Year: 2025
Type: article
Abstract: Bis(monoacylglycero)phosphates (BMPs) are biologically functional acidic lipids present in late endosomes and lysosomes. We recently reported that lysosomal phospholipase A2 (LPLA2, PLA2G15), the lysosomal enzyme mediating BMP catabolism, degrades BMP isomers with distinct substrate specificity. Specifically, sn -(3-oleoyl-2-hydroxy)-glycerol-1-phospho- sn -1'-(3′-oleoyl-2′-hydroxy)-glycerol (S,S-(3,3′-diC 18:1 )-BMP) is a significantly better substrate for LPLA2 than S,S-(2,2′-diC 18:1 )-BMP. S,S-(2,2′-diC 18:1 )-BMP is generally considered the only biologically relevant BMP isomer. We investigated the isomerization of S,S-(2,2′-diC 18:1 )-BMP to (S,S-(3,3′-diC 18:1 )-BMP) in vitro and in cells. Thin-layer chromatography was used to distinguish S,S-(3,3′-diC 18:1 )-BMP from S,S-(2,2′-diC 18:1 )-BMP. S,S-(2,2′-diC 18:1 )-BMP/1,2-di- O -(9Z-octadecenyl)- sn -glycero-3-phosphocholine liposomes were incubated at varying pH in the presence or absence of test substances. First, we studied bovine serum albumin, which is known to promote isomerization of 1-acyl-2-lysophosphatidylcholine. The formation of S,S-(3,3′-diC 18:1 )-BMP in the presence of albumin increased in a time-dependent and albumin concentration-dependent manner under neutral conditions and was dependent on pH and the molar ratio of S,S-(2,2′-diC 18:1 )-BMP in liposomes. Treatment of isomeric products generated during isomerization reaction with sn -1,3-specific lipase produced both oleic acid but also lyso-phosphatidylglycerol, indicating that the conversion of S,S-(2,2′-diC 18:1 )-BMP to S,S-(3,3′-diC 18:1 )-BMP is preceded via S,S-(2,3′-diC 18:1 )-BMP. S,S-(3,3′-diC 18:1 )-BMP formed was preferentially degraded by LPLA2 over the S,S-(2,2′-diC 18:1 )-BMP. Proteins such as HSP70 and human serum albumin and metal ions such as Fe 3+ and Zn 2+ acted as cofactors promoting the isomerization of S,S-(2,2′-diC 18:1 )-BMP under neutral conditions. At baseline, RAW 264.7 cells showed nonnegligible amounts of sn -1,3-specific lipase-sensitive BMPs. However, lipase-sensitive BMPs were increased by exposure to chloroquine or NH 4 Cl, suggesting that cells undergo S,S-(2,2′-diacyl)-BMP isomerization upon alkalinization of intracellular acidic compartments.
Source: Journal of Lipid Research
Institutions: University of Michigan, Michigan Medicine
Language: English
Subfield: Biochemistry
Domain: Life Sciences
Open Access status: gold
Estimated APC paid: $3,430
OpenAlex ID: W4409009975