Abstract 2893: Cell Culture Model for Structural Changes Occurring Before Onset of Atrial Fibrillation
Purpose: Structural remodeling already starts before onset of atrial fibrillation (AF), caused by underlying diseases like hypertension, and may set the stage for AF. Stretch is thought to be an important mediator in causing these structural changes. We aim to establish a cell culture model in which early remodeling in pressure overload of atria is mimicked. This represents the atrial situation after start of hypertension or heart failure but before start of AF.
Methods: HL-1 atrial cardiomyocytes and neonatal rat atrial cardiomyocytes were grown and set under cyclical stretch on elastic membranes using the Flexercell-4000 system. Cells were analyzed at different timepoints for occurrence of apoptosis, induction of the fetal gene program and breakdown of contractile elements as seen in myolysis. Apoptosis was determined by caspase-3 activity. Fetal gene expression was determined by measuring skeletal alpha-actin, alpha/beta-myosin heavy chain (MHC) ratio, and ANP and BNP mRNA expression. The amount of cardiac troponin T (cTNT) present, as measure of myolysis, was analyzed using Western blotting.
Results: Stretching of HL-1 cells for 24 hr with 3 Hz and 10% elongation significantly reduced cTNT protein expression. In contrast to pacing experiments this was due to a decrease in cTNT mRNA expression to 30% of control levels, but not proteolytic cleavage of the cTNT protein. Increased mRNA expression of skeletal alpha-actin and an increased beta/alpha-MHC ratio as markers for re-induction of the fetal gene program were found. Increased apoptosis was indicated by a 9-fold increase in caspase-3 activity. Interestingly, in HL-1 cells expression of the stress marker ANP was reduced by 50% whereas the known markers for ventricular stress, BNP and growth differentiation factor-15 expression were 3.8-fold and 4.1-fold increased upon stretch, respectively.
Conclusions: Stretch of atrial cardiomyocytes results in cellular changes seen before and in the early course of AF, including re-induction of the fetal gene program, apoptosis and reduced production of contractile proteins. This model can be used to test molecular mechanisms and signal transduction governing these effects and is a way of testing new or known pharmaceutical agents.