Titin is a target of matrix metalloproteinase-2: implications in myocardial ischemia/reperfusion injury.
BACKGROUND
Titin is the largest mammalian (≈3000 to 4000 kDa) and myofilament protein that acts as a molecular spring in the cardiac sarcomere and determines systolic and diastolic function. Loss of titin in ischemic hearts has been reported, but the mechanism of titin degradation is not well understood. Matrix metalloproteinase-2 (MMP-2) is localized to the cardiac sarcomere and, on activation in ischemia/reperfusion injury, proteolyzes specific myofilament proteins. Here we determine whether titin is an intracellular substrate for MMP-2 and if its degradation during ischemia/reperfusion contributes to cardiac contractile dysfunction.


RESULTS
Immunohistochemistry and confocal microscopy in rat and human hearts showed discrete colocalization between MMP-2 and titin in the Z-disk region of titin and that MMP-2 is localized mainly to titin near the Z disk of the cardiac sarcomere. Both purified titin and titin in skinned cardiomyocytes were proteolyzed when incubated with MMP-2 in a concentration-dependent manner, and this was prevented by MMP inhibitors. Isolated rat hearts subjected to ischemia/reperfusion injury showed cleavage of titin in ventricular extracts by gel electrophoresis, which was confirmed by reduced titin immunostaining in tissue sections. Inhibition of MMP activity with ONO-4817 prevented ischemia/reperfusion-induced titin degradation and improved the recovery of myocardial contractile function. Titin degradation was also reduced in hearts from MMP-2 knockout mice subjected to ischemia/reperfusion in vivo compared with wild-type controls.


CONCLUSIONS
MMP-2 localizes to titin at the Z-disk region of the cardiac sarcomere and contributes to titin degradation in myocardial ischemia/reperfusion injury.
Department of Pharmacology, Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada.
Mohammad A M
MA
Ali
Woo Jung
WJ
Cho
Bryan
B
Hudson
Zamaneh
Z
Kassiri
Henk
H
Granzier
Richard
R
Schulz
D000818:Animals; D064211:Connectin; D006801:Humans; D008297:Male; D020778:Matrix Metalloproteinase 2 / Q000235:genetics / Q000378:metabolism*; D061965:Matrix Metalloproteinase Inhibitors; D051379:Mice; D018345:Mice, Knockout; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D009200:Myocardial Contraction / Q000187:drug effects / Q000235:genetics; D015428:Myocardial Reperfusion Injury / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000473:pathology; D010647:Phenyl Ethers / Q000494:pharmacology; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012508:Sarcolemma / Q000235:genetics / Q000378:metabolism / Q000473:pathology
D064211:Connectin; D061965:Matrix Metalloproteinase Inhibitors; D009124:Muscle Proteins; C414368:N-hydroxy-5-ethoxymethyloxy-2-methyl-4-(4-phenoxybenzoyl)aminopentanamide; D010647:Phenyl Ethers; C577285:TTN protein, human; C577295:Ttn protein, rat; D011494:Protein Kinases; C522361:MMP2 protein, human; D020778:Matrix Metalloproteinase 2; C522362:Mmp2 protein, mouse; C522363:Mmp2 protein, rat