Comparison of the major cell populations among osteoarthritis, Kashin\u2013Beck disease and healthy chondrocytes by single-cell RNA-seq analysis

Xi Wang,Ruitian Huang,Minhan Hu,Yujie Ning,Cheng Li,Pan Zhang,Rong Zhou,Blandine Poulet,Mikko J Lammi,Yi Gong,Xiong Guo

doi:10.1038/s41419-021-03832-3

Abstract

Chondrocytes are the key target cells of the cartilage degeneration that occurs in Kashin–Beck disease (KBD) and osteoarthritis (OA). However, the heterogeneity of articular cartilage cell types present in KBD and OA patients and healthy controls is still unknown, which has prevented the study of the pathophysiology of the mechanisms underlying the roles of different populations of chondrocytes in the processes leading to KBD and OA. Here, we aimed to identify the transcriptional programmes and all major cell populations in patients with KBD, patients with OA and healthy controls to identify the markers that discriminate among chondrocytes in these three groups. Single-cell RNA sequencing was performed to identify chondrocyte populations and their gene signatures in KBD, OA and healthy cells to investigate their differences as related to the pathogenetic mechanisms of these two osteochondral diseases. We performed immunohistochemistry and quantitative reverse-transcription PCR (qRT-PCR) assays to validate the markers for chondrocyte population. Ten clusters were labelled by cell type according to the expression of previously described markers, and one novel population was identified according to the expression of a new set of markers. The homeostatic and mitochondrial chondrocyte populations, which were identified by the expression of the unknown markers MT1X and MT2A and MT-ND1 and MT-ATP6, were markedly expanded in KBD. The regulatory chondrocyte population, identified by the expression of CHI3L1, was markedly expanded in OA. Our study allows us to better understand the heterogeneity of chondrocytes in KBD and OA and provides new evidence of differences in the pathogenetic mechanisms between these two diseases.

Highlights

IntroductionWang et al Cell Death and Disease (2021)12:551 cellular pathways between Kashin–Beck disease (KBD) and OA chondrocytes[5,7,8], suggesting differences in multiple processes, such as metabolism, apoptosis, adaptive immune defence, cytoskeleton, cell movement and extracellular matrix turnover[4,9,10,11,12]
Introduction KashinBeck disease (KBD), an endemic and chronic degenerative osteochondral disease with irreversible pathological and clinical signs, is characterised with clinical manifestations including shortened and enlargedOfficial journal of the Cell Death Differentiation AssociationWang et al Cell Death and Disease (2021)12:551 cellular pathways between Kashin–Beck disease (KBD) and OA chondrocytes[5,7,8], suggesting differences in multiple processes, such as metabolism, apoptosis, adaptive immune defence, cytoskeleton, cell movement and extracellular matrix turnover[4,9,10,11,12]
We found that the root of the trajectory was mainly populated by cartilage progenitor cells (CPCs)-1 and CPCs2, while fibrocartilage chondrocytes (FCs)-1 was distributed in the middle of the trajectory, FC-2 was distributed along the trajectory, RegCs were located in front of FCs, and prehypertrophic chondrocytes (PreHTCs) were behind FCs

Summary

Introduction

Wang et al Cell Death and Disease (2021)12:551 cellular pathways between KBD and OA chondrocytes[5,7,8], suggesting differences in multiple processes, such as metabolism, apoptosis, adaptive immune defence, cytoskeleton, cell movement and extracellular matrix turnover[4,9,10,11,12]. These studies do not take into consideration the heterogeneity of articular cartilage cell types and may be missing important information on cartilage degeneration processes specific to KBD or OA. CPCs have the ability to selfrenew and differentiate along multiple lineages, thereby contributing to cartilage repair and homeostasis, and their dysregulation may affect and modulate cartilage loss in the processes of OA and KBD17,20

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