Clin Res Cardiol (2022). https://doi.org/10.1007/s00392-022-02002-5

Atrial tissue slices: a model to study mechanically-induced fibrosis
T. Schiatti1, J. Greiner1, E. Rog-Zielinska1, T. Seidel2, P. Kohl1, U. Ravens1, R. Peyronnet1
1Institut für Experimentelle Kardiovaskuläre Medizin, Universitäts-Herzzentrum Freiburg - Bad Krozingen GmbH, Freiburg im Breisgau; 2Institut für Zelluläre und Molekulare Physiologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen;

Fibrosis is a common phenotype of a number of cardiac diseases. This excess accumulation of extracellular matrix proteins can be both the cause and the consequence of electrophysiological or/ and mechanical remodelling. In the context of atrial fibrillation (AF), fibrosis constitutes a substrate contributing to the maintenance and progression of the arrhythmia. Since atrial fibrosis and mechanical overload are typically both associated with AF in the majority of patients, we postulate that mechanical overload applied to atrial tissue from patients in sinus rhythm (SR) can induce fibrosis patterns that resemble those found in AF. The aim of our study is to gain deeper insight into atrial fibrosis development in order to limit ‘domestication’ of AF. To this purpose we have developed an in-vitro model replicating key features of mechanically-induced fibrosis.

Rabbit and human atrial slices, 400 µm thickness and 3-5 mm length and width, were cultured in biomimetic chambers for up to 5 days. The tissue was paced at 2 Hz and a controlled preload was applied chronically from the beginning of the culture. Tissue quality over time was assessed by monitoring functional parameters: (i) systolic and diastolic forces; (ii) responses to mechanical stimuli (Frank-Starling mechanism, slow force response); (iii) responses to changes in stimulation frequency (force-frequency relationship, post-rest potentiation). Live staining of collagen and cell membranes was used to analyse tissue structure.

Our results show that slice contractility was stable over time for up to 5 days and cardiac canonical mechanically-induced responses (Frank-Starling and slow force response) were maintained. Cardiomyocyte shape as well as tranverse tubules were also conserved. Expected responses to well-known modulators of cardiomyocyte contractility such as isoproterenol were also observed. Tissue was mechanically stressed by the application of a constant preload of 2 mN over 3 days in order to mimic the mechanical overload observed in patients. This mechanical stimulation resulted in an increased deposition of collagen which was analysed using a tailor-made automated image analysis method.
Our work demonstrates that atrial tissue can be maintained in culture over 5 days with preserved contractile properties and typical mechanically-induced responses, making this model suitable for medium-term investigations of mechanical load effects on atrial functional and structural remodelling. The mechanical induction of fibrosis in these conditions will allow to monitor over time and in parallel both the organisation of collagen deposition and the consequences for active/ passive forces as well as for electrical conduction. Based on the changes in passive mechanics, it will also be interesting to explore to what extend collagen contributes to protect cardiomyocytes and nonmyocytes from excess diastolic strain. We envision that such a platform will facilitate drug testing and the identification of molecular targets which can potentially reduce, slow down, or stop fibrosis.


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