Table 2

 Main roles of some matrix metalloproteases (MMPs) and tissue inhibitors of metalloproteases (TIMPs)

MMP1• Upregulated in acute tendon tears3
• Upregulated in tendinopathy14
• Upregulated in response to shear stress15
• Downregulated in response to cyclical strain and static tensile load16,17
MMP2• Upregulated in tendinopathy8
• May be upregulated13 or downregulated3 in complete tendon tears
• Inhibits TIMP1 and TIMP2 in response to exercise10
MMP3• Plays a major role in maintenance and remodelling of normal tendon3,7
• Downregulated in tendinopathy and complete tendon tears3,6,8,12
• Upregulated in response to shear force8
MMP13Upregulated in complete tendon tears12
MMP9Upregulated following exercise9,10
TIMP1• Downregulated in tendinopathy7,14
• Upregulated transiently following an acute tendon tear13
• Inhibits excessive degeneration of ECM by MMP213
TIMP2, TIMP3, TIMP4Downregulated in tendinopathy7 and complete tendon tears12