Alzheimer type II astrocyte
The Alzheimer type II astrocyte is thought to be a pathological type of
They are not associated with
Background
Astrocytes belong to a class of
General characteristics
Alzheimer type II astrocytosis occurs when the
Characteristics of disease
When hyperammonemia occurs in hepatic encephalopathy, associated phenotypic changes in appearances occur in the cells as well as regulation of gene expression for proteins associated with regulation cell volume and transmission of neuronal impulses.[8] In previous studies of hepatic encephalopathy, the presence of Alzheimer type II astrocytes corresponded to mitochondrial degeneration, as well as previously known phenotypic characteristics such as a prominent nucleolus and enlarged pale nuclei.[8] Additionally, when these astrocytes are exposed to ammonia it causes gliopathy, the dysregulation and dysfunction of the astrocytes.[8] This gliopathy is what is thought to cause encephalopathy in HE.[8]
Pathology
Alzheimer type II astrocytes are present in hepatic encephalopathy and Wilson's disease.[9] The presence of Alzheimer type II astrocytes is a key indicator of hepatic encephalopathy, and may be induced by increased bodily ammonia.[10] In hepatic encephalopathy, Alzheimer type II astrocytes are characterized by thin chromatin and increased glycogen levels.[5] Although these astrocytes are present in this disease, it has not yet been determined if Alzheimer type II astrocytes are a pathological symptom for HE.[5]
The origin of Alzheimer type II astrocytes is unclear, although they are known to arise from astroglial cells in the development of Wilson's disease.[11] Experiments with mice have shown that exposure to manganese leads to the development of Alzheimer's type II astrocytes.[12] This suggests that manganism, a neurological disorder with Parkinson's-like symptoms, is caused by the development of these astrocytes through manganese poisoning.[12]
These cells are typically seen in conditions such as chronic liver disease, where hyperammonemia occurs. This is due to the presence of the enzyme glutamine synthetase, which is able to detoxify ammonia through the amidation of glutamate, producing glutamine in the process.[4] Swelling occurs in these astrocytes due to the increased intracellular glutamine levels which induces osmotic stress on the cell and results in edema.[4] This hypothesis is called the glutamine/osmolyte hypothesis, and has yet to be researched extensively.[13] However, it is generally thought that ammonia-induced astrocyte swelling can be attributed to oxidative stress that glutamine can exert on the cell, as well as the creation of free radicals that may cause astrocytic damage.[13] It is difficult for researchers to accept that excess intracellular glutamine produced in response to hyperammonemia is the direct cause of astrocytic cell swelling and therefore brain edema, however scientific data is beginning to support the effect that glutamine may have on other chemical reactions that occur in the brain such as the generation of free radicals.[13] This area has not been fully researched yet, and more information about the mechanism by which glutamine creates radicals in the brain and the effect that this has on edema must be elucidated.[13]
References
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- ^ Online Medical Dictionary at CancerWeb
- ^ [1], University of Rochester Medical Center. Retrieved 2 December 2015.
- ^ PMID 23316223.
- ^ Blueprints Neurology, 2nd ed.
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- PMID 11680638.
- ^ S2CID 6830969.
- ^ S2CID 12015650.