Efeitos dos ligantes de TSPO sobre a migração leucocitária: participação de receptores de glicorticóides

Abstract

Besides central benzodiazepine receptor (CBR) found on central nervous system (CNS) coupled to GABAA, another binding site for benzodiazepines was described and named peripheral benzodiazepine receptor (PBR) or Translocator protein (TSPO). The mainly function described to this TSPO is steroidogenesis. Additionally, its function as an immune modulator has been proposed with the involvement, at least in part, of endogenous glucocorticoids (EG). However, mechanisms of TSPO modulation on inflammatory process and the relation between the receptor and EG has not been totally established. This study aimed investigates effects of two synthetic TSPO ligands, a benzodiazepine, Ro5-4864, and an isoquinoline carboxamide, PK 11195, and their relation with EG on leukocyte migration. For this purpose, male Wistar rats were in vivo treated with RU 38486 (EG antagonist receptor) or vehicle and, in addition, TSPO ligands, Ro5-4864 and/or PK 11195, were topically applied on animal mesentery microcirculation to evaluate leukocyte rolling and adhesion, by intravital microscopy, under basal conditions or after stimulation by N-formylmethionine-leucine-phenylalanine (fMLP). In addition, peripheral leukocytes were collected and in vitro treated with TSPO ligands to evaluate adhesion molecules expression, chemotaxis and calcium influx. Endothelial cells obtained from cremaster muscle were in vitro treated with TSPO ligands to evaluate adhesion molecules expression under basal conditions or after stimulation by lipopolysaccharide from E.coli (LPS). Our results showed that: 1) TSPO ligand, Ro5-4864, altered the fMLP action since TSPO ligand inhibited the decrease of rolling, the increase of adherent cells, L-selectin cleavage, the increase of PECAM-1 expression, neutrophil chemotaxis and calcium influx; did not affect expression of PECAM1 and ICAM-1 induced by LPS on endothelial cells; 2) PK 11195 increased fMLP-induced neutrophil calcium influx and chemotaxis; 3) co-administration of TSPO ligands, Ro5-4864 and PK 11195, reverted Ro5-4864 effects on Lselectin and PECAM-1 expression, neutrophil and calcium influx, as well as PECAM-1 and ICAM-1 expression on endothelial cells; 3) a possible interrelation between TSPO and EG was observed since Ro5-4864 inhibited the increase of in vivo leukocyte rolling and adhesion induced by RU 38486 in vivo treatment; it inhibited the increase of neutrophil L-selectin, lymphocyte 2integrin and leukocyte PECAM-1 expressions; 4) It was showed that neutrophil have more TSPO than lymphocytes and endothelial cells, and this expression is increased by fMLP stimulation. Taken together, our results suggest that TSPO ligands differently modulate leukocyte adhesion and motility functions and endothelial cells adhesion, and further, they suggest an allosteric agonist/antagonist relation. Additionally, they showed a relation between TSPO and EG cytoplasmic receptor on the control of leukocyte-endothelial interaction.