Lecture 5 - White and Brown Adipose Tissue and the non shivering thermogenesis

What is the main function of white adipose tissue (WAT)?

provides energy, provides insulation, cushions organs

What is the main function of brown adipose tissue (BAT)?

produces heat through non shivering thermogenesis

What are the main differences between white and brown adipocytes?

white - one large lipid droplet with few mitochondria, brown - many small lipid droplets and lots of mitochondria

Why is brown adipose tissue brown?

many mitochondria which contains iron

Why does brown adipose tissue have many capillaries?

supply oxygen and nutrients, supply heat around the body

Where is brown adipose tissue mainly found in adults?

neck, shoulders, spinal cord, kidneys

What are beige (brite) adipocytes?

brown like fat cells that develop within white adipose tissue

What stimulates the development of beige adipocytes?

sympathetic nervous system, noradrenaline

What is browning of white adipose tissue?

conversion of white adipose tissue towards brown like heat producing state

Is browning reversible?

yes

What is the benefit of browning?

increases ability to produce heat through non shivering thermogenesis

What is shivering thermogenesis?

heat production through involuntary skeletal muscle contractions

What is non-shivering thermogenesis?

heat production without muscle contractions, uses brown adipose tissue

Why is shivering an inefficient way of producing heat?

muscle movement increases heat loss through blood flow and movement of air around the body

Why are newborn babies more vulnerable to cold?

high sa to volume ratio, less muscle mass, less thermal insulation, immature nervous system, cannot move themselves warmer environments

Why is brown fat important in newborns?

produces heat to maintain body temperature because newborns cannot shiver effectively

Where is brown adipose tissue found in human newborns?

shoulders, upper back, internal organs

What is UCP-1?

uncoupling protein 1, found in inner mitochondrial membrane of brown adipocytes

How does UCP-1 produce heat?

allows protons to flow across inner mitochondrial membrane without passing through atp synthase

What is a proton leak?

protons flow across mitochondrial membrane without producing atp

Why are brown adipocytes efficient at producing heat?

contain many mitochondria with high concentrations of UCP-1

What is DNP?

chemical that uncouples oxidative phosphorylation and increases metabolic rate

How does DNP cause weight loss?

destroys proton gradient, causing energy to be released as heat instead of atp, increases fat burning

Why is DNP dangerous?

causes uncontrolled heat production, leading to hyperthermia, organ failure or death

Why is DNP more dangerous than UCP-1?

ucp-1 controlled by cells, dnp not controlled by the body

What activates brown adipose tissue?

noradrenaline from sympathetic nervous system

Which receptor does noradrenaline mainly bind to on brown adipocytes?

b3-adrenoreceptors

What is the signalling pathway that increases UCP-1 production?

noradrenaline, b3 receptor, adenylyl cyclase, camp, pka, creb phosphorylation, increased ucp-1 gene expression

What does PKA activate to increase fat breakdown?

hormone sensitive lipase

What does perilipin do?

covers lipid droplets

What happens to fatty acids after they are released from brown adipocytes?

enter mitochondria, undergo b oxidation, stimulate ucp-1

What is the final result of UCP-1 activation?

proton gradient dissipated and energy released as heat