Semi-Quantitative Multiplex Profiling of the Complement System Identifies Associations of Complement Proteins with Genetic Variants and Metabolites in Age-Related Macular Degeneration

Abstract

Age-related macular degeneration (AMD) is a major cause of vision loss among the elderly in the Western world. The complement system has been identified as one of the main AMD disease pathways. We performed a comprehensive expression analysis of 32 complement proteins in plasma samples of 255 AMD patients and 221 control individuals using mass spectrometry-based semi-quantitative multiplex profiling. We detected significant associations of complement protein levels with age, sex and body-mass index (BMI), and potential associations of C-reactive protein, factor H related-2 (FHR-2) and collectin-11 with AMD. In addition, we confirmed previously described associations and identified new associations of AMD variants with complement levels. New associations include increased C4 levels for rs181705462 at the C2/CFB locus, decreased vitronectin (VTN) levels for rs11080055 at the TMEM97/VTN locus and decreased factor I levels for rs10033900 at the CFI locus. Finally, we detected significant associations between AMD-associated metabolites and complement proteins in plasma. The most significant complement-metabolite associations included increased high density lipoprotein (HDL) subparticle levels with decreased C3, factor H (FH) and VTN levels. The results of our study indicate that demographic factors, genetic variants and circulating metabolites are associated with complement protein components. We suggest that these factors should be considered to design personalized treatment approaches and to increase the success of clinical trials targeting the complement system.

A peptide dataset for target analysis of human complement system proteins

“…Although the data were not obtained from a cohort analysis, the determined protein concentrations reflect a strong alignment with existing literature values. These data reinforce and complement the importance of investigating these targets in view of their association with infectious [5] and degenerative [6] diseases, among others [7] , since both previously investigated peptides and new targets are mentioned in this study.…”

Genetic variability shapes the alternative pathway complement activity and predisposition to complement‐related diseases

“…As an effort to correlate disease associations with gene expression and to provide an explanation about how disease-associated SNPs located in these non-coding regions cause phenotypic changes, a number of recent studies have explored the contribution of these AMD-associated variants to modulate expression of complement genes, in plasma, liver and retinal cells and tissue, [124][125][126][127] stablishing a correlation between some of these SNPs with complement F I G U R E 6 Combinations of common variations in C3, FB, and FH dramatically alter AP activity. A, Figure depicts the functional analysis of the common variants in C3, FB, and FH that have been found associated with increased risk to AMD.…”

“…Since 2005, numerous GWAS studies have been carried out trying to delineate the genetic predisposition to AMD which has resulted in the identification of numerous SNPs conferring risk or protection to the disease located in intronic or intragenic regions. As an effort to correlate disease associations with gene expression and to provide an explanation about how disease‐associated SNPs located in these non‐coding regions cause phenotypic changes, a number of recent studies have explored the contribution of these AMD‐associated variants to modulate expression of complement genes, in plasma, liver and retinal cells and tissue, 124 , 125 , 126 , 127 stablishing a correlation between some of these SNPs with complement expression levels. One of the most significant of these correlations is that of rs6677604, 128 which is protective in AMD with the protective allele in strong LD with Δ CFHR3‐CFHR1 and, obviously, correlate with decreased expression of the FHR‐1 and FHR‐3 proteins.…”

“…For example, the AMD risk‐conferring variant rs570618[T] is associated with increased FHR‐1, FHR‐2, FHR‐3, and FHR‐4 levels, while the AMD‐protective variant rs10922109[A] is associated with decreased FHR‐1, FHR‐2, FHR‐3, and FHR‐4 levels (Figure 2 ). 82 , 129 , 130 Additional SNPs associated with AMD that have been shown to influence expression levels of complement proteins are the Leu9His (rs4151667) variant in the CFB gene, which is associated with reduced FB levels and it is protective for AMD, 131 , 132 and Gly119Arg (rs141853578) 133 and rs10033900 124 , 134 in the CFI gene that reduce FI levels and confers risk for AMD.…”

Age-Related Macular Degeneration and Diabetic Retinopathy

“…Finally, Acar et al report that multiplex profiling of complement proteins, demographic, factors, genetic variants, and systemic metabolites are correlated in patients with AMD. This holistic approach is exciting as it may ultimately provide clinicians with more options when treating patients [13].…”