Cultured interstitial cells from human heart valves express both specific skeletal muscle and non-muscle markers

Cardiac valve interstitial cells are a phenotypically diverse and dynamic population, comprising myofibroblasts, fibroblasts and smooth muscle cells. To understand how these contribute to valve function and to optimize the choice of cells for seeding tissue-engineered valves, we are fingerprinting interstitial cells from all four human heart valves for useful phenotypic markers. We have begun by selecting markers indicated as of interest from previous work on myofibroblast-like cell lines. We show that interstitial cells express a variety of skeletal muscle contractile proteins and the skeletal muscle transcription factor myogenin, but not the related factors MyoD, myf-5 and MRF4, suggesting partial activation of the muscle programme in these cells. Expression of non-muscle isoforms of creatine kinase (CK-B) and AMP deaminase (AMPD2 and AMPD3) was found in contrast to muscle-restricted isoforms. Non-muscle isoforms of α- and β-tropomyosins were detected specifically in contrast to skeletal muscle-specific isoforms. Several members of the Frizzled (FZD) family of Wnt receptors were also detected. In addition, intact cusps of all four valves from pig were capable of contacting to non-receptor and receptor-mediated stimulation in vitro. We conclude that interstitial cells from human heart valves express various sarcomeric proteins, and suggest that these cells have contractile potential due to a unique pattern of expression of both muscle-specific and non-muscle isoforms of metabolic and structural proteins. This may be under the control of myogenin, activated through specific Wnt/FZD signaling. Identifying such molecular markers could prove useful for engineering allogenic non-valve cell sources for seeding the synthetic valve.