Pathophysiology/Complications BMJ Open Diab Res Care: first published as 10.1136/bmjdrc-2019-001026 on 28 April 2020. Downloaded from Open access Original research Association of the IgG N- glycome with the course of kidney function in type 2 diabetes Sunny S Singh,1 Ralph Heijmans,1 Claudia K E Meulen,1 Aloysius G Lieverse,2 Olga Gornik,3 Eric J G Sijbrands,1 Gordan Lauc,3 Mandy van Hoek 1 To cite: Singh SS, Heijmans R, ABSTRACT Meulen CKE, et al. Association Introduction Inflammatory processes are thought to Significance of this study of the IgG N- glycome be involved in kidney function decline in individuals with the course of kidney with type 2 diabetes. Glycosylation of immunoglobulin G What is already known about this subject? function in type 2 diabetes. (IgG) is an important post- translation process affecting ► Inflammatory processes play a role in chronic kidney BMJ Open Diab Res Care disease in type 2 diabetes. 2020; :e001026. doi:10.1136/ the inflammatory potential of IgG. We investigated the 8 ► The variation in glycan sugar residues attached to bmjdrc-2019-001026 prospective relationship between IgG N- glycosylation patterns and kidney function in type 2 diabetes. the conserved glycosylation sites of the immuno- Research design and methods In the DiaGene study, globulin G (IgG) Fc part influences IgG effector func- ► Additional material is an all-lines- of- care case–control study (n=1886) with tion, modulating the immune response from either published online only. To view mean prospective follow- up of 7.0 years, the association pro- inflammatory to an anti- inflammatory response please visit the journal online between 58 IgG N- glycan profiles and estimated or vice versa. (http:// dx. doi. org/ 10. 1136/ glomerular filtration rate (eGFR) and albumin- to- creatinine ► The link between IgG glycosylation and renal func- bmjdrc- 2019- 001026). ratio (ACR) per year and during total follow- up was tion in type 2 diabetes has never been investigated. analyzed. Models were adjusted for clinical variables and What are the new findings? Received 4 November 2019 multiple comparisons. ► We found pro- inflammatory IgG N- glycosylation Results Eleven traits were significantly associated with Revised 5 March 2020 patterns associated with a faster decline of kidney Accepted 6 April 2020 eGFR change per year. Bisecting GlcNAc in fucosylated and function estimated glomerular filtration rate, but not fucosylated disialylated structures and monosialylation of albumin- to- creatinine ratio, possibly representing fucosylated digalactosylated structures were associated renal macroangiopathy. with a faster decrease of eGFR. Fucosylation of neutral and monogalactosylated structures was associated with less How might these results change the focus of eGFR decline per year. No significant associations between research or clinical practice? IgG glycans and ACR were found. http://drc.bmj.com/ ► Our findings suggest the involvement of the immune Conclusions In type 2 diabetes, we found IgG N- system in the pathophysiology of diabetic nephrop- glycosylation patterns associated with a faster decline athy in type 2 diabetes, representing a novel target of kidney function, reflecting a pro- inflammatory state of for future biomarker and therapeutics developments. IgG. eGFR, but not ACR, was associated with IgG glycans, which suggests these associations may represent renal macroangiopathy rather than microvascular disease. post- translational modification of proteins, influencing their function.6 7 N- Glycans affect on September 24, 2021 by guest. Protected copyright. INTRODUCTION the stability, activity and targeting of proteins, Chronic kidney disease (CKD) is one of as well as cell–cell and host–pathogen inter- © Author(s) (or their action.6 7 These complex oligosaccharides employer(s)) 2020. Re- use the most common complications in type 2 permitted under CC BY. diabetes mellitus, despite extensive preven- are assembled by the coordinated action Published by BMJ. tive efforts. Apart from known risk factors, of a range of glycosyltransferases and glyco- 1Internal Medicine, Erasmus a large residual risk remains for developing sidase enzymes, and are attached to the MC, Rotterdam, Zuid- Holland, CKD,1 2 which may be partly explained by nitrogen (N) atom of asparagine side chains Netherlands processes such as inflammation. Biomarkers of proteins within a specific sequon.6 N- Gly- 2Internal Medicine, Maxima Medical Centre, Eindhoven, that provide information, in addition to cosylation patterns of the IgG N- glycome Noord- Brabant, Netherlands known risk factors, can aid in better predic- and total plasma N-glycome have been asso- 3Faculty of Pharmacy and tion and tailored treatment to prevent and ciated with estimated glomerular filtration Biochemistry, University of delay kidney function decline.3 4 rate (eGFR) in non-diabetic individuals and Zagreb, Zagreb, Croatia A growing body of literature recognizes the those with type 1 diabetes.8 9 Furthermore, a Correspondence to association between type 2 diabetes and the cross- sectional study showed that character- 5 Dr Mandy van Hoek; N- linked glycosylation of proteins. N- Linked istic patterns of the total plasma N- glycome m. vanhoek@ erasmusmc. nl glycosylation is a co-translational and are associated with renal function in type 2 BMJ Open Diab Res Care 2020;8:e001026. doi:10.1136/bmjdrc-2019-001026 1 BMJ Open Diab Res Care: first published as 10.1136/bmjdrc-2019-001026 on 28 April 2020. Downloaded from Pathophysiology/Complications diabetes.10 However, the link between the immunoglob- biantennary glycan. Bisecting GlcNac and afucosylated ulin G (IgG) N- glycome and renal function in type 2 N- glycans have a pro- inflammatory effect, while the addi- diabetes patients has never been investigated. Immuno- tion of galactose and sialic acid has an anti-inflammator y globulin G (IgG) is the most abundant antibody in the effect on IgG (figure 1).12 IgG glycosylation patterns human body, involved in infectious and inflammatory are highly variable between individuals, but show good processes through several mechanisms: antigen neutral- temporal stability in a single healthy individual.13 Yet, ization, promotion of phagocytosis, microbial killing via IgG patterns are known to change in a single individual opsonization and macrophage activation, complement because of alterations in a person’s health status.13–15 IgG activation and induction of ADCC (antibody-dependent glycosylation contains a genetic, heritable component, cellular cytotoxicity).11 IgG consist of a fragment antigen as well an environmental component. Because of these binding (Fab) domain and fragment crystallizable features, glycosylation is considered an interface between (Fc) domain, which interacts with Fc gamma receptors genetic background and environment.14 1612 17 18 Because (FcyR). Single biantennary glycans are attached to each type 2 diabetes and chronic kidney disease are multifac- heavy chain on the Fc part asparagine-297 (Asn297). torial diseases displaying features of chronic inflamma- They are essential for binding to the FcyRs. The receptor tion, IgG N- glycosylation is promising as a biomarker, but interaction is lost if no glycans are attached. The varia- also from a pathophysiological perspective.19 tion in glycan sugar residues attached influences IgG We hypothesized that specific IgG-glycan profiles effector function, modulating the immune response prospectively associate with kidney function in type 2 from either pro- inflammatory to an anti- inflammatory diabetes, and could be a potential biomarker in the future response or vice versa. The variations consist of the addi- We, therefore, investigated the prospective relationship tion of bisecting N-acetylglucosamine (GlcNac), fucose to between IgG N- glycosylation and the course of kidney core, as well as galactose and sialic acid to the arms of the function during follow- up in type 2 diabetes individuals. http://drc.bmj.com/ on September 24, 2021 by guest. Protected copyright. Figure 1 Functional implications and inflammatory associations of IgG glycosylation. Dark-gr een spots on IgG molecule are conserved glycosylation sites Asn297 to which biantennary glycans are attached. 2 BMJ Open Diab Res Care 2020;8:e001026. doi:10.1136/bmjdrc-2019-001026 BMJ Open Diab Res Care: first published as 10.1136/bmjdrc-2019-001026 on 28 April 2020. Downloaded from Pathophysiology/Complications RESEARCH DESIGN AND METHODS performed, all IgG glycan traits were centered and scaled Study design to have mean 0 and SD 1. Data were derived from the DiaGene study, and the study characteristics have previously been described in more Glycan nomenclature 20 detail. Briefly, the DiaGene study is a large multicenter A glycan structure formula is described as follows: FAxB- prospective cohort study with 1886 patients with type 2 GxSx. The abbreviations stand for F=fucose, A=antennae, diabetes with prospective follow-up on kidney function B=bisection, G=galactose and S=sialic acid, and x indicates (mean follow- up time=7.0 years). Data were collected the number of the particular feature. When, for example, from two hospitals in and around the city of Eindhoven, F or S is not present in the structure formula, the glycan the Netherlands. In addition, the local primary care diag- has no fucose or sialic acids attached. For some glycans, nostic center participated in the study. All participants for example, GP9 with structure formula FA2[3]G1, [3] provided informed written consent. means the antennae