title: Complement alternative pathway activation in human nonalcoholic steatohepatitis.
abstract: The innate immune system plays a major role in the pathogenesis of nonalcoholic steatohepatitis (NASH). Recently we reported complement activation in human NASH. However, it remained unclear whether the alternative pathway of complement, which amplifies C3 activation and which is frequently associated with pathological complement activation leading to disease, was involved. Here, alternative pathway components were investigated in liver biopsies of obese subjects with healthy livers (n = 10) or with NASH (n = 12) using quantitative PCR, Western blotting, and immunofluorescence staining. Properdin accumulated in areas where neutrophils surrounded steatotic hepatocytes, and colocalized with the C3 activation product C3c. C3 activation status as expressed by the C3c/native C3 ratio was 2.6-fold higher (p<0.01) in subjects with NASH despite reduced native C3 concentrations (0.94±0.12 vs. 0.57±0.09; p<0.01). Hepatic properdin levels positively correlated with levels of C3c (rs = 0.69; p<0.05) and C3c/C3 activation ratio (rs = 0.59; p<0.05). C3c, C3 activation status (C3c/C3 ratio) and properdin levels increased with higher lobular inflammation scores as determined according to the Kleiner classification (C3c: p<0.01, C3c/C3 ratio: p<0.05, properdin: p<0.05). Hepatic mRNA expression of factor B and factor D did not differ between subjects with healthy livers and subjects with NASH (factor B: 1.00±0.19 vs. 0.71±0.07, p = 0.26; factor D: 1.00±0.21 vs. 0.66±0.14, p = 0.29;). Hepatic mRNA and protein levels of Decay Accelerating Factor tended to be increased in subjects with NASH (mRNA: 1.00±0.14 vs. 2.37±0.72; p = 0.22; protein: 0.51±0.11 vs. 1.97±0.67; p = 0.28). In contrast, factor H mRNA was downregulated in patients with NASH (1.00±0.09 vs. 0.71±0.06; p<0.05) and a similar trend was observed with hepatic protein levels (1.12±0.16 vs. 0.78±0.07; p = 0.08). Collectively, these data suggest a role for alternative pathway activation in driving hepatic inflammation in NASH. Therefore, alternative pathway factors may be considered attractive targets for treating NASH by inhibiting complement activation.
authors.affiliation: Department of General Surgery, Maastricht University Medical Centre+, Maastricht, the Netherlands.
authors.forename: Filip M
authors.initials: FM
authors.lastname: Segers
authors.affiliation: Department of General Surgery, Maastricht University Medical Centre+, Maastricht, the Netherlands.
authors.forename: Froukje J
authors.initials: FJ
authors.lastname: Verdam
authors.affiliation: Department of General Surgery, Maastricht University Medical Centre+, Maastricht, the Netherlands; Department of Surgery, Atrium Medical Centre Parkstad, Heerlen, the Netherlands.
authors.forename: Charlotte
authors.initials: C
authors.lastname: de Jonge
authors.affiliation: Department of General Surgery, Maastricht University Medical Centre+, Maastricht, the Netherlands.
authors.forename: Bas
authors.initials: B
authors.lastname: Boonen
authors.affiliation: Department of Pathology, Maastricht University Medical Centre+, Maastricht, the Netherlands.
authors.forename: Ann
authors.initials: A
authors.lastname: Driessen
authors.affiliation: Department of Genetics and Cell Biology, Maastricht University Medical Centre+, Maastricht, the Netherlands.
authors.forename: Ronit
authors.initials: R
authors.lastname: Shiri-Sverdlov
authors.affiliation: Department of General Surgery, Maastricht University Medical Centre+, Maastricht, the Netherlands.
authors.forename: Nicole D
authors.initials: ND
authors.lastname: Bouvy
authors.affiliation: Department of Surgery, Atrium Medical Centre Parkstad, Heerlen, the Netherlands.
authors.forename: Jan Willem M
authors.initials: JW
authors.lastname: Greve
authors.affiliation: Department of General Surgery, Maastricht University Medical Centre+, Maastricht, the Netherlands.
authors.forename: Wim A
authors.initials: WA
authors.lastname: Buurman
authors.affiliation: Department of General Surgery, Maastricht University Medical Centre+, Maastricht, the Netherlands.
authors.forename: Sander S
authors.initials: SS
authors.lastname: Rensen
mesh_terms: D000328:Adult; D001706:Biopsy; D003176:Complement C3 / Q000378:metabolism*; D050577:Complement C3-C5 Convertases / Q000378:metabolism; D011415:Complement Factor B / Q000378:metabolism; D011416:Complement Factor D; D017242:Complement Factor H / Q000378:metabolism; D003170:Complement Pathway, Alternative / Q000235:genetics*; D005786:Gene Expression Regulation; D006801:Humans; D007249:Inflammation / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D008099:Liver / Q000378:metabolism* / Q000473:pathology; D065626:Non-alcoholic Fatty Liver Disease / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D011414:Properdin / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis
chemical_list: D003176:Complement C3; D012333:RNA, Messenger; D011414:Properdin; D017242:Complement Factor H; D050577:Complement C3-C5 Convertases; D011416:Complement Factor D; D011415:Complement Factor B