Conditional deletion of IκBζ in hematopoietic cells promotes functional recovery after spinal cord injury in mice

Naoya Taki; Atsushi Kimura; Yasuyuki Shiraishi; Takashi Maruyama; Tsukasa Ohmori; Katsushi Takeshita

doi:10.1016/j.jos.2024.04.008

Conditional deletion of IκBζ in hematopoietic cells promotes functional recovery after spinal cord injury in mice

J Orthop Sci. 2024 May 16:S0949-2658(24)00088-5. doi: 10.1016/j.jos.2024.04.008. Online ahead of print.

Authors

Naoya Taki¹, Atsushi Kimura², Yasuyuki Shiraishi¹, Takashi Maruyama³, Tsukasa Ohmori⁴, Katsushi Takeshita¹

Affiliations

¹ Department of Orthopaedic Surgery, Jichi Medical University, 3311-1 Yakushiji, Shimotsuke, Tochigi, 329-0498, Japan.
² Department of Orthopaedic Surgery, Jichi Medical University, 3311-1 Yakushiji, Shimotsuke, Tochigi, 329-0498, Japan. Electronic address: akimura@jichi.ac.jp.
³ Mucosal Immunology Section, National Institute for Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20852, USA.
⁴ Department of Biochemistry, Jichi Medical University School of Medicine, Tochigi, 329-0498, Japan.

PMID: 38760245
DOI: 10.1016/j.jos.2024.04.008

Abstract

Background: Transcription factor protein IκBζ (encoded by the Nfkbiz gene) regulates nuclear factor-κB (NF-κB) and is involved in the pathophysiology of various inflammatory diseases. However, the role of IκBζ in secondary damage following spinal cord injury (SCI) remains to be determined. Here, we investigated the effect of IκBζ expressed in hematopoietic cells on the progression of secondary damage and functional recovery after SCI.

Methods: We used conditional IκBζ-knockout mice (Mx1-Cre;Nfkbiz^fl/f) to examine the role of IκBζ in hematopoietic cells after SCI. Contusion SCI was induced using a force of 60 kdyn. The recovery of locomotor performance was evaluated using the nine-point Basso Mouse Scale (BMS) until 42 days post-injury. Expression patterns of inflammatory cytokines and chemokines were examined by quantitative real-time PCR or proteome array analysis. Bone marrow transplantation (BMT) was performed to eliminate the effect of IκBζ deletion in non-hematopoietic cells.

Results: Mx1-Cre;Nfkbiz^fl/fl mice had significantly improved locomotor function compared with wild-type (WT) mice. The mRNA expression of Nfkbiz in WT mice peaked at 12 h after SCI and then decreased slowly in both the spinal cord and white blood cells. In situ hybridization showed that Nfkbiz mRNA was localized in cell nuclei, including macrophage-like cells, in the injured spinal cord of WT mice at 1 day after SCI. Compared with WT mice, Mx1-Cre;Nfkbiz^fl/fl mice had significantly increased mRNA expressions of interleukin (Il)-4 and Il-10 in the injured spinal cord. In addition, Mx1-Cre;Nfkbiz^fl/fl mice had significantly higher protein levels of granulocyte-macrophage colony-stimulating factor and C-C motif chemokine 11 compared with WT mice. BMT from Mx1-Cre;Nfkbiz^fl/fl mice into WT mice improved functional recovery after SCI compared with control mice (WT cells into WT mice).

Conclusions: IκBζ deletion in hematopoietic cells improved functional recovery after SCI, possibly by shifting the inflammatory balance towards anti-inflammatory and pro-regenerative directions.

Keywords: Bone marrow transplantation; Hematopoietic cells; Knockout mouse; Spinal cord injury; Transcription factor.