Multimodality imaging reveals a gradual increase in matrix metalloproteinase activity at aneurysmal lesions in live fibulin-4 mice.
BACKGROUND
We imaged the protease activity of matrix metalloproteinases (MMPs) upregulated during aneurysm formation, using protease-activatable near-infrared fluorescence probes. We tested whether these protease-activatable sensors can directly report the in vivo activity of the key biomarkers in aneurysm, using our genetically modified fibulin-4 mouse models for aneurysm formation. Mice homozygous for the fibulin-4 reduced-expression allele (fibulin-4(R/R)) show dilatation of the ascending aorta and a tortuous, stiffened aorta resulting from disorganized elastic fiber networks. Strikingly, even a moderate reduction in expression of fibulin-4 in the heterozygous fibulin-4(+/R) mice occasionally results in modest aneurysm formation.


RESULTS
Aorta transcriptome and protein expression analysis of fibulin-4(+/R) and fibulin-4(R/R) animals identified excessive transforming growth factor-β signaling as the critical event in the pathogenesis of aneurysm formation. To determine whether a perturbed elastin lamellar structure arose from induction of transforming growth factor-β-regulated MMPs, we performed gelatin zymography and used a protease-activatable near-infrared fluorescence probe to monitor and quantify MMP upregulation in animals, using various in vivo optical imaging modules and coregistration of the fluorescence signal with CT images of the same animals. Gelatin zymography demonstrated a significant increase in the presence of the active form of MMP-9 in the aortic arch of fibulin-4(R/R) mice. In vivo analysis of MMP upregulation using the near-infrared fluorescence probe and subsequent isosurface concentration mapping from reconstructed tomographic images from fibulin-4(+/R) and fibulin-4(R/R) mice revealed a graded increase in activation of MMPs within the aneurysmal lesions.


CONCLUSIONS
We aimed to develop molecular imaging procedures for faster, earlier, and easier recognition of aortic aneurysms. We show that in vivo coregistration of MMP activity by noninvasive tomographic imaging methods allows the detection of increased MMP activity, even before the aneurysm has actually formed.
Kaijzel
Eric L
EL
Department of Endocrinology and Metabolic Diseases, Leiden University Medical Center, Leiden, The Netherlands.
van Heijningen
Paula M
PM
Wielopolski
Piotr A
PA
Vermeij
Marcel
M
Koning
Gerben A
GA
van Cappellen
Wiggert A
WA
Que
Ivo
I
Chan
Alan
A
Dijkstra
Jouke
J
Ramnath
Natasja W M
NW
Hawinkels
Lukas J A C
LJ
Bernsen
Monique R
MR
Löwik
Clemens W G M
CW
Essers
Jeroen
J
D000818:Animals; D001013:Aorta, Thoracic / Q000000981:diagnostic imaging / Q000201:enzymology / Q000473:pathology*; D017545:Aortic Aneurysm, Thoracic / Q000175:diagnosis* / Q000201:enzymology / Q000235:genetics; D001027:Aortography / Q000379:methods; D015415:Biomarkers / Q000378:metabolism; D015374:Biosensing Techniques; D004195:Disease Models, Animal; D018450:Disease Progression; D042241:Early Diagnosis; D004549:Elastin; D004789:Enzyme Activation; D016326:Extracellular Matrix Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D005453:Fluorescence; D018810:Magnetic Resonance Angiography; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D020782:Matrix Metalloproteinases / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D057054:Molecular Imaging / Q000379:methods; D011237:Predictive Value of Tests; D015398:Signal Transduction; D019265:Spectroscopy, Near-Infrared; D014057:Tomography, X-Ray Computed; D016212:Transforming Growth Factor beta / Q000378:metabolism; D015854:Up-Regulation
D015415:Biomarkers; C403672:EFEMP2 protein, human; D016326:Extracellular Matrix Proteins; D016212:Transforming Growth Factor beta; D004549:Elastin; D020782:Matrix Metalloproteinases; D020780:Matrix Metalloproteinase 9; C501830:Mmp9 protein, mouse