Extracellular HSP60 triggers tissue regeneration and wound healing by regulating inflammation and cell proliferation.

Shawn M Burgess,Gaurav K Varshney,Shuo Lin,Jennifer Idol,Jason Sinclair,Wuhong Pei,Sunny C Huang,Haigen Huang,Baoying Liu,Lisha Xu,Robert B Nussenblatt,Ryoichi Mori,Katsuya Tanaka

doi:10.1038/npjregenmed.2016.13

Abstract

After injury, zebrafish can restore many tissues that do not regenerate well in mammals, making it a useful vertebrate model for studying regenerative biology. We performed a systematic screen to identify genes essential for hair cell regeneration in zebrafish, and found that the heat shock protein Hspd1 (Hsp60) has a critical role in the regeneration of hair cells and amputated caudal fins. We showed HSP60-injected extracellularly promoted cell proliferation and regeneration in both hair cells and caudal fins. We showed that hspd1 mutant was deficient in leukocyte infiltration at the site of injury. Topical application of HSP60 in a diabetic mouse skin wound model dramatically accelerated wound healing compared with controls. Stimulation of human peripheral blood mononuclear cells with HSP60 triggered a specific induction of M2 phase CD163-positive monocytes. Our results demonstrate that the normally intracellular chaperonin HSP60 has an extracellular signalling function in injury inflammation and tissue regeneration, likely through promoting the M2 phase for macrophages.

Highlights

Hearing loss, affecting millions of people worldwide, is primarily caused by the death of mechanosensory hair cells in the inner ear
It has previously been shown that Hspd[1] can induce an inflammatory response through several different receptors including TLR2, TLR4 and CD36.9–11 We show that Hspd[1] acts as an extracellular signal released from the injury site, acting both as a chemoattractant for leukocytes and as an inflammation-resolving signal that promotes cell division and regeneration in the surrounding tissues
The extracellular HSP60 acts both as an immunostimulant to attract leukocytes into the injury site and as a paracrine signal that induces intracellular hspd[1] expression in the neighbouring cells

Summary

INTRODUCTION

Hearing loss, affecting millions of people worldwide, is primarily caused by the death of mechanosensory hair cells in the inner ear. Macrophage migration was slightly reduced between the control siblings and the mutant embryos at 17 h post caudal fin amputation, but the reduction did not reach statistical significance (P = 0.11; Supplementary Figure S3C,D) These data suggest that macrophage migration is more weakly drawn to the injury site by hspd[1] than by neutrophils. To test whether the increased regeneration induced by injected GroEL is due to a tropic effect, we injected GroEL to unamputated fins and found no significant difference on caudal fin development (Supplementary Figure S5) These data, taken together with our observations of the normal hair cell development and defective hair cell regeneration in hspd[1] mutant, suggest that injury provides a sensitised background that can exaggerate HSP60’s function in regenerative cell proliferation. We found that the intermediate CD14++CD16+ cells after GroEL treatment exhibited a higher level of CD163 expression than the cells from LPS treatment (Figure 8c), suggesting that GroEL has a role in inducing the differentiation of intermediate monocytes to M2 macrophages, biasing the inflammation response towards resolution and regeneration

DISCUSSION

Findings

MATERIALS AND METHODS