Optic Nerve Regeneration in Adult Fish and Apolipoprotein A‐I

A. Harel, M. Fainaru, Z. Shafer, M. Hernandez, A. Cohen, M. Schwartz

Research output: Contribution to journalArticlepeer-review


Abstract Fish optic nerves, unlike mammalian optic nerves, are endowed with a high capacity to regenerate. Injury to fish optic nerves causes pronounced changes in the composition of pulse‐labeled substances derived from the surrounding non‐neuronal cells. The most prominent of these injury‐induced changes is in a 28‐kilodalton (kDa) polypeptide whose level increases after injury, as revealed by one‐dimensional gel electrophoresis and autoradiography. The present study identified as apolipoprotein A‐I (apo‐A‐I) a polypeptide of 28 kDa in media conditioned by regenerating fish optic nerves. The level of this polypeptide increased after injury by approximately 35%. Apo‐A‐I was isolated by gel‐permeation chromatography from delipidated high‐density lipoproteins (HDL) that had been obtained from carp plasma by sequential ultracentrifugation. Further identification of the purified protein as apo‐A‐I was based on its molecular mass (28 kDa) as determined by gel electrophoresis, amino acid composition, and microheterogeneity studies. The isolated protein was further analyzed by immunoblots of two‐dimensional gels and was found to contain six isoforms. Western blot analysis using antibodies directed against the isolated plasma protein showed that the 28‐kDa polypeptide in the preparation of soluble substances derived from the fish optic nerves (conditioned media, CM) cross‐reacted immunologically with the isolated fish plasma apo‐A‐I. Immunoblots of two‐dimensional gels revealed the presence of three apo‐A‐I isoforms in the CM of regenerating fish optic nerves (pIs: 6.49, 6.64, and 6.73). At least some of the apo‐A‐I found in the CM is derived from the nerve, as was shown by pulse labeling with [35S]methionine, followed by immunoprecipitation. The apo‐A‐I immunoactive polypeptides in the CM of the fish optic nerve were found in high molecular‐weight, putative HDL‐like particles. Immunocytochemical staining revealed that apo‐A‐I immunoreactive sites were present in the fish optic nerves. Higher labeling was found in injured nerves (between the site of injury and the brain) than in non‐injured nerves. The accumulation of apo‐A‐I in nerves that are capable of regenerating may be similar to that of apo‐E in sciatic nerves of mammals (a regenerative system); in contrast, although its synthesis is increased, apo‐A‐I does not accumulate in avian optic nerves nor does apo‐E in rat optic nerves (two nonregenerative systems).

Original languageEnglish
Pages (from-to)1218-1228
Number of pages11
JournalJournal of Neurochemistry
Issue number4
StatePublished - Apr 1989
Externally publishedYes


  • Apolipoprotein A‐I
  • High‐density lipoproteins
  • Optic nerve
  • Regeneration


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