Primary mitochondrial respiratory chain diseases are systemic disorders caused by sporadic or inherited mutations in nuclear or mitochondrial DNA (mtDNA). Cardiac involvement is reported in about 20-25% of patients with mitochondrial disorders, either as a part of severe multisystem disorders or as the key clinical feature of mitochondrial disease. The clinical course of mitochondrial cardiomyopathies is remarkably variable, ranging from early severe phenotype and sudden cardiac death in the pediatric age to lifelong, asymptomatic, mutation-carrier status. Although the molecular analysis efforts have revealed important insights regarding the role of oxidative phosphorylation defect in cardiac dysfunction, the mechanisms underlying the development of mitochondrial cardiomyopathies remain unclear.
The overall objective of the present project is to shed light on the molecular mechanisms linking OXPHOS defect to cardiac dysfunction. Accordingly we aim to generate induced pluripotent stem cells (iPSC)-derived cardiomyocytes from patients with isolated mitochondrial cardiomyopathy, and to characterize their pathological phenotype.
We have already generated and fully characterized a set of iPSCs from two unrelated patients with isolated mitochondrial cardiomyopathy bearing pathogenic homoplasmic mutations in mt-tRNAIle (m.4300A>G and m.4277C>T, respectively). We will now generate iPSCs-derived cardiomyocytes according to a well-established protocol and we will characterize their pathological phenotype, starting from the evaluation of cell viability and energetic proficiency. We expect that iPSC-derived cardiomyocytes will be a reliable cellular model useful to better define the molecular consequences of mt tRNAs mutations and to test the effects of therapeutic molecules. This will have a significant impact on the development of therapeutic strategies for mt-tRNA related disease.
One of the major challenges in mt-tRNAs related disease is to understand the molecular link between disease phenotypes and genotypes. The mechanisms underlying the heterogeneity of clinical phenotypes are not fully understood. Moreover, recent evidence suggests that the effects of MTTs mutations on respiratory chain (RC) activity may be modulated by the specific cellular context. This issue is particularly challenging in maternally inherited disorders that are characterized by a homoplasmic mtDNA pathogenic mutations. These last present variable penetrance and a stereotypical clinical expression, usually restricted to a single tissue (i.e. cardiac tissue). Current transgenic technologies are not efficient in manipulating mitochondrial DNA, limiting the targeted engineering of mutations in mtDNA. Thus, due to the relative lack of animal models of mt-tRNA disease, the most widely used model is still the transmitochondrial cybrid. This is an undifferentiated neoplastic cell, lacking tissue-specific features. The development of iPSC technology has opened up new possibilities for the use of patient material. We expect that iPSC-derived cardiomyocytes will be reliable cellular model useful to better define the molecular consequences of mt tRNAs mutations and to test the effects of therapeutic molecules. This will have a significant impact on the development of therapeutic strategies for mt-tRNA related disease.