RNA sequencing of olfactory bulb in Parkinson's disease reveals gene alterations associated with olfactory dysfunction.

The olfactory bulb is involved early in the pathophysiology of Parkinson's disease (PD), which is consistent with the early onset of olfactory dysfunction. Identifying the molecular mechanisms through which PD affects the olfactory bulb could lead to a better understanding of the pathophysiology and etiology of olfactory dysfunction in PD. We specifically aimed to assess gene expression changes, affected pathways and co-expression network by whole transcriptomic profiling of the olfactory bulb in subjects with clinicopathologically defined PD. Bulk RNA sequencing was performed on frozen human olfactory bulbs of 20 PD and 20 controls without dementia or any other neurodegenerative disorder, from the Arizona Study of Aging and Neurodegenerative disorders and the Brain and Body Donation Program. Differential expression analysis (19 PD vs 19 controls) revealed 2164 significantly differentially expressed genes (1090 upregulated and 1074 downregulated) in PD. Pathways enriched in downregulated genes included oxidative phosphorylation, olfactory transduction, metabolic pathways, and neurotransmitters synapses while immune and inflammatory responses as well as cellular death related pathways were enriched within upregulated genes. An overrepresentation of microglial and astrocyte-related genes was observed amongst upregulated genes, and excitatory neuron-related genes were overrepresented amongst downregulated genes. Co-expression network analysis revealed significant modules highly correlated with PD and olfactory dysfunction that were found to be involved in the MAPK signaling pathway, cytokine-cytokine receptor interaction, cholinergic synapse, and metabolic pathways. LAIR1 (leukocyte associated immunoglobulin like receptor 1) and PPARA (peroxisome proliferator activated receptor alpha) were identified as hub genes with a high discriminative power between PD and controls reinforcing an important role of neuroinflammation in the olfactory bulb of PD subjects. Olfactory identification test score positively correlated with expression of genes coding for G-coupled protein, glutamatergic, GABAergic, and cholinergic receptor proteins and negatively correlated with genes for proteins expressed in glial olfactory ensheathing cells. In conclusion, this study reveals gene alterations associated with neuroinflammation, neurotransmitter dysfunction, and disruptions of factors involved in the initiation of olfactory transduction signaling that may be involved in PD-related olfactory dysfunction.

Disease progression modelling reveals heterogeneity in trajectories of Lewy-type α-synuclein pathology.

Lewy body (LB) disorders, characterized by the aggregation of misfolded α-synuclein proteins, exhibit notable clinical heterogeneity. This may be due to variations in accumulation patterns of LB neuropathology. By applying data-driven disease progression modelling to regional neuropathological LB density scores from 814 brain donors, we describe three inferred trajectories of LB pathology that were characterized by differing clinicopathological presentation and longitudinal antemortem clinical progression. Most donors (81.9%) showed earliest pathology in the olfactory bulb, followed by accumulation in either limbic (60.8%) or brainstem (21.1%) regions. The remaining donors (18.1%) exhibited the first abnormalities in brainstem regions. Early limbic pathology was associated with Alzheimer's disease-associated characteristics. Meanwhile, brainstem-first pathology was associated with progressive motor impairment and substantial LB pathology outside of the brain. Our data provides evidence for heterogeneity in the temporal spread of LB pathology, possibly explaining some of the clinical disparities observed in LBDs.

Measuring Up: A Comparison of TapeStation 4200 and Bioanalyzer 2100 as Measurement Tools for RNA Quality in Postmortem Human Brain Samples.

The determination of RNA integrity is a critical quality assessment tool for gene expression studies where the experiment's success is highly dependent on the sample quality. Since its introduction in 1999, the gold standard in the scientific community has been the Agilent 2100 Bioanalyzer's RNA integrity number (RIN), which uses a 1-10 value system, from 1 being the most degraded, to 10 being the most intact. In 2015, Agilent launched 4200 TapeStation's RIN equivalent, and reported a strong correlation of r2 of 0.936 and a median error < ±0.4 RIN units. To evaluate this claim, we compared the Agilent 4200 TapeStation's RIN equivalent (RINe) and DV200 to the Agilent 2100 Bioanalyzer's RIN for 183 parallel RNA samples. In our study, using RNA from a total of 183 human postmortem brain samples, we found that the RIN and RINe values only weakly correlate, with an r2 of 0.393 and an average difference of 3.2 RIN units. DV200 also only weakly correlated with RIN (r2 of 0.182) and RINe (r2 of 0.347). Finally, when applying a cut-off value of 6.5 for both metrics, we found that 95.6% of samples passed with RIN, while only 23.5% passed with RINe. Our results suggest that even though RIN (Bioanalyzer) and RINe (TapeStation) use the same 1-10 value system, they should not be used interchangeably, and cut-off values should be calculated independently.

Measuring up: A Comparison of Tapestation 4200 and Bioanalyzer 2100 as Measurement Tools for RNA Quality in Postmortem Human Brain Samples.

Determining RNA integrity is a critical quality assessment tool for gene expression studies where the experiment's success is highly dependent on sample quality. Since its introduction in 1999, the gold standard in the scientific community has been the Agilent 2100 Bioanalyzer's RNA Integrity Number (RIN) which uses a 1-10 value system with 1 being the most degraded to 10 being the most intact. In 2015, Agilent launched the 4200 Tapestation's RIN equivalent and reported a strong correlation of r 2 of 0.936 and median error < ± 0.4 RIN units. To evaluate this claim, we compared the Agilent 4200 Tapestation's RIN equivalent (RINe) and DV200 to the Agilent 2100 Bioanalyzer's RIN for 183 parallel RNA samples. In our study, using RNA from a total of 183 human postmortem brain samples, we found that the RIN and RINe values only weakly correlate with an r 2 of 0.393 and an average difference of 3.2 RIN units. DV200 also only weakly correlated with RIN (r 2 of 0.182) and RINe (r 2 of 0.347). Finally, when applying a cut-off value of 6.5 for both metrics, we found that 95.6% of samples passed with RIN, while only 23.5% passed with RINe. Our results suggest that even though RIN (Bioanalyzer) and RINe (Tapestation) use the same 1-10 value system, they should not be used interchangeably, and cut-off values should be calculated independently.

Cerebral white matter rarefaction has both neurodegenerative and vascular causes and may primarily be a distal axonopathy.

Cerebral white matter rarefaction (CWMR) was considered by Binswanger and Alzheimer to be due to cerebral arteriolosclerosis. Renewed attention came with CT and MR brain imaging, and neuropathological studies finding a high rate of CWMR in Alzheimer disease (AD). The relative contributions of cerebrovascular disease and AD to CWMR are still uncertain. In 1181 autopsies by the Arizona Study of Aging and Neurodegenerative Disorders (AZSAND), large-format brain sections were used to grade CWMR and determine its vascular and neurodegenerative correlates. Almost all neurodegenerative diseases had more severe CWMR than the normal control group. Multivariable logistic regression models indicated that Braak neurofibrillary stage was the strongest predictor of CWMR, with additional independently significant predictors including age, cortical and diencephalic lacunar and microinfarcts, body mass index, and female sex. It appears that while AD and cerebrovascular pathology may be additive in causing CWMR, both may be solely capable of this. The typical periventricular pattern suggests that CWMR is primarily a distal axonopathy caused by dysfunction of the cell bodies of long-association corticocortical projection neurons. A consequence of these findings is that CWMR should not be viewed simply as "small vessel disease" or as a pathognomonic indicator of vascular cognitive impairment or vascular dementia.

SARS-CoV-2 Brain Regional Detection, Histopathology, Gene Expression, and Immunomodulatory Changes in Decedents with COVID-19.

Brains of 42 COVID-19 decedents and 107 non-COVID-19 controls were studied. RT-PCR screening of 16 regions from 20 COVID-19 autopsies found SARS-CoV-2 E gene viral sequences in 7 regions (2.5% of 320 samples), concentrated in 4/20 subjects (20%). Additional screening of olfactory bulb (OB), amygdala (AMY) and entorhinal area for E, N1, N2, RNA-dependent RNA polymerase, and S gene sequences detected one or more of these in OB in 8/21 subjects (38%). It is uncertain whether these RNA sequences represent viable virus. Significant histopathology was limited to 2/42 cases (4.8%), one with a large acute cerebral infarct and one with hemorrhagic encephalitis. Case-control RNAseq in OB and AMY found more than 5000 and 700 differentially expressed genes, respectively, unrelated to RT-PCR results; these involved immune response, neuronal constituents, and olfactory/taste receptor genes. Olfactory marker protein-1 reduction indicated COVID-19-related loss of OB olfactory mucosa afferents. Iba-1-immunoreactive microglia had reduced area fractions in cerebellar cortex and AMY, and cytokine arrays showed generalized downregulation in AMY and upregulation in blood serum in COVID-19 cases. Although OB is a major brain portal for SARS-CoV-2, COVID-19 brain changes are more likely due to blood-borne immune mediators and trans-synaptic gene expression changes arising from OB deafferentation.

Olfactory Bulb Amyloid-ß Correlates With Brain Thal Amyloid Phase and Severity of Cognitive Impairment.

The Alzheimer disease (AD) neuropathological hallmarks amyloid ß (Aß) and tau neurofibrillary (NF) pathology have been reported in the olfactory bulb (OB) in aging and in different neurodegenerative diseases, which coincides with frequently reported olfactory dysfunction in these conditions. To better understand when the OB is affected in relation to the hierarchical progression of Aß throughout the brain and whether OB pathology might be an indicator of AD severity, we assessed the presence of OB Aß and tau NF pathology in an autopsy cohort of 158 non demented control and 173 AD dementia cases. OB Aß was found in less than 5% of cases in lower Thal phases 0 and 1, in 20% of cases in phase 2, in 60% of cases in phase 3 and in more than 80% of cases in higher Thal phases 4 and 5. OB Aß and tau pathology significantly predicted a Thal phase greater than 3, a Braak NF stage greater than 4, and an MMSE score lower than 24. While OB tau pathology is almost universal in the elderly and therefore is not a good predictor of AD severity, OB Aß pathology coincides with clinically-manifest AD and might prove to be a useful biomarker of the extent of brain spread of both amyloid and tau pathology.

Hemispheric Asymmetry and Atypical Lobar Progression of Alzheimer-Type Tauopathy.

The spread of neurofibrillary tau pathology in Alzheimer disease (AD) mostly follows a stereotypical pattern of topographical progression but atypical patterns associated with interhemispheric asymmetry have been described. Because histopathological studies that used bilateral sampling are limited, this study aimed to assess interhemispheric tau pathology differences and the presence of topographically atypical cortical spreading patterns. Immunohistochemical staining for detection of tau pathology was performed in 23 regions of interest in 57 autopsy cases comparing bilateral cortical regions and hemispheres. Frequent mild (82% of cases) and occasional moderate (32%) interhemispheric density discrepancies were observed, whereas marked discrepancies were uncommon (7%) and restricted to occipital regions. Left and right hemispheric tau pathology dominance was observed with similar frequencies, except in Braak Stage VI that favored a left dominance. Interhemispheric Braak stage differences were observed in 16% of cases and were more frequent in advanced (IV-VI) versus early (I-III) stages. One atypical lobar topographical pattern in which occipital tau pathology density exceeded frontal lobe scores was identified in 4 cases favoring a left dominant asymmetry. We speculate that asymmetry and atypical topographical progression patterns may be associated with atypical AD clinical presentations and progression characteristics, which should be tested by comprehensive clinicopathological correlations.

Muscle compensation strategies to maintain glenohumeral joint stability with increased rotator cuff tear severity: A simulation study.

Rotator cuff tear (RCT) in older adults may cause decreased muscle forces and disrupt the force balance at the glenohumeral joint, compromising joint stability. Our objective was to identify how increased RCT severity affects glenohumeral joint loading and muscle activation patterns using a computational model. Muscle volume measurements were used to scale a nominal upper limb model's peak isometric muscle forces to represent force-generating characteristics of an average older adult male. Increased RCT severity was represented by systematically decreasing peak isometric muscle forces of supraspinatus, infraspinatus, and subscapularis. Five static postures in both scapular and frontal planes were evaluated. Results revealed that in both scapular and frontal planes, the peak glenohumeral joint contact force magnitude remained relatively consistent across increased RCT severity (average 1.5% and -4.2% change, respectively), and a relative balance of the transverse force couple is maintained even in massive RCT models. Predicted muscle activations of intact muscles, like teres minor, increased (average 5-30% and 4-17% in scapular and frontal planes, respectively) with greater RCT severity. This suggests that the system is prioritizing glenohumeral joint stability, even with severe RCT, and that unaffected muscles play a compensatory role to help stabilize the joint.