An in vitro study investigating the role of central nervous glial cells in neuronal apoptosis induced by the spirochete Borrelia burgdorferi
Description
Inflammation in the central nervous system (CNS) is thought to either cause or contribute to the pathogenesis of many neurodegenerative disorders including Lyme neuroborreliosis. The bacterial spirochete Borrelia burgdorferi causes Lyme disease and is known to readily induce the production of inflammatory mediators in CNS glia. While a similar inflammatory response has not been demonstrated in neuronal cells, neurological symptoms occur in nearly 20 percent of Lyme disease patients, and cognitive impairment is often a part of this scenario. As such, an investigation was conducted into which of the principal cell types residing in the CNS might be functioning to create the inflammatory environment that in addition to helping clear the pathogen, might be simultaneously harming nearby neurons In-vitro experiments were used to demonstrate that with regard to astrocytes, microglia and neurons, B. burgdorferi would elicit significantly more robust reactions in microglia. In addition to inducing potent and sustained production of the cytokines/chemokines IL-6, IL-8, CCL2 (MCP-1), CCL3 (MIP-1alpha), CCL4 (MIP-1beta) and CCL5 (RANTES) in microglia, B. burgdorferi also affected important inflammatory signaling pathways in these cells. Microglial TREM1, Pattern Recognition Receptor and Chemokine Signaling Pathways each exhibited upregulation in inflammatory signaling upon co-cultivation with B. burgdorferi. There was no observed induction of glial cell apoptosis during experiments where combinations of astrocytes, microglia and or neurons were co-cultured with B. burgdorferi. Importantly however, when neurons were cocultured with microglia and B. burgdorferi, significant neuronal apoptosis consistently occurred. Taken together, these findings indicate that the neurotoxic surroundings generated by microglial cell responses to B. burgdorferi in the CNS, may be creating a bystander effect which potentiates the neuronal cell damage responsible for symptoms observed in neuroborreliosis While the cultivation of primary microglia and astrocyte cells is reasonable to attain, there are inherent difficulties in the generation of primary neuronal cultures. As such, transformed SH-SY5Y (SY) neurons were incorporated into our model. A three-dimensional (3D) cell culture system was also developed and used throughout this study, as this technique has been shown to promote a more normal cell phenotype when compared to that of transformed cells grown in two dimensions (2D)