TNF signaling and macrophages govern fin regeneration in zebrafish larvae

Abstract

Macrophages are essential for appendage regeneration after amputation in regenerative species. The molecular mechanisms through which macrophages orchestrate blastema formation and regeneration are still unclear. Here, we use the genetically tractable and transparent zebrafish larvae to study the functions of polarized macrophage subsets during caudal fin regeneration. After caudal fin amputation, we show an early and transient accumulation of pro-inflammatory macrophages concomitant with the accumulation of non-inflammatory macrophages which, in contrast to pro-inflammatory macrophages, remain associated to the fin until the end of the regeneration. Chemical and genetic depletion of macrophages suggested that early recruited macrophages that express TNFα are critical for blastema formation. Combining parabiosis and morpholino knockdown strategies, we show that TNFα/TNFR1 signaling pathway is required for the fin regeneration. Our study reveals that TNFR1 has a necessary and direct role in blastema cell activation suggesting that macrophage subset balance provides the accurate TNFα signal to prime regeneration in zebrafish.

The zebrafish as a model for gastrointestinal tract–microbe interactions

“…During this time, colonisation of the larval gut by commensals can prime innate immune cells against infections through a Toll-like receptor (TLR) and myeloid differentiation primary response 88 (MyD88) dependent pathway (Galindo-Villegas, Garcia-Moreno, de Oliveira, Meseguer, & Mulero, 2012). One of the benefits of zebrafish is their optical transparency, allowing for the use of transgenic lines with fluorescently-marked innate immune cells like macrophages (Ellett, Pase, Hayman, Andrianopoulos, & Lieschke, 2011;Hall, Flores, Storm, Crosier, & Crosier, 2007;Nguyen-Chi et al, 2017;Redd, Kelly, Dunn, Way, & Martin, 2006;Sanderson et al, 2015;Walton, Cronan, Beerman, & Tobin, 2015;Ward, 2003), neutrophils (Buchan et al, 2019;Mathias et al, 2006;Renshaw et al, 2006), and eosinophils (Balla et al, 2010). These resources have given valuable insights into the role of innate immune cells in intestinal homeostasis and pathogenesis.…”

Determining macrophage versus neutrophil contributions to innate immunity using larval zebrafish

“…But, in other infections, such as the bacterial pathogen B. cenocepacia (Mesureur et al, 2017) or the fungal pathogens A. fumigatus (Rosowski et al, 2018a), T. marneffei or the C. neoformans spore form (Davis et al, 2016), macrophages actually provide a protective niche for pathogen survival and growth. In sterile wounding conditions, macrophages can modulate the inflammatory microenvironment (Tsarouchas et al, 2018;Hasegawa et al, 2017;Nguyen-Chi et al, 2017), use Vegfa activation and mechanical forces to promote angiogenesis and vascular repair (Liu et al, 2016;Gurevich et al, 2018), and promote the repair and regrowth of damaged nerve tissue (Carrillo et al, 2016;Tsarouchas et al, 2018). In response to infection, neutrophils often have roles in controlling pathogen invasive growth at later stages of infection (Gratacap et al, 2017).…”

“…Multiple recent papers have focused on the role of macrophages in modulating the immune environment at an injury site, especially through regulation of the pro-inflammatory cytokines il1b and tnfa (Box 3) (Tsarouchas et al, 2018;Morales and Allende, 2019;Nguyen-Chi et al, 2017;Hasegawa et al, 2017). These proinflammatory mediators are turned on early in the wound response and downregulated in later stages of repair (Tsarouchas et al, 2018;Hasegawa et al, 2017).…”

Dynamic control of proinflammatory cytokines Il-1β and Tnf-α by macrophages is necessary for functional spinal cord regeneration in zebrafish

“…Conversely, in wildtype animals, lack of Il-1β function had only a relatively small inhibitory effect on early regeneration, whereas Tnf-α was indispensable for axon regrowth. In fin regeneration, Tnf-α has an important promoting function for blastema formation 28 . This suggests that Tnf-α may be involved in remodelling repair cells in the lesion site after spinal injury, which then creates an axon growth-promoting environment.…”