Granulopoietic Dysregulation in a Patient-Tailored Mouse Model of Barth Syndrome

Barth syndrome (BTHS) is an X-linked recessive disorder characterized by cardiomyopathy, skeletal muscle myopathy and fatigue, growth restriction, and neutropenia. Neutropenia increases the risk of life-threatening bacterial infections, a major cause of death in individuals with BTHS. Currently, there is no curative treatment for BTHS or associated neutropenia. The development of therapeutic strategies to correct BTHS-associated neutropenia has been hindered by a limited understanding of the underlying molecular mechanisms involved. BTHS is caused by a mutation in the Tafazzin gene encoding a transacylase required for the maturation of cardiolipin, an inner mitochondrial membrane phospholipid crucial for mitochondrial structure and function. We introduced a BTHS patient's point mutation (TAZ^D75H) into the mouse Tafazzin enzyme's critical acyltransferase site using CRISPR/Cas9-mediated genome editing, resulting in a patient-tailored point mutant knock-in BTHS model (Taz^D75H) that expresses a stable mutant Taz^D75H protein lacking transacylase activity. Taz^D75H mice were then used to investigate how loss of Tafazzin enzymatic activity impacts hematopoiesis. Male Taz^D75H mice exhibited impaired granulopoiesis and neutropenia secondary to impaired function of hematopoietic progenitors. Furthermore, they demonstrated age-dependent neutrophil maturation impairment reflecting the variable neutropenia observed in BTHS patients. Additionally, male Taz^D75H mice exhibit chronic lymphopenia that persists post Taz^D75H bone marrow transplantation. Mechanistically, the TAZ^D75H point mutation caused hematopoietic cell mitochondrial dysfunction in patient-derived immortalized TAZ^D75H lymphoblasts, increasing reactive oxygen species production and mitochondrial membrane depolarization. Likewise, Cyclosporine A treatment rescued these mitochondrial phenotypes in vitro, confirming TAZ^D75H mitochondrial dysfunction. Overall, our findings demonstrate that mitochondrial dysfunction secondary to TAFAZZIN loss of enzymatic function underlies BTHS-associated neutropenia and lymphopenia.