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.

Regenerative medicine holds great promise for both degenerative diseases and traumatic tissue injury which represent significant challenges to the health care system. Hearing loss, which affects hundreds of millions of people worldwide, is caused primarily by a permanent loss of the mechanosensory receptors of the inner ear known as hair cells. This failure to regenerate hair cells after loss is limited to mammals, while all other non-mammalian vertebrates tested were able to completely regenerate these mechanosensory receptors after injury. To understand the mechanism of hair cell regeneration and its association with regeneration of other tissues, we performed a guided mutagenesis screen using zebrafish lateral line hair cells as a screening platform to identify genes that are essential for hair cell regeneration, and further investigated how genes essential for hair cell regeneration were involved in the regeneration of other tissues. We created genetic mutations either by retroviral insertion or CRISPR/Cas9 approaches, and developed a high-throughput screening pipeline for analyzing hair cell development and regeneration. We screened 254 gene mutations and identified 7 genes specifically affecting hair cell regeneration. These hair cell regeneration genes fell into distinct and somewhat surprising functional categories. By examining the regeneration of caudal fin and liver, we found these hair cell regeneration genes often also affected other types of tissue regeneration. Therefore, our results demonstrate guided screening is an effective approach to discover regeneration candidates, and hair cell regeneration is associated with other tissue regeneration.