Secreted mitochondrial aspartyl-tRNA synthetase (DARS2) regulates TNFα signaling

Aminoacyl-tRNA Synthetases (aaRS) are important regulators of cytokine signaling. Multiple cytoplasmic aaRS family members have been observed to be secreted in response to various stimuli to modulate downstream responses, however, agonist-induced cellular release of aaRS from mitochondria has not been described. In particular, TNFα is a potent mediator of aaRS release. BEAS-2B cells were utilized to study the release of mitochondrial Aspartyl-tRNA Synthetase (DARS2) in response to various cytokines. The role of DARS2 in paracrine signaling was evaluated using adoptive media transfer from BEAS-2B to recipient THP1 cells. To identify pathways governing DARS2 secretion, blocking antibodies chemical inhibitors and siRNA technology was employed. Herein, we describe DARS2 as the first mitochondrial aaRS released in response to TNFα from airway epithelia. Once secreted, DARS2 binds to macrophages, is internalized, thereby inducing an M1-like phenotype in recipient macrophages. DARS2 release from airway epithelia is in part, TNFα-receptor 1 dependent, and requires the endosomal sorting complex required for extracellular transport.