| Diabetic neuropathy is one of the common complications of diabetes mellitus. Among them, Diabetic Polyneuropathy ( DPN ) is the most common one, which is characterized by distal extremities symmetric sensorimotor deficits, the progressive slowing of motor and sensory nerve conduction velocities(MNCV, SNCV) and axonal-myelin degeneration.The pathogenesis of DPN is multifactorial and remains unresolved. The abnormalities in the synthesis and metabolism of carbohydrates, proteins and lipids of the nerve tissues in DPN suggest that some related enzymes may be changed. UDP-Galactose: Ceramide Galactosyltransferase(CGT) is the rate-limiting enzyme in the biosynthesis of galactocerebroside(GalC), which is a major glycolipid constituents in the myelin sheath. Calpainâ…¡,a calcium-activated neutral cysteine protease, which presents in myelin and axon and has a basal level of activity in normal sciatic nerves, is important for the maintenance of the structure and function in peripheral nerves. Both CGT and Calpainâ…¡are expressed in Schwann cells, the myelin forming cells in peripheral nervous system. However, the expressions of CGT and calpainâ…¡in sciatic nerves, especially in Schwann cells in experiment DPN and their implication in the pathogenesis of DPN are not reported. Deficiency of neurotrophic factors, particularly nerve growth factor (NGF) play a key role in the pathogenesis of DPN. Several studies indicated that administration of exogenous human recombinant nerve growth factor (hrNGF) can ameliorate experimental DPN functionally and pathologically. Recently, human nerve growth factor (hNGF) has been extracted from human placenta by researchers in our country. The effects of hNGF on experimental DPN and the expression of CGT and calpainâ…¡ in sciatic nerve are not clear.In this study, diabetic rats were induced by single intraperitoneal injection of Streptozotocin (STZ). Nerves conduction velocity,tailflick temperature threshold (TTT), and pathology of sciatic nerve and sural nerve were observed in order to define when DPN had been developed and the severity of DPN. RT-PCR, in situhybridization, and immunohistochemistry techniques were employed to observed the changes in the expressions of CGT mRNA, calpainâ…¡mRNA and protein. CGT and calpainâ…¡expressions were also observed in the cultured Schwann cells in high glucose by RT-PCR, in situ hybridization and immunocytochemistry techniques. In addition to that, the expression of NGFmRNA and protein in sciatic nerves of DPN rats were detected by RT-PCR and immunohistochemistry, and the effects of hNGF on function, morphology, and the expression of CGT and calpainâ…¡in the sciatic nerve of DPN rats were evaluated. The results show that: Decreased NCV developed two weeks after the induction of diabetes. At 4 weeks, TTT was increased and ultrastructural lesions was observed. These functional and morphological abnormalities became more sever along with the progresses of the experiment. The expression of CGTmRNA in sciatic nerve was not changed in DPN4W rats, but increased in DPN8W rats . Calpainâ…¡mRNA and protein expression were reduced significantly both in DPN4W and DPN8W rats. In vitro studies, the Schwann cells cultured in high glucose also had increased CGTmRNA expression and decreased calpainâ…¡mRNA and protein expressions, which is coincided with the in vivo studies. The expression of NGFmRNA in sciatic nerves of DPN rats was not decreased until DPN8W. However, the level of NGF protein was reduced statistically in sciatic nerves of DPN4W rats. Administration of hNGF on DPN rats for 4 weeks can reverse the reduction of NGF expression, increase MNCV and SNCV, decrease TTT, and ameliorate the abnormalities in morphology. It also reduced CGTmRNA expression and enchanced calpainâ…¡mRNA and protein expressions in PDN rats. Our conclusions are: (1) DPN was developed at the early stage in diabetic rats and was progressively severe. (2) Both CGT and Calpainâ…¡ expressions in the sciatic nerves of DPN rats or the Schwann cells cultured in high glucose we...
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