Barth syndrome (BTHS) is an X-linked disorder characterized by cardio- and skeletal myopathy, neutropenia,
and mitochondrial dysfunction, which limit the quality of life for BTHS patients. Despite improvements in
diagnosis, premature death is still commonplace due to the lack of effective therapies. Recently, clinical trials for
two potential BTHS drug treatments, bezafibrate and elamipretide, were conducted in BTHS patients. Neither of
these drugs showed a beneficial effect in their respective double-blind, placebo-controlled trials. These results
underscore the central problem - the leading pathogenic mechanism of BTHS is unknown. The gene mutated in
BTHS is TAFAZZIN, which codes for the transacylase tafazzin (Taz), which remodels the signature mitochondrial
lipid, cardiolipin (CL), a unique lipid containing four acyl chains and localized almost exclusively in the matrix-
facing leaflet of the inner mitochondrial membrane. Taz deficiency leads to decreased CL and accumulation of
the remodeling intermediate, monolyso-cardiolipin (MLCL), However, the mechanism linking defective CL
remodeling to the pathology in BTHS is not known. We established that both CL and MLCL can form a complex
with the hemoprotein, cytochrome c (cyt c), localized in the intermembrane space (IMS) of mitochondria, and
this complex acts as a peroxidase towards polyunsaturated (PUFA)-CL
. Normally, low steady-state levels of
MLCL and compartmentalization of CL and cyt c preclude the formation of this peroxidase complex. In Taz
deficiency, robust accumulation of MLCL in the IMS-facing leaflet of the IMM, the site of the
Taz-catalyzed
reaction, makes it available to interact with cyt c. We further discovered that polyunsaturated MLCL, CL and
other major phospholipids undergo robust peroxidation by the peroxidase complex.
Given the well-documented
membrane toxicity of lipid peroxidation products, we hypothesize that MLCL/cyt c complexes represent the
primary pathogenic mechanism underlying BTHS, and suppression of this peroxidase activity and lipid
peroxidation will protect mitochondria from BTHS-associated injury. We propose three mechanistic approaches
and small molecule inhibitors to quench the peroxidase activity of MLCL/cyt c complexes as a new therapeutic
strategy that will be tested in three Specific Aims: 1: Inhibiting MLCL/cyt c peroxidase catalytic activity. 2: Blocking
complex formation by competitively inhibiting MLCL-cyt c binding. 3: Eliminating sources of H2O2 required for
peroxidase activity. Our multi-PI team of experts in molecular genetics (M. Greenberg), redox biology (V. Kagan)
and LC-MS based redox lipidomics and MS-imaging (H. Bayir) will provide the interdisciplinary scientific
expertise required to implement the proposed experiments. Discovery of the MLCL/cyt c peroxidase complex as
the primary mitochondrial mechanism of BTHS pathogenesis will lead to new medicines - clinically relevant
inhibitors of pro-oxidant peroxidase activity.