Fat-releasing enzyme (ATGL)
ATGL — The Rate-Limiting Lipase
Also searched as ATGL — The Rate-Limiting Lipase.
You want it reachable. It is described as the rate-limiting enzyme of the whole process: it takes the first bond off a stored triglyceride, and nothing downstream can outrun it. The catch is that it is not switched on directly. Its activator is held hostage by the coat protein on the droplet, so the main way in is to phosphorylate the coat and let the activator go. That is why this pathway has almost no direct inputs — the control point is next door. And at least three separate proteins bind it to hold it shut.
In depth
The enzyme that makes the first cut into stored fat — and the one that sets the pace for everything after it.
What drives it
Fat droplet coating reduces it.
The hostage mechanism, and it is why ATGL has almost NO direct inputs. 'Under basal (fed) conditions, perilipin 1A provides a protective barrier against lipolysis of stored triacylglycerols and binds CGI-58, a coactivator of ATGL. When CGI-58 is sequestered on the perilipin scaffold, it cannot interact with OR activate ATGL' (PMC4274058). doi 10.3389/fphys.2022.826314 adds that ATGL is further held shut by direct binders: 'Other accessory proteins can further inhibit ATGL activity through their direct protein-protein interaction with ATGL, including G0/S2 switch protein 2 (G0S2), hypoxia-induced lipid droplet-associated protein (HILPDA), and fat specific protein 27 (FSP27).'. doi 10.3389/fphys.2022.826314 · PMC4274058
Lipase activator increases it.
The middle of the mechanism. 'CGI58/ABHD5 is a lipid droplet-associated ATGL activator... Upon activation by PKA-mediated phosphorylation of PLIN1 and CGI58, CGI58 is released from PLIN1 and LDs, which then recruits ATGL to LDs and increases its catalytic activity. Therefore, lipolysis involves interactions between ATGL, CGI58, and PLINs; CGI58 is a key molecule for lipolysis activation in adipocytes' (doi 10.3389/fphys.2022.826314). The source is candid about the residual gap: 'even though the exact mechanism by which CGI58 increases ATGL activity is not completely understood.'. doi 10.3389/fphys.2022.826314
Lipase brake reduces it.
The padlock nothing in this formula reaches. 'g0s2 inhibits ATGL activity and decreases lipolysis in rodents and humans with a dose-dependent, non-competitive mANNER even in the presence of the coactivator CGI58' (doi 10.3389/fphys.2022.826314). Mapped structurally: 'the central hydrophobic domain of G0S2 is required for interaction and inhibition of ATGL, as well as the N-terminal patatin-like region (up to Leu254) of ATGL.' ⇒ freeing the activator does not get past this. doi 10.3389/fphys.2022.826314
The Second Padlock reduces it.
'hilpda, also known as hypoxia-induced gene-2, inhibits ATGL activity through direct physical interaction as well, even though with a lower inhibitory potency tHAN G0S2' (doi 10.3389/fphys.2022.826314). An open question the source admits: 'the reasons for being equipped with two similar, endogenous ATGL inhibitors are unclear.' and it works both ends: 'independently of its effects on ATGL, HILPDA also stimulates DGAT1-mediated triglyceride synthesis.'. doi 10.3389/fphys.2022.826314
Droplet-fusion protein reduces it.
'Other accessory proteins can further inhibit ATGL activity through their direct protein-protein interaction with ATGL, including G0/S2 switch protein 2 (g0s2), hypoxia-induced lipid droplet-associated protein (HILPDA), and fat specific protein 27 (FSP27)' (doi 10.3389/fphys.2022.826314). Three separate PADLOCKS on one enzyme. doi 10.3389/fphys.2022.826314
Growth complex reduces it.
Insulin's second route — it stops the lipase being made. 'insulin may inhibit lipolysis by decreasing transcription of ATGL via the mTORC1-mediated pathway (mTORC1-Egr1-ATGL) or through FoxO1' (doi 10.3389/fphys.2022.826314). The source is candid about the whole area: 'the detailed mechanisms remain controversial and incomplete.' and it is not a villain: the same kinase is one of the two that induce the lysosomal route to fat breakdown. doi 10.3389/fphys.2022.826314
Early growth response reduces it.
10.3389/fcell.2022.1003030 — 'mTORC1-Egr1-ATGL' (doi 10.3389/fphys.2022.826314), and Egr1 is listed in the Figure 2 abbreviations as 'Early growth response protein 1'. Nothing in any botanical formula is known to ACT here; the node exists for completeness of the route, not as a target. doi 10.3389/fcell.2022.1003030
Stress-resistance switch (FOXO1) reduces it.
'insulin may inhibit lipolysis by decreasing transcription of ATGL via the mTORC1-mediated pathway... OR through FoxO1' (doi 10.3389/fphys.2022.826314). A third, parallel route to the same gene. doi 10.3389/fphys.2022.826314
Energy sensing increases it.
The other half of the AMPK story, and it resolves a contradiction carried here. AMPK phosphorylates ATGL at Ser406 and that phosphorylation is stimulatory. In adipose-specific AMPK alpha1/alpha2 double-knockout mice: 'Both models of AMPK-ASKO ablation don't show changes in desnutrin/ATGL levels, but have defective phosphorylation of desnutrin/ATGL at S406 to decrease its tag hydrolase activity, lowering basal lipolysis in adipose tissue' (PMC (Kim et al., AMPK-ASKO)). ⇒ remove AMPK and the basal arm falls. Summarized in the field's own words: 'AMPK has been proposed to stimulate basal lipolysis, but to inhibit cAMP-induced lipolysis' (doi 10.1016/j.tem.2023.08.001). Note what did not change: ATGL protein levels were unaffected — this is activation, not expression. doi 10.1016/j.tem.2023.08.001
The Factory Order increases it.
10.7875/first.author.2011.055 — the transcriptional master of both lipases — found only in the japanese literature. 'IRF4は脂肪細胞におけるおもなリパーゼであるATGLおよびHSLの遺伝子発現を制御することにより脂肪融解を促進し脂質生合成を抑制している' = IRF4 promotes lipolysis and suppresses lipid biosynthesis by controlling the gene expression of ATGL and HSL, the main lipases (ライフサイエンス 新着論文レビュー (first.lifesciencedb.jp/archives/2444)). Proven by deletion: adipocyte-specific IRF4 knockout suppresses lipolysis and causes an increase in whole-body fat mass. Why it matters: other routes switch the lipases on and off by phosphorylation. This one sets how much lipase exists. Drivers that raise lipase expression (theobromine, ashwagandha leaf, Moringa) act on this layer, not the activation layer. doi 10.7875/first.author.2011.055
Blocks new fat cells increases it.
The two lipases are coupled, not independent. 'ATGL is an established PPAR-gamma target, and its decreased expression in lipe-null adipocytes probably contributes to the global lipolytic defect' (doi 10.1056/NEJMoa1315496 (nejm)). ⇒ lose the second lipase and you lose some of the first one too, because the first is a transcriptional target of the receptor the second one's products activate. That is why a human without this enzyme has a global lipolytic failure rather than a partial one. doi 10.1056/NEJMoa1315496
What it drives
It increases Releases stored fat.
'ATGL, considered the rate-limiting enzyme, catalyzes the first step, hydrolyzing TGs to diglycerides, which in turn are degraded by HSL into monoglycerides, with the release of a FFA in each step' (doi 10.3389/fphys.2022.826314). And on division of labor: 'adipose triglyceride lipase mediates the hydrolysis of triglycerides during basal lipolysis'. doi 10.3389/fphys.2022.826314
It increases Triglyceride assembly.
The futile cycle is structural, not incidental — and the Russian literature puts a harder number on it than the English. 'Базальный распад и синтез триацилглицеролов в жировой ткани объединены в СУБСТРАТНЫЙ ЦИКЛ... 1,3-ДАГ, продукт малоактивной ATGL, является ПРЕДПОЧТИТЕЛЬНЫМ СУБСТРАТОМ одного из ферментов синтеза триацилглицеролов – ДАГ-ацил-трансферазы. В результате ATGL и ДАГ-ацил-ТФ действуют СКООРДИНИРОВАННО и поддерживают НЕПРЕРЫВНЫЙ ЦИКЛ ГИДРОЛИЗА-РЕЭТЕРИФИКАЦИИ ТАГ' = the product of the rate-limiting lipase is the preferred substrate of the re-esterifying enzyme; the two ACT in coordination and maintain a continuous hydrolysis-re-esterification cycle (biokhimija.ru/biokhimiya-zhirovoj-tkani/lipoliz.html (русский)). The rate: 'В состоянии покоя около 70% жирных кислот, высвобожденных при участии малоактивной ATGL, НЕ ПОКИДАЮТ КЛЕТКУ и включаются обратно в состав ТАГ' = at rest, about 70% of the fatty acids released do not leave the cell and ARE put back into triglyceride. The English literature gives ~40% for this. The Russian figure is 70% and it is specifically for the basal, low-activity state. Sources: PMID 23066022; PMC3510842. doi 10.1074/jbc.M112.400416. · PMID 23066022 · PMC3510842
It modulates Diacylglycerol signaling.
ATGL hydrolyzes triacylglycerol to diacylglycerol, a second source of the conventional-PKC activator. Sources: doi 10.1186/s12944-020-01286-8; PMC8829450; PMID 23066022. doi 10.1186/s12944-020-01286-8 · PMID 23066022 · PMC8829450
Blends that modulate it
Each blend page names this pathway and carries the study behind its claim.
See it on the map
Open the causal map to follow this pathway upstream and downstream, arrow by arrow, each with its study.