bims-microg 2024-08-11 papers

bims-microg

Biomed News

on Microglia in Health and Disease

Issue of 2024‒08‒11
ten papers selected by
Marcus Karlstetter, Universität zu Köln

Enhanced phagocytosis associated with multinucleated microglia via Pyk2 inhibition in an acute β-amyloid infusion model.
PPARγ activation ameliorates cognitive impairment and chronic microglial activation in the aftermath of r-mTBI.
Transplantation of miR-145a-5p modified M2 type microglia promotes the tissue repair of spinal cord injury in mice.
Microglia through MFG-E8 signaling decrease the density of degenerating neurons and protect the brain from the development of cortical infarction after stroke.
A dual target molecular magnetic resonance imaging probe for noninvasive profiling of pathologic alpha-synuclein and microgliosis in a mouse model of Parkinson's disease.
Microglia in the hypothalamic paraventricular nucleus sense hemodynamic disturbance and promote sympathetic excitation in hypertension.
Interleukin-35 alleviates neuropathic pain and induces an anti-inflammatory shift in spinal microglia in nerve-injured male mice.
A programmable microfluidic platform to monitor calcium dynamics in microglia during inflammation.
Role of Microglial Mitophagy in Alleviating Postoperative Cognitive Dysfunction: a Mechanistic Study.
Gamma-type immunoglobulin enhances phagocytosis of amyloid-beta fibrils by microglia.

J Neuroinflammation. 2024 Aug 06. 21(1): 196

Enhanced phagocytosis associated with multinucleated microglia via Pyk2 inhibition in an acute β-amyloid infusion model.

Ji-Won Lee, Kaito Mizuno, Haruhisa Watanabe, In-Hee Lee, Takuya Tsumita, Kyoko Hida, Yasutaka Yawaka, Yoshimasa Kitagawa, Akira Hasebe, Tadahiro Iimura, Sek Won Kong.

  Multinucleated microglia have been observed in contexts associated with infection, inflammation, and aging. Though commonly linked to pathological conditions, the larger cell size of multinucleated microglia might enhance their phagocytic functions, potentially aiding in the clearance of brain debris and suggesting a reassessment of their pathological significance. To assess the phagocytic capacity of multinucleated microglia and its implications for brain debris clearance, we induced their formation by inhibiting Pyk2 activity using the pharmacological inhibitor PF-431396, which triggers cytokinesis regression. Multinucleated microglia demonstrate enhanced phagocytic function, as evidenced by their increased capacity to engulf β-amyloid (Aβ) oligomers. Concurrently, the phosphorylation of Pyk2, induced by Aβ peptide, was diminished upon treatment with a Pyk2 inhibitor (Pyk2-Inh, PF-431396). Furthermore, the increased expression of Lamp1, a lysosomal marker, with Pyk2-inh treatment, suggests an enhancement in proteolytic activity. In vivo, we generated an acute Alzheimer's disease (AD) model by infusing Aβ into the brains of Iba-1 EGFP transgenic (Tg) mice. The administration of the Pyk2-Inh led to an increased migration of microglia toward amyloid deposits in the brains of Iba-1 EGFP Tg mice, accompanied by morphological activation, suggesting a heightened affinity for Aβ. In human microglia, lipopolysaccharide (LPS)-induced inflammatory responses showed that inhibition of Pyk2 signaling significantly reduced the transcription and protein expression of pro-inflammatory markers. These results suggest that Pyk2 inhibition can modulate microglial functions, potentially reducing neuroinflammation and aiding in the clearance of neurodegenerative disease markers. This highlights Pyk2 as a promising target for therapeutic intervention in neurodegenerative diseases.

Keywords:  Alzheimer’s disease; Microglia; Multinucleation; Phagocytosis; Protein Tyrosine Kinase 2B; β-amyloid

DOI:  https://doi.org/10.1186/s12974-024-03192-7
J Neuroinflammation. 2024 Aug 03. 21(1): 194

PPARγ activation ameliorates cognitive impairment and chronic microglial activation in the aftermath of r-mTBI.

Andrew Pearson, Milica Koprivica, Max Eisenbaum, Camila Ortiz, Mackenzie Browning, Tessa Vincennie, Cooper Tinsley, Michael Mullan, Fiona Crawford, Joseph Ojo.

Chronic neuroinflammation and microglial activation are key mediators of the secondary injury cascades and cognitive impairment that follow exposure to repetitive mild traumatic brain injury (r-mTBI). Peroxisome proliferator-activated receptor-γ (PPARγ) is expressed on microglia and brain resident myeloid cell types and their signaling plays a major anti-inflammatory role in modulating microglial responses. At chronic timepoints following injury, constitutive PPARγ signaling is thought to be dysregulated, thus releasing the inhibitory brakes on chronically activated microglia. Increasing evidence suggests that thiazolidinediones (TZDs), a class of compounds approved from the treatment of diabetes mellitus, effectively reduce neuroinflammation and chronic microglial activation by activating the peroxisome proliferator-activated receptor-γ (PPARγ). The present study used a closed-head r-mTBI model to investigate the influence of the TZD Pioglitazone on cognitive function and neuroinflammation in the aftermath of r-mTBI exposure. We revealed that Pioglitazone treatment attenuated spatial learning and memory impairments at 6 months post-injury and reduced the expression of reactive microglia and astrocyte markers in the cortex, hippocampus, and corpus callosum. We then examined whether Pioglitazone treatment altered inflammatory signaling mechanisms in isolated microglia and confirmed downregulation of proinflammatory transcription factors and cytokine levels. To further investigate microglial-specific mechanisms underlying PPARγ-mediated neuroprotection, we generated a novel tamoxifen-inducible microglial-specific PPARγ overexpression mouse line and examined its influence on microglial phenotype following injury. Using RNA sequencing, we revealed that PPARγ overexpression ameliorates microglial activation, promotes the activation of pathways associated with wound healing and tissue repair (such as: IL10, IL4 and NGF pathways), and inhibits the adoption of a disease-associated microglia-like (DAM-like) phenotype. This study provides insight into the role of PPARγ as a critical regulator of the neuroinflammatory cascade that follows r-mTBI in mice and demonstrates that the use of PPARγ agonists such as Pioglitazone and newer generation TZDs hold strong therapeutic potential to prevent the chronic neurodegenerative sequelae of r-mTBI.

DOI: https://doi.org/10.1186/s12974-024-03173-w
J Transl Med. 2024 Aug 05. 22(1): 724

Transplantation of miR-145a-5p modified M2 type microglia promotes the tissue repair of spinal cord injury in mice.

Penghui Li, Junlong Zhao, Yangguang Ma, Liang Wang, Shiqian Liang, Fan Fan, Tiaoxia Wei, Lei Feng, Xueyu Hu, Yiyang Hu, Zhe Wang, Hongyan Qin.

  BACKGROUND: The traumatic spinal cord injury (SCI) can cause immediate multi-faceted function loss or paralysis. Microglia, as one of tissue resident macrophages, has been reported to play a critical role in regulating inflammation response during SCI processes. And transplantation with M2 microglia into SCI mice promotes recovery of motor function. However, the M2 microglia can be easily re-educated and changed their phenotype due to the stimuli of tissue microenvironment. This study aimed to find a way to maintain the function of M2 microglia, which could exert an anti-inflammatory and pro-repair role, and further promote the repair of spinal cord injury.METHODS: To establish a standard murine spinal cord clip compression model using Dumont tying forceps. Using FACS, to sort microglia from C57BL/6 mice or CX3CR1GFP mice, and further culture them in vitro with different macrophage polarized medium. Also, to isolate primary microglia using density gradient centrifugation with the neonatal mice. To transfect miR-145a-5p into M2 microglia by Lipofectamine2000, and inject miR-145a-5p modified M2 microglia into the lesion sites of spinal cord for cell transplanted therapy. To evaluate the recovery of motor function in SCI mice through behavior analysis, immunofluorescence or histochemistry staining, Western blot and qRT-PCR detection. Application of reporter assay and molecular biology experiments to reveal the mechanism of miR-145a-5p modified M2 microglia therapy on SCI mice.
RESULTS: With in vitro experiments, we found that miR-145a-5p was highly expressed in M2 microglia, and miR-145a-5p overexpression could suppress M1 while promote M2 microglia polarization. And then delivery of miR-145a-5p overexpressed M2 microglia into the injured spinal cord area significantly accelerated locomotive recovery as well as prevented glia scar formation and neuron damage in mice, which was even better than M2 microglia transplantation. Further mechanisms showed that overexpressed miR-145a-5p in microglia inhibited the inflammatory response and maintained M2 macrophage phenotype by targeting TLR4/NF-κB signaling.
CONCLUSIONS: These findings indicate that transplantation of miR-145a-5p modified M2 microglia has more therapeutic potential for SCI than M2 microglia transplantation from epigenetic perspective.

Keywords:  M2 microglia; Neuroinflammation; Spinal cord injury; miR-145a-5p

DOI:  https://doi.org/10.1186/s12967-024-05492-1
PLoS One. 2024 ;19(8): e0308464

Microglia through MFG-E8 signaling decrease the density of degenerating neurons and protect the brain from the development of cortical infarction after stroke.

Eric Yuhsiang Wang, Hank Szuhan Chen, Meng-Chih Wu, Ya Lan Yang, Hwai-Lee Wang, Che-Wei Liu, Ted Weita Lai.

Neuronal loss is a hallmark of stroke and other neurodegenerative diseases, and as such, neuronal loss caused by microglia has been thought to be a contributing factor to disease progression. Here, we show that microglia indeed contribute significantly to neuronal loss in a mouse model of stroke, but this microglial-dependent process of neuronal clearance specifically targets stressed and degenerating neurons in the ischemic cortical region and not healthy non-ischemic neurons. Nonspecific stimulation of microglia decreased the density of neurons in the ischemic cortical region, whereas specific inhibition of MFG-E8 signaling, which is required for microglial phagocytosis of neurons, had the opposite effect. In both scenarios, the effects were microglia specific, as the same treatments had no effect in mice whose microglia were depleted prior to stroke. Finally, even though the inhibition of MFG-E8 signaling increased neuronal density in the ischemic brain region, it substantially exacerbated the development of cortical infarction. In conclusion, microglia through MFG-E8 signaling contribute to the loss of ischemic neurons and, in doing so, minimize the development of cortical infarction after stroke.

DOI: https://doi.org/10.1371/journal.pone.0308464
Front Neurosci. 2024 ;18 1428736

A dual target molecular magnetic resonance imaging probe for noninvasive profiling of pathologic alpha-synuclein and microgliosis in a mouse model of Parkinson's disease.

Xianwei Sun, Andrew Badachhape, Prajwal Bhandari, Jeannie Chin, Ananth Annapragada, Eric Tanifum.

  The pathogenesis of Parkinson's disease (PD) is characterized by progressive deposition of alpha-synuclein (α-syn) aggregates in dopaminergic neurons and neuroinflammation. Noninvasive in vivo imaging of α-syn aggregate accumulation and neuroinflammation can elicit the underlying mechanisms involved in disease progression and facilitate the development of effective treatment as well as disease diagnosis and prognosis. Here we present a novel approach to simultaneously profile α-syn aggregation and reactive microgliosis in vivo, by targeting oligomeric α-syn in cerebrospinal fluid with nanoparticle bearing a magnetic resonance imaging (MRI), contrast payload. In this proof-of-concept report we demonstrate, in vitro, that microglia and neuroblastoma cell lines internalize agglomerates formed by cross-linking the nanoparticles with oligomeric α-syn. Delayed in vivo MRI scans following intravenous administration of the nanoparticles in the M83 α-syn transgenic mouse line show statistically significant MR signal enhancement in test mice versus controls. The in vivo data were validated by ex-vivo immunohistochemical analysis which show strong correlation between in vivo MRI signal enhancement, Lewy pathology distribution, and microglia activity in the treated brain tissue. Furthermore, neuronal and microglial cells in brain tissue from treated mice display strong cytosolic signal originating from the nanoparticles, attributed to in vivo cell uptake of nanoparticle/oligomeric α-syn agglomerates.

Keywords:  MRI of alpha-synuclein; MRI of neuroinflammation; accelerated alpha-synuclein clearance; imaging of alpha-synuclein; molecular MRI of microgliosis

DOI:  https://doi.org/10.3389/fnins.2024.1428736
Immunity. 2024 Jul 31. pii: S1074-7613(24)00360-1. [Epub ahead of print]

Microglia in the hypothalamic paraventricular nucleus sense hemodynamic disturbance and promote sympathetic excitation in hypertension.

Bo Wei, Guo Cheng, Qianqian Bi, Cheng Lu, Qihang Sun, Li Li, Ningting Chen, Miner Hu, Haoran Lu, Xuancheng Xu, Genxiang Mao, Shu Wan, Zhechun Hu, Yan Gu, Jiaxin Zheng, Li Zhao, Xiao Z Shen, Xiaoli Liu, Peng Shi.

  Hypertension is usually accompanied by elevated sympathetic tonicity, but how sympathetic hyperactivity is triggered is not clear. Recent advances revealed that microglia-centered neuroinflammation contributes to sympathetic excitation in hypertension. In this study, we performed a temporospatial analysis of microglia at both morphological and transcriptomic levels and found that microglia in the hypothalamic paraventricular nucleus (PVN), a sympathetic center, were early responders to hypertensive challenges. Vasculature analyses revealed that the PVN was characterized by high capillary density, thin vessel diameter, and complex vascular topology relative to other brain regions. As such, the PVN was susceptible to the penetration of ATP released from the vasculature in response to hemodynamic disturbance after blood pressure increase. Mechanistically, ATP ligation to microglial P2Y12 receptor was responsible for microglial inflammatory activation and the eventual sympathetic overflow. Together, these findings identified a distinct vasculature pattern rendering vulnerability of PVN pre-sympathetic neurons to hypertension-associated microglia-mediated inflammatory insults.

Keywords:  ATP; P2Y(12); cerebral blood perfusion; hypertension; hypothalamic paraventricular nucleus; microglia; neuroinflammation; sympathetic nerve activity

DOI:  https://doi.org/10.1016/j.immuni.2024.07.011
Brain Behav Immun. 2024 Aug 01. pii: S0889-1591(24)00517-8. [Epub ahead of print]

Interleukin-35 alleviates neuropathic pain and induces an anti-inflammatory shift in spinal microglia in nerve-injured male mice.

Nathan T Fiore, Jessica P Hayes, Sarah I Williams, Gila Moalem-Taylor.

  Immune cells are critical in promoting neuroinflammation and neuropathic pain and in facilitating pain resolution, depending on their inflammatory and immunoregulatory cytokine response. Interleukin (IL)-35, secreted by regulatory immune cells, is a member of the IL-12 family with a potent immunosuppressive function. In this study, we investigated the effects of IL-35 on pain behaviors, spinal microglia phenotype following peripheral nerve injury, and in vitro microglial cultures in male and female mice. Intrathecal recombinant IL-35 treatment alleviated mechanical pain hypersensitivity prominently in male mice, with only a modest effect in female mice after sciatic nerve chronic constriction injury (CCI). IL-35 treatment resulted in sex-specific microglial changes following CCI, reducing inflammatory microglial markers and upregulating anti-inflammatory markers in male mice. Spatial transcriptomics analysis revealed that IL-35 suppressed microglial complement activation in the superficial dorsal horn in male mice after CCI. Moreover, in vitro studies showed that IL-35 treatment of cultured inflammatory microglia mitigated their hypertrophied morphology, increased their cell motility, and decreased their phagocytic activity, indicating a phenotypic shift towards homeostatic microglia. Further, IL-35 altered microglial cytokines/chemokines in vitro, suppressing the release of IL-9 and monocyte-chemoattractant protein-1 and increasing IL-10 in the supernatant of male microglial cultures. Our findings indicate that treatment with IL-35 modulates spinal microglia and alleviates neuropathic pain in male mice, suggesting IL-35 as a potential sex-specific targeted immunomodulatory treatment for neuropathic pain.

Keywords:  Interleukin-35; Microglia; Neuroimmune; Neuropathic pain; Peripheral nerve injury; Sex differences

DOI:  https://doi.org/10.1016/j.bbi.2024.07.043
Microsyst Nanoeng. 2024 ;10 106

A programmable microfluidic platform to monitor calcium dynamics in microglia during inflammation.

Adam Shebindu, Durga Kaveti, Linda Umutoni, Gia Kirk, Michael D Burton, Caroline N Jones.

  Neuroinflammation is characterized by the elevation of cytokines and adenosine triphosphate (ATP), which in turn activates microglia. These immunoregulatory molecules typically form gradients in vivo, which significantly influence microglial behaviors such as increasing calcium signaling, migration, phagocytosis, and cytokine secretion. Quantifying microglial calcium signaling in the context of inflammation holds the potential for developing precise therapeutic strategies for neurological diseases. However, the current calcium imaging systems are technically challenging to operate, necessitate large volumes of expensive reagents and cells, and model immunoregulatory molecules as uniform concentrations, failing to accurately replicate the in vivo microenvironment. In this study, we introduce a novel calcium monitoring micro-total analysis system (CAM-μTAS) designed to quantify calcium dynamics in microglia (BV2 cells) within defined cytokine gradients. Leveraging programmable pneumatically actuated lifting gate microvalve arrays and a Quake valve, CAM-μTAS delivers cytokine gradients to microglia, mimicking neuroinflammation. Our device automates sample handling and cell culture, enabling rapid media changes in just 1.5 s, thus streamlining the experimental workflow. By analyzing BV2 calcium transient latency to peak, we demonstrate location-dependent microglial activation patterns based on cytokine and ATP gradients, offering insights contrasting those of non-gradient-based perfusion systems. By harnessing advancements in microsystem technology to quantify calcium dynamics, we can construct simplified human models of neurological disorders, unravel the intricate mechanisms of cell-cell signaling, and conduct robust evaluations of novel therapeutics.

Keywords:  Engineering; Nanoscience and technology

DOI:  https://doi.org/10.1038/s41378-024-00733-1
Mol Neurobiol. 2024 Aug 07.

Role of Microglial Mitophagy in Alleviating Postoperative Cognitive Dysfunction: a Mechanistic Study.

Lina Zhang, Jiaying Li, Chenglong Li, Yujin Wu, Shuai Liu, Qi Li, Sihua Qi.

  Postoperative cognitive dysfunction (POCD), a common complication following anesthesia and surgery, is influenced by hippocampal neuroinflammation and microglial activation. Mitophagy, a process regulating inflammatory responses by limiting the accumulation of damaged mitochondria, plays a significant role. This study aimed to determine whether regulating microglial mitophagy and the cGAS-STING pathway could alleviate cognitive decline after surgery. Exploratory laparotomy was performed to establish a POCD model using mice. Western blotting, immunofluorescence staining, transmission electron microscopy, and mt-Keima assays were used to examine microglial mitophagy and the cGAS-STING pathway. Quantitative polymerase chain reaction (qPCR) was used to detect inflammatory mediators and cytosolic mitochondrial DNA (mtDNA) levels in BV2 cells. Exploratory laparotomy triggered mitophagy and enhanced the cGAS-STING pathway in mice hippocampi. Pharmacological treatment reduced microglial activation, neuroinflammation, and cognitive impairment after surgery. Mitophagy suppressed the cGAS-STING pathway in mice hippocampi. In vitro, microglia-induced inflammation was mediated by mitophagy and the cGAS-STING pathway. Small interfering RNA (siRNA) of PINK1 hindered mitophagy activation and facilitated the cytosolic release of mtDNA, resulting in the initiation of the cGAS-STING pathway and innate immune response. Microglial mitophagy inhibited inflammatory responses via the mtDNA-cGAS-STING pathway inducing microglial mitophagy and inhibiting the mtDNA-cGAS-STING pathway may be an effective therapeutic approach for patients with POCD.

Keywords:  Microglia; Mitophagy; PINK1-Parkin pathway; Postoperative cognitive dysfunction; cGAS-STING pathway

DOI:  https://doi.org/10.1007/s12035-024-04405-z
Neural Regen Res. 2024 Jul 29.

Gamma-type immunoglobulin enhances phagocytosis of amyloid-beta fibrils by microglia.

Tian Zhou, Yue Zhong, Shoujun Yu, Ruibing Sun, Zhenwei Zhang, Xiaoyan Du, Simon Ming-Yuen Lee, Zhitong Chen, Weiming Tian, Yuxiao Lai, Bing Song, Yiming Zheng, Zhen Xu.

The peripheral immune system has emerged as a regulator of neurodegenerative diseases such as Alzheimer's disease. Microglia are resident immune cells in the brain that may orchestrate communication between the central nervous system and peripheral immune system, though the mechanisms are unclear. Here, we found that gamma-type immunoglobulin, a product originating from peripheral blood B cells, localized in the brain parenchyma of multiple mouse models with amyloid pathology, and was enriched on microglia but not on other brain cell types. Further experiments showed that gamma-type immunoglobulin bound to microglial cell membranes and led to diverse transcriptomic changes, including upregulation of pathways related to phagocytosis and immunity. Functional assays demonstrated that gamma-type immunoglobulin enhanced microglial phagocytic capacity for amyloid-beta fibrils via its Fc, but not Fab, fragment. Our data indicate that microglia, when exposed to gamma-type immunoglobulin, exhibit an enhanced capacity for clearing amyloid-beta fibrils, potentially via the gamma-type immunoglobulin Fc fragment signaling pathway. This suggests that parenchymal gamma-type immunoglobulin should be further investigated to determine whether it may play a beneficial role against Alzheimer's disease by enhancing microglial function.

DOI: https://doi.org/10.4103/NRR.NRR-D-23-01942