Microsomal triglyceride transfer protein regulates intracellular lipolysis in adipocytes independent of its lipid transfer activity
BACKGROUND:The triglyceride (TG) transfer activity of microsomal triglyceride transfer protein (MTP) is essential for lipoprotein assembly in the liver and intestine; however, its function in adipose tissue, which does not assemble lipoproteins, is unknown. Here we have elucidated the function of MTP in adipocytes. APPROACH AND RESULTS/RESULTS:mice maintained higher body temperature by mobilizing more fatty acids. Biochemical studies indicated that MTP deficiency de-repressed adipose triglyceride lipase (ATGL) activity and increased TG lipolysis. Both wild type MTP and mutant MTP deficient in TG transfer activity interacted with and inhibited ATGL activity. Thus, the TG transfer activity of MTP is not required for ATGL inhibition. C-terminally truncated ATGL that retains its lipase activity interacted less efficiently than full-length ATGL. CONCLUSION/CONCLUSIONS:Our findings demonstrate that adipose-specific MTP deficiency increases ATGL-mediated TG lipolysis and enhances energy expenditure, thereby resisting diet-induced obesity. We speculate that the regulatory function of MTP involving protein-protein interactions might have evolved before the acquisition of TG transfer activity in vertebrates. Adipose-specific inhibition of MTP-ATGL interactions may ameliorate obesity while avoiding the adverse effects associated with inhibition of the lipid transfer activity of MTP.
Pain, Analgesic Use, and Patient Satisfaction With Spinal Versus General Anesthesia for Hip Fracture Surgery : A Randomized Clinical Trial
BACKGROUND:The REGAIN (Regional versus General Anesthesia for Promoting Independence after Hip Fracture) trial found similar ambulation and survival at 60 days with spinal versus general anesthesia for hip fracture surgery. Trial outcomes evaluating pain, prescription analgesic use, and patient satisfaction have not yet been reported. OBJECTIVE:To compare pain, analgesic use, and satisfaction after hip fracture surgery with spinal versus general anesthesia. DESIGN:Preplanned secondary analysis of a pragmatic randomized trial. (ClinicalTrials.gov: NCT02507505). SETTING:46 U.S. and Canadian hospitals. PARTICIPANTS:Patients aged 50 years or older undergoing hip fracture surgery. INTERVENTION:Spinal or general anesthesia. MEASUREMENTS:Pain on postoperative days 1 through 3; 60-, 180-, and 365-day pain and prescription analgesic use; and satisfaction with care. RESULTS:A total of 1600 patients were enrolled. The average age was 78 years, and 77% were women. A total of 73.5% (1050 of 1428) of patients reported severe pain during the first 24 hours after surgery. Worst pain over the first 24 hours after surgery was greater with spinal anesthesia (rated from 0 [no pain] to 10 [worst pain imaginable]; mean difference, 0.40 [95% CI, 0.12 to 0.68]). Pain did not differ across groups at other time points. Prescription analgesic use at 60 days occurred in 25% (141 of 563) and 18.8% (108 of 574) of patients assigned to spinal and general anesthesia, respectively (relative risk, 1.33 [CI, 1.06 to 1.65]). Satisfaction was similar across groups. LIMITATION:Missing outcome data and multiple outcomes assessed. CONCLUSION:Severe pain is common after hip fracture. Spinal anesthesia was associated with more pain in the first 24 hours after surgery and more prescription analgesic use at 60 days compared with general anesthesia. PRIMARY FUNDING SOURCE:
Ex Vivo Resection and Autotransplantation for Conventionally Unresectable Tumors - An 11-year Single Center Experience
BACKGROUND AND AIMS:Ex vivo surgery may provide a chance at R0 resection for conventionally unresectable tumors. However, long-term outcomes have not been well documented. In this study, we analyze our 11-year outcomes to define its role. STUDY DESIGN:We retrospectively analyzed 46 consecutive patients who underwent ex vivo surgery at our institution 2008-2019. RESULTS:The types of tumors were: carcinoma (n = 20), sarcoma (n = 20) and benign to low grade tumor (n = 6). The type of ex vivo surgery was chosen based on tumor location and vascular involvement. The most commonly performed procedure was ex vivo hepatectomy (n = 18), followed by ex vivo resection and intestinal autotransplantation (n = 12), ex vivo Whipple procedure and liver autotransplantation (n = 8) and multivisceral ex vivo procedure (n = 7). Twenty-three patients (50%) are currently alive with median follow-up of 4.0-years (11 months-11.8 years). The overall survival was 70%/59%/52%, at 1-/3-/5-years, respectively. Patient survival for benign to low grade tumors, sarcoma, and carcinoma was 100%/100%/100%, 65%/60%/50%, and 65%/45%/40%, at 1-/3-/5-years, respectively. Ninety-one percent patients had R0 resection, and 57% had no recurrence to date with median follow-up of 3.1-years. Two patients (4.3%) died within 30 days due to sepsis and gastroduodenal artety (GDA) stump blowout. Two additional patients died between 30 and 90 days due to sepsis. Perioperative mortality in the last 23 consecutive cases was limited to 1 patient who died of sepsis between 30 and 90 days. CONCLUSIONS:For a selected group of patients with conventionally unresectable tumors, ex vivo surgery can offer effective surgical removal with a reasonably low perioperative mortality at experienced centers.
Bile acid composition regulates GPR119-dependent intestinal lipid sensing and food intake regulation in mice
OBJECTIVES:mice) with normal total BA levels, but alterations in the composition of the BA pool that impact multiple aspects of intestinal lipid metabolism. We tested two hypotheses: BAs affect food intake by (1) regulating production of the bioactive lipid oleoylethanolamide (OEA), which enhances satiety; or (2) regulating the quantity and localisation of hydrolysed fat in small intestine, which controls gastric emptying and satiation. DESIGN:mice. RESULTS:mice. CONCLUSION:BAs regulate gastric emptying and satiation by determining fat-dependent GPR119 activity in distal intestine.
Oleoylethanolamide differentially regulates glycerolipid synthesis and lipoprotein secretion in intestine and liver
Dietary fat absorption takes place in the intestine, and the liver mobilizes endogenous fat to other tissues by synthesizing lipoproteins that require apoB and microsomal triglyceride transfer protein (MTP). Dietary fat triggers the synthesis of oleoylethanolamide (OEA), a regulatory fatty acid that signals satiety to reduce food intake mainly by enhancing neural PPARÎ± activity, in enterocytes. We explored OEA's roles in the assembly of lipoproteins in WT and Ppara -/- mouse enterocytes and hepatocytes, Caco-2 cells, and human liver-derived cells. In differentiated Caco-2 cells, OEA increased synthesis and secretion of triacylglycerols, apoB secretion in chylomicrons, and MTP expression in a dose-dependent manner. OEA also increased MTP activity and triacylglycerol secretion in WT and knockout primary enterocytes. In contrast to its intestinal cell effects, OEA reduced synthesis and secretion of triacylglycerols, apoB secretion, and MTP expression and activity in human hepatoma Huh-7 and HepG2 cells. Also, OEA reduced MTP expression and triacylglycerol secretion in WT, but not knockout, primary hepatocytes. These studies indicate differential effects of OEA on lipid synthesis and lipoprotein assembly: in enterocytes, OEA augments glycerolipid synthesis and lipoprotein assembly independent of PPARÎ±. Conversely, in hepatocytes, OEA reduces MTP expression, glycerolipid synthesis, and lipoprotein secretion through PPARÎ±-dependent mechanisms.
A direct tissue-grafting approach to increasing endogenous brown fat
There is widespread evidence that increasing functional mass of brown adipose tissue (BAT) via browning of white adipose tissue (WAT) could potentially counter obesity and diabetes. However, most current approaches focus on administration of pharmacological compounds which expose patients to highly undesirable side effects. Here, we describe a simple and direct tissue-grafting approach to increase BAT mass through ex vivo browning of subcutaneous WAT, followed by re-implantation into the host; this cell-therapy approach could potentially act synergistically with existing pharmacological approaches. With this process, entitled "exBAT", we identified conditions, in both mouse and human tissue, that convert whole fragments of WAT to BAT via a single step and without unwanted off-target pharmacological effects. We show that ex vivo, exBAT exhibited UCP1 immunostaining, lipid droplet formation, and mitochondrial metabolic activity consistent with native BAT. In mice, exBAT exhibited a highly durable phenotype for at least 8 weeks. Overall, these results enable a simple and scalable tissue-grafting strategy, rather than pharmacological approaches, for increasing endogenous BAT and studying its effect on host weight and metabolism.
Central Regulation of Endogenous Glucose Production Is Impaired in Type 2 Diabetes Mellitus [Meeting Abstract]
Cholinergic neurons in the dorsomedial hypothalamus regulate mouse brown adipose tissue metabolism
OBJECTIVE:Brown adipose tissue (BAT) thermogenesis is critical in maintaining body temperature. The dorsomedial hypothalamus (DMH) integrates cutaneous thermosensory signals and regulates adaptive thermogenesis. Here, we study the function and synaptic connectivity of input from DMH cholinergic neurons to sympathetic premotor neurons in the raphe pallidus (Rpa). METHODS:In order to selectively manipulate DMH cholinergic neuron activity, we generated transgenic mice expressing channelrhodopsin fused to yellow fluorescent protein (YFP) in cholinergic neurons (choline acetyltransferase (ChAT)-Cre::ChR2-YFP) with the Cre-LoxP technique. In addition, we used an adeno-associated virus carrying the Cre recombinase gene to delete the floxed Chat gene in the DMH. Physiological studies in response to optogenetic stimulation of DMH cholinergic neurons were combined with gene expression and immunocytochemical analyses. RESULTS:A subset of DMH neurons are ChAT-immunopositive neurons. The activity of these neurons is elevated by warm ambient temperature. A phenotype-specific neuronal tracing shows that DMH cholinergic neurons directly project to serotonergic neurons in the Rpa. Optical stimulation of DMH cholinergic neurons decreases BAT activity, which is associated with reduced body core temperature. Furthermore, elevated DMH cholinergic neuron activity decreases the expression of BAT uncoupling protein 1 (Ucp1) and peroxisome proliferator-activated receptor Î³ coactivator 1 Î± (Pgc1Î±) mRNAs, markers of BAT activity. Injection of M2-selective muscarinic receptor antagonists into the 4th ventricle abolishes the effect of optical stimulation. Single cell qRT-PCR analysis of retrogradely identified BAT-projecting neurons in the Rpa shows that all M2 receptor-expressing neurons contain tryptophan hydroxylase 2. In animals lacking the Chat gene in the DMH, exposure to warm temperature reduces neither BAT Ucp1 nor Pgc1Î± mRNA expression. CONCLUSION/CONCLUSIONS:DMH cholinergic neurons directly send efferent signals to sympathetic premotor neurons in the Rpa. Elevated cholinergic input to this area reduces BAT activity through activation of M2 mAChRs on serotonergic neurons. Therefore, the direct DMH(ACh)-Rpa(5-HT) pathway may mediate physiological heat-defense responses to elevated environmental temperature.
Post-transcriptional activation of PPAR alpha by KLF6 in hepatic steatosis
BACKGROUND & AIMS: Dysregulated glucose homeostasis and lipid accumulation characterize non-alcoholic fatty liver disease (NAFLD), but underlying mechanisms are obscure. We report here that Kruppel-like factor 6 (KLF6), a ubiquitous transcription factor that promotes adipocyte differentiation, also provokes the metabolic abnormalities of NAFLD by post-transcriptionally activating PPARalpha-signaling. METHODS: Mice with either hepatocyte-specific depletion of KLF6 ('DeltaHepKlf6') or global KLF6 heterozygosity (Klf6+/-) were fed a high fat diet (HFD) or chow for 8 or 16 weeks. Glucose and insulin tolerance tests were performed to assess insulin sensitivity. Overexpression and knockdown of KLF6 in cultured cells enabled the elucidation of underlying mechanisms. In liver samples from a cohort of 28 NAFLD patients, the expression of KLF6-related target genes was quantified. RESULTS: Mice with global- or hepatocyte-depletion of KLF6 have reduced body fat content and improved glucose and insulin tolerance, and are protected from HFD-induced steatosis. In hepatocytes, KLF6 deficiency reduces PPARalpha-regulated genes (Trb3, Pepck) with diminished PPARalpha protein but no change in Pparalpha mRNA, which is explained by the discovery that KLF6 represses miRNA 10b, which leads to induction of PPARalpha. In NAFLD patients with advanced disease and inflammation, the expression of miRNA 10b is significantly downregulated, while PEPCK mRNA is upregulated; KLF6 mRNA expression also correlates with TRB3 as well as PEPCK gene expression. CONCLUSIONS: KLF6 increases PPARalpha activity, whereas KLF6 loss leads to PPARalpha repression and attenuation of lipid and glucose abnormalities associated with a high fat diet. The findings establish KLF6 as a novel regulator of hepatic glucose and lipid metabolism in fatty liver.
Targeted loss of GHR signaling in mouse skeletal muscle protects against high-fat diet-induced metabolic deterioration
Growth hormone (GH) exerts diverse tissue-specific metabolic effects that are not revealed by global alteration of GH action. To study the direct metabolic effects of GH in the muscle, we specifically inactivated the growth hormone receptor (ghr) gene in postnatal mouse skeletal muscle using the Cre/loxP system (mGHRKO model). The metabolic state of the mGHRKO mice was characterized under lean and obese states. High-fat diet feeding in the mGHRKO mice was associated with reduced adiposity, improved insulin sensitivity, lower systemic inflammation, decreased muscle and hepatic triglyceride content, and greater energy expenditure compared with control mice. The obese mGHRKO mice also had an increased respiratory exchange ratio, suggesting increased carbohydrate utilization. GH-regulated suppressor of cytokine signaling-2 (socs2) expression was decreased in obese mGHRKO mice. Interestingly, muscles of both lean and obese mGHRKO mice demonstrated a higher interleukin-15 and lower myostatin expression relative to controls, indicating a possible mechanism whereby GHR signaling in muscle could affect liver and adipose tissue function. Thus, our study implicates skeletal muscle GHR signaling in mediating insulin resistance in obesity and, more importantly, reveals a novel role of muscle GHR signaling in facilitating cross-talk between muscle and other metabolic tissues.