The paper introduced this time is here.
Microglial-to-neuronal CCR5 signaling regulates autophagy in neurodegeneration
B. P. Festa, F. H. Siddiqi, M. Jimenez-Sanchez, H. Won, M. Rob, A. Djajadikerta, et al.
Neuron 2023
DOI: 10.1016/j.neuron.2023.04.006
A simple explanation…
- Microglia are immune cells resembling macrophages that exist in the central nervous system. They are widely distributed within the tissues of the brain and spinal cord, and by taking up and breaking down foreign substances and cellular waste, they play important roles in maintaining and repairing the health of nerve cells and in regulating inflammatory responses.
- Neurons are nerve cells, one of the fundamental cells that make up the nervous system. The nervous system includes the central nervous system, such as the brain and spinal cord, as well as the peripheral nervous system, and neurons exist in both. Neurons are composed of a cell body, dendrites, an axon, synapses, and so on, and carry out the role of transmitting information.
- Autophagy refers to a kind of intracellular recycling system that breaks down and reuses waste such as organelles, proteins, and cytoplasm present inside the cell. Autophagy is known as one of the mechanisms by which cells respond to environmental changes such as nutrient deficiency and stress, and it is involved in a variety of cellular functions. While excessive autophagy can destroy normal cellular function, insufficient autophagy is known to cause various problems such as the accumulation of waste and the induction of cell death.
- Huntington’s disease is a hereditary neurodegenerative disease, with symptoms such as movement disorders and decline in cognitive function. Mutation of the Htt gene, the causative gene of Huntington’s disease, is known to cause abnormalities in autophagy. Due to mutation of the Htt gene, the regulation of autophagy becomes insufficient, and waste and proteins accumulate inside the cell. This accumulation may cause the death of nerve cells and functional impairment of the nervous system in Huntington’s disease.
- This paper explains the role of activated microglia in inhibiting neuronal autophagy that is harmful to neurons. Microglia-derived CCL-5/-4/-3 activate neuronal CCR5 to inhibit neuronal autophagy, and CCR5 and CCL-3/-4/-5 are increased in the brains of mice with Huntington’s disease and tauopathy.
How was the experiment carried out?
This is an animal experiment using mice.
The methods used in this paper included:
- Generation of MRFP-GFP-LC3 (traffic light (Tfl)) mice. The generation of traffic light (Tfl) mice involves the creation of mice that have been modified using genetic engineering technology to introduce fluorescent dyes into specific cells so that those cells can be visualized. This makes it possible to study the behavior and interactions of cells in vivo.
- LC3 is labeled with two colors, MRFP in red and GFP in green; this is because LC3 is double-tagged with GFP and red fluorescent protein (mRFP), allowing non-acidified autophagosomes (red and green = yellow) to be distinguished from acidified autolysosomes (red only). Because GFP fluorescence is quenched more quickly when the lysosomal pH is low, autophagy flux can be evaluated. An explanation of autophagy flux is given below.
- Subcloning of MRFP-GFP-LC3 from pMRFP-EGFP-RLC3 into PCAGG by PCR. Subcloning is a type of genetic engineering technology that refers to the work of cutting out a specific DNA fragment (such as a gene or promoter) and inserting it into another plasmid vector. This makes it possible to extract the gene of interest in a form that can be used for research or genetic modification.
- Evaluation of MRFP-GFP-LC3 protein expression levels by Western blot
- By blotting of brain, muscle, and tissue, and by cryosectioning of fresh frozen tissue and direct observation of fluorescence levels.
Autophagy flux is an indicator showing the entire process of autophagy, and is used to evaluate the dynamics of the breakdown and recycling of intracellular materials by autophagy. Autophagy is a physiological process in which, under stress conditions or during nutrient deficiency, cells break down and recycle unnecessary or damaged intracellular structures and proteins, thereby reusing energy and components.
Autophagy consists of the following main steps.
- Formation of the autophagosome: a double-membrane structure that engulfs intracellular proteins and organelles is formed.
- Fusion with the lysosome: the autophagosome fuses with the lysosome to form an autophagic lysosome (autolysosome).
- Breakdown and recycling: within the autophagic lysosome, the contents are broken down by lysosomal enzymes, and their components are reused inside the cell.
Autophagy flux can measure the activity and efficiency of autophagy by evaluating the series of processes from the formation of the autophagosome to breakdown and recycling. Methods such as fluorescent labeling of proteins, Western blotting, and gene expression analysis are used to evaluate autophagy flux.
What kind of results were obtained?
The results of this study found that activated microglia inhibit neuronal autophagy that is harmful to neurons. In this study, microglia-derived CCL-5/-4/-3 activated neuronal CCR5 to inhibit neuronal autophagy. The researchers also found that CCR5 and CCL-3/-4/-5 are increased in the brains of mice with Huntington’s disease and tauopathy, indicating that this pathway may be involved in the pathogenesis of these diseases.
Furthermore, in this study, it was found that administering a drug that inhibits CCR5 prevented mTORC1 activation, the decrease of LC3-II, and the accumulation of mHTT in HeLa CCR5-GFP cells, suggesting that targeting this pathway may become a potential therapeutic strategy for neurodegenerative diseases.
What is the future of this research?
Possible directions include investigating the role of CCR5 in other neurodegenerative diseases, identifying other factors that regulate neuronal autophagy, and exploring the possibility of targeting this pathway as a therapeutic strategy for neurodegenerative diseases.
It suggests that further research is needed to determine whether this finding can be applied clinically.
Impressions
Autophagy is an extremely important mechanism in tissue repair. I am very interested in the involvement of this autophagy in stem cell therapy and exosome therapy as well. I think I will continue to study it further.
English Abstract
Microglia-to-neuronal CCR5 signaling regulates autophagy in neurodegeneration
In neurodegeneration diseases, microglia switch to an activated state, which results in excessive secretion of pro-inflammatory factors. Our work aims to investigate how this paracrine signaling affects neuronal function. Here, we show that activated microglia mediate non-cell-autonomous inhibition of neuronal autophagy, a degenerative pathway critical for removal toxic, aggregate-prompt proteins accumulating in neurodegenerative disease. We found that the microglia-derived CCL-3/-4/-5 bind and activate neural CCR5, which in turn promotes mTORC1 activation and disrupts autophagy and aggregate-protein clearance. CCR5 and its cognate chemokines are upregulated in the brains of pre-manifesting mouse models for Huntington’s disease (HD) and tauopathy, suggesting a pathological role of this microglia-neuronal axis in the early phase of these disease. CCR5 upregulation is self-sustaining, as CCL5-CCR5 autophagy inhibition impairs CCR5 degradation itself. Finally, pharmacological or genetic inhibition of CCR5 rescues mTORC1 hyperactivation and autophagy dysfunction, which ameliorates HD and tau pathologies in mouse models.
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