Mt1–Ca2+–Mitochondrial Metabolic Axis Maintains Temporomandibular Joint Condylar Cartilage Homeostasis Under Low Oxygen and Hypoxic Condition

Abstract

The adaptive capacity of chondrocytes to fluctuating oxygen levels during the process of osteoarthritis remains poorly understood. This study aimed to investigate the role and underlying mechanisms of the Mt1–Ca²⁺–mitochondrial metabolic axis in chondrocyte function and cartilage homeostasis. Primary rat condylar chondrocytes were cultured under physiological low oxygen (5% O₂) and hypoxia (<1% O₂) with Mt1 knockdown or overexpression. The role of Mt1 in chondrocyte functions were investigated. Transcriptomic analysis identified intracellular Ca²⁺ and metabolism-related pathways regulated by Mt1. Mitochondrial respiration and glycolytic capacity were evaluated by Seahorse XF assays, while intracellular Ca²⁺ concentration was quantified by Calcium Assay Kit. The effects of extracellular Ca²⁺ supplementation were analyzed to clarify the Mt1–Ca²⁺ interaction in metabolic regulation. In vivo, a rat model with intra-articular Mt1 knockdown and chronic sleep deprivation-induced hypoxia was established to verify the role of Mt1 in condylar cartilage homeostasis. Mt1 expression was significantly upregulated under hypoxia and positively correlated with chondrocyte viability, migration, and extracellular matrix synthesis. RNA-seq and enrichment analyses revealed that Mt1 regulates genes associated with mitochondrial respiration and Ca²⁺ binding. Mt1 knockdown significantly downregulated intracellular Ca²⁺, which were restored by extracellular Ca²⁺ supplementation. Seahorse analysis demonstrated that Mt1 knockdown significantly suppressed mitochondrial respiration and glycolytic capacity, whereas extracellular Ca²⁺ supplementation restored these deficits. In vivo, Mt1 knockdown aggravated condylar cartilage degeneration, which was further exacerbated under chronic sleep deprivation-induced hypoxia, as evidenced by surface erosion, matrix loss, and histological disorganization. Mt1 preserves TMJ condylar chondrocyte homeostasis under low oxygen and hypoxic conditions by coordinating mitochondrial and glycolytic metabolism through Ca²⁺ regulation. The Mt1–Ca²⁺–mitochondrial metabolic axis serves as a key adaptive mechanism sustaining cellular energy homeostasis and represents a potential therapeutic target for preventing temporomandibular joint osteoarthritis.