Letter to the Editor: Sclerostin knockdown in human umbilical cord mesenchymal stem cells confers superior therapeutic efficacy against steroid-induced osteonecrosis

Abstract

Mesenchymal stem cell-based therapies have emerged as promising candidates for the treatment of steroid-induced avascular necrosis of the femoral head (SANFH). A study by Lv et al published in the recent issue of the World Journal of Stem Cells, investigated a novel strategy aimed at enhancing the therapeutic potential of human umbilical cord mesenchymal stem cells (hUCMSCs) for SANFH through the genetic silencing of sclerostin (SOST), a key inhibitor of bone formation. In a murine model of SANFH, transplantation of SOST-silenced hUCMSCs yielded superior structural and histological outcomes compared with unmodified hUCMSCs. Micro-computed tomography confirmed marked restoration of the femoral head microarchitecture, including increased bone volume, trabecular number, and trabecular thickness. Histological examination revealed reduced adipocyte infiltration and fewer empty lacunae following SOST-silenced hUCMSCs treatment. Mechanistically, these improvements were associated with a shift in bone metabolism toward osteogenesis, reflected by an elevated serum osteoprotegerin/receptor activator of nuclear factor-kappa B ligand ratio, activation of the Wnt/β-catenin pathway, and downregulation of adipogenic markers (peroxisome proliferator-activated receptor gamma and CCAAT/enhancer-binding protein) in bone tissue. Collectively, these findings demonstrate that SOST knockdown corrects the osteogenic-adipogenic imbalance by modulating the Wnt/β-catenin pathway, thereby significantly augmenting the therapeutic efficacy of hUCMSCs in SANFH. However, this approach warrants further translational studies.

Key Words: Sclerostin; Human umbilical cord mesenchymal stem cells; Steroid-induced avascular necrosis of the femoral head; Bone metabolism; Wnt/β-catenin signaling; RNA interference; Gene therapy

Core Tip: This study demonstrates that sclerostin (SOST) gene silencing in human umbilical cord mesenchymal stem cells enhances their therapeutic efficacy in a steroid-induced osteonecrosis model. Genetically modified SOST-silenced human umbilical cord mesenchymal stem cells significantly improved bone microarchitecture, promoted osteogenic differentiation, and inhibited adipogenic formation by activating the Wnt/β-catenin pathway. This targeted approach effectively restored the bone metabolic balance, positioning SOST-silenced human umbilical cord mesenchymal stem cells as a promising advanced regenerative strategy for the treatment of steroid-induced femoral head necrosis.

TO THE EDITOR

Steroid-induced avascular necrosis of the femoral head (SANFH) results from prolonged glucocorticoid exposure and is characterized by impaired bone remodeling, trabecular collapse, and eventual structural failure of the femoral head[1]. Its pathogenesis is multifactorial, involving increased adipogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), impaired osteogenesis, and apoptosis of vascular endothelial cells[2]. Although mesenchymal stem cell (MSC) transplantation has emerged as a promising regenerative therapy, its therapeutic efficacy remains limited due to the compromised functionality of patient-derived cells and the adipocyte-favoring micro-environment within necrotic lesions[3]. Human umbilical cord MSCs (hUCMSCs) offer particular advantages owing to their easy accessibility, low immunogenicity, and strong osteogenic capacity[4]. Sclerostin (SOST), a glycoprotein predominantly secreted by osteocytes, functions as a critical negative regulator of the Wnt/β-catenin signaling pathway and thus inhibits bone formation[5]. Genetic silencing of SOST can significantly enhance the therapeutic efficacy of MSCs by promoting an intrinsically pro-osteogenic phenotype.

We read with great interest the recent article by Lv et al[6], titled “Sclerostin-silenced human umbilical cord mesenchymal stem cells ameliorate bone metabolism in steroid-induced femoral head necrosis”, published in the World Journal of Stem Cells. The authors used RNA interference to silence SOST in hUCMSCs, generated SOST-silenced hUCMSCs (sh-hUCMSCs), and evaluated their therapeutic efficacy in a murine SANFH model.

This study convincingly demonstrated that transplantation of sh-hUCMSCs yielded superior therapeutic outcomes compared with unmodified hUCMSCs. Micro-computed tomography analysis revealed substantial restoration of the femoral head microarchitecture, including increased bone volume, trabecular number, and trabecular thickness, as well as decreased trabecular separation. Histological analyses confirmed these findings, revealing reduced adipocyte infiltration and fewer empty lacunae, indicating mitigation of steroid-induced necrotic changes.

Mechanistically, the observed therapeutic benefits were associated with activation of Wnt/β-catenin signaling, increased expression of osteogenic markers (alkaline phosphatase, osteoprotegerin, and β-catenin), decreased expression of adipogenic markers (peroxisome proliferator-activated receptor gamma and CCAAT/enhancer-binding protein), and a favorable shift in systemic bone metabolism, reflected by an increased serum osteoprotegerin/receptor activator of nuclear factor-kappa B ligand ratio and decreased TRAP levels. Thus, continued research on mechanistic details is warranted. Recent studies have shed light on the roles of extracellular vesicles and long noncoding RNAs derived from MSCs in the therapeutic effects of SANFH. Peng et al[7] demonstrated that extracellular vesicles from human umbilical cord stem cells prevented SANFH via the phosphatidylinositol 3-kinase/protein kinase B pathway. Li et al[8] reported that exosomes from mutant-hypoxia-inducible factor-1α-modified BMSCs could attenuate early SANFH in rabbits. Wu et al[9] explored the mechanism of action of vascular endothelial cell-derived exosomes modified with vascular endothelial growth factor during steroid-induced femoral head necrosis. Moreover, Wang et al[10] reported that lncAABR07053481 inhibited BMSC apoptosis and promoted repair following steroid-induced avascular necrosis. Collectively, these findings, along with emerging insights into extracellular vesicles and long noncoding RNAs, support a model in which SOST knockdown corrects the osteogenic-adipogenic imbalance central to SANFH pathogenesis.

A key strength of this study is the development and characterization of a genetically modified MSC line that exhibits enhanced osteogenic capacity and reduced adipogenic potential without compromising intrinsic stem cell properties. The multi-target silencing of SOST represents a sophisticated approach to precisely modulate a critical pathological pathway in SANFH, aligning with the growing interest in leveraging gene-editing technologies to create “next-generation” MSC therapies with improved potency and specificity[11].

Despite these significant advances, several questions warrant further investigation. The long-term safety and stability of sh-hUCMSCs in vivo, including potential off-target effects, ectopic ossification, and tumorigenicity, should be evaluated in larger animal models with extended follow-up periods. Direct comparisons with other osteogenic enhancement strategies, such as SOST-neutralizing antibodies (e.g., romosozumab[12]), would further contextualize the relative efficacy and practicality of this cell-based gene therapy approach. In addition, optimization of the delivery methods is crucial. In addition to comparing local intra-articular injection with systemic administration to further improve targeting and therapeutic efficiency while minimizing systemic exposure, a more comprehensive discussion of the factors influencing in vivo delivery strategies is needed. These factors include charge density, molecular weight, intracellular accumulation, endosomal escape, and instability caused by nucleases.

In conclusion, Lv et al[6] provided robust preclinical evidence that SOST knockdown augments the therapeutic efficacy of hUCMSCs in SANFH. However, this study had several limitations. First, the sample size in the animal experiments was relatively small, which may limit the generalizability of the results. Second, although the therapeutic effect of SOST-silenced hUCMSCs in a steroid-induced SANFH model has been demonstrated, the long-term safety and efficacy of this approach remain to be validated in large-scale animal studies or clinical trials, and concerns regarding its clinical translation should be carefully addressed. Third, the molecular mechanisms linking SOST silencing to Wnt/β-catenin signaling require further in-depth investigation. Nevertheless, by genetically correcting the osteogenic-adipogenic imbalance central to disease pathology, this approach holds significant potential for clinical translation. We encourage further research into the mechanistic details, safety profiles, and scalable production of engineered MSCs to advance their development as viable treatment options for osteonecrosis and other bone metabolic disorders.