Activated alpha 2-macroglobulin and aggregated LDL regulate differential LRP1 activation and receptor accumulation at early endosomes

CAMPOS LONDERO A; CHIABRANDO G

Mendoza

Congreso; CONGRESO SAIB 2022; 2022

SAIB

Low-density lipoprotein (LDL) receptor-related protein-1 (LRP1) is an endocytic and signaling receptorexpressed in several cell types. This receptor binds more than 40 different ligands, included alpha 2-macroglobulin-proteinase complex (activated a2M or a2M*) and aggregated low-density lipoprotein(agLDL). Previously, we showed that a2M* induces the LRP1 endocytic recycling to plasma membrane,whereas agLDL leads this receptor to locate in degradation compartments. These data suggest that LRP1 follows different intracellular routes depending on the ligand interacting. Here we evaluate the effect of a2M* and agLDL on LRP1 expression, endocytosis and intracellular signaling activation in HeLa cells. By Western blot we found that a2M* induces a significant increase for LRP1 protein expression from 8 h of stimulation, whereas agLDL does not produce any change after 24 h of stimulus. Both ligands unmodified the sortilin protein expression, a sorting protein fundamental for LRP1 traffic. By confocal microscopy we showed that a2M* and agLDL promote LRP1 endocytosis with significant accumulation in EEA1+-early endosomes (EEA1+-EE) for 30 min of continuous incubation. Through image analysis we established that a2M* produces EEA+-EE vesicles with increased surface values compared to agLDL-stimulated and nonstimulated cells. Finally, a2M*, but not agLDL, activates Akt pathway. These data suggest that ligands produce different processes of membrane fusion at early endosomes during LRP1 endocytosis and regulate the receptor activation, which in part may explain non-redundant functions of a2M* and agLDL ligands.