OR19-06 Sepsis-Induced Critical Illness in Mice Alters Key Regulators of ACTH Production and Secretion Within the Anterior Pituitary Gland

Introduction Critical illness is hallmarked by high plasma cortisol without elevated ACTH. This is partly explained by low cortisol-binding proteins and reduced binding affinity and by suppressed cortisol metabolism, 3 peripheral drivers of increased free cortisol (corticosterone (CORT) in rodents).(1) We hypothesized that lack of elevated plasma ACTH is explained by CORT-induced feed-back inhibition either due to suppressed CRH or AVP pituitary signaling or to direct glucocorticoid receptor (GR)-mediated action within corticotrophs. To test this hypothesis, we documented alterations in ACTH precursors and key enzymes controlling ACTH maturation and secretion in a mouse model of sepsis-induced critical illness. Methods C57Bl/6 mice were randomly allocated to a healthy control group or to 4 critically ill groups sacrificed after increasing illness duration (30 hours (H), 3 days (D), 5D or 7D). Critical illness was induced by sepsis brought about by cecal-ligation and puncture followed by fluid-resuscitation and antibiotics treatment. The study was continued until 15 surviving animals per time cohort were reached (n=120). We quantified pituitary pro-opiomelanocortin (POMC) gene/protein expression and POMC plasma concentrations, pituitary POMC intracellular trafficking and cleavage via intracellular POMC sorting/trafficking receptor Carboxypeptidase E (CPE) and prohormone convertase 1 (PC1/3) gene/protein expression. Gene expression of Annexin A1, an inhibitor of mature ACTH secretion, was quantified as marker of GR-mediated CORT-induced feedback inhibition at corticotroph level. Results Plasma CORT concentrations were median 3-fold increased during critical illness (p<0.001 for all time cohorts) in the face of normal (for 30H, 3D and 5D cohorts) to low (7D time cohort; p=0.01) plasma ACTH concentrations. Plasma POMC concentrations were higher in critically ill than in control mice (p=0.05). POMC gene expression (but not protein, P=0.8) was a median 55% higher in critically ill mice than in controls (p<0.05 for all time cohorts). In contrast, pituitary mature ACTH protein concentration was median 61% lower in critically ill than in control mice (p<0.01). CPE gene expression was only increased in 30H time cohort (p<0.001). PC1/3 gene and protein expression were positively correlated (R(2) 0.1; p=0.001) and were reduced (by 37% and 43%, respectively) during the entire course of critical illness (p<0.01). Annexin A1 gene expression was increased during critical illness (p<0.05 for all time cohorts). Conclusion Suppressed CRH or AVP signaling and GR-mediated action within corticotrophs explained lack of elevated plasma ACTH in critical illness, as indicated by impaired POMC processing and ACTH maturation. However, increased POMC gene expression suggests ongoing corticotroph activation, the driver of which needs to be identified. 1. Teblick A et al. Nat Rev Endocrinol 2019