A polymorphism in the intronic region of the IL-1alpha gene and the risk for Parkinson's disease

Quantitative and causal analysis for inflammatory genes and the risk of Parkinson's disease

Background

The dysfunction of immune system and inflammation contribute to the Parkinson's disease (PD) pathogenesis. Cytokines, oxidative stress, neurotoxin and metabolism associated enzymes participate in neuroinflammation in PD and the genes involved in them have been reported to be associated with the risk of PD. In our study, we performed a quantitative and causal analysis of the relationship between inflammatory genes and PD risk.

Methods

Standard process was performed for quantitative analysis. Allele model (AM) was used as primary outcome analysis and dominant model (DM) and recessive model (RM) were applied to do the secondary analysis. Then, for those genes significantly associated with the risk of PD, we used the published GWAS summary statistics for Mendelian Randomization (MR) to test the causal analysis between them.

Results

We included 36 variants in 18 genes for final pooled analysis. As a result, IL-6 rs1800795, TNF-α rs1799964, PON1 rs854560, CYP2D6 rs3892097, HLA-DRB rs660895, BST1 rs11931532, CCDC62 rs12817488 polymorphisms were associated with the risk of PD statistically with the ORs ranged from 0.66 to 3.19 while variants in IL-1α, IL-1β, IL-10, MnSOD, NFE2L2, CYP2E1, NOS1, NAT2, ABCB1, HFE and MTHFR were not related to the risk of PD. Besides, we observed that increasing ADP-ribosyl cyclase (coded by BST1) had causal effect on higher PD risk (OR[95%CI] =1.16[1.10-1.22]) while PON1(coded by PON1) shown probably protective effect on PD risk (OR[95%CI] =0.81[0.66-0.99]).

Conclusion

Several polymorphisms from inflammatory genes of IL-6, TNF-α, PON1, CYP2D6, HLA-DRB, BST1, CCDC62 were statistically associated with the susceptibility of PD, and with evidence of causal relationships for ADP-ribosyl cyclase and PON1 on PD risk, which may help understand the mechanisms and pathways underlying PD pathogenesis.

Inflammation-related gene polymorphisms associated with Parkinson’s disease: an updated meta-analysis

Background

Strong evidence supports the involvement of inflammation processes in the development and progression of Parkinson’s disease (PD), where increasingly correlations have been identified between genetic variations in inflammation-related genes and PD. However, data varies between studies. Therefore, we conducted a meta-analysis to clarify associations between inflammation-related gene polymorphisms and PD risk.

Methods

All studies were identified through online databases. Pooled and stratified groups based on racial descent were assembled to evaluate associations between polymorphisms and PD.

Results

The pooled results showed that protective effects for PD were observed for (1) IL-1α -889 C/T in Asian populations (T vs. C, OR = 0.831, P = 0.031; TT + CT vs. CC, OR = 0.827, P = 0.049); (2) IL-6 -176 G/C in Caucasian populations (CC + GC vs. GG, OR = 0.656, P = 0.000; GC vs. GG, OR = 0.673, P = 0.000); (3) IL-8 -251 A/T (T vs. A, OR = 0.812, P = 0.041; TT vs. AT + AA, OR = 0.663, P = 0.012), particularly in Caucasian populations (TT vs. AT + AA, OR = 0.639, P = 0.010); (4) IL-10 -819 T/C (C vs. T, OR = 0.742, P = 0.034); (5) IL-18 -607 C/A (AA + CA vs. CC, OR = 0.597, P = 0.015; CA vs. CC, OR = 0.534, P = 0.005), and (6) CCR2 +190 G/A (AA vs. GA + GG, OR = 0.552, P = 0.018; AA vs. GG; OR = 0.554; 95% CI 0.336–0.914, P = 0.005). An increased risk of PD was associated with IL-10 -1082 G/A in Asian populations (A vs. G, OR = 1.731, P = 0.000; AA + GA vs. GG, OR = 1.910, P = 0.000). No significant associations with PD were observed for polymorphisms in IL-1β -511 C/T, IL-10 -592 C/A, IL-18 -137 G/C, TNFα -863 C/A, TNFα -857 C/T, TNFα -308 G/A, IFNΥ +874 T/A, and MCP1/CCL2 +2518 A/G.

Conclusions

We suggest that IL-1α -889, IL-6 -176, IL-8 -251, IL-10 -1082, IL-10 -819, IL-18 -607, and CCR2 +190 polymorphisms may be associated with PD risk; however, further studies must verify these conclusions.

Role of α-synuclein in inducing innate and adaptive immunity in Parkinson disease

Alpha-synuclein (α-syn) is central to the pathogenesis of Parkinson disease (PD). Gene duplications, triplications and point mutations in SNCA1, the gene encoding α-syn, cause autosomal dominant forms of PD. Aggregated and post-translationally modified forms of α-syn are present in Lewy bodies and Lewy neurites in both sporadic and familial PD, and recent work has emphasized the prion-like ability of aggregated α-syn to produce spreading pathology. Accumulation of abnormal forms of α-syn is a trigger for PD, but recent evidence suggests that much of the downstream neurodegeneration may result from inflammatory responses. Components of both the innate and adaptive immune systems are activated in PD, and influencing interactions between innate and adaptive immune components has been shown to modify the pathological process in animal models of PD. Understanding the relationship between α-syn and subsequent inflammation may reveal novel targets for neuroprotective interventions. In this review, we examine the role of α-syn and modified forms of this protein in the initiation of innate and adaptive immune responses.

Increased amoeboid microglial density in the olfactory bulb of Parkinson's and Alzheimer's patients

The olfactory bulb (OB) is affected early in both Parkinson's (PD) and Alzheimer's disease (AD), evidenced by the presence of disease-specific protein aggregates and an early loss of olfaction. Whereas previous studies showed amoeboid microglia in the classically affected brain regions of PD and AD patients, little was known about such changes in the OB. Using a morphometric approach, a significant increase in amoeboid microglia density within the anterior olfactory nucleus (AON) of AD and PD patients was observed. These amoeboid microglia cells were in close apposition to β-amyloid, hyperphosphorylated tau or α-synuclein deposits, but no uptake of pathological proteins by microglia could be visualized. Subsequent analysis showed (i) no correlation between microglia and α-synuclein (PD), (ii) a positive correlation with β-amyloid (AD), and (iii) a negative correlation with hyperphosphorylated tau (AD). Furthermore, despite the observed pathological alterations in neurite morphology, neuronal loss was not apparent in the AON of both patient groups. Thus, we hypothesize that, in contrast to the classically affected brain regions of AD and PD patients, within the AON rather than neuronal loss, the increased density in amoeboid microglial cells, possibly in combination with neurite pathology, may contribute to functional deficits.

Emerging roles of microglial activation and non-motor symptoms in Parkinson's disease

Recent data has indicated that the traditional view of Parkinson's disease (PD) as an isolated disorder of the nigrostriatal dopaminergic system alone is an oversimplification of its complex symptomatology. Aside from classical motor deficits, various non-motor symptoms including autonomic dysfunction, sensory and cognitive impairments as well as neuropsychiatric alterations and sleep disturbances are common in PD. Some of these non-motor symptoms can even antedate the motor problems. Many of them are associated with extranigral neuropathological changes, such as extensive α-synuclein pathology and also neuroinflammatory responses in specific brain regions, i.e. microglial activation, which has been implicated in several aspects of PD pathogenesis and progression. However, microglia do not represent a uniform population, but comprise a diverse group of cells with brain region-specific phenotypes that can exert beneficial or detrimental effects, depending on the local phenotype and context. Understanding how microglia can be neuroprotective in one brain region, while promoting neurotoxicity in another, will improve our understanding of the role of microglia in neurodegeneration in general, and of their role in PD pathology in particular. Since neuroinflammatory responses are in principle modifiable, such approaches could help to identify new targets or adjunctive therapies for the full spectrum of PD-related symptoms.

Cytokine gene polymorphisms and Parkinson's disease: a meta-analysis

BACKGROUND

Cytokines, which are involved in immunological responses, play and important role in the development and progression of Parkinson's disease (PD). The functional polymorphisms identified in cytokine genes are thought to influence PD risk. However the findings of studies investigating the association between cytokine gene polymorphisms and PD risk are still controversial. Therefore, we conducted a meta-analysis, in order to investigate the potential associations between cytokine gene polymorphisms and PD.

METHODS

Studies of PD and cytokine polymorphisms were identified by searches of PubMed and PDGene. Pooled analyses were performed to assess the association between cytokine gene polymorphisms and PD.

RESULTS

Our results indicated a positive association of TNFα -1031 CC genotype in overall analysis(CC vs. TT: OR=3.146; 95%CI: 1.631-6.070, p=0.008; CC vs. CT+TT: OR=3.187: 95%CI: 1.657-6.128,p=0.008), and an Asian subgroup, C variant(OR=1.328; 95%CI: 1.053-1.675, p=0.034) also conveyed an increased PD risk as well as CC genotype ( CC vs. TT: OR=3.207; 95%CI: 1.614-6.373, p=0.004; CC vs. CT+TT: OR=3.238; 95%CI: 1.636-6.410, p=0.004). A decreased risk for PD was associated with IL-6-174C allele (OR=0.761; 95%CI: 0.641-0.903, p=0.008) and IL-1RA VNTR 2 allele(OR=0.641; 95%CI: 0.456-0.826 p=0.004). For the polymorphisms of IL-1β C[-511]T, IL-1α C[-889]T , TNFα G[-308]A, and IL-10 G[-1082]A no significant association was found between the gene polymorphisms and PD risk.

CONCLUSIONS

Our meta-analysis suggested that gene polymorphisms of TNFα -1031, IL-6-174 and IL-1RA VNTR may be associated with PD risk. However, more large well-designed studies will be necessary to validate our findings.

Interleukin-10 promoter polymorphisms in Chinese patients with Parkinson's disease

Interleukin-10 (IL-10), an important anti-inflammatory cytokine, may influence the risk for the development of onset of sparadic Parkinson's disease (PD) in the inflammatory process. In this study, two DNA polymorphisms at IL-10 gene promoter (-819 T/C and -592 A/C) were examined in 355 sporadic PD patients and 200 healthy controls in Han Chinese Population. For both polymorphisms, no significant difference in genotype or allele distribution was found between PD patients and the controls. For -819 T/C polymorphisms, there was significant difference in genotype distribution between EOPD (EOPD, <50 years of age) patients and each healthy-matched control subgroup (P=0.011), as well as between female PD patients and each healthy-matched control subgroup (P=0.024), For -592 A/C polymorphisms, there were no significant gender- and age-related differences in genotype distribution between PD patients and the controls subgroup. Results from our study revealed that the IL-10 promoter (-819 and -592) polymorphism is not a risk factor of sporadic Parkinson's disease, but the IL-10 promoter -819 polymorphism is a risk factor of EOPD and female PD patients in Han Chinese population.

Interleukin-18 promoter polymorphisms and risk of Parkinson's disease in a Han Chinese population

The etiology of sporadic Parkinson's disease (PD) is not well established. Interleukin-18 (IL-18), a member of pro-inflammatory cytokines, might influence the risk of sporadic PD occurrence and development. In this study, two DNA polymorphisms at interleukin (IL)-18 promoter, -607C/A (rs1946518) and -137G/C (rs187238), were examined in sporadic PD patients in a Han Chinese population with 290 sporadic PD patients and 200 healthy controls. Direct sequencing was performed in 10% of the samples to validate the genotyping results. The results revealed that for -607C/A polymorphisms, there were significant differences in genotype distribution between PD and control in the total sample (P=0.017) and between LOPD and healthy-matched controls subgroup (P=0.011). For -137G/C polymorphisms, there were no significant differences in genotype distribution and gender and age-related differences between PD and control in the total sample (P=0.610). Results in this study revealed that the IL-18 607C/A polymorphism is a risk factor for sporadic LOPD in Han Chinese population, while IL-18 137G/C polymorphism is not a risk factor for sporadic PD in the Han Chinese population.

Lack of association between interleukin-1 alpha, beta polymorphisms and Parkinson's disease

The associations between interleukin-1 alpha (IL-1alpha-889) and beta (IL-1beta-511) single nucleotide polymorphisms (SNPs) and the risk for Parkinson's disease (PD) are still controversial and ambiguous. The aim of this study was to determine a more precise estimation of the relationship by meta-analysis. We searched databases through March 2010 for all publications on the association between these variations and PD. A total of 11 studies including 2803 PD patients and 2539 healthy controls were identified. The overall and geographic subgroups analysis was conducted, and odds ratios (OR) and 95% confidence intervals (95% CI) were calculated in the fixed- or random-effects model. We found that the overall OR (95% CI) for TT and CT genotypes versus CC genotype for IL-1alpha-889 was 1.01 (0.88-1.16), while the overall OR (95% CI) for TT and CT genotypes versus CC genotype for IL-1beta-511 was 1.19 (0.87-1.62). The sensitivity analysis strengthened our confidence in the validity of these null associations. There was no publication bias observed in this study. To sum up, there were no associations found between the SNPs of IL-1alpha-889, IL-1beta-511 and risk for PD.

Common inflammatory mechanisms in Lewy body disease and Alzheimer disease

Cortical Lewy body disease as a cause of dementia has been recognized for more than 40 years. Only in the past 15 to 20 years, however, has the true frequency of this entity come to be appreciated, primarily because of the advent of sensitive and specific immunohistochemical diagnostic techniques. We now know that there is frequent and extensive overlap, both clinically and pathologically, between Lewy body and Alzheimer diseases. Although some of this overlap may be attributable to common genetic and environmental risk factors, it is also now apparent that the 2 diseases share common neuroinflammatory mechanisms involving activation of microglia, overexpression of interleukin-1 and other inflammatory mediators, and inflammatory toxicity to neurons. Activated microglia are found in association with alpha-synuclein-containing neurons and glia in Parkinson disease, in dementia with Lewy bodies, and in multiple system atrophy, and these associations are reminiscent of microglial associations with neurofibrillary tangle-containing neurons in Alzheimer disease. In vitro and in vivo experimental work has shown reciprocal induction between alpha-synuclein and injured neurons on one hand and activated microglia and cytokine overexpression on the other. These neuroinflammatory processes may be a common link driving progression in both diseases and explaining the frequent overlap between the 2 diseases.

Interleukin-10 gene polymorphism in Parkinson's disease patients

BACKGROUND

The etiology of sporadic Parkinson's disease (PD) is not well established. Recent studies revealed that inflammatory processes might also play an important role in the pathogenesis of PD. We hypothesized that genetically determined differences in the immune response, especially in anti-inflammatory cytokines production, might influence the risk of sporadic PD development and/or onset. To prove this hypothesis, two DNA polymorphisms at IL-10 promoter (-1082 and -519) were examined in sporadic PD patients.

METHODS

The study enrolled 341 patients with diagnosed idiopathic PD. All cases of secondary parkinsonism were excluded from the study. For the purpose of this study the patients were also divided into two subgroups: group 1: patients with onset of Parkinson's disease, i.e., <50 years of age (early onset) included 60 patients, as well as group 2: patients with onset of Parkinson's disease >50 years of age (late onset) comprising 281 subjects. Control samples were from 315 randomly selected healthy individuals from the same geographical region who were free from signs of parkinsonism as evaluated by consultant neurologists. PCR-RFLP methods were used for genotyping.

RESULTS

No statistically significant differences between PD patients and controls were found in the frequency of a single locus (-1082, -519) of IL-10 promoter. Likewise, haplotype analysis did not demonstrate any significant differences between evaluated groups. The frequency of the evaluated IL-10 genotypes was also similar in EOPD and LOPD patients.

CONCLUSIONS

Results from our study revealed that the IL-10 (-1082G>A, -592C>A) polymorphism is not a risk factor of sporadic Parkinson's disease in a Polish population.

Interleukin-1 alpha polymorphism has influence on late-onset sporadic Parkinson's disease in Taiwan

Inflammatory events may contribute to the pathogenesis of Parkinson's disease (PD) and interleukin 1 (IL-1) may exert both neurotoxic and neuroprotective effects. We conducted a case-control study in a cohort of 493 PD cases and 388 ethnically matched controls to investigate the association of IL-1alpha C-889T and IL-1beta C-511T polymorphisms with the risk of PD. No significant difference in the genotype distribution of the analyzed polymorphisms was found between PD and controls. However, after stratification by age, individuals over 70 years of age carrying IL-1alpha-889 C/T genotype demonstrated a significant decrease in risk of developing PD (OR = 0.44; 95% CI = 0.22-0.88, p = 0.021) and the decrease is strengthened by IL-1beta-511 T-carrying genotype (OR = 0.28; 95% CI = 0.11-0.71, p = 0.008). Our data suggest that IL-1alpha, acting synergistically with IL-1beta, plays role in PD susceptibility among Taiwanese people older than 70 years of age.

Glial degeneration and reactive gliosis in alpha-synucleinopathies: the emerging concept of primary gliodegeneration

The concept of gliodegenerative diseases has not been widely established although there is accumulating evidence that glial cells may represent a primary target of degenerative disease processes. In the central nervous system (CNS), examples that provide a "proof of concept" include at least one alpha-synucleinopathy, multiple system atrophy (MSA), but this disease is conventionally discussed under the heading of "neurodegeneration". Additional evidence in support of primary glial affection has been reported in neurodegenerative disorders such as Parkinson's disease, Alzheimer's disease and transmissible spongiform encephalopathies. Based on biochemical, genetic and transcriptomic studies it is also becoming increasingly clear that the molecular changes measured in whole tissue extracts, e.g. obtained from Parkinson's disease brain, are not based on a purely neuronal contribution. This important evidence has been missed in cell culture or laser capture work focusing on the neuronal cell population. Studies of animal and in vitro models of disease pathogenesis additionally suggest glial accountability for some CNS degenerative processes. This review provides a critical analysis of the evidence available to date in support of the concept of gliodegeneration, which we propose to represent an essential although largely disregarded component of the spectrum of classical "neurodegeneration". Examples from the spectrum of alpha-synucleinopathies are presented.

Increased plasma levels of TNF-α but not of IL1-β in MPTP-treated monkeys one year after the MPTP administration

The cause of Parkinson's disease remains unknown although some evidence suggests that an inflammatory reaction, mediated by cytokines such as TNF-alpha and IL-1beta, is related with dopaminergic degeneration in the brain. In the present work we measured the plasma levels of TNF-alpha and IL-1beta in parkinsonian monkeys one year after MPTP administration. TNF-alpha levels were seen to have increased in parkinsonian monkeys reflecting the clinical symptoms observed, while IL-1beta levels remained unchanged. These results suggest that TNF-alpha plays a role in sustaining of dopaminergic degeneration in chronic parkinsonism.

Lack of association between the interleukin-1 alpha (−889) polymorphism and early-onset Parkinson's disease

An increasing number of studies have shown that an inflammatory process is part of Parkinson's disease (PD) brain pathology. Interleukin-1 (IL-1) is a multifunctional cytokine and is considered to contribute to several inflammatory diseases. Recently, we detected an associated risk in a subgroup of PD patients with a disease onset < 50 years and a C to T transition in the IL-1alpha promoter (-889). One-hundred-seventy-six German PD patients (42.1 +/- 6.4 years; 42.4% male) and 170 unrelated age-matched control individuals (40.4 +/- 8.7 years; 57.6% male) were investigated for the presence of the IL-1alpha (-889C/T) polymorphism. No significant difference in the allelic distribution of the analyzed IL-1alpha polymorphism has been found between PD and controls. We conclude that the C/T polymorphism in the IL-1alpha promoter region at -889 does not increase the risk to develop PD.

Association of interleukin-1 beta polymorphisms with idiopathic Parkinson's disease

Activated microglia surround degenerating substantia nigra neurons in Parkinson's disease (PD). Such microglia produce high levels of interleukin-1 beta (IL-1 beta) and interleukin-1 alpha (IL-1 alpha). T and C alleles exist for the IL-1 beta-511 regulatory region as well as for the IL-1 alpha-889 regulatory region. The T genotypes of both have been reported to increase the risk of Alzheimer's disease (AD) (Arch. Neurol. 58 (2001) 1790). Since the lesions of PD and AD have similar neuroinflammatory characteristics (Neurology 38 (1988) 1285), we genotyped 100 PD and 100 control postmortem brains for the same polymorphisms. We found a significant increase of the IL-1 beta T genotype in PD cases compared with controls (chi(2)=9.65, P=0.0019). A significant increase was not found for the IL-alpha T genotype (chi(2)=1.32, P=0.23), although there was a trend towards more frequent expression of the T allele.