Cytoglobin (Cygb), a member of the hexacoordinate globin superfamily (hxHb), is expressed in fibroblasts from a broad range of tissues. The physiological functions of hxHb are still unclear, but biochemical studies reveal that they can scavenge toxic species, such as nitric oxide, peroxynitrite, and hydrogen peroxide. We demonstrate that the overexpression of Cygb in rat hepatic stellate cells, both in vitro and in vivo, protects against oxidative stress, inhibiting their differentiation into a myofibroblast-like phenotype. Accordingly, the overexpression of Cygb reduces extracellular matrix deposition in both toxic and cholestatic models of liver injury. The overexpression of Cygb also promotes recovery from previously initiated damage-induced fibrogenesis. By inhibiting free radical-induced activation of hepatic stellate cells, Cygb plays an important role in controlling tissue fibrosis. Therefore, the normal upregulation of Cygb during tissue injury has a homeostatic effect, inhibiting free radical-induced fibroblast activation and tissue fibrosis.
