Depletion of complement factor 3 delays the neuroinflammatory response to intracortical microelectrodes.

The neuroinflammatory response to intracortical microelectrodes (IMEs) used with brain-machine interfacing (BMI) applications is regarded as the primary contributor to poor chronic performance. Recent developments in high-plex gene expression technologies have allowed for an evolution in the investigation of individual proteins or genes to be able to identify specific pathways of upregulated genes that may contribute to the neuroinflammatory response. Several key pathways that are upregulated following IME implantation are involved with the complement system. The complement system is part of the innate immune system involved in recognizing and eliminating pathogens - a significant contributor to the foreign body response against biomaterials. Specifically, we have identified Complement 3 (C3) as a gene of interest because it is the intersection of several key complement pathways. In this study, we investigated the role of C3 in the IME inflammatory response by comparing the neuroinflammatory gene expression at the microelectrode implant site between C3 knockout (C3-/-) and wild-type (WT) mice. We have found that, like in WT mice, implantation of intracortical microelectrodes in C3-/- mice yields a dramatic increase in the neuroinflammatory gene expression at all post-surgery time points investigated. However, compared to WT mice, C3 depletion showed reduced expression of many neuroinflammatory genes pre-surgery and 4 weeks post-surgery. Conversely, depletion of C3 increased the expression of many neuroinflammatory genes at 8 weeks and 16 weeks post-surgery, compared to WT mice. Our results suggest that C3 depletion may be a promising therapeutic target for acute, but not chronic, relief of the neuroinflammatory response to IME implantation. Additional compensatory targets may also be required for comprehensive long-term reduction of the neuroinflammatory response for improved intracortical microelectrode performance.

CITED2 limits pathogenic inflammatory gene programs in myeloid cells.

Monocyte-derived macrophages are the major innate immune cells that provide the first line of cellular defense against infections or injuries. These recruited macrophages at the site of inflammation are exposed to a broad range of cytokines that categorically incite a robust pro-inflammatory response. However, macrophage pro-inflammatory activation must be under exquisite control to avert unbridled inflammation. Thus, endogenous mechanisms must exist that rigorously preserve macrophage quiescence and yet, allow nimble pro-inflammatory macrophage response with precise spatiotemporal control. Herein, we identify the CBP/p300-interacting transactivator with glutamic acid/aspartic acid-rich carboxyl-terminal domain 2 (CITED2) as a critical intrinsic negative regulator of inflammation, which broadly attenuates pro-inflammatory gene programs in macrophages. Our in vivo studies revealed that myeloid-CITED2 deficiency significantly heightened macrophages and neutrophils recruitment to the site of inflammation. Our integrated transcriptomics and gene set enrichment analysis (GSEA) studies uncovered that CITED2 deficiency broadly enhances NFκB targets, IFNγ/IFNα responses, and inflammatory response gene expression in macrophages. Using complementary gain- and loss-of-function studies, we observed that CITED2 overexpression attenuate and CITED2 deficiency elevate LPS-induced NFκB transcriptional activity and NFκB-p65 recruitment to target gene promoter in macrophages. More importantly, blockade of NFκB signaling completely reversed elevated pro-inflammatory gene expression in macrophages. Collectively, our findings show that CITED2 restrains NFκB activation and curtails broad pro-inflammatory gene programs in myeloid cells.