Increased Inflammatory Gene Expression in Masseter Muscle of an Orthognathic Surgery Subject with Obstructive Sleep Apnea

Abstract

Objective: Obstructive sleep apnea (OSA) is defined by recurrent breathing cessations accompanied by a collapse of the pharyngeal airway. Co-morbid conditions include obesity, cardiovascular disease, diabetes, and in some cases, retrognathia and muscle dysfunction. The latter two conditions may prompt orthognathic correction. Past investigations have shown a genetic association with OSA. Given that masseter muscle influences skeletal malocclusion and is active during OSA, we investigated whether the expression of OSA-associated genes is altered in a Class II open bite OSA subject. Methods: Eleven mandibular advancement surgery patients were classified as skeletal Class II or III and open or deep bite malocclusion, including a Class II open bite patient with OSA. Masseter muscle samples were collected at surgery and frozen. Tissue was used for gene expression analysis on Affymetrix HT2.0 microarray chips and quantitative RT-PCR. Data for ten genes associated with OSA were individually evaluated in the microarray and compared between the OSA patient and eight symmetrical malocclusion subjects. In order to corroborate these expression data, one gene of interest, tumor necrosis factor (TNF), was quantified in the ten malocclusion subjects from the microarray, an OSA subject from the microarray and one additional OSA subject by RT-PCR. Results: Among OSA-associated genes on the microarray, interleukin genes IL1B, IL1R2, IL6 and IL8 were +2.5 to +9.2 fold greater (p < 0.02) and chemokine genes CCL2, CCL3, CCL3L3, CCL4 and CXCR1 were +2.0 to +12.1 fold greater (p < 0.05). Likewise, TNF expression differed significantly in the muscle of the OSA subject (+2.2 fold greater; p < 0.001). By quantitative RT-PCR, TNF expression was significantly greater in malocclusion subjects with OSA compared to those without OSA (p = 0.0004). Conclusions: Our findings support evidence that OSA is an inflammatory disorder, which may elicit hypoxia-induced inflammatory responses believed to promote skeletal muscle dysfunction. Specifically, we report that inflammatory gene expression is significantly increased in masseter muscle in Class II open bite subjects with OSA. In turn, malocclusion may contribute to OSA, which negatively affects masseter function, resulting in exacerbation of both disorders. Because OSA is reported to associate with a polymorphism in the TNF-alpha; gene in children, future studies are needed to test for similar genetic associations in malocclusion subjects with OSA.