M.P.J. de Winther

Disruption of the Cathepsin K Gene Reduces Atherosclerosis Progression and Induces Plaque Fibrosis but Accelerates Macrophage Foam Cell Formation

Background— Cathepsin K (catK), a lysosomal cysteine protease, was identified in a gene-profiling experiment that compared human early plaques, advanced stable plaques, and advanced atherosclerotic plaques containing a thrombus, where it was highly upregulated in advanced stable plaques. Methods and Results— To assess the function of catK in atherosclerosis, catK−/−/apolipoprotein (apo) E−/− mice were generated. At 26 weeks of age, plaque area in the catK−/−/apoE−/− mice was reduced (41.8%) owing to a decrease in the number of advanced lesions as well as a decrease in individual advanced plaque area. This suggests an important role for catK in atherosclerosis progression. Advanced plaques of catK−/−/apoE−/− mice showed an increase in collagen content. Medial elastin fibers were less prone to rupture than those of apoE−/− mice. Although the relative macrophage content did not differ, individual macrophage size increased. In vitro studies of bone marrow derived–macrophages confirmed this observation. Scavenger receptor–mediated uptake (particularly by CD36) of modified LDL increased in the absence of catK, resulting in an increased macrophage size because of increased cellular storage of cholesterol esters, thereby enlarging the lysosomes. Conclusions— A deficiency of catK reduces plaque progression and induces plaque fibrosis but aggravates macrophage foam cell formation in atherosclerosis.

Scavenger receptor class A type I/II determines matrix metalloproteinase-mediated cartilage destruction and chondrocyte death in antigen-induced arthritis

OBJECTIVE Scavenger receptor class A type I (SR-AI) and SR-AII are expressed by macrophages in particular and bind and internalize a broad range of molecules (including endotoxins, apoptotic bodies, and oxidized low-density lipoprotein). This study was undertaken to investigate the role of SR-AI/II in mediating severe cartilage destruction in antigen-induced arthritis (AIA). METHODS AIA was induced in the knee joints of SR-AI/II(-/-) mice and wild-type (WT) controls. Joint inflammation and cartilage destruction (chondrocyte death) were measured by examining the histology of total knee joints. Matrix metalloproteinase (MMP)-mediated neoepitopes were measured by immunolocalization using anti-VDIPEN antibodies and chondrocyte activation with anti-S100A8 antibodies. Messenger RNA (mRNA) levels were determined in inflamed synovium using microarray analysis and quantitative reverse transcriptase-polymerase chain reaction. In synovial washouts, cytokines (interleukin-1beta [IL-1beta], IL-10, and tumor necrosis factor alpha) and S100A8/S100A9 were measured using Luminex and enzyme-linked immunosorbent assay. RESULTS Levels of SR-AI/II mRNA were strongly elevated in inflamed synovium in AIA. On days 2, 8, and 14 after AIA induction, joint inflammation (exudates/infiltrate) was similar between the 2 groups. In WT mice, severe cartilage destruction was found in multiple cartilage surfaces of the inflamed knee joint on day 14 after AIA induction. MMP-mediated matrix destruction ranged between 40% and 60%, and chondrocyte death was prominent in 40-75% of the cartilage surfaces. In striking contrast, in SR-AI/II(-/-) mice, despite comparable joint inflammation, pronounced cartilage destruction was almost completely absent. Levels of IL-1beta and S100A8/S100A9 were significantly lower on days 7 and 14 after AIA induction, but levels of mRNA for various MMPs (MMP-2, MMP-3, MMP-9, and MMP-13) were comparable. CONCLUSION Our findings indicate that SR-AI and SR-AII are crucial receptors involved in mediating severe cartilage destruction in AIA.

IgG is elevated in obese white adipose tissue but does not induce glucose intolerance via Fc gamma-receptor or complement

Background/Objectives:In obesity, B cells accumulate in white adipose tissue (WAT) and produce IgG, which may contribute to the development of glucose intolerance. IgG signals by binding to Fcγ receptors (FcγR) and by activating the complement system. The aim of our study was to investigate whether activation of FcγR and/or complement C3 mediates the development of high-fat diet-induced glucose intolerance.Methods:We studied mice lacking all four FcγRs (FcγRI/II/III/IV−/−), only the inhibitory FcγRIIb (FcγRIIb−/−), only the central component of the complement system C3 (C3−/−), and mice lacking both FcγRs and C3 (FcγRI/II/III/IV/C3−/−). All mouse models and wild-type controls were fed a high-fat diet (HFD) for 15 weeks to induce obesity. Glucose metabolism was assessed and adipose tissue was characterized for inflammation and adipocyte functionality.Results:In obese WAT of wild-type mice, B cells (+142%, P<0.01) and IgG (+128% P<0.01) were increased compared to lean WAT. Macrophages of FcγRI/II/III/IV−/−mice released lower levels of cytokines compared to wild-type mice upon IgG stimulation. Only C3−/− mice showed reduced HFD-induced weight gain as compared to controls (−18%, P<0.01). Surprisingly, FcγRI/II/III/IV−/− mice had deteriorated glucose tolerance (AUC +125%, P<0.001) despite reduced leukocyte number (−30%, P<0.05) in gonadal WAT (gWAT), whereas glucose tolerance and leukocytes within gWAT in the other models were unaffected compared to controls. Although IgG in gWAT was increased (+44 to +174%, P<0.05) in all mouse models lacking FcγRIIb, only FcγRI/II/III/IV/C3−/− mice exhibited appreciable alterations in immune cells in gWAT, for example, increased macrophages (+36%, P<0.001).Conclusions:Lack of FcγRs reduces the activity of macrophages upon IgG stimulation, but neither FcγR nor C3 deficiency protects against HFD-induced glucose intolerance or reduces adipose tissue inflammation. This indicates that if obesity-induced IgG contributes to the development of glucose intolerance, this is not mediated by FcγR or complement activation.