HDAC6 Pathogenesis Of Disease Transgenic Model Mice In APPswe / PS1ΔE9 Alzheimer's

Background Alzheimer’s disease (AD), as the most common form of dementia among older individuals, is clinically characterized by progressive loss of cognitive function. Despite much progress, the pathogenesis of AD remains to be elucidated. Histone deacetylase6(HDAC6) was reported to increase in hippocampus and cortex in both patients and animal models of AD. However, whether HDAC6overexpression is an underlying cause of AD or a condition resulting from AD is controversial.Methods The regional distribution of HDAC6in the adult C57BL/6J mouse brain was analyzed by immunochemical staining. Double immunofluorescent staining was used to detect the co-location of HDAC6with markers of multiple brain cell types. The temporal expression patterns and expression changes of HDAC6and acetylation of a-tubulin (ace-a-tubulin) in the brain of wild type (WT) and APPswe/PS1ΔAE9(PAP) mice were analyzed by immunohistochemistry and western blotting.Next, we detected the effects of Hdac6knockout on the cognitive deficits of PAP mice. The genotype of mice was detected by PCR. The expression of HDAC6and ace-a-tubulin were analyzed by immunohistochemistry and western blotting. The locomotor activity was examined by open field test and cognitive abilities were detected using novel object recognition test and Morris water maze. Senile plaques were observed by Thioflavin-S staining. The levels of Aβ40/42were quantified by ELISA. The expression of hyperphosphorylated tau protein (P-tau) and P-GSK3β were examined by western blotting. The microtubule ultrastructures were observed by transmission electronic microscopy.Then we examined the effects of two selective HDAC6inhibitors-tubastatin A and ACY-1215on the cognition of PAP mice. PAP mice were randomly divided into model group, vehicle (DMSO/saline=1:10), SAHA (50mg/kg), tubastatin A (25mg/kg) and ACY-1215(25mg/kg) groups. The wild-type littermates were chosen as normal control group (WT). The mice (n=16/group, male/female=1:1) were treated for20consecutive days by daily intraperitoneal injection. After administration, a battery of behavioral tests including open field, novel object recognition and Morris water maze were performed. All animals were sacrificed and the brain weight and brain coefficient were tested. Amyloid depositions were quantified using immunohistochemistry and thioflavine-S staining. The soluble and insoluble Aβ40/42peptides were determined by ELISA. Western blotting and immunohistochemistry staining were used to detect levels of HDAC6and acetylated a-tubulin. The expression of proteins and intermediate products involved in processing of APP, autophagy-associated proteins, P-tau, P-GSK3(3, P-Akt and P-mTOR were detected by western blotting. The ultrastructures of brain tissues were observed by transmission electronic microscopy.Results Our data showed that HDAC6, primarily located in cytoplasm of various kinds of neurons, is ubiquitously expressed throughout the mouse brain. Interestingly, the highest HDAC6signals were observed in regions relevant to cognition, such as cortex, hippocampus and amygdala. The HDAC6expression level was significantly increased in the brain of PAP transgenic mice compared with WT mice. It was increased with age in both WTand PAP transgenic mice accompanied by the decrease of ace-a-tubulin.Hdac6knockout improved learning and memory abilities of PAP transgenic mice without obvious effect on the anxiety level of mice. Compared with PAP transgenic mice, the soluble Aβ42peptide of PAP×Hdac6KO mice was significantly decreased, though the deposition of senile plaques was not altered. The deletion of Hdac6in PAP mice down-regulated the hyperphosphorylation of tau protein and inhibited the activity of GSK3β In addition, ultrastructural analysis showed obviously microtubule morphological abnormality of PAP mice was rescued by loss of Hdac6.Both tubastatin A and ACY-1215alleviated the cognitive decline without obvious effect on the locomotor activity of PAP mice through inhibiting the activity of HDAC6rather than its expression level. They reduced soluble and insoluble Aβ levels and the deposition of plaques, and decreased the levels of BACE1, PS1, sAPPβ and β-CTF. They also upregulated the expression of autophagy-associated proteins and reduced the expression of P-tau, P-GSK3β and P-mTOR. Moreover, they decreased the accumulation of autophagy vesicles and rescued the damaged microtubule in PAP mice. In addition, there were no significant adverse effects of tubastatin A and ACY-1215on brain weight, brain coefficient, liver and kidney function of mice.Conclusion The normal expression of HDAC6may play an important role in the function of neurons in cognition-related regions. HDAC6overexpression is probably associated with AD etiopathogenesis and plays a potential detrimental role in AD. And HDAC6is likely to be a therapeutic target for AD. Our preclinical results offer prospective approaches for using tubastatin A/ACY-1215as potential therapeutic strategy for AD.