Laser-mediated osteoblast ablation triggers a pro-osteogenic inflammatory response regulated by reactive oxygen species and glucocorticoid signaling in zebrafish

Abstract

In zebrafish, transgenic labeling approaches, robust regenerative responses and excellent in vivo imaging conditions enable precise characterization of immune cell behavior in response to injury. Here, we monitored osteoblast-immune cell interactions in bone, a tissue which is particularly difficult to in vivo image in tetrapod species. Ablation of individual osteoblasts leads to recruitment of neutrophils and macrophages in varying numbers, depending on the extent of the initial insult, and initiates generation of cathepsin K+ osteoclasts from macrophages. Osteoblast ablation triggers the production of pro-inflammatory cytokines and reactive oxygen species, which are needed for successful macrophage recruitment. Excess glucocorticoid signaling as it occurs during the stress response inhibits macrophage recruitment, maximum speed and changes the macrophage phenotype. Although osteoblast loss is compensated for within a day by contribution of committed osteoblasts, macrophages continue to populate the region. Their presence is required for osteoblasts to fill the lesion site. Our model enables visualization of bone repair after microlesions at single-cell resolution and demonstrates a pro-osteogenic function of tissue-resident macrophages in non-mammalian vertebrates.

Compartmentalization and synergy of osteoblasts drive bone formation in the regenerating fin

“…However, depletion of some mmp9 -expressing myeloid cells in the fin regenerate 8 might possibly add to the seen additive regeneration defects, as indicated by larval and adult macrophage ablation experiments during zebrafish tissue regeneration. 52 , 53 …”

Osteoclast-mediated resorption primes the skeleton for successful integration during axolotl limb regeneration

“…To generate the Ctsk:mRuby3 or Ctsk:eGFP transgenic lines, a plasmid containing 4 kb of Ctsk promoter from zebrafish together with Tol2 sequences was used (kind gift from Knopf Lab at CRTD) ( Geurtzen et al, 2022 ). The mRuby3 or eGFP coding region was cloned 3’ from the promoter.…”