Chuncha Bao 1,2,✉, Siyi Zhu 1,2, Dejiang Pang 3, Ming Yang 4, Jiapeng Huang 5, Fengsheng Wang 6, Yue Hou 1,2, Xiangxiu Wang 1,2, Yuan Feng 1,2, Haolun Yang 1,2, Junliang Jiang 1,2, Jing He 1,2, Chengqi He 1,2,✉
Author information
PMCID: PMC11844298 PMID: 39990654
Abstract
Abnormalities in glycolytic pathways are prominent factors in the pathogenesis of osteoarthritis (OA). The key glycolytic enzyme Hexokinase 2 (HK2) is highly expressed in chondrocytes in OA; however, its role remains unclear. Pulsed electromagnetic field (PEMF) is commonly used for the treatment of OA. However, the role of PEMF in cartilage damage and the underlying mechanisms are not well understood. Herein, we found that HK2 suppression down-regulated catabolic pathways and alleviated inflammatory responses in OA chondrocytes, whereas HK2 overexpression stimulated inflammation and catabolic levels; moreover, inhibition of HK2 has potential anti-inflammatory and anti-catabolic properties by regulating the expression of HMGA2. PEMF dramatically inhibited the increase in glycolytic activity and catabolic metabolism level in OA and could alleviate the OA phenotype by modulating the HK2/HMGA2 signaling axis. Suppressing HK2 via adeno-associated virus (AAV) in articular cartilage demonstrated that PEMF reduces cartilage damage and OA symptoms through HK2 knockdown. Furthermore, the HK2 inhibitor Lonidamine, in combination with PEMF, more effectively ameliorated cartilage degeneration in OA. Overall, our findings improve understanding of HK2’s role in OA and offer new insights for targeting HK2 in treatment. Furthermore, our results provide new clues for the reducing of catabolism and cartilage damage using PEMF.
Keywords: Osteoarthritis, Pulsed electromagnetic field, Hexokinase 2, Cartilage damage
Introduction
Osteoarthritis (OA) is the most common chronic degenerative and disabling joint disease of the musculoskeletal system 1, 2. Cartilages are one of the important components of the knee joint, and chondrocytes maintain the integrity of cartilages through the homeostasis of the extracellular matrix (ECM) 3. The pathogenesis of OA is relatively complex, involving genetic, metabolic, and biochemical factors 4. Current evidence suggests that metabolic dysregulation plays various regulatory roles in the pathogenesis of OA, including mitochondrial metabolism, glycolysis metabolic pathways, the tricarboxylic acid cycle (TCA), lipid metabolism, and amino acid metabolism 5-8. In the OA environment and under inflammatory stimulations, chondrocytes undergo pathological changes in metabolic homeostasis and cartilage remodeling 9. In addition, metabolic abnormalities in chondrocytes can lead to an imbalance in collagen synthesis and degradation, cartilage degeneration, and ultimately result in the onset of OA 10. Additionally, metabolic abnormalities increase susceptibility to OA, and also impede the functional recovery of patients following joint replacement surgery 7. Results from cross-sectional clinical studies have indicated a significant positive correlation between the severity of symptomatic Knee Osteoarthritis (KOA) and the metabolic syndrome accumulation factor 11. Therefore, a comprehensive understanding of the complex mechanisms underlying the association between metabolic abnormalities and OA may lead to the development of new therapeutic strategies.
Glycolysis is the process of breaking down glucose to produce pyruvate. It occurs in the cytoplasm and is one of the most important pathways for glucose metabolism in the body 12. Abnormalities in the glycolytic metabolic pathway can lead to chondrocyte hypertrophy and ECM degradation in chondrocytes 13. Recent studies indicated that after stimulating chondrocytes using inflammatory factors, there was an upregulation of key glycolytic genes and an enhancement of glycolytic activity 14. Hexokinase 2 (HK2), the first rate-limiting enzyme in glycolysis, converts glucose to glucose-6-phosphate (G-6-P) 15. Studies have demonstrated that HK2 is highly expressed in fibroblast-like synovial cells (FLS) in OA, and overexpression of HK2 in chondrocytes could promote the secretion of inflammatory factors, including IL-6 and IL-8 16. However, although HK2 may be involved in the pathogenesis of OA, the specific mechanism underlying the involvement of HK2 in the progression of OA remains unclear.
High-mobility group AT-hook 2 (HMGA2) is an architectural transcription factor that directly binds to DNA sequences 17-19. HMGA2 has been shown to exhibit diverse biological functions and contribute to angiogenesis, tumor metastasis, self-renewal of hematopoietic stem cells and neuronal stem cells, and OA cartilage synthesis 19-22. A recent study demonstrated that HMGA2 activates Sox9 transcription by binding to regulatory sequences and promoters in chondrocytes. Furthermore, SOX9 promotes the expression levels of synthetic metabolic genes, such as COL2A1 and aggrecan. However, the role of HMGA2 in the pathogenesis of OA mediated by HK2 remains unclear. Therefore, it is crucial to clarify whether HK2 affects the pathogenesis of OA by regulating HMGA2, especially in promoting the potential mechanisms of chondrocyte synthesis and catabolism 19.
Due to the complex pathogenesis of OA, current clinical treatment methods for OA remain limited. Non-steroidal anti-inflammatory drugs (NSAIDs) and other analgesics only temporarily alleviate symptoms; furthermore, excessive use of these drugs can lead to hepatic and renal damage. Moreover, these drugs cannot reverse the progression of OA 23. Pulse electromagnetic field (PEMF) is a non-invasive, painless, cost-effective, and safe form of biophysical stimulation that can regulate metabolic processes such as oxidative stress 24, 25, mitochondrial dysfunction, and energy metabolism 26, thus offering therapeutic effects against a variety of diseases. Both clinical trials and preclinical studies have shown that PEMF can reduce inflammatory responses and enhance subchondral bone sclerosis, thereby ameliorating the progression of OA 27, 28. However, the mechanisms by which PEMF exerts its therapeutic effects on OA are unclear. Therefore, elucidating the mechanisms of PEMF treatment for OA will aid in its widespread adoption in clinical practice.
In this study, we found that the key glycolytic kinase, HK2, is significantly increased in the damaged human cartilages in OA and in IL-1β-induced primary chondrocytes from mice, with higher expression levels observed in the damaged regions compared to the undamaged areas. This study aims to investigate the role of HK2, a key glycolytic kinase, in the progression of OA and its potential as a therapeutic target. Specifically, we explore the expression patterns of HK2 in damaged human cartilage and IL-1β-induced primary chondrocytes, evaluate the involvement of the HK2/HMGA2 signaling pathway in OA-related catabolic processes, and assess the therapeutic effects of PEMF intervention. Additionally, we examine the combined effects of PEMF and the HK2 inhibitor Lonidamine on cartilage metabolism to identify strategies for balancing catabolic and anabolic processes in OA. This study seeks to provide a foundation for innovative approaches to OA treatment by targeting HK2.
