Microglial Phenotyping in Neurodegenerative Disease Brains: Identification of Reactive Microglia with an Antibody to Variant of CD105/Endoglin

Localization of Thioredoxin-Interacting Protein in Aging and Alzheimer's Disease Brains

Thioredoxin-Interacting Protein (TXNIP) has been shown to have significant pathogenic roles in many human diseases, particularly those associated with diabetes and hyperglycemia. Its main mode of action is to sequester thioredoxins, resulting in enhanced oxidative stress. The aim of this study was to identify if cellular expression of TXNIP in human aged and Alzheimer's disease (AD) brains correlated with pathological structures. This study employed fixed tissue sections and protein extracts of temporal cortex from AD and aged control brains. Studies employed light and fluorescent immunohistochemical techniques using the monoclonal antibody JY2 to TXNIP to identify cellular structures. Immunoblots were used to quantify relative amounts of TXNIP in brain protein extracts. The major finding was the identification of TXNIP immunoreactivity in selective neuronal populations and structures, particularly in non-AD brains. In AD brains, less neuronal TXNIP but increased numbers of TXNIP-positive plaque-associated microglia were observed. Immunoblot analyses showed no significant increase in levels of TXNIP protein in the AD samples tested. In conclusion, this study identified altered patterns of expression of TXNIP in human brains with progression of AD pathology.

Soluble Endoglin Stimulates Inflammatory and Angiogenic Responses in Microglia That Are Associated with Endothelial Dysfunction

Increased soluble endoglin (sENG) has been observed in human brain arteriovenous malformations (bAVMs). In addition, the overexpression of sENG in concurrence with vascular endothelial growth factor (VEGF)-A has been shown to induce dysplastic vessel formation in mouse brains. However, the underlying mechanism of sENG-induced vascular malformations is not clear. The evidence suggests the role of sENG as a pro-inflammatory modulator, and increased microglial accumulation and inflammation have been observed in bAVMs. Therefore, we hypothesized that microglia mediate sENG-induced inflammation and endothelial cell (EC) dysfunction in bAVMs. In this study, we confirmed that the presence of sENG along with VEGF-A overexpression induced dysplastic vessel formation. Remarkably, we observed increased microglial activation around dysplastic vessels with the expression of NLRP3, an inflammasome marker. We found that sENG increased the gene expression of VEGF-A, pro-inflammatory cytokines/inflammasome mediators (TNF-α, IL-6, NLRP3, ASC, Caspase-1, and IL-1β), and proteolytic enzyme (MMP-9) in BV2 microglia. The conditioned media from sENG-treated BV2 (BV2-sENG-CM) significantly increased levels of angiogenic factors (Notch-1 and TGFβ) and pERK1/2 in ECs but it decreased the level of IL-17RD, an anti-angiogenic mediator. Finally, the BV2-sENG-CM significantly increased EC migration and tube formation. Together, our study demonstrates that sENG provokes microglia to express angiogenic/inflammatory molecules which may be involved in EC dysfunction. Our study corroborates the contribution of microglia to the pathology of sENG-associated vascular malformations.

Effects of miRNAs in exosomes derived from α-synuclein overexpressing SH-SY5Y cells on autophagy and inflammation of microglia

Our previous study has revealed that GFP-α-synuclein overexpressing SH-SY5Y cells-derived exosomes (GFP-SNCA Exo) decrease autophagy in microglia via their load of miRNAs. However, it is unclear whether GFP-SNCA Exo can affect microglial inflammation via modulation of autophagy. In order to investigate the effects of miRNAs carried by GFP-SNCA Exo on autophagy and inflammation of microglia. SH-SY5Y cells were transfected with lentivirus expressing α-synuclein and then their exosomes were collected. Western blot and laser confocal images showed that α-synuclein transferred between SH-SY5Y cells and microglia through exosomes. Differentially expressed miRNAs between GFP-SNCA Exo and the vector exosomes were detected by microarray analysis. After bioinformatics analysis of the differentially expressed miRNAs, we found that their target genes were enriched in the MAPK and autophagy-associated signaling pathway. The expression of P62, p-JNK/JNK, and p-ERK/ERK and the release of IL-6 significantly increased whereas LC3 II/I decreased in microglia exposed to GFP-SNCA Exo for 48 h when compared to the control group. But rapamycin could reverse the increasing expression of p-JNK/JNK, p-ERK/ERK and the release of IL-6 induced by GFP-SNCA Exo. Dual immunofluorescence staining for LC3B and LAMP1 showed that the fluorescence density of LC3B decreased and the fluorescence of LC3B and LAMP1 were not co-located in microglia after 48 h co-culture with GFP-SNCA Exo compared with the control group, which indicated that these exosomes decreased autophagy and impaired the autophagy flux in recipient microglia. Taken together, our results indicate that GFP-SNCA Exo activate the MAPK signaling pathway and inflammation by decreasing autophagy in microglia.

Profiling Inflammatory Extracellular Vesicles in Plasma and Cerebrospinal Fluid: An Optimized Diagnostic Model for Parkinson's Disease

Extracellular vesicles (EVs) play a central role in intercellular communication, which is relevant for inflammatory and immune processes implicated in neurodegenerative disorders, such as Parkinson's Disease (PD). We characterized and compared distinctive cerebrospinal fluid (CSF)-derived EVs in PD and atypical parkinsonisms (AP), aiming to integrate a diagnostic model based on immune profiling of plasma-derived EVs via artificial intelligence. Plasma- and CSF-derived EVs were isolated from patients with PD, multiple system atrophy (MSA), AP with tauopathies (AP-Tau), and healthy controls. Expression levels of 37 EV surface markers were measured by a flow cytometric bead-based platform and a diagnostic model based on expression of EV surface markers was built by supervised learning algorithms. The PD group showed higher amount of CSF-derived EVs than other groups. Among the 17 EV surface markers differentially expressed in plasma, eight were expressed also in CSF of a subgroup of PD, 10 in MSA, and 6 in AP-Tau. A two-level random forest model was built using EV markers co-expressed in plasma and CSF. The model discriminated PD from non-PD patients with high sensitivity (96.6%) and accuracy (92.6%). EV surface marker characterization bolsters the relevance of inflammation in PD and it underscores the role of EVs as pathways/biomarkers for protein aggregation-related neurodegenerative diseases.

Inflaming the Brain with Iron

Iron accumulation and neuroinflammation are pathological conditions found in several neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson's disease (PD). Iron and inflammation are intertwined in a bidirectional relationship, where iron modifies the inflammatory phenotype of microglia and infiltrating macrophages, and in turn, these cells secrete diffusible mediators that reshape neuronal iron homeostasis and regulate iron entry into the brain. Secreted inflammatory mediators include cytokines and reactive oxygen/nitrogen species (ROS/RNS), notably hepcidin and nitric oxide (·NO). Hepcidin is a small cationic peptide with a central role in regulating systemic iron homeostasis. Also present in the cerebrospinal fluid (CSF), hepcidin can reduce iron export from neurons and decreases iron entry through the blood-brain barrier (BBB) by binding to the iron exporter ferroportin 1 (Fpn1). Likewise, ·NO selectively converts cytosolic aconitase (c-aconitase) into the iron regulatory protein 1 (IRP1), which regulates cellular iron homeostasis through its binding to iron response elements (IRE) located in the mRNAs of iron-related proteins. Nitric oxide-activated IRP1 can impair cellular iron homeostasis during neuroinflammation, triggering iron accumulation, especially in the mitochondria, leading to neuronal death. In this review, we will summarize findings that connect neuroinflammation and iron accumulation, which support their causal association in the neurodegenerative processes observed in AD and PD.

Oligodendrocyte Response to Pathophysiological Conditions Triggered by Episode of Perinatal Hypoxia-Ischemia: Role of IGF-1 Secretion by Glial Cells

Differentiation of oligodendrocyte progenitors towards myelinating cells is influenced by a plethora of exogenous instructive signals. Insulin-like growth factor 1 (IGF-1) is one of the major factors regulating cell survival, proliferation, and maturation. Recently, there is an ever growing recognition concerning the role of autocrine/paracrine IGF-1 signaling in brain development and metabolism. Since oligodendrocyte functioning is altered after the neonatal hypoxic-ischemic (HI) insult, a question arises if the injury exerts any influence on the IGF-1 secreted by neural cells and how possibly the change in IGF-1 concentration affects oligodendrocyte growth. To quantify the secretory activity of neonatal glial cells, the step-wise approach by sequentially using the in vivo, ex vivo, and in vitro models of perinatal asphyxia was applied. A comparison of the results of in vivo and ex vivo studies allowed evaluating the role of autocrine/paracrine IGF-1 signaling. Accordingly, astroglia were indicated to be the main local source of IGF-1 in the developing brain, and the factor secretion was shown to be significantly upregulated during the first 24 h after the hypoxic-ischemic insult. And conversely, the IGF-1 amounts released by oligodendrocytes and microglia significantly decreased. A morphometric examination of oligodendrocyte differentiation by means of the Sholl analysis showed that the treatment with low IGF-1 doses markedly improved the branching of oligodendroglial cell processes and, in this way, promoted their differentiation. The changes in the IGF-1 amounts in the nervous tissue after HI might contribute to the resulting white matter disorders, observed in newborn children who experienced perinatal asphyxia. Pharmacological modulation of IGF-1 secretion by neural cells could be reasonable solution in studies aimed at searching for therapies alleviating the consequences of perinatal asphyxia.

Microglia: Agents of the CNS Pro-Inflammatory Response

The pro-inflammatory immune response driven by microglia is a key contributor to the pathogenesis of several neurodegenerative diseases. Though the research of microglia spans over a century, the last two decades have increased our understanding exponentially. Here, we discuss the phenotypic transformation from homeostatic microglia towards reactive microglia, initiated by specific ligand binding to pattern recognition receptors including toll-like receptor-4 (TLR4) or triggering receptors expressed on myeloid cells-2 (TREM2), as well as pro-inflammatory signaling pathways triggered such as the caspase-mediated immune response. Additionally, new research disciplines such as epigenetics and immunometabolism have provided us with a more holistic view of how changes in DNA methylation, microRNAs, and the metabolome may influence the pro-inflammatory response. This review aimed to discuss our current knowledge of pro-inflammatory microglia from different angles, including recent research highlights such as the role of exosomes in spreading neuroinflammation and emerging techniques in microglia research including positron emission tomography (PET) scanning and the use of human microglia generated from induced pluripotent stem cells (iPSCs). Finally, we also discuss current thoughts on the impact of pro-inflammatory microglia in neurodegenerative diseases.

Exogenous hydrogen sulfide alleviates surgery-induced neuroinflammatory cognitive impairment in adult mice by inhibiting NO signaling

Background

To investigate the effect and mechanisms of exogenous hydrogen sulfide in surgery-induced neuroinflammatory cognitive dysfunction.

Methods

C57BL/6 J male mice (n = 140) were used and randomly divided into seven groups: the sham group, surgery group, GYY4137 group, L-NAME group, surgery+GYY4137 group, surgery +L-NAME group, and surgery+GYY4137 + L-NAME group. After the interventions, open field tests (OFT) and the Morris water maze (MWM) test were conducted to evaluate learning and memory abilities in the mice. ELISAs, nitrate reductase assays, and Western blots (WB) were conducted to evaluate interleukin-1 beta (IL-1β), tumor necrosis factor-alpha (TNF-α), nitric oxide (NO), inducible nitric oxide synthase (iNOS), malondialdehyde (MDA), and antioxidant enzyme superoxide dismutase (SOD) levels. Furthermore, the expression level of microglial marker ionized calcium binding adaptor molecule 1 (IBA) in the hippocampal CA1 and CA3 areas was detected by an immunohistochemical (IHC) assay and apoptotic cells were observed using terminal deoxynucleotidyl transferase dUTP end-labeling (TUNEL) staining kits.

Results

We found that surgery induced neuroinflammatory cognitive dysfunction, oxidative stress, microglial activation, and cell apoptosis in the hippocampus. Moreover, following surgery, NO and iNOS levels were elevated in the hippocampus. Notably, all the effects caused by surgery were reversed by the H₂S donor GYY4137 or the iNOS inhibitor N(gamma)-nitro-L-arginine methyl ester (L-NAME). However, the combined application of GYY4137 and L-NAME was not superior to treatment with either agent alone and the effect of GYY4137 was similar to that of L-NAME.

Conclusion

The long-acting hydrogen sulfide donor GYY4137 had an ability to reversed the cognitive deficits and inflammation caused by carotid artery exposure surgery. This implies that NO signaling pathways might participate in this process. These results indicate that exogenous H₂S may be a promising therapy for POCD.

Characterization of lysosomal proteins Progranulin and Prosaposin and their interactions in Alzheimer's disease and aged brains: increased levels correlate with neuropathology

Progranulin (PGRN) is a protein encoded by the GRN gene with multiple identified functions including as a neurotrophic factor, tumorigenic growth factor, anti-inflammatory cytokine and regulator of lysosomal function. A single mutation in the human GRN gene resulting in reduced PGRN expression causes types of frontotemporal lobar degeneration resulting in frontotemporal dementia. Prosaposin (PSAP) is also a multifunctional neuroprotective secreted protein and regulator of lysosomal function. Interactions of PGRN and PSAP affect their functional properties. Their roles in Alzheimer's disease (AD), the leading cause of dementia, have not been defined. In this report, we examined in detail the cellular expression of PGRN in middle temporal gyrus samples of a series of human brain cases (n = 45) staged for increasing plaque pathology. Immunohistochemistry showed PGRN expression in cortical neurons, microglia, cerebral vessels and amyloid beta (Aβ) plaques, while PSAP expression was mainly detected in neurons and Aβ plaques, and to a limited extent in astrocytes. We showed that there were increased levels of PGRN protein in AD cases and corresponding increased levels of PSAP. Levels of PGRN and PSAP protein positively correlated with amyloid beta (Aβ), with PGRN levels correlating with phosphorylated tau (serine 205) levels in these samples. Although PGRN colocalized with lysosomal-associated membrane protein-1 in neurons, most PGRN associated with Aβ plaques did not. Aβ plaques with PGRN and PSAP deposits were identified in the low plaque non-demented cases suggesting this was an early event in plaque formation. We did not observe PGRN-positive neurofibrillary tangles. Co-immunoprecipitation studies of PGRN from brain samples identified only PSAP associated with PGRN, not sortilin or other known PGRN-binding proteins, under conditions used. Most PGRN associated with Aβ plaques were immunoreactive for PSAP showing a high degree of colocalization of these proteins that did not change between disease groups. As PGRN supplementation has been considered as a therapeutic approach for AD, the possible involvement of PGRN and PSAP interactions in AD pathology needs to be further considered.

The Differences in the Characteristics of Insulin-producing Cells Using Human Adipose-tissue Derived Mesenchymal Stem Cells from Subcutaneous and Visceral Tissues

The aim of this study was to investigate the characteristics of insulin producing cells (IPCs) differentiated from adipose-tissue derived stem cells (ADSCs) isolated from human subcutaneous and visceral adipose tissues and identify ADSCs suitable for differentiation into efficient and functional IPCs. Subcutaneous and visceral adipose tissues collected from four (4) patients who underwent digestive surgeries at The Tokushima University (000035546) were included in this study. The insulin secretion of the generated IPCs was investigated using surface markers by: fluorescence activated cell sorting (FACS) analysis; cytokine release; proliferation ability of ADSCs; in vitro (glucose-stimulated insulin secretion: (GSIS) test/in vivo (transplantation into streptozotocin-induced diabetic nude mice). The less fat-related inflammatory cytokines secretions were observed (P < 0.05), and the proliferation ability was higher in the subcutaneous ADSCs (P < 0.05). Insulin expression and GISI were higher in the subcutaneous IPCs (P < 0.01 and P < 0.05, respectively). The hyperglycaemic state of all mice that received IPCs from subcutaneous fat tissue converted into normo-glycaemia in thirty (30) days post-transplantation (4/4,100%). Transplanted IPCs were stained using anti-insulin and anti-human leukocyte antigen antibodies. The IPCs generated from the ADSCs freshly isolated from the human fat tissue had sufficient insulin secreting ability in vitro and in vivo.