Cardiolipin is required for mitochondrial protein processing
Miriam Greenberg, PhD, Professor, Wayne State University, Detroit, MI

Award—US $50,000 over 1-year period

Abstract:

Barth syndrome (BTHS) is a severe genetic disorder caused by mutations in tafazzin, the transacylase that remodels the mitochondrial phospholipid cardiolipin (CL). The phenotypes of BTHS include cardio- and skeletal myopathy, neutropenia, and growth retardation. The mechanisms linking the pathology observed in BTHS and CL deficiency are not understood. Our long-term goal is to elucidate these mechanisms.

To gain insight into these mechanisms, we are implementing genetic analyses in yeast to generate molecular models that we test in mammalian cells. Yeast null mutants are available for each step of CL biosynthesis and remodeling, a pathway that is conserved from yeast to humans. In addition, we have utilized the CRISPR technology to generate a tafazzin knockout (KO) C2C12 mouse muscle cell line. We are using both the tafazzin-KO C2C12 cells and BTHS lymphoblasts as mammalian cell models.

We have recently determined that CL deficient cells are defective in mitochondrial protein processing. Our preliminary and published findings indicate that CL deficiency leads to defective Fe-S (iron-sulfur) biogenesis. Experiments to elucidate the mechanism underlying this defect revealed that levels of the mature form of frataxin, the iron chaperone required for Fe-S cluster formation, are decreased in both CL-deficient (crd1Δ) yeast cells and in BTHS lymphoblasts. Furthermore, we observed that the second step in processing of Yfh1 (yeast frataxin) is delayed in crd1Δ cells. Based on these findings, we hypothesize that CL is required for processing of mitochondrial proteins.

Defective processing of mitochondrial proteins leads to mitochondrial dysfunction. The severe genetic disorder Friedreich’s ataxia (FRDA), which is characterized by iron overload and cardiomyopathy, results from mutations in the frataxin gene (Koutnikova et al., 1997). Among these are mutations that perturb the second processing step of frataxin, which results in decreased levels of the mature frataxin protein (Cavadini et al., 2000a; Gordon et al., 1999). As the majority of mitochondrial proteins are imported into the mitochondria from the cytosol and subsequently processed into the mature active form, elucidating the role of CL in mitochondrial processing may identify specific mitochondrial defects that cause the pathology in BTHS.

Associated Publications to Date:

Lou W, Reynolds CA, Li Y, Liu J, Hüttemann M, Schlame M, Stevenson D, Strathdee D, Greenberg ML. Loss of tafazzin results in decreased myoblast differentiation in C2C12 cells: A myoblast model of Barth syndrome and cardiolipin deficiency. Biochim Biophys Acta. 2018 Apr 22. pii: S1388-1981(18)30080-5. doi:10.1016/j.bbalip.2018.04.015. [Epub ahead of print] (PubMed Abstract)*

Schlame M, Greenberg ML. Biosynthesis, remodeling and turnover of mitochondrial cardiolipin. Biochim Biophys Acta. 2016 Aug 21. pii: S1388-1981(16)30230-X. doi: 10.1016/j.bbalip.2016.08.010. [Epub ahead of print] Review. (PubMed Abstract)

Joshi AS, Fei N, Greenberg ML. Get1p and Get2p are required for maintenance of mitochondrial morphology and normal cardiolipin levels. FEMS Yeast Res. 2016 Feb 28. pii: fow019. [Epub ahead of print] (PubMed Abstract)

Associated Presentations to Date:

BSF 2016 Conference - July 22, 2016

Metabolic consequences of defective iron homeostasis in cardiolipin deficient cells