Myeloid-Specific Blockade of Notch Signaling by RBP-J Knockout Attenuates Spinal Cord Injury Accompanied by Compromised Inflammation Response in Mice

Abstract

The outcome of spinal cord injury (SCI) is determined by both neural cell-intrinsic survival pathways and tissue microenvironment-derived signals. Macrophages dominating the inflammatory responses in SCI possess both destructive and reparative potentials, according to their activation status. Notch signaling is involved in both cell survival and macrophage-mediated inflammation, but a comprehensive role of Notch signaling in SCI has been elusive. In this study, we compared the effects of general Notch blockade by a pharmaceutical γ-secretase inhibitor (GSI) and myeloid-specific Notch signal disruption by recombination signal binding protein Jκ (RBP-J) knockout on SCI. The administration of Notch signal inhibitor GSI resulted in worsened hind limb locomotion and exacerbated inflammation. However, mice lacking RBP-J, the critical transcription factor mediating signals from all four mammalian Notch receptors, in myeloid lineage displayed promoted functional recovery, attenuated glial scar formation, improved neuronal survival and axon regrowth, and mitigated inflammatory response after SCI. These benefits were accompanied by enhanced AKT activation in the lesion area after SCI. These findings demonstrate that abrogating Notch signal in myeloid cells ameliorates inflammation response post-SCI and promotes functional recovery, but general pharmaceutical Notch interception has opposite effects. Therefore, clinical intervention of Notch signaling in SCI needs to pinpoint myeloid lineage to avoid the counteractive effects of global inhibition.

Myeloid-Specific Blockade of Notch Signaling Attenuates Choroidal Neovascularization through Compromised Macrophage Infiltration and Polarization in Mice

“…One notion is that infiltrating myeloid cells are polarized and conditioned by cytokines and certain signal pathways. Previous studies in our group showed that Notch signaling is instructive for M1 and suppressive for M2 polarization in microglia, tumor-associated macrophages and macrophages in spinal cord injury 16 22 38 . However, in the current study, with RBP-J deletion, M2 macrophages appear to decrease while M1 type remains in a moderate level.…”

“…Notch signaling might not only be required for initial macrophage activation, but also participate in polarization at later inflammatory stages. Our group has provided evidence that Notch inhibition by GSI or RBP-J knockout skews macrophage polarization in tumor, hepatic fibrosis and spinal cord injury 16 21 22 . Notch1 signaling-dependent macrophage M2b polarization might play a pivotal role in the pathogenesis of systemic lupus erythematosus 23 .…”

Acetylation-Dependent Regulation of Notch Signaling in Macrophages by SIRT1 Affects Sepsis Development

“…Briefly, to generate myeloid-specific sirt1 −/− mice, mice carrying a floxed sirt1 allele ( Sirt1 flox/flox ; Jackson Laboratory), in which exon 4 of sirt1 was flanked by loxP sites, were crossed with Lyz2-Cre transgenic mice (Jackson Laboratory) ( 33 ). Similarly, to generate myeloid-specific RBP-J −/− mice, mice carrying the Lyz2-Cre transgene were crossed with RBP-J-floxed mice ( RBP-J flox/flox Jackson Laboratory) ( 34 ). Mice were genotyped by performing PCR on tail-derived DNA.…”

Biomaterial strategies for limiting the impact of secondary events following spinal cord injury

“…The Notch signaling pathway is known to regulate T and B cell differentiation, activation, and function [45] and neural stem cell (NSC) activation and self-renewal [46]. The effect of Notch signaling on SCI inflammation is not straightforward: globally blocking Notch signaling was found to increase the inflammation cascade, while inhibiting myeloid-specific Notch signaling decreased inflammation, resulting in increased functional outcomes [47]. Extracellular ATP, which is a strong activator of the innate immune system, is increased following SCI and is a major driver of allodynia (experiencing pain from non-painful stimuli) [48].…”