0.001) than in naive (<i>n</i> = 231) or sham-stimulated (<i>n</i> = 366) axons. (C). Frequency distribution of length of stationary mitochondria between groups showed a significantly lower number of long mitochondria (i.e., 4 µm) and higher number of short (i.e., 2 µm) in axons conducting at high frequency, than in sham-stimulated axons. (D) The number of mitochondria separated by 1.5 µm (measured between their mid-points) decreased in axons conducting at 50 Hz (<i>n</i> = 15 axons, <i>n</i> = 288 mitochondria), and was significantly lower for mitochondria separated by 3 µm (<i>p</i><0.001), than in sham-stimulated group (<i>n</i> = 13 axons, <i>n</i> = 309 mitochondria; three animals per group), i.e., mitochondria were less clustered in stimulated axons. In all groups axons were pulled from three independent experiments (animals).</p