Single-Cell RNA-Seq Analysis Reveals Macrophage Involved in the Progression of Human Intervertebral Disc Degeneration

Zemin Ling; Yong Liu; Zhe Wang; Ziji Zhang; Bolin Chen; Jiaming Yang; Baozhu Zeng; Yu Gao; Chang Jiang; Yulin Huang; Xuenong Zou; Xiuhui Wang; Fuxin Wei

doi:10.3389/fcell.2021.833420

Single-Cell RNA-Seq Analysis Reveals Macrophage Involved in the Progression of Human Intervertebral Disc Degeneration

Front Cell Dev Biol. 2022 Feb 28:9:833420. doi: 10.3389/fcell.2021.833420. eCollection 2021.

Authors

Zemin Ling¹, Yong Liu², Zhe Wang³, Ziji Zhang², Bolin Chen¹, Jiaming Yang⁴, Baozhu Zeng⁴, Yu Gao⁴, Chang Jiang³, Yulin Huang⁴, Xuenong Zou¹, Xiuhui Wang⁵, Fuxin Wei⁴

Affiliations

¹ Guangdong Provincial Key Laboratory of Orthopedics and Traumatology, Department of Spinal Surgery, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, China.
² Department of Joint Surgery, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, China.
³ Department of Orthopedics, Zhongshan Hospital, Fudan University, Shanghai, China.
⁴ Department of Orthopedics, The Seventh Affiliated Hospital of Sun Yat-sen University, Shenzhen, China.
⁵ Department of Orthopaedics, Shanghai University of Medicine and Health Sciences Affiliated Zhoupu Hospital, Shanghai, China.

Abstract

Intervertebral disc degeneration (IDD) has been considered as the primary pathological mechanism that underlies low back pain. Understanding the molecular mechanisms underlying human IDD is imperative for making strategies to treat IDD-related diseases. Herein, we report the molecular programs, lineage progression patterns, and paths of cellular communications during the progression of IDD using single-cell RNA sequencing (scRNA-seq) on nucleus pulposus (NP) cells from patients with different grades of IDD undergoing discectomy. New subtypes of cells and cell-type-specific gene signatures of the metabolic homeostatic NP cells (Met NPC), adhesive NP cells (Adh NPC), inflammatory response NP cells (IR NPC), endoplasmic reticulum stress NP cells (ERS NPC), fibrocartilaginous NP cells (Fc NPC), and CD70 and CD82⁺ progenitor NP cells (Pro NPC) were identified. In the late stage of IDD, the IR NPC and Fc NPC account for a large proportion of NPC. Importantly, immune cells including macrophages, T cells, myeloid progenitors, and neutrophils were also identified, and further analysis showed that significant intercellular interaction between macrophages and Pro NPC occurred via MIF (macrophage migration inhibitory factor) and NF-kB signaling pathways during the progression of IDD. In addition, dynamic polarization of macrophage M1 and M2 cell subtypes was found in the progression of IDD, and gene set functional enrichment analysis suggested a significant role of the macrophage polarization in regulating cell metabolism, especially the Pro NPC. Finally, we found that the NP cells in the late degenerative stage were mainly composed of the cell types related to inflammatory and endoplasmic reticulum (ER) response, and fibrocartilaginous activity. Our results provided new insights into the identification of NP cell populations at single-cell resolution and at the relatively whole-transcriptome scale, accompanied by cellular communications between immune cells and NP cells, and discriminative markers in relation to specific cell subsets. These new findings present clues for effective and functional manipulation of human IDD-related bioremediation and healthcare.

Keywords: gene; inflammation; intervertebral disc degeneration; metabolism; nucleus pulposus; single-cell RNA sequencing.