International Journal of Molecular Sciences Article Complement Components C3 and C4 Indicate Vasculitis Manifestations to Distinct Renal Compartments in ANCA-Associated Glomerulonephritis Samy Hakroush 1 ,Désirée Tampe 2, Peter Korsten 2 , Philipp Ströbel 1 and Björn Tampe 2,* 1 Institute of Pathology, University Medical Center Göttingen, 37075 Göttingen, Germany; [email protected] (S.H.); [email protected] (P.S.) 2 Department of Nephrology and Rheumatology, University Medical Center Göttingen, 37075 Göttingen, Germany; [email protected] (D.T.); [email protected] (P.K.) * Correspondence: [email protected]; Tel.: +49-551-39-10575 Abstract: Acute kidney injury (AKI) is a common and severe complication of antineutrophil cyto- plasmic antibodies (ANCA)-associated vasculitis (AAV) causing progressive chronic kidney disease (CKD), end-stage renal disease (ESRD) or death. Pathogenic ANCAs, in particular proteinase 3 (PR3) and myeloperoxidase (MPO), trigger a deleterious immune response resulting in pauci-immune necrotizing and crescentic glomerulonephritis (GN), a common manifestation of glomerular injury in AAV. However, there is growing evidence that activation of the complement pathway contributes to the pathogenesis and progression of AAV. We here aimed to compare glomerular and tubuloin- Citation: Hakroush, S.; Tampe, D.; terstitial lesions in ANCA GN and extrarenal manifestation of AAV in association with levels of Korsten, P.; Ströbel, P.; Tampe, B. circulating complement components C3c and C4. Methods: Plasma levels of C3c and C4 in a total Complement Components C3 and C4 number of 53 kidney biopsies with ANCA GN were retrospectively included between 2015 and 2020. Indicate Vasculitis Manifestations to Glomerular and tubulointerstitial lesions were evaluated according to established scoring systems for Distinct Renal Compartments in ANCA GN and analogous to the Banff classification. Results: We here show that circulating levels of ANCA-Associated C3c and C4 in ANCA GN were comparable to the majority of other renal pathologies. Furthermore, Glomerulonephritis. Int. J. Mol. Sci. hypocomplementemia was only detectable in a minor subset of ANCA GN and not correlated with 2021, 22, 6588. https://doi.org/ renal or extrarenal AAV manifestations. However, low levels of circulating C3c correlated with AKI 10.3390/ijms22126588 severity in ANCA GN independent of systemic disease activity or extrarenal AAV manifestation. By Academic Editors: Amandeep Bajwa systematic scoring of glomerular and tubulointerstitial lesions, we provide evidence that low levels and Navjot Pabla of circulating C3c and C4 correlated with vasculitis manifestations to distinct renal compartments in ANCA GN. Conclusions: We here expand our current knowledge about distinct complement Received: 25 May 2021 components in association with vasculitis manifestations to different renal compartments in ANCA Accepted: 16 June 2021 GN. While low levels of C4 correlated with glomerulitis, our observation that low levels of circulating Published: 19 June 2021 complement component C3c is associated with interstitial vasculitis manifestation reflected by intimal arteritis implicates that C3c contributes to tubulointerstitial injury in ANCA GN. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in Keywords: acute kidney injury; innate immunity; complement system activation; autoimmune published maps and institutional affil- diseases; systemic vasculitis; ANCA-associated glomerulonephritis iations. 1. Introduction Copyright: © 2021 by the authors. According to the 2012 revised Chapel Hill Consensus Conference Nomenclature of Licensee MDPI, Basel, Switzerland. Vasculitides, antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is This article is an open access article a small vessel vasculitis, most frequently presenting as microscopic polyangiitis (MPA) distributed under the terms and or granulomatosis with polyangiitis (GPA) [1,2]. Acute kidney injury (AKI) is a common conditions of the Creative Commons Attribution (CC BY) license (https:// and severe complication of AAV as it can cause progressive chronic kidney disease (CKD), creativecommons.org/licenses/by/ end-stage renal disease (ESRD) or death [3,4]. Pathogenic ANCAs, in particular proteinase 4.0/). 3 (PR3) and myeloperoxidase (MPO), trigger a deleterious immune response resulting in Int. J. Mol. Sci. 2021, 22, 6588. https://doi.org/10.3390/ijms22126588 https://www.mdpi.com/journal/ijms Int. J. Mol. Sci. 2021, 22, 6588 2 of 15 Int. J. Mol. Sci. 2021, 22, x FOR PEER REVIEW 2 of 16 pauci-immune necrotizing and crescentic glomerulonephritis (GN), a common manifesta- tion of glomerular injury in AAV [5]. Several studies have investigated determinants of 3 (PR3) and myeloperoxidase (MPO), trigger a deleterious immune response resulting in renalpauci-immune outcome necrotizing in ANCA GN,and crescentic including glomerulonephritis baseline kidney function(GN), a common and histopathological manifes- lesionstation of [ 6glomerular,7]. On a injury mechanistic in AAV level,[5]. Several neutrophils studies have are activated investigated by determinants pathogenic ANCAsof causingrenal outcome release in of ANCA inflammatory GN, including cytokines, baseline reactive kidney oxygen function species and andhistopathological lytic enzymes, and resultinglesions [6,7]. in excessive On a mechanistic formation level, of neutrophil neutrophils extracellular are activated traps by (NETs)pathogenic [8– 10ANCAs]. At least in part,causing these release mechanisms of inflammatory underly cytokines, the pathogenicity reactive oxygen of ANCAs species mediating and lytic enzymes, inflammation and and vascularresulting injury.in excessive Disease formation manifestations of neutrophil in the extracellular kidney are traps usually (NETs) characterized [8–10]. At byleast a pauci- immunityin part, these with mechanisms only minor, underly if any, the immunoglobulin pathogenicity of ANCAs and complement mediating inflammation deposition in the vascularand vascular system. injury. In general,Disease manifestations circulating complement in the kidney components are usually C3 characterized and C4 levels by a in AAV arepauci-immunity normal [11]. with However, only minor, there if isany, growing immunoglobulin evidence and that complement activation of deposition the complement in pathwaythe vascular contributes system. In to general, the pathogenesis circulating andcomplement progression components of AAV C3 [12 and–14]. C4 In levels experimental in models,AAV are pauci-immunenormal [11]. However, crescentic there GN is growing correlated evidence with thethat activationactivation of of the the comple- complement systemment pathway [15]. Furthermore, contributes to blocking the pathogenes the alternativeis and progression complement of AAV system [12–14]. resulted In exper- in protec- tionimental from models, crescentic pauci-immune GN, further crescentic supporting GN correlated an important with contributionthe activation ofof thethe alternativecom- complementplement system system [15]. Furthermore, in the pathogenesis blocking of the ANCA alternative GN [ 15complement]. Conversely, system complement resulted C4d in protection from crescentic GN, further supporting an important contribution of the al- has been found in the majority of renal biopsies, implicating that activation of the classical ternative complement system in the pathogenesis of ANCA GN [15]. Conversely, comple- complement system is also relevant in ANCA GN [16]. The mechanistic contribution of the ment C4d has been found in the majority of renal biopsies, implicating that activation of complement system in the pathogenesis of AAV was further substantiated by recent studies the classical complement system is also relevant in ANCA GN [16]. The mechanistic con- thattribution analyzed of the complementcomplement system components in the pathogenesis in different of activity AAV was states further of AAV substantiated [16–22]. This is especiallyby recent studies relevant that since analyzed the use complement of the anti-C5a components receptor in inhibitor different avacopanactivity states has of recently beenAAV shown[16–22]. to This sustain is especially effective relevant remission since in the AAV, use furtherof the anti-C5a supporting receptor the inhibitor importance of theavacopan complement has recently system been in shown the pathogenesis to sustain effective and progressionremission in AAV, of AAV further [23– support-25]. However, systematicing the importance analysis of the activationcomplement of system the complement in the pathogenesis system in and association progression with of distinct clinicalAAV [23–25]. and histopathological However, systematic lesions analysis in ANCAof the activation GN remains of the elusive.complement Therefore, system in we here aimedassociation to compare with distinct glomerular clinical and and histopathological tubulointerstitial lesions lesions in ANCA in ANCA GN remains GN analogous elu- to thesive. Banff Therefore, classification we here andaimed extrarenal to compare manifestation glomerular ofand AAV tubulointerstitial in association lesions with levelsin of circulatingANCA GN complementanalogous to the components Banff classification C3c and and C4. extrarenal manifestation of AAV in association with levels of circulating complement components C3c and C4. 2. Results 2.1.2. Results Description of Demographic