Could it all be about “Brown Fat”?

Proverbs 4

Get Wisdom at Any Cost

1 Listen, my sons, to a father’s instruction; pay attention and gain understanding. 

12 When you walk, your steps will not be hampered; when you run, you will not stumble. 

23 Above all else, guard your heart, for everything you do flows from it.

 Is it all about the “Brown Fat”?

Brown adipose tissue or brown fat is one of two types of fat or adipose tissue (the other being white adipose tissue) found in mammals.

It is especially abundant in newborns and in hibernating mammals. Its primary function is to generate body heat in animals or newborns that do not shiver. In contrast to white adipocytes (fat cells), which contain a single lipid droplet, brown adipocytes contain numerous smaller droplets and a much higher number of mitochondria, which contain iron and make it brown. Brown fat also contains more capillaries than white fat, since it has a greater need for oxygen than most tissues.

Biochemistry:

The mitochondria in a cell utilize fuels (glucose or ketones) to produce energy (in the form of ATP). This process involves storing energy as a proton gradient, also known as the proton motive force (PMF), across the mitochondrial inner membrane. This energy is used to synthesise ATP when the protons flow across the membrane (down their concentration gradient) through the ATP synthase enzyme; this is known as chemiosmosis.

In warm-blooded animals, body heat is maintained by signalling the mitochondria to allow protons to run back along the gradient without producing ATP. This can occur since an alternative return route for the protons exists through an uncoupling protein in the inner membrane. This protein, known as uncoupling protein 1 (thermogenin), facilitates the return of the protons after they have been actively pumped out of the mitochondria by the electron transport chain. This alternative route for protons uncouples oxidative phosphorylation and the energy in the PMF is instead released as heat.

Brown adipose tissue is highly specialised for this non-shivering thermogenesis. First, each cell has a higher number of mitochondria compared to more typical cells. Second, these mitochondria have a higher-than-normal concentration of thermogenin in the inner membrane.

Function in infants:

In neonates (newborn infants), brown fat, which then makes up about 5% of the body mass and is located on the back, along the upper half of the spine and toward the shoulders, is of great importance to avoid lethal cold (hypothermia is a major death risk for premature neonates). Numerous factors make infants more susceptible to cold than adults:

  • The higher ratio of body surface (proportional to heat loss) to body volume (proportional to heat production)
  • The higher proportional surface area of the head
  • The low amount of musculature and the inability or reluctance to shiver
  • A lack of thermal insulation, eg., subcutaneous fat and fine body hair (especially in prematurely born children)
  • The inability to move away from cold areas, air currents or heat-draining materials
  • The inability to use additional ways of keeping warm (eg., drying their skin, putting on clothing, moving into warmer areas, or performing physical exercise)
  • The nervous system is not fully developed and does not respond quickly and/or properly to cold (eg., by contracting blood vessels in and just below the skin).

Heat production in brown fat provides a baby with an alternative means of heat regulation and is critical to our survival of our species.

Deuteronomy 7:15

The LORD will keep you free from every disease.

Presence in adults:

It was believed that after infants grow up, brown adipose tissue should not be required for survival as the adult should have the skills to manage ALL the factors above.

Recent studies using Positron Emission Tomography scanning of adult humans have shown that brown fat is however still present in very small amounts in adults in the upper chest and neck. The remaining deposits become more visible and active in slim trim adults since brown fat takes calories from normal fat and burns it with high efficiency and increases metabolic rates.

Embryology:

Brown fat cells and muscle cells both seem to be derived from the same stem cells in the embryo. Both have the same marker on their surface (Myf5, myogenic factor), which white fat cells do not have. Brown fat cells and muscle cells both come from the middle embryo layer (mesoderm), the source of myocytes (muscle cells), adipocytes, and chondrocytes (cartilage cells). Adipocytes give rise to white fat cells and brown fat cells.

 

Researchers found that both muscle and brown fat cells expressed the same muscle factor Myf5, whereas white fat cells did not. This suggested that muscle cells and brown fat cells were both derived from the same stem cell. Furthermore, muscle cells that were cultured with the transcription factor PRDM16 were converted into brown fat cells, and brown fat cells without PRDM16 were converted into muscle cells.

This common stem cell theory may be an important for stimulating and activating brown fat through actively maintaining muscle mass as we age.

In my next BLOG on this subject I will talk on the mechanisms to increase activity and expression of Brown Fat.

Blessings

Cardiologydoc

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