Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Weixler, V.
Pathophysiological Mechanism of Endocardial Fibroelastosis Development in Hypoplastic Left Heart Syndrome.
Doktoratsstudium der Medizinischen Wissenschaft; Humanmedizin; [ Dissertation ] Graz Medical University; 2020. pp. 82
[OPEN ACCESS]
FullText
- Autor*innen der Med Uni Graz:
- Betreuer*innen:
- Koestenberger Martin
- Yates Ameli
- Altmetrics:
- Abstract:
- Background: Endothelial-to-mesenchymal-transition (EndMT) plays a major role in cardiac fibrosis, including endocardial fibrosis (EFE), which is associated with congenital heart defects such as hypoplastic left heart syndrome (HLHS). The stimuli for EndMT leading to EFE formation are still unknown but we speculate that mechanical forces and young age are associated with the development of this unique form of fibrosis. The aims of the study were to identify stimuli and regulator pathways leading to the development of EFE. Material and Methods: Endothelial cells (EC) in culture were exposed to 8hrs of 10% uniaxial stretch or direct stimulation of EndMT through addition of TGF-b to the media. Inhibition of the TGF-β pathway was performed by local application of: BMP7, a TGF-ß inhibitor SB431542 or Losartan. Immature and mature isolated perfused rat hearts (n=7/group) were exposed to 3h stretch through a weight attached to the apex of the LV. The same groups as in the isolated cell culture experiments were tested. Additionally, EFE tissue resected from the LV of 24 HLHS patients and macroscopically ‘EFE-like’ tissue of 6 non-HLHS patients with known flow disturbances in the LV outflow tract was analyzed. Amount of collagen/elastin, vascularity/cellularity and presence of active EndMT was determined by immunohistochemical staining. Tissue remodeling through degradation of elastic fibers/collagen by matrix metalloproteinases was determined by in situ zymography. Results: Stretch induced EndMT in isolated ECs in culture was determined by significantly more CD-31/alpha-SMA double-stained endothelial cells (46±13% of total cell count), and confirmed in whole hearts (15.9±2% of total cell count) compared to controls (cells: 7±2%; heart: 3.1±0.1; p<0.05). However, only immature hearts showed endocardial EndMT. Inhibition of the TGF-ß pathway significantly decreased the number of double-stained cells following stretch, comparable to controls (cells/heart: control: 7±2/3.1±0.1%, stretch: 46±13/15±2%, BMP7: 7±2/2.9±0.1%, 5.2±1.3%, Losartan (heart only): 0.89±0.1%; p<0.001). “EFE-like” tissue obtained from non-HLHS patients, showed the same characteristics as EFE tissue from HLHS patients. Active EndMT was found in all 24 HLHS samples and all 6 non-HLHS patients. In the “non-HLHS” patient group with valvar disease, predominantly a jet across a stenotic mitral valve was present. In situ zymography displayed a balance between degradation of elastin/collagen and elastase/gelatinase activity. Conclusion: EndMT was induced in in vitro and ex vivo experiments by mechanical strain on the endocardium, however, only in immature hearts. By use of specific inhibitors such as BMP-7 and Losartan, the TGF-ß pathway was identified as the main stimulator for EndMT development. Mechanical forces such as flow disturbances and stretch exposing endocardial endothelial cells to altered mechanical force are triggers for induction of EndMT. In human EFE pathology, prolonged exposure of endcardial endothelial cells to altered mechanical forces leads to reoccurrence of EFE displaying with a more infiltrative growth pattern into the underlying myocardium. These alterations are not limited to HLHS but are associated with severe congenital valve diseases with flow turbulences.