TGF-beta1 and TGF-beta2 expression after traumatic human spinal cord injury.

STUDY DESIGN: Immunohistochemical investigation in control and lesioned human spinal cords. OBJECTIVES: To assess the spatial and temporal expression patterns of transforming growth factor-beta1 and -beta2 (TGF-beta1 and TGF-beta2) in the human spinal cord after traumatic injury. SETTING: Germany, Aachen, Aachen University Hospital. METHODS: Sections from human spinal cords from 4 control patients and from 14 patients who died at different time points after traumatic spinal cord injury (SCI) were investigated immunohistochemically. RESULTS: In control cases, TGF-beta1 was confined to occasional blood vessels, intravascular monocytes and some motoneurons, whereas TGF-beta2 was only found in intravascular monocytes. After traumatic SCI, TGF-beta1 immunoreactivity was dramatically upregulated by 2 days after injury (the earliest survival time investigated) and was detected within neurons, astrocytes and invading macrophages. The staining was most intense over the first weeks after injury but gradually declined by 1 year. TGF-beta2 immunoreactivity was first detected 24 days after injury. It was located in macrophages and astrocytes and remained elevated for up to 1 year. In white matter tracts undergoing Wallerian degeneration, there was no induction of either isoform. CONCLUSION: The early induction of TGF-beta1 at the point of SCI suggests a role in the acute inflammatory response and formation of the glial scar, while the later induction of TGF-beta2 may indicate a role in the maintenance of the scar. Neither of these TGF-beta isoforms appears to contribute to the astrocytic scar formation in nerve fibre tracts undergoing Wallerian degeneration.

Sequential loss of myelin proteins during Wallerian degeneration in the human spinal cord.

Axons undergo Wallerian degeneration (WD) distal to a point of injury. In the lesioned PNS, WD may be followed by successful axonal regeneration and functional recovery. However, in the lesioned mammalian CNS, there is no significant axonal regeneration. Myelin-associated proteins (MAPs) have been shown to play significant roles in preventing axonal regeneration in the CNS. Since relatively little is known about such events in human CNS pathologies, we performed an immunohistochemical investigation on the temporal changes of four MAPs during WD in post-mortem spinal cords of 22 patients who died 2 days to 30 years after either cerebral infarction or traumatic spinal cord injury. In contrast to experimental studies in rats, the loss of myelin sheaths is greatly delayed in humans and continues slowly over a number of years. However, in agreement with animal data, a sequential loss of myelin proteins was found which was dependent on their location within the myelin sheath. Myelin proteins situated on the peri-axonal membrane were the first to be lost, the time course correlating with the loss of axonal markers. Proteins located within compact myelin or on the outer myelin membrane were still detectable 3 years after injury in degenerating fibre tracts, long after the disappearance of the corresponding axons. The persistence of axon growth-inhibitory proteins such as NOGO-A in degenerating nerve fibre tracts may contribute to the maintenance of an environment that is hostile to axon regeneration, long after the initial injury. The present data highlight the importance of correlating the well documented, lesion-induced changes that take place in controlled laboratory investigations with those that take place in the clinical domain.

Major histocompatibility complex class II expression by activated microglia caudal to lesions of descending tracts in the human spinal cord is not associated with a T cell response.

Lesion-induced microglial/macrophage responses were investigated in post-mortem human spinal cord tissue of 20 patients who had died at a range of survival times after spinal trauma or brain infarction. Caudal to the spinal cord injury or brain infarction, a strong increase in the number of activated microglial cells was observed within the denervated intermediate grey matter and ventral horn of patients who died shortly after the insult (4-14 days). These cells were positive for the leucocyte common antigen (LCA) and for the major histocompatibility complex class II antigen (MHC II), with only a small proportion staining for the CD68 antigen. After longer survival times (1-4 months), MHC II-immunoreactivity (MHC II-IR) was clearly reduced in the grey matter but abundant in the white matter, specifically within the degenerating corticospinal tract, co-localising with CD68. In this fibre tract, elevated MHC II-IR and CD68-IR were still detectable 1 year after trauma or stroke. It is likely that the subsequent expression of CD68 on MHC II-positive microglia reflects the conversion to a macrophage phenotype, when cells are phagocytosing degenerating presynaptic terminals in grey matter target regions at early survival times and removing axonal and myelin debris in descending tracts at later survival times. No T or B cell invasion or involvement of co-stimulatory B7 molecules (CD80 and CD86) was observed. It is possible that the up-regulation of MHC II on microglia that lack the expression of B7 molecules may be responsible for the prevention of a T cell response, thus protecting the spinal cord from secondary tissue damage.

GAP-43 (B-50) and C-Jun are up-regulated in axotomized neurons of Clarke's nucleus after spinal cord injury in the adult rat.

The growth-associated protein GAP-43 (B-50) and the transcription factor C-Jun are involved in regeneration of the injured nervous system. In this study, we investigated the possibility of the induction of GAP-43 and C-Jun in axotomized neurons of Clarke's nucleus (CN) in adult rats, of which a large population undergoes degeneration several weeks after a low thoracic lateral funiculotomy of the spinal cord. In situ hybridization and immunohistochemistry revealed a transient up-regulation of GAP-43 mRNA, C-Jun protein, and its activated, phosphorylated form, peaking around 7 days after injury in preferentially large diameter CN-neurons ipsilateral and caudal to the lesion. Our results document that some populations of axotomized central nervous system neurons, similar to axotomized regenerating neurons of the peripheral nervous system, can up-regulate GAP-43 and C-Jun, even if they are destined to degenerate. This might reflect a transient regenerative capacity, which fails over time.