Alpha-synuclein inclusion responsive microglia are resistant to CSF1R inhibition

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disorder that is characterized by the presence of proteinaceous alpha-synuclein (α-syn) inclusions (Lewy bodies), markers of neuroinflammation and the progressive loss of nigrostriatal dopamine (DA) neurons. These pathological features can be recapitulated in vivo using the α-syn preformed fibril (PFF) model of synucleinopathy. We have previously determined that microglia proximal to PFF-induced nigral α-syn inclusions increase in soma size, upregulate major-histocompatibility complex-II (MHC-II) expression, and increase expression of a suite of inflammation-associated transcripts. This microglial response is observed months prior to degeneration, suggesting that microglia reacting to α-syn inclusion may contribute to neurodegeneration and could represent a potential target for novel therapeutics. The goal of this study was to determine whether colony stimulating factor-1 receptor (CSF1R)-mediated microglial depletion impacts the magnitude of α-syn aggregation, nigrostriatal degeneration, or the response of microglial in the context of the α-syn PFF model.

METHODS

Male Fischer 344 rats were injected intrastriatally with either α-syn PFFs or saline. Rats were continuously administered Pexidartinib (PLX3397B, 600 mg/kg), a CSF1R inhibitor, to deplete microglia for a period of either 2 or 6 months.

RESULTS

CSF1R inhibition resulted in significant depletion (~ 43%) of ionized calcium-binding adapter molecule 1 immunoreactive (Iba-1ir) microglia within the SNpc. However, CSF1R inhibition did not impact the increase in microglial number, soma size, number of MHC-II immunoreactive microglia or microglial expression of Cd74, Cxcl10, Rt-1a2, Grn, Csf1r, Tyrobp, and Fcer1g associated with phosphorylated α-syn (pSyn) nigral inclusions. Further, accumulation of pSyn and degeneration of nigral neurons was not impacted by CSF1R inhibition. Paradoxically, long term CSF1R inhibition resulted in increased soma size of remaining Iba-1ir microglia in both control and PFF rats, as well as expression of MHC-II in extranigral regions.

CONCLUSIONS

Collectively, our results suggest that CSF1R inhibition does not impact the microglial response to nigral pSyn inclusions and that CSF1R inhibition is not a viable disease-modifying strategy for PD.

Deficits in basal and evoked striatal dopamine release following alpha-synuclein preformed fibril injection: An in vivo microdialysis study

Parkinson's disease (PD) is characterized by the accumulation of misfolded alpha-synuclein (α-syn) protein, forming intraneuronal Lewy body (LB) inclusions. The α-syn preformed fibril (PFF) model of PD recapitulates α-syn aggregation, progressive nigrostriatal degeneration and motor dysfunction; however, little is known about the time course of PFF-induced alterations in basal and evoked dopamine (DA). In vivo microdialysis is well suited for identifying small changes in neurotransmitter levels over extended periods. In the present study, adult male Fischer 344 rats received unilateral, intrastriatal injections of either α-syn PFFs or phosphate-buffered saline (PBS). At 4 or 8 months post-injection (p.i.), animals underwent in vivo microdialysis to evaluate basal extracellular striatal DA and metabolite levels, local KCl-evoked striatal DA release and the effects of systemic levodopa (l-DOPA). Post-mortem analysis demonstrated equivalent PFF-induced reductions in tyrosine hydroxylase (TH) immunoreactive nigral neurons (~50%) and striatal TH (~20%) at both time points. Compared with reduction in striatal TH, reduction in striatal dopamine transporter (DAT) was more pronounced and progressed between the 4- and 8-month p.i. intervals (36% ➔ 46%). Significant PFF-induced deficits in basal and evoked striatal DA, as well as deficits in motor performance, were not observed until 8 months p.i. Responses to l-DOPA did not differ regardless of PBS or PFF treatment. These results suggest that basal and evoked striatal DA are maintained for several months following PFF injection, with loss of both associated with motor dysfunction. Our studies provide insight into the time course and magnitude of PFF-induced extracellular dopaminergic deficits in the striatum.

Transcriptomic profiling of early synucleinopathy in rats induced with preformed fibrils

Examination of early phases of synucleinopathy when inclusions are present, but long before neurodegeneration occurs, is critical to both understanding disease progression and the development of disease modifying therapies. The rat alpha-synuclein (α-syn) preformed fibril (PFF) model induces synchronized synucleinopathy that recapitulates the pathological features of Parkinson's disease (PD) and can be used to study synucleinopathy progression. In this model, phosphorylated α-syn (pSyn) inclusion-containing neurons and reactive microglia (major histocompatibility complex-II immunoreactive) peak in the substantia nigra pars compacta (SNpc) months before appreciable neurodegeneration. However, it remains unclear which specific genes are driving these phenotypic changes. To identify transcriptional changes associated with early synucleinopathy, we used laser capture microdissection of the SNpc paired with RNA sequencing (RNASeq). Precision collection of the SNpc allowed for the assessment of differential transcript expression in the nigral dopamine neurons and proximal glia. Transcripts upregulated in early synucleinopathy were mainly associated with an immune response, whereas transcripts downregulated were associated with neurotransmission and the dopamine pathway. A subset of 29 transcripts associated with neurotransmission/vesicular release and the dopamine pathway were verified in a separate cohort of males and females to confirm reproducibility. Within this subset, fluorescent in situ hybridization (FISH) was used to localize decreases in the Syt1 and Slc6a3 transcripts to pSyn inclusion-containing neurons. Identification of transcriptional changes in early synucleinopathy provides insight into the molecular mechanisms driving neurodegeneration.

Microglial depletion does not impact alpha-synuclein aggregation or nigrostriatal degeneration in the rat preformed fibril model

Background

Parkinson's disease (PD) is a neurodegenerative disorder that is characterized by the presence of proteinaceous alpha-synuclein (α-syn) inclusions (Lewy bodies), markers of neuroinflammation and the progressive loss of nigrostriatal dopamine (DA) neurons. These pathological features can be recapitulated in vivo using the α-syn preformed fibril (PFF) model of synucleinopathy. We have previously described the time course of microglial major-histocompatibility complex-II (MHC-II) expression and alterations in microglia morphology in the PFF model in rats. Specifically, the peaks of α-syn inclusion formation, MHC-II expression, and reactive morphology in the substantia nigra pars compacta (SNpc) all occur two months post PFF injection, months before neurodegeneration occurs. These results suggest that activated microglia may contribute to neurodegeneration and could represent a potential target for novel therapeutics. The goal of this study was to determine whether microglial depletion could impact the magnitude of α-syn aggregation, nigrostriatal degeneration, or related microglial activation during the α-syn PFF model.

Methods

Male Fischer 344 rats were injected intrastriatally with either α-syn PFFs or saline. Rats were continuously administered Pexidartinib (PLX3397B, 600mg/kg), a colony stimulating factor-1 receptor (CSF1R) inhibitor, to deplete microglia for a period of either two or six months.

Results

PLX3397B administration resulted in significant depletion (45-53%) of ionized calcium-binding adapter molecule 1 immunoreactive (Iba-1ir) microglia within the SNpc. Microglial depletion did not impact accumulation of phosphorylated α-syn (pSyn) within SNpc neurons and did not alter pSyn associated microglial reactivity or expression of MHC-II. Further, microglial depletion did not impact SNpc neuron degeneration. Paradoxically, long term microglial depletion resulted in increased soma size of remaining microglia in both control and PFF rats, as well as expression of MHC-II in extranigral regions.

Conclusions

Collectively, our results suggest that microglial depletion is not a viable disease-modifying strategy for PD and that partial microglial depletion can induce a heightened proinflammatory state in remaining microglia.

Dopaminergic Positron Emission Tomography Imaging in the Alpha-Synuclein Preformed Fibril Model Reveals Similarities to Early Parkinson's Disease

BACKGROUND

Positron emission tomography (PET) imaging in early Parkinson's disease (PD) subjects reveals that increased dopamine (DA) turnover and reduced dopamine transporter (DAT) density precede decreases in DA synthesis and storage. The rat α-synuclein preformed fibril (α-syn PFF) model provides a platform to investigate DA dynamics during multiple stages of α-syn inclusion-triggered nigrostriatal degeneration.

OBJECTIVES

We investigated multiple aspects of in vivo dopaminergic deficits longitudinally and similarities to human PD using translational PET imaging readouts.

METHODS

Longitudinal imaging was performed every 2 months in PFF and control rats for 7 months. [18 F]-Fluoro-3,4-dihydroxyphenyl-L-alanine (FDOPA) imaging was performed to investigate DA synthesis and storage (Kocc ) and DA turnover, estimated by its inverse, the effective distribution volume ratio (EDVR). 11 C-Methylphenidate (MP) was used to estimate DAT density (BPND ).

RESULTS

Early DA turnover increases and DAT binding decreases were observed in the ipsilateral striatum of PFF rats, progressing longitudinally. EDVR decreased 26%, 38%, and 47%, and BPND decreased 36%, 50%, and 65% at the 2-, 4-, and 6-month time points, respectively, compared to ipsilateral control striatum. In contrast, deficits in DA synthesis and storage were not observed in the ipsilateral striatum of PFF rats compared to control injections and were relatively preserved up to 6 months (Kocc decreased 20% at 6 months).

CONCLUSIONS

The relative preservation of DA synthesis and storage compared to robust progressive deficits in DAT density and increases in DA turnover in the rat α-syn PFF model display remarkable face validity to dopaminergic alterations in human PD. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Beta2-adrenoreceptor agonist clenbuterol produces transient decreases in alpha-synuclein mRNA but no long-term reduction in protein

β2-adrenoreceptor (β2AR) agonists have been associated with a decreased risk of developing Parkinson's disease (PD) and are hypothesized to decrease expression of both alpha-synuclein mRNA (Snca) and protein (α-syn). Effects of β2AR agonist clenbuterol on the levels of Snca mRNA and α-syn protein were evaluated in vivo (rats and mice) and in rat primary cortical neurons by two independent laboratories. A modest decrease in Snca mRNA in the substantia nigra was observed after a single acute dose of clenbuterol in rats, however, this decrease was not maintained after multiple doses. In contrast, α-syn protein levels remained unchanged in both single and multiple dosing paradigms. Furthermore, clenbuterol did not decrease Snca in cultured rat primary cortical neurons, or decrease Snca or α-syn in mice. Additionally, compared to the single-dose paradigm, repeat dosing resulted in substantially lower levels of clenbuterol in plasma and brain tissue in rodents. Based on our observations of a transient decrease in Snca and no effect on α-syn protein in this preclinical study, these data support the conclusion that clenbuterol is not likely a viable disease-modifying strategy for PD.

Post-marathon decline in right ventricular radial motion component among amateur sportsmen

Introduction

Running the marathon may be followed by post-exercise “cardiac fatigue” manifesting as transient right ventricular (RV) systolic and diastolic impairment. It is the thin-walled RV that is predominantly affected by the exercise-induced overload, with little if any, impact on the left ventricle (LV) [1]. The 2-D echocardiographic (ECHO) assessment of RV is challenging and may be incomplete since conventional measures reflect only the longitudinal motion (displacement of tricuspid annulus towards the apex) [2]. The mechanics of RV can be separated into two more components, anteroposterior (stretching RV wall by contracting septum) and radial (internal relocation of the RV free wall) [2]. The significance and relative contribution of motion components to global RV function may not be equal, and their interplay can vary depending on concomitant diseases [3].

Purpose

We aimed to analyse the pathophysiology of RV exhaustion associated with a marathon run with 3-D ECHO, which allows precise estimation of all RV motion components and their contribution to RV global function.

Methods

The study included 34 healthy males (mean age of 40±8 years), amateurs, who finished the marathon in northern Poland. The 3-D ECHO was performed 2 weeks before (stage I), at the marathon finish line (stage II) and 2 weeks after the competition (stage III). According to the ReVISION method (Right ventricular separate wall motion quantification) the global RV function was decomposed to longitudinal (L_), anteroposterior (AP_) and radial (R_) [3]. By dividing componential ejection fractions (EF) with global RV EF, L_EFi, AP_EFi, and R_EFi ratios were obtained.

Results

When comparing results from stage I and III there were no significant differences (Table 1). The analysis revealed post-run decline in RV EF with no changes in LV EF. The quantification of the RV motion components showed reduction in R_EF after the marathon with no changes in AP_EF or L_EF. The relative contribution of componential EF to global RV function were permanent and was not influenced by the competition.

Conclusions

Marathon run resulted in transient RV dysfunction arising from decline in radial shortening. Noteworthy, the componential interplay between wall motion compartments was preserved in pre- and post-run assessment. The ReVISION method enables the comprehensive analysis of the competing RV.

Funding Acknowledgement

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): The study was supported by the project POWR.03.05.00-00-z082/18 co-financed by the European Union through the European Social Fund under the Operational Programme Knowledge Education Development 2014–2020

Preformed fibrils generated from mouse alpha-synuclein produce more inclusion pathology in rats than fibrils generated from rat alpha-synuclein

BACKGROUND

Alpha-synuclein (α-syn) preformed fibril (PFF)-induced pathology can be used to study the features and progression of synucleinopathies, such as Parkinson's disease. Intrastriatal injection of mouse α-syn PFFs produce accumulation of α-syn pathology in both mice and rats. Previous studies in mice have revealed that greater sequence homology between the α-syn amino acid sequence used to produce PFFs with that of the endogenous host α-syn increases α-syn pathology in vivo.

NEW METHODS

Based on the prediction that greater sequence homology will result in more α-syn pathology, PFFs generated from recombinant rat α-syn (rPFFs) were used instead of PFFs produced from recombinant mouse α-syn (mPFFs), which are normally used in the model. Rats received unilateral intrastriatal injections of either rPFFs or mPFFs and accumulation of α-syn phosphorylated at serine 129 (pSyn) was examined at 1-month post-surgery.

RESULTS

Rats injected with mPFFs exhibited abundant accumulation of α-syn inclusions in the substantia nigra and cortical regions, whereas in rats injected with rPFFs had significantly fewer SNpc neurons containing pSyn inclusions (≈60% fewer) and little, if any, pSyn inclusions were observed in the cortex.

CONCLUSIONS

Our results suggest that additional factors beyond the degree of sequence homology between host α-syn and injected recombinant α-syn impact efficiency of seeding and subsequent inclusion formation. More practically, these findings caution against the use of rPFFs in the rat preformed fibril model.

Neurologic sequelae associated with delayed identification of iatrogenic skull base injury during endoscopic sinus surgery (ESS)

BACKGROUND

Skull base injury is an infrequent complication during endoscopic sinus surgery (ESS). We hypothesize that late recognition and repair of CSF leaks during ESS is associated with increased neurologic morbidity.

METHODOLOGY

A retrospective review was performed of patients with skull base injury during ESS at a tertiary center from 1999-2015. The study population was separated into early (less than 72 hrs) and late (more than 72 hrs) intervention groups. Study parameters included time to diagnosis, imaging, site of injury, type of repair, neurologic complications, and clinical outcomes.

RESULTS

Seventeen patients were studied. The primary surgical interventions included ESS and balloon sinuplasty. Mean latency from primary surgery to presentation to our facility was 11 days. The most common injury site was the cribriform plate and the mean defect size 4.5 mm. Late diagnosis was associated with increased total neurologic complications and increased rates of postoperative meningitis. No neurologic complications occurred in patients diagnosed intraoperatively. All patients underwent successful endoscopic repair.

CONCLUSION

Skull base injury is a rare but major complication following both balloon sinuplasty and traditional primary ESS. Early diagnosis and endoscopic repair may prevent neurologic morbidity in these patients.

Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine: Brussels, Belgium. 15-18 March 2016

[This corrects the article DOI: 10.1186/s13054-016-1208-6.].

The potential of ki67 and p53 assessment in development of individualized targeted therapy in breast cancer patients

INTRODUCTION

Despite the improvement of diagnostic methods and chemotherapeutic regimens in breast cancer, overall 5-year survival significantly depends on the stage of the disease. Over expression of tumor suppressor gene p53 and the marker for cellular proliferation Ki67 in breast cancer may have prognostic significance.

METHODS

We evaluated 675 patients diagnosed with breast cancer at UF Health Jacksonville between January 2000 and June 2007 with up to 5-year follow up. The aim of the study was to determine whether immunohistochemical (IHC) assessment of Ki67 and p53 may predict outcome, the 'hazard' of dying. Cox's proportional hazards models were used to control for age (< 50 vs. ≥ 50), race (white vs. other), lymph node group (negative vs. positive), ER (estrogen receptor) group (negative vs. positive), PR (progesterone receptor) group (negative vs. positive), and tumor type.

RESULTS

When only p53 was considered in the model, the hazard of dying was significantly higher for p53 positive compared to p53 negative (HR = 1.32, 95% CI 1.02, 1.70, p = 0.036). When only ki67 was considered in the model, the hazard of dying was significantly higher for ki67 positive compared to ki67 negative (Hazard ratio = 1.64, 95% CI 1.08, 2.49, p = 0.021). Neither of the two markers, nor their interaction was significant when all variables were considered in the model.

DISCUSSION

This study confirms the expression of p53 and Ki67 as strong individual indicators of patient outcome. However, when controlling for the other variables, the two markers are not independent predictors. Future studies that will include these markers might help design targeted therapy.