[Neurotrophic factors and their receptor expressions in human neuropathies]

Currently, many neurotrophic factors are known to promote peripheral nerve regeneration after nerve injury or nerve degeneration. Among such neurotrophic factors, neurotrophin family (NGF, BDNF, NT-3, NT-4) and GDNF are most potent ones, and they have been demonstrated to express in the distal stump of the experimental nerve transection. In this study, we assessed the expression levels of neurotrophin mRNAs and GDNF mRNAs and their receptor mRNAs for p75, TrkA, TrkB, TrkC, GDNFR alpha and Ret in the sural nerve biopsy specimens from various human neuropathies. All the neurotrophin mRNAs and GDNF mRNAs were significantly elevated in the diseased nerves and their expression levels well correlated to the extent of T-cell and macrophage invasion. p75 and GDNFR alpha mRNAs were upregulated in correlation to the extent of axonal degeneration. On the other hand, the TrkB and TrkC mRNAs were likely downregulated. These findings suggest that the regulatory mechanism for expression of neurotrophins and GDNF mRNAs and their receptor mRNAs are different. Significant upreguration of the neurotrophic factor mRNAs in the nerve lesion would be the compensation mechanism reacting for the lesion, even in the lesions which are progressing in severity. Extrinsic supplement of these neurotrophins would be beneficial for promotion of repair of the peripheral nerve lesion particularly when they are progressive lesions.