Mammalian nerve globins in search of functions

Nerve globins are present in nonvertebrates and vertebrates, the first nerve globin having been recognized in the nerve cord of the polychaete annelid Aphrodite aculeata in 1872. Later, in 2000, the first vertebrate nerve globin, named neuroglobin (Ngb), has been identified in neuronal tissues of humans and mice. Recently, cytoglobin, hemoglobin, and myoglobin have also been reported to be expressed in the mammalian nervous system. The concentration of mammalian nerve globins is ~1 μM, with the exception of Ngb that reaches approximately 100-200 μM only in the retina rod cells. Mammalian nerve globins have been hypothesized to be involved in the excitability of the nervous system, in the metabolism of reactive nitrogen and oxygen species, and in intracellular signaling pathways leading to the neuronal cell survival. Only in retina cells, mammalian Ngb may help to sustain O2 supply to mitochondria, thereby supporting the visual process in the eye. Here, the putative roles of mammalian nerve globins are reviewed.