IDD is the most common pathological change in various spinal diseases, characterized by a gradual deterioration of disc structure and function due to aging or other external factors. The intervertebral disc, located between vertebral bodies, consists of the annulus fibrosus and nucleus pulposus, with its primary functions being to absorb mechanical stress during spinal movement and maintain spinal flexibility [21], [4], [8]. However, during the degeneration process, proteoglycan loss leads to reduced water retention in the nucleus pulposus, accompanied by decreased glycosaminoglycan (GAG) content, shortening of aggrecan aggregates, and disorganization of collagen fibrils within the extracellular matrix [22], [5]. This cascade results in structural failure of the annulus fibrosus, disc height reduction, and ultimately functional decline or even loss. IDD serves as the pathological basis for various spinal disorders, such as lumbar disc herniation, lumbar spinal stenosis, and chronic low back pain [20], [23], [27], [28]. With the accelerated aging of modern society, diseases related to IDD have become significant health issues that severely impact quality of life. Therefore, understanding the mechanisms of disc degeneration and developing effective interventions are critical for the prevention and treatment of related diseases. The mechanisms underlying disc degeneration are complex and typically involve multiple factors, including genetics, mechanical stress, cell apoptosis, inflammatory responses, and lifestyle factors, etc [2], [25], [3]. Among these, mechanical stress and extracellular matrix metabolic imbalance are considered primary contributors [12], [24]. However, the molecular mechanisms involved in the progression of disc degeneration remain incompletely understood, which has hindered the development of effective clinical treatments to reverse or slow the progression of disc degeneration.

Transcriptome sequencing and single-cell sequencing technologies provide powerful tools for studying IDD, offering profound insights into its molecular mechanisms and cellular heterogeneity. Transcriptome sequencing reveals the expression levels of all genes in disc tissues or cells, uncovering key genes, signaling pathways, and regulatory networks associated with disc degeneration. For example, transcriptome sequencing can identify differentially expressed genes (DEGs) related to extracellular matrix metabolism imbalance, inflammatory responses, and cell apoptosis during degeneration, providing clues for mechanistic research and laying the foundation for developing novel therapeutic targets [7]. In contrast, single-cell sequencing can analyze the characteristics of individual cell subpopulations within disc tissues and their specific roles in degeneration [26], [27], [28]. The intervertebral disc is composed of various cell types, including nucleus pulposus cells, annulus fibrosus cells, and cartilage endplate cells. Single-cell sequencing can identify the transcriptional profiles of these subpopulations and investigate how they act independently or collaboratively during the degeneration process. Moreover, this technology can reveal changes in cell-to-cell communication, heterogeneity, and dynamic shifts in rare cell populations, offering a fresh perspective on the complex pathology of disc degeneration [19], [32], [33]. In summary, the combination of transcriptome sequencing and single-cell sequencing can elucidate the molecular mechanisms of disc degeneration from both macroscopic and microscopic perspectives. This approach provides valuable data to support personalized treatment and targeted interventions, with the potential to advance research and clinical applications in IDD-related diseases.

IDD is a multifactorial pathological process, with programmed cell death considered one of its core mechanisms. During IDD, nucleus pulposus cells, annulus fibrosus cells, and cartilage endplate cells undergo various forms of programmed cell death, such as apoptosis, ferroptosis, pyroptosis, and autophagic cell death, due to multiple stress conditions, including mechanical load, oxidative stress, nutrient deprivation, and inflammatory microenvironments [15], [18], [2], [3]. The loss of these cells directly compromises the structural integrity and function of the intervertebral disc. However, recent studies have revealed that efferocytosis, the process by which macrophages clear apoptotic cells, plays a critical role in maintaining tissue homeostasis [29]. The dysfunction of efferocytosis in apoptotic cell clearance also plays an important role in IDD and may serve as a key driving factor accelerating the degenerative process.

PLAU is an important serine protease encoded by the PLAU gene [30]. Its primary function is to activate plasminogen to produce plasmin, thereby participating in the degradation of the extracellular matrix (ECM), tissue remodeling, cell migration, and signal transduction in various physiological and pathological processes. PLAU plays a complex dual role in the process of apoptosis, exhibiting both pro-apoptotic and anti-apoptotic functions depending on cell type, tissue environment, and upstream and downstream signaling pathways [13]. By activating plasminogen to generate plasmin, PLAU degrades the ECM and disrupts adhesion-dependent signals (such as integrin signaling) between cells and their microenvironment [10]. This disruption of the microenvironment can lead to the loss of survival support for cells, thereby triggering anoikis (detachment-induced apoptosis). However, the PLAU-uPAR complex can activate the PI3K/Akt signaling pathway, enhancing cell survival and inhibiting apoptosis [16]. In complex pathological processes such as IDD, the role of PLAU has not yet been fully elucidated.

This study utilizes transcriptome sequencing and single-cell sequencing technologies to screen and identify hub genes associated with IDD. It further experimentally validates the molecular mechanisms of hub gene in disc degeneration, providing new strategies for the treatment and delay of the degeneration process.