SIGNIFICANT PROLONGATION OF MURINE CARDIAC ALLOGRAFT SURVIVAL BY INHIBITION OF MATRIX METALLOPROTEINASE

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TITLE: SIGNIFICANT PROLONGATION OF MURINE CARDIAC ALLOGRAFT SURVIVAL BY INHIBITION OF MATRIX METALLOPROTEINASE–2

Andrés Jaramillo,¹ Wei Lu,¹ Lacey Campbell,¹ J. Michael Shipley,² Robert M. Senior,² Shigeyoshi Hitohara,³ T. Mohanakumar.^1,4

¹Surgery, Washington University School of Medicine, St. Louis, Missouri; ¹Cell Biology & Physiology, Washington University School of Medicine, St. Louis, Missouri; ³Brain Science Institute, Wako, Japan; ⁴Pathology & Immunology, Washington University School of Medicine, St. Louis, Missouri

Acute rejection is still the leading cause of cardiac allograft failure during the first post–operative year. The roles of immune mediator molecules, such as matrix metalloproteinases (MMP), in the pathogenesis of acute cardiac allograft rejection have not been addressed. The goal of this study was 1) to determine whether MMPs play a role in the pathogenesis of acute cardiac allograft rejection.

BALB/c cardiac allografts were transplanted into C57BL/6, 129, MMP–2–KO, and MMP–9–KO mice. Also, recipient C57BL/6 mice were treated with doxycycline, an inhibitor of MMP enzymatic activity. Rejection was defined by cessation of a palpable heartbeat and confirmed histologically. The intra–graft levels of MMP–2 and –9 mRNA were determined by RT–PCR. The intra–graft levels of MMP–2 and –9 enzymatic activity were determined by zymography and immunohistochemistry. C57BL/6 and 129/SvEv isografts did not show any histopathological signs of rejection at 30 days post–transplantation. These isografts revealed no MMP–2 or MMP–9 mRNA expression or enzymatic activity. BALB/c allografts were rejected by 129 mice and MMP–9–KO 129 mice after 15.2+/–2.6 and 10.5+/–4.5, respectively. In contrast, a BALB/c allograft transplanted into a MMP–2–KO 129 mouse had survived 26 days post–transplantation. BALB/c allografts were rejected by C57BL/6 mice after 8.5+/–0.6 days. In contrast, doxycycline treatment of C57BL/6 recipients prolonged the graft survival of BALB/c allografts to 27.7+/–1.5 days (P = 0.00008). Rejected allografts showed mononuclear infiltration and development of fibrosis and revealed a greater up–regulation of MMP–2 than MMP–9 mRNA transcription and enzymatic activity. Analysis of graft–infiltrating cells in rejected allografts showed that 80% expressed MMP–2 while only 20% expressed MMP–9.

These results indicate an important role for MMP–2 in the pathogenesis of acute cardiac allograft rejection and suggest that this enzyme is a suitable target for therapeutic intervention for the treatment of solid organ allograft rejection.