Effects of nerve segment supernatants on cultured Schwann cell proliferation and laminin production

Abstract

Mouse sciatic nerves were transected and 3 hr to 16 days later proximal segments were removed and homogenized. Supernatants of these segments or of normal sciatic nerves were added to Schwann cells maintained in Dulbecco's modified Eagle's medium (DMEM) + 15% fetal calf serum (FCS). After 6 days, Schwann cells were solubilized and the protein content was measured using a Bio-Rad (Melville, NY) protein assay. Samples containing the same amounts of protein were then applied to microtiter plates and the laminin content was determined by enzyme-linked immunosorbent assay (ELISA). Lysates of cultures treated with 24 hr proximal segment supernatants contained significantly higher levels of laminin than those prepared from other intervals, from distal segments, or from control nerves. Increased surface and cytoplasmic anti-laminin immunoreactivity also was found in Schwann cells treated with 24 hr supernatants. To identify the source(s) of this effect, proximal segments removed 24 hr after transection were bisected; supernatants were prepared from each half and tested. Significant increases in laminin production were produced by supernatants from both halves. When supernatants from proximal and distal halves were compared, the latter produced significantly higher laminin levels. Electron microscopic examination of both halves showed that distal halves contained sprouting neurites and growth cones ensheathed by Schwann cells which had a basal lamina and resembled those seen during development and regeneration. Proximal halves appeared normal. Schwann cell proliferation also was compared in supernatant-treated cultures by using a bromodeoxy-uridine (BrdU) ELISA. The 24 hr and 2 day supernatants increased Schwann cell proliferation significantly; 12 hr, 4 day, and 8 day supernatants produced smaller increases. Our observations suggest that axons undergoing early regenerative changes are one of several possible sources of substance(s) in our proximal segment supernatants which increased Schwann cell proliferation and laminin production.

GABAA Receptors Modulate Early Spontaneous Excitatory Activity in Differentiating P19 Neurons

“…Immunostaining for 5-bromo-2 '-deoxyuridine-5 '-monophosphate (BrdU) -incorporated DNA. Immunodetection of cells containing BrdU (Sigma) incorporated into DNA was performed as described previously (Zhang et al, 1994). P19 cells were pulse treated with 10 ,iM BrdU in sequential overnight (16 h) intervals before, during, and after exposure to RA.…”

Vasoactive intestinal peptide: Mediator of laminin synthesis in cultured Schwann cells

“…We used previously described methods for laminin determinations (Winston, 1992;Zhang et al, 1994). Cultured Schwann cells were lysed and centrifuged at 12,500 rpm.…”

Local administration of vasoactive intestinal peptide after nerve transection accelerates early myelination and growth of regenerating axons

“…Recently, we have been interested in whether neuropeptides regulate some axon‐Schwann cell interactions during the early stages of nerve regeneration. Initially, we found that supernatants prepared from proximal nerve segments 12–48 hours after transection upregulated laminin synthesis in cultured Schwann cells ( Zhang et al, 1994 ) . To test whether a neuropeptide might be responsible for this effect, we exposed cultured Schwann cells to medium containing VIP.…”