Complement Alternative Pathway Activation in Human Nonalcoholic Steatohepatitis

• Published in: PloS one Vol. 9; no. 10; p. e110053
• Main Authors: Segers, Filip M., Verdam, Froukje J., de Jonge, Charlotte, Boonen, Bas, Driessen, Ann, Shiri-Sverdlov, Ronit, Bouvy, Nicole D., Greve, Jan Willem M., Buurman, Wim A., Rensen, Sander S.
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 09.10.2014; Public Library of Science (PLoS)
• Subjects: Adult; Alternative pathway; Biology and Life Sciences; Biopsy; Cell activation; Complement; Complement activation; Complement C3 - metabolism; Complement C3-C5 Convertases - metabolism; Complement component C3; Complement Factor B - metabolism; Complement Factor D; Complement factor H; Complement Factor H - metabolism; Complement Pathway, Alternative - genetics; Cytokines; Decay-accelerating factor; Diabetes; Gastroenterology; Gastrointestinal surgery; Gene expression; Gene Expression Regulation; Hepatitis; Hepatocytes; Hepatology; Homeostasis; Humans; Immune system; Immunofluorescence; Immunology; Inflammation; Inflammation - genetics; Inflammation - metabolism; Inflammation - physiopathology; Innate immunity; Insulin resistance; Kinases; Lectins; Leukocytes (neutrophilic); Liver; Liver - metabolism; Liver - pathology; Liver diseases; Medicine and Health Sciences; Neutrophils; Non-alcoholic Fatty Liver Disease - genetics; Non-alcoholic Fatty Liver Disease - metabolism; Non-alcoholic Fatty Liver Disease - pathology; Obesity; Pathogenesis; Polymerase chain reaction; Properdin; Properdin - metabolism; Proteins; RNA; RNA, Messenger - biosynthesis; Rodents; Surveillance; TNF inhibitors; Western blotting; United States > US; Netherlands; Baltimore Maryland
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0110053

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.