Cell shape determines gene expression in cardiomyocytes

Abstract

The fundamental biological processes involve sensing biophysical stress, strain and forces along with conversion of these stimuli into chemical signals. These processes are linked to the atrophic and hypertrophic responses. Deficiencies in these biological processes are associated with different diseases, particularly in the circulation system. Although cardiomyocytes are exposed to significant hemodynamic stimuli that alter their shapes, it was not known until recently whether changes in cardiomyocyte shape impact gene expression. However, recent progress in single-cell RNA sequencing have enabled the profiling of transcriptomes of individual cardiomyocytes with engineered geometries, which are specific to normal or pathological conditions such as preload or afterload.

Cardiomyocytes undergo considerable changes in cell morphology, either due to mutations, causing various cardiomyopathies such as hypertrophic cardiomyopathy or dilated cardiomyopathy or via changes in hemodynamic conditions. Moreover, because of various patterns of contraction-relaxation cycles, the membrane of cardiomyocytes is dynamically reshaped in each beating cycle. The overall aim of this thesis was to investigate the effects of cardiomyocyte geometry on gene expression and signaling.

In study I, we engineered a novel platform to study cardiomyocyte morphology. In this article, we presented a single-cardiomyocyte trapping strategy, consisting of a method for growing neonatal rat cardiomyocytes with different aspect ratios. The study also proposes a protocol to sort patterned cardiomyocytes based on their acquired geometrical aspect ratios and pick up these adherent cells from their pattern. The described approach paved the way to profile the transcriptome of single cardiomyocytes with specific geometric aspect ratio.

In study II, we employed single-cell RNA sequencing to investigate impacts of cardiomyocyte aspect ratio on its transcriptome, using the approach proposed in study I. We observed that distinct morphotypic cardiomyocytes had noticeably varied gene expression patterns, implying that the shape of a cardiomyocyte plays a role in gene expression. This was apparent from the separate cluster of cells, detected in unsupervised clustering analyses.

In study III, we proposed a mathematical model of a sarcomere to examine whether and how signaling activity at the membrane of cardiomyocyte depends on its beating rate. Based on this model, a multiphysics program was designed to simulate the cardiomyocyte dynamic geometry throughout the contraction and relaxation phases. The main finding of this study was that an increase in the rate of cardiomyocyte contraction leads to an increase in the concentration of activated Src kinase, especially underneath the costameres. Since hypertrophy of cardiomyocyte modifies the ratio of surface to volume at the plane of membrane, the finding of this study suggests that hypertrophy might be considered as part of a feedback, equilibrating membrane-mediated signaling cascades. These studies identify the shape of the cardiomyocyte as a significant determinant of its gene expression and signaling. Our findings illustrate a novel and important observation, with potentially far-reaching impacts in medicine and biology.