Basics of Fat Loss | Simple Science that You can Use
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Basics of Fat Loss | Simple Science that You can Use – Thomas DeLauer
HSL
Hormone sensitive lipase is a complex chemically structured enzyme that acts as a catalyst for the hydrolysis of fat in your body
The levels of hormone-sensitive lipase (HSL) in your body are inversely proportional to the serum levels of insulin – what this means is that as the levels of HSL decrease, the insulin levels in your blood increase
Simply put, it’s what burns your fat deposits
The only site for regulation of fatty acid oxidation is at the level of hormone-sensitive lipase in adipose tissue (more later)
Under fasting conditions, with minimal insulin in the blood, glucagon promotes formation of the phosphorylated, active form of hormone-sensitive lipase
When epinephrine is present, it further shifts the equilibrium to active hormone-sensitive lipase, increasing the hydrolysis of triglycerides to produce free fatty acids (FFA) and glycerol
The glycerol is carried to the liver, where it enters gluconeogenesis, while the FFA are carried on serum albumin to the tissues where they are catabolized for energy
The liver uses some of the energy from fat mobilization to support gluconeogenesis
Adipose Triglyceride Lipase
Hormone-sensitive lipase (HSL) was the first lipase known to hydrolyze triacylglycerols in rat adipose tissue (1988) until the identification of adipose triglyceride lipase (ATGL) in 2004
While HSL could catalyze the hydrolysis of triacylglycerides and diacylglycerides as well as various cholesterol ester species, ATGL showed high substrate specificity for triacylglycerides
To date, three major lipases have been identified: Adipose triglyceride lipase (ATGL) performs the first step of TG hydrolysis, generating diglycerides (DGs) and FAs
Hormone-sensitive lipase (HSL) performs the second step and hydrolyzes DGs, generating monoglycerides (MGs) and FAs
In contrast to ATGL, HSL exhibits a broader substrate specificity, also hydrolyzing TGs, cholesteryl esters, MGs, and retinyl esters in addition to DGs
Monoglyceride lipase (MGL) is selective for MGs and generates glycerol and the third FA – thus, lipolysis constitutes a coordinated three-step process catalyzed by three different enzymes, which degrade TG into glycerol and FAs
End
Hormone-sensitive lipase (HSL) is presumed to be essential for lipolysis, which is defined as the mobilization of free fatty acids from adipocytes
Lipolysis is under the control of various hormones and cytokines in adipocytes – Lipolytic hormones such as catecholamines and ACTH stimulate cAMP-dependent protein kinase (PKA), which in turn phosphorylates hormone-sensitive lipase (HSL) and perilipin in adipocytes
References
1) Hormone-Sensitive Lipase – an overview | ScienceDirect Topics. (n.d.). Retrieved from https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/hormone-sensitive-lipase
2) Hormone-sensitive lipase. (n.d.). Retrieved from http://www.jlr.org/content/43/10/1585.full
3) Ruiz G , et al. (n.d.). Cyclic AMP-dependent protein kinase activity and lipolysis in adipose tissue. Effect of fasting, oligomycin and iodoacetamide. – PubMed – NCBI. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/6280256
4) What is Hormone-Sensitive Lipase? (n.d.). Retrieved from https://bodytomy.com/hormone-sensitive-lipase
5) Lipolysis in the Absence of Hormone-Sensitive Lipase. (2002, December 1). Retrieved from http://diabetes.diabetesjournals.org/content/51/12/3368
6) Perilipin – an overview | ScienceDirect Topics. (n.d.). Retrieved from https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/perilipin
7) Perilipin Promotes Hormone-sensitive Lipase-mediated Adipocyte Lipolysis via Phosphorylation-dependent and -independent Mechanisms. (n.d.). Retrieved from http://www.jbc.org/content/281/23/15837.full
8) The Phosphorylation of Serine 492 of Perilipin A Directs Lipid Droplet Fragmentation and Dispersion. (n.d.). Retrieved from http://www.jbc.org/content/281/17/11901.full
9) Elkins DA and Spurlock DM. (n.d.). Phosphorylation of perilipin is associated with indicators of lipolysis in Holstein cows. – PubMed – NCBI. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/19585405
10) Schweiger M , et al. (n.d.). Adipose triglyceride lipase and hormone-sensitive lipase are the major enzymes in adipose tissue triacylglycerol catabolism. – PubMed – NCBI. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/17074755
11) Kershaw EE , et al. (n.d.). Adipose triglyceride lipase: function, regulation by insulin, and comparison with adiponutrin. – PubMed – NCBI. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/16380488
12) Adipose Triglyceride Lipase – an overview | ScienceDirect Topics. (n.d.). Retrieved from https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/adipose-triglyceride-lipase