Awakening endogenous repair: salidroside boosts mitophagy in NPMSCs via SIRT1/FOXO3 to combat intervertebral disc degeneration

Abstract

Background: Intervertebral disc degeneration (IVDD) is a major cause of low back pain, characterized by mitochondrial dysfunction and impaired mitophagy in nucleus pulposus-derived mesenchymal stem cells (NPMSCs). Sirtuin 1 (SIRT1), a key regulator of mitochondrial quality control, is downregulated in degenerated discs. Salidroside (Sal), a natural compound from Rhodiola rosea, has shown potential in enhancing mitophagy, but its mechanism in IVDD remains unclear. Methods: Using network pharmacology, molecular docking, and dynamics simulations, we identified SIRT1 as a key target of Sal. Human and rat NPMSCs were isolated and treated with tert-butyl hydroperoxide (TBHP) to induce degeneration. In vitro assays included CCK-8, EdU, SA-β-Gal, JC-1, Western blot, immunofluorescence, and transmission electron microscope (TEM). An in vivo rat IVDD model was established via needle puncture and treated with Sal and/or the autophagy inhibitor 3-MA. Histological, immunohistochemical, and imaging analyses were performed to evaluate IVDD. Results: Sal bound stably to SIRT1 and activated SIRT1/FOXO3 pathway, promoting mitophagic flux, reducing reactive oxygen species accumulation, and suppressing apoptosis in NPMSCs. SIRT1 knockdown or 3-MA treatment abolished Sal’s protective effects. In vivo, Sal treatment preserved disc height, reduced apoptosis, and enhanced mitophagy, while 3-MA exacerbated degeneration. Conclusions: Sal attenuates IVDD by activating SIRT1/FOXO3-mediated mitophagy, restoring mitochondrial homeostasis, and reducing NPMSCs apoptosis. These results suggest that the activation of the SIRT1/FOXO3-mitophagy axis may represent a potential therapeutic strategy for mitigating IVDD.

1. Introduction

Intervertebral disc degeneration (IVDD) represents a primary underlying etiology of low back pain (LBP), a pervasive global health concern imposing substantial socioeconomic burdens through diminished productivity and escalating healthcare expenditures [1]. This progressive, multifactorial condition is characterized by a complex cascade of pathological alterations within the disc microenvironment. Key features include the progressive degradation of the extracellular matrix (ECM), notably loss of proteoglycans like aggrecan and the disorganization of collagen fibrils, coupled with aberrant cellular responses such as senescence, apoptosis, and a shift towards a pro-inflammatory phenotype [2]. Despite extensive research, the precise molecular mechanisms orchestrating the initiation and perpetuation of IVDD remain incompletely elucidated, particularly concerning the intricate interplay between mechanical stress, inflammatory cascades (e.g., Tumor Necrosis Factor-α (TNF-α) and Interleukin-1 β (IL-1β)), and abnormal autophagy process. Therefore, delving deeper into the fundamental pathobiological pathways driving IVDD is imperative for identifying novel therapeutic targets aimed at mitigating degeneration or promoting functional regeneration.

Mesenchymal stem cells (MSCs) can be harvested and expanded from various adult and perinatal tissues, including adipose tissue, bone marrow (BM), dental pulp, and umbilical cord (UC), exhibiting diverse pharmacological properties [3–5]. Currently, MSCs are widely investigated for therapeutic applications in IVDD; however, endogenous nucleus pulposus-derived mesenchymal stem cells (NPMSCs) offer distinct inherent advantages. Compared to exogenous MSCs, NPMSCs demonstrate superior adaptation to the unique intradiscal microenvironment, positioning them as critical targets for IVDD therapy [6, 7]. Consistent with our prior findings, NPMSCs reside within the nucleus pulposus (NP) tissue and possess intrinsic capacities for self-renewal and differentiation, thereby contributing to the mitigation of disc degeneration [8]. Notably, endogenous NPMSCs exhibit significant regenerative potential, primarily through differentiation into functional NP-like cells and inhibition of apoptosis [9]. Nevertheless, this functional capacity deteriorates with advancing age and IVDD progression, highlighting the necessity to preserve NPMSCs viability for effective endogenous repair strategies [10]. Our prior research confirmed the presence of endogenous NPMSCs within the NP tissue. Furthermore, we demonstrated that mitochondrial dysfunction is a hallmark of senescent NPMSCs, and crucially, that enhancing mitochondrial function attenuates oxidative stress-induced NPMSCs senescence. This mitochondrial restoration facilitates endogenous repair mechanisms, thereby mitigating IVDD [8, 11]. However, the precise molecular mechanisms underlying mitochondrial impairment in degenerated NPMSCs remain incompletely understood. In the present study, we therefore elucidate the specific mechanisms governing mitochondrial damage within degenerated NPMSCs, aiming to provide novel therapeutic strategies for delaying IVDD progression.