Early Spinal Microglial and Non-microglial Cell Responses to Systemic LPS in Rats

Abstract

Systemic inflammation associated with a wide range of clinical disorders elicits neuroinflammation in the CNS, exacerbating neurodegeneration or traumatic/ischemic injuries. Neuroinflammation also impairs important forms of neuroplasticity associated with cognitive and motor learning. Several mechanisms propagate systemic inflammation into the CNS, although important details are not yet understood. Reports suggest propagation via vagal pro—inflammatory sensory afferent neurons, and/or cytokines crossing the blood-brain barrier. Microglia are the resident CNS immune cells, and are key contributors to CNS neuroinflammation, producing cytokines, chemokines, NO and ROS. Important contributions are also known from other CNS cells ( e.g. astrocytes, pericytes and neurons). Here, we investigated CNS responses to systemic inflammation induced by systemic LPS injection (1mg/kg, i.p.) in 3 months old Sprague-Dawley rats to test an early stage in the neuroinflammatory process. Three hours post-LPS injection, rats were perfused with PBS followed by microglia isolation from cortex and cervical spinal cord via immunomagnetic separation; the microglia-free fraction (neurons, astrocytes, pericytes, and other cells) was also collected for analysis. The efficacy of microglial isolation was verified by flow cytometry, and both microglial and non-microglial mRNAs were analyzed via qRT-PCR. CD200 and CX3CL1 (fractalkine) are two proteins expressed exclusively by neurons that mediate neuron-microglial communication by interacting with microglial receptors. Post-LPS, both CD200 and CX3CL1 increased 2.5 and 8 fold, respectively. Colony stimulating factor 1 (CSF-1), a protein produced by astrocytes and oligodendrocytes that is crucial for microglial survival, increased 5-fold. Surprisingly, inflammatory cytokines IL6, IL1β, CCL2, iNOS and TNFα were significantly elevated in non-microglial cells, but only IL6 and iNOS were increased in microglia 3 hours post-LPS. Thus, non-microglial cell responses to systemic inflammation appear to occur prior to full microglial activation. We hypothesize that peripheral pro-inflammatory signals propagate into CNS via pericytes and/or astrocytes that are in close contact with blood vessels. Further studies are needed to identify specific cellular sources of pro-inflammatory cytokines. Since CD200 prevents excessive inflammation in peripheral tissues, we also hypothesize that neuronal CD200 upregulation limits microglial immune responses, preventing inappropriate over-activation. Supported by: R01 HL149800 & HL147554 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.