What Are Microglia?

Microglia are the only cells derived from mesoderm in neural tissue. The cell body is small, short stick-shaped, with several stick-like protrusions protruding, the surface of the protrusion is rough, showing spines, and few branches. The nucleus is small, about 5 m, irregular in shape, and can be kidney-shaped, oval-shaped, or triangular in shape, with many nuclear chromatin. This cell is less distributed in the central nervous system. It is mostly located near the cell body of neurons or around small blood vessels in gray matter, and is also seen in white matter.

Microglia are the only cells derived from mesoderm in neural tissue. The cell body is small, short stick-shaped, with several stick-like protrusions protruding, the surface of the protrusion is rough, showing spines, and few branches. The nucleus is small, about 5 m, irregular in shape, and can be kidney-shaped, oval-shaped, or triangular in shape, with many nuclear chromatin. This cell is less distributed in the central nervous system. It is mostly located near the cell body of neurons or around small blood vessels in gray matter, and is also seen in white matter.

Chinese name

a

Foreign name

microglia

Nature

Glial cell

Attributes

Innate immune cells in CNS

Microglia I. Source:

Views on the origin of microglia include: neuroectoderm (with similar origin to oligodendrocytes and astrocytes); adventitia of blood vessels; inherent hematopoietic stem cells in the central nervous system; Germ layer / mesenchymal tissue; monocytes in circulating blood. The claim that microglia originate from bone marrow monocytes and / or bone marrow hematopoietic stem cells is accepted by most scholars.

Microglia II. Physiology:

The shape of microglia is highly plastic, which is closely related to its biological function. In normal brain tissue, microglia are highly branched, with tertiary and quadratic branch structures, and the branches between cells rarely overlap. Branched microglia are often referred to as "resting microglia". However, today the concept of "resting microglia" is being challenged. In vivo studies have found that resting microglia come into direct contact with neuronal synapses approximately once per hour. This contact is neuronal activity-dependent, and microglia monitor synapses through contact with synapses. The functional status of the touch. Therefore, under normal circumstances, highly branched resting microglia provide the brain with a highly dynamic and efficient monitoring system. When inflammation, infection, trauma, or other neurological diseases occur in the brain, microglia are quickly activated and gain phagocytosis. The definition of microglial activation was primarily based on changes in its morphology. The activated microglia has a larger cell body, shorter protrusions, and a round or rod-like cell shape; the activated microglia are further activated and adjusted, the cell protrusions disappear, the cell form is amoebic, and it has phagocytosis Features. The morphological changes of microglia reflect the activation status of microglia, which is closely related to the severity of damaged parts in the brain.

Microglia III. Biological functions:

Microglia have the characteristics of multiple synapses and plasticity. They are inherent immune effector cells in the central nervous system and play an extremely important role in the physiological process of the central nervous system. First, microglia are necessary for the normal development of the nervous system. In the early stages of brain development, about 20% to 80% of neurons with long projection axons undergo apoptosis and are quickly cleared. Extracellular signals such as hormones, neurotransmitters, or secreted proteins can be specific to neurons. Receptor binding promotes neuron survival or initiates programmed cell death of neurons, thereby regulating the number of neurons in the central nervous system.

Microglia are involved in a series of neurodegenerative diseases. Microglia activation and neuroinflammation are the main features of neuropathology. It mediates an endogenous immune response to central nervous system injury and disease, thereby exerting neuroprotective or neurotoxic effects. Any nervous system disorder can usually lead to inflammation and microglial activation. At the same time, the number of glial cells increases and the phenotype changes. This phenomenon is called "reactive glial hyperplasia". In acute neurodegenerative diseases (stroke, cerebral hypoxia, traumatic brain injury), the microglial phenotype changes and releases inflammatory mediators, which are mainly cytokines and chemokines. These acute inflammatory reactions are generally beneficial to the survival of nerve cells, reduce secondary damage in the brain, and repair damaged tissue. Microglia-mediated chronic inflammation is involved in the pathological process of a variety of chronic neurodegenerative diseases, including: Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, etc. During chronic inflammation, microglia are activated for a long period of time, and then continue to release a series of inflammatory mediators, leading to oxidative stress response. It is generally believed that chronic chronic inflammatory reactions mediated by microglia are harmful to the body and can cause nerve tissue damage.