Session Type: ACR Poster Session C
Session Time: 9:00AM-11:00AM
Background/Purpose: Obesity is associated with the development and progression of osteoarthritis (OA). Although the mechanisms involved in this association are poorly understood, it is well appreciated that obesity-induced changes in adipose tissue could affect whole body metabolism and inflammatory responses through secreted mediators. The infrapatellar fat pad (IFP) is an adipose tissue depot in the knee joint. Due to its intracapsular and extrasynovial localization, it is conceivable that the IFP could contribute to the pathophysiology of OA through release of soluble mediators. However, it is still unclear whether and how the IFP is affected by obesity. Therefore, we set-out to investigate whether obesity-related changes described in other adipose tissue depots can also be found in IFP.
Methods: IFP volume was determined in 83 knee OA patients with MRI using sagittal T1 and T2-weighted images. IFP and subcutaneous adipose tissue (SCAT) were obtained from 76 knee OA patients, all undergoing joint replacement surgery (total N=129: 69% women, mean age 65 years, mean (SD) body mass index (BMI) 29.7 kg/m2 (5.31)). IFP volume was measured by manual segmentation of the IFP boundaries on section-by-section sagittal T1-weighted images, using the software program OsiriX. Sagittal T2-weighted images were used to distinguish and compare between IFP and non-IFP structures. The software program OsiriX measured the IFP volume by making a 3D-model of the drawn contours. Crown-like structures (CLS) were determined using immunohistochemistry. Adipocyte size was determined by light microscopy and histology. Stromal vascular fraction (SVF) cells were characterized by flow cytometry.
Results: The IFP volume determined by MRI associated with gender (B = 0.610, p <0.001) and height (B = 0.692, p < 0.001), but not with BMI. The mean volume of IFP adipocytes was 271 pL and was not correlated with BMI; in contrast, SCAT adipocytes were larger (551 pL) and did correlate with BMI (r = 0.38, p = 0.004). Few CLS were observed in IFP, with no differences between overweight/obese and lean individuals. Moreover, obesity was not associated with higher infiltrating immune cell numbers in IFP. Likewise, the percentage of CD3, CD4, CD8 or CD14 positive cells did not correlate with obesity. Extensive characterization of IFP macrophages revealed that CD206 and CD163, usually associated with an anti-inflammatory phenotype, were the most abundantly expressed surface markers on macrophages (81% and 41 % respectively), but macrophages produced predominantly IL-6 and TNFα, and little IL-10. Interestingly, CD163+ macrophages had an activated and pro-inflammatory phenotype.
Conclusion: In conclusion, we did not find obesity-related changes in IFP regarding IFP volume, adipocyte size and volume, CLS, number and phenotype of infiltrating cells, although we did found obesity-related changes in SCAT. This indicates that IFP is affected differently by obesity than other fat depots such as SCAT and visceral adipose tissue, suggesting that IFP might have a different function than the standard fat depots.
To cite this abstract in AMA style:de Jong A, klein-Wieringa IR, Andersen S, Kwekkeboom J, van Toorn L, de Lange B, van Delft D, Garcia J, Wei W, van der Heide H, Bastiaansen-Jenniskens Y, van Osch G, Zuurmond AM, Stojanovic-Susulic V, Nelissen R, Toes R, Kloppenburg M, Ioan-Facsinay A. Lack of Obesity-Related Changes in Adipocytes and Inflammatory Cells in the Infrapatellar Fat Pad (IFP): A Different Type of Fat? [abstract]. Arthritis Rheumatol. 2016; 68 (suppl 10). https://acrabstracts.org/abstract/lack-of-obesity-related-changes-in-adipocytes-and-inflammatory-cells-in-the-infrapatellar-fat-pad-ifp-a-different-type-of-fat/. Accessed November 11, 2019.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/lack-of-obesity-related-changes-in-adipocytes-and-inflammatory-cells-in-the-infrapatellar-fat-pad-ifp-a-different-type-of-fat/