Module 8: Adipose Tissue Role in Metabolic Complications Flashcards
Insulin resistant adipose tissue is associated with (3 answers)
-high blood FFA
-low levels adiponectin (insulin-sensitizing adipokine)
-decreased expression of key adipogenic transcription factors (PPARγ, C/EBP, etc)
Blood Markers in Type 2 Diabetes
increased blood NEFA and triglyceride levels. also higher bl glu and ins
NEFA in blood bound to
albumin
What does NEFA serve as
source of energy for liver, muscle, and other organs
4 fates of NEFA in liver
- Used for energy
- Stored as TAG in lipid droplets
- Packaged as TAG into VLDL
- If glucose levels are low (i.e., during starvation), NEFA are used to make ketone bodies for use by the brain
NEFA and insulin sensitivity
strong inverse relationship between blood NEFA levels and insulin sensitivity
NEFA levels during the day
Blood NEFA levels are highest in the morning (after an overnight fast), drop strongly after breakfast, and then increase gradually during the day.
Role of insulin on fat uptake in adipose (4)
- glucoseuptake by promoting GLUT4
translocation to the plasma membrane. - induces Lipoprotein Lipase (LPL), promotes breakdown of TAGs in lipoproteins to allow for fatty acid uptake.
3.induces diacylglycerol acyltransferase (DGAT) activity, which is necessary for TAG synthesis and fatstorage.
4.Insulin inhibits hormone sensitive lipase (HSL) activity, thereby preventing lipolysis.
LPL and fat uptake into adipose tissue relationship
-correlated w fat uptake into adipose tissue
Is LPL activity in adipose tissue
regulated by nutritional status?
Mice that are fasted have low LPL activity (which limits fat uptake)
food-increase in LPL
HSL-/- mice
-larger adipocytes (less lipolysis)
-reduced TAG activity in white adipose tissue, no change in brown
VLDL production/secretion and insulin sensitivity relationship
VLDL production & secretion is inversely associated with insulin sensitivity
VLDL production/secretion and obesity relationship
Obesity is associated with increased VLDL secretion
What does HSL control
adipose tissue lipolysis
Primary adipose tissue depots
-subcutaneous
-visceral
Primary role of adipose tissue
store excess energy in adipocytes
Hyperplasia
increase in cell number
Hyptertrophy
increase in cell size
Bariatric surgery cell vol and number change
Lower cell volume, no change in number
Lifespan and production of fat cells lean vs obese
The average lifespan for an adipocyte is the same in lean and obese individuals, but the production rate of adipocytes is higher in individuals with obesity
changes in size and number of fat cells between depots
Adipocyte cell size increased in both depots (subcutaneous & viceral), but only the lower body subcutaneous
adipose tissue cell number increased
How does TZD treatments treat T2D
-improve ins sensitivity in peripheral tissue
(increase adiponectin?)
-promote glu uptake(increase GLUT-4)
-reduce inflammation (reduce MCP-1)
-decrease hepatic glu production (gluconeogenesis), Hb1Ac & bl lipids
Gene responsible for variability in obese response to 12 week aerobic training
PPAR-alpha gene rs 4253778
PPAR-alpha gene rs 4253778 genotypes and responsiveness
CA+AA most responded
CC lower amount of response
ECM remodelling is a balance between what processes
constructive and destructive
Major component of ECM
Collagen
2 primary types of proteins in ECM
- structural
- collagens (12 types)
- adhesion
- proteoglycan, laminin, elastin
What does decellularizing adipocyte ECM
-leaves ECM but no adipocyte
destructive enzymes
Plasmin
Matrix metalloproteinases (MMP)
What is plasmin activity regulated by
urokinase-type (u-PA) and tissue-type (t-PA) plasminogen activators
Inhibitors that regulates destructive enzymes
PAI-1
-inhibits u-PA and t-PA (prevents breakdown)
Tissue inhibitors of metalloproteinases (TIMP)
PAI-1 and obesity relationship
increased in obese adipose tissue and by pro-inflammatory signals (E.g. TNF-α)
=up w obesity, down w weight loss
Increased PAI-1 in obesity prevents
prevents ECM remodelling, which creates a stress in adipocyte promotes IR and impairs glu uptake
PAI-1KO mice
-protected from obesity-induced IR (increase in plasmin activity)
allowed cells to intake more
glucose in the presence of a pro-inflammatory cytokine
How to MMPs break down ECM
cleave collagen - must be cleaved by plasmin or other MMPS to become active
TIMP1 and obesity relaionship
TIMP1 expression is up with obesity and
down with weight loss
TIMP1 over-expression
-increase bl glu, ins, NEFA, liver TAG
-reduce ins stim glu uptake
(subcutaneous)
Dominant collagen in adipose tissue depots
Collagen 6
Affect on ECM when col 6 knocked out
weakened ECM
-lower body weight than obese mice at early age, lost affect after 10 weeks
-improved fasting glu levels and glu tolerance
-lower bl and liver TAG
-larger adipocyte
DESPITE BEING OBESE
Collagen w/ insulin resistance vs sensitivity
-increase w diabetes
-decrease w insulin sens
Paradox associated w weakened ECM (absense of collagen 6)
-larger adipocytes
-we normally think of this being associated w metabolic problems
-instead there are less metabolic problems
Healthy vs pathological adipose tissue expansion
Healthy:
Hyperplasic Obesity
(problems develop eventually
Pathological:
Hypertrophic Obesity
(problems develop more quickly)
What is adipose tissue hypoxia
Low O2
What transcription factor is activated in hypoxic conditions and what does it trigger
HIF1 activated, triggers ER stress response
What is HIF1α and its relationship.w obesity
HIF1α is a subunit of the
HIF1 transcription factor. Expression increases w obesity
What does over-expression of HIF1α do
increases plasma glucose -impairs glucose tolerance
Over-expression of adipose tissue HIF1α in animals fed a high fat diet or on a ob/ob genetic background (3 points)
– Increases liver TAG levels.
–Increases expression of F4/80 (a marker for macrophages) in adipose tissue.
– Increases the number of crown-like structures (CLS) in adipose tissue
3 roles of the endoplasmic reticulum (ER)
- protein synthesis
2.lipid droplet formation
3.Nutrient sensing
what assists with protein folding
-chaperone proteins
(BiP, calnexin, etc)
Where do correctly and incorrectly folded proteins go
Correctly:
-golgi
Incorrectly:
-proteasomes (degradation)
Where and what forms TAGS
3 fatty acids + 1 glycerol in ER membrane by enzymes
where/how does the lipid droplet form
forms within ER membrane, buds off (takes cytoplasmic layer of the ER membrane and associated proteins
How can lipids still be incorporated into droplet after budding off (2)
- caveolae brings lipids from out to in via receptor-mediated endocytosis, then fuse w droplet
- all enzymes for lipogenesis expressed in lipid droplet, TGs can be produced within
What does SREBP acts as and what does it regulate
-cholesterol sensor
regulates the expression of genes involved in lipid metabolism
What is the unfolded protein response (UPR)
When is cellular stress induced
Cellular stress is induced with chronic nutrient overload, hypoxia, glucose & energy shortages, ↑
protein synthesis, inhibition of protein glycosylation, imbalance of Ca2+ levels, etc
What is the unfolded protein response (UPR)
The unfolded protein response (UPR) is how the cell reacts to re-establish cellular homeostasis (the UPR is a protective response for the cell)
How does the UPR re-establish homeostasis (3 answers)
- Increase the capacity of the ER to fold and translocate proteins
- Slow down the synthesis of new proteins
- And if stress is not resolved (i.e., chronic ER stress), will ultimately induce apoptosis (cell death)
3 proteins that control UPR and their state in an unstressed ER
ATF-6
PERK
IRE1
Bound to BiP in unstressed ER = kept inactive
Role of ATF-6
ATF-6 moves to the Golgi, -cleaved by S1P and S2P.
-releases the active ATF-6, which can then move to the nucleus.
-turn on gene express. by interacting w ERSE
Role of IRE1
-Activates XBP1, turn on gene express in nucleus
-Causes the degradation of IKB and activation of JNK
–> NFkB promote inflam, gene express
-Inactivate IRS1
Role of PERK
Phosphorylate eIF2α - inhibit general translation
-reduce new protein production
-exceptionsL (BiP,ATF-4,SREBP) ATF-4 = apoptosis when homeostasis not restored
4 causes of ER stress
1.nutrient excess & adipocyte expansion
-increased demand for protein synthesis
2.Glucose deprivation
- insulin resistance: take up less glucose, lack of glucose causes stress
-reduced vascularization: less blood vessels, less glu to adipocytes
3. High levels of specific nutrients
- ex.diet sat fats pro inflam.
4.Inflam signal pathways
-TNFα activates the UPR via the production of reactive oxygen species (ROS).
-LPS activates the UPR by signalling via toll-like receptors.
What is UPR-induced insulin res mediated by
IRE1 and JNK
(increase in phorsphorylated JNK and serine-phosphorylated IRS)
-ER stress not induced in IRE-/- cells
What UPR markers were reduced following bariatric surgery
XSP1s, Phosphorylated levels of eIF2α and JNK w
What do chemical chaperones do in targeting ER stress
-stabalize protein
conformation, improve ER
protein folding capacity,
and facilitate trafficking of
misfolded proteins.
-lower p-PERK, p-eIF2α, p-
JNK, and XBP1s levels
-improve whole-body markers of metabolic
health (reduce blood glucose, lower blood insulin, and improve glucose tolerance)
Example of a chemical chaperone
4-phenyl butyric acid (PBA)
Obesity-induced insulin
resistance characterized by
-Pancreatic β-cell dysfunction
– Impaired suppression of
gluconeogenesis in liver
– Increased lipolysis in adipose tissue
– ER stress and impaired ECM remodelling
4 immune cells residing in adipose tissue
– Macrophages
– Lymphocytes (T-cell, B-cell)
– Eosinophils
– Mast cells
Relationship
between TNFα and insulin resistance
TNFα influences insulin
resistance
Positive associations were seen between TNFα
and.. (3 answers)
– BMI
– Fasting glucose levels
– Fasting insulin levels
Association between and insulin resistance (IR). - how?
TNFα promotes serine phosphorylation of
IRS1, thus blocking an early step in the
insulin signalling pathway
F4/80
macrophage marker
What do macrophages primarily secrete
Pro-inflammatory adipokines
2 macrophage phenotypes
M1: pro-inflammatory
-form crown like structures around dying adipocytes
M2: anti-inflammatory (less inflammatory)
-uniformly dispersed
Anti-inflammatory adipokines (2)
-Adiponectin
-SFRP5
Pro-inflammatory adipokines
-leptin
-resisten
-RBP4
-lipocalin
-ANGPTL2
-TNF
-IL-6
-IL-18
Role of M1 macrophages in insulin resistance
- macrophage recruitment
- adipocyte-muscle crosstalk
3.TNFa signal pathwat
4.GPR120 mediates omega-3 PUFA benefits
- Macrophage recruitment
-adipocytes secrete CCL2 (MCP1)
-MCP1 interacts w CCR2 (receptor on macrophages
(1)MCP1 expression and obesity
MCP1 expression increase w obesity
(1)What happens when macrophage CCR2 or MCP1 is deleted
reduction in macrophague infiltration, reduces inflammatory markers, improve ins sens
- Adipocyte-marcophage crosstalk in lean individuals
– Adipocytes secrete factors (IL4,IL13) that promote a M2
phenotype in macrophages.
– M2 macrophages secrete anti-inflammatory molecules (IL10) and
possibly other insulin sensitizers
PROMOTE ANTI-INFLAM
- Adipocyte-marcophage crosstalk in obese individuals
-Adipocytes secrete factors (TNFα,saturated fatty acids, chemokines)that promote a M1 phenotype in
macrophages.
– Macrophage secrete pro-
inflammatory molecules (TNFα, IL-1β, IL-6, etc.).
PROMOTE PRO-INFLAM
- What does TNFα signal through
TNFα signals through it’s cell
surface receptor, TNFR.
(3)What 2 pathways does TNFα signalling activate
Activation of two serine kinases
(IKK and JNK),
(3)Two consequences of activating of JKK and JNK serine kinases
- IKK serine phosphorylates IκB, causes IκB to dissociate
from NFκB. NFκB can then
move to the nucleus to turn on pro-inflammatory gene
expression. - JNK and IKK serine
phosphorylate IRS1, which
inhibits the insulin signalling
pathway
(4) what is GPR120
omega-3 PUFA (DHA)
receptor / sensor
GPR120 KO mice (3 points)
-eliminated anti-inflammatory effects of omega-3 (DHA)
(PS stimulates inflammation,
but co-treating macrophage and adipocytes with LPS and DHA (omega-3) reduced the expression of pro-inflammatory genes (TNFα,
IL-6, MCP1)
-reduced glu tolerance, needs more ins to clear bl. glu
-DHA reduced macrophage recruitment, cant occur w/o GPR120
Evidence suggests that one can drive a M1 to M2 phenotype switch by:
- Switching from a HFD to chow diet
- Increasing n-3 PUFA consumption
- Using a TZD
Other immune cells in adipose tissue (3)
-Eosinophils (anti-inflam)
-Mast cells (pro-inflam)
-B-lmphocytes (B-cells) (pro-inflam)
What do T-cells do
play an equally important role in determining the inflammatory status of adipose tissue
IL-4
activates several pathways in macrophages to suppress the expression of pro-inflammatory genes and promote the alternate activation of macrophage
What do M2 macrophages secrete
IL-10 - insulin-sensitizing cytokine
What does genetic deletion of PAR δ or
KLF4 cause
insulin resistance
What helps to block pro inflam signals in macrophages (2 answers)
-adiponectin and omega-3 fatty acids
