Context: Elevated ␤-secretase (␤-site amyloid precursor protein-cleaving enzyme 1 [BACE1]) activity has been found in the brains of patients with sporadic Alzheimer disease (AD) compared with controls. Now we are particularly interested in whether BACE1 can be identified in the cerebrospinal fluid (CSF) of patients with mild cognitive impairment (MCI), a population at high risk for AD. The possible presence of BACE1 in the CSF of patients with AD and MCI has so far gone unreported.Objective: To examine whether BACE1 can be identified in the CSF of patients with MCI.Design: We evaluated CSF BACE1 levels using 2 sandwich enzyme-linked immunosorbent assays, BACE1 enzymatic activities by means of synthetic fluorescence substrate, and total amyloid-␤ peptide levels using a sandwich enzyme-linked immunosorbent assay.Setting: Two independent research centers.Participants: Eighty patients with sporadic AD, 59 patients with MCI, and 69 controls.Main Outcome Measures: BACE1 levels and enzymatic activities and amyloid-␤ peptide levels. Conclusion: Significant elevation of BACE1 levels and activity in CSF is an indicator of MCI, which could be an early stage of AD. Psychiatry. 2007;64:718-726 A LZHEIMER DISEASE (AD) IS characterized by the progressive formation of insoluble amyloid plaques and vascular deposits consisting of the 4-kDa amyloid-␤ peptide (A␤) in the brain. Arch Gen1 ␤-Secretase (␤-site amyloid precursor protein-cleaving en-2 is one of the 2 key enzymes in amyloid precursor protein (APP) processing. Amyloid-␤ peptide results from cleavage of APP initially by BACE1 to produce a C99 fragment and release soluble APP␤; C99 is then further cleaved by ␥-secretase, leading to A␤. Increased BACE1 activity and elevated levels of insoluble A␤ have been shown in the brains of patients with sporadic AD. 3,4 Because cerebrospinal fluid (CSF) is in direct contact with the extracellular space of the central nervous system, biochemical changes in the brain could potentially be reflected in CSF. The CSF-based detection of BACE1 levels and activity might be valuable in aiding the early diagnosis of AD, especially in patients with mild cognitive impairment (MCI), who show a higher risk of AD.5 Several recent studies [6][7][8] showed that BACE1 activity can be detected in the CSF. However, whether changes could occur in BACE1 activity or protein levels in the CSF of patients with AD or MCI remains unknown.In the present study, we quantitatively analyzed the enzymatic activities and protein levels of BACE1 and total A␤ levels in CSF samples from 208 individuals. We aim to determine whether BACE1 levels and activity can be detected in CSF, whether they are altered in AD compared with healthy aging, and whether levels of BACE1 protein and activity may be useful to discriminate patients with AD or MCI from healthy individuals.

As brain testosterone plays both androgenic and estrogenic actions due to its conversion into estrogen via aromatase naturally, it is unclear that the age-related reduction of testosterone increased risk of Alzheimer’s disease (AD) in men is mediated through androgen alone or both androgen and estrogen mechanisms. Our previous studies using a gene-based approach in mouse model to block the conversion of testosterone into estrogen (aromatase gene knock-out, ArKO), found a depletion of estrogen and increase in testosterone endogenously in males. Here, we use crossing the ArKO mice with APP23 transgenic mice, a mouse model of AD, to produce APP23/Ar+/− mice to study the estrogen-independent effect of testosterone on AD. We found a significant reduction in brain plaque formation, improved cognitive function and increase NEP activity in male APP23/Ar+/− mice compared with age-matched male APP23 controls. In addition, we found, for the first time, a reduction of β-secretase (BACE1) enzyme activity, mRNA level and protein expression in the male APP23/Ar+/− mice, suggesting that endogenous testosterone, independent from estrogen, may protect against AD in males via two major mechanisms, downregulation of BACE1 activities at transcriptional level to reduce β amyloid production and upregulation of NEP activities to enhance bate amyloid degradation.

Estrogen therapy used in combination with selective serotonin reuptake inhibitor (SSRI) treatment improves SSRI efficacy for the treatment of mood disorders. Desensitization of serotonin 1A (5-HT1A) receptors, which takes one to two weeks to develop in animals, is necessary for SSRI therapeutic efficacy. Estradiol modifies 5-HT1A receptor signaling and induces a partial desensitization in the paraventricular nucleus (PVN) of the rat within two days, but the mechanisms underlying this effect are currently unknown. The purpose of this study was to identify the estrogen receptor necessary for estradiol-induced 5-HT1A receptor desensitization. We previously showed that estrogen receptor β is not necessary for 5-HT1A receptor desensitization and that selective activation of estrogen receptor GPR30 mimics the effects of estradiol in rat PVN. Here, we used a recombinant adenovirus containing GPR30 siRNAs to decrease GPR30 expression in the PVN. Reduction of GPR30 prevented estradiol-induced desensitization of 5-HT1A receptor as measured by hormonal responses to the selective 5-HT1A receptor agonist, (+)8-OH-DPAT. To determine the possible mechanisms underlying these effects, we investigated protein and mRNA levels of 5-HT1A receptor signaling components including 5-HT1A receptor, Gαz, and RGSz1. We found that two days of estradiol increased protein and mRNA expression of RGSz1, and decreased 5-HT1A receptor protein but increased 5-HT1A mRNA; GPR30 knockdown prevented the estradiol-induced changes in 5-HT1A receptor protein in the PVN. Taken together, these data demonstrate that GPR30 is necessary for estradiol-induced changes in the 5-HT1A receptor signaling pathway and desensitization of 5-HT1A receptor signaling.

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A major problem with current anti-depressant therapy is that it takes on average 6–7 weeks for remission. Since desensitization of serotonin (5-HT)1A receptor signaling contributes to the anti-depressive response, acceleration of the desensitization may reduce this delay in response to antidepressants. The purpose of the present study was to test the hypothesis that estradiol accelerates fluoxetine-induced desensitization of 5-HT1A receptor signaling in the paraventricular nucleus of the hypothalamus (PVN) of rats, via alterations in components of the 5-HT1A receptor signaling pathway. Ovariectomized rats were injected with estradiol and/or fluoxetine, then adrenocorticotropic hormone (ACTH) and oxytocin responses to a 5-HT1A receptor agonist (+)8-hydroxy-2-dipropylaminotetralin (8-OH-DPAT) were examined to assess the function of 5-HT1A receptors in the PVN. Treatment with estradiol for either 2 or 7 days or fluoxetine for 2 days produced at most a partial desensitization of 5-HT1A receptor signaling, whereas 7 days of fluoxetine produced full desensitization. Combined treatment with estradiol and fluoxetine for 2 days produced nearly a full desensitization, demonstrating an accelerated response compared to either treatment alone. With two days of combined treatments, estradiol prevented the fluoxetine-induced increase in 5-HT1A receptor protein, which could contribute to the more rapid to the desensitization. Furthermore, EB treatment for 2 days decreased the abundance of the 35 kD Gαz protein which could contribute to the desensitization response. We found two isoforms of Gαz proteins with molecular mass of 35 and 33 kD, which differentially distributed in the detergent resistant microdomain (DRM) and in Triton X-100 soluble membrane region, respectively. The 35 kD Gαz proteins in the DRM can be sumoylated by SUMO1. Stimulation of 5-HT1A receptors with 8-OH-DPAT increases the sumoylation of Gαz proteins and reduces the 33 kD Gαz proteins, suggesting that these responses may be related to the desensitization of 5-HT1A receptors. Treatment with estradiol for 2 days also reduced the levels of the G-protein coupled estrogen receptor GPR30, possibly limiting to the ability of estradiol to produce only a partial desensitization response. These data provide evidence that estradiol may be effective as a short-term adjuvant to SSRIs to accelerate the onset of therapeutic effects.