1. ENERGY HOMEOSTASIS2. GPRC RECEPTORS3. SCFAS4. INSULIN SIGNAING

Background

Conceptual Flow

Keywords

Adipocytes

Abbreviations

MA: mature adipocytes (PPAR)γ: peroxisomes proliferator-activated receptor

GLP1: glucagon-like peptide aP2: Adipocyte fatty acid binding protein

Background: Adipocytes

Adipocytes Adipocyte differentiation

White adipose tissue (WAT) is the major energy reserve in higher eukaryotes, and storing triacylglycerol in periods of energy excess and its mobilization during energy deprivation are its primary purposes

Mature adipocytes, the main cellular component of WAT, are uniquely equipped to function in energy storage and balance under tight hormonal control.

PPARγ is the obligatory transcription factor indispensable for the differentiation and survival of both white and brown adipocytes 

Background: WAT and energy homeostasis

 Fasting State Post-prandial 

http://www.nature.com/cr/journal/v17/n6/full/cr200748a.html#fig2

Background: Insulin the anabolic hormone

Insulin stimulates glucose uptake in the liver, fat cells and skeletal muscle.  Glucose is stored as either glycogen in liver and muscle, or as triglycerides in adipocytes. 

Glucose is stored as either glycogen in liver and muscle, or as triglycerides in adipocytes.

 Important actions of insulin include inhibition of lipolysis, glycogenolysis, and gluconeogenesis.   

http://www.medbio.info/horn/time%203-4/how_insulin_works.htm

Background: The role of SCFAs in energy homeostasis

de novo synthesis of lipids, glucose

signaling molecules

G protein-coupled receptorsGPR41 GPR43

GPR43

• Regulation of inflammatory responses• GPR43 promotes leptin secretion,adipogenesis and inhibition of lipolysis in adipose tissue andadipocytes

Bacterial fermentation of “indigestible” prebiotics

GPR43-knockout

mice exhibit obesity

GPR43 is abundantl

y expressed

in WAT

Adipose-specific GPR43

transgenic mice are

lean

GPR43 suppresses insulin signaling in adipose

tissue

GPR43 promotes energy

expenditure

GPR43 suppressess

insulin signalling

via G(i/o)βγ-PLC-PKC-

PTEN

General Methodology

1. Trasgenic mice:

Gpr43 is abundantly expressed in the WATs

Gpr43 was most abundantly expressed in the WAT and was not expressed in the BAT.

During adipogenesis, Gpr43 was expressed in the later stages of differentiation than aP2 and PPARg.

3T3-L1 and 3T3-F442A mouse cell lines differentiate spontaneously when exposed to a hormonal cocktail

I. Gpr43 is abundantly expressed in the WATs

GPR43 was expressed in the later stages of differentiation than aP2 and PPARγ

http://www.hindawi.com/journals/ppar/2008/679137/fig1/

aP2 is a key mediator of intracellular transport and metabolism of fatty acids. Its expression during adipocyte differentiation is regulated through the actions of PPARγ and CCAAT/enhancer binding protein alpha (C/EBPalpha).

PPARγ induces the expression of genes involved in lipid synthesis and storage through enhancers activated during adipocyte differentiation.

Gpr43 is abundantly expressed in the WATs

Stromal vascular fraction (VSF) - preadipocytes, fibroblasts, vascular endothelial cells and a variety of immune cells (i.e. adipose tissue macrophages (ATMs))

Gpr43 knockout mice are obeseP1 WATand BAT were stained with oil red P1 Body weight P1 fat mass

Protein expression

Expression of aP2 and Pparg mRNA

Haematoxylin–eosin stained WAT and mean area of adipocytes

Gpr43 knockout mice are obese

Insulin tolerance test

Glucose tolerance test

Euglycaemic hyperinsulinaemic clamp in HFD-fed mice

Glucose infusion ratio

Glucose disposal rate

Hepatic glucose productionsuppression

Hyperinsulinemic Euglycemic Glucose Clamp Technique. After an overnight fast, insulin is infused intravenously at a constant rate that may range from 5~120 mU/m2/min (dose per body surface area per minute). This constant insulin infusion results in a new steady-state insulin level that is above the fasting level (hyperinsulinemic). As a consequence, glucose disposal in skeletal muscle and adipose tissue is increased while hepatic glucose production is suppressed. Under these conditions, a bedside glucose analyzer is used to frequently monitor blood glucose levels at 5~10 min intervals while 20% dextrose is given intravenously at a variable rate in order to "clamp" blood glucose concentrations in the normal range (euglycemic). An infusion of potassium phosphate is also given to prevent hypokalemia resulting from hyperinsulinemia and increased glucose disposal. After several hours of constant insulin infusion, steady-state conditions can typically be achieved for plasma insulin, blood glucose, and the glucose infusion rate (GIR). Assuming that the hyperinsulinemic state is sufficient to completely suppress hepatic glucose production, and since there is no net change in blood glucose concentrations under steady-state clamp conditions, the GIR must be equal to the glucose disposal rate (M). Thus, whole body glucose disposal at a given level of hyperinsulinemia can be directly determined (Adopted from Muniyappa R, et al. Am J Physiol Endocrinol Metab 294:E15-26, 2008).

Mechanisms of insulin sensitivity and resistance in muscle and liver(A) Insulin-sensitive muscle. (B) Insulin-resistant muscle. (C) Insulin-sensitive liver. (D) Insulin-resistant liver. IRS=insulin-receptor substrate. IR=insulin receptor. PI3K=1-phosphatidylinositol 3-kinase. GLUT4=glucose transporter 4. DAG=diacylglycerol. PKC=protein kinase C. Ser=serine. Thr=threonine. FOX01=forkhead box O1. FOXA2=forkhead box A2. G6P=glucose-6-phosphate. GS=glycogen synthase. GSK=glycogen synthase kinase. Green circle with plus sign represents activation. Red circle with minus sign represents inactivation. Solid line with arrowhead represents increase or accumulation of substrate. Dotted line indicates inhibition of pathway.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2995547/pdf/nihms250988.pdf

Gpr43 knockout mice are obese

Level of inflammation

Expression of F4/80 and TNF-α

Fecal major SCFA andplasma acetate contents in HFD-fed mice

Comparison of microbial communities in HFD-fed mice

Communities of gut microbiota in Gpr43/ mice exhibited an increase in firmicutes, an SCFA- producing phylum, and a decrease in γ- proteobacteria and actinobacteria

Body weights of HFD-fed mice under GF conditions

Body weight changes under GF to CONV conditions

Gpr43 knockout mice are obese

Insulin and glucose tolerance under antibiotic treatment

Acetate and glucose plasma concentrations after 1 h of feeding (24 h fasting)

Plasma acetate concentrationwith or without antibiotic treatment during feeding

Effect of acetate on body weights and fat mass under antibiotic treatment

Adipose tissue-specific Gpr43 transgenic mice are leanSubcutaneous WAT & inters-capular BAT of P1 were stained with oil red O P1 Body weight

P1 fat mass

Protein expression

Expression of aP2 and Pparg mRNA

Haematoxylin–eosin stained WAT and mean area of adipocytes

Adipose tissue-specific Gpr43 transgenic mice are lean

Comparison of microbial communties Fecal & plasma major

SCFA

Body weight & fat mass of aP2-Gpr43TG mice fed an HFD

Body weight & fat mass under antibiotic treatment

Adipose tissue-specific Gpr43 transgenic mice are lean

ITT & GTT of aP2-Gpr43TG mice fed an HFD

Plasma glucose concentration in aP2-Gpr43TG mice fed an HFD

Euglycaemic hyperinsulinaemic clamp aP2-Gpr43TG mice fed an HFD

Glucose infusion ratio

Glucose disposal rate

Hepatic glucose productionsuppression

ITT & GTT of aP2-Gpr43TG mice fed an HFD under antibiotic treatment

Oil red O-stained liver and hepatic triglyceride content in aP2-Gpr43 TG mice fed an HFD

Level of WAT inflammation

Gpr43 suppresses insulin signaling in the adipose tissues but not in muscles or liver

Insulin-stimulated Akt phosphorylation of Ser473 in the WAT, muscles & liver

Inhibitory effects of acetate on insulin signaling

Gpr43 suppresses insulin signaling in the adipose tissues but not in muscles or liver

Effect of acetate on glucose uptake in MEF-derived adipocytes from Gpr43-/-or aP2-Gpr43TG mice

Effect of acetate on the fatty acid uptake in MEF-derived adipocytes from Gpr43-/- or aP2-Gpr43TG mice

Gpr43 suppresses insulin signaling in the adipose tissues but not in muscles or liver

LPL activity in the WAT and the muscles

LPL activity of Gpr43-/- mice fed an HFD under GF conditions or aP2-Gpr43TG mice treated with antibiotics

Gpr43 suppresses insulin signaling via G(i/o)βγ-PLC-PKC-PTEN signaling

Inhibitory effects of GPR43 agonists and a GPR41 agonist on insulin-induced Akt phosphorylation

Effects of Gi/o signaling inhibition on suppression of insulin-induced Akt phosphorylation by acetate

Effects of Gq signaling inhibition using siRNA on suppression of insulin-induced Akt phosphorylation by acetate

Effects of Gβγ signaling inhibition on suppression of insulin-induced Akt phosphorylation by acetate

Effects of GPR43 stimulation on PTEN phosphorylation

Gpr43 suppresses insulin signaling via G(i/o)βγ-PLC-PKC-PTEN signaling

Effects of PTEN signalling inhibition on suppression ofinsulin-induced Akt phosphorylation by acetate

Effect of GPR43 agonists (10mM acetate and 10mM PA) on insulin-induced glucose uptake

Effect of acetate on insulin-induced LPL activity

Schematic diagram of the mechanism for GPR43-mediated suppression of fat accumulation.

Gpr43 promotes energy expenditure by increasing the consumption of lipids

Biochemical analysis of plasma obtained from Gpr43/mice on an HFD as well as aP2-Gpr43TG mice

Triglycerides Free fatty acidsmRNA levels of genes involved in energy expenditure

Energy expenditure of Gpr43/ mice on an HFD

Total activity in Gpr43/ mice fed an HFD

RER of Gpr43/ mice fed an HFD

Gpr43 promotes energy expenditure by increasing the consumption of lipids

Energy expenditure of aP2-Gpr43TG mice Total activity in

aP2-Gpr43TG mice

RER of aP2-Gpr43TG mice

Schematic model of suppression of fat accumulation via Gpr43

After feeding, SCFAs, produced by microbial fermentation in thegut, activate GPR43 in adipose tissues.

SCFA-mediated GPR43 activation suppresses insulin-mediated fat accumulation and thereby regulates the energy balance by suppressing accumulation of excess energy andpromoting fat consumption.

www.intechopen.com/books/alternative-medicine/investigation-on-the-mechanism-of-qi-invigoration-from-a-perspective-of-effects-of-sijunzi-decoction

www.jci.org/articles/view/58109/figure/1

Leptin is a 16-kDa protein hormone, which is secreted by adipocytes

https://www.google.co.kr/search?biw=1160&bih=812&tbm=isch&imgil=upI1HvMKnr_jOM%253A%253Bhttps%253A%252F%252Fencrypted-tbn1.gstatic.com%252Fimages%253Fq%253Dtbn%253AANd9GcRMFosrMfkVfMkhSROLTxEHhvW0a67EFErZ84RR8f6XBBzrMP6B6w%253B1068%253B1280%253B_Plnz4VJEUUOOM%253Bhttp%25253A%25252F%25252Fajpcell.physiology.org%25252Fcontent%25252F298%25252F5%25252FC973&source=iu&usg=__bfGMjcekJx8iAmb7uEj5IRdsDJA%3D&sa=X&ei=icOFU8fFIoG-kAWY0oDYDA&ved=0CFsQ9QEwBA&q=differentiation%20bat%20and%20wat#facrc=_&imgdii=CHxu26CGDzrIGM%3A%3BmvIXZd5FxaeXdM%3BCHxu26CGDzrIGM%3A&imgrc=CHxu26CGDzrIGM%253A%3BaRL8RcqFx46ZXM%3Bhttp%253A%252F%252Fwww.nature.com%252Fijo%252Fjournal%252Fv34%252Fn1s%252Fimages%252Fijo2010178f1.jpg%3Bhttp%253A%252F%252Fwww.nature.com%252Fijo%252Fjournal%252Fv34%252Fn1s%252Ffig_tab%252Fijo2010178f1.html%3B625%3B417

Representative H&E stained sections of (F) brown (BAT) and (G) white (WAT) adipose tissues from aP2-SufuKO and control littermate mice.

(A and B) Microscopic view of Oil Red O-stained cell cultures