Single-Cell RNA-Seq Reveals Transcriptomic Heterogeneity and Post-Traumatic Osteoarthritis-Associated Early Molecular Changes in Mouse Articular Chondrocytes.

Aimy Sebastian,Nicholas R Hum,Stephen P Wilson,Deepa K Murugesh,Jillian L Mccool,Gabriela G Loots,Blaine A Christiansen

doi:10.3390/cells10061462

Abstract

Articular cartilage is a connective tissue lining the surfaces of synovial joints. When the cartilage severely wears down, it leads to osteoarthritis (OA), a debilitating disease that affects millions of people globally. The articular cartilage is composed of a dense extracellular matrix (ECM) with a sparse distribution of chondrocytes with varying morphology and potentially different functions. Elucidating the molecular and functional profiles of various chondrocyte subtypes and understanding the interplay between these chondrocyte subtypes and other cell types in the joint will greatly expand our understanding of joint biology and OA pathology. Although recent advances in high-throughput OMICS technologies have enabled molecular-level characterization of tissues and organs at an unprecedented resolution, thorough molecular profiling of articular chondrocytes has not yet been undertaken, which may be in part due to the technical difficulties in isolating chondrocytes from dense cartilage ECM. In this study, we profiled articular cartilage from healthy and injured mouse knee joints at a single-cell resolution and identified nine chondrocyte subtypes with distinct molecular profiles and injury-induced early molecular changes in these chondrocytes. We also compared mouse chondrocyte subpopulations to human chondrocytes and evaluated the extent of molecular similarity between mice and humans. This work expands our view of chondrocyte heterogeneity and rapid molecular changes in chondrocyte populations in response to joint trauma and highlights potential mechanisms that trigger cartilage degeneration.

Highlights

Introduction iationsOsteoarthritis (OA) is a degenerative joint disorder that affects more than 300 million people worldwide, often resulting in diminished quality of life and disability [1,2]
About 1 mm wide articular cartilage tissue was dissected from the ends of tibia and femora, enzymatically digested to a single cell suspension, and depleted of immune and blood cells to obtain a chondrocyte-enriched (CD45− ; Ter119− ) cell fraction that was subjected to sequencing (Figure 1A)
Considerable efforts have been invested in understanding joint biology and pathophysiology of OA, using joint tissues from both human patients and animal models

Summary

Introduction

Osteoarthritis (OA) is a degenerative joint disorder that affects more than 300 million people worldwide, often resulting in diminished quality of life and disability [1,2]. OA prevalence is on the rise and the Center for Disease Control estimates that as many as 78 million Americans (or one in four) will suffer from OA by 2040, an in-depth understanding of the joint microarchitecture and molecular mechanisms that contribute to OA initiation and progression is still in its infancy [1]. The lack of sufficient progress in this area has severely hindered the development of effective therapeutic approaches for the early diagnosis, prevention, and treatment of OA. The knee joint is a complex structure composed of several tissues including articular cartilage, synovial membrane, joint capsule, menisci, subchondral bone, infrapatellar and suprapatellar fat pads, and tensile connective tissues including tendons and ligaments [3].

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