Inflammation induced by infection potentiates tau pathological features in transgenic mice

Comorbidities that promote the progression of Alzheimer's disease (AD) remain to be uncovered and evaluated in animal models. Because elderly individuals are vulnerable to viral and bacterial infections, these microbial agents may be considered important comorbidities that could potentiate an already existing and tenuous inflammatory condition in the brain, accelerating cognitive decline, particularly if the cellular and molecular mechanisms can be defined. Researchers have recently demonstrated that triggering inflammation in the brain exacerbates tau pathological characteristics in animal models. Herein, we explore whether inflammation induced via viral infection, compared with inflammation induced via bacterial lipopolysaccharide, modulates AD-like pathological features in the 3xTg-AD mouse model and provide evidence to support the hypothesis that infectious agents may act as a comorbidity for AD. Our study shows that infection-induced acute or chronic inflammation significantly exacerbates tau pathological characteristics, with chronic inflammation leading to impairments in spatial memory. Tau phosphorylation was increased via a glycogen synthase kinase-3β-dependent mechanism, and there was a prominent shift of tau from the detergent-soluble to the detergent-insoluble fraction. During chronic inflammation, we found that inhibiting glycogen synthase kinase-3β activity with lithium reduced tau phosphorylation and the accumulation of insoluble tau and reversed memory impairments. Taken together, infectious agents that trigger central nervous system inflammation may serve as a comorbidity for AD, leading to cognitive impairments by a mechanism that involves exacerbation of tau pathological characteristics.

Glucose-dependent insulinotropic peptide receptor expression in the hippocampus and neocortex of mesial temporal lobe epilepsy patients and rats undergoing pilocarpine induced status epilepticus

The glucose-dependent insulinotropic peptide receptor (GIPR) has been implicated with neuroplasticity and may be related to epilepsy. GIPR expression was analyzed by immunohistochemistry in the hippocampus (HIP) and neocortex (Cx) of rats undergoing pilocarpine induced status epilepticus (Pilo-SE), and in three young male patients with left mesial temporal lobe epilepsy related to hippocampal sclerosis (MTLE-HS) treated surgically. A combined GIPR immunohistochemistry and Fluoro-Jade staining was carried out to investigate the association between the GIPR expression and neuronal degeneration induced by Pilo-SE. GIPR was expressed in the cytoplasm of neurons from the HIP CA subfields, dentate gyrus (DG) and Cx of animals and human samples. The GIPR expression after the Pilo-SE induction increases significantly in the HIP after 1h and 5 days, but not after 12h or 50 days. In the Cx, the GIPR expression increases after 1h, 12h and 5 days, but not 50 days after the Pilo-SE. The expression of GIPR 12h after Pilo-SE was inversely proportional to the Fluoro-Jade staining intensity. In the human tissue, GIPR expression patterns were similar to those observed in chronic Pilo-SE animals. No Fluoro-Jade stained cells were observed in the human sample. GIPR is expressed in human HIP and Cx. There was a time and region dependent increase of GIPR expression in the HIP and Cx after Pilo-SE that was inversely associated to neuronal degeneration.

Folic acid plus α-tocopherol mitigates amyloid-β-induced neurotoxicity through modulation of mitochondrial complexes activity

Early symptoms of Alzheimer's disease (AD) have been attributed to amyloid-β (Aβ) toxicity. The pathophysiology of AD is complex and involves several different biochemical pathways, including defective Aβ protein metabolism, neuroinflammation, oxidative processes, and mitochondrial dysfunction. In the current study, we assessed the molecular mechanisms, mainly the modifications in the activity of mitochondrial complexes, whereby the association of folic acid and α-tocopherol protects mice against the Aβ-induced neurotoxicity. Oral treatment with folic acid (50 mg/kg) plus α-tocopherol (500 mg/kg), once a day during 14 consecutive days, protected mice against the Aβ₁₋₄₀-induced cognitive decline, synaptic loss, and neuronal death. However, chronic treatment comprising folic acid plus α-tocopherol was ineffective on Aβ-induced glial cell activation, suggesting that the effect of this treatment is independent of anti-inflammatory features. Interestingly, the results obtained in our study suggest that mitochondrial energy metabolism is impaired by the Aβ peptide, and upregulation of mitochondrial genes may be a compensatory response, as demonstrated by the increase in mitochondrial complexes I, II, and IV activity, in the hippocampus of mice, after Aβ₁₋₄₀ injection. Of note, the chronic treatment comprising folic acid plus α-tocopherol prevented the increase in the activity of mitochondrial complexes I and IV induced by Aβ₁₋₄₀. Together, these results show the antioxidant effect of the combination of folic acid and α-tocopherol, as observed by the decrease in NO generation from iNOS and nNOS, preventing an increase in the activity of mitochondrial complexes, mainly I and IV, and the neuronal death induced by the Aβ₁₋₄₀ peptide.

The role of tau in Alzheimer's disease and related disorders

Tau, the microtubule-associated protein, forms insoluble filaments that accumulate as neurofibrillary tangles in Alzheimer's disease (AD) and related tauopathies. Under physiological conditions, tau regulates the assembly and maintenance of the structural stability of microtubules. In the diseased brain, however, tau becomes abnormally hyperphosphorylated, which ultimately causes the microtubules to disassemble, and the free tau molecules aggregate into paired helical filaments. A large body of evidence suggests that tau hyperphosphorylation results from perturbation of cellular signaling, mainly through imbalance in the activities of different protein kinases and phosphatases. In AD, it appears that ß-amyloid peptide (Aß) plays a pivotal role in triggering this imbalance. In this review, we summarize our current understanding of the role of tau in AD and other tauopathies, and highlight key issues that need to be addressed to improve the success of developing novel therapies.

Involvement of phosphoinositide 3-kinase gamma in the neuro-inflammatory response and cognitive impairments induced by beta-amyloid 1-40 peptide in mice

Alzheimer disease (AD) is the most common form of dementia in the elderly, and the neuro-pathological hallmarks of AD include neurofibrillary tangles (NFT), and deposition of beta-amyloid (Abeta) in extracellular plaques. In addition, chronic inflammation due to recruitment of activated glial cells to amyloid plaques are an invariant component in AD, and several studies have reported that the use of non-steroidal anti-inflammatory drugs (NSAIDs) may provide a measure of protection against AD. In this report we have investigated whether phosphoinositide 3-kinase gamma (PI3Kgamma), which is important in inflammatory cell migration, plays a critical role in the neuro-inflammation, synaptic dysfunction, and cognitive deficits induced by intracerebroventricular injection of Abeta(1-40) in mice. We found that the selective inhibitor of PI3Kgamma, AS605240, was able to attenuate the Abeta(1-40)-induced accumulation of activated astrocytes and microglia in the hippocampus, and decrease immuno-staining for p-Akt and cyclooxygenase-2 (COX-2). Interestingly, Abeta(1-40) activated macrophages treated with AS605240 or another PI3Kgamma inhibitor, AS252424, displayed impaired chemotaxis in vitro, but their expression of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) was unaffected. Finally, AS605240 prevented Abeta(1-40)-induced cognitive deficits and synaptic dysfunction, but failed to modify scopolamine-induced amnesia. Our data suggests that inhibition of PI3Kgamma may represent a novel therapeutic target for treating AD patients.

The role of TNF-alpha signaling pathway on COX-2 upregulation and cognitive decline induced by beta-amyloid peptide

Alzheimer's disease (AD), a chronic degenerative and inflammatory brain disorder characterized by neuronal dysfunction and loss, is linked to accumulation of beta-amyloid (Abeta) peptide. Tumor necrosis factor-alpha (TNF-alpha) and cyclooxygenase-2 (COX-2) are proteins that have key roles in immune cell activation, inflammation and cognitive function in the brain. Here, we evaluated the link between TNF-alpha and COX-2 on the acute responses elicited by Abeta. Behavioral and molecular analyses were performed in mice after an intracerebroventricular (i.c.v.) injection of Abeta(1-40). Genetic and/or pharmacological approaches were used to inhibit TNF-alpha and COX-2. I.c.v. Abeta(1-40) injection in mice activates TNF-alpha signaling pathway resulting in COX-2 upregulation, synaptic loss and cognitive decline. Pharmacological studies revealed that COX-2 is involved in the cognitive impairment mediated by TNF-alpha. However, COX-2 inhibition failed in reducing the synaptophysin loss induced by Abeta(1-40). The COX-2 upregulation induced by Abeta(1-40) was attributed to activation of different protein kinases and transcriptional factors that are greatly regulated by TNF-alpha. Together, these results indicate that Abeta(1-40) induces the activation of several TNF-alpha-dependent intracellular signaling pathways that play a key role in the control of COX-2 upregulation and activation, synaptic loss and cognitive decline in mice. Therefore, selective TNF-alpha inhibitors may be potentially interesting tools for AD drug development.

Role of the macrophage inflammatory protein-1alpha/CC chemokine receptor 5 signaling pathway in the neuroinflammatory response and cognitive deficits induced by beta-amyloid peptide

The hallmarks of Alzheimer's disease include the deposition of beta-amyloid (Abeta), neuroinflammation, and cognitive deficits. The accumulation of activated glial cells in cognitive-related areas is critical for these alterations, although little is known about the mechanisms driving this event. Herein we used macrophage inflammatory protein-1alpha (MIP-1alpha(-/-))- or CC-chemokine receptor 5 (CCR5(-/-))-deficient mice to address the role played by chemokines in molecular and behavioral alterations induced by Abeta(1-40). Abeta(1-40) induced a time-dependent increase of MIP-1alpha mRNA followed by accumulation of activated glial cells in the hippocampus of wild-type mice. MIP-1alpha(-/-) and CCR5(-/-) mice displayed reduced astrocytosis and microgliosis in the hippocampus after Abeta(1-40) administration that was associated with decreased expression of cyclooxygenase-2 and inducible nitric oxide synthase, as well as reduced activation of nuclear factor-kappaB, activator protein-1 and cyclic AMP response element-binding protein. Furthermore, MIP-1alpha(-/-) and CCR5(-/-) macrophages showed impaired chemotaxis in vitro, although cytokine production in response to Abeta(1-40) was unaffected. Notably, the cognitive deficits and synaptic dysfunction induced by Abeta(1-40) were also attenuated in MIP-1alpha(-/-) and CCR5(-/-) mice. Collectively, these results indicate that the MIP-1alpha/CCR5 signaling pathway is critical for the accumulation of activated glial cells in the hippocampus and, therefore, for the inflammation and cognitive failure induced by Abeta(1-40). Our data suggest MIP-1alpha and CCR5 as potential therapeutic targets for Alzheimer's disease treatment.