Participation of microglial activation in endocrine, neurologic and immune alterations during sepsis

Author(s)

Luís Henrique Angenendt da Costa

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2020-04-15

Examining board members

Maria Jose Alves da Rocha; Evelin Capellari Carnio; Norberto Cysne Coimbra; Felipe Dal Pizzol

• Advisor: Maria Jose Alves da Rocha

Abstract

Sepsis, a systemic inflammation triggered by an infectious agent, produces an inflammatory state in the central nervous system (CNS) that may cause autonomic, cognitive, behavioral and endocrine changes. Microglia, a resident cell type of the CNS with an important role in local immune and synaptic regulation, is activated in several brain regions during sepsis, suggesting its participation in the neuroendocrine dysfunction observed in this disease. This study aimed to: (1) evaluate the role of microglial activation on neuroimmunoendocrine parameters in septic animals and (2) investigate the modulation of paraventricular nucleus (PVN) activation during sepsis. For the first objective, Wistar rats received intracerebroventricular injection of minocycline (100µg / animal), an inhibitor of microglial activation, just before sepsis induction by ligation and cecal puncture (CLP-10 holes, 16G needle). Six and 24 hours after surgery we analyzed the hormonal parameters, central and peripheral inflammation and markers of apoptosis and synaptic function in the hypothalamus. For the second objective, microglial morphology and activation of projections to the PVN during sepsis were analyzed in mice by injecting a retrograde neurotracer (CTB) into this nucleus. Six or 24 hours after sepsis also induced by CLP (2 holes, 21G needle) an immunohistochemical analysis was performed to identify neuronal activation, in addition to inflammation markers. The results showed that sepsis differently affects hormonal secretion, depending on the stage of the disease: there may be a decrease (ACTH, prolactin), an increase (corticosterone) or a mixed response (vasopressin, oxytocin). We observed an increase in neuroinflammation and in apoptosis markers. The administration of minocycline decreased microglial activation, the production of inflammatory mediators and expression of cell death markers, especially in the late phase. Regarding the endocrine parameters, after 6 hours of sepsis, microglial inhibition decreased plasma levels of oxytocin and increased corticosterone and vasopressin, while in the late phase it decreased oxytocin and increased ACTH and corticosterone. Prolactin levels were not affected by minocycline administration. Changes in microglial cell morphology were observed in the PVN of septic animals, in addition to decreased activation of AVP and OT-producing neurons in the late stage of sepsis. We also showed that different brain regions that project to the PVN are activated in sepsis, potentially modulating its activity. A source of important efferences to the PVN during sepsis, the subfornical organ (SFO) also undergoes a neuroinflammatory processes that may influence its activity and endocrine control. We conclude that the regulation of the endocrine system is largely affected by sepsis, mainly through the action of inflammatory mediators produced central and peripherally. Microglial activation is important in this process, distinctly affecting the secretion of different hormones. (AU)

• FAPESP's process: 16/07803-0 - Effect of inhibition of microglial activation on neuroimmunoendocrine parameters during sepsis
• Grantee: Luís Henrique Angenendt da Costa
• Support Opportunities: Scholarships in Brazil - Doctorate