Glial response to axonal injury: In vitro manifestation and implication for regeneration

Abstract

Crushed fish optic axons readily regenerate, while similarly injured rat optic axons do not; the reasons for the differences in regeneration ability may lie in differences in the environment of the axons. We have cultured glial cells from previously crushed optic nerves of fish and rat to determine whether a relationship exists between the ability to regenerate and the nature of the responses of the associated nonneuronal cells to injury. The glial cells were examined using indirect immunofluorescence with antibodies to known glial markers. In the rat cultures, mature GalC oligodendrocytes, which are known to be nonpermissive for axonal growth, were abundant. In contrast, in the fish cultures mature oligodendrocytes were rare, but A2B5 positive cells were abundant. The high number of A2B5 positive cells in the fish may suggest a high number of immature cells. This interpretation, however, should wait until evidence for glial cell lineage of the fish is available. Additional indication is provided also in the present study that the number of mature oligodendrocytes in the fish is regulated by elements external to the nerve. This study thus demonstrates an important difference between rat and fish optic nerves in the response of glial cells to the optic nerve injury.

Identification of an interleukin 2-like substance as a factor cytotoxic to oligodendrocytes and associated with central nervous system regeneration.

“…We have shown in the past that CM derived from regenerating fish optic nerves can facilitate axonal growth in vivo (15,16). Independently, we showed that in vitro this preparation possesses a number of activities, including cytotoxicity to mature oligodendrocytes of both fish and rat (12)(13)(14).…”

“…Carp (Cyprinus carpio, 800-1200 g; Tnuva, Israel) were anesthetized with 0.05% 3-aminobenzoic acid ethyl ester (Sigma), and their optic nerves were crushed with forceps (for 30 sec). Eight days later, the nerves were removed by dissection and incubated in serum-free medium for 1.5 hr (four nerve segments per 300 pLI of medium) at 250C (15). The resulting medium, defined as CM, was then collected, and its protein content was determined by the Bradford assay (17).…”

“…In line with these observations is our finding that the high regenerative capacity of the fish optic nerve is correlated with the presence of a factor or factors cytotoxic to oligodendrocytes (12)(13)(14). This factor(s) was detected among the soluble substances derived from regenerating fish optic nerves, which were collectively termed conditioned medium (CM) and, when applied in vivo, helped to create conditions conducive to axonal growth in other species-e.g., in injured optic nerves of rabbit (15,16). Recent studies in our laboratory suggest that the cytotoxic factor(s) in the fish might be associated with the postinjury inflammatory reaction-i.e., with the early invasion of injured nerves by blood-derived cells (14).…”

Presence of growth inhibitors in fish optic nerve myelin: Postinjury changes

“…The expression of laminin, a molecule supportive of neuritic outgrowth, was shown to be elevated in the fish optic nerve following injury (Hopkins et al, 1985;Liesi, 1985). The possible removal of inhibitory elements is supported by the presence of oligodendrocyte-cytotoxic molecules in the regenerating fish optic nerve Sivron et al, 1990Sivron et al, , 1991Eitan et al, 1992) and by the elevation of apolipoprotein A-I (apo-A-I) and myelin-degrading enzymes (Hare1 et al, 1989;Salles et al, 1990). It thus seems likely that the combined action of several factors is responsible for the increase in growth permissiveness of the fish optic nerve following injury.…”

Zebrafish myelination: a transparent model for remyelination?

“…Nevertheless, the structural properties and cell lineage relationship of oligodendrocytes is highly comparable between zebrafish and mammals (Jeserich et al, 2008;Jeserich and Stratmann, 1992;Jeserich and Waehneldt, 1986;Sivron et al, 1990). Also, orthologous genes for all of the major mammalian myelinassociated genes have been found in zebrafish (dm20, mbp and p 0 ) (Brosamle and Halpern, 2002).…”