The Role Of Proteasomal Dysfunction In The Pathogenesis Of Parkinson's Disease

Objective: To observe the nigral degeneration with inclusion-like formation and motor behavior changes induced by proteasome inhibitor in the substantia nigra, and to investigate the role of proteasomal dysfunction in the pathogenesis of Parkinson's disease.Methods: (1)10μg /2μlLactacystin, a selective proteasome inhibitor, was unilaterally injected stereotaxically into the left substantia nigral pars compacta of rats. Equal volume of saline were injected in control group. (2)The spontaneous behavioral abnormalities and apomorphine-induced contralateral rotations of rats were observed. (3)The spontaneous motor behavioral changes in the open-field were observed, and behavioral parameters tested were as follows: total ambulation time, total resting time, total number of rearings, distance covered in grids, the number of spontaneous left and right quarter-turns, the number of left and right forelimb use when leaning against the wall in rearing and the number of runs along the walls of the open-field with left of right side of the animals. (4)The pathologic abnormalities of substantia nigra were viewed by HE staining and Nissl staining. (5)The morphological changes of the TH-positive cells in substantia nigral pars compacta were viewed by immunohistochemistry and TH-postive cells in SNc were counted. (6)The amount and distribution ofα-synuclein in nigral cells were viewed by immunohistochemistry. (7)The number of TH-positive nerve fibers in striatum was investigated by immunohistochemistry. (8)The ultrastructural changes in SNc and striatum were observed by transmission electron microscope.Results: (1)The rats became progressively bradykinetic and displayed contralateral head tilting, tremor and apomorphine-induced contralateral rotation 7 days after Lactacystin injection. On the 21st day after the injection of Lactacystin, the number of apomorphine-induced contralateral rotations in 30 minutes was 266.92±9.19. (2) Total ambulation time, total resting time, total number of rearings and distance covered in grids were less in the Lactacystin group compared with saline group. The numbers of spontaneous left quarter-turns, left forelimb use when leaning against the wall in rearing and runs along the walls of the open-field with left side of the animals were significantly more than those of right side. (3)It was viewed that the number of neurons in the left SNc decreased in Lactacystin group and some nigral cells contained eosinophilic inclusions using HE staining. (4)It was observed that the number of Nissl bodies in the neurons of the left SNc in Lactacystin group decreased using Nissl staining. (5)The number of TH-positive cells in the left SNc in Lactacystin group significantly decreased and there was a 81.33% loss of TH-positive cells compared with right SNc(p<0.05). (6)The amount ofα-synuclein in the neurons of left SNc increased in Lactacystin group. Some neurons contained round/oval inclusions with intense immune response toα-synuclein. (7)The number of TH-positive nerve fibers in left striatum was much less than this in right striatum in Lactacystin group. The averages OD of right and left striatum were 0.2165±0.0017and 0.0406±0.0006, respectively. The difference between them was significant(p<0.05). (8)It is observed that the neurons in left SNc of Lactacystin group were rare using transmission electron microscope. Most of survival neurons showed characteristics of apoptosis. The layers of myelin sheath loosen. Several nerve fibers swelled and contained many little aggregates with a dense core and filaments around. Few gliocytes also showed characteristics of apoptosis. The number of nerve fibers in the left striatum of Lactacystin group decreased, and The layers of survival myelin sheath loosen. Conclusion: 10μg /2μl Lactacystin, a selective proteasome inhibitor, unilaterally injected stereotaxically into the left substantia nigral pars compacta of rats, can induce the degeneration of substantia nigra with inclusion-like formation and motor behavioral changes just like the clinical symptoms of PD. Lactacystin may be used for the establishment of new PD animal model. Proteasomal dysfunction may play an important role in the pathogenesis of PD.