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

• A Titin fragment was identified in human urine.
• The Titin fragment was shown to be produced primarily by MMP-2 cleavage.
• Titin-MMP2 fragment had higher expression in rat extensor digitorum longus muscle.
• Titin-MMP2 decreased initially and gradually increased in muscle atrophy studies.

PurposeIn this study we sought to determine whether a Titin peptide fragment can serve as a clinical biomarker for changes in muscle mass.MethodsMass 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.ResultsA 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.ConclusionsWe 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.