Differential expression of Hedgehog/Notch and transforming growth factor-β in human abdominal aortic aneurysms.
OBJECTIVE
The molecular mechanisms leading to the development of abdominal aortic aneurysms (AAAs) remain poorly understood. The aim of this study was to determine the expression of Sonic Hedgehog (SHh), transforming growth factor β (TGF-β), and Notch signaling components in human aneurysmal and nonaneurysmal aorta in vivo.


METHODS
Paired tissue samples were obtained from aneurysmal and nonaneurysmal (control) segments of the aortic wall of eight patients with suitable anatomy undergoing open repair of infrarenal AAAs. Protein and messenger RNA (mRNA) expression levels were determined by Western blot and quantitative real-time polymerase chain reaction analysis.


RESULTS
Aneurysm development resulted in a significant reduction in vascular smooth muscle (vSMC) differentiation genes α-actin and SMC22α at both mRNA and protein levels. In parallel experiments, an 80.0% ± 15% reduction in SHh protein expression was observed in aneurysmal tissue compared with control. SHh and Ptc-1 mRNA levels were also significantly decreased, by 82.0% ± 10% and 75.0% ± 5%, respectively, in aneurysmal tissue compared with nonaneurysmal control tissue. Similarly, there was a 50.0% ± 9% and 60.0% ± 4% reduction in Notch receptor 1 intracellular domain and Hrt-2 protein expression, respectively, in addition to significant reductions in Notch 1, Notch ligand Delta like 4, and Hrt-2 mRNA expression in aneurysmal tissue compared with nonaneurysmal tissue. There was no change in Hrt-1 expression observed in aneurysmal tissue compared with control. In parallel experiments, we found a 2.2 ± 0.2-fold and a 5.6 ± 2.2-fold increase in TGF-β mRNA and protein expression, respectively, in aneurysmal tissue compared with nonaneurysmal tissue. In vitro, Hedgehog signaling inhibition with cyclopamine in human aortic SMCs resulted in decreased Hedgehog/Notch signaling component and vSMC differentiation gene expression. Moreover, cyclopamine significantly increased TGF-β1 mRNA expression by 2.6 ± 0.9-fold.


CONCLUSIONS
These results suggest that SHh/Notch and TGF-β signaling are differentially regulated in aneurysmal tissue compared with nonaneurysmal tissue. Changes in these signaling pathways and the resulting changes in vSMC content may play a causative role in the development of AAAs.
Department of Surgery, University of Rochester Medical Center, Rochester, NY.
Adam J
AJ
Doyle
Department of Surgery, University of Rochester Medical Center, Rochester, NY.
Eileen M
EM
Redmond
Heart and Vascular Center, South Coast Health Systems, Fall River/New Bedford, Mass.
David L
DL
Gillespie
Department of Surgery, University of Rochester Medical Center, Rochester, NY.
Peter A
PA
Knight
Department of Surgery, University of Rochester Medical Center, Rochester, NY.
John P
JP
Cullen
Vascular Biology and Therapeutics Laboratory, School of Biotechnology, Dublin City University, Dublin, Ireland.
Paul A
PA
Cahill
Department of Surgery, University of Rochester Medical Center, Rochester, NY. Electronic address: david_morrow@urmc.rochester.edu.
David J
DJ
Morrow
D000199:Actins / Q000096:biosynthesis / Q000235:genetics; D017544:Aortic Aneurysm, Abdominal / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D005260:Female; D015870:Gene Expression; D053823:Hedgehog Proteins / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism* / Q000503:physiopathology; D032389:Myocytes, Smooth Muscle / Q000378:metabolism; D051880:Receptors, Notch / Q000096:biosynthesis* / Q000235:genetics; D016212:Transforming Growth Factor beta / Q000096:biosynthesis* / Q000235:genetics
D000199:Actins; D053823:Hedgehog Proteins; D051880:Receptors, Notch; C509239:SHH protein, human; D016212:Transforming Growth Factor beta