TREM-1 Expression Research Articles

Natural antiviral compound silvestrol modulates human monocyte-derived macrophages and dendritic cells.

Outbreaks of infections with viruses like Sars‐CoV‐2, Ebola virus and Zika virus lead to major global health and economic problems because of limited treatment options. Therefore, new antiviral drug candidates are urgently needed. The promising new antiviral drug candidate silvestrol effectively inhibited replication of Corona‐, Ebola‐, Zika‐, Picorna‐, Hepatis E and Chikungunya viruses. Besides a direct impact on pathogens, modulation of the host immune system provides an additional facet to antiviral drug development because suitable immune modulation can boost innate defence mechanisms against the pathogens. In the present study, silvestrol down‐regulated several pro‐ and anti‐inflammatory cytokines (IL‐6, IL‐8, IL‐10, CCL2, CCL18) and increased TNF‐α during differentiation and activation of M1‐macrophages, suggesting that the effects of silvestrol might cancel each other out. However, silvestrol amplified the anti‐inflammatory potential of M2‐macrophages by increasing expression of anti‐inflammatory surface markers CD206, TREM2 and reducing release of pro‐inflammatory IL‐8 and CCL2. The differentiation of dendritic cells in the presence of silvestrol is characterized by down‐regulation of several surface markers and cytokines indicating that differentiation is impaired by silvestrol. In conclusion, silvestrol influences the inflammatory status of immune cells depending on the cell type and activation status.

Niche-Specific Reprogramming of Epigenetic Landscapes Drives Myeloid Cell Diversity in Nonalcoholic Steatohepatitis

Tissue-resident and recruited macrophages contribute to both host defense and pathology. Multiple macrophage phenotypes are represented in diseased tissues, but we lack deep understanding of mechanisms controlling diversification. Here, we investigate origins and epigenetic trajectories of hepatic macrophages during diet-induced non-alcoholic steatohepatitis (NASH). The NASH diet induced significant changes in Kupffer cell enhancers and gene expression, resulting in partial loss of Kupffer cell identity, induction of Trem2 and Cd9 expression, and cell death. Kupffer cell loss was compensated by gain of adjacent monocyte-derived macrophages that exhibited convergent epigenomes, transcriptomes, and functions. NASH-induced changes in Kupffer cell enhancers were driven by AP-1 and EGR that reprogrammed LXR functions required for Kupffer cell identity and survival to instead drive a scar-associated macrophage phenotype. These findings reveal mechanisms by which disease-associated environmental signals instruct resident and recruited macrophages to acquire distinct gene expression programs and corresponding functions.

Sleep Disruption Exacerbates and Prolongs the Inflammatory Response to Traumatic Brain Injury.

Traumatic brain injury (TBI) alters stress responses, which may influence neuroinflammation and behavioral outcome. Sleep disruption (SD) is an understudied post-injury environmental stressor that directly engages stress-immune pathways. Thus, we predicted that maladaptive changes in the hypothalamic-pituitary-adrenal (HPA) axis after TBI compromise the neuroendocrine response to SD and exacerbate neuroinflammation. To test this, we induced lateral fluid percussion TBI or sham injury in female and male C57BL/6 mice aged 8-10 weeks that were then left undisturbed or exposed to 3 days of transient SD. At 3 days post-injury (DPI) plasma corticosterone (CORT) was reduced in TBI compared with sham mice, indicating altered HPA-mediated stress response to SD. This response was associated with approach-avoid conflict behavior and exaggerated cortical neuroinflammation. Post-injury SD specifically enhanced neutrophil trafficking to the injured brain in conjunction with dysregulated aquaporin-4 (AQP4) polarization. Delayed and persistent effects of post-injury SD were determined 4 days after SD concluded at 7 DPI. SD prolonged anxiety-like behavior regardless of injury and was associated with increased cortical Iba1 labeling in both sham and TBI mice. Strikingly, TBI SD mice displayed an increased number of CD45+ cells near the site of injury, enhanced cortical glial fibrillary acidic protein (GFAP) immunolabeling, and persistent expression of Trem2 and Tlr4 7 DPI compared with TBI mice. These results support the hypothesis that post-injury SD alters stress-immune pathways and inflammatory outcomes after TBI. These data provide new insight to the dynamic interplay between TBI, stress, and inflammation.

Pinitol Prevents Lipopolysaccharide (LPS)-Induced Inflammatory Responses in BV2 Microglia Mediated by TREM2.

Microglia-involved neuroinflammation in the central nervous system (CNS) has been shown to aggravate brain damage and is associated with the pathogenesis of various neurodegenerative diseases. Thus, suppression of microglial activity has the potential to be a strategy for the treatment of neurodegenerative diseases. Pinitol, a methylated product of D-chiro-inositol, has been used as a treatment for blood-sugar metabolism and as an anti-tumor agent via its anti-inflammatory effects in cancer. However, whether or not pinitol can inhibit microglia-associated neuroinflammation is still unknown. This study aims to determine the effects of pinitol on inflammatory responses in BV2 microglia induced by LPS. Here, we found that the presence of pinitol ameliorates LPS-induced oxidative stress by reducing the production of ROS. Pinitol suppresses the expression and secretion of pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6. Notably, pinitol prevents the production of NO and PGE2 by inhibiting the expression of iNOS and COX-2. Mechanistically, our findings demonstrate that pinitol inhibits the phosphorylation and degradation of IκBα and subsequent activation of NF-κB. Furthermore, we show that pinitol increases the expression of TREM2 in BV2 microglia, and silencing of TREM2 abolished the anti-inflammatory effects of pinitol. These findings suggest that TREM2 mediates the protective effects of pinitol against LPS in microglia. In summary, our results display that pinitol possesses a robust and beneficial effect against the LPS-induced inflammatory response in microglia.

Trem2 Splicing and Expression are Preserved in a Human A\u03b2-producing, Rat Knock-in Model of Trem2-R47H Alzheimer\u2019s Risk Variant

The R47H variant of the Triggering-Receptor-Expressed on Myeloid cells 2 (TREM2) increases the risk of Alzheimer’s disease (AD). Mutagenesis of exon 2 in Knock-in (KI) mouse models of the R47H variant introduced a cryptic splice site, leading to nonsense mediated decay. Since haploinsufficiency does not model Trem2-R47H function, a new rat KI model, the Trem2R47H KI rat was created. Human Aβ has higher propensity to form toxic Aβ species, which are considered the main pathogenic entity in AD, as compared to rodent Aβ, the rat Amyloid Precursor Protein (App) gene was mutated to produce human Aβ. Trem2 splicing and expression was measured in Trem2R47H KI rat brains and microglia by qualitative and quantitative RT-PCR. Trem2 levels and Trem2 processing was assessed by Western analysis. APP metabolite levels were determined by enzyme-linked immunosorbent assay (ELISA), for Human Aβ and soluble APP, and Western analysis, for full length APP, βCTF and αCTF. Trem2 expression and Trem2 levels are unchanged in Trem2R47H KI rats. The artifactual splicing seen in KI mouse models is not present; additionally, two novel isoforms of rat Trem2 are described. Trem2R47H rat brains have lower human Aβ38, sAPPα and sAPPβ levels. Thus, Trem2R47H KI rats may prove valuable to define pathogenic mechanisms triggered by the Trem2 R47H variant, including those mediated by toxic species of human Aβ peptides.

Expression of triggering receptor expressed on myeloid cells in periventricular leukomalacia of neonatal rat model

Objective To investigate the expression of triggering receptor expressed on myeloid cells(TREMs)in periventricular leukomalacia(PVL) of the neonatal rat model. Methods Thirty-two 3-day-old neonatal rats were double-blinded randomly divided into Sham group and Model group.The PVL rat model was established by ligating right carotid artery and oxygen deprivation.Hematoxylin-eosin (HE) was adopted to compare pathological changes of brain tissue between the two groups, and immunofluorescence was adopted to detect the expression of myline basic protein (MBP) in the right hemisphere of the two groups.Western blot was performed to detect the expression of TREM1 and TREM2 in the right hemisphere of the two groups. Results The results of HE staining showed that the brain tissues of Model group were significantly damaged compared with that of Sham group, and the mean fluorescence intensity of MBP in Model group(26.629±2.317) was significantly lower than that in Sham group(33.579±2.824), with statistically significant differences(t=9.124, P<0.05). The expression of TREM1 in Model group(0.789 ±0.120) was higher than that in Sham group(0.567±0.093), with statistically significant differences(t=-3.891, P<0.05). The expression of TREM2 in Model group(0.544±0.133) was lower than that in Sham group(0.791±0.118), with statistically significant differences(t=3.667, P<0.05). Conclusion The expressions of TREM1 and TREM2 in the neonatal rat model of PVL change abnormally, suggesting that TREMs may be involved in the pathological process of preterm white matter injury. Key words: Periventricular leukomalacia; White matter injury; Brain injury; Triggering receptor expressed on myeloid cells; Rat

Molecular hydrogen attenuates sepsis-induced neuroinflammation through regulation of microglia polarization through an mTOR-autophagy-dependent pathway

Sepsis-associated encephalopathy (SAE) is the cognitive impairment resulting from sepsis and is associated with increased morbidity and mortality. Hydrogen has emerged as a promising therapeutic agent to alleviate SAE. The mechanism, however, remains unclear. This research aimed to determine whether hydrogen alleviates SAE by regulating microglia polarization and whether it is mediated by the mammalian target of rapamycin (mTOR)-autophagy pathway. Septic models were established by cecal ligation and puncture (CLP) performed on mice. The Morris Water Maze was used to evaluate cognitive function. M1/M2 microglia polarization was assessed by immunofluorescence. Inflammatory cytokines were determined by ELISA. Septic cell models were established using BV-2 cells incubated with 1 μg/ml lipopolysaccharide (LPS). M1/M2 microglia polarization was assessed by flow cytometry. Inflammatory cytokines from culture medium supernatant were determined by ELISA, and associated protein expression levels of mTOR-autophagy pathway were assessed by Western blot. Hydrogen inhalation attenuated sepsis-induced cognitive impairment with improved escape latency, time spent in the target platform quadrant and number of times crossing the target platform. In both animal and cell research, hydrogen reduced TNF-α, IL-6 and HMGB1 levels and M1 polarization, but increased IL-10 and TGF-β levels and M2 polarization. Hydrogen treatment decreased the ratio of p-mTOR/mTOR and the expression of p62 and increased the ratio of p-AMPK/AMPK, LC3II/LC3I and the expression of TREM-2 and Beclin-1 in LPS-treated BV-2 cells. MHY1485, an mTOR activator, abolished the protective effects of hydrogen in vitro. Taken together, these results demonstrated that hydrogen attenuated sepsis-induced neuroinflammation by modulating microglia polarization, which was mediated by the mTOR-autophagy signaling pathway.

Abstract WP312: Rosiglitazone Ameliorates Tissue Plasminogen Activator-Induced Hemorrhagic Transformation After Stroke via Promoting Phagocytic Activity of Microglia

Objective: Delayed thrombolytic treatment with recombinant tissue plasminogen activator (tPA) may lead to lethal hemorrhagic transformation (HT) after ischemic stroke. Rosiglitazone(RSG) is one of the PPAR-γ agonists and has been reported to protect against cerebral ischemia. However, whether RSG can alleviate HT after tPA treatment still remains unknown. In this study, we sort to examine the role of RSG on tPA-induced HT. Methods and results: We used the murine suture middle cerebral artery occlusion (MCAO) models of stroke to investigate the therapeutic potential of RSG against tPA-induced HT. Delayed administration of tPA (10mg/kg, 2 hours after reperfusion) resulted in HT in the ischemic territory 1 day after ischemia. When RSG(6mg/kg) were intraperitoneally administered 1 hour before MCAO , HT was significantly decreased. In addition, we found the BBB disruption and tight junction damage in tPA-treated MCAO mice can be mitigated after RSG treatment. Using flow cytometry and immunostaining, we confirmed that the expression of CD206 was significantly upregulated while the expression of iNOS was down-regulated in microglia of the tPA and RSG treated MCAO mice. Simultaneously, the expression of arg-1, CD36, CD68 and TREM2 were upregulated in tPA and RSG treated stroke mice. To further address our hypothesis that RSG could exert protection against the BBB disruption via phenotypic change into enhanced phagocytosis activity, we intend to use the two-photon live imaging to elucidate that CX3CR1-GFP + microglia could phagocytose more exogenously injected rhodamine-dextran while treated with RSG and tPA compared with those treated with tPA alone. In addition, we plan to inject pH-sensitive beads through the lateral ventricle to demonstrate an increased engulfment of pH-sensitive beads after co-treatment with RSG and tPA. In vitro, phagocytic efficiency in primary microglia and BV2 cells will be verified through adding latex beads after co-administrating RSG and tPA. Conclusions: In conclusion, our data demonstrates that RSG treatment ameliorates HT in delayed tPA-treated stroke mice. Enhanced phagocytic activity of microglia may be responsible for the RSG afforded protection against the BBB disruption in the tPA-induced HT after stroke.

Abstract TP288: Hypoxic Human Umbilical-Derived Mesenchymal Stem Cell (hUC-MSC) Secretome in a Murine Experimental Subarachnoid Hemorrhage (SAH) Model

Background: Recent evidence indicates the critical role of neuroinflammation in the pathogenesis of SAH. Mesenchymal stem cells represent a new frontier in the treatment of numerous diseases and have been shown to have therapeutic effects in neurological disease model such as ischemic stroke. Methods: We employed a murine model of endovascular filament perforation for experimental SAH and tail vein injections were performed for hypoxic hUC-MSC secretome treatment and phosphate buffer treatment (control). The data were expressed as mean+/-SEM and statistical analyses were performed with IBM SPSS 23.0 software. Results: Microglia exhibited suppressed M1 polarization in hypoxic-hUC-MSC-secretome-treated mice at day 3 as compared to phosphate-buffer-treated mice. mRNA expressions of M1-polarization markers (CD16: 0.59+/-0.07; CD32: 0.62+/-0.11, p=0.024; CD68: 0.72+/-0.07. p=0.049) were downregulated and M2-polarization marker TREM2 expression were upregulated (1.57+/-0.13, p=0.013). Confocal microscopy at day 1 showed decreased CD16/32 expression in hypoxic-hUC-MSC-secretome-treated mice as compared to phosphate-buffer-treated mice, and CD206 positive cells were observed in hypoxic-hUC-MSC-secretome-treated mice. mRNA expression of IL-4 was upregulated in hypoxic-hUC-MSC-secretome-treated mice at day 1 as compared to phosphate-buffer-treated mice. Conclusions: Hypoxic hUC-MSC treatment had a positive effect in the modulation of neuroinflammation in a murine experimental SAH model and should be further investigated.

Quercetin Alleviates LPS-Induced Depression-Like Behavior in Rats via Regulating BDNF-Related Imbalance of Copine 6 and TREM1/2 in the Hippocampus and PFC.

Quercetin is a polyphenol with multiple biological activities, and results of our preliminary study showed that it could shorten the immobility time of mice in the forced swimming test and tail suspending test. The aim of this study was to investigate its effects on the behavioral performance of lipopolysaccharide (LPS)-challenged rats and explore the potential mechanism. The results showed that intragastrical administration of quercetin (40 mg/kg) could improve the bodyweight gain of LPS-challenged rats, increase the saccharin preference index in the saccharin preference test and the novel arm preference index in the Y-maze, and decrease the immobility time in the FST. However, it showed no significant effect on the performance of LPS-challenged rats in the Morris water maze and the plasma concentrations of nesfatin-1, C-reactive protein (CRP), and IL-6. Results of western blot showed that the expression levels of BDNF, Copine 6, p-TrkB, and the triggering receptors expressed on myeloid cells (TREM) 1 were decreased in both the hippocampus and the prefrontal cortex (PFC) of LPS-challenged rats, while the expression of TREM2 was increased. The protein expression of synapsin-1 was decreased in the hippocampus without significant changes in the PFC. These imbalance protein expressions could be balanced by treatment with quercetin. The results suggested that quercetin could alleviate LPS-induced depression-like behaviors and impairment of learning and memory in rats, the mechanism of which might be involved with regulating the BDNF-related imbalance expression of Copine 6 and TREM1/2 in the hippocampus and the PFC.

TREM-2-p38 MAPK signaling regulates neuroinflammation during chronic cerebral hypoperfusion combined with diabetes mellitus

BackgroundDiabetes mellitus (DM) and chronic cerebral hypoperfusion(CCH)are both risk factors for cognitive impairment. However, whether DM and CCH can synergistically promote cognitive impairment and the related pathological mechanisms remain unknown.MethodsTo investigate the effect of DM and CCH on cognitive function, rats fed with high-fat diet (HFD) and injected with low-dose streptozotocin (STZ) followed by bilateral common carotid artery occlusion (BCCAO) were induced to mimic DM and CCH in vivo and mouse BV2 microglial cells were exposed to hypoxia and/or high glucose to mimic CCH complicated with DM pathologies in vitro. To further explore the underlying mechanism, TREM-2-specific small interfering RNA and TREM-2 overexpression lentivirus were used to knock out and overexpress TREM-2, respectively.ResultsCognitive deficits, neuronal cell death, neuroinflammation with microglial activation, and TREM-2-MAPK signaling were enhanced when DM was superimposed on CCH both in vivo and in vitro. Manipulating TREM-2 expression levels markedly regulated the p38 MAPK signaling and the inflammatory response in vitro. TREM-2 knockout intensified while TREM-2 overexpression suppressed the p38 MAPK signaling and subsequent pro-inflammatory mediator production under high glucose and hypoxia condition.ConclusionsThese results suggest that TREM-2 negatively regulates p38 MAPK-mediated inflammatory response when DM was synergistically superimposed on CCH and highlight the importance of TREM-2 as a potential target of immune regulation in DM and CCH.

Niche-Specific Re-Programming of Epigenetic Landscapes Drives Myeloid Cell Diversity in NASH

Tissue resident macrophages and recruited monocyte-derived macrophages contribute to host defense but also play pathological roles in a diverse range of human diseases. Multiple macrophage phenotypes are often represented in a diseased tissue, but we lack a deep understanding of the mechanisms that control diversification. Here we use a combination of genetic, genomic, and imaging approaches to investigate the origins and epigenetic trajectories of hepatic myeloid cells during diet-induced non-alcoholic steatohepatitis (NASH). The NASH diet induces striking changes in Kupffer cell enhancers and gene expression, resulting in partial loss of Kupffer cell identity, induction of Trem2 and Cd9 expression, and cell death. Kupffer cell loss is compensated by gain of adjacent monocyte derived macrophages that exhibit convergent epigenomes, transcriptomes and functions. NASH-induced changes in Kupffer cell enhancers are driven by AP-1 and Egr factors that reprogram the Kupffer cell specific functions of Liver X receptors. These findings reveal mechanisms by which disease-associated environmental signals instruct resident and recruited macrophages to acquire distinct programs of gene expression and corresponding phenotypes.

Effects and mechanism of TREM-1 on inflammatory response and lipid metabolism in mice with nonalcoholic fatty liver disease

Objective Analysis of the effect of triggering receptor-1 expressed on myeloid cells (TREM-1) in nonalcoholic fatty liver disease (NAFLD) and the mechanism. Methods The oleic acid-treated HepG2 cells were divided into model group, overexpression group, interference group A, interference group B and negative control group. The mouse model of NAFLD was generated and randomly divided into (nuclear factor-κB) NF-κB inhibition group, protein kinase B (AKT) inhibition group, knockout group A, knockout group B and control group. The expression of inflammatory factors and TREM-1 in liver tissue was detected by PCR, and fat accumulation was detected by oil red O staining. Western blotting was used to detect the expression of TREM-1 and signaling pathway proteins, and HE staining was used to detect liver tissue changes. Results TREM-1 was up-regulated in liver tissue of NAFLD mice [(0.936±0.127) vs. (0.432±0.105)] and in oleic acid-treated HepG2 cells. In oleic acid-treated HepG2 cells, overexpression of TREM-1 increased inflammatory factor expression and increased lipid droplets; inhibition of TREM-1 expression decreased inflammatory factor expression, and lipid droplets decreased. Knockout of TREM-1 and inhibition of NF-κB in NAFLD mice reduced hepatocyte inflammatory factor expression and reduced liver damage; knockout of TREM-1 and inhibition of AKT reduced liver tissue lipids and drops accumulate. Conclusions The overexpression of TREM-1 in NAFLD mice liver tissue can regulate inflammatory factor expression and lipid droplets through NF-κB and AKT signal pathway. TREM-1 might be a potential therapeutic target of NAFLD. Key words: Inflammation; Nonalcoholic fatty liver disease; Triggering receptor-1 expressed on myeloid cells; Lipid accumulation

Transcriptome landscape of myeloid cells in human skin reveals diversity, rare populations and putative DC progenitors

BackgroundThe heterogeneous functions of dermal myeloid cells in antigen presentation, and scavenging pathogens and cell debris places them centrally in cutaneous inflammation. Single cell transcriptomics can provide new understanding of the heterogeneity and function of yet incompletely understood human dermal myeloid cell subsets. ObjectiveInvestigate the transcriptome landscape of myeloid cells in healthy human skin. MethodsSingle cell RNA-sequencing was performed on skin biopsies from ten healthy donors and analyzed to identify myeloid cell populations. ResultsOne LIN− HLA-DR+ cluster with expression of myeloid-specific genes was identified as a cluster of myeloid cells. Upon reanalysis of this cluster, we identified three macrophage subsets, marked by high expression of CCR1, MARCO or TREM2; and six dendritic cell subsets, marked by high expression of CLEC9A, CXorf21, MCOLN2, LAMP3, KIAA0101 and Langerin, representing respectively cDC1, two subsets of cDC2, a novel DC type, a cluster of proliferating DC, and a Langerhans cell subset. GO term analysis indicated specialized functions for the discrete rare populations of myeloid cells: TREM2 Mφ in lipid metabolism and LAMP3 DC as a mature cDC. Proliferating DCs appeared to represent cDC2 progenitors. ConclusionThe transcriptional landscape of myeloid cell populations in human skin indicates several, novel populations with specialized functions, as well as a rare proliferating DC population that likely accounts for local regeneration or expansion of dermal DCs. We provide robust gene expression markers for each of these populations that should permit better understandings of their roles in various homeostatic and pathologic immune processes in the skin.

Stavudine Reduces NLRP3 Inflammasome Activation and Modulates Amyloid-β Autophagy.

Alzheimer's disease (AD) is associated with the accumulation of amyloid-β (Aβ) within senile plaques in the brain and neuroinflammation, possibly driven by the activation of the NLRP3 inflammasome. Nucleoside reverse transcriptase inhibitors (NRTI) hamper the NLRP3 inflammasome assembly. We utilized an in vitro model reproducing the Aβ-driven inflammation seen in AD to analyze whether stavudine (D4T), a prototypical NRTI, modulates Aβ-mediated inflammasome activation and the ability of macrophages to eliminate Aβ via phagocytosis and autophagy. THP-1-derived macrophages were stimulated in vitro with Aβ42 or with Aβ42 after LPS-priming in the presence/absence of D4T. NLRP3 and TREM2 expression was analyzed by RT-PCR; phagocytosis, as well as ASC-Speck formation, was analyzed by Amnis FlowSight Imaging; NLRP3-produced cytokines were quantified by ELISA and, finally, autophagy was analyzed by measuring p-ERK1/2, p-AKT, beclin, p70-S6Kinase, and Lamp by ELISA and western blot. IL-1β, IL-18, and caspase-1 were increased whereas Aβ phagocytosis and TREM2 were reduced in LPS+Aβ42-stimulated cells. D4T reduced NLRP3 assembly as well as IL-18 and caspase-1 production, but did not affect IL-1β production and TREM2 expression. Notably, whereas D4T reduced Aβ phagocytosis, Aβ autophagy by macrophages was stimulated by D4T, as witnessed by the down-modulation of ERK1/2 and AKT phosphorylation and the upregulation of beclin, LAMP, and p70-S6K, their downstream targets. In this in vitro model of AD, D4T reduces NLRP3 inflammasome-associated inflammation and stimulates Aβ autophagy by macrophages. It will be interesting to verify the possibly beneficial effects of D4T in the clinical scenario.

Stroke and Amyloid-β Downregulate TREM-2 and Uch-L1 Expression that Synergistically Promote the Inflammatory Response.

Neuroinflammation is involved in the pathogenesis of Alzheimer's disease, and the transcription factor NF-κB is a player in this event. We found here that the ischemic damage alone or in association with Aβ1-42 activates the NF-κB pathway, induces an increase of BACE1 and a parallel inhibition of Uch-L1 and TREM2, both in vitro and in vivo, in Tg 5XFAD and in human brains of sporadic AD. This mechanism creates a synergistic loop that fosters inflammation. We also demonstrated a significant protection exerted by the restoration of Uch-L1 activity. The rescue of the enzyme is able to abolish the decrease of TREM2 and the parameters of neuroinflammation.

Macrophage phenotype and its relationship with renal function in human diabetic nephropathy

This study aimed to examine the macrophage phenotype and its relationship to renal function and histological changes in human DN and the effect of TREM-1 on high-glucose-induced macrophage activation. We observed that in renal tissue biopsies, the expression of CD68 and M1 was apparent in the glomeruli and interstitium, while accumulation of M2 and TREM-1 was primarily observed in the interstitium. The numbers of CD68, M1, and M2 macrophages infiltrating in the DN group were increased in a process-dependent manner compared with the control group, and the intensities of the infiltrates were proportional to the rate of subsequent decline in renal function. M1 macrophages were recruited into the kidney at an early stage (I+IIa) of DN. The M1-to-M2 macrophage ratio peaked at this time, whereas M2 macrophages predominated at later time points (III) when the percentage of M1/M2 macrophages was at its lowest level. In an in vitro study, we showed that under high glucose conditions, macrophages began to up-regulate their expression of TREM-1, M1, and marker iNOS and decreased the M2 marker MR. However, the above effects of high-glucose were abolished when TREM-1 expression was inhibited by TREM-1 siRNA. In conclusion, our study demonstrated that there was a positive correlation between the M1/M2 activation state and the progress of DN, and TREM-1 played an important role in high-glucose-induced macrophage phenotype transformation.

Functionalization of Brain Region-specific Spheroids with Isogenic Microglia-like Cells

Current brain spheroids or organoids derived from human induced pluripotent stem cells (hiPSCs) still lack a microglia component, the resident immune cells in the brain. The objective of this study is to engineer brain region-specific organoids from hiPSCs incorporated with isogenic microglia-like cells in order to enhance immune function. In this study, microglia-like cells were derived from hiPSCs using a simplified protocol with stage-wise growth factor induction, which expressed several phenotypic markers, including CD11b, IBA-1, CX3CR1, and P2RY12, and phagocytosed micron-size super-paramagnetic iron oxides. The derived cells were able to upregulate pro-inflammatory gene (TNF-α) and secrete anti-inflammatory cytokines (i.e., VEGF, TGF-β1, and PGE2) when stimulated with amyloid β42 oligomers, lipopolysaccharides, or dexamethasone. The derived isogenic dorsal cortical (higher expression of TBR1 and PAX6) and ventral (higher expression of NKX2.1 and PROX1) spheroids/organoids displayed action potentials and synaptic activities. Co-culturing the microglia-like cells (MG) with the dorsal (D) or ventral (V) organoids showed differential migration ability, intracellular Ca2+ signaling, and the response to pro-inflammatory stimuli (V-MG group had higher TNF-α and TREM2 expression). Transcriptome analysis exhibited 37 microglia-related genes that were differentially expressed in MG and D-MG groups. In addition, the hybrid D-MG spheroids exhibited higher levels of immunoreceptor genes in activating members, but the MG group contained higher levels for most of genes in inhibitory members (except SIGLEC5 and CD200). This study should advance our understanding of the microglia function in brain-like tissue and establish a transformative approach to modulate cellular microenvironment toward the goal of treating various neurological disorders.

Microglial TREM-1 receptor mediates neuroinflammatory injury via interaction with SYK in experimental ischemic stroke

Neuroinflammation is initiated in response to ischemic stroke, generally with the hallmarks of microglial activation and collateral brain injury contributed by robust inflammatory effects. Triggering receptor expressed on myeloid cells (TREM)-1, an amplifier of the innate immune response, is a critical regulator of inflammation. This study identified that microglial TREM-1 expression was upregulated following cerebral ischemic injury. After pharmacologic inhibition of TREM-1 with synthetic peptide LP17, ischemia-induced infarction and neuronal injury were substantially alleviated. Moreover, blockade of TREM-1 can potentiate cellular proliferation and synaptic plasticity in hippocampus, resulting in long-term functional improvement. Microglial M1 polarization and neutrophil recruitment were remarkably abrogated as mRNA levels of M1 markers, chemokines, and protein levels of myeloperoxidase and intracellular adhesion molecule-1 (ICAM-1) were decreased by LP17. Mechanistically, both in vivo and in vitro, we delineated that TREM-1 can activate downstream pro-inflammatory pathways, CARD9/NF-κB, and NLRP3/caspase-1, through interacting with spleen tyrosine kinase (SYK). In addition, TREM-1-induced SYK initiation was responsible for microglial pyroptosis by elevating levels of gasdermin D (GSDMD), N-terminal fragment of GSDMD (GSDMD-N), and forming GSDMD pores, which can facilitate the release of intracellular inflammatory factors, in microglia. In summary, microglial TREM-1 receptor yielded post-stroke neuroinflammatory damage via associating with SYK.

Amplifying stroke damage.

In a mouse model of stroke, induction of TREM1 expression on peripheral myeloid cells magnifies inflammatory responses and neurological dysfunction.