Fibroblasts that reside in mouse and frog injured peripheral nerves produce apolipoproteins.

Apolipoprotein synthesis and secretion is upregulated in wallerian degenerating peripheral nerves. A commonly expressed view has been that macrophages are solely responsible for their production. In the present study we provide evidence that (1) nerve-derived fibroblasts contribute to apolipoprotein production, (2) apolipoprotein production is confined to regions where myelin destruction and phagocytosis occur, and (3) some experimental procedures are detrimental for the production of apolipoproteins. Apolipoprotein production was studied in C57BL/6/NHSD (N) and C57/BL/6-WLD/OLA/NHSD (W) mice that display, respectively, rapid and slow progression of wallerian degeneration. In N nerves, apolipoprotein E (apo-E) is produced during in vitro and in vivo degeneration, and in vivo after freeze damage. In W nerves, apo-E is produced at the injury region where degeneration occurs but not farther distally where degeneration fails to develop. Apo-E is also produced in W nerves during in vitro degeneration and in vivo after freeze damage. In culture, N and W mice nerve-derived fibroblasts, but neither macrophages nor Schwann cells produced apo-E. Two apolipoproteins are produced in in vivo wallerian degenerating and freeze-damaged frog nerves, i.e., apo-39 and apo-29. Only apo-39 is produced in in vitro degenerating nerves. Neither apo-39 nor apo-29 is produced during in vivo degeneration in diffusion chambers. In culture, apo-39 is produced by nerve-derived fibroblasts and macrophages but not by Schwann cells.

The roles of the synaptic basal lamina and of innervation in directing the accumulation of a synaptic molecule, mAb 3B6 antigen, in regenerating skeletal muscles.

We have recently described a novel nonhomogeneous distribution of a muscle synaptic molecule following denervation. Monoclonal antibody (mAb) 3B6 antigen, a molecule concentrated at endplate/junctional regions and myotendinous junctions in innervated muscles, appears in denervated muscles in restricted perijunctional regions that are continuous with and centered on endplates. In the present study we examine the roles of the synaptic basal lamina and of innervation in directing the accumulation of the molecule in newly formed regenerating muscle fibres. In denervated regenerating muscle fibres, mAb 3B6 antigen was associated with the plasma membrane and localized at former junctional and perijunctional regions. In those muscle fibres which displayed the perijunctional distribution, the molecule was preferentially colocalized with and centered on former endplate areas. Altogether, a preference for the localization of mAb 3B6 at former endplate regions was observed in 86-90% of denervated regenerating myofibres. A similar preference was observed in 97-99% of innervated regenerating muscle fibres. However, whereas 85.9% of denervated regenerating muscle fibres displayed a perijunctional distribution of the molecule, only 50.5% of innervated regenerating myofibres exhibited a perijunctional distribution. In addition, mAb 3B6 antigen was detected in the cytoplasm of most of the denervated regenerating myofibres but in none of the innervated ones. These results indicate that the basal lamina directs the preferential accumulation of mAb 3B6 antigen at original synaptic sites. Innervation, which is not a prerequisite for the expression of the molecule by regenerating muscle, down-regulates its overall production and presence in perijunctional regions.