adipose tissue metabolism

1. Esterification of fatty acids to form triacylglycerol

2. Esterification of fatty acids to form triacylglycerol
Occurs primarily in the liver and adipose tissue

3. Esterification of fatty acids to form triacylglycerol
TAG composed of glycerol and fatty acids
Process of formation involves adding fatty acids onto a
glycerol backbone
Glycerol backbone required is in the form of glycerol
phosphate
Fatty acids added are in their activated forms (fatty acyl
CoA)

4. GLYCOLYSIS
Glucose
DHAP
NADH
Glycerol phosphate
NAD+
Glycerol
Glycerol kinase
Glycerol-P dehydrogenase
ADP ATP
LIVER
ADIPOSE
TISSUE
Prodution of glycerol phosphate
LIVER

5. CoA – C – R1
SYNTHESIS OF TRIACYLGLYCEROL
CH2OH
HO – C - H O
CH2 – O – P – O-
O-
Glycerol phosphate
O
Acyl transferase
CoA
O
CH2 – O – C – R1
HO – C - H O
CH2 – O – P – O-
O-
Lysophosphatidic acid

8. SYNTHESIS OF TRIACYLGLYCEROL (cont…)
Lysophosphatidic acid
R2 – C – O – C – H
O Acyl transferase
CoA – C – R2 CoA
O CH2 – O – C – R1
O
O
CH2 – O – P –O-
Phosphatidic acid O-
2
H O
Pi
Phosphatase
O
O CH2 – O – C – R1
R2 – C – O – C – H
CH2OH
Diacylglycerol

9. SYNTHESIS OF TRIACYLGLYCEROL (cont…)
O
CoA – C – R3 CoA
Acyl transferase
Diacylglycerol
R2 – C – O – C – H
O
O CH2 – O – C – R1
O
CH2 – O – C – R3
Triacylglycerol

10. Fate of TAG
TAG produced in the liver packaged into very-low
density lipoproteins (VLDL)
TAG produced in the adipose tissue stored at this site

11. Metabolism in adipose tissue

12. Formation of TAG in adipose tissue

13. Adipose tissue

15. TAG in adipose tissue
Serve as a fuel reserve
Ready to be mobilized when the body requires fuel to
produce energy

16. Mobilization of stored TAG
Involves hydrolysis of TAG to release fatty acids and
glycerol
Process initiated by hormone-sensitive lipase
It removes fatty acid from TAG
Additional lipases specific for DAG or MAG remove
the additional fatty acids

18. Hormone-sensitive lipase
Present in adipocytes
Activated by glucagon and epinephrine binding to their
receptors on the cell membrane

19. Hormone-sensitive lipase (cont’d)
Glucagon and epinephrine cause lipolysis
Results in release of free fatty acids and glycerol

20. Hormone-sensitive lipase (cont’d)
• Converted into its inactive form by insulin
• Hence insulin inhibits lipolysis

21. Metabolism in adipose tissue
TAG in adipose tissue simultaneously undergo
metabolism (anabolism [lipogenesis] and catabolism
[lipolysis])
Both processes do not occur at the same rate

22. Metabolism in adipose tissue
TAG
(Chylomicrons,
VLDL)
Plasma
Glucose – 6-P Adipose tissue
Glycolysis
Acetyl Lipogenesis Glycerol
CoA phosphate
Acyl CoA
TCA Esterification
TAG
Lipolysis (HSL)
FFA FFA Glycerol
+ Insulin FFA Glycerol
Glucose

23. Factors that favour lipogenesis
Well-fed state
High levels of insulin

24. Factors that favour lipolysis
Fasting, starvation
High levels of glucagon or epinephrine

25. Fate of fatty acids released
Released fatty acids (free or unesterified) move out of
adipocytes
Bind to albumin in the plasma
Transported to other tissues
Enter the cells in these tissues

26. Fate of fatty acids released
Fatty acids get activated
Undergo beta-oxidation
Used as fuel by most tissues
Exceptions:
RBC
(no mitochondria)
Brain
(albumin-FFA complex cannot cross blood-brain
barrier)

27. Adipose tissue
Adipose tissue is now considered to be more than just a
storage organ for TAG
It is considered an active endocrine organ that secretes a
variety of factors that regulate glucose and fat
metabolism
Eg, leptin and adiponectin

28. Obesity
• Genetics
• Environment
food intake
exercise
• Psychological factors
• Unknown factors

29. Metabolic syndrome
Obesity
Insulin resistance
Abnormal blood lipid levels
Individuals with metabolic syndrome are at risk to
develop diabetes mellitus and cardiovascular disease