AIE-enabled transfection-free identification and isolation of viable cell subpopulations differing in the level of autophagy

ABSTRACT Elevated macroautophagy/autophagy, typically characterized by increased autophagosome accumulation, occurs in a wide variety of physiological and pathophysiological processes, but the current methodology for studying autophagy aberration in native non-transfected cells is rather limited. Here we show that LKT, an engineered molecular probe composed of a cell-penetrating peptide, an LC3-interacting motif and the aggregation-inducedemission (AIE) luminogen tetraphenylethylene, achieved robust identification and isolation of viable autophagy-varying cell subpopulations without the need of foreign reporter gene expression. Non-fluorescent in water, LKT fluorescence is activated upon interaction with liposomes in an AIE-dependent fashion, and the presence of LC3 on the liposome membrane dramatically boosted LKT fluorescence enhancement. In LKT-treated GFP-LC3 HeLa cells, induction of autophagy with rapamycin or trehalose, and blockade of autophagy with chloroquine, both produced bright GFP-LC3-colocalizing LKT puncta, leading to an increase in LKT fluorescence that facilitated efficient separation of cells based on the level of autophagosome accumulation. Using fluorescence-activated cell sorting, we were able to isolate cell subpopulations varying in the level of basal autophagy from a variety of cultured cell lines and primary cells. In a proof-of-concept study, we isolated autophagy-high and autophagy-low subpopulations from differentiated THP-1 cells and revealed that the autophagy-high THP-1 cells, compared to their autophagy-low counterparts, exhibited a higher level of NLRP3 protein expression and a stronger NLRP3 inflammasome activation following nigericin challenge. Our work demonstrated the unique power of the AIE technology and LKT, filling a void, should prove valuable for autophagy research. Abbreviations 3-MA, 3-methyladenine; AIE, aggregation-induced emission; AIEgens, aggregation-induced emission luminogens; ATG5, autophagy related 5; BMDM, bone marrow-derived macrophage; CQ, chloroquine; DiD, 1,1’-dioctadecyl-3,3,3’,3’-tetramethylindodicarbocyanine perchlorate; DiO, 3,3’-dioctadecyloxacarbocyanine perchlorate; DMSO, dimethyl sulfoxide; d-THP-1, differentiated THP-1; FACS, fluorescence activated cell sorting; FBS, fetal bovine serum; FCCP, carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone; GABARAP, GABA type A receptor-associated protein; GFP, green fluorescent protein; HBSS, Hanks’ balanced salt solution; HPLC, high-performance liquid chromatography; HRP, horseradish peroxidase; IL1B, interleukin 1 beta; KT, an AIE probe composed of a cell-penetrating peptide and an AIEgen tetraphenyl ethylene; LC3-II, lipidated LC3; LDH, lactate dehydrogenase; LIR, LC3-interacting region; LKR, engineered molecular probe composed of an LC3-interacting peptide, a cell-penetrating peptide and a non-AIE fluorescent molecule rhodamine; LKT, engineered molecular probe composed of an LC3-interacting peptide, a cell-penetrating peptide and an AIEgen tetraphenyl ethylene; LPS, lipopolysaccharide; MAP1LC3/LC3, microtubule associated protein 1 light chain 3; MEF, mouse embryonic fibroblast; mRFP, monomeric red fluorescent protein; NHS, N-hydroxysuccinimide; NLRP3, NLR family pyrin domain containing 3; PBS, phosphate-buffered saline; PCC, pearson’s correlation coefficient; PL, photoluminescence; PMA, phorbol 12-myristate 13-acetate; RAP, rapamycin; RIM, restriction of intramolecular motions; s.e.m., standard error of the mean; SPR, surface plasmon resonance; SQSTM1/p62, sequestosome 1; TAX1BP1, Tax1 binding protein 1; TPE, tetraphenylethylene; TPE-yne, 1-(4-ethynylphenyl)-1,2,2-triphenylethene; Tre, trehalose; u-THP-1: undifferentiated THP-1; UV-Vis, ultraviolet visible