Neutrophil extracellular traps impair regeneration

Area of Science:

• Regenerative medicine
• Wound healing biology
• Immunology

Background:

• Fibrosis presents a significant global health challenge.
• Wound-induced hair follicle neogenesis (WIHN) serves as a model for non-fibrotic healing, mimicking embryonic development for new hair follicle formation post-injury.
• Toll-like receptor 3 (TLR3) was previously shown to promote WIHN by binding to double-stranded RNA (dsRNA), but the origin of this dsRNA remained unknown.

Purpose of the Study:

• To investigate the role of neutrophils and neutrophil extracellular traps (NETs) in WIHN.
• To determine if neutrophils and NETs modulate WIHN, specifically the release of nuclear spliceosomal U1 dsRNA.
• To understand the impact of mature neutrophils on regenerative processes.

Main Methods:

• Analysis of neutrophil signatures in contexts of high WIHN.
• Investigating the effect of mature neutrophil depletion on WIHN.
• Utilizing Pad4 knockout mice (deficient in NET production) to assess WIHN.
• Employing single-cell RNA sequencing to analyze immune cell populations in wound beds of Tlr3-/- mice.

Main Results:

• High WIHN contexts consistently exhibited a strong neutrophil presence.
• Depletion of mature neutrophils or deficiency in NET production (Pad4 null mice) led to enhanced WIHN.
• Low regenerating Tlr3-/- mice showed a significant increase in mature and activated neutrophils within wound beds.
• Contrary to initial hypothesis, mature neutrophils and NETs were found to inhibit, rather than promote, WIHN.

Conclusions:

• Mature neutrophils and their associated NETs impede WIHN, acting as a barrier to regeneration.
• Despite being activated by common pro-regenerative signals, neutrophils hinder the regenerative process.
• Targeting neutrophils or NETs may represent a therapeutic strategy to improve non-fibrotic wound healing and hair follicle regeneration.