Background: Mutations in tafazzin ( TAZ ), a gene required for biogenesis of cardiolipin, the signature phospholipid of the inner mitochondrial membrane, causes Barth syndrome (BTHS). Cardiomyopathy and risk of sudden cardiac death are prominent features of BTHS, but the mechanisms by which impaired cardiolipin biogenesis causes cardiac muscle weakness and arrhythmia are poorly understood. Methods: We performed in vivo electrophysiology to define arrhythmia vulnerability in cardiac specific TAZ knockout mice. Using cardiomyocytes derived from human induced pluripotent stem cells (iPSC-CMs) and cardiac specific TAZ knockout mice as model systems, we investigated the effect of TAZ inactivation on Ca 2+ handling. Through genome editing and pharmacology, we defined a molecular link between TAZ mutation and abnormal Ca 2+ handling and contractility. Results: A subset of mice with cardiac-specific TAZ inactivation developed arrhythmias including bidirectional ventricular tachycardia, atrial tachycardia, and complete atrioventricular block. Compared to WT, BTHS iPSC-CMs had increased diastolic Ca 2+ and decreased Ca 2+ transient amplitude. BTHS iPSC-CMs had higher levels of mitochondrial and cellular ROS than WT, which activated Ca 2+ /calmodulin-dependent protein kinase II (CaMKII). Activated CaMKII phosphorylated the cardiac ryanodine receptor (RYR2) on serine 2814, increasing Ca 2+ leak through RYR2. Inhibition of this ROS-CaMKII-RYR2 pathway through pharmacological inhibitors or genome editing normalized aberrant Ca 2+ handling in BTHS iPSC-CMs and improved their contractile function. Murine Taz knockout cardiomyocytes also exhibited elevated diastolic Ca 2+ and decreased Ca 2+ transient amplitude. These abnormalities were ameliorated by CaMKII or ROS inhibition. Conclusions: This study identified a molecular pathway that links TAZ mutation to abnormal Ca 2+ handling and decreased cardiomyocyte contractility. This pathway may offer therapeutic opportunities to treat BTHS and potentially other diseases with elevated mitochondrial ROS production.

Modulation of mucus production by the human ecto- and endo-cervical epithelium by steroid hormones and associated interactions with commensal microbiome play a central role in the physiology and pathophysiology of the female reproductive tract. However, most of our knowledge about these interactions is based on results from animal studies or in vitro models that fail to faithfully mimic the mucosal environment of the human cervix. Here we describe microfluidic organ-on-a-chip (Organ Chip) models of the human cervical mucosa that recreate the cervical epithelial-stromal interface with a functional epithelial barrier and produce abundant mucus that has compositional, biophysical, and hormone-responsive properties similar to the living cervix. Use of continuous fluid flow promoted ecto-cervical differentiation, whereas use of periodic flow including periods of stasis stimulated endo-cervical specialization. Similar results with minor differences were obtained using epithelial cells isolated from three donors each from a different ethnic background (African American, Hispanic, and Caucasian). When the endo-Cervix Chips were co-cultured with living Lactobacillus crispatus and Gardnerella vaginalis bacterial communities to respectively mimic the effects of human host interactions with optimal (healthy) or non-optimal (dysbiotic) microbiome, significant differences in tissue innate immune responses, barrier function, cell viability, and mucus composition were detected reminiscent of those observed in vivo. Thus, human Cervix Chips provide a physiologically relevant experimental in vitro model to study cervical mucus physiology and its role in human host-microbiome interactions as well as a potential preclinical testbed for development of therapeutic interventions to enhance women's health.