Hormone sensitive lipase is to mediate the hydrolysis not only of triacyl glycerol stored in adipose tissue but also of cholesterol esters in the adrenals, ovaries, testes, and macrophages (Holm, 2003). For those that lack of HSL is breakdown of cellular fat stores fuels energy production and multiple anabolic processes (Zechner & Langin, 2014). HSL is a main enzyme to mobilase of fatty acids from acylglycerols in adipocytes for non-adipocytes. In adipocytes, catecholamines function for lipolysis mainly through protein kinase. A mediated phosphorylation of HSL and perilipin, a protein coating the lipid droplet. The anti-lipolytic action of insulin is mediated mainly via lowered camp levels, accomplished through activation of phosphodiesterase 3B (Osuga et al., 2000).
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'Hormone Sensitive Lipase'
Then, HSL alone catalyses the hydrolysis of triglycerides and diglycerides, whereas the participation of monoglyceride lipase is required to obtain complete hydrolysis of monoglycerides. HSL and monoglyceride lipase appear to play a key role in the hydrolysis of acylglcyerols also in non-adipocytes, but the involvement of additional lipases can be anticipated (Holm, 2003). It is encoded by a gene located on chromosome 19, and lacks homology to members of the pancreatic lipase gene family such as lipoprotein lipase (LPL). The lipolytic activities of HSL are under acute neuronal and hormonal control. Catecholamines and other lipolytic hormones stimulate these activities through the reversible phosphorylation of serine by cyclic adenosine 39,59-monophosphate (cAMP)-dependent protein kinase (PKA). Conversely, insulin, an antilipolytic hormone, suppresses its activities by preventing phosphorylation (Osuga et al., 2000).
Therefore, the activation of this enzyme in adipose tissues is thought to account for the elevation of plasma free fatty acid (FFA) levels in various conditions such as starvation or diabetes mellitus. Since mice lacking b3-adrenergic receptor, a dominant form of b-adrenergic receptor expressed in adipocytes, are obese and since mice lacking the RIIb subunit of PKA are lean because of increased PKA activity , it is reasonable to speculate that HSL mediates the regulation of adiposity by the adrenergic signaling pathway (Zechner & Langin, 2014). The studies reported below were undertaken in an at, tempt to characterize and to study the hormone-sensitive lipase activity in adipose tissue without interference from other lipases. By devising suitable assay conditions, me have been able to measure a lipase activity that apparently reflects rather well the hormone-sensitive lipolytic activity of the intact tissue (Vaughan, Berger, & Steinberg, 1964).
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The structural and biochemical of hormone sensitive lipase is located on chromosome 19q13.3 and was initially described to contain 9 exons spanning approximately 11 and 10 kB in human and mouse, respectively, that encode an mRNA of 2.8 kB. Subsequently, two additional exons (termed A and B) that differentiallyencode 170 and 70 nt 5untranslated regions were identified approximately 12.5 and 1.5 kB upstream of exon 1, respectively. Only the smaller HSL mRNA product is expressed in human adipose tissue. In contrast, five different exons have been reported within 7 kB of the translation start site of exon 1 in mouse HSL, each of which can be alternatively utilized and expressed in mouse adipose tissue to varying degrees (Kraemer & Shen, 2002).
