MerTK is a mediator of alpha-synuclein fibril uptake by human microglia.

Mer tyrosine kinase (MerTK) is a receptor tyrosine kinase that mediates non-inflammatory, homeostatic phagocytosis of diverse types of cellular debris. Highly expressed on the surface of microglial cells, MerTK is of importance in brain development, homeostasis, plasticity and disease. Yet, involvement of this receptor in the clearance of protein aggregates that accumulate with ageing and in neurodegenerative diseases has yet to be defined. The current study explored the function of MerTK in the microglial uptake of alpha-synuclein fibrils which play a causative role in the pathobiology of synucleinopathies. Using human primary and induced pluripotent stem cell-derived microglia, the MerTK-dependence of alpha-synuclein fibril internalization was investigated in vitro. Relevance of this pathway in synucleinopathies was assessed through burden analysis of MERTK variants and analysis of MerTK expression in patient-derived cells and tissues. Pharmacological inhibition of MerTK and siRNA-mediated MERTK knockdown both caused a decreased rate of alpha-synuclein fibril internalization by human microglia. Consistent with the non-inflammatory nature of MerTK-mediated phagocytosis, alpha-synuclein fibril internalization was not observed to induce secretion of pro-inflammatory cytokines such as IL-6 or TNF, and downmodulated IL-1ß secretion from microglia. Burden analysis in two independent patient cohorts revealed a significant association between rare functionally deleterious MERTK variants and Parkinson's disease in one of the cohorts (P = 0.002). Despite a small upregulation in MERTK mRNA expression in nigral microglia from Parkinson's disease/Lewy body dementia patients compared to those from non-neurological control donors in a single-nuclei RNA-sequencing dataset (P = 5.08 × 10-21), no significant upregulation in MerTK protein expression was observed in human cortex and substantia nigra lysates from Lewy body dementia patients compared to controls. Taken together, our findings define a novel role for MerTK in mediating the uptake of alpha-synuclein fibrils by human microglia, with possible involvement in limiting alpha-synuclein spread in synucleinopathies such as Parkinson's disease. Upregulation of this pathway in synucleinopathies could have therapeutic values in enhancing alpha-synuclein fibril clearance in the brain.

Analysis of the microglia transcriptome across the human lifespan using single cell RNA sequencing.

BACKGROUND: Microglia are tissue resident macrophages with a wide range of critically important functions in central nervous system development and homeostasis. METHOD: In this study, we aimed to characterize the transcriptional landscape of ex vivo human microglia across different developmental ages using cells derived from pre-natal, pediatric, adolescent, and adult brain samples. We further confirmed our transcriptional observations using ELISA and RNAscope. RESULTS: We showed that pre-natal microglia have a distinct transcriptional and regulatory signature relative to their post-natal counterparts that includes an upregulation of phagocytic pathways. We confirmed upregulation of CD36, a positive regulator of phagocytosis, in pre-natal samples compared to adult samples in situ. Moreover, we showed adult microglia have more pro-inflammatory signature compared to microglia from other developmental ages. We indicated that adult microglia are more immune responsive by secreting increased levels of pro-inflammatory cytokines in response to LPS treatment compared to the pre-natal microglia. We further validated in situ up-regulation of IL18 and CXCR4 in human adult brain section compared to the pre-natal brain section. Finally, trajectory analysis indicated that the transcriptional signatures adopted by microglia throughout development are in response to a changing brain microenvironment and do not reflect predetermined developmental states. CONCLUSION: In all, this study provides unique insight into the development of human microglia and a useful reference for understanding microglial contribution to developmental and age-related human disease.

MicroRNA-210 regulates the metabolic and inflammatory status of primary human astrocytes.

BACKGROUND: Astrocytes are the most numerous glial cell type with important roles in maintaining homeostasis and responding to diseases in the brain. Astrocyte function is subject to modulation by microRNAs (miRs), which are short nucleotide strands that regulate protein expression in a post-transcriptional manner. Understanding the miR expression profile of astrocytes in disease settings provides insight into the cellular stresses present in the microenvironment and may uncover pathways of therapeutic interest. METHODS: Laser-capture microdissection was used to isolate human astrocytes surrounding stroke lesions and those from neurological control tissue. Astrocytic miR expression profiles were examined using quantitative reverse transcription polymerase chain reaction (RT-qPCR). Primary human fetal astrocytes were cultured under in vitro stress conditions and transfection of a miR mimic was used to better understand how altered levels of miR-210 affect astrocyte function. The astrocytic response to stress was studied using qPCR, enzyme-linked immunosorbent assays (ELISAs), measurement of released lactate, and Seahorse. RESULTS: Here, we measured miR expression levels in astrocytes around human ischemic stroke lesions and observed differential expression of miR-210 in chronic stroke astrocytes compared to astrocytes from neurological control tissue. We also identified increased expression of miR-210 in mouse white matter tissue around middle cerebral artery occlusion (MCAO) brain lesions. We aimed to understand the role of miR-210 in primary human fetal astrocytes by developing an in vitro assay of hypoxic, metabolic, and inflammatory stresses. A combination of hypoxic and inflammatory stresses was observed to upregulate miR-210 expression. Transfection with miR-210-mimic (210M) increased glycolysis, enhanced lactate export, and promoted an anti-inflammatory transcriptional and translational signature in astrocytes. Additionally, 210M transfection resulted in decreased expression of complement 3 (C3) and semaphorin 5b (Sema5b). CONCLUSIONS: We conclude that miR-210 expression in human astrocytes is modulated in response to ischemic stroke disease and under in vitro stress conditions, supporting a role for miR-210 in the astrocytic response to disease conditions. Further, the anti-inflammatory and pro-glycolytic impact of miR-210 on astrocytes makes it a potential candidate for further research as a neuroprotective agent.

Comparison of clinical and histopathological characteristics of short-term progressive and non-progressive blood blister-like aneurysms.

BACKGROUND: Many blood blister aneurysms (BBAs) have been documented with a rapid progression history in repeated angiography. The underlying mechanism and clinical significance remained elusive. This current study aims to clarify the clinical and histopathological differences between short-term progressive BBA and non-progressive BBAs. METHODS AND MATERIALS: Eighty-one patients with BBAs were consecutively included for this single-center retrospective analysis. Clinical and radiological data on these patients were retrieved from 2017 to 2019. BBAs were defined as either progressive or non-progressive based on observed growth based on repeated imaging. Histopathological examinations of a saccular aneurysm, a progressive BBA, and a non-progressive BBA were conducted using representative aneurysm samples. RESULTS: Among all enrolled patients, 26 of the them were identified with progressive BBAs, while the other 55 with non-progressive BBAs. Progressive BBAs were diagnosed significantly earlier in angiography (3.36 ± 0.61 vs. 6.53 ± 1.31 days, p < 0.05) and showed a higher presence rate of daughter sacs (61.5 vs. 38.2%, p < 0.05). Three different progression patterns were identified. BBAs that developed daughter sac enlargement are diagnosed significantly later than BBAs exhibiting other progression patterns. Patients with progressive and non-progressive BBAs exhibited similar overall clinical outcomes and incidence for complications. For patients with non-progressive BBAs, microsurgery appears to be inferior to endovascular treatment, while for patients with progressive BBAs, the short-term outcomes between microsurgery and endovascular treatment were identical. Histopathological analysis revealed that both subtypes shared a similar pseudoaneurysms structure, but non-progressive BBAs had more histologically destructed aneurysm wall with less remnant fibrillar collagen in adventitia. CONCLUSIONS: Progressive and non-progressive BBAs may not be distinct pathological lesions but represent different stages during the BBA development. Early intervention, regardless of treatment methods, is recommended for salvageable patients with progressive BBAs, but microsurgery should be performed with caution for non-progressive BBAs due to increased surgical risk.

Lesion stage-dependent causes for impaired remyelination in MS.

Multiple sclerosis (MS) is the most frequent demyelinating disease and a leading cause for disability in young adults. Despite significant advances in immunotherapies in recent years, disease progression still cannot be prevented. Remyelination, meaning the formation of new myelin sheaths after a demyelinating event, can fail in MS lesions. Impaired differentiation of progenitor cells into myelinating oligodendrocytes may contribute to remyelination failure and, therefore, the development of pharmacological approaches which promote oligodendroglial differentiation and by that remyelination, represents a promising new treatment approach. However, this generally accepted concept has been challenged recently. To further understand mechanisms contributing to remyelination failure in MS, we combined detailed histological analyses assessing oligodendroglial cell numbers, presence of remyelination as well as the inflammatory environment in different MS lesion types in white matter with in vitro experiments using induced-pluripotent stem cell (iPSC)-derived oligodendrocytes (hiOL) and supernatants from polarized human microglia. Our findings suggest that there are multiple reasons for remyelination failure in MS which are dependent on lesion stage. These include lack of myelin sheath formation despite the presence of mature oligodendrocytes in a subset of active lesions as well as oligodendroglial loss and a hostile tissue environment in mixed active/inactive lesions. Therefore, we conclude that better in vivo and in vitro models which mimic the pathological hallmarks of the different MS lesion types are required for the successful development of remyelination promoting drugs.

Presence of vasa vasorum in human intracranial aneurysms.

OBJECTIVES: Vasa vasorum is associated with the pathogenesis of various cerebrovascular diseases, but its presence in intracranial aneurysms (IA) and its ability to act as a predicting factor of IA rupture remain unrevealed. METHODS: Histological investigation was performed for 3 middle meningeal arteries and 25 human IAs that were sequentially collected from 2017 to 2019. Relevant medical information was collected from the hospital information and imaging system. Fisher's exact tests and Student's t tests were performed to identify the histological and clinical differences between aneurysms with and without vasa vasorum. RESULTS: Vasa vasorum were present in 14/25 (56%) aneurysm samples. They were detected at a similar frequency in male patients (4/9, 44.4%) and (10/16, 62.5%) female patients. Patients with vasa vasorum present aneurysms (47.07 ± 3.668 years, n = 14) or vasa vasorum absent aneurysms (50.27 ± 2.289 years, n = 11) did not differ in age (p = 0.49). True aneurysms and pseudoaneurysms also shared a similar rate of vasa vasorum presence (10/16, 62.5% in true aneurysms vs 4/9, 44.4% in pseudoaneurysms). The average size of aneurysms with vasa vasorum varied from 21.70 to 3.00 mm, and no statistical difference in size was detected when comparing aneurysms with and without vasa vasorum (p = 0.71). The vasa vasorum in almost all IAs had uniform vascular trajectory with occasional exceptions. The presence of vasa vasorum appears to be tightly associated with important histopathological changes of myointimal hyperplasia and increased immune cell infiltration in IAs (both p value < 0.05), though it does not appear to be indicative of IA rupture or other rupture-related histological degenerations (all p values > 0.05). CONCLUSIONS: The presence of vasa vasorum is common in IAs. While it is associated with aneurysm wall remodeling and robust inflammatory cell infiltration, our results indicate that it is not a single specific marker of rupture-prone aneurysms.

Unraveling molecular mechanism underlying biomaterial and stem cells interaction during cell fate commitment using high throughput data analysis.

Stem cell differentiation towards various somatic cells and body organs has proven to be an effective technique in the understanding and progression of regenerative medicine. Despite the advances made, concerns regarding the low efficiency of differentiation and the remaining differences between stem cell products and their in vivo counterparts must be addressed. Biomaterials that mimic endogenous growth conditions represent one recent method used to improve the quality and efficiency of stem cell differentiation, though the mechanisms of this improvement remain to be completely understood. The effectiveness of various biomaterials can be analyzed through a multidisciplinary approach involving bioinformatics and systems biology tools. Here, we aim to use bioinformatics to accomplish two aims: 1) determine the effect of different biomaterials on stem cell growth and differentiation, and 2) understand the effect of cell of origin on the differentiation potential of multipotent stem cells. First, we demonstrate that the dimensionality (2D versus 3D) and the degradability of biomaterials affects the way that the cells are able to grow and differentiate at the transcriptional level. Additionally, according to transcriptional state of the cells, the particular cell of origin is an important factor in determining the response of stem cells to same biomaterial. Our data demonstrates the ability of bioinformatics to understand novel molecular mechanisms and context by which stem cells are most efficiently able to differentiate. These results and strategies can be used to suggest proper combinations of biomaterials and stem cells to achieve high differentiation efficiency and functionality of desired cell types.

Intracranial Aneurysm Presenting Robust Metal Artifact.

BACKGROUND: Intracranial aneurysm (IA) is a debilitating cerebrovascular degeneration. Current clinical diagnosis relies mainly on conventional angiogram except for some peculiar aneurysms. Nonetheless, there is no documentation of aneurysm showing robust intracranial artifact on computed tomography or magnetic resonance imaging. CASE DESCRIPTION: Herein, we report a 45-year-old female with an IA showing a robust intracranial metal artifact. During surgery, the culprit lesion for the artifact was discovered to be hard plaque on the ventral part of the aneurysm. Craniotomy clipping and vessel reconstruction were successful, but minor vasospasm was observed postoperatively. Postoperative pathology and optical emission spectrometer analyses showed elevated iron and copper level in the plaque on the IA. After comparing with other aneurysm samples, we believe the overenriched local iron deposition contributed to the metal artifact on imaging. CONCLUSIONS: Taken together, accidental findings of intracranial metal artifacts on computed tomography and magnetic resonance imaging can be indicative to iron deposition on intracranial aneurysm. Neuroimaging using magnetic field should be performed with caution. Local accumulation of lysed products from erythrocyte might contribute to the occurrence of this enriched iron deposition, but further evidence regarding the pathogenesis of copper deposition should be provided. Surgically, measures should be taken to avoid perioperative complications like vasospasm and delayed cerebral ischemia. Future report of similar cases would be helpful in optimizing the treatment modality for the aneurysm with metallic plaque.

Novel Molecular Leads for the Prevention of Damage and the Promotion of Repair in Neuroimmunological Disease.

Neuroinflammation is a prominent pathological feature of all neuroimmunological diseases, including, but not limited to, multiple sclerosis (MS), myasthenia gravis, neuromyelitis optica, and Guillain-Barré syndrome. All currently-approved therapies for the treatment of these diseases focus on controlling or modulating the immune (innate and adaptive) responses to limit demyelination and neuronal damage. The primary purpose of this review is to detail the pre-clinical data and proposed mechanism of action of novel drugs currently in clinical trial, with a focus on novel compounds that promote repair and regeneration in the central nervous system (CNS). As the most recent advances have been made in the field of MS research, this review will focus primarily on this disease and its animal models. However, these compounds are likely to be effective for a range of indications with a neuroinflammatory component. Traditionally, MS was thought to proceed through two distinct phases. The first, predominantly inflammatory stage, is characterized by acute episodes of clinical relapse, followed by periods of partial or total recovery with an apparent absence of overall disease progression. In the vast majority of patients, this relapsing-remitting disease subsequently progresses into a second more chronic, neurodegenerative phase, which is characterized by oligodendrocyte damage and axonal destruction leading to brain atrophy and an accumulation of disability. Recent work has shown that rather than occurring independently, both the inflammatory and degenerative phases may run concurrently. This, combined with evidence that early therapeutic intervention slows accumulation of disability and delays progression, highlights the need for novel therapeutic approaches that promote repair and regeneration early in the disease trajectory. Such compounds may be used as monotherapies or in conjunction with classical anti-inflammatory therapies. This review will highlight novel therapies currently in clinical trial, and likely to appear in clinical practice in the near future, focusing on compounds that target the immune system and/or enhance endogenous repair mechanisms in the CNS.