Journal of zyxwvutsrqponmlkj Neurochemistr.v zyxwvutsrqpon Raven Press, Ltd., New York 0 1992 International Society for Neurochemistry zyxwvutsrqp Lesion-Induced Changes in the Production of Newly Synthesized and Secreted Apo-E and Other Molecules zy Are Independent of the Concomitant Recruitment of Blood-Borne Macrophages into Injured Peripheral Nerves S. Aamar, A. Saada, and S. Rotshenker Department of Anatomy and Embryology, Hebrew University-Hadassah Medical School, Jerusalem, Israel Abstract: Peripheral nerve injury produces Wallenan de- generation characterized by a change in the composition of resident nonneuronal cells: macrophages are recruited from the circulation to join Schwann, fibroblast, and endothelial cells. At the same time, the nonneuronal cell population exhibits, as a whole, alterations in synthesis and secretion of diffusible molecules, some of which are instrumental in nerve repair mechanisms. In this study, we determined whether changes in the production of secreted molecules depend on the concomitant modification in cell composi- tion. Therefore, we studied the secretion of newly synthe- sized molecules by defined cell populations of intact nerves, intact nerve explants undergoing in vitro axonal degenera- tion, in vivo degenerating nerves, and recruited cells. Nerves were incubated in serum-free, [35S]methionine-containing media. Secreted, radioactivelylabeled proteins were precipi- tated from the medium and analyzed by gel electrophoresis. Reduced production of 43-, 46-, and 48-kDa proteins and increased production of 33-34-, 37-, 49-, 59-, and 67-kDa proteins were detected in in situ degenerating nerves. High- density ultracentrifugation and immunoblot analysis re- vealed that the 33-34-kDa protein is apolipoprotein-E (apo-E). Similar alterations in the production of these molecules were detected in intact nerve explants from which blood-borne cells were excluded. Apo-E, 37-, 49-, 59-, and 67-kDa proteins were also produced in frozen nerves that lacked the intact nerve nonneuronal cell popula- tion. Instead, these preparations contained blood-borne cells, primarily macrophages. Thus, change in the produc- tion of a substantial number of secreted molecules, apo-E included, is a characteristic response to axonal disintegra- tion of the nonneuronal cells resident in intact nerves. Re- cruited macrophages, although not required, contribute to the production of apo-E and other secreted molecules. The production of apo-E and 45-kDa proteins was inhibited, and that of 37-kDa proteins increased in the presence of NH4CI, further suggesting that lysosomal activity plays a role in the regulation of the production of these molecules. Key Words: Nerve injury-Nerve degeneration-Nerve re- generation- Apolipoprotein-E-Macrophages-Schwann cells. Aamar S. et al. Lesion-induced changes in the produc- tion of newly synthesized and secreted apo-E and other mol- ecules are independent of the concomitant recruitment of blood-borne macrophages into injured peripheral nerves. J. Neurochem. zyxw 59, 1287-1292 (1992). Peripheral nerve injury is followed by Wallerian de- generation of the nerve segment distal to the lesion site: axons break down, Schwann cells proliferate, macrophages increase in number, and degraded my- elin is phagocytosed by macrophages and Schwann cells. Regeneration of severed axons begins in the neu- roma segment, the portion of nerve locatdjust proxi- ma1 to the site of injury. The preferred path for regen- eration is the degenerating nerve, which provides axons with a growth-supporting environment (Ra- mon y Cajal, 1928). The support of growth is me- diated, in part, by diffusible molecules (Richardson and Ebendal, 1982). Some of the identified molecules are interleukin-1 (Rotshenker et zyx al., 199 l), nerve Received January 27, 1992; revised manuscript received March 24, 1992; accepted zyxwvutsrq March zyxwvuts 25, 1992. Address correspondence and reprint requests to Dr. S. Rot- shenker at Department ofAnatomy and Embryology, Hebrew Uni- versity-Hadassah Medical School, P.O. Box 1172, Jerusalem 91010, Israel. Abbreviation used: apo-E, apolipoprotein-E. 1287