Study On The Modifiers Of Huntington Disease And Neuroprotection Of 3-nitropropionic Acid Preconditioning

Objectives: HD is an autosomal dominant neurodegenerative disease, characterized by chorea, dementia and emotional impair. HD is caused by an unstable and abnormal expand of CAG repeat. CAG repeat is inversely correlated with age of onset, but the variance in age of onset is not fully explained by CAG repeat. There are likely other modifiers and environmental factor influencing on age of onset. Our sturdy is to detect the relationship between CAG repeat and clinical manifestations, to analyze the relationship between Δ2642 , ApoE polymorphism and HD.Methods: We apply PCR-RFLP, non-denaturing polyacrylamide gel eletrophorisis methods to detect CAG repeat, A2642 and ApoE genotypes. Clinical manifestations are scored by UHDRS and MMSE. The relationship between CAG, A2642 , ApoE polymorphism and HD is explored. Results: (1) Genotypes of IT15 are heterozygous in all 29 HD patients. CAG repeat in the HD chromosome is 42-62, 13-28 in normal chromosome. 4 out of 9 sporadic patients are identified. CAG repeat is inversely correlated with age of onset. The increased motor signs, declined cognitive and psychiatrical symptoms correlated with decreased functional capacity.(2) A2642 genotype A/B is overrepresented in HD. Genotype A/B patients have an earlier onset than genotype A/A patients.(3) There is no difference on ApoE genotype between control andHD. ApoE e 3/4 patients have an earlier onset than ApoE ￡ 3/3 patients. Conclusions: (1) The method to detect CAG repeat is accurate and safe using PCR, polyacrylamide gel eletrophorisis and silver staining.(2) CAG repeat is negatively associated with age of onset. CAG repeat can not be an independent factor to predict age of onset, because only explaining about 36% variance on age at onset.(3) Clinical manifestations including motor, cognitive and psychiatrical symptoms strongly influence on the functional capacity.(4) A2642 genotype A/B advances age of onset in HD patients.(5) ApoE e 3/4 patients have a earlier onset compared with those ApoE ￡ 3/3.Objectives: The neuropathology is characterized by a wave of degeneration in the striatum. Several endogenous neuroprotective response are activated against harmful stimuli? The regulation of the trophic activity is an important mechanism that it is triggered after excitotoxic insults. A transneuronal regulation of BDNF expression has been observed in the substantia nigra and cortex after thr striatal exitotoxic lesion. 3-nitropropionic acid (3-NP) is a selective inhibitor of succinate dehydrogenase. It is harmful to neurons with high doses or repeated low doses injection of 3-NP. Several studies have shown that a low dose of 3-NP can prompt the ischemic tolerance of the neurons and protect dopamine neurons. The purpose of our study is to investigate the machinism of protective effect of 3-NP preconditioning (PC) on HD.Mathods: The rat HD models were established after intrastriatal quinilinic acid (QA) injection. The rats in the PC group received 3-NP (20mg/kg, ip) 24h before QA-lesioned, those in the 3-NP group were only administered 3-NP. The HD model was assessed 14d after intrastriatal injection by apomorphine, climbing-net test and Morris water maze. Expression of BDNF mRNA and protein, calbidin immunoactive neurons were detected using RT-PCR, Western Blotting and immunohistochemistary. Results: (1) In the HD group, the escape letancy and distant in thewater maze were prolonged, the memory frequency of platform quadrant and the time of climbing shortened. Expressions of calbidin neurons in the striata were increased.(2) Expression of BDNF mRNA and protein in the cortex ipsilateral to the injection were upregulated, reaching the highest level at 6h, returned to the basal level at 24h, and lowered at 14d. No significant increase of BDNF Expression was detected in the striata within 24h, the level was decreased at 14d.(3) The scales of the behavioural tests were improved after 3-NP preconditioning. Exprossion of calbidin neurons were also increased. There was no significant change of BDNF Exprossion after 3~NP preconditioning.Conclusions: (1) The HD model by intrastriatal QA injection is a good sample, reproducing the similar behavioural and histopathological characteristics of HD.(2) The transneuronal BDNF expression in the cortex is stimulated by the lack of the target area.Cortical BDNF upregulation could also constitute part of a trophic effect to the cortical neurons from the loss of its taroet, and retrogradely transport to the target.(3) 3-NP preconditioning can provide neuroprotective effect on HD, the machinism is not achieved by expression of BDNF.