Cardiac-restricted overexpression of membrane type-1 matrix metalloproteinase in mice: effects on myocardial remodeling with aging.

BACKGROUND: The direct consequences of a persistently increased myocardial expression of the unique matrix metalloproteinase (MMP) membrane type-1 (MT1-MMP) on myocardial remodeling remained unexplored. METHODS AND RESULTS: Cardiac-restricted MT1-MMPexp was constructed in mice using the full-length human MT1-MMP gene ligated to the myosin heavy chain promoter, which yielded approximately a 200% increase in MT1-MMP when compared with age/strain-matched wild-type (WT) mice. Left ventricular (LV) function and geometry was assessed by echocardiography in 3-month ("young") WT (n=32) and MT1-MMPexp (n=20) mice and compared with 14-month ("middle-aged") WT (n=58) and MT1-MMPexp (n=35) mice. LV end-diastolic volume was similar between the WT and MT1-MMPexp young groups, as was LV ejection fraction. In the middle-aged WT mice, LV end-diastolic volume and ejection fraction was similar to young WT mice. However, in the MT1-MMPexp middle-aged mice, LV end-diastolic volume was approximately 43% higher and LV ejection fraction 40% lower (both P<0.05). Moreover, in the middle-aged MT1-MMPexp mice, myocardial fibrillar collagen increased by nearly 2-fold and was associated with approximately 3-fold increase in the processing of the profibrotic molecule, latency-associated transforming growth factor binding protein. In a second study, 14-day survival after myocardial infarction was significantly lower in middle-aged MT1-MMPexp mice. CONCLUSIONS: Persistently increased myocardial MT1-MMP expression, in and of itself, caused LV remodeling, myocardial fibrosis, dysfunction, and reduced survival after myocardial injury. These findings suggest that MT1-MMP plays a mechanistic role in adverse remodeling within the myocardium.

Targeted myocardial microinjections of a biocomposite material reduces infarct expansion in pigs.

BACKGROUND: Left ventricular (LV) remodeling after myocardial infarction (MI) commonly causes infarct expansion (IE). This study sought to interrupt IE through microinjections of a biocompatible composite material into the post-MI myocardium. METHODS: MI was created in 21 pigs (coronary ligation). Radiopaque markers (2-mm diameter) were placed for IE (fluoroscopy). Pigs were randomized for microinjections (25 injections; 2- x 2-cm array; 200 microL/injection) at 7 days post-MI of a fibrin-alginate composite (Fib-Alg; fibrinogen, fibronectin, factor XIII, gelatin-grafted alginate, thrombin; n = 11) or saline (n = 10). RESULTS: At 7 days after injection (14 days post-MI), LV posterior wall thickness was higher in the Fib-Alg group than in the saline group (1.07 +/- 0.11 vs 0.69 +/- 0.07 cm, respectively, p = 0.002). At 28 days post-MI, the area within the markers (IE) increased from baseline (1 cm2) in the saline (1.71 +/- 0.13 cm2, p = 0.010) and Fib-Alg groups (1.44 +/- 0.23 cm2, p < 0.001). However, the change in IE at 21 and 28 days post-MI was reduced in the Fib-Alg group (p=0.043 and p=0.019). Total collagen content within the MI region was similar in the saline and Fib-Alg groups (12.8 +/- 1.7 and 11.6 +/- 1.5 microg/mg, respectively, p = NS). However, extractable collagen, indicative of solubility, was lower in the Fib-Alg group than the saline group (59.1 +/- 3.5 vs 71.0 +/- 6.1 microg/mL, p = 0.020). CONCLUSIONS: Targeted myocardial microinjection of the biocomposite attenuated the post-MI decrease in LV wall thickness and infarct expansion. Thus, intraoperative microinjections of biocompatible material may provide a novel approach for interrupting post-MI LV remodeling.

Differential protein kinase C isoform abundance in ascending aortic aneurysms from patients with bicuspid versus tricuspid aortic valves.

BACKGROUND: It is recognized that different events contribute to the initiation of ascending thoracic aortic aneurysms (ATAAs) in patients with bicuspid aortic valves (BAV) versus patients with tricuspid aortic valves (TAV), but the molecular signaling pathways driving aneurysm formation remain unclear. Protein kinase C (PKC) is a superfamily of kinases which differentially mediate signaling events that lead to altered gene expression and cellular function, and may regulate downstream mediators of vascular remodeling. The present study tested the hypothesis that ATAA development in patients with BAV versus TAV proceeds by independent signaling pathways involving differential PKC signaling. METHODS AND RESULTS: ATAA samples were collected from BAV (n=57) and TAV (n=55) patients and assessed for 10 different PKC isoforms by immunoblotting. Results were expressed as a percent change in abundance (mean+/-SEM) from a nonaneurysmal control group (100%, n=21). Correlation analysis was performed, and relationships between PKC and matrix metalloproteinase abundance were reported. In the BAV group, classic and novel PKC isoforms (PKC-alpha, betaI, gamma, epsilon, theta) were increased, whereas PKC-eta and atypical PKC-zeta were decreased. In the TAV group, classic and novel isoforms were decreased and atypical PKC-zeta was elevated. Positive correlations between PKC and matrix metalloproteinase abundance were identified. CONCLUSIONS: Differential PKC isoform abundance was observed in ATAA samples from patients with BAV versus TAV, suggesting independent molecular signaling pathways may be operative. Induction of independent transcriptional programs may result and may provide a mechanistic foundation for developing selective diagnostic/therapeutic strategies for patients with ATAAs secondary to BAV or TAV.

Temporal disparity in the induction of matrix metalloproteinases and tissue inhibitors of metalloproteinases after thoracic aortic aneurysm formation.

BACKGROUND: An important component of matrix remodeling during thoracic aortic aneurysm progression is the balance between matrix metalloproteinases and their endogenous inhibitors (tissue inhibitors of metalloproteinases). However, whether and to what degree matrix metalloproteinase/tissue inhibitor of metalloproteinases profiles change over time with an evolving thoracic aortic aneurysm remains unclear. METHODS: Descending thoracic aortic aneurysms were induced in mice (FVB strain, 15 minutes of 0.5 mol/L CaCl2 exposure) and followed for 24 hours, 72 hours, 1 week, 2 weeks, 4 weeks, or 8 weeks (each group, n = 13). Thoracic aortic aneurysm size was determined by means of video micrometry, and immunoblotting was used to measure aortic matrix metalloproteinase 2, 8, 9, and 12 and tissue inhibitor of metalloproteinases 1 and 4 levels (expressed as a percentage of control values, n = 13). RESULTS: Increased aortic diameter was detected by 72 hours and reached a maximal size at 4 weeks (135% +/- 4% increase from baseline, P < .05), which is consistent with thoracic aortic aneurysm progression. Active matrix metalloproteinase 8 (collagenase) levels increased at 72 hours (178% +/- 49%, P < .05 from control), and active matrix metalloproteinase 12 (elastase) levels increased by 24 hours (138% +/- 11%, P < .05), whereas active matrix metalloproteinase 2 levels increased at 72 hours and 1 week after thoracic aortic aneurysm induction (72 hours: 158% +/- 12%, 1 week: 162% +/- 19%; P < .05). At 1 week after thoracic aortic aneurysm induction, active matrix metalloproteinase 9 and 12 levels decrease (matrix metalloproteinase 9: 55% +/- 5%; matrix metalloproteinase 12: 63% +/- 5%; P < .05); however, matrix metalloproteinase 9 and 12 levels were increased from these values at 4 and 8 weeks (P < .05). Tissue inhibitor of metalloproteinases 1 levels were decreased at 1 week (52% +/- 15%, P < .05) and later returned to control values, whereas tissue inhibitor of metalloproteinases 4 levels increased at the late thoracic aortic aneurysm time points (4 weeks: 278% +/- 46%; 8 weeks: 213% +/- 40%; P < .05). CONCLUSIONS: These findings show 2 phases of matrix metalloproteinase abundance during murine thoracic aortic aneurysm formation. The late tissue inhibitor of metalloproteinases 4 increase might explain prevention of further aortic dilation past 4 weeks. Unique matrix metalloproteinase/tissue inhibitor of metalloproteinases temporal relationships occurred during the natural history of thoracic aortic aneurysm progression that might hold both diagnostic and therapeutic relevance.