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Y elective pathobiochemistry > Obesity lecture/chapter in book > Flashcards

Obesity lecture/chapter in book Flashcards

1
Q

What kind of receptor is the Insulin receptor?

A

A tyrosine kinase receptor, it directly phosphorylates its insulin receptor substrates, IRSs.

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2
Q

What pathways does the Insulin receptor activate?

A

via SH2 domains, it binds GRB2 which couples it to the Ras/MAPK growth factor pathway, and PI3K which activates most of its metabolic effects.

PI3K
activates AKT, also called Protein kinase B,
Inhibits GSK3, which disinhibits glycogen synthase, and glycogen synthesis increases.

activates FOxO transcription factors, inhibiting gluconeogenesis

activates mTOR signaling, increasing protein synthesis.

activates SREBP (sterol regulator element binding proteins) transcription factors, increasing lipid synthesis.

GRB2, activates SOS, a

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3
Q

What are the major pathways that inhibit insulin receptor substrates?

A

JNK : c-jun N terminal kinases
and
IKKbeta : I-kappa-B kinase beta.

Both are serine kinases that phosphoinhibit IRS at serine residues, while the activating insulin receptor phosphorylates tyrosines.

SOCS3, Suppressor of cytokine signaling, binds and inhibits the insulin receptor on its cytosolic side.

All of these pathways are induced by IL-6 and TNFalpha.

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4
Q

What are the two major insulin sensitising adipokines?

A

Leptin and adiponectin

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5
Q

What are the effects of leptin in the liver

A

Stimulates gluconeogenesis by activating PEPCK
Increases glycogen consumption.

Increases beta oxidation by activating PPAR alpha

inhibits lipogenesis, and inhibits expression of SREBPs

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6
Q

Leptins actions in muscle

A

Stimulates AMPK

Stimulates fatty acid oxidation. via PPARalpha activation.

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7
Q

What doe levels of leptin correlate best with.

A

The amount of adipose tissue in a person. Obese people have higher leptin levels, and also can develop leptin resistance much like insulin resistance.

Leptin does not increase during acute overfeeding.

Leptin levels drop during starvation.

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8
Q

Where is adiponectin synthesized?

What are its main targets?

A

Adipose tissue.

Its receptors are in the liver and muscles.

Its essential function is to enhance liver and muscle responses to insulin.

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9
Q

What are the effects of adiponectin on skeletal muscle

A

The activation (tyrosine phosphorylation of) the insulin receptor is enhances.

Enhances FA oxidation
Increases glucose uptake
Increases lactate production
Phosphoinhibits acetyl-CoA carboxylase (inhibiting FA syntehsis)

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10
Q

Effects of adiponectin on liver

A 
Inhibits FFA uptake and VLDL production. 
Increases FA oxidation
Increases aerobic glucose utilization 
Increases glycogen synthesis
Inhibits gluconeogenesis.
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11
Q

What are the major inhibitors of the adipokines?

A

Inflammatory cytokines TNFalpha and IL-6

Their levels are increased in obesity, and they decreases the level of adiponectin specifically.

Levels of TNF-alpha are correlated with BMI increases.

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12
Q

What signaling pathways do inflammatory cytokines activate that can cause insulin resistance?

A

JNK and IKKbeta serine kinase pathways.

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13
Q

What are major factors in insulin resistance?

A

TNFalpha, IL-6 proinflammatory signaling.

ER stress of beta cells, inhibiting insulin synthesis.

ER stress in adipocytes, decreasing adiponectin synthesis.

TKR2 and TLR4 expression are also increased on adipocytes in obesity, and can be activated at low levels by saturated fatty acids, causing a loop or pro-inflammatory signaling.

The Unfolded Protein Response, also induces pro-inflammatory signaling, insulin resistance.

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14
Q

What transcription factor is the major regulator of adipocyte differentiation/function

A

PPARgamma. and its receptor RXR, retinoid X receptor.

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15
Q

How is BMI calculated

A

Kg body weight / height in meters squared

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16
Q

Normal BMI?

A

18.5-25 kg/m2

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17
Q

Overweight BMI

A

25-29.9 kg/m2

18
Q

Obese BMI’s

mild, moderate, severe

A

30-35 kg/m2
35-40
Above 40

19
Q

What is the threshold for abdominal obesity?

A

men above 94 centimeters

women above 80 centimeters.

20
Q

What is the percentage of obesity in the US?

In Europe?

A

above 25% in the US

about 20% in europe.

21
Q

Which glucose transporter is insulin sensitive?

A

GLUT4

22
Q

Which glucose transporter is expressed on beta cells?

Where else is it expressed?

A

GLUT-2

Hepatocytes
Kidney
Enterocytes

It is low affinity

23
Q

Which glucose transporter(s) is involved in basal glucose uptake and is not insulin sensitive?

Where is it express

A

GLUT-1 expressed throughout body, is saturated at normal glucose levels for continual glucose uptake.
In brain, RBCs, encothelial cells, many body tissues.

GLUT-3 high affinity, neurons and other neural cells specifically.

24
Q

Basic differences between
Hormone sensitive lipase
and
Lipoprotein Lipase

A

Hormone sensitive lipase breaks down triglyceride into fatty acid and glycerol during fasting under influence of increased epinephrine/cortisol or decreased insulin.

Lipoprotein lipase breaks down chylomicron/VLDL and is involved in uptake of triglyceride into adipose tissues It needs Apo-CII cofactor.

25
Q

How does insulin affect HSL

How does glucagon affect HSL

A

Insulin causes phosphoprotein phosphatase to dephosphorylate and inactivate HSL.

Glucagon causes PKA to activate HSL by phosphorylation.

26
Q

What reaction does HSL catalyze?

A

It converts TAGs to DAGs and DAGs to MAGs.

It cannot remove the final FA from a MAG.
That requires MAG lipase.

27
Q

What other lipases can degrade TAGS besides HSL?

A

TAG lipase found in lysosomes, in liver and adipose.

Esterase, High affinity to short chain fatty acids.

28
Q

High yield facts about leptin and ghrelin.

A

High yield facts about Satiety regulation :

  • Leptin is secreted from Adipose tissue, and it induces satiety through its action on the hypothalamic ARCUATE nucleus, exerting its effect through 2 main actions :
    1) Decreases Neuropeptide Y (NPY) and Agoutin-Related Peptide(AgRP) ( an appetite stimulant )

2) Increases ProOpioMelanoCortin( POMP) and Cocaine Amphetamine Regulated Transcript (CART) ( Appetite suppressants)

  • Ghrelin is secreted from the stomach FUNDUS and the pancreatic Epsilon cells. It is the hunger hormone, and it counteracts Leptin’s actions.
  • Obese patient usually has high Leptin levels due to high adipose tissue –> leads to Leptin desensitization –> Loss of Leptin action ( much like DM2 )
  • Sleep deprivation increases Ghrelin and decreases Leptin.
29
Q

How does leptin affect appetite?

A

Decreases appetite, induces satiety.
In the hypothalamic arcuate nucleus:
Decreasing Neuropeptide Y (NPY)
Decreasing Agoutin-Related Peptide(AgRP)

Increasing POMC
Increasing Cocain amphetamine regulated transcript (CART)
Increases CRH, TRH

30
Q

How does leptin affect carbohydrate metabolism

A

decreases insulin secretion

Increases liver gluconeogenesis
activates Glucose 6 phosphatase
Activates PEPCK

Increases muscle GLUT4 expression.

31
Q

How does leptin affect lipid metabolism

A

increases beta oxidation,
by inducing carnitine palmitoyltransferase, increasing FA transport into the mitochondria

Decreases lipid synthesis, by lowering expression of SREBP.

32
Q

How does leptin affect body temperature?

A

It increases temperature, by increasing UCP2 expression, uncoupler.

33
Q

How does leptin inhibit insulin signal transduction?

A

Activates JAK2, then STAT3, then

SOCS. the Suppressor of Cytokine Signalling.

It can bind and inhibit the activity of BOTH
the Insulin Receptor and/or the Leptin receptor

It is induced by IL-6 and TNF-alpha as well.

34
Q

What enzymes of fatty acid metabolism are affected by insulin?

A

Insulin activates Acetyl-CoA Carboxylase ACC. First step in cytosolic FA synthesis.

Increases glucose uptake GLUT4 activity
Insulin increases PFK-2 activity (by dephosphorylating it with, which generates Fructose 2,6 bisphosphate F26BP, which potently activates PFK-1, the committed, rate limiting step of glycolysis.

F26BP also inhibits Fructose 1,6 bisphosphatase, inhibiting gluconeogenesis.

35
Q

What is are some genetic cause of obesity

A

MC4R mutations are the most frequent genetic cause of obesity. Melanocortin receptor which is found to also have a strong role in satiety.
Responsible for some of the satiating effercts of POMC and the stress response.

Null mutations of Leptin or the Leptin Receptor.

36
Q

Effect of AgRP

A

Agouti-related peptide.

An inverse agonist (inhibitor/silencer) of MC3R and MC4Rs.

Causes increased food intake

37
Q

Effect of NPY

A

Synthesized by arcuate nucleus acts on paraventricular nucleus and ventromedial nucleus to increase food intake

Weight loss increases NPY.

38
Q

Effect of Tyrosine-Tyrosine Protein (PYY)

A

decreases intestinal motility, emptying of stomach,
decreases appetite

PYY defects can cause obesity.

39
Q

What is metabolic syndrome

A

having at least 3 of these 5 symptoms

Hypertension >130mmHg
High blood TAGs
High fasting glucose Above 5.6mmol/L
Low HDL 
Central obesity above 102cm males above 88cm females.
40
Q

What are the consequences of obesity for this exam?

A

Metabolic syndrome
T2DM, insulin resistance

Non-alcoholic fatty liver
Ischemic heart disease
Stroke

Hyperuricemia, Gout

Breast cancer,
Endometrial cancer
Colorectal cancer
Polycystic ovarian syndrome

Sleep apnea
Asthma
Depressed respiration, lung infections
Depression
Fatigue

Vertebral compression,
Hernia

41
Q

Obesity therapy

A

lifestyle change.
lose 5-10% of current body mass over 6 months. Goal is for heart to be at aerobic range, 220bpm minus the age.
150 minutes of exercise a week, walking or running. no more than 2 consecutive days off.

Psychiatric support to gain motivation.

Medicine only recommended if BMI is above 30, or if it is above 27 and there is notable comorbidities.

Orlistat, inhibits intestinal lipases, preventing absorption of intestinal fats.

Surgical gastrectomy, only with severe comorbidity if BMI is above 35 kg/m2

Y elective pathobiochemistry (11 decks)

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