Abstract Growth factors play a central role in the regulation of normal and injury‐induced regenerative cell growth. The purpose of this article is to summarize the available data on the expression of different growth factors and their receptors in the injured peripheral nervous system and to discuss their possible role in promoting peripheral nerve regeneration.
Abstract CD44 is a cell adhesion molecule which plays an important role in cell movement and adhesion, e.g. in lymphocyte homing and tumour metastasis. Here we studied the expression of CD44 mRNA and protein immunoreactivity in the facial nucleus after nerve injury and during the ensuing regeneration. Transection of the facial nerve led to a strong up‐regulation of CD44, peaking 4 days after injury on the motoneurons of the axotomized facial nucleus. Use of the polymerase chain reaction confirmed the de novo expression of CD44 and detected only the standard haematopoietic CD44 isoform. Western blotting also detected the 76 kDa protein subtype, in line with the predicted size of the haematopoietic CD44 variant. At the ultrastructural level, CD44 immunoreactivity was restricted to the surface of the neuronal perikarya, their dendrites and axons. It was not seen in the adjacent activated astrocytes, microglia or vascular endothelia. This study shows strong up‐regulation of the cell adhesion molecule CD44 on the regenerating rnotoneurons in the axotomized facial nucleus. These data suggest that CD44 may play a role in neurite outgrowth, in synaptic stripping or in the adhesion of activated glial cells to the perikaryal surface of the axotomized motoneurons.
The extracellular signal-regulated kinase (ERK) cascade, a key component of mitogen-activated protein kinase signalling, is important in synaptic plasticity, in mediating mitogenic and trophic effects, as well as for cell proliferation in normal and transformed non-neuronal cells. Here, we explored phosphorylated ERK immunoreactivity (pERK-IR) following hypoxic-ischaemic (HI) insult in postnatal day 7–8 mice (equivalent to approx 31–32 week human gestation) by unilateral carotid artery occlusion, followed by hypoxia (8% O2/N2). Exposure to 30 min HI resulted in massive increase in forebrain pERK-IR followed by strong white matter (WM) damage, but only mild involvement of the overlying cortical grey matter. Mapping for activated pERK revealed a time-clock sequence of cellular events, beginning with periventricular WM axons (15–45 min post HI onset), followed by white and grey matter glia and cortical neurons (1–4 h post HI onset), returning to normal by 8 h. Systemic inhibition of MEK1/2 with SL327 resulted in significant decrease in WM damage. This could point to activated MEK1/2 and ERK as promising targets for therapeutic intervention in neonatal brain damage, and in prevention of periventricular leukomalacia.
Blocking sodium protein transporters improves neuroprotection in vitro and in small animal models (Robertson1; Kendall2), In the current study we investigated the effects of treatment with the blood-brain permeable methyl isobutyl amiloride analogue (MIA) in the large animal model of neonatal hypoxic ischaemic encephalopathy.
Methods
18 male piglets (<24 h of age) underwent transient global hypoxia-ischaemia and were randomized to (1) normothermia or (2) 2.5 mg/kg of MIA at 10 min after resuscitation and 8 hourly thereafter. 1H MRS (Lac/Cr, Cho/Cr, NAA/Cr and Lac/NAA) in the thalamic and the dorsal subcortical white matter voxels. and 31P (Pi/ePP, PCr/ePP, NTP/ePP and pH) MRS were acquired serially up to 48 h after injury.
Results
Post-insult treatment with MIA led to a significant decrease in thalamic Lac/NAA and Lac/Cr AUC (−45% and −24%, respectively, p<0.05, one-sided t-test). There was a reduction in TUNEL+ staining density in dorsoparietal and midtemporal cerebral cortex, thalamus and subcortical white matter. Piglets with progressive cerebral secondary energy failure (SEF) with NTP/ePP<40% of initial levels, showed massive intracerebral acidosis, with a trend towards reduced incidence in the MIA-treated group (p=0.05). Surprisingly, in animals without SEF, treatment with MIA did not cause a decrease in intracerebral pH.
Conclusion
Treatment with MIA shows neuroprotection in post-ischaemic forebrain, and should be tested for synergistic effects in combination with cooling. The reduction in acidotic SEF and the absence of pH effects in animals without SEF suggest that the MIA neuroprotection is not exerted by reducing secondary intracellular alkalosis.
Although neural c-Jun is essential for successful peripheral nerve regeneration, the cellular basis of this effect and the impact of c-Jun activation are incompletely understood. In the current study, we explored the effects of neuron-selective c-Jun deletion, substitution of serine 63 and 73 phosphoacceptor sites with non-phosphorylatable alanine, and deletion of Jun N-terminal kinases 1, 2 and 3 in mouse facial nerve regeneration. Removal of the floxed c-jun gene in facial motoneurons using cre recombinase under control of a neuron-specific synapsin promoter (junΔS) abolished basal and injury-induced neuronal c-Jun immunoreactivity, as well as most of the molecular responses following facial axotomy. Absence of neuronal Jun reduced the speed of axonal regeneration following crush, and prevented most cut axons from reconnecting to their target, significantly reducing functional recovery. Despite blocking cell death, this was associated with a large number of shrunken neurons. Finally, junΔS mutants also had diminished astrocyte and microglial activation and T-cell influx, suggesting that these non-neuronal responses depend on the release of Jun-dependent signals from neighboring injured motoneurons. The effects of substituting serine 63 and 73 phosphoacceptor sites (junAA), or of global deletion of individual kinases responsible for N-terminal c-Jun phosphorylation were mild. junAA mutants showed decrease in neuronal cell size, a moderate reduction in post-axotomy CD44 levels and slightly increased astrogliosis. Deletion of Jun N-terminal kinase (JNK)1 or JNK3 showed delayed functional recovery; deletion of JNK3 also interfered with T-cell influx, and reduced CD44 levels. Deletion of JNK2 had no effect. Thus, neuronal c-Jun is needed in regeneration, but JNK phosphorylation of the N-terminus mostly appears to not be required for its function.
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