Microglia differentiation using a culture system for the expansion of mice non-adherent bone marrow stem cells

Dietary Intake of Yeast-Derived β-Glucan and Rice-Derived Arabinoxylan Induces Dose-Dependent Innate Immune Priming in Mice

Beta-glucans and arabinoxylans are known for their immunostimulatory properties. However, in vivo these have been documented almost exclusively following parenteral administration, underemphasizing oral intake. C57BL/6 mice are fed either a control diet or a diet supplemented with yeast-derived whole β-glucan particle (yWGP) or with rice-derived arabinoxylan (rice bran-1) at a concentration of 1%, 2.5%, or 5% weight/weight (w/w) for 2 weeks. Thereafter, cells from blood, bone marrow, and spleen are collected for ex vivo stimulation with various microbial stimuli. Dietary intake of yWGP for 2 weeks at concentrations of 1% and 2.5% w/w increases ex vivo cytokine production in mouse blood and bone marrow, whereas 5% w/w yWGP shows no effect. In the spleen, cytokine production remains unaffected by yWGP. At a concentration of 1% w/w, rice bran-1 increases ex vivo cytokine production by whole blood, but 2.5% and 5% w/w cause inhibitory effects in bone marrow and spleen. This study demonstrates that dietary yWGP and rice bran-1 induce immune priming in mouse blood and bone marrow, with the strongest effects observed at 1% w/w. Future human trials should substantiate the efficacy of dietary β-glucans and arabinoxylans to bolster host immunity, focusing on dose optimization.

A Core Transcription Regulatory Circuitry Defining Microglia Cell Identity Inferred from the Reanalysis of Multiple Human Microglia Differentiation Protocols

Microglia, the immune cells in the brain involved in both homeostasis and injury/infection control, play a predominant role in neurodegenerative diseases. In vivo studies on microglia are limited due to the requirement of surgical intervention, which can lead to the destruction of the tissues. Over the last few years, multiple protocols-presenting a variety of strategies-have described microglia differentiation issued from human pluripotent stem cells. Herein, we have reanalyzed the transcriptomes released on six different microglia differentiation protocols and revealed a consensus core of master transcription regulatory circuitry defining microglia identity. Furthermore, we have discussed the major divergencies among the studied protocols and have provided suggestions to further enhance microglia differentiation assays.

CD34 Identifies a Subset of Proliferating Microglial Cells Associated with Degenerating Motor Neurons in ALS

Amyotrophic lateral sclerosis (ALS) is characterized by degeneration of upper and lower motor neurons accompanied by proliferation of reactive microglia in affected regions. However, it is unknown whether the hematopoietic marker CD34 can identify a subpopulation of proliferating microglial cells in the ALS degenerating spinal cord. Immunohistochemistry for CD34 and microglia markers was performed in lumbar spinal cords of ALS rats bearing the SOD1^G93A mutation and autopsied ALS and control human subjects. Characterization of CD34-positive cells was also performed in primary cell cultures of the rat spinal cords. CD34 was expressed in a large number of cells that closely interacted with degenerating lumbar spinal cord motor neurons in symptomatic SOD1^G93A rats, but not in controls. Most CD34⁺ cells co-expressed the myeloid marker CD11b, while only a subpopulation was stained for Iba1 or CD68. Notably, CD34⁺ cells actively proliferated and formed clusters adjacent to damaged motor neurons bearing misfolded SOD1. CD34⁺ cells were identified in the proximity of motor neurons in autopsied spinal cord from sporadic ALS subjects but not in controls. Cell culture of symptomatic SOD1^G93A rat spinal cords yielded a large number of CD34⁺ cells exclusively in the non-adherent phase, which generated microglia after successive passaging. A yet unrecognized CD34⁺ cells, expressing or not the microglial marker Iba1, proliferate and accumulate adjacent to degenerating spinal motor neurons, representing an intriguing cell target for approaching ALS pathogenesis and therapeutics.

Role of microglia in embryonic neurogenesis

Microglia begin colonizing the developing brain as early as embryonic day 9, prior to the emergence of neurons and other glia. Their ontogeny is also distinct from other central nervous system cells, as they derive from yolk sac hematopoietic progenitors and not neural progenitors. In this review, we feature these unique characteristics of microglia and assess the spatiotemporal similarities between microglia colonization of the central nervous system and embryonic neurogenesis. We also infer to existing evidence for microglia function from embryonic through to postnatal neurodevelopment to postulate roles for microglia in neurogenesis.

Development of a culture system to induce microglia-like cells from haematopoietic cells

Aims

Microglia are the resident immune cells in the central nervous system, originating from haematopoietic-derived myeloid cells. A microglial cell is a double-edged sword, which has both pro-inflammatory and anti-inflammatory functions. Although understanding the role of microglia in pathological conditions has become increasingly important, histopathology has been the only way to investigate microglia in human diseases.

Methods

To enable the study of microglial cells in vitro, we here establish a culture system to induce microglia-like cells from haematopoietic cells by coculture with astrocytes. The characteristics of microglia-like cells were analysed by flow cytometry and functional assay.

Results

We show that triggering receptor expressing on myeloid cells-2-expressing microglia-like cells could be induced from lineage negative cells or monocytes by coculture with astrocytes. Microglia-like cells exhibited lower expression of CD45 and MHC class II than macrophages, a characteristic similar to brain microglia. When introduced into brain slice cultures, these microglia-like cells changed their morphology to a ramified shape on the first day of the culture. Moreover, we demonstrated that microglia-like cells could be induced from human monocytes by coculture with astrocytes. Finally, we showed that interleukin 34 was an important factor in the induction of microglia-like cells from haematopoietic cells in addition to cell–cell contact with astrocytes. Purified microglia-like cells were suitable for further culture and functional analyses.

Conclusion

Development of in vitro induction system for microglia will further promote the study of human microglial cells under pathological conditions as well as aid in the screening of drugs to target microglial cells.

Direct induction of ramified microglia-like cells from human monocytes: dynamic microglial dysfunction in Nasu-Hakola disease

Microglia have been implicated in various neurological and psychiatric disorders in rodent and human postmortem studies. However, the dynamic actions of microglia in the living human brain have not been clarified due to a lack of studies dealing with in situ microglia. Herein, we present a novel technique for developing induced microglia-like (iMG) cells from human peripheral blood cells. An optimized cocktail of cytokines, GM-CSF and IL-34, converted human monocytes into iMG cells within 14 days. The iMG cells have microglial characterizations; expressing markers, forming a ramified morphology, and phagocytic activity with various cytokine releases. To confirm clinical utilities, we developed iMG cells from a patient of Nasu-Hakola disease (NHD), which is suggested to be directly caused by microglial dysfunction, and observed that these cells from NHD express delayed but stronger inflammatory responses compared with those from the healthy control. Altogether, the iMG-technique promises to elucidate unresolved aspects of human microglia in various brain disorders.

Intranasal Delivery of Bone Marrow-Derived Mesenchymal Stem Cells, Macrophages, and Microglia to the Brain in Mouse Models of Alzheimer's and Parkinson's Disease

In view of the rapid preclinical development of cell-based therapies for neurodegenerative disorders, traumatic brain injury, and tumors, the safe and efficient delivery and targeting of therapeutic cells to the central nervous system is critical for maintaining therapeutic efficacy and safety in the respective disease models. Our previous data demonstrated therapeutically efficacious and targeted delivery of mesenchymal stem cells (MSCs) to the brain in the rat 6-hydroxydopamine model of Parkinson's disease (PD). The present study examined delivery of bone marrow-derived MSCs, macrophages, and microglia to the brain in a transgenic model of PD [(Thy1)-h[A30P] aS] and an APP/PS1 model of Alzheimer's disease (AD) via intranasal application (INA). INA of microglia in naive BL/6 mice led to targeted and effective delivery of cells to the brain. Quantitative PCR analysis of eGFP DNA showed that the brain contained the highest amount of eGFP-microglia (up to 2.1 × 104) after INA of 1 × 106 cells, while the total amount of cells detected in peripheral organs did not exceed 3.4 × 103. Seven days after INA, MSCs expressing eGFP were detected in the olfactory bulb (OB), cortex, amygdala, striatum, hippocampus, cerebellum, and brainstem of (Thy1)-h[A30P] aS transgenic mice, showing predominant distribution within the OB and brainstem. INA of eGFP-expressing macrophages in 13-month-old APP/PS1 mice led to delivery of cells to the OB, hippocampus, cortex, and cerebellum. Both MSCs and macrophages contained Iba-1-positive population of small microglia-like cells and Iba-1-negative large rounded cells showing either intracellular amyloid β (macrophages in APP/PS1 model) or α-synuclein [MSCs in (Thy1)-h[A30P] aS model] immunoreactivity. Here, we show, for the first time, intranasal delivery of cells to the brain of transgenic PD and AD mouse models. Additional work is needed to determine the optimal dosage (single treatment regimen or repeated administrations) to achieve functional improvement in these mouse models with intranasal microglia/macrophages and MSCs. This manuscript is published as part of the International Association of Neurorestoratology (IANR) special issue of Cell Transplantation.