Brown Fat Biology

Intro

This lecture is all about brown fat. We’ll cover what brown fat is, how it functions, and how we can try to make more of it to improve our metabolism.

We’ll talk about the different types of fat, specifically white, beige (also called brite) and brown fat. We’ll discuss how they differ in function and morphology, and what induces the formation of each type of fat. We’ll also cover the biology of the UCP1 protein and how it works in contrast to ATP synthase.

Lastly, we’ll discuss ways that we can induce the formation of brown fat through nutrition and lifestyle changes.

Key take-aways

At the end of this lecture, you should be able to:

Name the three types of fat tissues Know which type of fat has the most mitochondria Know what cold temperature does to brown fat formation/activity Understand the correlation between brown fat and markers of obesity and white fat Understand how UCP1 works compared to ATP synthase Know how the hypothalamus controls brown fat activity Know the lifestyle factors that can influence the activity of brown fat

Key terms

Key terms we will cover:

• Brown fat

• Beige fat

• UCP1

• ATP synthase

• Hypothalamus

• Most people think only of white adipose tissue when they hear the word “fat”, but there are in fact other types

• Brown fat/Beige fat is energetically more active than white fat

• We can control the activity of our brown fat through lifestyle choices

Types of adipose tissue

white fat is all lipid droplet beige has some mitochondria brown fat has a lot of mitochondria

more brown fat in the winter

brown fat has significant inverse relations to BMI. total fat, and visceral fat

What’s purpose of brown fat?

• Despite high mitochondria content, brown adipocytes have a remarkably low capacity for ATP synthesis and express LOW levels of ATP synthase
• Instead they express a protein called UCP1 which induces the generation of HEAT, not ATP when hydrogen ions pass through its pore

How do you turn it on

norepinephrine is signaled -> innervates brown fat brown fat activates a lipolytic cascade, fuel electron transport chain

induces lipolysis in white fat as well

UCP1 is activated when free fatty acids are in a massive excess to ATP — excessive food intake

What is beige fat?

can form and unform from white fat.

mice didn’t seem to get as obese when they had more beige fat

impact on hormonal biology

• Forced expression of UCP1 in white fat improves leptin and insulin sensitivity
• Transplantation of brown fat into obese mice improves insulin sensitivity and glucose uptake in numerous tissues

Induction of brown and beige fat

• cold exposure exposed to mild cold (66ºF) with light clothing for 2 hours repeated cold exposure over 6 weeks

• dietary interventions fish oil

• endurance exercise

Summary

• Brown and beige fat are important aspects of overall human metabolism
• Cold exposure is the most well studied and validated method to increase brown/beige fat formation & activation
• Dietary and exercise interventions also have the potential to increase brown & beige fat activity
• The overall capacity of these pathways to reduce body fat remains unknown