Adipose Tissue Function and Dysfunction

Question 1

What are the three major types of adipose tissue? Describe them.

Answer 1

• White (WAT) - UCP1 negative; low mitochondria density; one large lipid droplet
• Beige - UCP1 positive; medium mitochondria density; few-many lipid droplets
• Brown (BAT) - UCP1 positive; high mitochondria density; numerous small lipid droplets

Question 2

Describe the physiological functions of WAT

Answer 2

• Insulate and cushion the body
• Store excess energy in the form of TAG - accepts FAs from VLDLs and chylomicrons and stores them
• Provide energy resources via releasing FAs
• Endocrine function - produces and secretes adipokines (esp adiponectin)

Question 3

What is the physiological function of beige and brown adipose tissue?

Answer 3

THERMOGENESIS - to maintain core body temperature in response to cold stress by generating heat

Question 4

Name and briefly describe two factors involved in regulation of BAT activity and browning

Answer 4

1. Neurons and immune cells (NOREPINEPHRINE) - when cold terminal neurons at adipose tissue release norepinephrine, this increases UCP1 expression helping you resist cold environment and release heat
   - more heat generated using FAs, so don’t accumulate fat
2. Muscles (IRISIN-INDUCED BROWNING) - Exercise increases conversion of WAT to beige
   - increasing basal body temperature so you burn more nutrients, losing weight

Question 5

Describe possible results of adipose tissue dysregulation (enlarging of WAT)

Answer 5

• Increased pro-inflammatory cytokines (TNF-a)
• Increased FFAs
• Decreased adiponectin

These work together to induce adipose tissue dysfunction:

• insulin resistance
• releasing large amounts of FAs
• Endothelial cell dysfunction

Question 6

Describe TNF’s role in adipose dysfunction. What are the consequences?

Answer 6

• When adipose tissues are enlarged they produce more TNF-a, a proinflammatory cytokine (higher TNF-a levels in obese individuals)
• Excessive TNF production can result in chronic inflammation
• TNF-a inhibits insulin-signalling pathway by preventing tyrosine binding, inducing insulin resistance

Question 7

Name and describe some factors that contribute to a healthy vs unhealthy obesity

Answer 7

• HYPERPLASIA VS HYPERTROPHY
- hyperplasia - creates more fat cells (more adiponectin, less inflammatory adipokines)
- hypertrophy - larger fat cells (less adiponectin, more inflammatory cytokines, less bloodflow)
• VISCERAL VS SUBCUTANEOUS -
- visceral - produces more substances that cause metabolic abnormalities (TNF, FFA, etc); more direct access to liver