Proinflammatory microglial activation impairs in vitro cortical tissue repair via zinc-dependent ADAM17 cleavage of the CSF-1 receptor.

Abstract

Infection and subsequent inflammatory processes negatively impact prognosis in individuals with traumatic brain injury (TBI). Tissue repair following TBI is tightly regulated by microglia, promoting or, importantly, preventing astrocyte-mediated repair processes, depending on the activation state of the neuroimmune cells. This study investigated the poorly understood mechanism linking proinflammatory microglia activation and astrocyte-mediated tissue repair using an in vitro mechanical injury model in mixed cortical cultures of rat neurons and glia. We hypothesized that proinflammatory activation disrupts the microglial response to colony-stimulating factor 1 (CSF-1), which stimulates microglia migration and proliferation, both essential for astrocyte-mediated tissue repair. Following mechanical damage, cultures were treated with lipopolysaccharide (LPS) and interferon-gamma (IFNγ) to induce a proinflammatory state. Immunocytochemical and biochemical analyses were used to evaluate glial repair. Proinflammatory activation dramatically impeded wound closure, reducing microglial levels via upregulation of the zinc-dependent disintegrin and metalloprotease 17 (ADAM17), leading to the cleavage of the CSF-1 receptor (CSF-1R). Indeed, pharmacological inhibition of ADAM17 effectively promoted wound closure during inflammation. Moreover, zinc chelation prevented ADAM17-mediated cleavage of CSF-1R and induced the release of trophic factors, dramatically improving tissue recovery. Our findings strongly identify ADAM17 as a primary regulator of CSF-1R-mediated signaling and establish a mechanism defining the association between pro-inflammatory microglial activation and tissue repair following injury.