Microenvironmental Transthyretin Amyloid Deposition Alters Cardiac Myocyte Structure and Function

Wild-type transthyretin amyloidosis is caused by the systemic deposition of amyloid fibrils in the extracellular environment of many organs. These fibrils consist of misfolded transthyretin (TTR) that derive from the disassembly of the physiological tetrameric state of the native protein. The deposit of TTR fibrils in the heart leads to cardiac dysfunction and it is estimated to be a major cause of heart failure with preserved ejection fraction (HFpEF) in the elderly. The underlying hypothesis of this work is that TTR deposited in the extracellular matrix disrupts the internal sarcomere structure and the mechanical and electrical coupling of myocytes, altering contractility and calcium transient parameters. To test this, a simple bioengineered constructs in vitro model was developed using the physiological stiffness of 10 kPa, microgrooves for cell orientation, and coated with TTR fibrils. Neonatal rat ventricular myocytes cultured on microgrooved polydimethylsiloxane substrates coated with TTR fibrils featured a disorganized sarcomere structure and decreased cell alignment. In addition, N-cadherin content and index for cellular distribution were significantly decreased when cells were plated on TTR fibril-coated dishes. On glass-bottom dishes, TTR fibrils induced a decreased connexin 43 content, and, on soft 10kPa polyacrylamide substrates, myocytes demonstrated an overall decreased contractility when TTR fibrils were present, and delayed and irregular calcium intensity profiles. A deeper knowledge of this disease and a better understanding of the effects of TTR fibrils on cardiomyocytes could potentially lead to more effective and more affordable therapies.