Hmox1/CO regulates retina regeneration via modulation of Wnt/β-catenin signalling and induction of vaspb in zebrafish

Abstract

Muller glia (MG) in the zebrafish retina retain a latent stem cell capacity that is absent in mammals, yet the injury responsive signals that drive this reprogramming remain incompletely defined. Here, we identify heme oxygenase-1 (Hmox1), the stress-inducible, rate-limiting enzyme of heme catabolism, as a previously unrecognized regulator of this process. Following injury, hmox1a is selectively and rapidly induced among the heme oxygenase gene family, localizing to photoreceptors with expression peaking during the MG proliferation window. Pharmacological inhibition and morpholino mediated knockdown of Hmox1 dysregulate the acute inflammatory response, impair Muller glia-derived progenitor cell (MGPC) proliferation, and produce lasting deficits in retinal lamination, establishing Hmox1 as a potentially non-redundant, early-acting node required for structural recovery. Exogenous delivery of carbon monoxide (CO), a bioactive Hmox1 metabolite, partially rescues each of these phenotypes, functionally implicating CO as a key downstream effector. Mechanistically, Hmox1/CO signalling stabilizes {beta}-catenin likely via transcriptional repression of the Wnt antagonist dkk1b. This stabilized {beta}-catenin is enriched at a predicted Tcf7l2 site in the promoter of vaspb, which encodes an actin binding protein and is newly identified here as an injury-induced Wnt target gene. Bioinformatic and functional analyses further implicate Nfe2l2a (Nrf2) as a candidate intermediary bridging Hmox1/CO to Wnt regulation, with putative antioxidant response elements identified within the dkk1b locus. Together, these findings outline a putative Hmox1[->]CO[->]Nrf2[->]dkk1b[->]{beta}-catenin[->]vaspb relay coupling redox biology to Wnt-dependent glial reprogramming. Notably, HO-1 is similarly induced in stressed mammalian retina, yet Wnt/{beta}-catenin activation fails to sustain regeneration, positioning the Hmox1/CO axis as a candidate target for future investigation in mammalian retina regeneration.