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PURPOSE: Heat shock protein 47 (Hsp47) is a collagen-specific molecular chaperone required for maturation of collagen type 1. Little is known about the role of Hsp47 in the heart. This study aims to investigate whether Hsp47 is important for cardiomyocyte maturation and assembly into functional syncytia.METHODS: We made use of recently developed 2D and 3D culture platforms to scrutinize the role of Hsp47 for cardiomyocyte maturation and function, i.e., (1) 2D model: culture of embryonic stem cell-derived cardiomyocytes (ESC-CM) on ECMs derived from both mouse embryonic wild type (WT)- and Hsp47 (-/-) fibroblasts and (2) 3D model: construction of engineered heart muscle (EHM) consisting of purified ESC-CMs with WT- or Hsp47 (-/-) fibroblasts. Cultures were investigated using confocal microscopy and isometric force measurements.RESULTS: ESC-CMs showed mainly immature polygonal shaped morphology and disorganized sarcomeric structures when cultured on ECM secreted by Hsp47 (-/-) fibroblasts; this morphology was in clear contrast to the mostly anisotropic cardiomyocyte appearance in control conditions. EHM with Hsp47 (-/-) fibroblasts did not develop measurable contractile forces. In contrast, WT fibroblast-supplemented EHMs contracted regularly (WT: 0.14±0.1 mN at 2.4 mM Ca2+; n=8/group). Histological analysis of Hsp47 (-/-) EHMs showed mainly rounded and underdeveloped cardiomyocytes comparable to the cardiomyocyte phenotype observed in EHMs containing only ESC-CMs, without fibroblasts.CONCLUSIONS: Hsp47 influences the deposition of ECM-collagen and affects cardiomyocyte morphology and functionality in our 2D and 3D culture models. Our data collectively suggest that Hsp47 may be an attractive target for the regulation of cardiac tissue homeostasis.