Lipids and Alzheimer's disease!

Written by Qiu Shulan, edited by Han Xianlin, Wang Sizhen Alzheimer's disease (AD) is the most common cause of dementia in the elderly, but there is still a lack of effective treatment methods, and more understanding of the disease mechanism is needed [1]
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Human genome-wide association studies have pointed out that in addition to β-amyloid (Aβ) and tau protein, immune response and lipid metabolism are also the main pathways for the etiology of AD [2,3]
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More and more evidences show that chronic neuroinflammation, mainly mediated by microglia and astrocytes, is one of the causes of AD neurodegeneration [4-6]
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At the same time, the brain is the organ with the most abundant lipid content and diversity, mainly due to lipid-rich myelin [7], but the relationship between lipids and AD diseases and related mechanisms are very lacking
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The author and others have reported a significant decrease in cerebrosulfatide (sulfatide) in AD patients and AD-related animal models at an early stage of the disease, and this decrease in cerebrosulfatide is dependent on the ApoE subtype, the highest risk gene for AD Mediated [8-13]
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But so far, it is still unclear whether changes in specific brain lipids are sufficient to drive the course of AD-related diseases
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 In September 2021, authors such as Qiu Shulan and Han Xianlin from the University of Texas Medical Center at San Antonio published an article entitled "Adult-onset CNS myelin sulfatide deficiency is sufficient to cause Alzheimer's disease-like neuroinflammation and cognitive impairment" on Molecular Neurodegeneration.
, Found that the loss of myelin sulfatide in the central nervous system (CNS) in adulthood is sufficient to activate disease-related microglia and astrocytes, increasing multiple AD risk genes and confirmed AD-related The expression of key regulators of immune/microglia regulation ultimately leads to AD-like chronic neuroinflammation and mild cognitive impairment
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At the same time, neuroinflammation and mild cognitive impairment showed gender differences, and female mice were more obvious than male mice
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Subsequent mechanism studies revealed the relationship between CNS myelin sulfatide loss, chronic inflammation of the brain, activation of astrocytes and microglia, the highest risk of AD gene ApoE, and glial cell activation-related transcription factor pathways
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Cerebroside sulfotransferase (CST, also known as Gal3st1) catalyzes the last step of sulfatide biosynthesis
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Lipoprotein gene (Plp1) is expressed in large amounts in CNS myelin forming cells, that is, oligodendrocytes, but it is expressed to a low degree in myelin forming cells of the peripheral nervous system (PNS) [14]
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 Here, in order to study the effect of sulfatide decline on brain homeostasis and cognitive function and related molecular mechanisms in AD patients and animal models in the early stage of onset, the authors established CST gene Flox mice, referred to as CSTfl/fl mice
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CSTfl/fl mice and Plp1-CreERT mice were crossed to establish CST conditional knockout (CST cKO) mice, and tamoxifen (TX) was used to induce the knockout of CST in myelin-forming cells in adult mice.
Gene, thereby mimicking the decline of sulfatides in the early stage of AD patients (Figure 1A)
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 The authors used Nanostring high-throughput mRNA detection methods, lipidomics and protein level detection to determine that this mouse showed CST gene expression in the CNS (Figure 1B) and brain The level of glycosides (Figure 1C) was significantly down-regulated, but the decrease in cerebrosides in PNS was not significant (Figure 1C)
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At the same time, the authors made it clear that the CST complete knockout (CST KO) mice, which are different from the embryonic stage knockout of cerebrosides, did not cause other myelin lipids in the loss of CNS cerebrosides in adult CST cKO mice at the age of 12 months.
At the same time, the gene expression of oligodendrocytes (Figure 1D, E) or the level of myelin structure protein (Figure 1F) did not change
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It shows that the down-regulation of CNS myelin cerebrosides in mice started after adulthood does not destroy myelin homeostasis
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At the same time, the loss of cerebrosides did not cause the death of nerve cells or other cells in the CNS
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Figure 1 A new type of glial cell-specific conditional knockout of CST (CST cKO) mouse model that can induce myelination, which simulates CNS in adulthood without affecting the homeostasis of oligodendrocytes Loss of AD-like myelin glucosinolates (CRM: brain, SC: spinal cord, SN: sciatic nerve)
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(Picture quoted from: Qiu, S.
, et al.
, Mol Neurodegener, 2021; 16: 64) Next, the author performed a test on 13-month-old CST cKO mice that passed the preliminary screening of neurological function-related behaviors (Figure 2A).
Morris water maze (MWM) and new object recognition (novel object recognition, NOR) experiments showed that although CST cKO mice may have increased swimming time that has nothing to do with muscle function (Figure 2B) (Figure 2C), The sixth day probe results (Figure 2F-I) and NOR of MWM, such as decreased swimming speed (Figure 2D), increased floating time (Figure 2E) and other cognitive or motor-related dysfunctions, but not related to motor function The results (Figure 2J) all proved that although the loss of myelin sulfatides in the CNS at the beginning of adulthood did not cause changes in myelin homeostasis, it was sufficient to cause damage to cognitive function and the destruction of spatial and non-spatial memory-related functions
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Figure 2 The loss of sulfatides in adulthood is enough to cause cognitive impairment (Picture quoted from: Qiu, S.
, et al.
, Mol Neurodegener, 2021; 16: 64) Further, the author studied the sulfur in the CNS in adulthood.
The specific cellular and molecular mechanisms of the loss of glycosides leading to cognitive impairment
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First, the Nanostring mouse AD-related kit was used to detect 770 genes in brain and spinal cord samples 4.
5 months and 9 months after TX injection.
It was found that the loss of sulfatide in CST cKO mice induced immunity and inflammation in the CNS.
Reaction (Figure 3A, B)
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Next, the Nanostring mouse neuroinflammation-related kit was used to further discover that 76 genes with significantly up-regulated mRNA levels in CNS samples of CST cKO mice were enriched in microglia/astrocytes/immune activation functions
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The results of comparing the expression changes of neuroinflammation-related genes in Nanostring mice of CST cKO and CST KO mice showed that although sulfatide deficiency in CST KO mice caused CNS myelin damage, sulfatide in CST cKO mice became mature after adulthood.
Loss did not cause significant changes in CNS myelin sheath homeostasis (Figure 1D, E), but the loss of CNS sulfatides caused similar activation of microglia and astrocytes, and led to chronic immunity , Inflammation (Figure 3C-E)
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Through gene enrichment analysis, it is found that the gene expression changes caused by myelin glucosinolate deletion point to the most significant related disease is AD (Figure 4A)
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The up-regulated genes include four AD risk genes Apoe, Trem2, Cd33 and Mmp12 (Figure 4B-E), as well as the key AD regulatory genes Tyrobp, Dock and Fcerg1 (Figure 4F-H) that have been reported
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Combining existing literature reports and the author’s results, it is further clarified that the gene expression of microglia and astrocytes activated by sulfatide deficiency is similar to that of AD disease-related microglia and astrocytes.
(Figure 4 I, J)
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Figure 3 The loss or absence of CNS sulfatides induces the gradual activation of microglia and astrocytes, resulting in chronic neuroimmunity and inflammation
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(Picture quoted from: Qiu, S.
, et al.
, Mol Neurodegener, 2021; 16: 64) Figure 4 CNS sulfolipid deficiency leads to AD-like neuroinflammation, leading to disease-related microglia and astrocytes Features
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(Picture quoted from: Qiu, S.
, et al.
, Mol Neurodegener, 2021; 16: 64) Then, the author used mass spectrometry imaging of sulfatides in the brain (Figure 5A), and activated stars caused by sulfatide deficiency.
Comparison of the distribution of astrocytes and microglia (Figure 5B-E), the co-localization of activated astrocytes and myelin (Figure 5F), and activated astrocytes in the spinal cord of CST cKO mice Electron microscopic observation of plasma cells and myelin (Figure 5H) experiments showed that there is a spatial correlation between sulfatide and glial cell activation in CST cKO and CST KO mice: glial cell activation caused by sulfatide deficiency is distributed in CST cKO and CST KO mice.
An area rich in myelin sheath
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Figure 5 Loss of sulfatides on the myelin sheath leads to significant astrocyte and microglia activation in the brain regions rich in myelin sheath
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(Picture quoted from: Qiu, S.
, et al.
, Mol Neurodegener, 2021; 16: 64) ApoE is the main extracellular lipid carrier in the CNS, transporting a variety of lipids, including sulfatides
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At the same time, Apoe4 is the highest risk gene for AD, and ApoE4 is necessary to reduce the level of brain sulfatides [15]
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The authors found that ApoE was up-regulated in the CNS of CST cKO and KO (Figure 4B), indicating that the absence of sulfatides in the CNS myelin and the up-regulation of ApoE formed a positive feedback
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Then the author used ApoE and CST double knockout (ApoE-/-/CST-/-) mice combined with immunofluorescence staining (Figure 6A, B) and Nanostring neuroinflammation kit (Figure 6C-F) and found that ApoE knockout It cannot prevent and affect the glial cell activation and related immune and inflammatory activation caused by CST knockout, which clarifies that although ApoE is involved in sulfatide transport, it does not directly affect the glial cell activation and the activation of myelin sulfatide deficiency.
Neuroinflammation, ApoE may cause AD-related chronic neuroinflammation by participating in the loss of sulfatides
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Figure 6 AD-like neuroinflammation induced by myelin sulfatide deficiency does not directly depend on ApoE
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(Picture quoted from: Qiu, S.
, et al.
, Mol Neurodegener, 2021; 16: 64) Existing research results show that the activation of astrocytes and microglia affect each other, and ApoE is mainly composed of astrocytes Plasma cells are produced
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Then the authors used a colony stimulating factor 1 receptor (CSF1R) inhibitor, namely PLX3397, to eliminate most of the microglia in the whole brain to study the mutual regulation of astrocytes, microglia and ApoE
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Interestingly, although PLX3397 eliminated most of the CST+/+ mouse brain and most of the microglia in the CST-/- mouse brain, immunostaining (Figure 7A, E) and Nanostring neuroinflammatory reagent The results of the box (Figure 7B-D) showed that the elimination of microglia could not affect the activation of astrocytes related to sulfatide deficiency and the up-regulation of ApoE expression
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This proves that the activation of astrocytes and microglia related to sulfatide deficiency exists through independent pathways, and proves that the up-regulation of ApoE caused by sulfatide deficiency exists in astrocytes
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Figure 7 Astrocyte hyperplasia and ApoE up-regulation caused by CNS sulfolipid deficiency are not secondary to microglia activation
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(Picture quoted from: Qiu, S.
, et al.
, Mol Neurodegener, 2021; 16: 64) In order to further study the molecular mechanism of neuroinflammation caused by sulfatide deficiency in the myelin sheath in the CNS, the authors analyzed the transcription Factor scoring, the main targets include IRF8, STAT3, SPI1 and C/EBPβ (Figure 8A).
Existing research reports also show that they are involved in the activation of microglia or astrocytes [16-19], and Spi1 is An AD risk gene enriched in microglia [18]
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The western blotting results also verified the significant up-regulation of STAT3 and PU.
1/Spi1 in the brain and spinal cord samples of CST cKO mice, as well as the partial up-regulation of other transcription factors C/EBPβ and IRF8 (Figure 8B, C)
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In addition, in the samples where PLX3397 eliminated microglia, the phosphorylation and up-regulation of STAT3 protein in the brains of CST knockout mice were not affected by the loss of microglia, indicating that STAT3 may be astrocyte activation Specific transcriptional regulation pathway (Figure 8D)
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Figure 8 The lack of sulfatides in the myelin sheath leads to the up-regulation of SPI1, STAT3 and C/EBP transcription factors in the central nervous system
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(Picture quoted from: Qiu, S.
, et al.
, Mol Neurodegener, 2021; 16: 64) Conclusion and discussion of the article, inspiration and outlook In general, in this study: 1) It is the first time to establish induction in adulthood The mouse model of myelin sulfatide loss successfully simulated the down-regulation of sulfatide in the brain of AD patients, and proved that the myelin sulfatide loss induced in adulthood does not affect myelin stability at the time point of detection.
2) For the first time, it is elucidated that a lipid, the sulfatide of the CNS myelin sheath, is lost in adulthood enough to activate microglia and astrocytes, and increase multiple AD risk genes and It has been confirmed that the expression of key regulators of AD-related immune/microglia regulation ultimately leads to AD-like chronic neuroinflammation and mild cognitive impairment; 3) It is stated that the AD risk gene ApoE is involved in sulfatide transport, but It does not directly affect the glial cell activation and neuroinflammation induced by the loss of sulfatide on the myelin sheath.
ApoE may participate in the loss of sulfatide and cause AD-related chronic neuroinflammation; 4) It is proved that astrocytes related to the loss of sulfatide The activation of plasmocytes and microglia exists through independent pathways, and it is proved that the up-regulation of ApoE caused by sulfatide deficiency is present in astrocytes; 5) clarifies the microglia caused by sulfatide deficiency in the myelin sheath The activation of cells and astrocytes is mainly regulated by PU1/SPI1 and STAT3 transcription factors, respectively
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 The results of this article strongly indicate that specific lipid abnormalities in the brain, such as the lack of sulfatides on the myelin sheath, may also be an important driving and promoting factor of neuroinflammation and mild cognitive impairment in AD pathology, and are related to tau disease.
Irrelevant
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However, follow-up studies are needed to continue to clarify how the lack of myelin sulfatide activates microglia and astrocytes, respectively
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1186/s13024-021-00488-7 Qiu Shulan (left, the first author), Han Xianlin (right, the corresponding author) (photo provided from: Han Xianlin Laboratory) Selection of previous articles [1] eLife︱ sorting protein SNX27 passed the mutation The new mechanism of contact adhesion protein LRFN2 to regulate AMPA receptor transport [2] Brain︱ new method! Plasma soluble TREM2 can be used as a potential detection marker for white matter damage in cerebral small vessel diseases [3] EMBO J︱neuron Miro1 protein deletion destroys mitochondrial autophagy and overactivates the integrated stress response [4]Science frontier review interpretation︱nicotinic acetylcholine The regulatory mechanism of receptor-assisted molecules and the application prospects of disease treatment and transformation [5] Cereb Cortex︱ oxytocin can regulate the individualized processing of facial identities and the classification and processing of facial races in early facial regions of the brain [6] Nat Commun | Qi Xin Project The group revealed the molecular mechanism of the compound CHIR99021 in the treatment of Huntington’s disease by regulating mitochondrial function [7] Cereb Cortex︱ Ku Yixuan’s team revealed the ipsilateral sensory cortex representation pattern of working memory [8] Neurosci Bull︱ synapse-associated protein Dlg1 through inhibition Activation of microglia improves depression-like behavior in mice [9] Brain | For the first time! PAX6 may be a key factor in the pathogenesis of Alzheimer's disease and a new therapeutic target [10] Sci Adv︱ blockbuster! DNA methylation protein DNMT1 mutation can induce neurodegenerative diseases [11] Cell︱ new discovery! New enlightenment of midbrain-regulated movement phenomenon for the treatment of Parkinson’s disease [12] Cereb Cortex︱MET tyrosine kinase signal transduction timing abnormality is a key mechanism affecting the development and behavior of normal cortical neural circuits in mice [13] Nat Biomed Eng︱ The team of academician Ye Yuru develops a new strategy for whole-brain gene editing-mediated treatment of Alzheimer’s disease [14] Luo Liqun Science's heavy review System interpretation ︱ Neural circuit structure-a system that makes the brain "computer" run at high speed [15] Sci Adv ︱Important discovery! The calcium homeostasis regulatory protein Calhm2 regulates the activation of microglia and participates in the process of Alzheimer's disease.
Recommended high-quality scientific research training courses [1] Data map life-saving guide! How good is it to learn these software? 【2】Single-cell sequencing data analysis and project design network practical class (October 16-17)【3】JAMA Neurol︱ Attention! Young people are more likely to suffer from "Alzheimer's disease"? [4] Patch clamp and optogenetics and calcium imaging technology seminar (October 30-31) References (slide up and down to view) [1] Cummings, J.
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