Identification of matrix metalloproteinases and their tissue inhibitors type 1 and 2 in human masseter muscle

Changes in masticatory muscle structure and function are either development al, as seen in anomalies of facial Form, or adaptive, as seen during proced ures such as orthognathic surgery and functional-appliance orthodontic ther apy. Remodelling of muscle extracellular matrix is pivotal in these process es. This turnover is mediated via members of the family of enzymes known as matrix metalloproteinases (MMP) and inhibited by the tissue inhibitors of metalloproteinases (TIMP). The aim here was to investigate the in vivo patt ern of expression and distribution of MMPs and TIMPs in masseter muscle of humans with both normal and abnormal facial forms. Masseter muscle biopsies were taken from 10 patients, four with long-face syndrome and six normal c ontrols as confirmed by cephalometry, Immunohistochemical techniques were u sed to show the pattern and distribution of MMPs and TIMP proteins in the m uscle. Zymography of tissue extracts was used to determine the presence of MMP activity. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to detect the presence of MMP and TIMP-2 mRNA, MMP-1 was expressed aro und the individual muscle fibres, especially in those fibre surfaces in con tact with the interstices of the connective tissue and around blood vessels . MMP-9 staining was less intense and was expressed in the interstices of t he connective tissue and around blood vessels. Zymography of protein extrac ts confirmed that MMP-9 activity was present. MMP-2 and MMP-3 were not expr essed in the samples, although MMP-2 mRNA could be detected by RT-PCR and i ts activity could be detected by zymography. Intense TIMP-1 staining was pr esent around each muscle fibre, in the interstices of the connective tissue and surrounding blood vessels; TIMP-2 mRNA could be detected in all sample s. These staining patterns were seen in all biopsies examined and were irre spective of the facial form of the donor. These findings provide evidence t hat the mechanisms required for matrix remodelling are present in the human masseter muscle. (C) 2000 Elsevier Science Ltd. All rights reserved.