The ability of sensory axons to stimulate Schwann cell proliferation by contact was established in the 1970s. Although the mitogen responsible for this proliferation has been localized to the axon surface and biochemically characterized, it has yet to be identified. Recently a family of proteins known as heregulins (HRGs) has been isolated, characterized, and shown to interact with a number of class 1 receptor tyrosine kinases, including the erbB2, erbB3, and erbB4 gene products. These factors include glial growth factor, a Schwann cell mitogen. We The phenomenon of Schwann cell (SC) proliferation driven by axonal contact was demonstrated nearly 20 years ago by in vitro observations using both rat (1) and chick (2) tissues. Characterization of this mitogenic activity has shown it to be associated with the surface of the axon and to be sensitive to trypsin, heat, and glutaraldehyde treatment, indicating the involvement of a protein component (3). This protein is salt extractable, indicating that it is peripherally, rather than integrally, membrane bound (4). Mitogenic activity can be detected in the solubilized fraction (130,000 x g, 1 hr) of the extract, and can be inhibited by low concentrations (half-maximally at 0.5-0.7 jig/ml) of heparin (4). Further, treatment of axons with heparatinase removes the mitogenic activity from the axon (5). These results indicate that the axonal mitogen is a protein or protein-proteoglycan complex peripherally associated with the axonal membrane (see ref. 6 for review).The primary sequence for one of the best-characterized SC mitogens, glial growth factor (GGF), has been elucidated and expression plasmids containing the appropriate cDNA have allowed the production of these purified factors (7). Sequence analysis has shown that GGF is a member of a family of proteins which include GGF II (7), acetylcholine receptorinducing activity (ARIA) (8), Neu differentiation factorThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.(NDF) (9), and heregulin (HRG) a and ,B (see refs. 10 and 11 for review). Chemical crosslinking experiments (12) have shown HRG to interact with pl85erbB2. These proteins have also been shown to stimulate the phosphorylation of a number of class 1 receptor tyrosine kinases, including those encoded by erbB2, erbB3, and erbB4 (7,10,(12)(13)(14).Studies by us (15) and by others (16) have shown other members of the HRG family (NDF, HRG,B1) to be effective mitogens for SCs. The stimulation of human SC proliferation by purified, soluble recombinant HRG can be blocked by a monoclonal antibody raised against the p185erbB2 receptor (2C4) (15).Our recent observations on human SC proliferation have shown that rat sensory neurons are mitogenic for human SCs. In this study we have cocultured human (and rat) adult-derived SCs with purified rat sensory neurons in the presence or absence of antibodies against pl85er...

The use of Schwann cell (SC) autotransplantation to influence neural repair in humans is dependent upon identifying mitogens that will effectively expand human Schwann cells (SCs) in culture. The recent purification and molecular cloning of glial growth factor (GGF), a potent mitogen for rat Schwann cells, has led to the recognition that a family of proteins (GGF/HRG/NDF/ARIA) are alternatively spliced products of a single gene. The heregulins (HRGs) have been characterized with respect to their influence on human breast cancer cell lines; here we examined whether the HRGs have mitogenic activity for human SCs. Using DNA synthesis assays and serial passaging of cells in culture, we demonstrate that HRG is an effective mitogen for human SCs and that, in the presence of agents that elevate cAMP, it is possible to expand these cells over multiple passages without overwhelming fibroblast contamination. One putative target for this family of proteins is p185erbB2, and EGF-like receptor tyrosine kinase that is encoded by the erbB2 protooncogene. In this report we also demonstrate that the erbB2/3/4 messages as well as the erbB2/3 receptor proteins are present within cultured human SCs. The addition of HRG to human SCs results in tyrosine phosphorylation of a 185 kDa protein. In the presence of stimulatory concentrations of HRG, a blocking monoclonal antibody (2C4) to p185erbB2 is capable of significantly inhibiting phosphorylation of a 185 kDa protein as well as the subsequent incorporation of 3H-thymidine within the human SC. These latter results implicate an important role for p185erbB2 in mediating the mitogenic response of human SCs to HRGs.

WE REVIEW OUR current understanding of the development and potential clinical applications of bone morphogenetic protein (BMP) in spine surgery. We also review the evidence for adverse events associated with the use of BMP and suggest potential reasons for these events and means of complication avoidance. Bone morphogenetic protein 2 (rhBMP-2) is approved by the Food and Drug Administration for anterior lumbar interbody fusion; rhBMP-7, on the other hand, is approved for long bone defects and has received a humanitarian device exemption for revision posterolateral lumbar operations and recalcitrant long bone unions. Nevertheless, "off-label" use in various spinal procedures has been reported and is increasing in frequency. Specific guidelines for rhBMP-2 and rhBMP-7 use are lacking because of the limited availability of randomized controlled clinical trials and its diverse use in many spinal applications. Mechanisms of delivery, carrier type, graft position, surgical location, and variations in BMP concentration may differ from one surgery to the next. Adverse events linked to either rhBMP-2 or rhBMP-7 use include ectopic bone formation, bone resorption or remodeling at the graft site, hematoma, neck swelling, and painful seroma. Other potential theoretical concerns include carcinogenicity and teratogenic effects. In this review, we provide the reader with a historical perspective on BMP, current and past research to support its use in spinal procedures, and a critical analysis of the complications reported thus far.

These results support the hypothesis that apoptosis occurs in human SCIs and is accompanied by the activation of caspase-3 of the cysteine protease family. This mechanism of cell death contributes to the secondary injury processes seen after human SCI and may have important clinical implications for the further development of protease inhibitors to prevent programmed cell death.

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The authors retrospectively reviewed 452 consecutively treated patients who underwent a spinal instrumentation procedure at a single institution to establish which patients and which surgical approaches might be associated with an increased risk of developing deep wound infections and to determine the efficacy with which the institution's current treatment strategy eradicates these infections. Wound infections occurred in 17 patients (10 men and seven women) with spinal instrumentation (incidence 3.8%). All infections occurred after posterior spinal instrumentation procedures (7.2%); there were no infections after anterior instrumentation procedures regardless of the level. Each patient was assigned an infection risk factor (RF) score depending on the number of RFs identified in an individual patient preoperatively. The mean RF score of patients who developed infections was 2.18, whereas the mean RF score for a procedure-matched, infection-free control group was 0.71. The mean number of days from surgery to clinical presentation was 27.6 days (range 4-120 days), and the mean increase in hospitalization time for the subset of patients who developed infections was 16.6 days. The most common organism isolated from wound cultures was Staphylococcus aureus (nine of 17 cases). Of the 17 patients, five had infections involving multiple organisms. All patients were infection free at a minimum of 8 months follow-up review. The current treatment regimen advocated at this institution consists of operative debridement of the infected wound, a course of intravenous followed by oral antibiotic medications, insertion of an antibiotic-containing irrigation-suction system for a mean of 5 days, and maintenance of the instrumentation system within the infected wound.

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The use of human Schwann cells (SCs) in transplantation to promote regeneration in central and peripheral neural tissues must be preceded by efforts to define the factors that regulate their functional expression. Adult-derived human SCs can be isolated and purified in culture, but the culture conditions that allow their full differentiation have not yet been defined. We tested the functional capacity of these cells to enhance axonal regeneration and myelinate regenerating axons in vivo by transplanting them into the damaged PNS of an immune-deficient rat. SCs were purified from human peripheral nerve obtained from organ donors. Semi-permeable guidance channels were filled with a 30% Matrigel containing solution with or without human SCs suspended at a density of 80 x 10(6) cells/ml. Channels were implanted within an 8 mm gap of the transfected sciatic nerve of nude female rats for a period of 4 weeks. Survival of the transplanted human SCs was established by dissociating nerve explants taken from the regenerated cable (after first placing them in culture for 5 d) and staining individual cells for a primate-specific NGF receptor (PNGFr) and S 100. Only one-half of the S 100-positive cells stained for the PNGFr, which indicated that the regenerated cable contained an approximately equal number of human and rat (host) SCs. The presence of some human myelin segments was confirmed by immune staining with an HNK- 1 antibody that specifically labels human but not rat myelin. The majority of the myelin segments in the regenerated cable, however, were produced by the rat SCs. The number of myelinated axons and the cross- sectional area of the cable were significantly greater in channels seeded with human SCs when compared to channels containing the diluted Matrigel solution alone. We conclude that purified cultured human SCs can survive and substantially enhance axonal regeneration when transplanted into the injured PNS of an immune-deficient rat. Some of the transplanted human SCs are capable of myelinating regenerating rat axons but are less successful than the host SCs.