Gene Transcription in End Stage Ankle Osteoarthritis Differs Markedly From Knee Arthritis and Non- Arthritic Ankles
Authors: Buckley Sara E. , Hamati Mary C. , Hewitt Michael A. , Ackert-Bicknell Cheryl L. , Zuscik Michael J. , Metzl Joshua A. , Moon Daniel K. , Hunt Kenneth J. 
Published: November 2022

Category: Ankle Arthritis; Arthroscopy; Basic Sciences/Biologics; Trauma Introduction/Purpose: Post-traumatic Osteoarthritis (OA) of the ankle is a debilitating condition that impacts millions of people. However, little is known about the genetic and epigenetic risk factors for progression to OA following injury. In order to better understand these factors, a thorough knowledge of the molecular signature in ankle OA relative to non-arthritic ankles is critical. The objective of this study was to perform RNA-sequencing of ankle joint synovial samples from OA and non-OA ankles to better characterize the synovial transcriptome. We compared synovial gene expression patterns in patients with end-stage OA with ankle synovium from non-OA ankles to investigate the unique biological pathways altered in ankle OA. Methods: Patients undergoing total ankle arthroplasty or ankle arthrodesis for end stage OA and patients undergoing ankle arthroscopic surgery for non-arthritic conditions (negative control), were consented for participation. Patients with immune disorders or inflammatory arthropathies were excluded. Patient demographics and medical history were collected. Synovial samples were harvested during surgery and RNA was isolated. Bulk 150 bp, paired-end RNA seq was performed using the Illumina NovaSeq6000 platform. Differential expression was determined using the edgeR (v3.16.5) package for R, after adjustment using a scaling normalization factor and P-values were corrected using the Benjamini Hochberg method. Similarities between samples were determined using Spearman Correlation and degree of similarity was visualized considering the first three Principal Components. Gene Ontology terms were identified to classify gene properties. Results: A total of 8 synovial samples from total ankle OA and 24 synovial samples from ankle non-OA were available for analysis. We found 808 genes uniquely expressed in OA synovium and another 786 different genes expressed in synovium from the control group. GO enrichment term analysis revealed an upregulation in endomembrane system organization, ubiquitin system/proteasomal degradation, and membrane transport processes including cytoskeletal, endosomal, and vacuolar in ankle OA samples compared to controls (Figure 1). These signatures differ from those previously identified in knee OA. Reactome analysis revealed pathways to those previously identified in OA of other joints, including TGF-beta signaling modulation. However, several signatures unique to ankle OA included extracellular matrix organization, integrin signaling, and AKT signaling modulation, among others. In addition, unlike in knee OA, reactome analyses of ankle OA synovium did not present with an inflammatory component associated with M1 macrophage infiltration. Conclusion: Ankle synovium in patients with end-stage ankle OA exhibit a transcriptomic signature distinct from ankle synovium collected from non-OA patients. More intriguing, we find that the ankle OA synovial transcriptome signature is distinct from previously published datasets studying synovium from patients with OA in other joints, particularly the knee. GO term and Reactome analyses identified signatures in bulk membrane transport, proteasome, matrix organization, integrin signaling, and AKT signaling, which are different from phenotypes previously reported in the knee. We conclude that development of effective disease modifying treatments for OA require attention to joint-specific biology and disease progression.