Molecular characterization of interstitial cells isolated from human heart valves

Myofibroblasts have been described as possessing certain characteristics of both fibroblasts and skeletal myocytes. These cells are of mesenchymal origin, were first described in wound healing, and have been found in many tissues. Myofibroblasts from other tissues have been shown to contract and to express sarcomeric (muscle) genes. In addition, these cells express certain regulatory (transcription factor) genes. The specific alignment of the cells may, at least in part, be governed by tissue polarity signals transmitted by members of the frizzled family of vertebrate tissue polarity genes. The aim of the present study was to characterize interstitial cells, with regard to the expression of myofibroblasts markers, isolated from the human heart valves. The expression of muscle structural, regulatory and tissue polarity genes has been undertaken with a view to understanding the development and contribution of interstitial cells to valve function and structure.

Interstitial cells were isolated and cultured from aortic, pulmonary, tricuspid and mitral valves of recipient hearts obtained during transplantation. Specific oligonucleotide primer pairs suitable for polymerase chain reaction (PCR) were designed for the genes of interest. Total RNA was extracted from the cultured cells and reverse transcriptase-PCR was used to determine gene expression.

Cells from the four valve types were found to express various muscle structural genes. These include the thin filament sarcomeric genes for the cardiac isoforms of troponin T, I and C. Evidence was also found for expression of beta-myosin heavy chain (beta-MHC), alpha-MHC and cardiac myosin light chain 2 (MLC2) in these cells. The tissue polarity genes frizzled 2 (fz2) were expressed in all four valve types analyzed.

Interstitial cells express a number of genes whose products may have functional significance for heart valves. These include members of the contractile apparatus such as MHC and troponins. The presence of members of the frizzled family, which specify the orientation of cell polarization, in these cells could indicate that interstitial cells are not randomly arranged in the valve tissue. Therefore, interstitial cells isolated from the human heart valves express a number of functionally important genes, suggesting a role in their specialized function.