Increased intestinal lipid absorption caused by Ire1β deficiency contributes to hyperlipidemia and atherosclerosis in apolipoprotein E-deficient mice

Cannabidiol promotes intestinal cholesterol uptake mediated by Pregnane X receptor

Background

Cannabidiol (CBD), a non-psychoactive phytocannabinoid of cannabis, is therapeutically used as an analgesic, anti-convulsant, anti-inflammatory, and anti-psychotic drug. There is a growing concern about the adverse side effects posed by CBD usage. Pregnane X receptor (PXR) is a nuclear receptor activated by a variety of dietary steroids, pharmaceutical agents, and environmental chemicals. In addition to the role in xenobiotic metabolism, the atherogenic and dyslipidemic effects of PXR have been revealed in animal models. CBD has a low affinity for cannabinoid receptors, thus it is important to elucidate the molecular mechanisms by which CBD activates cellular signaling and to assess the possible adverse impacts of CBD on pro-atherosclerotic events in cardiovascular system, such as dyslipidemia.

Objective

Our study aims to explore the cellular and molecular mechanisms by which exposure to CBD activates human PXR and increases the risk of dyslipidemia.

Methods

Both human hepatic and intestinal cells were used to test if CBD was a PXR agonist via cell-based transfection assay. The key residues within PXR's ligand-binding pocket that CBD interacted with were investigated using computational docking study together with site-directed mutagenesis assay. The C57BL/6 wildtype mice were orally fed CBD in the presence of PXR antagonist resveratrol (RES) to determine how CBD exposure could change the plasma lipid profiles in a PXR-dependent manner. Human intestinal cells were treated with CBD and/or RES to estimate the functions of CBD in cholesterol uptake.

Results

CBD was a selective agonist of PXR with higher activities on human PXR than rodents PXRs and promoted the dissociation of human PXR from nuclear co-repressors. The key amino acid residues Met246, Ser247, Phe251, Phe288, Trp299, and Tyr306 within PXR's ligand binding pocket were identified to be necessary for the agonistic effects of CBD. Exposure to CBD increased the circulating total cholesterol levels in mice which was partially caused by the induced expression levels of the key intestinal PXR-regulated lipogenic genes. Mechanistically, CBD induced the gene expression of key intestinal cholesterol transporters, which led to the increased cholesterol uptake by intestinal cells.

Conclusion

CBD was identified as a selective PXR agonist. Exposure to CBD activated PXR signaling and increased the atherogenic cholesterol levels in plasma, which partially resulted from the ascended cholesterol uptake by intestinal cells. Our study provides potential evidence for the future risk assessment of CBD on cardiovascular disease, such as dyslipidemia.

Comprehensive Analysis of 1-Year-Old Female Apolipoprotein E-Deficient Mice Reveals Advanced Atherosclerosis with Vulnerable Plaque Characteristics

Apolipoprotein E-knockout (Apoe-/-) mice constitute the most widely employed animal model of atherosclerosis. Deletion of Apoe induces profound hypercholesterolemia and promotes the development of atherosclerosis. However, despite its widespread use, the Apoe-/- mouse model remains incompletely characterized, especially at late time points and advanced disease stages. Thus, it is unclear how late atherosclerotic plaques compare to earlier ones in terms of lipid deposition, calcification, macrophage accumulation, smooth muscle cell presence, or plaque necrosis. Additionally, it is unknown how cardiac function and hemodynamic parameters are affected at late disease stages. Here, we used a comprehensive analysis based on histology, fluorescence microscopy, and Doppler ultrasonography to show that in normal chow diet-fed Apoe-/- mice, atherosclerotic lesions at the level of the aortic valve evolve from a more cellular macrophage-rich phenotype at 26 weeks to an acellular, lipid-rich, and more necrotic phenotype at 52 weeks of age, also marked by enhanced lipid deposition and calcification. Coronary artery atherosclerotic lesions are sparse at 26 weeks but ubiquitous and extensive at 52 weeks; yet, left ventricular function was not significantly affected. These findings demonstrate that atherosclerosis in Apoe-/- mice is a highly dynamic process, with atherosclerotic plaques evolving over time. At late disease stages, histopathological characteristics of increased plaque vulnerability predominate in combination with frequent and extensive coronary artery lesions, which nevertheless may not necessarily result in impaired cardiac function.

Trimethylamine increases intestinal fatty acid absorption: in vitro studies in a Caco-2 cell culture system

Although elevated blood levels of trimethylamine N-oxide (TMAO) have been associated with atherosclerosis development in humans, the role of its gut microbiota-derived precursor, TMA, in this process has not been yet deciphered. Taking this into account, and the fact that increased intestinal fatty acid absorption contributes to atherosclerosis onset and progression, this study aimed to evaluate the effect of TMA on fatty acid absorption in a cell line that mimics human enterocytes. Caco-2 cells were treated with TMA 250 μM for 24 h. Fatty acid absorption was assessed by measuring the apical-to-basolateral transport and the intracellular levels of BODIPY-C12, a fluorescently labelled fatty acid analogue. Gene expression of the main intestinal fatty acid transporters was evaluated by real-time quantitative reverse transcription PCR. Compared to control conditions, TMA increased, in a time-dependent manner and by 20-50 %, the apical-to-basolateral transport and intracellular levels of BODIPY-C12 fatty acid in Caco-2 cells. Fatty acid transport protein 4 (FATP4) and fatty acid translocase (FAT)/CD36 gene expression were not stimulated by TMA, suggesting that TMA-induced increase in fatty acid transport may be mediated by an increase in FAT/CD36 and/or FATP4 activity and/or fatty acid passive transport. This study demonstrated that TMA increases the intestinal absorption of fatty acids. Future studies are necessary to confirm if this may constitute a novel mechanism that partially explains the existing positive association between the consumption of a diet rich in TMA sources (e.g. red meat) and the increased risk of atherosclerotic diseases.

ATP-Binding Cassette Protein ABCC10 Deficiency Prevents Diet-Induced Obesity but Not Atherosclerosis in Mice

Excess plasma lipid levels are a risk factor for various cardiometabolic disorders. Studies have shown that improving dyslipidemia lowers the progression of these disorders. In this study, we investigated the role of ATP-binding cassette transporter C10 (ABCC10) in regulating lipid metabolism. Our data indicate that deletion of the Abcc10 gene in male mice results in lower plasma and intestinal triglycerides by around 38% and 36%, respectively. Furthermore, deletion of ABCC10 ameliorates diet-induced obesity in mice and leads to a better response during insulin and glucose tolerance tests. Unexpectedly, ABCC10 deficiency does not affect triglyceride levels or atherosclerosis in ApoE-deficient mice. In addition, our studies demonstrate low oleate uptake by enterocytes (~25-30%) and less absorption (~37%) of triglycerides in the small intestine of ABCC10 knockout mice. Deletion of the Abcc10 gene also alters several lipid metabolism genes in the intestine, suggesting that ABCC10 regulates dietary fat absorption, which may contribute to diet-induced obesity in mice.

Gene losses in the common vampire bat illuminate molecular adaptations to blood feeding

Vampire bats are the only mammals that feed exclusively on blood. To uncover genomic changes associated with this dietary adaptation, we generated a haplotype-resolved genome of the common vampire bat and screened 27 bat species for genes that were specifically lost in the vampire bat lineage. We found previously unknown gene losses that relate to reduced insulin secretion (FFAR1 and SLC30A8), limited glycogen stores (PPP1R3E), and a unique gastric physiology (CTSE). Other gene losses likely reflect the biased nutrient composition (ERN2 and CTRL) and distinct pathogen diversity of blood (RNASE7) and predict the complete lack of cone-based vision in these strictly nocturnal bats (PDE6H and PDE6C). Notably, REP15 loss likely helped vampire bats adapt to high dietary iron levels by enhancing iron excretion, and the loss of CYP39A1 could have contributed to their exceptional cognitive abilities. These findings enhance our understanding of vampire bat biology and the genomic underpinnings of adaptations to blood feeding.

Role of Endoplasmic Reticulum Stress Sensor IRE1α in Cellular Physiology, Calcium, ROS Signaling, and Metaflammation

Inositol-requiring transmembrane kinase endoribonuclease-1α (IRE1α) is the most prominent and evolutionarily conserved unfolded protein response (UPR) signal transducer during endoplasmic reticulum functional upset (ER stress). A IRE1α signal pathway arbitrates yin and yang of cellular fate in objectionable conditions. It plays several roles in fundamental cellular physiology as well as in several pathological conditions such as diabetes, obesity, inflammation, cancer, neurodegeneration, and in many other diseases. Thus, further understanding of its molecular structure and mechanism of action during different cell insults helps in designing and developing better therapeutic strategies for the above-mentioned chronic diseases. In this review, recent insights into structure and mechanism of activation of IRE1α along with its complex regulating network were discussed in relation to their basic cellular physiological function. Addressing different binding partners that can modulate IRE1α function, UPRosome triggers different downstream pathways depending on the cellular backdrop. Furthermore, IRE1α are in normal cell activities outside the dominion of ER stress and activities under the weather of inflammation, diabetes, and obesity-related metaflammation. Thus, IRE1 as an ER stress sensor needs to be understood from a wider perspective for comprehensive functional meaning, which facilitates us with assembling future needs and therapeutic benefits.

Resveratrol inhibits lipid accumulation in the intestine of atherosclerotic mice and macrophages

Disordered intestinal metabolism is highly correlated with atherosclerotic diseases. Resveratrol protects against atherosclerotic diseases. Accordingly, this study aims to discover novel intestinal proatherosclerotic metabolites and potential therapeutic targets related to the anti‐atherosclerotic effects of resveratrol. An untargeted metabolomics approach was employed to discover novel intestinal metabolic disturbances during atherosclerosis and resveratrol intervention. We found that multiple intestinal metabolic pathways were significantly disturbed during atherosclerosis and responsive to resveratrol intervention. Notably, resveratrol abolished intestinal fatty acid and monoglyceride accumulation in atherosclerotic mice. Meanwhile, oleate accumulation was one of the most prominent alterations in intestinal metabolism. Moreover, resveratrol attenuated oleate‐triggered accumulation of total cholesterol, esterified cholesterol and neutral lipids in mouse RAW 264.7 macrophages by activating ABC transporter A1/G1‐mediated cholesterol efflux through PPAR (peroxisome proliferator‐activated receptor) α/γ activation. Furthermore, we confirmed that PPARα and PPARγ activation by WY14643 and pioglitazone, respectively, alleviated oleate‐induced accumulation of total cholesterol, esterified cholesterol and neutral lipids by accelerating ABC transporter A1/G1‐mediated cholesterol efflux. This study provides the first evidence that resveratrol abolishes intestinal fatty acid and monoglyceride accumulation in atherosclerotic mice, and that resveratrol suppresses oleate‐induced accumulation of total cholesterol, esterified cholesterol and neutral lipids in macrophages by activating PPARα/γ signalling.

The atypical antipsychotic quetiapine induces hyperlipidemia by activating intestinal PXR signaling

Quetiapine, one of the most prescribed atypical antipsychotics, has been associated with hyperlipidemia and an increased risk for cardiovascular disease in patients, but the underlying mechanisms remain unknown. Here, we identified quetiapine as a potent and selective agonist for pregnane X receptor (PXR), a key nuclear receptor that regulates xenobiotic metabolism in the liver and intestine. Recent studies have indicated that PXR also plays an important role in lipid homeostasis. We generated potentially novel tissue-specific PXR-KO mice and demonstrated that quetiapine induced hyperlipidemia by activating intestinal PXR signaling. Quetiapine-mediated PXR activation stimulated the intestinal expression of cholesterol transporter Niemann-Pick C1-Like 1 (NPC1L1) and microsomal triglyceride transfer protein (MTP), leading to increased intestinal lipid absorption. While NPC1L1 is a known PXR target gene, we identified a DR-1-type PXR-response element in the MTP promoter and established MTP as a potentially novel transcriptional target of PXR. Quetiapine's effects on PXR-mediated gene expression and cholesterol uptake were also confirmed in cultured murine enteroids and human intestinal cells. Our findings suggest a potential role of PXR in mediating adverse effects of quetiapine in humans and provide mechanistic insights for certain atypical antipsychotic-associated dyslipidemia.

microRNA-30c reduces plasma cholesterol in homozygous familial hypercholesterolemic and type 2 diabetic mouse models

High plasma cholesterol levels are found in several metabolic disorders and their reductions are advocated to reduce the risk of atherosclerosis. A way to lower plasma lipids is to curtail lipoprotein production; however, this is associated with steatosis. We previously showed that microRNA (miR)-30c lowers diet-induced hypercholesterolemia and atherosclerosis in C57BL/6J and Apoe-/- mice. Here, we tested the effect of miR-30c on plasma lipids, transaminases, and hepatic lipids in different mouse models. Hepatic delivery of miR-30c to chow-fed leptin-deficient (ob/ob) and leptin receptor-deficient (db/db) hypercholesterolemic and hyperglycemic mice reduced cholesterol in total plasma and VLDL/LDL by ∼28% and ∼25%, respectively, without affecting triglyceride and glucose levels. And these mice had lower plasma transaminases and creatine kinase activities than controls. Moreover, miR-30c significantly lowered plasma cholesterol and atherosclerosis in Western diet-fed Ldlr-/- mice with no effect on plasma triglyceride, glucose, and transaminases. In these studies, hepatic lipids were similar in control and miR-30c-injected mice. Mechanistic studies showed that miR-30c reduced hepatic microsomal triglyceride transfer protein activity and lipid synthesis. Thus miR-30c reduced plasma cholesterol in several diet-induced and diabetic hypercholesterolemic mice. We speculate that miR-30c may be beneficial in lowering plasma cholesterol in different metabolic disorders independent of the origin of hypercholesterolemia.

Batf3-dependent CD8α+ Dendritic Cells Aggravates Atherosclerosis via Th1 Cell Induction and Enhanced CCL5 Expression in Plaque Macrophages

Dendritic cells (DCs) play an important role in controlling T cell-mediated adaptive immunity in atherogenesis. However, the role of the basic leucine zipper transcription factor, ATF-like 3 (Batf3)-dependent CD8α+ DC subset in atherogenesis remains unclear. Here we show that Batf3-/-Apoe-/- mice, lacking CD8α+ DCs, exhibited a significant reduction in atherogenesis and T help 1 (Th1) cells compared with Apoe-/- controls. Then, we found that CD8α+ DCs preferentially induce Th1 cells via secreting interleukin-12 (IL-12), and that the expression of interferon-gamma (IFN-γ)or chemokine (C-C motif) ligand 5 (CCL5) in aorta were significantly decreased in Batf3-/-Apoe-/- mice. We further demonstrated that macrophages were the major CCL5-expressing cells in the plaque, which was significantly reduced in Batf3-/-Apoe-/- mice. Furthermore, we found CCL5 expression in macrophages was promoted by IFN-γ. Finally, we showed that Batf3-/-Apoe-/- mice displayed decreased infiltration of leukocytes in the plaque. Thus, CD8α+ DCs aggravated atherosclerosis, likely by inducing Th1 cell response, which promoted CCL5 expression in macrophages and increased infiltration of leukocytes and lesion inflammation.

MicroRNA-30c Mimic Mitigates Hypercholesterolemia and Atherosclerosis in Mice

High plasma cholesterol levels are a major risk factor for atherosclerosis. Plasma cholesterol can be reduced by inhibiting lipoprotein production; however, this is associated with steatosis. Previously we showed that lentivirally mediated hepatic expression of microRNA-30c (miR-30c) reduced hyperlipidemia and atherosclerosis in mice without causing hepatosteatosis. Because viral therapy would be formidable, we examined whether a miR-30c mimic can be used to mitigate hyperlipidemia and atherosclerosis without inducing steatosis. Delivery of a miR-30c mimic to the liver diminished diet-induced hypercholesterolemia in C57BL/6J mice. Reductions in plasma cholesterol levels were significantly correlated with increases in hepatic miR-30c levels. Long term dose escalation studies showed that miR-30c mimic caused sustained reductions in plasma cholesterol with no obvious side effects. Furthermore, miR-30c mimic significantly reduced hypercholesterolemia and atherosclerosis in Apoe(-/-) mice. Mechanistic studies showed that miR-30c mimic had no effect on LDL clearance but reduced lipoprotein production by down-regulating microsomal triglyceride transfer protein expression. MiR-30c had no effect on fatty acid oxidation but reduced lipid synthesis. Additionally, whole transcriptome analysis revealed that miR-30c mimic significantly down-regulated hepatic lipid synthesis pathways. Therefore, miR-30c lowers plasma cholesterol and mitigates atherosclerosis by reducing microsomal triglyceride transfer protein expression and lipoprotein production and avoids steatosis by diminishing lipid syntheses. It mitigates atherosclerosis most likely by reducing lipoprotein production and plasma cholesterol. These findings establish that increasing hepatic miR-30c levels is a viable treatment option for reducing hypercholesterolemia and atherosclerosis.

Pre-germinated brown rice prevented high fat diet induced hyperlipidemia through ameliorating lipid synthesis and metabolism in C57BL/6J mice

Pre-germinated brown rice (PGBR) can ameliorate hyperlipidemia, but the action mechanism is not clear. We focus the mechanisms of PGBR prevented hyperlipidemia. Six-week-old mice were divided into: standard-regular diet (SRD), high-fat diet (HFD) and HFD with PGBR (HFD + PGBR) groups for 16 weeks. The HFD group has higher concentrations of TG, TC, HDL and Non-HDL in the blood, and a higher atherosclerosis index (AI). The TG levels in the liver, and TG, bile acid levels in the feces were enhanced; and the total adipocytokines level in adipose tissue was reduced. The HFD group had higher protein expressions of SREBP-1, SCD-1, FAS, LDLR, and CYP7α1 in the liver. Moreover, the greater expressions of SREBP-1, SCD-1, FAS and the less expressions of PPAR-α and adiponectin were in adipose tissue. In the HFD + PGBR group, the PGBR regulated the levels of TG, TC, HDL, Non-HDL, AI and adipocytokines. PGBR increased more cholesterol and bile acid exhaust in feces. The SREBP-1, SCD-1, FAS, HMGCR, LDLR, CYP7α1 and PPAR-α proteins in the liver; and the SREBP-1, SCD-1, FAS, PPAR-α and adiponectin proteins in adipose tissue were reversed by PGBR. Taken together, PGBR can improve lipid synthesis and metabolism, and we suggest PGBR is a recommendable food for controlling hyperlipidemia.

Transcriptional signatures of unfolded protein response implicate the limitation of animal models in pathophysiological studies

Background

The unfolded protein response (UPR) refers to intracellular stress signaling pathways that protect cells from the stress caused by accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER). The UPR signaling is crucially involved in the initiation and progression of a variety of human diseases by modulating transcriptional and translational programs of the stressed cells. In this study, we analyzed the gene expression signatures of primary stress sensors and major mediators of UPR pathways in a variety of tissues/organs of human and murine species.

Methods

We first analyzed protein sequence similarities of major UPR transducers and mediators of human and murine species, and then examined their gene expression profiles in 26 human and mouse common tissues based on the microarray datasets of public domains. The differential expression patterns of the UPR genes in human diseases were delineated. The involvements of the UPR genes in mouse pathology were also analyzed with mouse gene knockout models.

Results

The results indicated that expression patterns and pathophysiologic involvements of the major UPR stress sensors and mediators significantly differ in 26 common tissues/organs of human and murine species. Gene expression profiles suggest that the IRE1α/XBP1-mediated UPR pathway is induced in secretory and metabolic tissues or organs. While deletion of the UPR trans-activator XBP1 leads to pathological phenotypes in mice, alteration in XBP1 is less associated with human disease conditions.

Conclusions

Expression signatures of the major UPR genes differ among tissues or organs and among human and mouse species. The differential induction of the UPR pathways reflects the pathophysiologic differences of tissues or organs. The difference in UPR induction between human and mouse suggests the limitation of using animal models to study human pathophysiology or drugology associated with environmental stress.

Source and role of intestinally derived lysophosphatidic acid in dyslipidemia and atherosclerosis

We previously reported that i) a Western diet increased levels of unsaturated lysophosphatidic acid (LPA) in small intestine and plasma of LDL receptor null (LDLR(-/-)) mice, and ii) supplementing standard mouse chow with unsaturated (but not saturated) LPA produced dyslipidemia and inflammation. Here we report that supplementing chow with unsaturated (but not saturated) LPA resulted in aortic atherosclerosis, which was ameliorated by adding transgenic 6F tomatoes. Supplementing chow with lysophosphatidylcholine (LysoPC) 18:1 (but not LysoPC 18:0) resulted in dyslipidemia similar to that seen on adding LPA 18:1 to chow. PF8380 (a specific inhibitor of autotaxin) significantly ameliorated the LysoPC 18:1-induced dyslipidemia. Supplementing chow with LysoPC 18:1 dramatically increased the levels of unsaturated LPA species in small intestine, liver, and plasma, and the increase was significantly ameliorated by PF8380 indicating that the conversion of LysoPC 18:1 to LPA 18:1 was autotaxin dependent. Adding LysoPC 18:0 to chow increased levels of LPA 18:0 in small intestine, liver, and plasma but was not altered by PF8380 indicating that conversion of LysoPC 18:0 to LPA 18:0 was autotaxin independent. We conclude that i) intestinally derived unsaturated (but not saturated) LPA can cause atherosclerosis in LDLR(-/-) mice, and ii) autotaxin mediates the conversion of unsaturated (but not saturated) LysoPC to LPA.

Impaired cholesterol metabolism and enhanced atherosclerosis in clock mutant mice

BACKGROUND

Clock is a key transcription factor that positively controls circadian regulation. However, its role in plasma cholesterol homeostasis and atherosclerosis has not been studied.

METHODS AND RESULTS

We show for the first time that dominant-negative Clock mutant protein (Clock(Δ19/Δ19)) enhances plasma cholesterol and atherosclerosis in 3 different mouse models. Detailed analyses revealed that Clk(Δ19/Δ19)Apoe(-/-) mice display hypercholesterolemia resulting from the accumulation of apolipoprotein B48-containing cholesteryl ester-rich lipoproteins. Physiological studies showed that enhanced cholesterol absorption by the intestine contributes to hypercholesterolemia. Molecular studies indicated that the expression of Niemann Pick C1 Like 1, Acyl-CoA:Cholesterol acyltransferase 1, and microsomal triglyceride transfer protein in the intestines of Clk(Δ19/Δ19)Apoe(-/-) mice was high and that enterocytes assembled and secreted more chylomicrons. Furthermore, we identified macrophage dysfunction as another potential cause of increased atherosclerosis in Clk(Δ19/Δ19)Apoe(-/-) mice. Macrophages from Clk(Δ19/Δ19)Apoe(-/-) mice expressed higher levels of scavenger receptors and took up more modified lipoproteins compared with Apoe(-/-) mice, but they expressed low levels of ATP binding casette protein family A member 1 and were defective in cholesterol efflux. Molecular studies revealed that Clock regulates ATP binding casette protein family A member 1 expression in macrophages by modulating upstream transcription factor 2 expression.

CONCLUSIONS

Clock(Δ19/Δ19) protein enhances atherosclerosis by increasing intestinal cholesterol absorption, augmenting uptake of modified lipoproteins by macrophages, and reducing cholesterol efflux from macrophages. These studies establish that circadian Clock activity is crucial in maintaining low plasma cholesterol levels and in reducing atherogenesis in mice.

Regulating intestinal function to reduce atherogenic lipoproteins

Significant knowledge regarding different molecules involved in the transport of dietary fat into the circulation has been garnered. Studies point to the possibility that accumulation of intestine-derived lipoproteins in the plasma could contribute to atherosclerosis. This article provides a brief overview of dietary lipid metabolism and studies in mice supporting the hypothesis that intestinal lipoproteins contribute to atherosclerosis. Deficiencies in lipoprotein lipase and Gpihbp1, and overexpression of heparanse in mice, are associated with increases in atherosclerosis, suggesting that defects in catabolism of larger lipoproteins in the plasma contribute to atherosclerosis. Furthermore, inositol-requiring enzyme 1β-deficient mice that produce more intestinal lipoproteins also develop more atherosclerosis. Thus, increases in plasma intestinal lipoproteins due to either overproduction or reduced catabolism result in augmented atherosclerosis. Intestinal lipoproteins tend to adhere strongly to subendothelial proteoglycans, elicit an inflammatory response by endothelial cells and activate macrophages, contributing to the initiation and progression of the disease. Thus, molecules that reduce intestinal lipid absorption can be useful in lowering atherosclerosis.

MicroRNA-30c reduces hyperlipidemia and atherosclerosis in mice by decreasing lipid synthesis and lipoprotein secretion

Hyperlipidemia is a risk factor for various cardiovascular and metabolic disorders. Overproduction of lipoproteins, a process critically dependent on microsomal triglyceride transfer protein (MTP), can contribute to hyperlipidemia. We show that microRNA-30c (miR-30c) interacts with the 3′-untranslated region of the MTP mRNA and induces degradation leading to reductions in its activity and media apolipoprotein B. Further, miR-30c reduces hyperlipidemia and atherosclerosis in Western diet fed mice by decreasing lipid synthesis and secretion of triglyceride-rich apoB-containing lipoproteins. Therefore, miR-30c coordinately reduces lipid biosynthesis and lipoprotein secretion to control hepatic and plasma lipids and might be useful in treating hyperlipidemias and associated disorders.

Direct association of unfolded proteins with mammalian ER stress sensor, IRE1β

IRE1, an ER-localized transmembrane protein, plays a central role in the unfolded protein response (UPR). IRE1 senses the accumulation of unfolded proteins in its luminal domain and transmits a signal to the cytosolic side through its kinase and RNase domains. Although the downstream pathways mediated by two mammalian IRE1s, IRE1α and IRE1β, are well documented, their luminal events have not been fully elucidated. In particular, there have been no reports on how IRE1β senses the unfolded proteins. In this study, we performed a comparative analysis to clarify the luminal event mediated by the mammalian IRE1s. Confocal fluorescent microscopy using GFP-fused IRE1s revealed that IRE1β clustered into discrete foci upon ER stress. Also, fluorescence correlation spectroscopy (FCS) analysis in living cells indicated that the size of the IRE1β complex is robustly increased upon ER stress. Moreover, unlike IRE1α, the luminal domain of IRE1β showed anti-aggregation activity in vitro, and IRE1β was coprecipitated with the model unfolded proteins in cells. Strikingly, association with BiP was drastically reduced in IRE1β, while IRE1α was associated with BiP and dissociated upon ER stress. This is the first report indicating that, differently from IRE1α, the luminal event mediated by IRE1β involves direct interaction with unfolded proteins rather than association/dissociation with BiP, implying an intrinsic diversity in the sensing mechanism of mammalian sensors.