Measurement of a MMP-2 degraded Titin fragment in serum reflects changes in muscle turnover induced by atrophy

Purpose: In this study we sought to determine whether a Titin peptide fragment can serve as a clinical biomarker for changes in muscle mass. Methods: Mass spectrometry was used to identify Titin fragment in urine. An antibody against this Titin sequence was raised and used to develop a competitive ELISA assay for measurement in serum. Rat tissue extractions in the presence or absence of a series of proteases of interest were used to identify its enzymatic origin. A rat model of dexamethasone (DEX) induced muscle atrophy and a human 56-day bed rest study with and without vibration therapy were used to assess biological and clinical relevance. Results: A technically robust ELISA measuring the Titin fragment was developed against a Titin peptide fragment identified in human urine. The fragment was shown to be produced primarily by MMP-2 cleavage of Titin. In the rat muscle DEX induced atrophy model, Titin-MMP2 fragment was decreased in the beginning of DEX treatment, and then significantly increased later on during DEX administration. In the human bed rest study, the Titin-MMP2 fragment was initially decreased 11.9 (+/- 3.7) % after 1 day of bed rest, and then gradually increased ending up at a 16.4 (+/- 4.6) % increase at day 47. Conclusions: We developed a robust ELISA measuring a muscle derived MMP-2 generated Titin degradation fragment in rat and human serum. Importantly, the fragment can be measured in serum and that these levels are related to induction of skeletal muscle atrophy. (C) 2014 Elsevier Inc. All rights reserved.