LRRC15, A POTENTIAL KEY PLAYER IN CARTILAGE OSSIFICATION IN OSTEOARTHRITIS DISEASE

INTRODUCTION

OA is a joint condition characterized by cellular stress and the deterioration of the ECM. Its onset is manifested by both minor and major injuries triggering molecular, anatomical, and physiological disturbances. Minor alterations initiate OA by disrupting chondrocyte equilibrium, promoting an hypertrophic state causing cartilage degeneration by impacting not only cartilage itself but all tissues within the joint.

OBJECTIVE

This study aims to investigate the transcriptional alterations present in the knee joint tissues for both OA patients and healthy individuals, with a focus on identifying potential genes implications for the development of OA and cartilage ossification.

METHODS

We used eight datasets from the NCBI Gene Expression Omnibus and categorize it into three groups: 1) mRNA expression profiling, which contains joint synovial biopsies, cartilage stromal cells and mesenchymal stromal cells, cartilage tissues, and peripheral blood mononuclear cells (PBMC); 2) non-coding RNA (miRNA) profiling, encompassing two synovial membrane datasets and plasma from OA patients; and 3) single-cell sequencing, including synovial membrane and cartilage from the same patients and subchondral bone. An independent differentially expressed genes (DEG) analysis was performed on each dataset using EdgeR and gene ontology was investigated.

RESULTS

Our findings indicated various DEGs in the different tissues, with three upregulated genes (COL1A1, COL11A1, and LRRC15) and six downregulated genes in mRNA datasets after overlapping. For miRNA datasets, two miRNAs were downregulated and only one miRNA was upregulated. Target research revealed that miR-1-3p targets COL1A1, COL11A1, and LRRC15 from one of miRNA. Gene ontology identified structures involved in collagen, cartilage formation, and mechanical response. We used single cell sequencing to identify cell populations in cartilage, synovial membrane, and subchondral bone. COL1A1 was found in all cell types in the synovial membrane, cartilage cells, and subchondral bone chondrocytes. Subchondral bone and cartilage chondrocytes expressed COL11A1, while synovial membrane cells did not. LRRC15 is expressed in synovial fibroblasts, cartilage progenitors, subchondral bone chondrocytes, and cartilage fibrochondrocytes. The heatmap and bar chart analyses supported these findings, demonstrating gene expression differences and correlation scores between the OA and control groups.

CONCLUSIONS

Our results identified LRRC15, COL11A1, and COL1A1 as potential genes that may play a role into the anabolic phenotypic change and disruption of extracellular matrix remodeling, providing an intriguing insight into the change alterations happening in joint tissues during OA. In animal models, LRRC15 has been linked to changes in chondrocyte phenotype, stress response coordination, and ECM degradation. Furthermore, LRRC15 has been discovered as a key regulator of mesenchymal stem cell (MSC) osteogenesis, implying that MSCs undergo osteogenic differentiation rather than chondrogenic differentiation, resulting in cartilage calcification and ossification. These results give an intriguing perspective on the transcriptional alterations happening in joint tissues during OA and will be supplemented by tissue sample collection, allowing continued validation using deep sequencing and RT-PCR.