20 results on '"Man WC"'
Search Results
2. How hospital autonomy affects provider payment reform effectiveness.
- Author
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Tsuei SH and Yip WC
- Subjects
- Humans, China, Reimbursement Mechanisms, Fee-for-Service Plans, Economics, Hospital, Efficiency, Organizational, Health Expenditures, Health Care Reform
- Abstract
Background: Provider payment reforms (PPRs) have demonstrated mixed results for improving health system efficiency. Since PPRs require health care organisations to interpret and implement policies, the organizational characteristics of hospitals may affect the effectiveness of PPRs. Hospitals with more autonomy have the flexibility to respond to PPRs more efficiently, but they may not if the autonomy previously facilitated behaviours that counter the PPR's objective. This study examines whether hospitals with higher autonomy responds to PPRs more effectively., Methods: We used data from a matched-pair, cluster randomized controlled PPR intervention in a resource-limited Chinese province between 2014 and 2018. The intervention reformed the reimbursement method from the publicly administered New Cooperative Medical Scheme (NCMS) from fee-for-service to global budget. We interacted measures of hospital autonomy over surplus, hiring, and procurement (drugs, consumables, equipment, and overall index) with the difference-in-difference estimator to examine how autonomy moderated the intervention's effect., Results: Autonomy over surplus (p < 0.01) and procurement of equipment (p < 0.01) were associated with relatively faster NCMS expenditure growth, demonstrating worse PPR response. They were also associated with higher expenditure shifting to out-of-pocket expenditures (p > 0.05). Post hoc analysis suggests that hospitals with surplus autonomy had higher OOP per admission (p < 0.01), suggesting profiteering tendencies. Other dimensions of autonomy demonstrated imprecise association., Discussion: Hospitals with more autonomy may not necessarily respond more effectively to PPRs that incentivise efficiency when they had previously been encouraged to maximise profit. Policymakers should assess the extent of perverse incentives before granting autonomy and adjust the incentives accordingly., (© 2024 The Authors. The International Journal of Health Planning and Management published by John Wiley & Sons Ltd.)
- Published
- 2024
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3. Delayed Pneumothorax: A Potential Complication Of Transbronchial Lung Biopsy.
- Author
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Narula N, Siddiqui F, Siddiqui AH, Man WC, and Chalhoub M
- Abstract
The purpose of this article is to report a case of secondary tension pneumothorax presenting seven weeks post Transbronchial Lung biopsy. A 62 year old male with a known history of germ cell tumor was found to have a left-sided pneumothorax which later complicated to a tension pneumothorax.To the best of our knowledge this is the second case being reported for a delayed pneumothorax post a Transbronchial Lung Biopsy .The purpose of this case report is to create awareness among physicians to consider this diagnosis even at a later stage and the importance of patient education regarding the signs and symptoms of pneumothorax. Our case adds to the medical literature, a new presentation of a rare complication of delayed pneumothorax post TBB.
- Published
- 2018
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4. Realigning demand and supply side incentives to improve primary health care seeking in rural China.
- Author
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Powell-Jackson T, Yip WC, and Han W
- Subjects
- Adolescent, Adult, Capitation Fee organization & administration, Child, China, Female, Health Services statistics & numerical data, Humans, Insurance Benefits economics, Male, Middle Aged, National Health Programs organization & administration, Primary Health Care organization & administration, Quality Indicators, Health Care, Reimbursement, Incentive economics, Motivation, National Health Programs economics, Patient Acceptance of Health Care statistics & numerical data, Primary Health Care economics, Rural Population statistics & numerical data
- Abstract
China's recent and ambitious health care reform involves a shift from the reliance on markets to the reaffirmation of the central role of the state in the financing and provision of services. In collaboration with the Government of the Ningxia province, we examined the impact of two key features of the reform on health care utilisation using panel household data. The first policy change was a redesign of the rural insurance benefit package, with an emphasis on reorientating incentives away from inpatient towards outpatient care. The second policy change involved a shift from a fee-for-service payment method to a capitation budget with pay-for-performance amongst primary care providers. We find that the insurance intervention, in isolation, led to a 47% increase in the use of outpatient care at village clinics and greater intensity of treatment (e.g. injections). By contrast, the two interventions in combination showed no effect on health care use over and above that generated by the redesign of the insurance benefit package., (Copyright © 2014 John Wiley & Sons, Ltd.)
- Published
- 2015
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5. Early appraisal of China's huge and complex health-care reforms.
- Author
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Yip WC, Hsiao WC, Chen W, Hu S, Ma J, and Maynard A
- Subjects
- China, Clinical Governance, Cost-Benefit Analysis, Drug Prescriptions statistics & numerical data, Hospitals, Public economics, Hospitals, Public standards, Hospitals, Public trends, Humans, Outcome and Process Assessment, Health Care, Universal Health Insurance, Delivery of Health Care economics, Delivery of Health Care standards, Delivery of Health Care trends, Health Care Reform economics, Health Care Reform methods, Health Care Reform trends, Hospitals, Public organization & administration, Insurance Coverage, Insurance, Health economics, Insurance, Health organization & administration, Insurance, Health standards, Insurance, Health trends
- Abstract
China's 3 year, CN¥850 billion (US$125 billion) reform plan, launched in 2009, marked the first phase towards achieving comprehensive universal health coverage by 2020. The government's undertaking of systemic reform and its affirmation of its role in financing health care together with priorities for prevention, primary care, and redistribution of finance and human resources to poor regions are positive developments. Accomplishing nearly universal insurance coverage in such a short time is commendable. However, transformation of money and insurance coverage into cost-effective services is difficult when delivery of health care is hindered by waste, inefficiencies, poor quality of services, and scarcity and maldistribution of the qualified workforce. China must reform its incentive structures for providers, improve governance of public hospitals, and institute a stronger regulatory system, but these changes have been slowed by opposition from stakeholders and lack of implementation capacity. The pace of reform should be moderated to allow service providers to develop absorptive capacity. Independent, outcome-based monitoring and evaluation by a third-party are essential for mid-course correction of the plans and to make officials and providers accountable., (Copyright © 2012 Elsevier Ltd. All rights reserved.)
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- 2012
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6. Transforming growth interacting factor expression in leiomyoma compared with myometrium.
- Author
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Yen-Ping Ho J, Man WC, Wen Y, Polan ML, Shih-Chu Ho E, and Chen B
- Subjects
- Female, Gene Expression Regulation, Neoplastic drug effects, Homeodomain Proteins metabolism, Humans, Leiomyoma metabolism, Leiomyoma pathology, Myometrium drug effects, Myometrium pathology, Plasminogen Activator Inhibitor 1 genetics, Plasminogen Activator Inhibitor 1 metabolism, RNA, Messenger metabolism, Repressor Proteins metabolism, Signal Transduction drug effects, Signal Transduction genetics, Transforming Growth Factor beta1 pharmacology, Tumor Cells, Cultured, Uterine Neoplasms metabolism, Uterine Neoplasms pathology, Homeodomain Proteins genetics, Leiomyoma genetics, Myometrium metabolism, Repressor Proteins genetics, Uterine Neoplasms genetics
- Abstract
Objective: To investigate the expression of transforming growth interacting factor (TGIF), a Smad transcriptional corepressor, in leiomyoma and matched myometrial tissue samples and the effect of TGIF overexpression in myometrial cells., Design: Experimental study., Setting: Tertiary university hospital., Patient(s): Uterine leiomyoma and myometrial tissues from 16 patients., Intervention(s): None., Main Outcome Measure(s): The distribution of TGIF in leiomyoma and myometrial tissues by immunohistochemistry stain, mRNA, and protein expression levels by real-time quantitative polymerase chain-reaction (QPCR) and Western blot. Transcriptional regulation of TGIF in myometrial cells with overexpressed TGIF., Result(s): Although TGIF is present in the smooth muscle cells of the leiomyoma and the myometrium, it is not found in the extracellular matrix. The TGIF mRNA and protein expressions were statistically significantly higher in the leiomyoma compared with the matched, unaffected myometrial tissues in both phases of the menstrual cycle. There were no differences in mRNA or protein expression throughout the menstrual cycle. Overexpression of TGIF protein in myometrial cells statistically significantly suppressed up-regulation of plasminogen activator inhibitor (PAI-1) induced by TGF-beta1 treatment., Conclusion(s): Expression of TGIF is increased in leiomyoma compared with myometrium. This increase in TGIF expression is not affected by endogenous ovarian hormones. Thus, TGIF is a potential repressor of TGF-beta pathways in myometrial cells., (Copyright (c) 2010 American Society for Reproductive Medicine. Published by Elsevier Inc. All rights reserved.)
- Published
- 2010
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7. Realignment of incentives for health-care providers in China.
- Author
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Yip WC, Hsiao W, Meng Q, Chen W, and Sun X
- Subjects
- China, Community Health Centers economics, Community Health Centers organization & administration, Delivery of Health Care economics, Health Services Misuse, Humans, Primary Health Care economics, Primary Health Care organization & administration, Delivery of Health Care organization & administration, Fee-for-Service Plans, Health Care Reform, Reimbursement, Incentive
- Abstract
Inappropriate incentives as part of China's fee-for-service payment system have resulted in rapid cost increase, inefficiencies, poor quality, unaffordable health care, and an erosion of medical ethics. To reverse these outcomes, a strategy of experimentation to realign incentives for providers with the social goals of improvement in quality and efficiency has been initiated in China. This Review shows how lessons that have been learned from international experiences have been improved further in China by realignment of the incentives for providers towards prevention and primary care, and incorporation of a treatment protocol for hospital services. Although many experiments are new, preliminary evidence suggests a potential to produce savings in costs. However, because these experiments have not been scientifically assessed in China, evidence of their effects on quality and health outcome is largely missing. Although a reform of the provider's payment can be an effective short-term strategy, professional ethics need to be re-established and incentives changed to alter the profit motives of Chinese hospitals and physicians alike. When hospitals are given incentives to achieve maximum profit, incentives for hospitals and physicians must be separated., (Copyright 2010 Elsevier Ltd. All rights reserved.)
- Published
- 2010
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8. Is lysyl oxidase-like protein-1, alpha-1 antitrypsin, and neutrophil elastase site specific in pelvic organ prolapse?
- Author
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Man WC, Ho JY, Wen Y, Sokol ER, Polan ML, and Chen B
- Subjects
- Adult, Aged, Aged, 80 and over, Female, Humans, Middle Aged, Amino Acid Oxidoreductases metabolism, Leukocyte Elastase metabolism, Pelvic Organ Prolapse enzymology, Vagina enzymology, alpha 1-Antitrypsin metabolism
- Abstract
Introduction and Hypothesis: We investigated whether the expression of alpha-1 antitrypsin (ATT), neutrophil elastase (NE), and lysyl oxidase-like protein 1 (LOXL-1) vary within the vagina in subjects with pelvic organ prolapse (POP)., Methods: Biopsies were obtained from the anterior and posterior vaginal wall of 22 women with POP (> or =stage 2 by POP-Q). The subjects were grouped by the most prominent defect: cystocele, cystocele plus uterine prolapse, and rectocele. Comparative real-time PCR, Western blotting, and NE enzyme activity assay were performed., Results: The ratio of anterior and posterior vaginal wall ATT, NE, and LOXL-1 expression varied between individuals within the same defect group., Conclusions: ATT, NE, and LOXl-1 expression was variable among different biopsy sites in the vagina. No consistent pattern was present when the subjects were grouped by the most prominent defect. We recommend careful consideration of biopsy sites in future studies on POP to enhance reproducibility of data.
- Published
- 2009
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9. Is alpha2-macroglobulin important in female stress urinary incontinence?
- Author
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Wen Y, Man WC, Sokol ER, Polan ML, and Chen BH
- Subjects
- Adult, Cells, Cultured, Female, Fibroblasts metabolism, Fibroblasts pathology, Follicular Phase metabolism, Humans, Luteal Phase metabolism, Menstrual Cycle metabolism, Middle Aged, Premenopause metabolism, Protease Inhibitors metabolism, RNA, Messenger metabolism, Urinary Incontinence, Stress pathology, Vagina pathology, alpha-Macroglobulins genetics, Urinary Incontinence, Stress metabolism, Vagina metabolism, alpha-Macroglobulins metabolism
- Abstract
Background: Loss of mechanical stability of the urethra and bladder is thought to be important in the development of stress urinary incontinence (SUI). The vaginal wall is the main supporting tissue for pelvic organs and changes in components of supporting tissues are known to be involved in the pathophysiology of SUI., Methods: We evaluated changes in expression of alpha2-macroglobulin (alpha2-M), a protease inhibitor, in vaginal wall tissues from premenopausal women (aged 42-45 years) with SUI (n = 28) compared with menstrual cycle-matched continent women (controls, n = 29). The distribution of alpha2-M in vaginal wall tissues and fibroblasts was analysed by immunohistochemistry and immunofluorescence. Expression levels of alpha2-M mRNA and protein was determined by relative real-time quantitative PCR and enzyme-linked immunosorbent assay, respectively. Protease inhibition was measured to assess bioactivity., Results: Vaginal wall tissues do express alpha2-M. Expression of alpha2-M mRNA and protein was significantly higher in tissues from controls compared to women with SUI in both proliferative and secretory phases (P < 0.05). Protease inhibitory activity of alpha2-M was significantly higher in tissues from controls compared to women with SUI in the secretory phase (P < 0.05), but we found no difference in the proliferative phase between groups. alpha2-M protein level was lower in the proliferative phase than the secretory phase in both controls and SUI patients, while for alpha2-M mRNA this was found only in controls., Conclusions: Decreased expression of alpha2-M mRNA and protein and protease inhibitory activity in the vaginal wall tissues of women with SUI may contribute to the development of SUI.
- Published
- 2008
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10. Colocalization of SCD1 and DGAT2: implying preference for endogenous monounsaturated fatty acids in triglyceride synthesis.
- Author
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Man WC, Miyazaki M, Chu K, and Ntambi J
- Subjects
- Animals, Blotting, Western methods, Diacylglycerol O-Acyltransferase genetics, Flow Cytometry methods, Fluorescence Resonance Energy Transfer methods, HeLa Cells, Humans, Immunoprecipitation methods, Mice, Mice, Inbred Strains, Microscopy, Confocal methods, Mitochondrial Membranes metabolism, Models, Biological, Recombinant Fusion Proteins genetics, Recombinant Fusion Proteins metabolism, Stearoyl-CoA Desaturase genetics, Diacylglycerol O-Acyltransferase metabolism, Fatty Acids, Monounsaturated metabolism, Stearoyl-CoA Desaturase metabolism, Triglycerides biosynthesis
- Abstract
Stearoyl-coenzyme A desaturase (SCD) is an endoplasmic reticulum (ER) protein that catalyzes the Delta9-cis desaturation of saturated fatty acids. Mice with targeted disruption in SCD1 (Scd1(-/-)) have significant reduction in the tissue content of triglycerides, suggesting that monounsaturated fatty acids endogenously synthesized by SCD1 are important for triglyceride synthesis. Acyl-coenzyme A:diacylglycerol acyltransferase (DGAT) is the enzyme that catalyzes the final reaction in the synthesis of triglycerides. The lack of DGAT2, one of the two DGAT isoforms, results in almost a complete loss of tissue triglycerides. We hypothesize that SCD1 participates in triglyceride synthesis by providing a more accessible pool of monounsaturated fatty acids through substrate channeling. In this study, we test whether SCD1 is proximal to DGAT2 by colocalization study with confocal microscopy, coimmunoprecipitation, and fluorescence resonance energy transfer using HeLa cells as the model of study. All of the results suggest that SCD1 and DGAT2 are located very close to each other in the ER, which is a very important criterion for the channeling of substrate. By performing subcellular fractionation using mouse livers, we also show, for the first time, that SCD is present in the mitochondria-associated membrane.
- Published
- 2006
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11. Stearoyl-coenzyme A desaturase 1 deficiency protects against hypertriglyceridemia and increases plasma high-density lipoprotein cholesterol induced by liver X receptor activation.
- Author
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Chu K, Miyazaki M, Man WC, and Ntambi JM
- Subjects
- Animals, Base Sequence, DNA-Binding Proteins agonists, Humans, Hydrocarbons, Fluorinated, Lipid Metabolism drug effects, Lipids blood, Liver X Receptors, Mice, Molecular Sequence Data, Orphan Nuclear Receptors, Pregnane X Receptor, Protein Binding drug effects, Receptors, Cytoplasmic and Nuclear agonists, Receptors, Retinoic Acid metabolism, Receptors, Steroid metabolism, Response Elements drug effects, Response Elements genetics, Sequence Deletion genetics, Sterol Regulatory Element Binding Protein 1 deficiency, Sulfonamides pharmacology, Cholesterol, HDL blood, DNA-Binding Proteins metabolism, Hypertriglyceridemia pathology, Receptors, Cytoplasmic and Nuclear metabolism, Stearoyl-CoA Desaturase deficiency
- Abstract
Stearoyl-coenzyme A desaturase (SCD) is the rate-limiting enzyme necessary for the biosynthesis of monounsaturated fatty acids. In this study, we investigated the regulation of mouse SCD1 by liver X receptor (LXR) and its role in plasma lipoprotein metabolism upon LXR activation. In vivo, the SCD1 gene remained induced upon LXR activation in the absence of sterol regulatory element-binding protein 1c (SREBP-1c), a known transcriptional regulator of SCD1. Serial deletion and point mutation analyses in reporter gene assays, as well as a gel mobility shift assay, identified an LXR response element in the mouse SCD1 promoter. In addition, SCD1 deficiency prevented the hypertriglyceridemic effect and reduced hepatic triglyceride accumulation associated with LXR activation despite induced hepatic expression of SREBP-1c protein and several SREBP1c and LXR target genes involved in lipoprotein metabolism. Unlike wild-type mice, SCD1-deficient mice failed to elevate the hepatic triglyceride monounsaturated acid (MUFA)/saturated fatty acid (SFA) ratio despite induction of the SCD2 gene. Together, these findings suggest that SCD1 plays a pivotal role in the regulation of hepatic and plasma triglyceride accumulation, possibly by modulating the MUFA-to-SFA ratio. In addition, SCD1 deficiency also increased plasma high-density lipoprotein cholesterol levels induced by LXR activation.
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- 2006
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12. Incorporating inertia into multiagent systems.
- Author
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Man WC and Chau HF
- Abstract
We consider a model that demonstrates the crucial role of inertia and stickiness in multiagent systems, based on the minority game. The inertia of an agent is introduced into the game model by allowing agents to apply hypothesis testing when choosing their best strategies, thereby reducing their reactivity toward changes in the environment. We find by extensive numerical simulations that our game shows a remarkable improvement of global cooperation throughout the whole phase space. In other words, the maladaptation behavior due to over-reaction of agents is removed. These agents are also shown to be advantageous over the standard ones, which are sometimes too sensitive to attain a fair success rate. We also calculate analytically the minimum amount of inertia needed to achieve the above improvement. Our calculation is consistent with the numerical simulation results. Finally, we review some related works in the field that show similar behaviors and compare them to our work.
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- 2006
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13. Membrane topology of mouse stearoyl-CoA desaturase 1.
- Author
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Man WC, Miyazaki M, Chu K, and Ntambi JM
- Subjects
- Amino Acid Sequence, Amino Acids chemistry, Animals, Catalysis, Cell Membrane metabolism, Cysteine chemistry, DNA Primers chemistry, Endopeptidase K chemistry, Endoplasmic Reticulum metabolism, Epitopes chemistry, Fluorescent Antibody Technique, Indirect, HeLa Cells, Humans, Immunoblotting, Mice, Microscopy, Fluorescence, Molecular Sequence Data, Mutation, Octoxynol pharmacology, Plasmids metabolism, Protein Binding, Protein Conformation, Protein Isoforms, Protein Structure, Secondary, Protein Structure, Tertiary, Recombinant Proteins chemistry, Serine chemistry, Stearoyl-CoA Desaturase metabolism, Stearoyl-CoA Desaturase chemistry
- Abstract
Stearoyl-CoA desaturase (SCD) is an integral membrane protein anchored in the endoplasmic reticulum. It catalyzes the biosynthesis of monounsaturated fatty acids that are required for the synthesis of triglycerides, cholesteryl esters, and phospholipids. Four mouse isoforms of SCD (SCD1-4) and two human isoforms have been characterized. In the current study, we characterize the topology of the mouse SCD1 isoform. Hydropathy analysis of the 355-amino acid mouse SCD1 protein predicts that the protein contains four transmembrane domains (TMDs) and three loops connecting the membrane-spanning domains. To define the topology of the protein, recombinant SCD1 constructs containing epitope tags were transiently expressed in HeLa cells and analyzed by indirect immunofluorescence and cysteine derivatization. Our data provide evidence that the N and C termini of SCD1 are oriented toward the cytosol with four transmembrane domains separated by two very short hydrophilic loops in the ER lumen and one large hydrophilic loop in the cytosol. In addition, based on the previous observation that SCD is a thiol enzyme, we sought to investigate whether the cysteine residues were essential for enzyme activity through mutagenesis studies, and our data suggest that the cysteines in SCD are not catalytically essential.
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- 2006
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14. Memory is relevant in the symmetric phase of the minority game.
- Author
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Ho KH, Man WC, Chow FK, and Chau HF
- Abstract
Minority game is a simple-mined econophysical model capturing the cooperative behavior among selfish players. Previous investigations, which were based on numerical simulations up to about 100 players for a certain parameter alpha in the range 0.1 < approximately alpha < approximately 1, suggested that memory is irrelevant to the cooperative behavior of the minority game in the so-called symmetric phase. Here using a large scale numerical simulation up to about 3000 players in the parameter range 0.01 < approximately alpha < approximately 1, we show that the mean variance of the attendance in the minority game actually depends on the memory in the symmetric phase. We explain such dependence in the framework of crowd-anticrowd theory. Our findings conclude that one should not overlook the feedback mechanism buried under the correlation in the history time series in the study of minority game.
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- 2005
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15. Reduced adiposity and liver steatosis by stearoyl-CoA desaturase deficiency are independent of peroxisome proliferator-activated receptor-alpha.
- Author
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Miyazaki M, Dobrzyn A, Sampath H, Lee SH, Man WC, Chu K, Peters JM, Gonzalez FJ, and Ntambi JM
- Subjects
- AMP-Activated Protein Kinases, Animal Feed, Animals, Body Weight, Fatty Acids metabolism, Liver metabolism, Male, Mice, Mice, Transgenic, Mitochondria metabolism, Mitochondria, Liver metabolism, Multienzyme Complexes metabolism, Mutation, Oxygen metabolism, Palmitoyl Coenzyme A metabolism, Phosphorylation, Protein Isoforms, Protein Serine-Threonine Kinases metabolism, RNA metabolism, Time Factors, Transcription, Genetic, Triglycerides metabolism, Up-Regulation, Adipose Tissue metabolism, Dietary Fats, Liver pathology, Receptors, Cytoplasmic and Nuclear metabolism, Stearoyl-CoA Desaturase deficiency, Stearoyl-CoA Desaturase genetics, Transcription Factors metabolism
- Abstract
Stearoyl-CoA desaturase catalyzes the rate-limiting step in the biosynthesis of monounsaturated fatty acids, which are required for normal rates of synthesis of triglycerides, cholesterol esters, and phospholipids. Mice with a targeted disruption of the stearoyl-CoA desaturase 1 (SCD1) isoform are protected against diet and leptin deficiency-induced adiposity, have increased energy expenditure, and have up-regulated expression of hepatic genes encoding enzymes of fatty acid beta-oxidation. Because peroxisome proliferator-activated receptor-alpha (PPARalpha) is a key transcription factor that induces the transcription of fatty acid beta-oxidation and thermogenic genes, we hypothesized that the increased fatty acid oxidation observed in SCD1 deficiency is dependent on activation of the PPARalpha pathway. Here we show that mice nullizygous for SCD1 and PPARalpha are still protected against adiposity, have increased energy expenditure, and maintain high expression of PPARalpha target genes in the liver and brown adipose tissue. The SCD1 deficiency rescued hepatic steatosis of the PPARalpha(-/-) mice. The SCD1 mutation increased the phosphorylation of both AMP-activated protein kinase and acetyl-CoA carboxylase, thereby increasing CPT activity and stimulating the oxidation of liver palmitoyl-CoA in the PPARalpha null mice. The findings indicate that the reduced adiposity, reduced liver steatosis, increased energy expenditure, and increased expression of PPARalpha target genes associated with SCD1 deficiency are independent of activation of the PPARalpha pathway.
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- 2004
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16. Stearoyl-CoA desaturase 1 gene expression is necessary for fructose-mediated induction of lipogenic gene expression by sterol regulatory element-binding protein-1c-dependent and -independent mechanisms.
- Author
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Miyazaki M, Dobrzyn A, Man WC, Chu K, Sampath H, Kim HJ, and Ntambi JM
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- Animals, Fructose metabolism, Liver metabolism, Mice, Mice, SCID, Stearoyl-CoA Desaturase physiology, Sterol Regulatory Element Binding Protein 1, Triglycerides biosynthesis, CCAAT-Enhancer-Binding Proteins physiology, DNA-Binding Proteins physiology, Fructose administration & dosage, Gene Expression Regulation, Lipids biosynthesis, Stearoyl-CoA Desaturase genetics, Transcription Factors
- Abstract
Stearoyl-CoA desaturase (SCD) synthesizes oleate necessary for the biosynthesis of triglycerides and other lipids. Mice with a targeted disruption of the SCD1 gene are deficient in tissue oleate and have reduced expression of the sterol regulatory element-binding protein (SREBP) and its target genes. The SREBP-1c isoform is a known mediator of insulin action on hepatic gene expression, but its transcriptional effects due to glucose or fructose are still unclear. We found that fructose compared with glucose is a stronger inducer of SREBP-1c and lipogenic gene expression, causing a dramatic increase in hepatic triglyceride levels. However, when fed to the SCD1-/- mice, fructose failed to induce SREBP-1 or lipogenic genes and the triglyceride levels were not increased. Instead fructose feeding caused a decrease in hepatic glycogen and plasma glucose levels. The induction of SREBP-1 and lipogenic gene expression as well as the levels of liver triglycerides, glycogen, and plasma glucose was partially restored when the fructose diet was supplemented with very high levels of oleate (20% by weight) but not with palmitate, stearate, or linoleate. Fructose in a long term feeding induced the expression of SCD1 and that of other lipogenic genes in the liver of SREBP-1c-/- mice, and a further increase in expression of these genes occurred when the fructose diet was supplemented with oleate. Our observations demonstrated that oleate produced by SCD is necessary for fructose-mediated induction of lipogenic gene expression through SREBP-1c-dependent and -independent mechanisms and suggested that SCD1 gene expression is important in lipid and carbohydrate homeostasis.
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- 2004
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17. Identification and characterization of murine SCD4, a novel heart-specific stearoyl-CoA desaturase isoform regulated by leptin and dietary factors.
- Author
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Miyazaki M, Jacobson MJ, Man WC, Cohen P, Asilmaz E, Friedman JM, and Ntambi JM
- Subjects
- Amino Acid Sequence, Animal Nutritional Physiological Phenomena, Animals, Blotting, Northern, Carbohydrate Metabolism, Cell Line, DNA, Complementary metabolism, DNA-Binding Proteins, Diet, Fatty Acids metabolism, Fatty Acids, Unsaturated metabolism, Heart physiology, Humans, Leptin chemistry, Liver metabolism, Liver X Receptors, Mice, Mice, Obese, Microsomes metabolism, Models, Genetic, Molecular Sequence Data, Orphan Nuclear Receptors, Protein Isoforms, Protein Structure, Tertiary, RNA, Messenger metabolism, Receptors, Cytoplasmic and Nuclear metabolism, Sequence Homology, Amino Acid, Stearoyl-CoA Desaturase biosynthesis, Tissue Distribution, Leptin metabolism, Myocardium enzymology, Stearoyl-CoA Desaturase chemistry, Stearoyl-CoA Desaturase physiology
- Abstract
Stearoyl-CoA desaturase (SCD) is the rate-limiting enzyme in the biosynthesis of monounsaturated fatty acids. Thus far, three isoforms of SCD (SCD1, SCD2, and SCD3) have been identified and characterized. Regulation of the SCD1 isoform has been shown to be an important component of the metabolic actions of leptin in liver, but the effects of leptin on SCD isoforms in other tissues have not been investigated. We found that although the mRNA levels of SCD1 and SCD2 were not affected by leptin deficiency in the hearts of ob/ob mice, the SCD activity and levels of monounsaturated fatty acids were increased, implying the existence of another SCD isoform. This observation has led to the cDNA cloning and characterization of a fourth SCD isoform (SCD4) that is expressed exclusively in the heart. SCD4 encodes a 352-amino acid protein that shares 79% sequence identity with the SCD1, SCD2, and SCD3 isoforms. Liver X receptor alpha (LXR alpha) agonists and a high carbohydrate fat-free diet induced SCD4 expression, but unlike SCD1, SCD4 expression was not repressed by dietary polyunsaturated fatty acids. SCD4 mRNA levels were elevated 5-fold in the hearts of leptin-deficient ob/ob mice relative to wild type controls. Treatment of ob/ob mice with leptin decreased mRNA levels of SCD4, whereas levels of SCD1 and SCD2 were not affected. Furthermore, in the hearts of SCD1-deficient mice, SCD4 mRNA levels were induced 3-fold, whereas the levels of SCD2 were not altered. The current studies identify a novel heart-specific SCD isoform that demonstrates tissue-specific regulation by leptin and dietary factors.
- Published
- 2003
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18. Sterol regulatory element-binding proteins (SREBPs) as regulators of lipid metabolism: polyunsaturated fatty acids oppose cholesterol-mediated induction of SREBP-1 maturation.
- Author
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Kim HJ, Miyazaki M, Man WC, and Ntambi JM
- Subjects
- Animals, Blotting, Northern, Blotting, Western, Fatty Acid Synthases genetics, Female, Hydroxymethylglutaryl CoA Reductases genetics, Mice, Mice, Inbred C57BL, RNA, Messenger genetics, Sterol Regulatory Element Binding Protein 1, CCAAT-Enhancer-Binding Proteins physiology, Cholesterol metabolism, DNA-Binding Proteins physiology, Fatty Acids, Unsaturated metabolism, Transcription Factors
- Abstract
Cellular cholesterol and fatty acid metabolism in mammals is controlled by a family of transcription factors called sterol regulatory element-binding protein isoforms, three of which (SREBP-1a, 1c, and 2) are well characterized. These proteins, which are synthesized as precursors, are inserted into the endoplasmic reticulum (ER) membrane with both the amino and carboxylic acid domains facing the cytosolic face of the membrane. In sterol-deficient cells, proteolytic cleavage of SREBPs occurs, thereby releasing their N-terminal mature and active forms and enabling them to enter the nucleus, where they bind to the sterol regulatory response element (SRE) and/or E-box sequences and activate genes involved in cholesterol, triglyceride, and fatty acid biosynthesis. Of the three SREBP isoforms, SREBP-1c gene expression is induced by cholesterol and repressed by polyunsaturated fatty acids (PUFA). We have examined the changes in SREBP-1c mRNA and protein levels as well as the mRNA levels of several SREBP-1c target genes when a high-cholesterol diet is combined with diets rich in PUFA of the n-6 series. Our studies show that PUFA oppose the cholesterol-mediated SREBP-1 maturation without affecting the cholesterol-mediated increase of SREBP-1c mRNA and precursor protein. The decrease in SREBP-1 mature protein paralleled the decrease in mRNAs for genes of fatty acid and cholesterol biosynthesis, such as HMG-CoA synthase and fatty acid synthase, but interestingly gene expression of stearoyl-CoA desaturase 1 (SCD1) was instead induced. These studies suggest that the main point of control of PUFA-mediated suppression of lipogenic gene expression is the inhibition of SREBP-1 maturation. The studies also reveal that the induction of SCD1 gene expression by cholesterol occurs through a mechanism independent of SREBP-1 maturation.
- Published
- 2002
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19. Oleoyl-CoA is the major de novo product of stearoyl-CoA desaturase 1 gene isoform and substrate for the biosynthesis of the Harderian gland 1-alkyl-2,3-diacylglycerol.
- Author
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Miyazaki M, Kim HJ, Man WC, and Ntambi JM
- Subjects
- Animals, Blotting, Northern, Chromatography, Thin Layer, Fatty Acids metabolism, Immunoblotting, Lipid Metabolism, Mice, Mice, Transgenic, Models, Biological, Protein Binding, Protein Isoforms, RNA metabolism, Substrate Specificity, Time Factors, Acyl Coenzyme A biosynthesis, Acyl Coenzyme A chemistry, Diglycerides biosynthesis, Harderian Gland metabolism, Stearoyl-CoA Desaturase chemistry, Stearoyl-CoA Desaturase genetics
- Abstract
1-Alkyl-2,3-diacylglycerol (ADG) is a unique neutral lipid found in the eyeball-associated Harderian gland (HG) of the mouse and acts as a lubricant to facilitate eyelid movement. We found that the HG of the mice with a disruption in the gene for stearoyl-CoA desaturase 1 (SCD1) (SCD1-/-) is deficient in ADG. The amount of C20:1n-9, which is a major fatty acid of ADG, was reduced by greater than 90% despite normal elongase enzyme activity proposed to elongate it from C18:1n-9. HG from SCD1-/- mice exhibited high desaturase activity toward C16:0-CoA as substrate but had very low desaturase activity toward C18:0-CoA. Feeding diets containing high levels of oleate to the SCD1-/- mice did not increase the levels of C18:1n-9 or C20:1n-9 in the HG and failed to restore the ADG to the levels found in the HG of the wild-type mouse. De novo ADG synthesis as measured by the incorporation of [(3)H]glycerol and [(14)C]glucose was high in the SCD1+/+ mouse but was reduced by greater than 90% in the HG of SCD1-/- mouse. The deficiencies in the levels of ADG and C20:1n-9 were not compensated for by the expression of SCD2 and SCD3 isoforms in the HG of the SCD1-/- mouse. These observations demonstrate that SCD1-synthesized oleoyl-CoA is a major substrate required for the biosynthesis of normal levels of ADG and that the SCD isoforms present in the HG have different substrate specificity.
- Published
- 2001
- Full Text
- View/download PDF
20. Targeted disruption of stearoyl-CoA desaturase1 gene in mice causes atrophy of sebaceous and meibomian glands and depletion of wax esters in the eyelid.
- Author
-
Miyazaki M, Man WC, and Ntambi JM
- Subjects
- Animals, Atrophy, Cholesterol Esters metabolism, Diet, Isoenzymes deficiency, Isoenzymes genetics, Mice, Mice, Knockout genetics, Oleic Acid administration & dosage, Oleic Acid pharmacology, Skin drug effects, Skin metabolism, Stearoyl-CoA Desaturase genetics, Triglycerides metabolism, Esters metabolism, Eyelids metabolism, Meibomian Glands pathology, Sebaceous Glands pathology, Stearoyl-CoA Desaturase deficiency
- Abstract
Stearoyl-CoA desaturase (SCD) is a microsomal rate-limiting enzyme in the cellular synthesis of monounsaturated fatty acids (MUFA), mainly oleate (18:1) and palmitoleate (16:1), which are the major MUFA of membrane phospholipids, cholesterol esters and triglycerides. Three well-characterized isoforms of SCD, SCD1, SCD2 and SCD3, exist in mice. To investigate the physiologic functions of SCD1, we generated SCD1 null (SCD1-/-) mice. The skin and eyelid of SCD1-/- mice are deficient in triglycerides and cholesterol esters, and the eyelid also is deficient in wax esters. Furthermore, the eyelid and skin of SCD1-/- mice have higher levels of free cholesterol. SCD1-/- mice develop cutaneous abnormalities and narrow eye fissure with atrophic sebaceous and meibomian glands. Consumption of diets containing high levels of oleate, failed to restore the levels of triglycerides, cholesterol esters and wax esters in SCD1-/- mice to the levels found in the eyelid of wild-type mice. These results reveal a physiologic role of SCD in cholesterol homeostasis as well as in the de novo biosynthesis of cholesterol esters, triglycerides and wax esters required for normal skin and eyelid function.
- Published
- 2001
- Full Text
- View/download PDF
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