Biology subjects

CASHIKAR, A. G.

Publications and source records attributed to CASHIKAR, A. G..

3 recordsLinked to original sources

bioRxiv2023

25-hydroxycholesterol mediates brain cytokine production and neutrophil infiltration in a mouse model of lipopolysaccharide-induced neuroinflammation

Neuroinflammation has been implicated in the pathogenesis of several neurologic and psychiatric disorders. Microglia are key drivers of neuroinflammation and in response to different inflammatory stimuli overexpress a proinflammatory signature of genes. Among these, Ch25h is a gene overexpressed in brain tissue from Alzheimers disease as well as various mouse models of neuroinflammation. Ch25h encodes cholesterol 25-hydroxylase, an enzyme that hydroxylates cholesterol to form 25-hydroxycholesterol (25HC). 25HC, an immune-oxysterol primarily produced by activated microglia, is further metabolized to 7,25-dihydroxycholesterol, which is a potent chemoattractant for leukocytes. We have also previously shown that 25HC increases production and secretion of the proinflammatory cytokine, IL-1{beta}, by mouse microglia treated with lipopolysaccharide (LPS). In the present study, wildtype (WT) and Ch25h-knockout (CKO) mice were peripherally administered LPS to induce an inflammatory state in the brain. In LPS-treated WT mice, Ch25h expression and 25HC levels increased in brain relative to vehicle-treated WT mice. Interestingly, 25HC levels were significantly higher in LPS-treated WT female compared to male mice. Activation of microglia and astrocytes in response to systemic LPS was suppressed in CKO mice relative to WT mice. Proinflammatory cytokine production and intra-parenchymal infiltration of neutrophils strongly correlated with brain 25HC levels and were significantly lower in CKO compared to WT mice. Overall, our results show that 25HC mediates a sex-specific proinflammatory response in the brain characterized by activation of both microglia and astrocytes but also by neutrophil migration into the brain parenchyma presumably due to 7,25-diHC produced from 25HC.

neuroscience↗

bioRxiv2023

Microglial 25-hydroxycholesterol mediates neuroinflammation and neurodegeneration ina tauopathy mouse model

Alzheimers disease (AD) is characterized by amyloid plaques and neurofibrillary tangles in addition to neuroinflammation and changes in brain lipid metabolism. Recent findings have demonstrated that microglia are key drivers of neurodegeneration in tauopathy mouse models. A subset of microglia referred to as disease-associated microglia (DAM) display gene signatures signifying changes in proinflammatory signaling and lipid metabolism in mouse models of amyloid and tau pathology. Ch25h is a DAM gene encoding cholesterol 25-hydroxylase that produces 25-hydroxycholesterol (25HC), a known modulator of inflammation as well as lipid metabolism. However, whether Ch25h influences tau-mediated neuroinflammation and neurodegeneration is unknown. Here, we show that in the absence of Ch25h and the resultant reduction in 25HC there is strikingly reduced age-dependent neurodegeneration and neuroinflammation in the hippocampus and entorhinal/piriform cortex of PS19 mice, which express the P301S mutant human tau transgene. Transcriptomic analyses of bulk hippocampal tissue and single nuclei revealed that Ch25h deficiency in PS19 mice strongly suppressed proinflammatory cytokine and chemokine signaling in microglia and restored sterol synthesis. Our results suggest a key role for Ch25h/25HC in potentiating proinflammatory signaling to promote tau-mediated neurodegeneration. Ch25h may represent a novel therapeutic target for primary tauopathies, AD, and other neuroinflammatory diseases.

neuroscience↗

bioRxiv2022

Regulation of astrocyte lipid metabolism and ApoE secretion by the microglial oxysterol, 25-hydroxycholesterol

Neuroinflammation is a major hallmark of Alzheimers disease and several other neurological and psychiatric disorders and is often associated with dysregulated cholesterol metabolism. Relative to homeostatic microglia, activated microglia express higher levels of Ch25h, an enzyme that hydroxylates cholesterol to produce 25-hydroxycholesterol (25HC). 25HC is an oxysterol with interesting immune roles stemming from its ability to regulate cholesterol biosynthesis. Since astrocytes synthesize cholesterol in the brain and transport it to other cells via apolipoprotein E (ApoE)-containing lipoproteins, we hypothesized that secreted 25HC from microglia may influence lipid metabolism as well as extracellular ApoE derived from astrocytes. Here we show that astrocytes take up externally added 25HC and respond with altered lipid metabolism. 25HC increased extracellular levels of ApoE lipoprotein particles without altering Apoe mRNA expression, due to elevated Abca1 expression via activation of LXRs and decreased ApoE reuptake due to suppressed Ldlr expression via inhibition of SREBP. Astrocytes metabolized 25HC to limit its effects on lipid metabolism via Cyp7b1, an enzyme responsible for 7-hydroxylation of 25HC. Knockdown of Cyp7b1 expression with siRNA prolonged the effects of 25HC on astrocyte lipid metabolism. 25HC also suppressed Srebf2 expression to reduce cholesterol synthesis in astrocytes but did not affect fatty acid levels or the genes required for fatty acid synthesis. We further show that 25HC led to a doubling of the amount of cholesterol esters and their concomitant storage in lipid droplets. Our results suggest an important role for 25HC in regulating astrocyte lipid metabolism.

cell biology↗