Osteoarthritis (OA) is a prevalent chronic joint disease characterized by the degeneration of cartilage and inflammation (1). The risk factors for OA encompass obesity, injury, genetic predisposition, among others. It is noteworthy that the incidence is higher among females compared to males, and age stands as the foremost risk factor (2, 3). The pathogenesis of osteoarthritis primarily involves the articular cartilage, subchondral bone, and synovium, yet its specific mechanisms remain not fully elucidated (4). Therapeutic interventions for OA mainly include non-pharmacologic management, pharmacologic management, and surgical interventions. Recommended non-pharmacological approaches include education, self-management, exercise, and weight loss (5). Nonsteroidal anti-inflammatory drugs (NSAIDs) and acetaminophen are frontline pharmaceuticals in the treatment of OA, recommended for use in clinical guidelines. However, the cautious administration of NSAIDs is imperative to avert potential adverse effects. While acetaminophen’s efficacy falls short of that of NSAIDs, its safety profile renders it suitable for patients contraindicated for NSAIDs (6). Surgical interventions exhibit notable efficacy in long-term improvement of patients’ physiological function and alleviation of pain; nevertheless, they are not exempt from potential side effects (7). Moreover, an increasing body of evidence suggests a correlation between psychological factors and the onset of OA pain. Utilizing psychological approaches, such as coping skills training (CST) and emotional disclosure, has proven effective in alleviating OA pain (8). As the pathogenic mechanisms of OA are continually elucidated, an increasing number of pharmaceuticals targeting the pathophysiological mechanisms of the disease are under development to replace the current predominantly palliative treatments, such as chondroitin sulfate and hyaluronan, collectively known as disease-modifying osteoarthritis drugs (DMOADs). These drugs, targeting cartilage, inflammatory pathways, and subchondral bone, hold promising prospects (9).

RNA interference (RNAi) denotes the duplex RNA’s inhibitory effect on genes, constituting a natural mechanism within organisms to silence genes (10). Small interfering RNA (siRNA) represents a category of double-stranded RNA molecules, spanning 21–23 nucleotides, formed through enzymatic cleavage of double-stranded RNA (11). siRNA associates with various proteins to form the RNA-induced silencing complex (RISC). Subsequently, it pairs with target mRNA, cleaving the mRNA and ultimately impeding the transcriptional process (12). Given its selective ability to silence almost any gene, siRNA therapy holds promise as a clinical approach for targeting specific genes in the treatment of OA. The first siRNA therapy was approved in 2018, utilized for the treatment of transthyretin-mediated amyloidosis. Since then, siRNA-based therapies for various diseases have entered clinical trials, indicating the broad prospects of siRNA in treating diseases (13). Furthermore, diverse delivery systems based on siRNA have been developed to enhance the efficiency of siRNA reaching its target, encompassing polymers, lipids, antibodies, nanocarriers, and peptide segments (14). This review comprehensively summarizes the progress in utilizing siRNA for the treatment of OA from a cellular perspective, including targeting chondrocytes, fibroblast-like synoviocytes, and osteoblasts, offering a novel outlook on the application of siRNA in OA therapy.

The pathological manifestations of OA are diverse, with the degeneration of articular cartilage being a primary characteristic. Articular cartilage primarily comprises water and organic extracellular components. Chondrocytes represent the exclusive cell type within the cartilage matrix, responsible for maintaining the synthesis and degradation equilibrium of the extracellular matrix (ECM) (15). Upon exposure to mechanical, inflammatory, and metabolic factors, anomalies arise in the function of chondrocytes. This results in a reduction in the generation of ECM molecules and an augmentation in the production of proteinases. The disruption of ECM homeostasis is thus initiated, consequently promoting the degeneration of articular cartilage (16).

Synovial inflammation is another characteristic feature of OA. The aberrant function of chondrocytes leads to the secretion of proteolytic enzymes, causing the production of inflammatory and metabolic products that affect the adjacent synovium. The progression of synovial inflammation can further exacerbate cartilage damage (46).

The production of pro-inflammatory cytokines such as IL-1β, TNF-α, IL-6, can exacerbate cartilage degradation and is associated with hyperalgia in OA (47, 48). Silencing NLR family pyrin domain containing 1 (NLRP1) reduces the production of IL-1β induced by P2X4 purinoceptor (P2X4) in OA fibroblast-like synoviocytes (49). RELA proto-oncogene, NF-kB subunit (RELA) siRNA significantly inhibits the induction of IL-1β and TNF-α in the synovial fluid, thereby alleviating synovial inflammation and cartilage degradation in early-stage OA rats through inhibition of the NF-κB pathway (50). Utilizing nanoparticles to deliver cyclin dependent kinase inhibitor 2A (CDKN2A) siRNA results in a reduction of IL-1β, IL-6, and TNF-α expression in fibroblast-like synoviocytes of model rats, and reduces cartilage destruction and pain (51). Hyaluronan contributes to the composition of synovial fluid for joint lubrication. In OA, hyaluronan degradation occurs, promoting inflammation. The expression of cell migration inducing hyaluronidase 1 (CEMIP) increases in OA fibroblast-like synoviocytes, and knocking down CEMIP reduces the degradation of hyaluronan in OA fibroblast-like synoviocytes (52). Glutaminase (GLS) siRNA inhibits glutamine–glutamate metabolism, reducing the IL-6 inflammatory response in OA fibroblast-like synoviocytes (53).

Proliferation of fibroblast-like synoviocytes is one of the characteristics of synovial inflammation and can lead to hyperplasia of the synovial lining (54). Knocking down latent transforming growth factor beta binding protein 1 (LTBP-1) using siRNA reduces fibroblast-like synoviocytes proliferation by downregulating the transforming growth factor β (TGF-β) signaling pathway (55).

Methyltransferase like 3 (METTL3) mediated m6A modification inhibits autophagy in OA fibroblast-like synoviocytes by regulating autophagy related 7 (ATG7) RNA and promotes cell senescence. METTL3 siRNA is able to inhibit expression of SASP-related genes and alleviate senescence in fibroblast-like synoviocytes. Furthermore, intra-articular injection of METTL3 siRNA delayed the progression of DMM-induced OA in mice (56). Fibroblast-like synoviocytes are considered the primary cells involved in synovial fibrosis in OA, and chronic joint pain is closely associated with synovial fibrosis (57). Inhibiting the upregulated expression of hypoxia inducible factor 1 subunit alpha (HIF-1A) in knee OA model rats reduces pyroptosis in fibroblast-like synoviocytes and significantly decreases the expression of synovial fibrogenic markers (58).

In OA, subchondral bone undergoes remodeling due to excessive loading and changes in mechanical environment (59). The abnormal remodeling of subchondral bone can further exacerbate cartilage degradation (60). Osteoblasts regulate bone formation, remodeling and mineralization (61). Osteoblasts undergo changes in phenotype in OA, such as elevated alkaline phosphatase activity and increased secretion of osteocalcin. Additionally, alterations in signaling pathways like wingless-type MMTV integration site family (WNT) and TGF-β contribute to the abnormal remodeling of subchondral bone (62, 63). Hence, targeting osteoblasts with siRNA represents a potential therapeutic approach.

In OA, there is an increased production of endogenous hepatocyte growth factor (HGF), which, by stimulating the production of TGF-β1, inhibits osteoblast responsiveness to bone morphogenetic protein 2 (BMP-2), leading to abnormal mineralization. HGF siRNA restores osteoblast responsiveness to BMP-2 and upregulates the WNT signaling pathway to nearly normal levels (64). Leptin expression is significantly increased in OA osteoblasts and can lead to elevated levels of alkaline phosphatase and osteocalcin, as well as increased osteoblast proliferation. Partially reducing the alkaline phosphatase activity and osteocalcin release is possible by inhibiting leptin or its receptor using siRNA, indicating the potential to inhibit bone remodeling (65). Silencing ALOX15 promotes AMPK phosphorylation, inhibits mechanistic target of rapamycin complex 1 (mTORC1) phosphorylation, thereby suppressing expression levels of TGF-β1. This, in turn, enhances osteoblast autophagy and ultimately alleviates the progression of OA (66). Activation of Toll-like receptor 4 (TLR4) and innate immune activation can exacerbate cartilage degradation in OA. The antidepressant amitriptyline can bind to TLR4, inhibiting TLR4, IL-1 receptor, and NLR family pyrin domain containing 3 (NLRP3) dependent innate immune responses in OA chondrocytes, synoviocytes, and osteoblasts. Similarly, silencing NLRP3 using siRNA has a comparable effect (67).

The pathological changes in OA involve the entire joint, and current research predominantly focuses on the abnormalities in cartilage. Research on other cells to treat OA is limited, such as macrophages or mesenchymal stem cells (68). Nevertheless, siRNA targeting these cells has shown promising prospects.

Xu Chen et al. engineered nanoparticles capable of releasing nitric oxide and notch receptor 1 (NOTCH1) siRNA. By inhibiting macrophage inflammatory responses, these nanoparticles reduced OA cartilage damage without significant side effects (69).

Mesenchymal stem cells derived from bone marrow are ideal for tissue repair due to their differentiation potential. Inhibiting BLACAT1 overlapping LEMD1 locus (BLACAT1) promotes the proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells under inflammatory conditions, demonstrating potential for treating OA (70).

OA is a chronic degenerative joint disease that, as it progresses, often leads to disability and pain, significantly impacting the quality of life (71). Currently, the treatment approach for OA primarily focuses on mitigating disease symptoms and arresting its progression. In recent years, with an increasingly profound understanding of OA, it is recognized as a comprehensive, multifactorial joint disorder, intimately connected to the interactions among articular cartilage, synovium, subchondral bone, and their constituent cells. Due to its inherent property of selectively silencing genes, siRNA stands as a potential candidate among DMOADs. Recent investigations have disclosed that employing siRNA to target chondrocytes, fibroblast-like synoviocytes, osteoblasts, osteoblasts, and other cells and molecules involved in the development of OA can effectively decelerate the progression of the ailment. Additionally, a substantial volume of research centered around siRNA delivery systems has enhanced the precision and duration of siRNA delivery to target tissues. While there is currently no siRNA therapy specifically targeting osteoarthritis (according to clinicaltrials.gov), an increasing number of siRNA therapies targeting various diseases are entering clinical trials or gaining approval. These include cancer, hypertension, hypercholesterolemia, as well as some rare genetic disorders such as hemophilia and primary hyperoxaluria (72). These studies collectively highlight the broad potential of employing siRNA in the treatment of OA.

However, the constraints of current siRNA therapies cannot be disregarded. The primary method of siRNA therapy involves intravenous administration using nano-carriers, including lipid carriers, polymer carriers, and inorganic carriers (12). Lipid carriers, due to their positively charged nature, may undergo aggregation with serum proteins (73). On the other hand, negatively charged siRNA can distribute through the bloodstream to the reticuloendothelial system (RES) and are more readily phagocytosed, compared to neutral or positively charged counterparts (11). Furthermore, siRNA permits a degree of mismatch with the target mRNA, resulting in the silencing of non-target genes, known as off-target effects (74). Competition with the endogenous RNAi pathway and off-target effects can lead to hepatotoxicity (75). Cationic lipids and polymers, among other delivery methods involving internalization, can also induce immune responses by activating Toll-like receptor 7 (TLR7) and Toll-like receptor 8 (TLR8) (76). To address these issues, numerous improvement strategies have been applied to optimize siRNA delivery, including chemical modifications, siRNA-ligand conjugation, siRNA-polymer conjugation, and others (77).

Beyond the inherent limitations of siRNA therapy, the selection of target genes represents one of the challenges in utilizing siRNA therapy for OA treatment. Given that OA is a disease affecting the entire joint, silencing target genes for OA may also potentially diminish therapeutic efficacy through the impact on physiological activities of other tissues, or even inadvertently accelerate disease progression. The activation of the PI3K/AKT/mTOR pathway can enhance skeletal muscle protein synthesis, whereas inhibition of the PI3K/AKT/mTOR pathway can increase protein breakdown, marking a signature of muscle atrophy. Moreover, muscular weakness constitutes a risk factor in the development of OA (78, 79). IL-6 is released during and after exercise to enhance muscle energy supply and plays a crucial role in the repair of acute muscle injuries by activating satellite cells (80, 81). Inhibiting IL-6 could have repercussions on muscle function, potentially exacerbating the progression of OA.

In this review, we summarized the advancements in utilizing siRNA to target various cells for the treatment of OA, including chondrocytes, fibroblast-like synoviocytes, osteoblasts, and others ( Table 1 and Figure 1 ). These studies, encompassing both in vitro experiments and in vivo trials, consistently demonstrate the potential of siRNA therapy. However, siRNA therapy still confronts numerous challenges, such as the selection of therapeutic targets, more efficient carriers for siRNA delivery, and addressing the immunogenicity of siRNA. Hence, the therapeutic potential of siRNA remains vast, with significant room for further advancement.

YL: Writing – original draft, Writing – review & editing. JZ: Writing – original draft, Writing – review & editing. SG: Writing – review & editing. DH: Writing – review & editing.