Session Type: ACR Poster Session B
Session Time: 9:00AM-11:00AM
Background/Purpose: Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by immune complex- deposition in the synovium, leading to increased bone destruction. In RA, joint destruction has been associated with high cholesterol levels, largely transported in low density lipoprotein (LDL) particles and enhanced LDL oxidation (oxLDL). Apolipoprotein E (Apo E) is an important regulator of LDL transportation and its absence strongly elevates LDL levels in the serum, which may lead to increased oxLDL levels during inflammation. In this study, we investigated the effects of high LDL levels on bone destruction during antigen-induced arthritis (AIA), which is largely immune complex driven and how increased LDL/oxLDL levels affect osteoclast formation.
Methods: AIA was induced by injection of methylated BSA (mBSA) into the right knee joint of Apo E-/- and wild type (WT) control mice previously immunized with mBSA and complete Freund’s adjuvant (CFA). WT and ApoE -/- Hoxb8 myeloid precursor cells were differentiated into osteoclasts using 20 ng/mL RANKL and 30 ng/mL M-CSF, then stimulated for 24h with 10 µg/mL LDL/oxLDL. Oil Red O staining was performed to assess lipid uptake by osteoclasts. mRNA levels of NFATc1, DC-STAMP, TRAP, CTR and Cat K were measured by qPCR, whereas TRAP activity in culture supernatants was detected using a spectrophotometric assay. Bone erosion was quantified by histological analysis using an arbitrary scale from 0 to 3 and TRAP+ cells were determined using immunohistochemistry.
Results: Apo E-/- mice showed significantly higher LDL serum levels than WT controls. Histology showed that at day 21 after AIA induction, bone destruction was significantly decreased in the Apo E-/- mice, as indicated by the reduction of erosion pits (25% reduction from 1.5±0.2 to 1.1 ±0.1). ). In line with that, ApoE-/- mice showed a lower number of osteoclasts within the knee joints (36% lower from 20±4 osteoclasts/section in WT mice to 12±5 in ApoE-/- mice), as determined by image analysis of TRAP staining. To study the role of ApoE and high LDL levels on osteoclastogenesis in more detail, we differentiated WT and ApoE-/- myeloid precursor cells (Hoxb8) into osteoclasts and found similar mRNA levels of osteoclast markers. Whereas the number of osteoclasts was comparable between WT and ApoE-/- osteoclasts, we observed significantly decreased mRNA expression of TRAP (2.6 fold decrease) in ApoE-/- cells as compared to WT cells. In line with this, TRAP activity was reduced by 49%, suggesting a decreased osteoclast activity in ApoE-/- cells. Stimulation of osteoclasts by oxLDL strongly impaired cell fusion keeping them in a mononuclear state. mRNA levels of DC-STAMP were significantly down-regulated in both WT and ApoE-/- osteoclasts (1.4 and 2.3 fold decrease, respectively) as well as TRAP activity (49% and 58% reduction in WT and ApoE-/- osteoclasts, respectively), indicating a major role of oxLDL in the inhibition of osteoclastogenesis.
Conclusion: High LDL/oxLDL levels by apoE deficiency affect bone destruction by reducing the number of osteoclasts within the synovium during AIA probably by interfering osteoclastogenesis.
To cite this abstract in AMA style:Ascone G, Di Ceglie I, Blom AB, Walgreen B, Sloetjes AW, van der Kraan PM, Lindhout E, Martens M, van Lent PL. High Cholesterol Levels By ApoE Defenciency Reduce Bone Destruction in Murine Antigen-Induced Arthritis Via Inhibition of Osteoclastogenesis [abstract]. Arthritis Rheumatol. 2017; 69 (suppl 10). https://acrabstracts.org/abstract/high-cholesterol-levels-by-apoe-defenciency-reduce-bone-destruction-in-murine-antigen-induced-arthritis-via-inhibition-of-osteoclastogenesis/. Accessed September 19, 2021.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/high-cholesterol-levels-by-apoe-defenciency-reduce-bone-destruction-in-murine-antigen-induced-arthritis-via-inhibition-of-osteoclastogenesis/