Optic nerve regeneration in adult fish and apolipoprotein A-I.
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).
Harel
A
A
Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel.
Fainaru
M
M
Shafer
Z
Z
Hernandez
M
M
Cohen
A
A
Schwartz
M
M
D000818:Animals; D016632:Apolipoprotein A-I; D001054:Apolipoproteins A / Q000378:metabolism*; D002347:Carps / Q000378:metabolism*; D055598:Chemical Phenomena; D002621:Chemistry; D003470:Culture Media; D003530:Cyprinidae / Q000378:metabolism*; D008074:Lipoproteins / Q000097:blood; D009409:Nerve Crush; D009416:Nerve Regeneration; D009900:Optic Nerve / Q000378:metabolism / Q000502:physiology*; D020221:Optic Nerve Injuries; D051381:Rats; D011919:Rats, Inbred Strains
D016632:Apolipoprotein A-I; D001054:Apolipoproteins A; D003470:Culture Media; D008074:Lipoproteins