Lipopolysaccharide increases exosomes secretion from endothelial progenitor cells by toll‐like receptor 4 dependent mechanism

Abstract

Background Information Endothelial progenitor cells (EPCs) can exert angiogenic effects by a paracrine mechanism, where exosomes work as an important mediator. Recent studies reported functional expression of toll‐like receptor (TLR) 4 on human EPCs and dose‐dependent effects of lipopolysaccharide (LPS) on EPC angiogenic properties. To study the effects of TLR4/LPS signaling on EPC‐derived exosomes (Exo) and clarify the mechanism, we investigated the role of LPS on exosomes secretion from human EPCs and tested their anti‐oxidation/senescence functions. We employed the inhibitors of the plasma membrane Ca2+‐ATPase (PMCA), endoplasmic reticulum Ca2+‐ATPase (ERCA), PLC‐IP3 pathway and store‐operated calcium entry to assess the effects of LPS on EPC intracellular calcium signalings which critical for exosome secretion. Results LPS induced the release of Exo in a TLR4‐dependent manner in vitro, which effect can be partly abrogated by an membrane‐permeable IP 3 R antagonist, 2‐aminoethyl diphenylborinate (2‐APB), but not PLC inhibitor, U‐73122. The LPS can significantly delay the fallback of [Ca2+]i after isolating the cellular PMCA activity, and disturb PMCA 1/4 expression. The distribution of elevated intracellular calcium seemed coincident with the development of the multivesicular bodies (MVBs). furthermore, the anti‐oxidation/senescence properties of LPS‐induced Exo were validated by the senescence‐associated β‐galactosidase activity assay and reactive oxygen species (ROS) related H2DCF‐DA assay. Conclusions The mechanism of PMCA downregulation and IP3R‐dependent ER Ca2+ release may contribute to the pro‐exosomal effects of LPS on EPCs. Significance This study provides new insights into the potential role of LPS/TLR4 pathway in regulating EPC‐derived exosomes, which may help to develop some feasible approach to manipulate the Exo secretion and promote the clinical application of EPCs therapy in future.

Exosome biogenesis: machinery, regulation, and therapeutic implications in cancer

“…shown that an overload of cytosolic Ca 2+ due to either release from the intracellular Ca 2+ store or influx from the extracellular milieu facilitates exosome biogenesis in both physiological and pathological conditions [97,171] (Fig. 6A).…”

“…Dysregulation of Ca 2+ signaling and altered levels of intracellular Ca 2+ are involved in a plethora of processes in carcinogenesis, progression and chemoresistance of multiple cancer cell types [ 170 ]. Mounting evidence has shown that an overload of cytosolic Ca 2+ due to either release from the intracellular Ca 2+ store or influx from the extracellular milieu facilitates exosome biogenesis in both physiological and pathological conditions [ 97 , 171 ] (Fig. 6 A).…”