Microglial reactivity induced by bacterial insult can be modulated by a tyrosine kinase inhibitor

Introduction: Microglia defend the central nervous system, maintaining homeostasis. In response to bacterial insults, they acquire a pro-inflammatory phenotype characterized by morphological changes and the production of cytokines and nitric oxide (NO) via TLR4, which recognizes LPS from Gram-negative bacteria and activates MAPKs and NFκB. Src family kinases (SFKs) regulate inflammation, their inhibition attenuates leukocyte responses. Bosutinib (BOS) is a multi-kinase inhibitor with potent effects on SFK. Objectives: To evaluate if BOS modulates microglial responses to bacterial stimulation. Methods: Murine microglia (BV2) were pretreated with 500 nM BOS 30 min before stimulation with LPS (50/100 ng/ml) or Escherichia coli (MOI 10). At 30 min, cell lysates were collected to evaluate MAPK p38 and p65 (NFκB) by Western blot. At 24 h, viability, Griess (NO), and ELISA assays were performed. Immunostaining evaluated p65 translocation and morphology (β-tubulin). Immunohistochemistry (IBA-1) assessed microglial reactivity in brain sections of mice with polymicrobial sepsis treated with BOS (3 mg/kg). Results and conclusion: BOS showed potent immunomodulatory activity on stimulated BV2. It protected against LPS-induced cytotoxicity (100 ng/ml) and significantly reduced TNF-α in all groups, associated with potential modulation of p65 nuclear translocation. BOS controlled NO increases under stronger stimuli (LPS 100 ng/ml). Interestingly, BOS maintained high IL-6 levels and did not reduce p38 phosphorylation. Increased IL-6 with reduced TNF-α may favor a pro-resolving profile, cytoskeleton remodeling, and phagocytosis. Furthermore, BOS altered microglial morphology in vitro and in vivo, possibly promoting a ramified, surveillance profile. These results support the immunomodulatory potential of BOS, contributing to a more pro-resolving and less pro-inflammatory profile. Funding: FAPERJ, UNIRIO, CNPq, CAPES (Grant 001), COI, FIOCRUZ, BCM. CEUA-IOC (L026/2022).