Summary

End-stage ankle OA synovium samples demonstrated a unique transcriptomic signature as compared to non-OA samples.

Abstract

Introduction

Osteoarthritis (OA) of the ankle is a prevalent and debilitating condition that impacts millions of people and typically results from injury. However, current treatment strategies are focused on symptom management only and little is known about the cellular and gene level drivers of disease progression. Current literature has reported synovium specific findings in OA, but a clear understanding of its contribution to OA has not been established. The objective of the study was to use RNA-sequencing of synovium from OA and non-OA ankles to characterize the synovial transcriptome, and assess patient reported outcomes (PROs) of the cohort. We compared gene expression patterns in both OA and non-OA ankles to investigate alterations specific to ankle OA.

Methods

Patients undergoing surgery for end stage ankle OA and patients undergoing arthroscopic surgery for non-OA conditions, were consented, samples harvested during surgery, and affected joint was scored using the Outerbridge scoring classification. PROs were collected from patients preoperatively and at 3, 6, and 12 months post operatively. PROMIS Physical Function (PF), Pain Interference (PI), Depression, Foot and Ankle SANE, Global Mental Health, and Global Physical Health scores were collected. Bulk 150 bp, paired-end RNA seq was performed using the Illumina NovaSeq6000 platform, and alignments made to Human Reference genome (GRCh38/hg38) using Hisat2 (v2.0.5). Adjustment using a scaling normalization factor and P-values were corrected using the Benjamini Hochberg method prior to differential expression was determined using the edgeR (3.22.5) package for R. Differences in PRO outcomes between non-OA and end-stage OA patients were determined non-parametrically using Mann-Whitney U tests.

Results

Synovial samples from 30 end stage ankle OA and 31 from non-OA were used for analysis. Clear clustering of OA and non-OA samples were observed on principal component analysis. Functional enrichment analyses displayed enrichment in genes and pathways related to the extracellular matrix (ECM) and its organization, and collagen formation and degradation in the OA samples. Preoperative Foot and Ankle SANE (p=2.75X10-5), PF (p=0.027), and PI (p=0.011) were significantly worse in the OA subjects compared to the non-OA subjects. The increases in foot and ankle SANE scores from pre-op to most recent follow-up were significant in both the OA (p=0.001) and non-OA (p=0.02) groups.

Conclusion

Synovium samples from end-stage OA display a unique transcriptomic signature from non-OA. We identified an upregulation in genes and pathways related to gene expression and macromolecule processing in OA samples. Knowledge of specific cellular changes in OA tissues is crucial, as it identifies potential mechanisms of disease progression and targets for future disease modifying therapies. End-stage ankle OA patients demonstrated worse pre-operative PROs compared to the non-OA cohort, however no significant difference was observed at six months post-op. Further investigations of specific epigenetic signals associated with ankle OA may lead to therapeutic pathways mitigating OA following ankle injury.