Association Study of Mannose-Binding Lectin Levels and Genetic Variants in Lectin Pathway Proteins with Susceptibility to Age-Related Macular Degeneration: A Case-Control Study

BACKGROUND

In age-related macular degeneration (AMD) the complement system is thought to be activated by chronic oxidative damage with genetic variants identified in the alternative pathway as susceptibility factors. However, the involvement of the lectin pathway of complement, a key mediator of oxidative damage, is controversial. This study investigated whether mannose-binding lectin (MBL) levels and genetic variants in lectin pathway proteins, are associated with the predisposition to and severity of AMD.

METHODS

MBL levels and single nucleotide polymorphisms (SNPs) in the MBL2 and the ficolin-2 (FCN2) gene were determined in 109 patients with AMD and 109 age- and sex-matched controls.

RESULTS

MBL expression levels were equally distributed in both cases (early and late AMD) and controls (p>0.05). However, there was a trend towards higher median MBL levels in cases with late AMD compared to cases with early AMD (1.0 vs. 0.4 μg/ml, p = 0.09) and MBL deficiency (<0.5 μg/ml) was encountered less frequently in the late AMD group (35% vs 56%, p = 0.03). FCN2 and MBL2 allele frequencies were similarly distributed in early and late AMD cases compared with controls (p>0.05 for all analyses) as were MBL2 genotypes. Similarly, there was no significant difference in allele frequencies in any SNPs in either the MBL2 or FCN2 gene in cases with early vs. late AMD.

CONCLUSIONS

SNPs of lectin pathway proteins investigated in this study were not associated with AMD or AMD severity. However, MBL levels deserve further study in a larger cohort of early vs. late AMD patients to elucidate any real effect on AMD severity.

A rare P2X7 variant Arg307Gln with absent pore formation function protects against neuroinflammation in multiple sclerosis

Multiple sclerosis (MS) is a chronic relapsing-remitting inflammatory disease of the central nervous system characterized by oligodendrocyte damage, demyelination and neuronal death. Genetic association studies have shown a 2-fold or greater prevalence of the HLA-DRB1*1501 allele in the MS population compared with normal Caucasians. In discovery cohorts of Australasian patients with MS (total 2941 patients and 3008 controls), we examined the associations of 12 functional polymorphisms of P2X7, a microglial/macrophage receptor with proinflammatory effects when activated by extracellular adenosine triphosphate (ATP). In discovery cohorts, rs28360457, coding for Arg307Gln was associated with MS and combined analysis showed a 2-fold lower minor allele frequency compared with controls (1.11% for MS and 2.15% for controls, P = 0.0000071). Replication analysis of four independent European MS case-control cohorts (total 2140 cases and 2634 controls) confirmed this association [odds ratio (OR) = 0.69, P = 0.026]. A meta-analysis of all Australasian and European cohorts indicated that Arg307Gln confers a 1.8-fold protective effect on MS risk (OR = 0.57, P = 0.0000024). Fresh human monocytes heterozygous for Arg307Gln have >85% loss of 'pore' function of the P2X7 receptor measured by ATP-induced ethidium uptake. Analysis shows Arg307Gln always occurred with 270His suggesting a single 307Gln-270His haplotype that confers dominant negative effects on P2X7 function and protection against MS. Modeling based on the homologous zP2X4 receptor showed Arg307 is located in a region rich in basic residues located only 12 Å from the ligand binding site. Our data show the protective effect against MS of a rare genetic variant of P2RX7 with heterozygotes showing near absent proinflammatory 'pore' function.

Toluene diisocyanate: Induction of the autotaxin-lysophosphatidic acid axis and its association with airways symptoms

Diisocyanates are industrial chemicals which have a wide range of applications in developed and developing countries. They are notorious lung toxicants and respiratory sensitizers. However, the mechanisms behind their adverse effects are not adequately characterized. Autotaxin (ATX) is an enzyme producing lysophosphatidic acid (LPA), and the ATX-LPA axis has been implicated in lung related inflammatory conditions and diseases, including allergic asthma, but not to toxicity of environmental low-molecular-weight chemicals. We investigated effects of toluene diisocyanate (TDI) on ATX induction in human lung epithelial cell models, and we correlated LPA-levels in plasma to biomarkers of TDI exposure in urine collected from workers exposed to <5ppb (parts per billion). Information on workers' symptoms was collected through interviews. One nanomolar TDI robustly induced ATX release within 10min in vitro. A P2X7- and P2X4-dependent microvesicle formation was implicated in a rapid ATX release and a subsequent protein synthesis. Co-localization between purinergic receptors and ATX was documented by immunofluorescence and confocal microscopy. The release was modulated by monocyte chemoattractant protein-1 (MCP-1) and by extracellular ATP. In workers, we found a dose-response relationship between TDI exposure biomarkers in urine and LPA levels in plasma. Among symptomatic workers reporting "sneezing", the LPA levels were higher than among non-symptomatic workers. This is the first report indicating induction of the ATX-LPA axis by an environmental low-molecular-weight chemical, and our data suggest a role for the ATX-LPA axis in TDI toxicity.

Extracellular ATP protects against sepsis through macrophage P2X7 purinergic receptors by enhancing intracellular bacterial killing

Extracellular ATP binds to and signals through P2X7 receptors (P2X7Rs) to modulate immune function in both inflammasome-dependent and -independent manners. In this study, P2X7(-/-) mice, the pharmacological agonists ATP-magnesium salt (Mg-ATP; 100 mg/kg, EC50 ≈ 1.32 mM) and benzoylbenzoyl-ATP (Bz-ATP; 10 mg/kg, EC50 ≈ 285 μM), and antagonist oxidized ATP (oxi-ATP; 40 mg/kg, IC50 ≈ 100 μM) were used to show that P2X7R activation is crucial for the control of mortality, bacterial dissemination, and inflammation in cecal ligation and puncture-induced polymicrobial sepsis in mice. Our results with P2X7(-/-) bone marrow chimeric mice, adoptive transfer of peritoneal macrophages, and myeloid-specific P2X7(-/-) mice indicate that P2X7R signaling on macrophages is essential for the protective effect of P2X7Rs. P2X7R signaling protects through enhancing bacterial killing by macrophages, which is independent of the inflammasome. By using the connexin (Cx) channel inhibitor Gap27 (0.1 mg/kg, IC50 ≈ 0.25 μM) and pannexin channel inhibitor probenecid (10 mg/kg, IC50 ≈ 11.7 μM), we showed that ATP release through Cx is important for inhibiting inflammation and bacterial burden. In summary, targeting P2X7Rs provides a new opportunity for harnessing an endogenous protective immune mechanism in the treatment of sepsis.

The P2X7 receptor channel: recent developments and the use of P2X7 antagonists in models of disease

The P2X7 receptor is a trimeric ATP-gated cation channel found predominantly, but not exclusively, on immune cells. P2X7 activation results in a number of downstream events, including the release of proinflammatory mediators and cell death and proliferation. As such, P2X7 plays important roles in various inflammatory, immune, neurologic and musculoskeletal disorders. This review focuses on the use of P2X7 antagonists in rodent models of neurologic disease and injury, inflammation, and musculoskeletal and other disorders. The cloning and characterization of human, rat, mouse, guinea pig, dog, and Rhesus macaque P2X7, as well as recent observations regarding the gating and permeability of P2X7, are discussed. Furthermore, this review discusses polymorphic and splice variants of P2X7, as well as the generation and use of P2X7 knockout mice. Recent evidence for emerging signaling pathways downstream of P2X7 activation and the growing list of negative and positive modulators of P2X7 activation and expression are also described. In addition, the use of P2X7 antagonists in numerous rodent models of disease is extensively summarized. Finally, the use of P2X7 antagonists in clinical trials in humans and future directions exploring P2X7 as a therapeutic target are described.

Purinergic signalling and immune cells

This review article provides a historical perspective on the role of purinergic signalling in the regulation of various subsets of immune cells from early discoveries to current understanding. It is now recognised that adenosine 5'-triphosphate (ATP) and other nucleotides are released from cells following stress or injury. They can act on virtually all subsets of immune cells through a spectrum of P2X ligand-gated ion channels and G protein-coupled P2Y receptors. Furthermore, ATP is rapidly degraded into adenosine by ectonucleotidases such as CD39 and CD73, and adenosine exerts additional regulatory effects through its own receptors. The resulting effect ranges from stimulation to tolerance depending on the amount and time courses of nucleotides released, and the balance between ATP and adenosine. This review identifies the various receptors involved in the different subsets of immune cells and their effects on the function of these cells.

Genome-wide association studies: getting to pathogenesis, the role of inflammation/complement in age-related macular degeneration

Age-related macular degeneration (AMD) is a chronic, degenerative, and significant cause of visual impairment and blindness in the elderly. Genetic and epidemiological studies have confirmed that AMD has a strong genetic component, which has encouraged the application of increasingly sophisticated genetic techniques to uncover the important underlying genetic variants. Although various genes and pathways have been implicated in the risk for AMD, complement activation has been emphasized repeatedly throughout the literature as having a major role both physiologically and genetically in susceptibility to and pathogenesis of this disease. This article explores the research efforts that brought about the discovery and characterization of the role of inflammatory and immune processes (specifically complement) in AMD. The focus herein is on the genetic evidence for the role of complement in AMD as supported specifically by genome-wide association (GWA) studies, which interrogate hundreds of thousands of variants across the genome in a hypothesis-free approach, and other genetic interrogation methods.

Non-synonymous single nucleotide polymorphisms in the P2X receptor genes: association with diseases, impact on receptor functions and potential use as diagnosis biomarkers

P2X receptors are Ca2+-permeable cationic channels in the cell membranes, where they play an important role in mediating a diversity of physiological and pathophysiological functions of extracellular ATP. Mammalian cells express seven P2X receptor genes. Single nucleotide polymorphisms (SNPs) are widespread in the P2RX genes encoding the human P2X receptors, particularly the human P2X7 receptor. This article will provide an overview of the non-synonymous SNPs (NS-SNPs) that have been associated with or implicated in altering the susceptibility to pathologies or disease conditions, and discuss the consequences of the mutations resulting from such NS-SNPs on the receptor functions. Disease-associated NS-SNPs in the P2RX genes have been valuable in understanding the disease etiology and the receptor function, and are promising as biomarkers to be used for the diagnosis and development of stratified therapeutics.

Human CNS immune senescence and neurodegeneration

Microglial cells comprising the brain's immune system are essential for ensuring neuroprotection in the normal and pathological CNS. On the basis of histopathological observations in human brain, we believe that the ability of microglia to provide neuroprotection deteriorates as our brains get older and that such CNS immune senescence is a major factor contributing to the development of aging-related neurodegenerative diseases, notably Alzheimer's disease. The idea is consistent with the fact that immune senescence occurs naturally in the periphery, rendering the elderly people more susceptible to infections and cancers. There is an analogous situation in the brain, except that here the main impact comes down to diminished neuroprotection and resultant neurodegeneration.

Exaggerated renal fibrosis in P2X4 receptor-deficient mice following unilateral ureteric obstruction

Background

The ATP-sensitive P2X7 receptor (P2X7R) has been shown to contribute to renal injury in nephrotoxic nephritis, a rodent model of acute glomerulonephritis, and in unilateral ureteric obstruction (UUO), a rodent model of chronic interstitial inflammation and fibrosis. Renal tubular cells, endothelial cells and macrophages also express the closely related P2X4 receptor (P2X4R), which is chromosomally co-located with P2X7R and has 40% homology; it is also pro-inflammatory and has been shown to interact with P2X7R to modulate its pro-apoptotic and pro-inflammatory effects. Therefore, we chose to explore the function of P2X4R in the UUO model of renal injury using knockout mice. We hypothesized that UUO-induced tubulointerstitial damage and fibrosis would also be attenuated in P2X4R^−/− mice.

Method

P2X4R^−/− and wild-type (WT) mice were subjected to either UUO or sham operation. Kidney samples taken on Days 7 and 14 were evaluated for renal inflammation and fibrosis, and expression of pro-fibrotic factors.

Results

To our surprise, the obstructed kidney in P2X4R^−/− mice showed more severe renal injury, more collagen deposition (picrosirius red staining, increase of 53%; P < 0.05) and more type I collagen staining (increase of 107%; P < 0.01), as well as increased mRNA for TGF-β (increase of 102%, P < 0.0005) and CTGF (increase of 157%; P < 0.05) by Day 14, compared with the UUO WT mice.

Conclusion

These findings showed that lack of P2X4R expression leads to increased renal fibrosis, and increased expression of TGF-β and CTGF in the UUO model.