Pivotal role of mitochondria in development and treatment of severe phenotypes of desmin-mutated cardiomyocytes from a patient with myofibrillar myopathy
Desmin-related myofibrillar myopathy, a severe muscle disease, is caused by mutations in the desmin-encoding gene, leading to skeletal myopathies and/or cardiomyopathy. Although previous studies suggested that desmin mutations alter the cellular structure and mitochondria function in myocyte, the pathophysiological mechanism by which mutated desmin impairs cardiac function has been poorly explored in physiologically relevant human disease models.  In this attempt, we generated cardiomyocytes from induced pluripotent stem cells (hiPSC) of a patient carrying the heterozygous DESE439K mutation together with an isogenic pair of mutant hiPSC harboring the same mutation. Using 2D and 3D models as well as cardiac biopsies, we demonstrated that in mutant cardiomyocytes this heterozygous desmin mutation leads to disorganization in their cytoarchitecture and to a perturbation of their mitochondrial architecture and function. Finally, we then demonstrated that transfer of exogenous healthy mitochondria rescues the phenotypic impairment of mitochondrial function in desmin-mutated cardiomyocytes leading to the reversion of the diseased phenotype. This work advances our understanding on the critical role of mitochondria in the development of cardiomyopathy related to desmin mutation and opens up new potential therapeutic perspectives for this debilitating and still incurable disease. Overall design: We used PBMC of the patient CIII who was diagnosed with desmin-related myofibrillar myopathy (MFM1) with cardiac manifestation at the age of 36 years and carries the DESE439K (Desmine) variant present in his family. PBMC of CIII patient were reprogrammed into induced pluripotent stem cells (iPSCs) using a non-integrative method (Epi5™ Episomal iPSC Reprogramming Kit, Thermo Fisher Scientific). The clone c15 was isolated and used in transcriptome analysis.  Gibco Human Episomal iPSC clone (Control 1, Thermo Fisher Scientific) derived from healthy individuals without any cardiac pathology, was used as control. Frozen iPSC-CM (cardiomyocytes derived from induced pluripotent stem cells) from Clone c15 and Gibco Human Episomal iPSC clone (Control 1), Thermo Fisher Scientific) were thawed, centrifuged at 200xg to remove freezing medium and directly seeded on Matrigel-coated 12 well plates. They were then cultured 20 days in maturation medium, detached using TrypLE Select 1X, pelleted and flash frozen in liquid nitrogen. The cells were afterwards submitted to mRNA sequencing.