Choroidal Thickness Correlates with Clinical and Imaging Metrics of Parkinson's Disease: A Pilot Study

BACKGROUND

Parkinson's disease (PD) is marked clinically by motor symptoms and pathologically by Lewy bodies and dopamine neuron loss in the substantia nigra pars compacta (SNc). Higher iron accumulation, assessed by susceptibility MRI, also is observed as PD progresses. Recently, evidence has suggested that PD affects the retina.

OBJECTIVE

To better understand retinal alterations in PD and their association to clinical and SNc iron-related imaging metrics.

METHODS

Ten PD and 12 control participants (2 eyes each) from an ongoing PD imaging biomarker study underwent enhanced depth imaging optical coherence tomography evaluation. Choroidal (vascular) thickness and nerve layers were measured in 4 subregions [superior, temporal, inferior, and nasal] and at 3 foveal distances (1, 1.5, and 3 mm). These metrics were compared between PD and control groups. For significantly different metrics, their associations with clinical [levodopa equivalent daily dosage (LEDD), motor and visuospatial function] and SNc susceptibility MRI metrics [R2* and quantitative susceptibility mapping (QSM)] were explored.

RESULTS

Compared to control participants, PD participants had a thicker choroid (p = 0.005), but no changes in nerve layers. Higher mean choroidal thickness was associated with lower LEDD (p < 0.01) and better visuospatial function (p < 0.05). Subregion analyses revealed higher choroidal thickness correlated with lower LEDD and better motor and visuospatial measures. Higher mean choroidal thickness also was associated with lower nigral iron MRI (p < 0.05).

CONCLUSION

A small cohort of PD research participants displayed higher choroidal thickness that was related to better clinical performance and less nigral pathology. These intriguing findings warrant further investigation.

Lexical-semantic search related to side of onset and putamen volume in Parkinson's disease

Parkinson's disease (PD) is characterized by dopaminergic cell loss and reduced striatal volume. Prior studies have demonstrated striatal involvement in access to lexical-semantic knowledge and damage to this structure may be evident in the lexical properties of responses. Semantic fluency task responses from early stage, non-demented PD participants with right (PD-R) or left (PD-L) lateralizing symptoms were compared to matched controls on lexical properties (word frequency, age of acquisition) and correlated with striatal volumes segmented from T1-weighted brain MR images. PD-R participants produced semantic fluency responses of a lower age of acquisition than PD-L and control participants (p < 0.05). PD-R age of acquisition responses correlated positively with putamen volume (p < 0.05), while age of acquisition of responses correlated negatively with caudate volume in controls (p < 0.05). Findings provide evidence for a role of the striatum in lexical-semantic access and qualitative changes in lexical access in select PD patients.

Tryptophan Metabolites Are Associated With Symptoms and Nigral Pathology in Parkinson's Disease

Background

The objective of this study was to determine whether neurotoxic kynurenine metabolites, induced by inflammation, in plasma and cerebrospinal fluid (CSF) are associated with symptom severity and nigral pathology in Parkinson's disease (PD).

Methods

Clinical and MRI data were obtained from 97 PD and 89 controls. We used ultra‐performance liquid chromatography to quantify kynurenine metabolites and high‐sensitivity multiplex assays to quantify inflammation in plasma and CSF. We evaluated group‐wise differences as well as associations between the biomarkers, motor and nonmotor symptoms, and nigral R2* (MRI metric reflecting iron content).

Results

PD subjects had >100% higher 3‐hydroxykynurenine and 14% lower 3‐hydroxyanthranilic acid in plasma. The 3‐HK in plasma was closely associated with both symptom severity and disease duration. PD subjects also had 23% lower kynurenic acid in the CSF. Higher CSF levels of the excitotoxin quinolinic acid were associated with more severe symptoms, whereas lower levels of the neuroprotective kynurenic acid were linked to olfactory deficits. An elevated quinolinic acid/picolinic acid ratio in the CSF correlated with higher R2* values in the substantia nigra in the entire cohort. Plasma C‐reactive protein and serum amyloid alpha were associated with signs of increased kynurenine pathway activity in the CSF of PD patients, but not in controls.

Conclusions

In PD, the kynurenine pathway metabolite levels are altered in both the periphery and the central nervous system, and these changes are associated with symptom severity. Replication studies are warranted in other cohorts, and these can also explore if kynurenine metabolites might be PD biomarkers and/or are involved in PD pathogenesis. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Phosphatidic acid-dependent localization and basal de-phosphorylation of RA-GEFs regulate lymphocyte trafficking

Background

Lymphocytes circulate between peripheral lymphoid tissues via blood and lymphatic systems, and chemokine-induced migration is important in trafficking lymphocytes to distant sites. The small GTPase Rap1 is important in mediating lymphocyte motility, and Rap1-GEFs are involved in chemokine-mediated Rap1 activation. Here, we describe the roles and mechanisms of Rap1-GEFs in lymphocyte trafficking.

Results

In this study, we show that RA-GEF-1 and 2 (also known as Rapgef2 and 6) are key guanine nucleotide exchange factors (GEF) for Rap1 in lymphocyte trafficking. Mice harboring T cell-specific knockouts of Rapgef2/6 demonstrate defective homing and egress of T cells. Sphingosine-1-phosphate (S1P) as well as chemokines activates Rap1 in a RA-GEF-1/2-dependent manner, and their deficiency in T cells impairs Mst1 phosphorylation, cell polarization, and chemotaxis toward S1P gradient. On the other hand, B cell-specific knockouts of Rapgef2/6 impair chemokine-dependent retention of B cells in the bone marrow and passively facilitate egress. Phospholipase D2-dependent production of phosphatidic acid by these chemotactic factors determines spatial distribution of Rap1-GTP subsequent to membrane localization of RA-GEFs and induces the development of front membrane. On the other hand, basal de-phosphorylation of RA-GEFs is necessary for chemotactic factor-dependent increase in GEF activity for Rap1.

Conclusions

We demonstrate here that subcellular distribution and activation of RA-GEFs are key factors for a directional movement of lymphocytes and that phosphatidic acid is critical for membrane translocation of RA-GEFs with chemokine stimulation.

Phospholipase D2 restores endothelial barrier function by promoting PTPN14-mediated VE-cadherin dephosphorylation

Increased permeability of vascular lung tissues is a hallmark of acute lung injury and is often caused by edemagenic insults resulting in inflammation. Vascular endothelial (VE)-cadherin undergoes internalization in response to inflammatory stimuli and is recycled at cell adhesion junctions during endothelial barrier re-establishment. Here, we hypothesized that phospholipase D (PLD)-generated phosphatidic acid (PA) signaling regulates VE-cadherin recycling and promotes endothelial barrier recovery by dephosphorylating VE-cadherin. Genetic deletion of PLD2 impaired recovery from protease-activated receptor-1-activating peptide (PAR-1-AP)-induced lung vascular permeability and potentiated inflammation in vivo In human lung microvascular endothelial cells (HLMVECs), inhibition or deletion of PLD2, but not of PLD1, delayed endothelial barrier recovery after thrombin stimulation. Thrombin stimulation of HLMVECs increased co-localization of PLD2-generated PA and VE-cadherin at cell-cell adhesion junctions. Inhibition of PLD2 activity resulted in prolonged phosphorylation of Tyr-658 in VE-cadherin during the recovery phase 3 h post-thrombin challenge. Immunoprecipitation experiments revealed that after HLMVECs are thrombin stimulated, PLD2, VE-cadherin, and protein-tyrosine phosphatase nonreceptor type 14 (PTPN14), a PLD2-dependent protein-tyrosine phosphatase, strongly associate with each other. PTPN14 depletion delayed VE-cadherin dephosphorylation, reannealing of adherens junctions, and barrier function recovery. PLD2 inhibition attenuated PTPN14 activity and reversed PTPN14-dependent VE-cadherin dephosphorylation after thrombin stimulation. Our findings indicate that PLD2 promotes PTPN14-mediated dephosphorylation of VE-cadherin and that redistribution of VE-cadherin at adherens junctions is essential for recovery of endothelial barrier function after an edemagenic insult.

Novel role of dynamin-related-protein 1 in dynamics of ER-lipid droplets in adipose tissue

Dynamin-Related-Protein 1 (DRP1) critically regulates mitochondrial and peroxisomal fission in multicellular organisms. However, the impact of DRP1 on other organelles, especially its direct influence on ER functions remains largely unclear. Here, we report that DRP1 translocates to endoplasmic reticulum (ER) in response to β-adrenergic stimulation. To further investigate the function of DRP1 on ER-lipid droplet (LD) dynamics and the metabolic subsequences, we generated an adipose tissue-specific DRP1 knockout model (Adipo-Drp1^flx/flx ). We found that the LDs in adipose tissues of Adipo-Drp1^flx/flx mice exhibited more unilocular morphology with larger sizes, and formed less multilocular structures upon cold exposure. Mechanistically, we discovered that abnormal LD morphology occurs because newly generated micro-LDs fail to dissociate from the ER due to DRP1 ablation. Conversely, the ER retention of LDs can be rescued by the overexpressed DRP1 in the adipocytes. The alteration of LD dynamics, combined with abnormal mitochondrial and autophagy functions in adipose tissue, ultimately lead to abnormalities in lipid metabolism in Adipo-Drp1^flx/flx mice.

Higher Hippocampal Mean Diffusivity Values in Asymptomatic Welders

Chronic high-level manganese (Mn)-induced neurotoxicity has been associated with Mn accumulation in the basal ganglia and higher risk for developing parkinsonism. Recent studies in Mn-exposed animals revealed Mn accumulation in the hippocampus, the presence of Aβ diffuse plaques, and deficits in associative learning, the latter being hallmarks of Alzheimer's disease (AD) or related disorders. This and recent evidence of hippocampal Mn accumulation in welders prompted us to test the hypothesis that welders with chronic Mn exposure would display changes in the hippocampus. Subjects with (welders; n = 42) or without (controls; n = 31) welding history were studied. Mn exposure was estimated by occupational questionnaires, whole blood Mn, and R1 imaging (estimate of short-term brain Mn accumulation). Hippocampal diffusion tensor imaging (DTI; estimate of microstructural brain changes) and volume were determined. Compared with controls, welders displayed no significant difference in hippocampal volume (p = .165). Welders, however, exhibited higher DTI hippocampal mean diffusivity (MD) values compared with controls (p = .035) that was evident particularly in older welders (>50 years, p = .002). Hippocampal MD was associated significantly with age in welders (R = 0.59; p < .001) but not in controls (p = .16). Moreover, higher hippocampal MD values (age adjusted) were associated with long-term cumulative Mn exposure (R = 0.36, p = .021). Welders with chronic exposure have higher MD values in the hippocampus that become greater with increasing age, a brain change that is similar to that observed in those at risk for AD. The current results suggest that Mn exposure, coupled with aging, may make welders more vulnerable to AD or AD-like changes.

Phosphatidic acid regulates subcellular distribution of RA-GEFs critical for chemokine-dependent migration

Integrin activation by Rap1-GTP is pivotal for lymphocyte trafficking. In this study, we show the phosphatidic acid (PA)-dependent membrane distribution of RA-GEF-1 and -2 (also known as Rapgef2 and 6), which are guanine nucleotide exchange factors for Rap1, plays important roles in lymphocyte migration. RA-GEF-1 associates with PA through 919-967 aa within CDC25 homology domain, and the deletion of this region of RA-GEF-1 inhibits chemokine-dependent migration. Chemokine stimulation induces temporal production of PA on the plasma membrane, which is not necessary for Rap1 activation, but the translocation of RA-GEFs. Thus, chemokine-dependent generation of PA is critical for lymphocyte migration through membrane localization of RA-GEFs.

Clinical Progression of Parkinson's Disease: Insights from the NINDS Common Data Elements

BACKGROUND/OBJECTIVE

To synchronize data collection, the National Institute of Neurological Disorders and Stroke (NINDS) recommended Common Data Elements (CDEs) for use in Parkinson's disease (PD) research. This study delineated the progression patterns of these CDEs in a cohort of PD patients.

METHODS

One hundred-twenty-five PD patients participated in the PD Biomarker Program (PDBP) at Penn State. CDEs, including MDS-Unified PD Rating Scale (UPDRS)-total, questionnaire-based non-motor (-I) and motor (-II), and rater-based motor (-III) subscales; Montreal Cognitive Assessment (MoCA); Hamilton Depression Rating Scale (HDRS); University of Pennsylvania Smell Identification Test (UPSIT); and PD Questionnaire (PDQ-39) were obtained at baseline and three annual follow-ups. Annual change was delineated for PD or subgroups [early = PDE, disease duration (DD) <1 y; middle = PDM, DD = 1-5 y; and late = PDL, DD > 5 y] using mixed effects model analyses.

RESULTS

UPDRS-total, -II, and PDQ-39 scores increased significantly, and UPSIT decreased, whereas UPDRS-I, -III, MoCA, and HDRS did not change, over 36 months in the overall PD cohort. In the PDE subgroup, UPDRS-II increased and UPSIT decreased significantly, whereas MoCA and UPSIT decreased significantly in the PDM subgroup. In the PDL subgroup, UPDRS-II and PDQ-39 increased significantly. Other metrics within each individual subgroup did not change. Sensitivity analyses using subjects with complete data confirmed these findings.

CONCLUSION

Among CDEs, UPDRS-total, -II, PDQ-39, and UPSIT all are sensitive metrics to track PD progression. Subgroup analyses revealed that these CDEs have distinct stage-dependent sensitivities, with UPSIT for DD < 5 y, PDQ-39 for DD > 5 y, UPDRS-II for early (DD < 1) or later stages (DD > 5).

Rapid affinity purification of intracellular organelles using a twin strep tag

Cells are internally organized into compartmentalized organelles that execute specialized functions. To understand the functions of individual organelles and their regulations, it is critical to resolve the compositions of individual organelles, which relies on a rapid and efficient isolation method for specific organellar populations. Here, we introduce a robust affinity purification method for rapid isolation of intracellular organelles (e.g. lysosomes, mitochondria and peroxisomes) by taking advantage of the extraordinarily high affinity between the twin strep tag and streptavidin variants. With this method, we can isolate desired organelles with high purity and yield in 3 min from the post-nuclear supernatant of mammalian cells or less than 8 min for the whole purification process. Using lysosomes as an example, we show that the rapid procedure is especially useful for studying transient and fast cellular activities, such as organelle-initiated signaling and organellar contents of small-molecular metabolites. Therefore, our method offers a powerful tool to dissect spatiotemporal regulation and functions of intracellular organelles.

Multimodal MRI evaluation of parkinsonian limbic pathologies

Previous multimodal magnetic resonance imaging (MRI) studies of parkinsonian syndromes have focused primarily on motor-related basal ganglia structures. The present study investigated MRI changes in nonmotor-related limbic structures in 35 Parkinson's disease, 16 multiple system atrophy parkinsonian subtype, 17 progressive supranuclear palsy, and 37 control subjects. Mean diffusivity (MD), fractional anisotropy, transverse relaxation rate (R2*), quantitative susceptibility mapping, and volume measurements were obtained from the amygdala, hippocampus, and nucleus accumbens (NAc) to examine differences between groups and to test for associations with clinical scores. Compared with controls, Parkinson's disease subjects had lower NAc volume; multiple system atrophy parkinsonian subtype subjects had higher NAc transverse relaxation rate; and progressive supranuclear palsy subjects had higher amygdala and hippocampus MD and lower hippocampus fractional anisotropy (p's ≤ 0.008). Among parkinsonian subjects, amygdala and hippocampus MD associated positively with Unified Parkinson's Disease Rating Scale nonmotor and activities of daily living scores (p's ≤ 0.005). Together, these findings support the inclusion of limbic structures in future MRI studies of parkinsonian syndromes.

PLD-dependent phosphatidic acid microdomains are signaling platforms for podosome formation

Local membrane phospholipid enrichment serves as docking platform for signaling proteins involved in many processes including cell adhesion and migration. Tissue-resident dendritic cells (DCs) assemble actomyosin-based structures called podosomes, which mediate adhesion and degradation of extracellular matrix for migration and antigen sampling. Recent evidence suggested the involvement of phospholipase D (PLD) and its product phosphatidic acid (PA) in podosome formation, but the spatiotemporal control of this process is poorly characterized. Here we determined the role of PLD1 and PLD2 isoforms in regulating podosome formation and dynamics in human primary DCs by combining PLD pharmacological inhibition with a fluorescent PA sensor and fluorescence microscopy. We found that ongoing PLD2 activity is required for the maintenance of podosomes, whereas both PLD1 and PLD2 control the early stages of podosome assembly. Furthermore, we captured the formation of PA microdomains accumulating at the membrane cytoplasmic leaflet of living DCs, in dynamic coordination with nascent podosome actin cores. Finally, we show that both PLD1 and PLD2 activity are important for podosome-mediated matrix degradation. Our results provide novel insight into the isoform-specific spatiotemporal regulation of PLD activity and further our understanding of the role of cell membrane phospholipids in controlling localized actin polymerization and cell protrusion.

Brain cholesterol metabolism and Parkinson's disease

BACKGROUND

Circulating cholesterol levels have been linked to PD, but not directly to brain physiology.

OBJECTIVE

To assess whether brain cholesterol metabolism is related to PD.

METHODS

Sixty PD patients and 64 controls were recruited from an academic movement disorder clinic (2009-2012). Thirty-five PD patients and 33 controls returned approximately 36 months later. Fasting plasma (S)24-OH-cholesterol (brain-derived cholesterol metabolite) and 27-OH-cholesterol (peripheral cholesterol metabolite) were quantified. Odds ratios for PD were derived from logistic regression models, adjusting for potential confounders. Relationships between the oxysterols and clinical measurements were explored using Spearman correlation coefficients.

RESULTS

Mean age of PD subjects was 63.8 ± 8.3 years and disease duration was 5.0 ± 5.4 years. Plasma (S)24-OH-cholesterol levels were inversely associated with the odds of having PD, with an odds ratio of 0.92 (95% confidence interval: 0.87-0.97) for each 1-ng/mL increase (P = 0.004). Compared to the lowest tertile, the odds ratio was 0.34 (0.12-0.98) for the second tertile (P = 0.045) and 0.08 (0.02-0.31) for the highest tertile (P < 0.001). Higher (S)24-OH-cholesterol levels also were correlated with better sense of smell (r = 0.35; P = 0.01). No significant associations were found between clinical measures and 27-OH-cholesterol, a peripheral cholesterol metabolite. Furthermore, (S)24-OH-cholesterol levels were stable over time, whereas 27-OH-cholesterol decreased with time in both cases and controls.

CONCLUSIONS

Results indicate that plasma (S)24-OH-cholesterol (possibly reflecting brain cholesterol metabolism) is inversely linked to PD, is relatively stable over time, and may serve as a new biomarker for PD. Further investigation is necessary to determine the mechanistic and clinical implications. © 2019 International Parkinson and Movement Disorder Society.

Phosphatidic acid generated by PLD2 promotes the plasma membrane recruitment of IQGAP1 and neointima formation

Very little is known about how lipid signaling regulates intima hyperplasia after vascular injury. Herein, we report that deletion and pharmacological inhibition of phospholipase D (PLD)2, which generates the signaling lipid phosphatidic acid (PA), reduced neointimal formation in the mouse carotid artery ligation model. PLD2 deficiency inhibits migration of vascular smooth muscle cells (VSMCs) into the intima in mice as well as migration and formation of membrane ruffles in primary VSMCs. PA specifically binds to the IQ motif-containing guanosine triphosphatase-activating protein 1 (IQGAP1) scaffold protein. The binding between PA and IQGAP is required for the plasma membrane recruitment of IQGAP1. Similar to PLD2 inhibition, knockdown of IQGAP1 blocks ruffle formation and migration in VSMCs, which are rescued by expression of the exogenous IQGAP1 but not the PA binding-deficient mutant. These data reveal that the PLD2-PA-IQGAP1 pathway plays an important role in VSMC migration and injury-induced vascular remodeling, and implicate PLD2 as a candidate target for therapeutic interventions.-Wang, Z., Cai, M., Tay, L. W. R., Zhang, F., Wu, P., Huynh, A., Cao, X., Di Paolo, G., Peng, J., Milewicz, D. M., Du, G. Phosphatidic acid generated by PLD2 promotes the plasma membrane recruitment of IQGAP1 and neointima formation.

Magnetic resonance T1w/T2w ratio: A parsimonious marker for Parkinson disease

OBJECTIVE

Newer magnetic resonance imaging (MRI) techniques have shown promise in capturing early Parkinson disease (PD)-related changes in the substantia nigra pars compacta (SNc), the key pathological loci. Their translational value, however, is hindered by technical complexity and inconsistent results.

METHODS

A novel yet simple MRI contrast, the T1w/T2w ratio, was used to study 76 PD patients and 70 controls. The T1w/T2w ratio maps were analyzed using both voxel-based and region-of-interest approaches in normalized space. The sensitivity and specificity of the SNc T1w/T2w ratio in discriminating between PD and controls also were assessed. In addition, its diagnostic performance was tested in a subgroup of PD patients with disease duration ≤2 years (PDE). A second independent cohort of 73 PD patients and 49 controls was used for validation.

RESULTS

Compared to controls, PD patients showed a higher T1w/T2w ratio in both the right (cluster size = 164mm3 , p < 0.0001) and left (cluster size = 213mm3 , p < 0.0001) midbrain that was located ventrolateral to the red nucleus and corresponded to the SNc. The region-of-interest approach confirmed the group difference in the SNc T1w/T2w ratio between PD and controls (p < 0.0001). The SNc T1w/T2w ratio had high sensitivity (0.908) and specificity (0.80) to separate PD and controls (area under the curve [AUC] = 0.926), even for PDE patients (AUC = 0.901, sensitivity = 0.857, specificity = 0.857). These results were validated in the second cohort.

INTERPRETATION

The T1w/T2w ratio can detect PD-related changes in the SNc and may be used as a novel, parsimonious in vivo biomarker for the disease, particularly for early stage patients, with high translational value for clinical practice and research. ANN NEUROL 2019;85:96-104.

Linking seed germination and plant height: a case study of a wetland community on the eastern Tibet Plateau

Seed germination is the earliest trait expressed in a plant's life history, and it can directly affect the expression of post-germination traits. Plant height is central to plant ecological strategies, because it is a major determinant of the ability of a species to compete for light. Thus, linking seed germination and plant height at the community level is very important to understanding plant fitness and community structure. Here, we tested storage condition and temperature requirements for germination of 31 species from a wetland plant community on the eastern Tibet Plateau and analysed correlation of germination traits with plant height in relation to storage condition. Germination percentage was positively related to plant height, and this relationship disappeared when seeds were incubated at a low temperature (i.e. 5 °C) or after they were stored under wet-cold conditions. The response of seeds to dry+wet-cold storage was negatively related to plant height. Based on the scores of each species on the first two principal components derived from PCA, species were classified into two categories by hierarchical clustering, and there was a significant difference between germination and plant height of species in these two categories. These results suggest that the requirements for seed germination together with seasonal change in environmental conditions determine the window for germination and, in turn, plant growth season and resource utilisation and ultimately plant height.

Susceptibility MRI captures nigral pathology in patients with parkinsonian syndromes

BACKGROUND

Parkinsonisms are neurodegenerative disorders characterized pathologically by α-synuclein-positive (e.g., PD, diffuse Lewy body disease, and MSA) and/or tau-positive (e.g., PSP, cortical basal degeneration) pathology. Using R2* and quantitative susceptibility mapping, susceptibility changes have been reported in the midbrain of living parkinsonian patients, although the exact underlying pathology of these alterations is unknown.

OBJECTIVE

The current study investigated the pathological correlates of these susceptibility MRI measures.

METHODS

In vivo MRIs (T1- and T2-weighted, and T2*) and pathology were obtained from 14 subjects enrolled in an NINDS PD Biomarker Program (PDBP). We assessed R2* and quantitative susceptibility mapping values in the SN, semiquantitative α-synuclein, tau, and iron values, as well as neuronal and glial counts. Data were analyzed using age-adjusted Spearman correlations.

RESULTS

R2* was associated significantly with nigral α-synuclein (r = 0.746; P = 0.003). Quantitative susceptibility mapping correlated significantly with Perls' (r = 0.758; P = 0.003), but not with other pathological measurements. Neither measurement correlated with tau or glial cell counts (r ≤ 0.11; P ≥ 0.129).

CONCLUSIONS

Susceptibility MRI measurements capture nigral pathologies associated with parkinsonian syndromes. Whereas quantitative susceptibility mapping is more sensitive to iron, R2* may reflect pathological aspects of the disorders beyond iron such as α-synuclein. They may be invaluable tools in diagnosing differential parkinsonian syndromes, and tracking in living patients the dynamic changes associated with the pathological progression of these disorders. © 2018 International Parkinson and Movement Disorder Society.

Properties of oscillatory neuronal activity in the basal ganglia and thalamus in patients with Parkinson's disease

Background

The cardinal features of Parkinson’s disease (PD) are bradykinesia, rigidity and rest tremor. Abnormal activity in the basal ganglia is predicted to underlie the mechanism of motor symptoms. This study aims to characterize properties of oscillatory activity in the basal ganglia and motor thalamus in patients with PD.

Methods

Twenty-nine patients with PD who underwent bilateral or unilateral electrode implantation for subthalamic nucleus (STN) DBS (n = 11), unilateral pallidotomy (n = 9) and unilateral thalamotomy (n = 9) were studied. Microelectrode recordings in the STN, globus pallidus internus (GPi) and ventral oral posterior/ventral intermediate of thalamus (Vop/Vim) were performed. Electromyography of the contralateral limbs was recorded. Single unit characteristics including interspike intervals were analyzed. Spectral and coherence analyses were assessed. Mean spontaneous firing rate (MSFR) of neurons was calculated. Analysis of variance and X² test were performed.

Results

Of 76 STN neurons, 39.5% were 4–6 Hz band oscillatory neurons and 28.9% were β frequency band (βFB) oscillatory neurons. The MSFR was 44.2 ± 7.6 Hz. Of 62 GPi neurons, 37.1% were 4–6 Hz band oscillatory neurons and 27.4% were βFB neurons. The MSFR was 80.9 ± 9.6 Hz. Of 44 Vop neurons, 65.9% were 4–6 Hz band oscillatory neurons and 9% were βFB neurons. The MSFR was 24.4 ± 4.2 Hz. Of 30 Vim oscillatory neurons, 70% were 4–6 Hz band oscillatory neurons and 13.3% were βFB neurons. The MSFR was 30.3 ± 3.6 Hz. Further analysis indicated that proportion of βFB oscillatory neurons in STN and GPi was higher than that of similar neurons in the Vop and Vim (P < 0.05). Conversely, the proportion of 4–6 Hz band oscillatory neurons and tremor related neurons in the Vim and Vop was higher than that of STN and GPi (P < 0.05). The highest MSFR was for GPi oscillatory neurons whereas the lowest MSFR was for Vop oscillatory neurons (P < 0.005).

Conclusion

The alterations in neuronal activity in basal ganglia play a critical role in generation of parkinsonism. β oscillatory activity is more prominent in basal ganglia than in thalamus suggesting that the activity likely results from dopaminergic depletion. While both basal ganglia and thalamus have tremor activity, the thalamus appears to play a more important role in tremor production, and basal ganglia β oscillatory activity might be the trigger.

Lateralized Basal Ganglia Vulnerability to Pesticide Exposure in Asymptomatic Agricultural Workers

Pesticide exposure is linked to Parkinson's disease, a neurodegenerative disorder marked by dopamine cell loss in the substantia nigra of the basal ganglia (BG) that often presents asymmetrically. We previously reported that pesticide-exposed agricultural workers (AW) have nigral diffusion tensor imaging (DTI) changes. The current study sought to confirm this finding, and explore its hemisphere and regional specificity within BG structures using an independent sample population. Pesticide exposure history, standard neurological exam, high-resolution magnetic resonance imaging (T1/T2-weighted and DTI), and [123I]ioflupane SPECT images (to quantify striatal dopamine transporters) were obtained from 20 AW with chronic pesticide exposure and 11 controls. Based on median cumulative days of pesticide exposure, AW were subdivided into high (AWHi, n = 10) and low (AWLo, n = 10) exposure groups. BG (nigra, putamen, caudate, and globus pallidus [GP]) fractional anisotropy (FA), mean diffusivity (MD), and striatal [123I]ioflupane binding in each hemisphere were quantified, and compared across exposure groups using analysis of variance. Left, but not right, nigral and GP FA were significantly lower in AW compared with controls (p's < .029). None of the striatal (putamen and caudate) DTI or [123I]ioflupane binding measurements differed between AW and controls. Subgroup analyses indicated that significant left nigral and GP DTI changes were present only in the AWHi (p ≤ .037) but not the AWLo subgroup. AW, especially those with higher pesticide exposure history, demonstrate lateralized microstructural changes in the nigra and GP, whereas striatal areas appear relatively unaffected. Future studies should elucidate how environmental toxicants cause differential lateralized- and regionally specific brain vulnerability.

Paired related homeobox 1 transactivates dopamine D2 receptor to maintain propagation and tumorigenicity of glioma-initiating cells

Glioblastoma multiforme (GBM) is a highly invasive brain tumor with limited therapeutic means and poor prognosis. Recent studies indicate that glioma-initiating cells/glioma stem cells (GICs/GSCs) may be responsible for tumor initiation, infiltration, and recurrence. GICs could aberrantly employ molecular machinery balancing self-renewal and differentiation of embryonic neural precursors. Here, we find that paired related homeobox 1 (PRRX1), a homeodomain transcription factor that was previously reported to control skeletal development, is expressed in cortical neural progenitors and is required for their self-renewal and proper differentiation. Further, PRRX1 is overrepresented in glioma samples and labels GICs. Glioma cells and GICs depleted with PRRX1 could not propagate in vitro or form tumors in the xenograft mouse model. The GIC self-renewal function regulated by PRRX1 is mediated by dopamine D2 receptor (DRD2). PRRX1 directly binds to the DRD2 promoter and transactivates its expression in GICs. Blockage of the DRD2 signaling hampers GIC self-renewal, whereas its overexpression restores the propagating and tumorigenic potential of PRRX1-depleted GICs. Finally, PRRX1 potentiates GICs via DRD2-mediated extracellular signal-related kinase (ERK) and AKT activation. Thus, our study suggests that therapeutic targeting the PRRX1-DRD2-ERK/AKT axis in GICs is a promising strategy for treating GBMs.

Distinct progression pattern of susceptibility MRI in the substantia nigra of Parkinson's patients

BACKGROUND

Susceptibility MRI may capture Parkinson's disease-related pathology. This study delineated longitudinal changes in different substantia nigra regions.

METHODS

Seventy-two PD patients and 62 controls were studied at both baseline and after 18 months with MRI. R2* and quantitative susceptibility mapping values from the substantia nigra pars compacta and substantia nigra pars reticulata were calculated. Mixed-effects models compared controls with PD or PD subgroups having different disease durations: early (<1 year), middle (<5 years, middle-stage PD), and late (>5 years, late-stage PD). Pearson's correlation assessed associations between imaging and clinical measures.

RESULTS

At baseline, R2* and quantitative susceptibility mapping were higher in both the substantia nigra pars compacta and substantia nigra pars reticulata in all PD patients (group effect, P ≤ 0.003). Longitudinally, the substantia nigra pars compacta R2* showed a faster increase in PD compared with controls (time × group, P = 0.002), whereas quantitative susceptibility mapping did not (P = 0.668). The substantia nigra pars reticulata R2* and quantitative susceptibility mapping did not differ between PD and controls (time × group, P ≥ 0.084), although both decreased longitudinally (time effect, P ≤ 0.004). Baseline substantia nigra pars compacta R2* was higher in all PD subgroups (group, P ≤ 0.006), but showed a significantly faster increase only in later-stage PD (time × group, P < 0.0001) that correlated with changes in nonmotor symptoms (r = 0.746, P = 0.002). Baseline substantia nigra pars reticulata quantitative susceptibility mapping was higher in middle-stage PD and later-stage PD (group, P ≤ 0.002), but showed a longitudinal decrease (time × group, P = 0.004) only in later-stage PD that correlated with changes in motor signs (r = 0.837, P < 0.001).

CONCLUSION

Susceptibility MRI revealed distinct patterns of PD progression in the substantia nigra pars compacta and substantia nigra pars reticulata. The different patterns are particularly clear in later-stage patients. These findings may resolve past controversies and have implications in the pathophysiological processes during PD progression. © 2018 International Parkinson and Movement Disorder Society.