ASSOCIATION OF MASSETER MUSCLE CACNA2D1, CACNA1S, GABARAP, AND TRPM7 GENE EXPRESSION IN TEMPOROMANDIBULAR JOINT DISORDERS

Abstract

A major physiological risk factor of temporomandibular disorders (TMD) is sensitization of peripheral and central nervous system pain processing pathways. Calcium channel, voltage-dependent, alpha-2/delta subunit-1 (CACNA2D1) has a crucial role in relaying nociceptive information in the spinal dorsal horn. Up-regulation of CACNA2D1 results in abnormal excitatory synapse formation and enhanced presynaptic excitatory neurotransmitter release. Blocking CACNA2D1 with gabapentinoid-class drugs relieves orofacial hypersensitivity. Drs. Foley, Horton, and Sciote previously reported that in a small sample group (n=12), CACNA2D1 expression was greater in males than females, but increased in women with TMD. The objectives of this study are to corroborate these data and investigate expression patterns of other ion channel and conducting system genes. Additionally, since the null polymorphism ACTN3-577XX associates with muscle fiber microdamage during eccentric contraction, we tested for possible gene associations with ACTN3-R577XX genotypes. Masseter muscle samples came from human subjects (n=23 male; 48 female) with malocclusions undergoing orthognathic surgery. This population had skeletal disharmony of the jaws and thus was prone to eccentric contraction. Three males and eighteen females were diagnosed with localized masticatory myalgia. Muscle total RNA was isolated and CACNA2D1, CACNA1S, GABARAP, and TRPM7 expression was quantified using RT-PCR. Expression of these genes were compared based on TMD status and various characteristics that may influence TMD including: sex, age, facial symmetry, sagittal dimension, vertical dimension, ACTN3-577 genotype and fiber type. CACNA2D1 expression differed significantly between sexes, overall (p<0.02), and without TMD (p=0.001). Women with (n=13) and without (n=23) TMD differed significantly (p<0.03). CACNA2D1 expression was also significantly higher (p=0.031) in subjects below age 25. Similarly, GABARAP expression was significantly higher (p=0.001) for patients younger than 25 and for patients less than or equal to age 18 (p=0.013). Otherwise, CACNA1S, TRPM7 and GABARAP differences were not significant. GABARAP expression differed, but not significantly by sex and for the ACTN3-577XX-null genotype. In a population of malocclusion patients, masseter muscle CACNA2D1 expression is significantly higher than CACNA1S, TRPM7, and GABARAP. CACNA2D1 expression is greater in males than females without TMD. However, CACNA2D1 expression increases significantly in females with TMD-associated myalgia. This may support evidence for calcium channel regulation of nociception differences seen between sexes in TMD. It was also found that expression of CACNA2D1 and GABARAP is significantly higher in younger subjects. Additionally, observations presented here suggest potential influence of ACTN3-null condition on function of GABARAP.