Escitalopram Alleviates Alzheimer's Disease-Type Tau Pathologies in the Aged P301L Tau Transgenic Mice.

BACKGROUND: The inhibition of tau hyperphosphorylation is one of the most promising therapeutic targets for the development of Alzheimer's disease (AD) modifying drugs. Escitalopram, a kind of selective serotonin reuptake inhibitor antidepressant, has been previously reported to ameliorate tau hyperphosphorylation in vitro. OBJECTIVE: In this study, we determined whether escitalopram alleviates tau pathologies in the aged P301L mouse. METHODS: Mice were intraperitoneal injected with either escitalopram or saline for 4 weeks, and a battery of behavioral tests were conducted before tissue collection and biochemical analyses of brain tissue with western blot and immunohistochemistry. RESULTS: Wild-type (Wt) mice statistically outperformed the aged pR5 mice in the Morris water maze, while escitalopram treatment did not significantly rescue learning and memory deficits of aged pR5 mice. Tau phosphorylation at different phosphorylation sites were enhanced in the hippocampus of aged pR5 mice, while escitalopram treatment significantly decreased tau phosphorylation. The levels of phosphorylated GSK-3ß and phosphorylated Akt were significantly decreased in the hippocampus of aged pR5 mice, while escitalopram administration markedly increased the expression level. The aged pR5 mice showed significant decreases in PSD95 and PSD93, while the administration of escitalopram significantly increased PSD95 and PSD93 to levels comparable with the Wt mice. CONCLUSION: The protective effects of escitalopram exposure during advanced AD are mainly associated with significant decrease in tau hyperphosphorylation, increased numbers of neurons, and increased synaptic protein levels, which may via activation of the Akt/GSK-3ß signaling pathway.

Spatial Training Ameliorates Long-Term Alzheimer's Disease-Like Pathological Deficits by Reducing NLRP3 Inflammasomes in PR5 Mice.

Recent studies have suggested that cognitive training could delay memory loss in Alzheimer's disease (AD). However, whether and how cognitive training produces long-term benefits remains unclear. Here, 10-month-old PR5 mice were spatially trained in a water maze for 4 consecutive weeks. The novel object recognition test (NORT), Western blots, Golgi staining, and ELISA were used to examine behavioral, biochemical, and pathological measures immediately after training and 3 months later. Immediately after training, we found that spatial training significantly improved cognitive performance; reduced tau neuropathology; increased the expression level of synaptophysin, PSD93, and PSD95 in the hippocampus; and increased the number of dendritic spines in PR5 mice. The expression levels of NLRP3, caspase-1, and interleukin (IL)-1ß, which were significantly elevated in PR5 mice, were reversed by spatial training. Interestingly, these effects persisted 3 months later. To further detect the role of NLRP3 in spatial training, PR5/NLRP3-/- mice and PR5/NLRP3+/- mice were also used in our study. PR5/NLRP3-/- mice showed better cognitive performance than PR5 mice. After 1 week of spatial training, these changes (including those in expression levels of synaptophysin, PSD93, and PSD95; the number of dendritic spines; and caspase-1 and IL-1ß content in PR5 mice) could be totally reversed in PR5/NLRP3-/- and PR5/NLRP3+/- mice. In addition, there was a positive correlation between NLRP3 content and the expression levels of caspase-1 and IL-1ß. These results show an important role for the NLRP3/caspase-1/IL-1ß axis in ameliorating the effect of spatial training on cognitive impairment in PR5 mice.

Escitalopram alleviates stress-induced Alzheimer's disease-like tau pathologies and cognitive deficits by reducing hypothalamic-pituitary-adrenal axis reactivity and insulin/GSK-3ß signal pathway activity.

Chronic stress, a causal factor for depression, can also cause cognitive impairments and tau pathology. However, whether and how the selective serotonin reuptake inhibitor antidepressant escitalopram ameliorates these effects are still unclear. In the present study, rats were subjected to chronic mild unpredictable stress for 8 weeks. Following the initial 4 weeks, the stressed animals were separated into susceptible (depressive) and unsusceptible (resistant) groups based on behavioral tests. Then, escitalopram (10 mg/kg i.p.) was administered for 28 days. Pathophysiological changes were assessed by performing behavioral and biochemical analyses. The results showed that both depressive and resistant rats displayed spatial memory deficits and an accumulation of tau in the hippocampus. Increased levels of corticosterone and insulin and a decreased level of glucocorticoid receptor were found in both depressive and resistant rats. We also found that activity-dependent phosphorylated insulin receptor substrate and glycogen synthase kinase-3ß (Ser9 site) were significantly decreased in both depressive and resistant rats. However, other important kinases, such as cyclin-dependent kinase 5 and mitogen-activated protein kinase kinase-1/2, did not change in our study. Furthermore, we found that the mRNA expression of tau was increased in depressive and resistant rats. No significant change in LC3B expression was found. Interestingly, almost all the pathological changes in depressive and resistant rats previously mentioned could be reversed by escitalopram. Our results suggested that escitalopram ameliorates cognitive impairments and selectively attenuates phosphorylated tau accumulation in stressed rats through the regulation of hypothalamic-pituitary-adrenal axis activity and the insulin receptor substrate/glycogen synthase kinase-3ß signaling pathway.

Low plasma BDNF is not a biomarker for cognitive dysfunction in elderly T2DM patients.

Type 2 diabetes mellitus (T2DM) is a known cause of cognitive dysfunction, and brain-derived neurotrophic factor (BDNF) is a key protein in promoting memory growth and survival of neurons. However, the relationship between plasma BDNF and diabetic cognitive dysfunction is still elusive. A total of 89 patients over 60 years with T2DM and 40 well-matched health controls were enrolled. All participants received a set of multi-dimensional neuropsychological tests for the cognitive assessment. The subjects were divided into amnesic mild cognitive impairment (aMCI) and non-aMCI groups. An enzyme-linked immunosorbent assay (ELISA) was used to measure plasma BDNF concentrations for all subjects. No significant difference was found between T2DM patients and healthy control in MMSE scores. The T2DM patients performed significantly worse in four cognitive domains (including episodic memory, executive function, visuospatial function, and information processing speed) compared with the controls (all p < 0.05). The prevalence of aMCI in T2DM population was higher [OR = 4.032 (1.536~10.582), 37/89-6/40]. Additionally, the plasma concentration of BDNF in T2DM patients was significantly lower than that in controls (p < 0.01). However, no significant correlation was found between plasma BDNF and cognitive function in T2DM. Our results suggested that T2DM have a higher prevalence of cognitive impairment. The plasma BDNF concentration in T2DM patients was significantly lower than that in controls, but low BDNF was not a biomarker for cognitive dysfunction in T2DM patients.

Citalopram Ameliorates Synaptic Plasticity Deficits in Different Cognition-Associated Brain Regions Induced by Social Isolation in Middle-Aged Rats.

Our previous experiments demonstrated that social isolation (SI) caused AD-like tau hyperphosphorylation and spatial memory deficits in middle-aged rats. However, the underlying mechanisms of SI-induced spatial memory deficits remain elusive. Middle-aged rats (10 months) were group or isolation reared for 8 weeks. Following the initial 4-week period of rearing, citalopram (10 mg/kg i.p.) was administered for 28 days. Then, pathophysiological changes were assessed by performing behavioral, biochemical, and pathological analyses. We found that SI could cause cognitive dysfunction and decrease synaptic protein (synaptophysin or PSD93) expression in different brain regions associated with cognition, such as the prefrontal cortex, dorsal hippocampus, ventral hippocampus, amygdala, and caudal putamen, but not in the entorhinal cortex or posterior cingulate. Citalopram could significantly improve learning and memory and partially restore synaptophysin or PSD93 expression in the prefrontal cortex, hippocampus, and amygdala in SI rats. Moreover, SI decreased the number of dendritic spines in the prefrontal cortex, dorsal hippocampus, and ventral hippocampus, which could be reversed by citalopram. Furthermore, SI reduced the levels of BDNF, serine-473-phosphorylated Akt (active form), and serine-9-phosphorylated GSK-3ß (inactive form) with no significant changes in the levels of total GSK-3ß and Akt in the dorsal hippocampus, but not in the posterior cingulate. Our results suggest that decreased synaptic plasticity in cognition-associated regions might contribute to SI-induced cognitive deficits, and citalopram could ameliorate these deficits by promoting synaptic plasticity mainly in the prefrontal cortex, dorsal hippocampus, and ventral hippocampus. The BDNF/Akt/GSK-3ß pathway plays an important role in regulating synaptic plasticity in SI rats.

Escitalopram attenuates ß-amyloid-induced tau hyperphosphorylation in primary hippocampal neurons through the 5-HT1A receptor mediated Akt/GSK-3ß pathway.

Tau hyperphosphorylation is an important pathological feature of Alzheimer's disease (AD). To investigate whether escitalopram could inhibit amyloid-ß (Aß)-induced tau hyperphosphorylation and the underlying mechanisms, we treated the rat primary hippocampal neurons with Aß1-42 and examined the effect of escitalopram on tau hyperphosphorylation. Results showed that escitalopram decreased Aß1-42-induced tau hyperphosphorylation. In addition, escitalopram activated the Akt/GSK-3ß pathway, and the PI3K inhibitor LY294002 blocked the attenuation of tau hyperphosphorylation induced by escitalopram. Moreover, the 5-HT1A receptor agonist 8-OH-DPAT also activated the Akt/GSK-3ß pathway and decreased Aß1-42-induced tau hyperphosphorylation. Furthermore, the 5-HT1A receptor antagonist WAY-100635 blocked the activation of Akt/GSK-3ß pathway and the attenuation of tau hyperphosphorylation induced by escitalopram. Finally, escitalopram improved Aß1-42 induced impairment of neurite outgrowth and spine density, and reversed Aß1-42 induced reduction of synaptic proteins. Our results demonstrated that escitalopram attenuated Aß1-42-induced tau hyperphosphorylation in primary hippocampal neurons through the 5-HT1A receptor mediated Akt/GSK-3ß pathway.

Escitalopram Ameliorates Tau Hyperphosphorylation and Spatial Memory Deficits Induced by Protein Kinase A Activation in Sprague Dawley Rats.

Here, we investigated the effect of escitalopram pretreatment on protein kinase A (PKA)-induced tau hyperphosphorylation and spatial memory deficits in rats using western blot and behavioral tests, respectively. We demonstrated that escitalopram effectively ameliorated tau hyperphosphorylation and the spatial memory deficits induced by PKA activation. We measured the total and activity-dependent Ser9-phosphorylated levels of glycogen synthase kinase (GSK)-3ß in hippocampal extracts. No significant change in the total level of GSK-3ß was observed between the different groups. However, compared with forskolin injection alone, pretreatment with escitalopram increased the level of Ser9-phosphorylated GSK-3ß. We also demonstrated that escitalopram increased Akt phosphorylation at Ser473 (the active form of Akt). Furthermore, we identified other important kinases and phosphatases, such as protein phosphatase 2A, extracellular signal-regulated kinases 1 and 2, and MAP kinase kinase-1/2, that have previously been reported to play a crucial role in tau phosphorylation; however, we did not detect any significant change in the activation of these kinases or phosphatases in our study. We unexpectedly demonstrated that forskolin caused anxiety-like behavior in rats, and pretreatment with escitalopram did not significantly ameliorate the anxiety-like behavior induced by forskolin. These data provide the first evidence that escitalopram ameliorates forskolin-induced tau hyperphosphorylation and spatial memory impairment in rats; these effects do not occur via the anti-anxiety activity of escitalopram but may involve the Akt/GSK-3ß signaling pathway.

Changed Synaptic Plasticity in Neural Circuits of Depressive-Like and Escitalopram-Treated Rats.

BACKGROUND: Although progress has been made in the detection and characterization of neural plasticity in depression, it has not been fully understood in individual synaptic changes in the neural circuits under chronic stress and antidepressant treatment. METHODS: Using electron microscopy and Western-blot analyses, the present study quantitatively examined the changes in the Gray's Type I synaptic ultrastructures and the expression of synapse-associated proteins in the key brain regions of rats' depressive-related neural circuit after chronic unpredicted mild stress and/or escitalopram administration. Meanwhile, their depressive behaviors were also determined by several tests. RESULTS: The Type I synapses underwent considerable remodeling after chronic unpredicted mild stress, which resulted in the changed width of the synaptic cleft, length of the active zone, postsynaptic density thickness, and/or synaptic curvature in the subregions of medial prefrontal cortex and hippocampus, as well as the basolateral amygdaloid nucleus of the amygdala, accompanied by changed expression of several synapse-associated proteins. Chronic escitalopram administration significantly changed the above alternations in the chronic unpredicted mild stress rats but had little effect on normal controls. Also, there was a positive correlation between the locomotor activity and the maximal synaptic postsynaptic density thickness in the stratum radiatum of the Cornu Ammonis 1 region and a negative correlation between the sucrose preference and the length of the active zone in the basolateral amygdaloid nucleus region in chronic unpredicted mild stress rats. CONCLUSION: These findings strongly indicate that chronic stress and escitalopram can alter synaptic plasticity in the neural circuits, and the remodeled synaptic ultrastructure was correlated with the rats' depressive behaviors, suggesting a therapeutic target for further exploration.

Escitalopram Ameliorates Forskolin-Induced Tau Hyperphosphorylation in HEK239/tau441 Cells.

To investigate the effect of escitalopram (a widely used and highly efficacious antidepressant from the SSRI class) on tau hyperphosphorylation, HEK293/tau441 cells were pretreated with 4 µM of forskolin for 2 h. Then we treated the cells with different doses of escitalopram (0, 5, 10, 20, 40, 80 µM) for 22 h. We measured the phosphorylation level of tau by Western blotting. It was shown that escitalopram could protect tau from hyperphosphorylation induced by pharmacological activation of protein kinase A (PKA) at a dose of 20, 40, and 80 µM in vitro. Interestingly, the same dose of escitalopram could also increase the level of serine-9-phosphorylated GSK-3ß (inactive form) and the phosphorylation level of Akt at Ser473 (active form) with no significant change in the level of total GSK-3ß and Akt. Unexpectedly, 5-hydroxytryptamine 1A receptor (5-HT1A) agonist 8-OH-DPAT did not decrease forskolin-induced tau hyperphosphorylation. Our results suggest that escitalopram can ameliorate forskolin-induced tau hyperphosphorylation, which is not through the typical 5-HT1A pathway, and Akt/GSK-3ß signaling pathway is involved. These findings may support an effective role of antidepressants in the prevention of dementia associated with depression in patients.

Citalopram attenuates tau hyperphosphorylation and spatial memory deficit induced by social isolation rearing in middle-aged rats.

Social isolation (SI) is considered as a chronic stress. Here, middle-aged rats (8 months) were group or isolation reared for 6 weeks. Following the initial two-week period of rearing, citalopram (10 mg/kg i.p.) was administered for 28 days. Changes in recognition memory, depression and anxiety-like behavior, and phosphorylated tau were investigated. We found that SI did not lead to obvious depression/anxiety-like behavior in middle-aged rats. Memory deficits and increased tau hyperphosphorylation at Tau-1, Ser396 episodes could be almost reversed by citalopram. The level of Ser9-phosphorylated GSK-3ß (inactive form) was significantly decreased in the SI group which also could be almost reversed by citalopram, suggesting that the citalopram could prevent GSK-3ß from SI-induced overactivation. The melatonin level was decreased in SI group compared with group housed (GH) group, and citalopram could partly restore the level of melatonin. We also found that citalopram could increase MT1 and MT2 in mRNA level. Our results demonstrate that citalopram increases the level of melatonin which negatively regulates GSK-3ß and attenuates tau hyperphosphorylation and spatial memory deficit induced by SI in middle-aged rats. Suggesting that SI might constitute a risk factor for Alzheimer's disease (AD), and citalopram may represent a therapeutic strategy for the treatment of AD.