Unique Patterns of Gene Expression in Equine Articular Chondrocytes

Introduction: The normal repair capacity of articular cartilage is limited, which contributes to the chronic and progressive pathogenesis of osteoarthritis. Repair tissue produced endogenously or generated following the introduction of cell-based therapies is often fibrocartilage in structure, poorly integrated into surrounding healthy tissue, and biomechanically deficient. A detailed understanding of articular chondrocyte gene expression, especially relative to other types of chondrocytes, remains an important knowledge gap limiting efforts to improve articular cartilage repair. The aim of this study is to characterize the mRNA transcriptome of normal articular chondrocytes at different developmental stages. Initial data comparing adult equine articular cartilage to nasal septum cartilage is presented here.

Hypothesis:Chondrocytes in different types of cartilage have unique and tissue-restricted patterns of gene expression.

Methods: Total RNA from paired samples of equine articular cartilage and nasal septum was sequenced. Illumina® paired-end, strand-specific 2x100 bp reads were mapped to the equine reference genome using MapSplice software. Read counts from the two cartilaginous tissues with five biological replicates were compared to identify differentially expressed genes.

Preliminary Results and Discussion: Expression from 16,394 protein coding gene loci was represented in the two tissues. At p-value thresholds of <0.1, <0.05, and <0.01, a total of 7082, 5093, and 2015 gene loci respectively were differentially expressed. Within loci differentially expressed at p<0.01, thresholds reflecting differences in steady-state mRNA levels at 2-fold, 5-fold and 10-fold identified 1648, 713, and 418 gene loci respectively. These data document substantial gene expression differences between these two adult equine cartilaginous tissues.