We examined the biosynthesis and post-translational processing of the brain-derived neurotrophic factor precursor (pro-BDNF) in cells infected with a pro-BDNF-encoding vaccinia virus. Metabolic labeling, immunoprecipitation, and SDS-polyacrylamide gel electrophoresis reveal that pro-BDNF is generated as a 32-kDa precursor that is N-glycosylated and glycosulfated on a site, within the pro-domain. Some pro-BDNF is released extracellularly and is biologically active as demonstrated by its ability to mediate TrkB phosphorylation. The precursor undergoes N-terminal cleavage within the trans-Golgi network and/or immature secretory vesicles to generate mature BDNF (14 kDa). Small amounts of a 28-kDa protein that is immunoprecipitated with BDNF antibodies is also evident. This protein is generated in the endoplasmic reticulum through N-terminal cleavage of pro-BDNF at the Arg-Gly-Leu-Thr⁵⁷-↓-Ser-Leu site. Cleavage is abolished when Arg⁵⁴ is changed to Ala (R54A) by in vitromutagenesis. Blocking generation of 28-kDa BDNF has no effect on the level of mature BDNF and blocking generation of mature BDNF with α₁-PDX, an inhibitor of furin-like enzymes, does not lead to accumulation of the 28-kDa form. These data suggest that 28-kDa pro-BDNF is not an obligatory intermediate in the formation of the 14-kDa form in the constitutive secretory pathway.

Nerve growth factor (NGF) is released through the constitutive secretory pathway from cells in peripheral tissues and nerves where it can act as a target-derived survival factor. In contrast, brain-derived neurotrophic factor (BDNF) appears to be processed in the regulated secretory pathway of brain neurons and secreted in an activity-dependent manner to play a role in synaptic plasticity. To determine whether sorting differences are intrinsic to the neurotrophins or reflect differences between cell types, we compared NGF and BDNF processing in cultured hippocampal neurons using a Vaccinia virus expression system. Three independent criteria (retention or release from cells after pulse–chase labeling, depolarization-dependent release, and immunocytochemical localization) suggest that the bulk of newly synthesized NGF is sorted into the constitutive pathway, whereas BDNF is primarily sorted into the regulated secretory pathway. Similar results occurred with AtT 20 cells, including those transfected with cDNAs encoding neurotrophin precursor–green fluorescent protein fusions. The NGF precursor, but not the BDNF precursor, is efficiently cleaved by the endoprotease furin in thetrans-Golgi network (TGN). Blocking furin activity in AtT 20 cells with α1-PDX as well as increasing the expression of NGF precursor partially directed NGF into the regulated secretory pathway. Therefore, neurotrophins can be sorted into either the constitutive or regulated secretory pathways, and sorting may be regulated by the efficiency of furin cleavage in the TGN. This mechanism may explain how neuron-generated neurotrophins can act both as survival factors and as neuropeptides.

Nerve conduits have emerged as alternatives to autologous nerve grafts, but their use in large-diameter nerve deficits remains untested. We report four patients who underwent repair of large-diameter nerves using absorbable nerve conduits and discuss the failed clinical outcomes. The reported cases demonstrate the importance of evaluating the length, diameter, and function of nerves undergoing conduit repair. In large-diameter nerves, the use of conduits should be carefully considered.

Hippocampal neurons release nerve growth factor (NGF) through the constitutive secretory pathway, thus allowing the protein to be continuously available for promoting nerve cell survival. In contrast, hippocampal neurons use the regulated secretory pathway to process brain-derived neurotrophic factor (BDNF), which alters synaptic activity when released acutely from dense-core vesicles. Thus, understanding how neurons sort and deliver neurotrophins may provide clues to their functions in brain. In this study, we monitored the processing and delivery of neurotrophin-3 (NT-3). Pulse–chase studies, immunocytochemistry, and secretagogue-induced release experiments were performed on cultured hippocampal neurons and AtT-20 cells infected with vaccinia viruses encoding the NT-3 precursor (pro-NT-3). Results show that most newly synthesized NT-3 is released through the constitutive secretory pathway as a result of furin-mediated endoproteolytic cleavage of pro-NT-3 in thetrans-Golgi network. Pro-NT-3 can also be diverted into the regulated secretory pathway when cells are treated with α1-PDX, a selective inhibitor of furin-like enzymes, or when pro-NT-3 expression is increased by transient transfection methods. In cells coinfected with viruses coding for pro-NT-3 and pro-BDNF, NT-3 is sorted into the regulated pathway, stored in secretory granules, and released in response to extracellular cues together with BDNF, apparently as a result of heterodimerization, as suggested by coimmunoprecipitation data. Taken together, these data show that sorting of the NT-3 precursor can occur in both the constitutive and regulated secretory pathways, which is consistent with NT-3 having both survival-promoting and synapse-altering functions.

Myelin basic protein (MBP) is required for normal myelin compaction and is implicated in both experimental and human demyelinating diseases. In this study, as an initial step in defining the regulatory network controllingMBPtranscription, we located and characterized the function of evolutionarily conserved regulatory sequences. Long-range human-mouse sequence comparison revealed over 1 kb of conserved noncodingMBP5′ flanking sequence distributed into four widely spaced modules ranging from 0.1 to 0.4 kb. We demonstrate first that a controlled strategy of transgenesis provides an effective means to assign and compare qualitative and quantitativein vivoregulatory programs. Using this strategy, single-copy reporter constructs, designed to evaluate the regulatory significance of modular and intermodular sequences, were introduced by homologous recombination into the mousehprt(hypoxanthine-guanine phosphoribosyltransferase) locus. The proximal modules M1 and M2 confer comparatively low-level oligodendrocyte expression primarily limited to early postnatal development, whereas the upstream M3 confers high-level oligodendrocyte expression extending throughout maturity. Furthermore, constructs devoid of M3 fail to target expression to newly myelinating oligodendrocytes in the mature CNS. Mutation of putative Nkx6.2/Gtx sites within M3, although not eliminating oligodendrocyte targeting, significantly decreases transgene expression levels. High-level and continuous expression is conferred to myelinating or remyelinating Schwann cells by M4. In addition, when isolated from surroundingMBPsequences, M3 confers transient expression to Schwann cells elaborating myelin. These observations define thein vivoregulatory roles played by conserved noncodingMBPsequences and lead to a combinatorial model in which different regulatory modules are engaged during primary myelination, myelin maintenance, and remyelination.

Variable and unpredictable spontaneous recovery can occur following acute cervical traumatic spinal cord injury (tSCI). Despite the critical clinical and interventional trial planning implications of this tSCI feature, baseline measures to accurately predict neurologic recovery are not well defined. In this study, we used data derived from 99 consecutive patients (78 male, 21 female) with acute cervical tSCIs to assess the sensitivity and specificity of various clinical and radiologic factors in predicting recovery at one year after injury. Categorical MR-imaging parameters included maximum canal compromise (MCC), maximum spinal cord compression (MSCC), longitudinal length of intramedullary lesion (IML), Brain and Spinal Injury Center (BASIC) score, and a novel derived Combined Axial and Sagittal Score (CASS). Logistic regression analysis of the area under the receiver operator characteristic curve (AUC) was applied to assess the differential predictive value of individual imaging markers. Admission American Spinal Injury Association Impairment Scale (AIS) grade, presence of a spinal fracture and central cord syndrome were predictive of AIS conversion at 1-year. Both BASIC and IML were stronger predictors of AIS conversion as compared to MCC and MSCC (P=0.0002 and P=0.04). The BASIC score demonstrated the highest overall predictive value for AIS conversion at 1-year (AUC 0.94). We conclude that admission intrinsic cord signal findings are robust predictive surrogate markers of neurologic recovery after cervical tSCI. Direct comparison of imaging parameters in this cohort of patients indicates that the BASIC score is the single best acute predictor of the likelihood of AIS conversion.