Journal of Lipid Research最新文献

Oxylipins-oxidized metabolites of polyunsaturated fatty acids (PUFAs)-are associated with several pathological conditions. We previously showed that oxylipin metabolites of linoleic acid (LA) and alpha-linolenic acid positively correlate with obesity in wild-type (WT) mice fed a high fat diet (35% kcal fat) based on soybean oil (SO). Here, we compare the effect of the SO diet (10% kcal LA) to an isocaloric diet based on coconut oil (CO) that is low in LA (2% kcal) in HNF4α exon swap male mice that express only the P2 form of HNF4α (α7HMZ). α7HMZ mice gained significantly less weight on the SO diet than WT mice and exhibited neither glucose intolerance nor fatty liver as did the WT mice. Untargeted metabolomics of the liver revealed increased levels of LA and decreased levels of PUFA-derived C18 diols in α7HMZ compared to WT. Proteomics identified decreased levels of several enzymes involved in PUFA metabolism (CYP2Cs, EPHX1, FADS2, ACOX1/2) as the likely cause of decreased diols. Correlation analysis of hepatic oxylipins with body weight, coupled with a 16-weeks treatment with a soluble epoxide inhibitor (sEHI), identified the oxylipins most likely to be potential drivers of obesity as 9,10-DiHOME, 12,13-DiHOME, 9,10-DiHODE and 12,13-DiHODE. Hepatic accumulation of omega-6 and omega-3 oxylipin metabolites of the essential fatty acids, linoleic and alpha-linolenic, are necessary but not sufficient for diet-induced obesity.

Women face a higher lifetime risk of developing neurodegenerative diseases such as Alzheimer's disease and related dementias. The menopausal transition, characterized by a decline in estrogen levels, may affect cholesterol metabolism and neurodegenerative processes. Oxysterols, oxidized cholesterol derivatives, play a role in these pathways, with 24(S)-hydroxycholesterol (24HC) reflecting brain cholesterol turnover and 27-hydroxycholesterol (27HC) linked to systemic cholesterol metabolism. We investigated associations of plasma oxysterols with circulating sex hormones and characteristics of reproductive history in 1,974 postmenopausal women with no history of dementia from the Women's Health Initiative, taking into account APOE4 status and cholesterol-lowering medication. We found that higher levels of bioavailable estradiol were associated with higher 24HC and 27HC levels, and higher estrone was associated with higher 24HC (all P values <0.05). Associations of estradiol with 24HC and 27HC were stronger among APOE4 carriers and those not using cholesterol-lowering medication, with a significant interaction between bioavailable estradiol and APOE4 in relation to 27HC (p for interaction = 0.04). Having an older age at menopause was associated with lower 24HC among those taking cholesterol medication (p for interaction = 0.03). Our findings suggest that 24HC and 27HC may be proxy biomarkers of neuronal health and estrogen status in postmenopausal women. The stronger associations between estradiol and oxysterols among APOE4 carriers and those not using cholesterol medication suggest the need to account for hormonal, genetic, and pharmacological factors when evaluating neurodegenerative risk. Longitudinal studies are warranted to further investigate oxysterols as potential early biomarkers of risk for Alzheimer's disease and related dementias.

Voltage-gated potassium (Kv) channels possess distinct voltage-sensor (VSD) and pore (PD) domains, making it challenging to study domain-specific lipid effects. Here, we examined the functional modification of a prototypical Kv channel, KvAP, by phosphatidylglycerol (POPG) and phosphatidylserine (POPS) in mono-component asymmetric bilayers using the contact bubble bilayer (CBB) method. In these membranes, specific chemical modifications were distinguished from non-specific electrostatic (surface potential) effects by using the channel's gating as an intrinsic probe. No specific effects were observed when charged lipids were in the outer leaflet. When present in the inner leaflet, POPS exerted only a single specific effect: the acceleration of activation kinetics. In contrast, inner-leaflet POPG induced multiple, profound modifications: it also accelerated activation kinetics, but additionally shifted the conductance-voltage (G-V) curve hyperpolarized, attenuated the G-V slope, and accelerated inactivation kinetics. This clear contrast allows a domain-specific interpretation: the shared acceleration of activation is attributed to a general kinetic modulation of the VSD, while POPG's unique effects-impaired electromechanical coupling (attenuated slope) and accelerated inactivation-are attributed to specific chemical interactions with the VSD-PD linker and the PD, respectively. These results reveal a multi-site mechanism of lipid modulation dictated by leaflet asymmetry and headgroup chemistry.

Early placentation relies on temporal changes in intrauterine oxygen tension that regulate trophoblast differentiation events. Studies have highlighted the contribution of bioactive sphingolipids to the pathogenesis of placental disorders, characterized by hypoxia. However, it is unknown whether placental sphingolipid metabolism changes during the switch from a hypoxic to an oxygenated environment in the first trimester of gestation and if sustained hypoxia is causative of sphingolipid alterations seen in preeclampsia. Herein, we performed sphingolipid analysis of first-trimester human placentae as well as placentae from conditional (placenta-specific) Phd2 knockout mice (Phd2^-/- cKO) that exhibit preeclampsia-like features, including placental hypoxia. Analysis revealed elevated long chain ceramide (Cer16:0, Cer18:0, Cer20:0 and Cer22:0) and reduced sphingosine-1-phosphate (So-1-P) content in Phd2^-/- cKO placentae. Expression of key regulatory sphingolipid enzymes, acid ceramidase (ASAH1) and sphingosine kinase 1 (SPHK1), was reduced in Phd2^-/- cKO placentae, while that of alkaline ceramidase ACER2 remained unchanged. Human placentae from 5-9 weeks of gestation, when intrauterine oxygen tension is low, exhibited heightened long chain ceramide (Cer14:0, Cer16:0, Cer18:0, Cer 18:1) and sphingosine content and reduced ASAH1 and SPHK1 expression, highlighting the relevance of low oxygen in regulating sphingolipid metabolism under physiological (placental development) and pathological (Phd2^-/- cKO induced preeclampsia) conditions. Ultrastructural analyses of early (5-9 weeks) human and murine Phd2^-/- cKO placentae revealed that increased trophoblast mitochondrial fission events accompanied elevated ceramide. Together, the data support the concept that a chronic low-oxygen environment leads to placental ceramide buildup, which may alter mitochondrial homeostasis and potentially contribute to cell death events characteristic of preeclampsia.

Nonshivering thermogenesis plays an important role in maintaining body temperature and energy homeostasis. Elongation of very long-chain fatty acid protein 3 (ELOVL3), which catalyzes the synthesis of C20-C24 fatty acids, is induced in brown adipose tissue (BAT) by cold exposure and regarded as a thermogenic gene. However, its precise role in thermogenesis remains elusive. BAT-specific KO mice of Elovl3 were generated by the Cre/LoxP approach and phenotypically analyzed under cold exposure. Gene expression changes in BAT were characterized by quantitative RT-PCR and Western blotting, BAT remodeling was evaluated by histological examination, and lipid composition was examined by lipidomic analysis. BAT-specific deletion of the Elovl3 gene resulted in cold intolerance because of impaired BAT thermogenesis, without a significant effect on muscle shivering thermogenesis. Mechanistically, Elovl3 deficiency impaired cold-induced BAT remodeling and Ucp1 expression, with a defect in mitochondrial cristae remodeling. Lipidomics analysis showed a marked reduction in the contents of lysophosphatidylcholine, cardiolipin, and acylcarnitine in BAT in the absence of Elovl3. Taken together, our findings reveal the critical role of ELOVL3 in BAT thermogenesis and provide new ideas for the intervention and treatment of obesity-related diseases.

Apolipoprotein A-I (APOA1) oligomerization is thought to be essential for high-density lipoprotein (HDL) formation and metabolism. Naturally occurring mutations can disrupt normal APOA1 folding and self-association, leading to dysfunctional HDL formation and cardiovascular disease. The congenital APOA1 variant p.K131del (APOA1^K107del) has been associated with cardiovascular pathologies such as low HDL-cholesterol levels and aortic amyloidosis, and multiple studies indicate structural changes in APOA1 conformation underlie associated dysfunction. In the current study, we confirmed that APOA1^K107del exhibits no notable defect in lipid-binding. However, using polyacrylamide gel electrophoresis (PAGE) and size-exclusion chromatography (SEC), we found that loss of lysine 107 resulted in a remarkable shift in the distribution of APOA1 oligomers with a much higher proportion of monomers present in APOA1^K107del compared to wild-type APOA1. Further investigation using quantitative cross-linking revealed a major disruption of interactions in helical regions reported to participate in domain swaps necessary for proper self-association. This structural disruption appears to impair N- and C-termini interactions and dynamics that lead to non-specific aggregation. These findings support the hypothesis that lysine 107 is critical for proper folding and self-association of lipid-free APOA1 which could impact HDL biogenesis.

Hydrophobic bile acid-mediated hepatobiliary injury is a major driver of cholestasis progression. Most anticholestasis treatments being tested clinically are based on a single agent, which does not always sufficiently alleviate bile acid toxicity to slow disease progression. This study investigates a therapeutic strategy of combining glycine-conjugated β-muricholic acid (Gly-βMCA) and fibroblast growth factor-15 (FGF15) to alleviate bile acid hepatobiliary toxicity in Cyp2c70 KO mice that lack endogenous muricholic acid (MCA) synthesis and have a "humanized" hydrophobic bile acid pool composition. The effects of the single and combination treatments on bile acid metabolism, liver injury, and gut microbiome were investigated in female Cyp2c70 KO mice with progressive cholangiopathy and portal fibrosis. While all three treatments significantly reduced biochemical and histologic features of liver injury, the Gly-βMCA and FGF15 combination achieved a remarkably higher reduction in both bile acid pool size and hydrophobicity than either single treatment. Mechanistically, this resulted from synergistically increased biliary hydrophilic MCA species derived from Gly-βMCA, inhibited intestine endogenous bile acid absorption by Gly-βMCA, and repressed cholesterol 7α-hydroxylase (CYP7A1) by FGF15, which counteracted the undesirable farnesoid X receptor antagonism activity of Gly-βMCA. Furthermore, a hydrophobic bile acid pool in Cyp2c70 KO mice was associated with markedly reduced beneficial Lactobacillaceae family bacteria abundance, which was enriched by Gly-βMCA and the combination treatments. In conclusion, the Gly-βMCA and FGF15 combination shows enhanced efficacy in decreasing humanized bile acid pool size and hydrophobicity and holds potential as a therapeutic strategy to decrease bile acid burden in cholestasis.

n-3 PUFAs possess numerous health benefits. The FAT-1 desaturase in the model organism Caenorhabditis elegans is a Δ15-desaturase that converts n-6 PUFAs into n-3 PUFAs. Transgenic expression of FAT-1 has been used in organisms, such as pigs, mice, and fish, to improve n-3 PUFA levels. However, the determination of FAT-1 activity and substrate preference per se remains unclear. AlphaFold structure prediction revealed that FAT-1 is an integral membrane protein located in the endoplasmic reticulum, and it consists of four transmembrane helices (1-4) with a functional CYTB5 domain in the N terminus and a desaturase domain containing three histidine-rich sequences (His boxes) in the C terminus. A small region in the desaturase domain containing amino acids 210-217, especially G212, G216, and S217, is essential for its activity. FAT-1 can convert all four n-6 PUFAs to corresponding or downstream n-3 PUFAs in both C. elegans and mammalian cells and may prioritize the conversion of C20:4n6 (arachidonic acid) to C20:5n3 (EPA). These results uncover the significant mechanism of the activity and substrate preference of the FAT-1 desaturase, providing insights into the transgenic application of FAT-1.

Understanding the processes and/or the key factors involved in the formation as well as degradation of lipid droplets (LDs) within the adipocytes is of immense importance, especially in the context of health, obesity, cancer, and other diseases. While cold temperature and/or menthol (an edible cooling agent), seem to have diverse and confounding effects on obesity and/or thermogenesis, so far there is no direct evidence that specific pharmacological modulation of the Transient Receptor Potential cation channel subfamily Melastatin member 8 (TRPM8), a cold-temperature-activated ion channel, can indeed affect LD status within the mature adipocytes. Here, we used highly specific antagonists and agonists of TRPM8 to modulate TRPM8 in cultured adipocyte cells in vitro and monitored the expression of TRPM8 as well as other adipogenic functions. Our results indicate that specific activation of TRPM8 in mature adipocytes by a specific agonist, that is, WS12 ((1R∗,2S∗)-N-(4-methoxyphenyl)-5-methyl-2-(1-methylethyl)cyclohexanecarboxamide), results in increased expression of PPARγ protein. However, TRPM8 inhibition by N-(3-aminopropyl)-2-[(3-methylphenyl)methoxy]-N-(2-thienylmethyl)benzamidehydrochloride results in no change in the PPARγ expression, yet causes decreased Oil Red O intensity, a reduction in LD sizes, and an increase in LD numbers. BODIPY (4,4-difluoro-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indacene) labeling in live cells also suggests the same findings. Altogether, data suggest that in the absence of any confounding factors, specific inhibition of TRPM8 results in either less fusion of LDs or enhanced fragmentation of LDs in vitro. These findings may have broad implications in the field of adipogenesis and in cancer.

Astrocytes comprise approximately 40% of CNS cells and have pivotal roles in brain functions. Under steady-state conditions, astrocytes maintain homeostasis in the CNS through the uptake or release of neurotransmitters. However, in neurodegenerative conditions, astrocytes are activated by inflammatory cytokines, such as interleukin-1alpha (IL-1α) and TNF-α, which are released from activated microglia. Activated astrocytes release several inflammatory cytokines and neurotoxic substances, resulting in neuronal injury. Sphingolipids are a series of bioactive lipids involved in several biological processes, such as apoptosis, inflammatory response, cell cycle, and immune response. SM is a sphingolipid that is a major component of the cellular membrane and is also involved in inflammatory responses. We report that SM promotes IL-1α/TNF-α-induced expressions of representative astrocyte mRNAs and astrocyte activation through the NF-κB pathway. In contrast, reduction of SM by knockdown of sphingomyelin synthase 1 (SMS1) and/or SMS2 suppresses astrocyte activation. Furthermore, removal of SM by the blockade of ceramide transfer protein suppresses astrocyte activation via the induction of histone deacetylase (HDAC) 1 and HDAC3; subsequently, the levels of acetylated p65 (Lys 310) are reduced, leading to the suppression of the NF-κB pathway. Our findings further the understanding of the regulation of astrocyte activation by sphingolipids.