ANGPTL8 requires ANGPTL3 to inhibit lipoprotein lipase and plasma triglyceride clearance

Abstract

Angiopoietin-like (ANGPTL)3 and ANGPTL8 are secreted proteins and inhibitors of LPL-mediated plasma triglyceride (TG) clearance. It is unclear how these two ANGPTL proteins interact to regulate LPL activity. ANGPTL3 inhibits LPL activity and increases serum TG independent of ANGPTL8. These effects are reversed with an ANGPTL3 blocking antibody. Here, we show that ANGPTL8, although it possesses a functional inhibitory motif, is inactive by itself and requires ANGPTL3 expression to inhibit LPL and increase plasma TG. Using a mutated form of ANGPTL3 that lacks LPL inhibitory activity, we demonstrate that ANGPTL3 activity is not required for its ability to activate ANGPTL8. Moreover, coexpression of ANGPTL3 and ANGPTL8 leads to a far more efficacious increase in TG in mice than ANGPTL3 alone, suggesting the major inhibitory activity of this complex derives from ANGPTL8. An antibody to the C terminus of ANGPTL8 reversed LPL inhibition by ANGPTL8 in the presence of ANGPTL3. The antibody did not disrupt the ANGPTL8:ANGPTL3 complex, but came in close proximity to the LPL inhibitory motif in the N terminus of ANGPTL8. Collectively, these data show that ANGPTL8 has a functional LPL inhibitory motif, but only inhibits LPL and increases plasma TG levels in mice in the presence of ANGPTL3.

On the mechanism of angiopoietin-like protein 8 for control of lipoprotein lipase activity

“…By itself, ANGPTL8 has no detectable effect on the activity of LPL. Reduction of LPL activity by ANGPTL8 occurs only in the presence of ANGPTL3 (15,18). It was recently demonstrated that ANGPTL8 needs to be coexpressed with ANGPTL3, by the same host cell, in order to have an effect on LPL activity (18).In this report, we show that recombinant ANGPTL8 produced in Escherichia coli has to be refolded together with Abstract Angiopoietin-like (ANGPTL) 8 is a secreted inhibitor of LPL, a key enzyme in plasma triglyceride metabolism.…”

“…It was previously demonstrated that the N-terminal ccd of ANGPTL3 reduces the activity of LPL in oxidative tissues in the fed state, thus directing the flow of lipoprotein-derived FAs to WAT for storage (14). In molar terms, ANGPTL3 is a relatively weak regulator of LPL in comparison to ANGPTL4 (10,15,16). Recent studies have shown, however, that the effect of ANGPTL3 on LPL is greatly enhanced by ANGPTL8 (15,17,18).…”

Angptl8 antisense oligonucleotide improves adipose lipid metabolism and prevents diet-induced NAFLD and hepatic insulin resistance in rodents

“…However, ANGPTL8's primary functions may be better ascribed to local, tissue-specific actions. ANGPTL8 is an LPL inhibitor that is expressed strongly in the white adipose tissue (WAT) [17,21]; it complexes with circulating ANGPTL3 to potently inhibit LPL [22]. Notably, ANGPTL8 expression is increased by insulin stimulation [23], so in the immediate postprandial period, a high level of circulating insulin increases ANGPTL8 expression and decreases adipose tissue LPL action and lipid uptake, potentially balancing insulin's primary actions at adipose tissue, suppression of lipolysis and promotion of lipid storage.…”

Can targeting ANGPTL proteins improve glucose tolerance?

“…Thus, a systemic effect mediated by liver-derived ANGPTL8 remains a possible explanation. Also favouring a role for liver ANGPTL8 is the reliance of ANGPTL8 on ANGPTL3 [13, 14], a protein that is expressed only in liver. Again, tissue-specific targeting of ANGPTL8 may be necessary to resolve this matter.…”

“…All three proteins inhibit the activity of lipoprotein lipase (LPL), the enzyme primarily responsible for plasma triacylglycerol clearance. While ANGPTL4 is a capable inhibitor of LPL on its own [2, 11, 12], ANGPTL3 and ANGPTL8 must form a complex to efficiently inhibit LPL [13, 14]. …”