Bile acids-mediated intracellular cholesterol transport promotes intestinal cholesterol absorption and NPC1L1 recycling.

Niemann-Pick C1-like 1 (NPC1L1) is essential for intestinal cholesterol absorption. Together with the cholesterol-rich and Flotillin-positive membrane microdomain, NPC1L1 is internalized via clathrin-mediated endocytosis and transported to endocytic recycling compartment (ERC). When ERC cholesterol level decreases, NPC1L1 interacts with LIMA1 and moves back to plasma membrane. However, how cholesterol leaves ERC is unknown. Here, we find that, in male mice, intracellular bile acids facilitate cholesterol transport to other organelles, such as endoplasmic reticulum, in a non-micellar fashion. When cholesterol level in ERC is decreased by bile acids, the NPC1L1 carboxyl terminus that previously interacts with the cholesterol-rich membranes via the A1272LAL residues dissociates from membrane, exposing the Q1277KR motif for LIMA1 recruitment. Then NPC1L1 moves back to plasma membrane. This study demonstrates an intracellular cholesterol transport function of bile acids and explains how the substantial amount of cholesterol in NPC1L1-positive compartments is unloaded in enterocytes during cholesterol absorption.

Inhibition of ASGR1 decreases lipid levels by promoting cholesterol excretion.

High cholesterol is a major risk factor for cardiovascular disease1. Currently, no drug lowers cholesterol through directly promoting cholesterol excretion. Human genetic studies have identified that the loss-of-function Asialoglycoprotein receptor 1 (ASGR1) variants associate with low cholesterol and a reduced risk of cardiovascular disease2. ASGR1 is exclusively expressed in liver and mediates internalization and lysosomal degradation of blood asialoglycoproteins3. The mechanism by which ASGR1 affects cholesterol metabolism is unknown. Here, we find that Asgr1 deficiency decreases lipid levels in serum and liver by stabilizing LXRα. LXRα upregulates ABCA1 and ABCG5/G8, which promotes cholesterol transport to high-density lipoprotein and excretion to bile and faeces4, respectively. ASGR1 deficiency blocks endocytosis and lysosomal degradation of glycoproteins, reduces amino-acid levels in lysosomes, and thereby inhibits mTORC1 and activates AMPK. On one hand, AMPK increases LXRα by decreasing its ubiquitin ligases BRCA1/BARD1. On the other hand, AMPK suppresses SREBP1 that controls lipogenesis. Anti-ASGR1 neutralizing antibody lowers lipid levels by increasing cholesterol excretion, and shows synergistic beneficial effects with atorvastatin or ezetimibe, two widely used hypocholesterolaemic drugs. In summary, this study demonstrates that targeting ASGR1 upregulates LXRα, ABCA1 and ABCG5/G8, inhibits SREBP1 and lipogenesis, and therefore promotes cholesterol excretion and decreases lipid levels.

Ablation of Plasma Prekallikrein Decreases Low-Density Lipoprotein Cholesterol by Stabilizing Low-Density Lipoprotein Receptor and Protects Against Atherosclerosis.

BACKGROUND: High blood cholesterol accelerates the progression of atherosclerosis, which is an asymptomatic process lasting for decades. Rupture of atherosclerotic plaques induces thrombosis, which results in myocardial infarction or stroke. Lowering cholesterol levels is beneficial for preventing atherosclerotic cardiovascular disease. METHODS: Low-density lipoprotein (LDL) receptor (LDLR) was used as bait to identify its binding proteins in the plasma, and the coagulation factor prekallikrein (PK; encoded by the KLKB1 gene) was revealed. The correlation between serum PK protein content and lipid levels in young Chinese Han people was then analyzed. To investigate the effects of PK ablation on LDLR and lipid levels in vivo, we genetically deleted Klkb1 in hamsters and heterozygous Ldlr knockout mice and knocked down Klkb1 using adeno-associated virus-mediated shRNA in rats. The additive effect of PK and proprotein convertase subtilisin/kexin 9 inhibition also was evaluated. In addition, we applied the anti-PK neutralizing antibody that blocked the PK and LDLR interaction in mice. Mice lacking both PK and apolipoprotein e (Klkb1-/-Apoe-/-) were generated to assess the role of PK in atherosclerosis. RESULTS: PK directly bound LDLR and induced its lysosomal degradation. The serum PK concentrations positively correlated with LDL cholesterol levels in 198 young Chinese Han adults. Genetic depletion of Klkb1 increased hepatic LDLR and decreased circulating cholesterol in multiple rodent models. Inhibition of proprotein convertase subtilisin/kexin 9 with evolocumab further decreased plasma LDL cholesterol levels in Klkb1-deficient hamsters. The anti-PK neutralizing antibody could similarly lower plasma lipids through upregulating hepatic LDLR. Ablation of Klkb1 slowed the progression of atherosclerosis in mice on Apoe-deficient background. CONCLUSIONS: PK regulates circulating cholesterol levels through binding to LDLR and inducing its lysosomal degradation. Ablation of PK stabilizes LDLR, decreases LDL cholesterol, and prevents atherosclerotic plaque development. This study suggests that PK is a promising therapeutic target to treat atherosclerotic cardiovascular disease.

Feeding induces cholesterol biosynthesis via the mTORC1-USP20-HMGCR axis.

Cholesterol is an essential lipid and its synthesis is nutritionally and energetically costly1,2. In mammals, cholesterol biosynthesis increases after feeding and is inhibited under fasting conditions3. However, the regulatory mechanisms of cholesterol biosynthesis at the fasting-feeding transition remain poorly understood. Here we show that the deubiquitylase ubiquitin-specific peptidase 20 (USP20) stabilizes HMG-CoA reductase (HMGCR), the rate-limiting enzyme in the cholesterol biosynthetic pathway, in the feeding state. The post-prandial increase in insulin and glucose concentration stimulates mTORC1 to phosphorylate USP20 at S132 and S134; USP20 is recruited to the HMGCR complex and antagonizes its degradation. The feeding-induced stabilization of HMGCR is abolished in mice with liver-specific Usp20 deletion and in USP20(S132A/S134A) knock-in mice. Genetic deletion or pharmacological inhibition of USP20 markedly decreases diet-induced body weight gain, reduces lipid levels in the serum and liver, improves insulin sensitivity and increases energy expenditure. These metabolic changes are reversed by expression of the constitutively stable HMGCR(K248R). This study reveals an unexpected regulatory axis from mTORC1 to HMGCR via USP20 phosphorylation and suggests that inhibitors of USP20 could be used to lower cholesterol levels to treat metabolic diseases including hyperlipidaemia, liver steatosis, obesity and diabetes.

IDOL G51S Variant Is Associated With High Blood Cholesterol and Increases Low-Density Lipoprotein Receptor Degradation.

OBJECTIVE: A high level of LDL-C (low-density lipoprotein cholesterol) is a major risk factor for cardiovascular disease. The E3 ubiquitin ligase named IDOL (inducible degrader of the LDLR [LDL receptor]; also known as MYLIP [myosin regulatory light chain interacting protein]) mediates degradation of LDLR through ubiquitinating its C-terminal tail. But the expression profile of IDOL differs greatly in the livers of mice and humans. Whether IDOL is able to regulate LDL-C levels in humans remains to be determined. Approach and Results: By using whole-exome sequencing, we identified a nonsynonymous variant rs149696224 in the IDOL gene that causes a G51S (Gly-to-Ser substitution at the amino acid site 51) from a Chinese Uygur family. Large cohort analysis revealed IDOL G51S carriers (+/G51S) displayed significantly higher LDL-C levels. Mechanistically, the G51S mutation stabilized IDOL protein by inhibiting its dimerization and preventing self-ubiquitination and subsequent proteasomal degradation. IDOL(G51S) exhibited a stronger ability to promote ubiquitination and degradation of LDLR. Adeno-associated virus-mediated expression of IDOL(G51S) in mouse liver decreased hepatic LDLR and increased serum levels of LDL-C, total cholesterol, and triglyceride. CONCLUSIONS: Our study demonstrates that IDOL(G51S) is a gain-of-function variant responsible for high LDL-C in both humans and mice. These results suggest that IDOL is a key player regulating cholesterol level in humans.

[Intestinal absorption of phenolic acids in Rhus chinensis extracts by in situ single-pass perfusion model in rats].

The intestinal absorption properties of four main effective components(gallic acid, ocinolglucoside, ethyl gallate and penta-O-galloyl-ß-D-glucose) in Rhus chinensis extracts were investigated by in situ single-pass intestinal perfusion model in rats. The liquid accumulation of perfusion was corrected by gravimetry. The HPLC method was established to determine the concentration of the four effective components in the intestinal perfusion. It showed significant differences(P<0.05) in absorption rate constant(K_a) and effective permeability(P_(eff)) among the three concentrations of components, and the absorption of the four effective components in different intestinal segments was saturated at high concentrations. At the same concentration, there were significant differences in K_a and P_(eff) of the four components in each intestinal segment(P<0.05). The order of K_a and P_(eff) of the four components in the intestine was penta-O-galloyl-ß-D-glucose>ethyl gallate>gallic acid>ocinolglucoside, with significant differences between them(P<0.05). In conclusion, gallic acid, orpheolglucoside, ethyl gallate and pentacyl-glucose could be absorbed in the whole intestine. Their absorption rate and permeation ability were related to the intestinal section and the perfusate concentration. These results indicated potential active transport or facilitated diffusion in the intestinal transport process of the four effective components.

[Preparation of Rhus chinensis total phenolic acid pellets by extrusion-spheronisation method].

Extrusion-spheronisation method was used to prepare Rhus chinensis total phenolic acid pellets. The formula and preparation of R. chinensis total phenolic acid pellets were optimized. The formulas( drug loading capacity,diluent,wetting agent and anti-sticking agent) were determined by the single factor test with yield,appearance and performance as the indexes. The preparation was optimized by Box-Behnken design and response surface method,with the rate of extrusion,rate of spheronization and time of spheronization as the independent variables and the overall desirability value of yield,friability and roundness as the dependent variables. The optimal formula of pellets was as follows: drug loading capacity 28. 7%,MCC-lactose 9 ∶1,silicon dioxide as anti-sticking agent,and 60% ethanol as wetting agent. The optimal preparation was determined as follows: the rate of extrusion was 43 r·min-1,the rate of spheronization was 1 800 r·min-1,and the time of spheronization was 4 min. The absolute deviation between predicted value and estimated value under the conditions was less than 5. 0%,with a high degree of model fit. The preparation parameters obtained were accurate,reliable and reproducible. Under scanning electron microscopy( SEM),R. chinensis total phenolic acid pellets were uniform in diameter,round and smooth. The optimal formulation and process are stable and feasible for preparing R. chinensis total phenolic acid pellets.

[Overview of chronic myelogenous leukemia and its current diagnosis and treatment patterns in 15 hospitals in China.].

OBJECTIVE: To explore demographic characteristics, current diagnosis and treatment patterns of chronic myelogenous leukemia (CML) patients in China. METHODS: Data of hospitalized CML patients in 2005 whole year and outpatient information (July 1 through September 30, 2006) from 15 hospitals throughout China were analyzed. RESULTS: A total of 1824 CML cases were analyzed, including 722 inpatients and 1102 outpatients. The male/female ratio was 1.78:1. The median age at diagnosis was 40.02 (2.45 - 83.29) years old, 90.41% of the patients were diagnosed at chronic phase. Proportion of accelerated phase or blast crisis patients increased to 21.66% during study period. 93.20% of the patients received blood routine and bone marrow morphologic examination at diagnosis and in monitoring; 70.29% were performed cytogenetic analysis and 51.54% performed molecular measurement in addition. The most common therapy for CML treatment was hydroxycarbamide. The proportion of patients treated with imatinib and interferon was 37.45% and 25.55%, respectively. Of 722 inpatients, 164 (22.72%) received hemotopoietic stem cell transplantation (HSCT). The proportions of accelerated phase and blast crisis patients treated with imatinib were 48.28% and 48.42%, respectively, being significantly higher than that of chronic phase patients (35.9%) (P < 0.05). The mean imatinib dosage administered in the three phases patients did not differ significantly. Imatinib resistance rates were 6.87% and 16.28% for outpatient and inpatient, respectively. In the outpatient group, the primary resistance to imatinib occurred comparably to the secondary resistance (68.75%), while primary resistance was predominant in inpatient group (65.71%). The intolerance rates of imatinib for outpatient and inpatient were 3.21%, 11.63%, respectively. The majority of patients treated with imatinb were not monitored in time: 63.38% patients evaluated hematologic response after 3 months of treatment, proportions of patients received cytogenetic examination after 6 months and 12 months of treatment were 41.41% and 27.35%, respectively. Mean cost for HSCT was 213 092 +/- 125 890 RMB. CONCLUSIONS: CML in China tends to afflict younger population than in Western countries. Most patients were diagnosed in the chronic phase. Due to restriction of financial support, only one third of CML patients were treated with imatinib, and the majority of the treated were not monitored in time. Clinicians should pay attention to resistance and intolerance to imatinib treatment in accelerated phase or blast crisis patients.

[Tryptase relation to VEGF in acute leukemia].

In order to investigate the role of tryptase in angiogenesis of acute leukemia (AL), the expressions of tryptase and vascular endothelial growth factor (VEGF) in leukemic cells from 61 patients with AL were examined by using immunocytochemical method, and the correlation between tryptase and VEGF was analyzed. The results showed that tryptase positive expression was found in 15 out of 51 patients with acute myeloid leukemia (AML) (M(1) 1/3, M(2) 7/15, M(3) 5/20, M(5) 2/8). Tryptase positive expression was 29.4% in AML. However, none of 10 patients with acute lymphocytic leukemia (ALL) showed tryptase expression. There were no correlations between the amounts of cells with tryptase expression and patient age, WBC count, numbers of blood or marrow myeloblasts and neutrophil POX. VEGF expression was revealed in 41 patients with AML (80.4%) and only 3 with ALL (30%). Significant correlation has been found between the expression of tryptase and that of VEGF in AML-M(2) (r = 0.65, P < 0.05). It is concluded that tryptase appears to be a myeloid-specific marker in AML and may be involved in the angiogenesis of AML-M(2).