Re-expression of tafazzin isoforms in TAZ-deficient C6 glioma cells restores cardiolipin composition but not proliferation rate and alterations in gene expression

Tafazzin an acyltransferase is involved in cardiolipin (CL) remodeling. CL is associated with mitochondrial function, structure and more recently with cell proliferation. Various tafazzin isoforms exists in humans. The role of these isoforms in cardiolipin remodeling is unknown. Aim of this study is to investigate if isoform Δ5, which is lacking exon 5, full length rat TAZ, and mutant full-length rat Taz (enzymatically dead H69L) could restore wild type phenotype in C6 TAZ cells with respect to CL composition, cellular proliferation and gene expression profile. In addition, we aim to determine the molecular mechanism by which tafazzin can modulate gene expression by applying promoter analysis and IPA to genes regulated by TAZ-deficiency. Expression of Δ5 and rat full length TAZ in C6-TAZ- cells can fully restore CL composition and – as proven for 5 – this is naturally associated with restoration of mitochondrial respiration. A similar restoration of CL-composition could not be observed after re-expression of an enzymatically dead full-length rat TAZ (H69L; TAZmut3). The re-expression of none of the TAZ isoforms used led to the restoration of the proliferation rate and gene expression profiles. Very likely TAZ-deficiency provokes substantial long-lasting changes in cellular lipid metabolism which contribute to changes in proliferation and gene expression, and are not or only very slowly reversible.tafazzin是一种参与心磷脂（cardiolipin，CL）重塑的酰基转移酶。心磷脂与线粒体的功能、结构紧密相关，近年来更被证实与细胞增殖存在关联。人类体内存在多种tafazzin同工型，此类同工型在心磷脂重塑过程中的具体作用尚未明确。本研究旨在探究：缺失外显子5的Δ5同工型、全长大鼠TAZ，以及酶学失活的全长大鼠Taz突变体（H69L），能否使C6-TAZ⁻细胞在CL组成、细胞增殖及基因表达谱层面恢复野生型表型。此外，本研究还拟通过对TAZ缺陷所调控的基因开展启动子分析与Ingenuity通路分析（IPA），以阐明tafazzin调控基因表达的分子机制。在C6-TAZ⁻细胞中表达Δ5与全长大鼠TAZ，可完全恢复CL组成；且如针对Δ5的实验所证实，这一恢复过程自然伴随线粒体呼吸功能的修复。但重新表达酶学失活的全长大鼠TAZ（H69L；TAZmut3）时，无法实现CL组成的类似恢复。本研究中所采用的全部TAZ同工型，均未能使细胞增殖速率与基因表达谱恢复至野生状态。研究结果强烈提示：TAZ缺陷会引发细胞脂质代谢发生显著且持久的改变，进而导致细胞增殖与基因表达异常，此类改变无法或仅能以极慢的速度被逆转。