Cell and Transcriptomic Diversity of Infrapatellar Fat Pad during Knee Osteoarthritis

Abstract Objectives In this study, we employ a multi-omic approach to identify major cell types and subsets, and their transcriptomic profiles within the infrapatellar fat pad (IFP), and to determine differences in the IFP based on knee osteoarthritis (KOA), sex, and obesity status. Methods Single-nucleus RNA sequencing of 82,924 nuclei from 21 IFPs (n=6 healthy control and n=15 KOA donors), spatial transcriptomics and bioinformatic analysis were used to identify contributions of the IFP to KOA. We mapped cell subclusters from other white adipose tissues using publicly available literature. The diversity of fibroblasts within the IFP was investigated by bioinformatic analyses, comparing by KOA, sex, and obesity status. Metabolomics was used to further explore differences in fibroblasts by obesity status. Results We identified multiple subclusters of fibroblasts, macrophages, adipocytes, and endothelial cells with unique transcriptomic profiles. Using spatial transcriptomics, we resolved distributions of cell types and their transcriptomic profiles, and computationally identified putative cell-cell communication networks. Furthermore, we identified transcriptomic differences in fibroblasts from KOA versus healthy control donor IFPs, female versus male KOA-IFPs, and obese versus normal body mass index (BMI) KOA-IFPs. Finally, using metabolomics, we defined differences in metabolite levels in supernatants of naïve, profibrotic- and proinflammatory stimuli-treated fibroblasts from obese compared to normal BMI KOA-IFP. Conclusions Overall, by employing a multi-omic approach, this study provides the first comprehensive map of cellular and transcriptomic diversity of human IFP and identifies IFP fibroblasts as a key cell type contributing to transcriptomic and metabolic differences related to KOA disease, sex, or obesity.