Biosynthetic nerve grafts are desired as alternative to autologous nerve grafts in peripheral nerve reconstruction. Artificial nerve conduits still have their limitations and are not widely accepted in the clinical setting. Here we report an analysis of fine-tuned chitosan tubes used to reconstruct 10 mm nerve defects in the adult rat. The chitosan tubes displayed low, medium and high degrees of acetylation (DAI: ≈ 2%, DA: ≈ 5%, DAIII: ≈ 20%) and therefore different degradability and microenvironments for the regenerating nerve tissue. Short and long term investigations were performed demonstrating that the chitosan tubes allowed functional and morphological nerve regeneration similar to autologous nerve grafts. Irrespective of the DA growth factor regulation demonstrated to be the same as in controls. Analyses of stereological parameters as well as the immunological tissue response at the implantation site and in the regenerated nerves, revealed that DAI and DAIII chitosan tubes displayed some limitations in the support of axonal regeneration and a high speed of degradation accompanied with low mechanical stability, respectively. The chitosan tubes combine several pre-requisites for a clinical acceptance and DAII chitosan tubes have to be judged as the most supportive for peripheral nerve regeneration.

As a rule, hepatocyte growth factor/scatter factor (HGF/SF) is produced by mesenchymal cells, while its receptor, the tyrosine kinase encoded by the met proto-oncogene, is expressed by the neighboring epithelial cells in a canonical paracrine fashion. In the present work we show that both HGF/SF and met are coexpressed by undifferentiated C2 mouse myoblasts. In growing cells, the autocrine loop is active as the receptor exhibits a constitutive phosphorylation on tyrosine that can be abrogated by exogenously added anti-HGF/SF neutralizing antibodies. The transcription of HGF/SF and met genes is downregulated when myoblasts stop proliferating and differentiate. The coexpression of HGF/SF and met genes is not exclusive to C2 cells since it has been assessed also in other myogenic cell lines and in mouse primary satellite cells, suggesting that HGF/SF could play a role in muscle development through an autocrine way.To analyze the biological effects of HGF/SF receptor activation, we stably expressed the constitutively activated receptor catalytic domain (p65tpr-met) in C2 cells. This active kinase determined profound changes in cell shape and inhibited myogenesis at both morphological and biochemical levels. Notably, a complete absence of muscle regulatory markers such as MyoD and myogenin was observed in p65tpr-met highly expressing C2 clones. We also studied the effects of the ectopic expression of human isoforms of met receptor (h-met) and of HGF/SF (h-HGF/SF) in stable transfected C2 cells. Single constitutive expression of h-met or h-HGF/SF does not alter substantially the growth and differentiation properties of the myoblast cells, probably because of a species-specific ligand–receptor interaction. A C2 clone expressing simultaneously both h-met and h-HGF/SF is able to grow in soft agar and shows a decrease in myogenic potential comparable to that promoted by p65tpr-met kinase. These data indicate that a met kinase signal released from differentiation-dependent control provides a negative stimulus for the onset of myogenic differentiation.

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Activation of the receptor tyrosine kinase ErbB4 leads to various cellular responses such as proliferation, survival, differentiation, and chemotaxis. Two pairs of naturally occurring ErbB4 isoforms differing in their juxtamembrane (JMa/JMb) and C termini (cyt1/cyt2) have been described. To examine the role of ErbB4 in neuron migration, we cloned and stably transfected each of the four ErbB4 isoforms in ST14A cells (a neural progenitor cell line derived from the striatum of embryonic day 14 rats) endogenously expressing the other members of the ErbB family: ErbB1, ErbB2, and ErbB3. Using immunoprecipitation assays, we showed that the neuregulin-1␤1 (NRG1␤1) stimulus induced ErbB4 tyrosine phosphorylation and phosphatidylinositol 3-kinase (PI3K) recruitment and activation (as demonstrated by Akt phosphorylation) either directly (ErbB4 cyt1 isoform) or indirectly (ErbB4 cyt2 isoform). We examined the ability of the four ErbB4 isoforms to induce chemotaxis and cell proliferation in response to NRG1␤1 stimulation. Using migration assays, we observed that only ErbB4-expressing cells stimulated with NRG1␤1 showed a significant increase in migration, whereas the growth rate remained unchanged. Additional assays showed that inhibition of PI3K (but not of phospholipase C␥) dramatically reduced migratory activity. Our data show that ErbB4 signaling via PI3K activation plays a fundamental role in controlling NRG1␤1-induced migration.The ErbB receptor family consists of four receptor tyrosine kinases named the epidermal growth factor (EGF) 1 receptor, ErbB2, ErbB3, and ErbB4 (reviewed in Ref. 1). Ligand-dependent activation of ErbB receptors results in homo-or heterodimerization, which stimulates receptor trans-phosphorylation on cytoplasmic tyrosine residues, creating binding sites for adaptor or enzymatic proteins. EGF receptor and ErbB4 homodimers are active kinases in the absence of coreceptors, whereas ErbB3 (which has little or no intrinsic tyrosine kinase activity) and ErbB2 (for which no ligand has been identified) necessitate coreceptor interaction for signal transduction (2). Thus, whereas ErbB2 and ErbB3 are limited to heterodimerization, the EGF receptor and ErbB4 can be activated by either homo-or heterodimerization.An interesting ErbB4 feature (recently reviewed in Ref.3) is the existence of isoforms generated by alternative splicing (4). One isoform pair (5) is characterized by alternative splicing of exons located in the extracellular juxtamembrane region conferring (JMa), or not (JMb), susceptibility to proteolytic cleavage (6) by a member of the ADAM (a disintegrin and metalloprotease) family, the tumor necrosis factor-␣-converting enzyme (7). ErbB4 proteolytic cleavage produces a membraneassociated 80-kDa fragment that can be degraded by proteasome activity following polyubiquitination (8) or that can be the substrate for subsequent ␥-secretase cleavage, which releases the cytoplasmic domain from the membrane and allows, intriguingly, nuclear translocation of a fragment (9, 10) that can act as cotranscrip...