Activation of SREBP in Alveolar Type II Cells Enhances Lipogenesis Causing Pulmonary Lipotoxicity
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ABSTRACT: Background: Lung function is dependent upon the precise regulation of the synthesis, storage, and catabolism of tissue and alveolar lipids. Results: Activation of SREBP (Sterol Response Element Binding Protein) induced lipogenesis in alveolar epithelial cells, causing neutral lipid accumulation, lung inflammation, and tissue remodeling. Conclusions: The accumulation of neutral lipids in type II epithelial cells and alveolar macrophages caused lung inflammation, consistent with findings in lipid storage disorders. Significance: Pulmonary lipotoxicity may contribute to the pathogenesis of lung dysfunction associated with diabetes, obesity, and other metabolic disorders. Genome-wide transcription profiling comparison between doxycycline-exposed SFTPC-rtTAWT/Tg/(tetO)7CMV-CreWT/Tg/Insig1flox/flox/Insig2-/- mice (i.e., Insig1/2∆/∆ ) and Insig1flox/flox/Insig2-/- . Three independent pooled RNA from isolated lung type 2 cells of each genotype were used.
Project description:Background: Lung function is dependent upon the precise regulation of the synthesis, storage, and catabolism of tissue and alveolar lipids. Results: Activation of SREBP (Sterol Response Element Binding Protein) induced lipogenesis in alveolar epithelial cells, causing neutral lipid accumulation, lung inflammation, and tissue remodeling. Conclusions: The accumulation of neutral lipids in type II epithelial cells and alveolar macrophages caused lung inflammation, consistent with findings in lipid storage disorders. Significance: Pulmonary lipotoxicity may contribute to the pathogenesis of lung dysfunction associated with diabetes, obesity, and other metabolic disorders.
Project description:Pulmonary function after birth is dependent upon surfactant lipids that reduce surface tension in the alveoli. The sterol-responsive element-binding proteins (SREBPs) are transcription factors regulating expression of genes controlling lipid homeostasis in many tissues. To identify the role of SREBPs in the lung, we conditionally deleted the SREBP cleavage-activating protein gene, Scap, in respiratory epithelial cells (Scap∆/∆) in vivo. Prior to birth (E18.5), deletion of Scap decreased the expression of both SREBPs and a number of genes regulating fatty acid and cholesterol metabolism. Nevertheless, Scap∆/∆ mice survived postnatally, surfactant and lung tissue lipids being substantially normalized in adult Scap∆/∆ mice. Although phospholipid synthesis was decreased in type II cells from adult Scap∆/∆ mice, lipid storage, synthesis, and transfer by lung lipofibroblasts were increased. mRNA microarray data indicated that SCAP influenced two major gene networks, one regulating lipid metabolism and the other stress-related responses. Deletion of the SCAP/SREBP pathway in respiratory epithelial cells altered lung lipid homeostasis and induced compensatory lipid accumulation and synthesis in lung lipofibroblasts. To identify the role of SREBPs in the lung, we conditionally deleted the SREBP cleavage-activating protein gene, Scap, in respiratory epithelial cells (Scap∆/∆) in vivo.Lung cRNA was hybridized to the murine genome MOE430 V2 chips.
Project description:Lipid homeostasis is dysregulated in several forms of neurodegeneration. Here we examined changes in sterols, neutral lipids and transcripts that control their homeostasis during the neuronal death induced in the CA1 region of mouse hippocampus by focal kainic acid (KA) injection. We defined changes in the lipid economy of neurons and glial cells by staining for neutral lipids and for free cholesterol. Lipid droplets filled with neutral lipids were induced in microglia at ~24 hrs after KA-treatment. At 2-4 days after injection, filipin staining revealed punctate deposits of free cholesterol in neuronal somata. These changes were correlated with alterations in cellular organelles observed in electron microscopy and transcriptomic changes obtained with RNA-seq of tissue from the CA1 region. Mitochondria, the innate inflammatory response and lipids. Lipid droplet transcriptome. Cholesterol economy. Lipids and phagocytosis.
Project description:Dilated cardiomyopathy (DCM) and heart failure are associated with mitochondrial dysfunction and dysregulated lipid metabolism. Recent studies have implicated a pivotal role of Hippo pathway activation in the development of DCM with profound metabolic remodelling. However, alterations in the cardiac lipid profile and responsible molecular mechanisms, including upregulated galectin-3, remain unclear in the setting of DCM. Mice with DCM induced by Hippo pathway activation (Mst1 gene overexpression alone or with galectin-3 gene deletion) were studied by lipidomic profiling, transcriptomic profiling and immunoblotting for mRNA and protein expression. Profound alterations in cardiac lipid classes were observed, notably elevated sphingolipids, reduced triacylglycerol (TG) and ether lipids, alterations in phospholipid species, elevated lysophosphatidylcholine, and a profound reduction in mitochondria-specific cardiolipin and coenzyme Q10. Relative to adult mice with advanced DCM, reduced TG content was evident but sphingolipid accumulation was absent in young mice at early phase of DCM. Mechanistically, the lipidomic profile in DCM heart was in consistent with dysregulated expression of specific gene sets for biosynthesis of ceramides or TG, TG storage/hydrolysis, mitochondrial lipid metabolism, peroxisome biogenesis, and suppressed PPAR-alpha signaling. Furthermore, galectin-3 gene deletion resulted in changes in some lipid classes and numerous lipid species in settings of healthy and DCM. Multiple alterations in cardiac lipids were identified by lipidomics in a mouse model of DCM due to activation of the Hippo pathway. By employing transcriptome and galectin-3 gene deletion, we revealed underlying mechanisms for lipid abnormalities involving upregulated galectin-3, downregulated expression of specific gene sets of lipid metabolism, and attenuated PPAR-alpha signaling.
Project description:Perilipin A (PeriA) exclusively locates on adipocyte lipid droplets and is essential for lipid storage and lipolysis. Adipocyte specific overexpression of PeriA caused resistance to diet-induced obesity and resulted in improved insulin sensitivity. In order to better understand the biological basis for this observed phenotype we performed DNA microarray analysis on white adipose tissue (WAT) from PeriA transgenic (Tg) and control wildtype (WT) mice. We generated transgenic mice that overexpressed human PeriA using the adipocyte specific aP2 promoter/enhancer (Miyoshi, et al. J Lipid Res 2010). All PeriA Tg mice used for the study were female, and heterozygous for the transgene. Littermates that lacked the transgene were used as controls (WT). All mice were housed at room temperature, maintained on a 12 h light/dark cycle, given free access to water, and fed a high-fat diet (HFD) until the age of 30 weeks. On the day prior to tissue harvest at 30 weeks, WAT from perigonadal were rapidly dissected out, extracted total RNA, and hybridized on Affymetrix microarrays.
Project description:Peroxisomes are essential but often overlooked metabolic organelles. To explore how macrophage peroxisomes protect the lung, we conducted single-cell RNA sequencing (scRNA-seq) on lungs from both naïve and SARS-CoV-2-infected Pex5^flox/flox (WT) and Cd11c-cre Pex5^flox/flox (KO) mice at 7 days post-infection (d.p.i). scRNA-seq revealed an increased proportion of inflammatory monocytes, neutrophils, and monocyte-derived macrophages (MDMs) in the lungs of infected KO mice, alongside a marked reduction in alveolar type 2 (AT2) cells and alveolar macrophages (AMs) compared to infected WT mice. AMs from KO mice showed elevated expression of genes involved in inflammatory responses, innate immunity, and cellular stress signaling, while genes related to wound healing, cell differentiation, and lipid metabolism were downregulated, compared to AMs from WT mice at 7 d.p.i.
Project description:Pulmonary function after birth is dependent upon surfactant lipids that reduce surface tension in the alveoli. The sterol-responsive element-binding proteins (SREBPs) are transcription factors regulating expression of genes controlling lipid homeostasis in many tissues. To identify the role of SREBPs in the lung, we conditionally deleted the SREBP cleavage-activating protein gene, Scap, in respiratory epithelial cells (Scap∆/∆) in vivo. Prior to birth (E18.5), deletion of Scap decreased the expression of both SREBPs and a number of genes regulating fatty acid and cholesterol metabolism. Nevertheless, Scap∆/∆ mice survived postnatally, surfactant and lung tissue lipids being substantially normalized in adult Scap∆/∆ mice. Although phospholipid synthesis was decreased in type II cells from adult Scap∆/∆ mice, lipid storage, synthesis, and transfer by lung lipofibroblasts were increased. mRNA microarray data indicated that SCAP influenced two major gene networks, one regulating lipid metabolism and the other stress-related responses. Deletion of the SCAP/SREBP pathway in respiratory epithelial cells altered lung lipid homeostasis and induced compensatory lipid accumulation and synthesis in lung lipofibroblasts.
Project description:Lipid droplets (LDs) of foam cells within atheroma contain abundant cholesterol, but also serve as reservoirs of central bioactive lipids. The mechanisms of storage and mobilization of many of these lipids remain obscure. LD-associated hydrolase (LDAH) localizes to LDs, has a lipase structure, and is abundant in atheroma. However, its lipid substrates and role in atherogenesis are unknown. Using knockout and transgenic mice we found that LDAH protects against atherosclerosis. Myeloid LDAH expression is sufficient to inhibit lesion progression and promote stable architectures, less necrotic, and richer in fibrillar collagen. Lipidomics coupled with RNA sequencing revealed that LDAH facilitates mobilization of esters of oxysterols that are liver X receptor agonists, leading to induction of cholesterol efflux transporters, reduced foam cell inflammation, and pro-fibrotic gene signatures. These studies identify LDAH as a novel player in neutral hydrolysis of esterified regulatory sterols that promotes atheroprotective and pro-stabilizing mechanisms beyond mass cholesterol removal.
Project description:SKBR3 cells expressing NDRG1 shRNA1 or vector control were harvested by trypsinization and total RNA was extracted. Silencing NDRG1 reduces cell proliferation rates, causing lipid metabolism dysfunction including increased fatty acid incorporation into neutral lipids and lipid droplets. global changes in transcriptome due to NDRG1 silencing were observed
Project description:Lysosomal acid lipase (LAL) is the key enzyme of lysosomal lipid hydrolysis, which degrades cholesteryl esters (CE), triacylglycerols (TG), diacylglycerols (DG), and retinyl esters. The role of LAL in various cellular processes has mostly been studied in LAL-deficient (Lal-/-) mice, which share phenotypical characteristics with humans suffering from LAL deficiency. In vitro, the cell-specific functions of LAL have been commonly investigated by using the LAL inhibitors Lalistat-1 (L1) and Lalistat-2 (L2). Here, we show that pharmacological LAL inhibition but not genetic loss of LAL impairs isoproterenol-stimulated lipolysis and neutral TG hydrolase (TGH) and CE hydrolase (CEH) activities in mature adipocytes, indicating that L1 and L2 inhibit other lipid hydrolases apart from LAL. Since adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) are the major enzymes that degrade cytosolic TG and CE, respectively, at neutral pH, we hypothesized that L1 and L2 also inhibit ATGL and/or HSL through off-target effects. In fact, both inhibitors drastically reduced neutral CEH activity in cells overexpressing mouse and human HSL and neutral TGH activity in cells overexpressing mouse and human ATGL, albeit to a lesser extent. By performing serine hydrolase-specific activity-based labeling in combination with quantitative proteomics, we confirmed that L2 inhibits HSL and other lipid hydrolases, whereas L1 treatment results in less pronounced inhibition of neutral lipid hydrolases. These results demonstrate that commonly used concentrations of L2 (and L1) are not suitable for investigating the role of LAL-specific lipolysis in lysosomal function, signaling pathways, and autophagy.