CD14 receptor polymorphism and Alzheimer's disease risk

Association of CD14-260 (-159) C/T and Alzheimer's disease: systematic review and trial sequential analyses

Current studies have evaluated the association between CD14-260 (also known as -159) C/T polymorphism and Alzheimer's disease (AD) susceptibility. However, the association remains inconclusive. The aim of this study was to draw an accurate conclusion of the association. The literature search was conducted using PubMed, Embase, Chinese National Knowledge Infrastructure, China Biological Medicine Database, and Wanfang Databases for related articles. Four case-control studies with a total of 868 cases and 766 controls were eligible to be included in this meta-analysis. The association was evaluated by calculating the odds ratios (ORs) with the corresponding 95% confidence intervals (CIs). Overall, there was no significant association between CD14-260C/T polymorphism and AD risk in all genetic models (the allele model T vs. C: OR = 1.06, 95% CI 0.92-1.21, p = 0.44; the homozygous model TT vs. CC: OR = 1.09, 95% CI 0.83-1.44, p = 0.53; the heterozygote model CT vs. CC: OR = 0.95, 95% CI 0.75-1.22, p = 0.71; the dominant model TT + CT vs. CC: OR = 1.05, 95% CI 0.84-1.32, p = 0.66; the recessive model TT vs. CT + CC: OR = 1.14, 95% CI 0.92-1.43, p = 0.24). The sample size of 5064 was calculated by applying trial sequential analysis. Cumulative z curve does not cross trial sequential monitoring boundary. In conclusion, the present meta-analysis suggests that the CD14-260C/T polymorphism may not be associated with genetic susceptibility of AD, but the association remains indeterminate due to the insufficient evidence.

Interleukin-8 gene polymorphism -251T>A contributes to Alzheimer's disease susceptibility

BACKGROUND

Published association studies have investigated the correlation between interleukin-8 (IL-8) gene polymorphism -251T>A and susceptibility to Alzheimer's disease (AD); however, the results are conflicting. Thus, we conducted the meta-analysis to reassess the effect of IL-8 gene -251T>A variant on the risk of AD.

METHODS

Relevant studies regarding this association were electronically searched and identified from the PubMed, Embase, Cochrane Library, China National Knowledge Infrastructure, and the Chinese Biomedicine Database. The odds ratios (ORs) with the corresponding 95% confidence intervals (95% CIs) were pooled to calculate the strength of this association.

RESULTS

Nine studies with a total of 1406 cases and 2152 controls were included in the meta-analysis. Overall, a significant association of IL-8 gene -251T>A polymorphism with increased risk of AD was observed in several genetic models (allele, A vs T: OR=1.32, 95%CI=1.16-1.50; homozygous, AA vs TT: OR=1.70, 95%CI=1.21-2.21; heterozygous, TA vs TT: OR=1.37, 95%CI=1.12-1.69; recessive, AA vs TA+TT: OR=1.40, 95%CI=1.12-1.75). Similarly, such association was also revealed both in Asian and European populations in the subgroup analysis by ethnicity.

CONCLUSION

The current study suggested that IL-8 gene polymorphism -251T>A may contribute to the susceptibility to AD.

Expression of HLA-DR, CD80, and CD86 in Healthy Aging and Alzheimer's Disease

Although monocytes and macrophages could serve as new therapeutic targets for treatment of Alzheimer's disease (AD) and aging of the human innate immune system, its role in the pathogenesis of neurodegenerative disorders such as AD are only poorly understood. We have addressed this here by determining the number of CD14+ monocytes and the frequency of HLA-DR-, CD80-, and CD86-expression in peripheral blood from healthy volunteers aged 20-79 years, and in AD patients at diagnosis and after 12, 30, and 52 weeks of rivastigmine treatment. While the number of CD14+ monocytes remained constant, the expression of HLA-DR, CD80, and CD86 by monocytes increased with age. However, no differences were identified by comparing AD patients with age-matched healthy controls or following treatment of AD patients with rivastigmine. These results indicate that changes in the expression of HLA-DR, CD80, and CD86 are caused by immunosenescence rather than by AD pathology or treatment of AD patients with rivastigmine.

Lipid metabolism and neuroinflammation in Alzheimer's disease: a role for liver X receptors

Liver X receptors (LXR) are nuclear receptors that have emerged as key regulators of lipid metabolism. In addition to their functions as cholesterol sensors, LXR have also been found to regulate inflammatory responses in macrophages. Alzheimer's disease (AD) is a neurodegenerative disease characterized by a progressive cognitive decline associated with inflammation. Evidence indicates that the initiation and progression of AD is linked to aberrant cholesterol metabolism and inflammation. Activation of LXR can regulate neuroinflammation and decrease amyloid-β peptide accumulation. Here, we highlight the role of LXR in orchestrating lipid homeostasis and neuroinflammation in the brain. In addition, diabetes mellitus is also briefly discussed as a significant risk factor for AD because of the appearing beneficial effects of LXR on glucose homeostasis. The ability of LXR to attenuate AD pathology makes them potential therapeutic targets for this neurodegenerative disease.

Fractalkine Mediates Communication between Pathogenic Proteins and Microglia: Implications of Anti-Inflammatory Treatments in Different Stages of Neurodegenerative Diseases

The role of inflammation in neurodegenerative diseases has been widely demonstrated. Intraneuronal protein accumulation may regulate microglial activity via the fractalkine (CX3CL1) signaling pathway that provides a mechanism through which neurons communicate with microglia. CX3CL1 levels fluctuate in different stages of neurodegenerative diseases and in various animal models, warranting further investigation of the mechanisms underlying microglial response to pathogenic proteins, including Tau, β-amyloid (Aβ), and α-synuclein. The temporal relationship between microglial activity and localization of pathogenic proteins (intra- versus extracellular) likely determines whether neuroinflammation mitigates or exacerbates disease progression. Evidence in transgenic models suggests a beneficial effect of microglial activity on clearance of proteins like Aβ and a detrimental effect on Tau modification, but the role of CX3CL1 signaling in α-synucleinopathies is less clear. Here we review the nature of fractalkine-mediated neuronmicroglia interaction, which has significant implications for the efficacy of anti-inflammatory treatments during different stages of neurodegenerative pathology. Specifically, it is likely that anti-inflammatory treatment in early stages of disease during intraneuronal accumulation of proteins could be beneficial, while anti-inflammatory treatment in later stages when proteins are secreted to the extracellular space could exacerbate disease progression.

The promise of anti-inflammatory therapies for CNS injuries and diseases

It remains controversial as to whether the inflammatory response plays a beneficial or detrimental role for cerebral tissue. There is substantial evidence that molecules of the innate immune reaction can be harmful to neurons and oligodendrocytes, whereas other observations indicate that inflammation is actually beneficial to recovery after injuries. One of the beneficial consequences of the immune reaction by microglia is the release of neurotrophic factors that have essential roles in brain homeostasis, neuroprotection and repair in cases of injury. Another important action of microglia is the clearance of cell debris and toxic proteins in order to prevent their accumulation in the extracellular space. Such beneficial effects of subsets of innate immune cells have to be taken into serious consideration in the planning of clinical trials using anti-inflammatory drugs for CNS diseases, which have failed so far. This very important subject has been discussed at the 13th Annual Meeting of the American Society for Experimental Neurotherapeutics in Bethesda, MD, USA.

Inflammation in the early stages of neurodegenerative pathology

Inflammation is secondary to protein accumulation in neurodegenerative diseases, including Alzheimer's, Parkinson's and Amyotrophic Lateral Sclerosis. Emerging evidence indicate sustained inflammatory responses, involving microglia and astrocytes in animal models of neurodegeneration. It is unknown whether inflammation is beneficial or detrimental to disease progression and how inflammatory responses are induced within the CNS. Persistence of an inflammatory stimulus or failure to resolve sustained inflammation can result in pathology, thus, mechanisms that counteract inflammation are indispensable. Here we review studies on inflammation mediated by innate and adaptive immunity in the early stages of neurodegeneration and highlight important areas for future investigation.

Regulation of innate immune responses in the brain

Microglial cells are the main innate immune cells of the complex cellular structure of the brain. These cells respond quickly to pathogens and injury, accumulate in regions of degeneration and produce a wide variety of pro-inflammatory molecules. These observations have resulted in active debate regarding the exact role of microglial cells in the brain and whether they have beneficial or detrimental functions. Careful targeting of these cells could have therapeutic benefits for several types of trauma and disease specific to the central nervous system. This Review discusses the molecular details underlying the innate immune response in the brain during infection, injury and disease.

Non-apolipoprotein E and apolipoprotein E genetics of sporadic Alzheimer's disease

The genetic epidemiology of sporadic Alzheimer's disease (SAD) remains a very active area of research,making it one of the most prolifically published areas in medicine and biology. Numerous putative candidate genes have been proposed. However, with the exception of apolipoprotein E (APOE), the only confirmed genetic risk factor for SAD, all the other data appear to be not consistent. Nevertheless, the genetic risk for SAD attributable to the APOE gene in the general population is 20-0%, providing a strong evidence for the existence of additional genetic risk factors. The first part of the present article was dedicated to non-APOE genetics of SAD, reviewing chromosomes-by-chromosomes the available data concerning the major candidate genes. The second part of this article focused on some recently discovered aspects of the APOE polymorphism and their implications for SAD. An attempt to identify the future directions for non-APOE genetic research in SAD was also discussed.

Toll-like receptor 2 acts as a natural innate immune receptor to clear amyloid beta 1-42 and delay the cognitive decline in a mouse model of Alzheimer's disease

Microglia are the immune cells of the brain, they are activated in the brain of Alzheimer's disease (AD) patients and mouse models of AD, and they express the innate immune receptor toll-like receptor 2 (TLR2). The present study investigated role of this receptor in the progression of AD-like pathologies. Here we show that amyloid beta (A beta) stimulates TLR2 expression in a small proportion of microglia. We then generated triple transgenic mice that are deficient in TLR2 from mice that harbor a mutant human presenelin 1 and a chimeric mouse/human amyloid precursor protein (APP) genes. TLR2 deficiency accelerated spatial and contextual memory impairments, which correlated with increased levels of A beta(1-42) and transforming growth factor beta1 in the brain. NMDA receptors 1 and 2A expression levels were also lower in the hippocampus of APP-TLR2(-/-) mice. Gene therapy in cells of the bone marrow using lentivirus constructs expressing TLR2 rescued the cognitive impairment of APP-TLR2(-/-) mice. Indeed, lenti-green fluorescent protein/TLR2 treatment had beneficial effects by restoring the memory consolidation process disrupted by TLR2 deficiency in APP mice. These data suggest that TLR2 acts as an endogenous receptor for the clearance of toxic A beta by bone-marrow-derived immune cells. The cognitive decline is markedly accelerated in a context of TLR2 deficiency. Upregulating this innate immune receptor may then be considered as a potential new powerful therapeutic approach for AD.

Interaction between CD14 and LXRβ genes modulates Alzheimer's disease risk

A chronic inflammatory process with activation of microglial cells contribute to the neurodegeneration associated with Alzheimer's disease (AD). CD14 and LXRbeta are receptors involved in the regulation of inflammatory responses of microglia in response to bacterial infection or lipopolysaccharide stimulation. In a case-control study in 266 AD patients and 273 healthy controls, we examined whether the combined gene effects between CD14 (-260) polymorphism and LXRbeta (intron 5) polymorphism might be responsible for susceptibility to AD. Subjects carrying both the CD14 (-260) C/C and the LXRbeta (intron 5) G/G genotypes had a six times lower risk of developing AD than subjects without these risk genotypes (OR 0.16, 95% CI 0.04-0.67, p=0.01). These data support a role for innate immune response genes in risk for AD.

Polymorphisms of pro-inflammatory genes and Alzheimer's disease risk: A pharmacogenomic approach

Clinically and pathologically Alzheimer's disease (AD) represents a sequential progressive neurodegenerative disorder. AD is etiologically heterogeneous and accounts for a majority of dementia in western societies. Inflammation clearly occurs in pathologically vulnerable regions of the AD brain and the search for genetic factors influencing the pathogenesis of AD has lead to the identification of numerous gene polymorphisms that might act as susceptibility modifiers. Accordingly, several reports have indicated that the risk of AD is substantially influenced by several genetic polymorphisms in the promoter region, or other untranslated regions, of genes encoding inflammatory mediators, although not all the studies were replied. Here, we review several data suggesting that inflammatory genetic variation may contribute to AD susceptibility. All together this information may represent the basis both for future recognition of individuals at risk and for the pharmacogenomic driving of drug responsiveness.

Increment of Plasma Soluble CD14 Level in Carrageenan-Primed Endotoxin Shock Model Mice

CD14 is membrane-associating or free soluble glycoprotein which recognizes lipopolysaccharide (LPS) and is assumed to be involved in the onset of endotoxin shock. There are some reports suggesting the relationship between increased expression of CD14 in infectious or inflammatory diseases. However, little has been reported concerning the soluble CD14 (sCD14) level, especially in mice. In this study, we measured the plasma level of sCD14, TNF-alpha and IL-6 in the iota-carrageenan (CAR)-primed endotoxin shock model in addition to the D-galactosamine (D-galN)-primed endotoxin shock model mice. It was confirmed that all mice were dead within 12 h after a higher dose of LPS-treatment in both animal models. The level of TNF-alpha, IL-6 and sCD14 significantly increased in the CAR-primed endotoxin shock model mice. However, the D-galN-primed endotoxin shock model mice showed only a slight increment of TNF-alpha and IL-6 level, and sCD14 was below the detectable level. In the examination using several doses of LPS in CAR-primed model mice, IL-6 and sCD14 were increased dependent on the LPS dose, but TNF-alpha remained at an almost equal level at any dose of LPS in this study condition. In conclusion, the production of TNF-alpha, IL-6 and sCD14 was significantly enhanced in the CAR-primed model mice, compared to the D-galN-primed model mice. Therefore, these data indicate the possibility that the sCD14 level did not increase consistently, even under a fatal condition in endotoxin shock. Also, CAR-primed endotoxin shock would be an important experimental model to examine the elevation mechanisms for sCD14 and IL-6 production.