Alzheimer's disease (AD) is the leading cause of dementia in elderly people and is characterized by two major neuropathological hallmarks: amyloid β-protein (Aβ)-containing senile plaques and neurofibrillary tangles (NFTs) consisting of abnormal phosphorylated τ protein (p-τ). Besides these proteins, transactive response DNA-binding protein 43 (TDP-43) was also discovered to accumulate in the limbic regions of AD brains, by forming cytoplasmic inclusions [1, 2, 10]. Studies have shown that in AD, TDP-43 is associated with smaller hippocampal volumes and more severe cognitive impairment [7]. Accordingly, patients with abnormal TDP-43 immunoreactivity were shown to have a clinically more severe degree of dementia, compared to those without TDP-43 inclusions [6, 8]. Some studies have shown the co-localization of TDP-43 and p-τ pathology in the AD brain, as well as the presence of TDP-43 in NFTs [3, 12, 13]. Moreover, TDP-43 spreading pattern in the brain reminisces that of p-τ [5]. However, whether these two proteins interact and how they are associated during AD pathogenesis was not yet addressed.Here, we report the association and interaction of TDP-43 with p-τ in human symptomatic and nonsymptomatic AD cases using histochemical and biochemical approaches. We have analyzed 13 nondiseased controls and 10 pathologically-defined pre-clinical AD cases (p-preAD) with TDP-43 pathology, which exhibited AD-related neuropathological changes but lacked AD symptoms during their lifetime. We also included 25 symptomatic AD cases (sympAD) with TDP-43 pathology and used 9 FTLD-TDP cases as positive controls for TDP-43 pathology (Suppl. Tab. 1, online-resource).To investigate the co-occurrence of pTDP-43 and p-τ in the different morphological TDP-43 lesions, we first performed double-label immunofluorescence with anti-phosphorylated TDP-43 (pTDP-43) and anti-p-τ antibodies (Suppl. Tab. 2, online-resource). We observed that sympAD cases displayed dystrophic neurites positive for both proteins (Fig. 1a). As for neuronal cytoplasmic inclusions (NCIs), we observed some inclusions positive for pTDP-43, but negative for p-τ (Fig. 1a). Further, we observed neurofibrillary tangle-like structures positive for pTDP-43 and p-τ (Fig. 1a).We then quantified the severity of pTDP-43 lesions (DNs, NCIs or NFT-like material), as well as p-τ pathology (p-τ-positive NFTs) in our cohort. The severity of pTDP-43 pathology was significantly increased in sympAD and FTLD-TDP cases, when compared to non-AD cases (Fig. 1b, Suppl. Tab. 3, online-resource). Additionally, NFT severity was also significantly increased in sympAD cases compared to non-AD and FTLD-TDP cases (Fig. 1c). p-preAD cases showed a trend towards an increased severity compared to non-AD and FTLD-TDP cases (Suppl. Tab. 4, online-resource).To address whether neurons that present NFTs still contain physiological nuclear TDP-43, we performed co-staining with antibodies against non-phosphorylated N-(N-t, 1-50aa.) or C-terminal (C-t, 260-414aa.) epitopes of TDP-43 and p-τ (Suppl. Tab. 2, onli...

Alzheimer’s disease (AD) is a major and devastating neurodegenerative disease, and the amyloid-β (Aβ) hypothesis is still the central theory for AD pathogenesis. Meanwhile, another major mental illness, depression, is one of the risk factors for AD. From a high-throughput screening (HTS), amoxapine, a typical secondary amine tricyclic antidepressant (TCA), was identified to reduce Aβ production. A follow-up investigation on antidepressants showed that most of the TCAs harbour similar activity. Previous studies have indicated that TCAs improve cognitive function in AD mouse models as well as in preliminary clinical data; however, the underlying mechanism is controversial, and the effect on Aβ is elusive. Thus, we developed a secondary screening to determine the molecular target of amoxapine, and serotonin receptor 6 (HTR6) was identified. Knockdown of HTR6 reduced the amoxapine’s effect, while the HTR6 antagonist SB258585 mimicked the activity of amoxapine. Further mechanistic study showed that amoxapine and SB258585 reduced Aβ generation through multiple HTR6-mediated targets, including β-arrestin2 and CDK5. Taken together, our study suggests that amoxapine, though no longer a first-line drug for the treatment of depression, may be beneficial for AD and further structural modification of TCAs may lead to desirable therapeutic agents to treat both AD and depression.

γ-secretase mediates the intramembranous proteolysis of amyloid precursor protein (APP) and determines the generation of Aβ which is associated with Alzheimer’s disease (AD). Here we identified that an anti-Parkinson’s disease drug, Istradefylline, could enhance Aβ generation in various cell lines and primary neuronal cells of APP/PS1 mouse. Moreover, the increased generation of Aβ42 was detected in the cortex of APP/PS1 mouse after chronic treatment with Istradefylline. Istradefylline promoted the activity of γ-secretase which could lead to increased Aβ production. These effects of Istradefylline were reduced by the knockdown of A2AR but independent of A2AR-mediated G protein- or β-arrestin-dependent signal pathway. We further observed that A2AR colocalized with γ-secretase in endosomes and physically interacted with the catalytic subunit presenilin-1 (PS1). Interestingly, Istradefylline attenuated the interaction in time- and dosage-dependent manners. Moreover the knockdown of A2AR which in theory would release PS1 potentiated both Aβ generation and γ-secretase activity. Thus, our study implies that the association of A2AR could modulate γ-secretase activity. Istradefylline enhance Aβ generation and γ-secretase activity possibly via modulating the interaction between A2AR and γ-secretase, which may bring some undesired effects in the central nervous system (CNS).