Mod 1 PPAR

Question 15

PPAR subfamily

Answer 15

PPARa

PPARo

PPARy

Question 16

PPARy

Answer 16

Regulates adipose tissues development and function

Induced during fat cell differentiation

-/- = fail to develop adipose tisses, die of placental and cardiac defect in utero - LETHAL

Acts as a lipid sending TF, changes gene expression in metabolically active tissues

Drug target - insulin sensitising drugs

Question 17

PPARy in ADIPOSE

Answer 17

KO = progressive loss of fat

Fatty liver - accumuluation of lipids

Hyperlipidaemia

Hepatic insulin resistance

Question 18

PPARY in LIVER

Answer 18

Glucose homeostais

KO = elevated plasma glucose and insulin

Increased adiposity

Hyperlipidaemia

Question 19

PPARy in MUSCLE

Answer 19

Insulin resistant

KO = Lipid accumulation in liver

Question 20

PPARy as drug target

Answer 20

Binds to high affinity ligands which are Thiazolidinedione class of insulin sensitising drugs - Rosiglitazone

Improves glycemic control Type II diabetes and reduces circulating TAG and FA

Question 21

Lipid Steal Hypothesis

Answer 21

Insulin-sensitising effects of TZDs

Adipose remodelling enance insulin sensitivity by favouring lipid accretion in depot that are:

• less hormonlaly sensitive
• without direct access to portal circulation
• i.e. Liver

TZDs act on adipose tissue to enhance its capasity to act as a dumping ground for dietary FAs and keeps them away from other insulin-sensitive tissues i.e. skeletal muscle

Question 22

Thiazolidinedione (TZD)

Answer 22

Activates PPARs, especially PPARy

Endogenous ligands for these receptors are FAs and eicosanoids

Receptor binds to DNA with RXR and increases gene transcription (also decreases some)

For PPARy: Increases fat storage in adipse, weight gain and insulin sensitivity

• Turns off TNFa and resistin, therefore decreasing insulin resistance in peripheral tissues
• Increases Adiponectin: promotes FA oxidation and insulin sensitivity in skeletal muscle and **liver **
• Increases LPL (lipoprotein lipase): hydroylsis of lipoprotein TAG into FFAs. Reuptake of FA by cells.
• Increases ACS (AcylCoA synthase): converts FAs to AcylCoA
• Increases CD36: scavenger rc, uptake of oxidised LDL
• Increases FATP (FA transport protein): uptake of FAs by cell

Question 23

PPARy ligand resistance (PLR) syndrome

Answer 23

Severe insulin resistance (SIR) cohort

Pre-diabetic

System under strain

Increased insulin in blood to keep BGL normal

Acanthosis Nigricans - brown lesion under arm

Fasting plasma insulin > 100 pmol/L

OR

Plasma insulin > 100 pmol/L at 2h post-glucose load

OR

Insulin requirement of > 200 U/day if lean, 300 if obese

Question 24

In vitro responses of mMT PPARy to ROSIGLITAZONE

Answer 24

Transfected into cell with reporter and assayed for reporer

Activity of PPARy increased as rosa increased

MT receptor doesn’t respond until super physiological levels

Patients can’t get drugs at this level

Question 25

PPARo

Answer 25

Obesity prevention, increases serum HDL cholesterol (good)

Ubiquitous expression (in every cell)

Binds DNA as permissive heterodimer w/ RXR (obligate, needs it)

PPARo null transgenic mice: embryonically lethal - placental defects

Natural ligands: 1418 carbon sat. FA, 20 carbon polyunsat. FA, eicosanoids (Prostaglandin A1, carbaprostacyclin)

Synthetic ligands: high affinity ligands under development

Question 26

PPARo drugs

Answer 26

Induce resistance to obesity

Experiment: Mice administered agonist (same effect) gained less weight on high fat diet vs. control

Reduced fat deposition

Improved glycemic control

Target genes: increased expression of genes in FA transport, B-oxidation and mitochondrial respiration

In

Question 27

PPARo in ADIPOSE

Answer 27

Experiment: Bound to aP2 promoter (fat specific), VP16 viral protein, increased PPARo

Expressed only in fat tissue

Resulted in no fat compared to wt.

Increased thermogenesis >> burns fat

Question 28

PPARo in SKELETAL MUSCLE

Answer 28

Skeletal actin promtor, VP16, PPARo

Gained less weight vs. wt w/ high fat diet

Smaller fat cells - increased FA oxidation

Improved glucose tolerance

Question 29

PPARo and Oxidative Type I fibres

Answer 29

Increased

Type I (slow/red) aerobic B-oxidation of fat

Type II (fast/white) anaerobic glycolysis

Increased physical endurance

Increased mitochondrial biogenesis

Question 30

PPARo summary - different targets

Answer 30

Heart: increased contractile function, FA transport and oxid.

Muscles: Increased muscle capacity, FA t&o, thermogenesis, slow-twitch fibres

Adipose: prevention of obesity, FA t&o, thermogenesis

Artery: Increased HDL cholesterol

Liver: Decreased glucose output

Question 31

Halofenate vs. Rosiglitazone

Answer 31

Rosi = very rapid booting off of CoR therfore increasing concentration = strength goes down. Robust recruitment of CoA

Halo = eventually reaches end point, CoA recruitment is flat. As though drug promotes PPARy de-repressoin but doesn’t really promote activation of target genes either.

Relieves repression by receptor

Different drugs promote different co-regulator interaction

Question 32

In vitro responses of mt PPARy to rosiglitazone

Answer 32

Cloned receptor, lucifersae assay

Wt rc responds, increased transcriptional output in response to drug

Mt doesn’t respond until super physiological concentrations