Adipocytes Flashcards
What is adipose tissue?
Fat
More than just an energy store, also an endocrine organ
Adipose tissue mass =?
Adipocytes (number and volume)
How do you calculate BMI?
weight kg/ height m^2
What is a healthy BMI?
18.5 to 24.9
What are the different fat depots?
Subcutaneous depot
Visceral depot
What are visceral fat pads?
Epicardial Mesenteric Omental Retroperitoneal Gonadal
What are subcutaneous fat pads?
Abdominal
Gluteal
Femoral
Body fat distribution is an independent determinant of?
Health
Describe white adipose tissue morphology
Uniocular adipocytes
Preadipocytes
Stromal cells
Blood vessels
How is adipose tissue mass regulated?
Pluripotent stem cell Preadipocyte Many preadipocytes Differentiation Adipocytes
How does adipose tissue differentiate?
Pluripotent stem cells
Mesenchymal precursors
What mesenchymal precursors form which adipose tissue?
MYF5- produced white adipose tissue
MYF+ produce both, but predominantly brown
What can muscle satellite cells form?
Brown adipose tissue
What can endothelial precursors form?
Both adipose tissue types
What are the three types of adipose tissue?
Brown
Beige
White
What are transcriptional regulators of adipogenesis?
Different transcriptional factors
Tightly controlled
Time dependent expression
Transcription factors interact with each other, co-activators and miRNA
Name some typical white adipose tissue genes?
Fatty acid synthase Fatty acid binding protein Hormone sensitive lipase Glut4 Acetyl coA carboxylase Adipokines: adiponectin, leptin
Models for adipose tissue
3T3 L1 rodent fibroblasts
SGBS human cells
Human primary pre-adipocytes
What are the functions for white adipose tissue?
Energy storage
Physical protection
Cold protection
Endocrine organ
How is energy best stored in the body?
Short term - glycogen
Long term - triglycerides
How is dietary lipid uptake facilitated?
A challenge because they’re hydrophobic
Absorbed into the lymphatics
By lipoproteins
How are lipids digested?
Triglycerides gut lumen are broken down to glycerol and fatty acids by pancreatic lipase
Fatty acids mix with bile acids and salts. Form water soluble micelle
How are lipids absorbed?
Absorbed by enterocytes
Dissociate from bile acids and salts
Return to triglyceride
Packaged into a chylomicron and enters the lymphatics
What are the major lipoproteins?
Chylomicrons
VLDL
LDL
HDL
What is the role of chylomicrons?
Transport of triglycerides into the body
Made of triglycerides
What is the role of VLDL?
Transport of triglycerides from the liver to the tissues
Made of cholesterol and triglycerides
What is the role of LDL and HDL?
Mechanisms of moving cholesterol
Made of cholesterol and little triglyceride
How are fatty acids deposited in tissues?
Chylomicrons in the blood stream
Some triglyceride used immediately for energy
The rest is deposited in adipose tissue
How is fatty acid transported into adipose tissue?
Chylomicrons in adipose tissue capillaries
Come in contact with lipoprotein lipase
LPL hydrolyses the triglycerideand frees the fatty acid in the lumen
Taken up into adipocytes by transporters
What is the effect of insulin on adipose tissue?
Insulin release increases lipoprotein lipase expression and translocation
Takes 2-3 hours
What happens to the remnant of the chylomicron?
Returns to the liver
Any triglyceride is packaged into VLDL
None wasted
Describe the process of de novo lipogenesis
The synthesis of lipids from glucose
Glucose + acetyl coA to malonyl coA to free fatty acids + glycerol to triglyceride
What enzymes are involved in de novo lipogenesis?
Acetyl coA carboxylase
Fatty acid synthase
Esterification
What is lipolysis?
Release of fatty acids stored in lipid droplets
Driven by catecholamines or absence of insulin
Catalysed by lipases
How is the lipid droplet maintained?
Perilipin in the phospholipid layer protects from lipases
When phosphorylated, folds back, unprotected
What lipases are involved in lipolysis?
Adipose triglyceride lipase
Hormone sensitive lipase
Monogylglycerol lipase
Triglyceride to diaglyceride to monoglyceride to glycerol requires which enzymes?
ATGL
HSL
MGL
What is NEFA?
Non-esterified fatty acid
Enters the blood stream and binds to albumin
Goes to tissues that need energy
Glucose also enters blood
How is lipolysis regulated?
Hormone sensitive lipase controlled by hormones Promoted by adrenaline and noradrenaline Inhibited by insulin Always a basal level by ATGL Catecholamines increase rate
What does adipose tissue secrete?
Resistin TNFalpha IL-6 RBP4 Leptin Adiponectin Visfatin Omentin
What is leptin?
Appetite regulator
When leptin levels decrease, the brain increases food intake
What is adiponectin?
Widespread effects on liver, skeletal muscle, heart and vasculature, monocytes and macrophages
Improves metabolism when secreted
What is brown adipose tissue?
High thermogenic capacity
Main function is heat production
Multiple small lipid droplets
Stain brown because many mitochondria
What is thermogenesis?
Driven by catecholamines
Beta3-AR is activated by (nor)adrenaline
Signals via adenylyl cyclase, oAMP and PKA
Triggers lipolysis
Majority of fatty acids travel to the mitochondria
What is UCP1?
Uncoupling protein
Transports H+ from the inter membrane space into the matrix
Produces heat
What is the role of brown adipose tissue in infants?
Maintaining constant body temperature Mass declines with age Is present in adults Activated by the cold Beta adrenergic stimulation increases temperatures Could be an obesity treatment
