Triggering Receptor Expressed on Myeloid Cells-2 (TREM2) Inhibits Steroidogenesis in Adrenocortical Cell by Macrophage-derived Exosomes in Lipopolysaccharide-induced Septic Shock

Abstract

Background: Endogenously produced glucocorticoids exhibit immunomodulating properties and are of pivotal importance for sepsis outcome. Uncontrolled activation of the immune-adrenal crosstalk increases the risk of sepsis-related death. Triggering receptor expressed on myeloid cells-2 (TREM2) is richly expressed on macrophages and has been demonstrated to improve outcome of sepsis by enhancing elimination of pathogens. However, the role and mode of action of macrophage TREM2 on adrenocortical steroidogenesis remains unclear in septic shock.Methods: The acute septic shock model was established by intraperitoneally challenging wild-type (WT) and TREM2 knock-out (Trem2-/-) mice with lipopolysaccharide (30 mg/kg). The mice were assessed for TREM2 expression and local inflammation in adrenal gland and synthesis of corticotropin releasing hormone (CRH) and adrenocorticotropic hormone (ACTH) in vivo. Bone marrow-derived macrophages or macrophage-derived exosomes were isolated from WT and Trem2-/- mice and co-cultured with adrenocortical cells. The expression of steroidogenic enzymes and corticosterone production were assessed.Results: Genetic deficiency of TREM2 caused significantly higher corticosterone levels (326.6 ± 73.0 ng/ml in Trem2-/- mice vs. 151.1 ± 58.9 ng/ml in WT mice; p < 0.001) at the early stage of LPS-induced septic shock. While TREM2 deficiency neither increased CRH and ACTH, nor exacerbated the inflammation in adrenocortical tissue during septic shock. Ex vivo study revealed that Trem2-/- macrophages significantly promoted the expression of steroidogenic enzymes and increased production of corticosterone (27.73 ± 1.78 ng/ml in Trem2-/- mice vs. 22.96 ± 1.94 ng/ml in W T mice; p < 0.01). Furthermore, Trem2-/- macrophage-derived exosomes were able to mimic Trem2-/- macrophages in enhancing adrenocortical steroidogenesis. Conclusions: At the early stage of lipopolysaccharide-induced septic shock, macrophage TREM2 inhibited the steroid synthesis and corticosterone production in adrenocortical cells, which may be partially associated with macrophage-derived exosomes.