MiP2005: Session 4

Mitochondrial Physiology Network 10.9: 53 (2005) - download pdf

 

Keratinocyte-specific knockout of the Tfam protein allows to elucidate the role of the mitochondrial respiratory chain for cell proliferation in vivo.

M Schauen1, A Wille1, C Wickenhauser2, C Niessen3, T Krieg4, Rudi J Wiesner1

1Inst. Vegetative Physiology, 2Dept. Pathology, 3Ctr. Molecular Medicine, 4Dept. Dermatology, University of Köln, 50931 Köln, Germany. -

    The Tfam protein controls the amount of mitochondrial DNA (mtDNA) in the cell [1-3]. Without mtDNA, the mitochondrial respiratory chain is not functional, because mtDNA encodes 13 of its ca. 80 polypeptide subunits. A HeLa cell line without mtDNA (ρ0) shows a profound proliferation defect, an effect which is however not simply due to energetic or biosynthetic problems, since levels of ATP, UTP, heme containing proteins and FeS cluster enzymes were normal. These results point to a hitherto unknown role of the mitochondrial respiratory chain in cell proliferation. To elucidate this role in vivo, we have bred mice with a keratinocyte-specific deletion of the Tfam protein by crossing mice having exons 6 and 7 of the TFAM gene flanked by loxP-sites (2) with mice carrying the Cre-recombinase transgene under control of the keratinocyte-specific human K14 promoter. At the day of birth, Tfam protein is still detectable, but older knockout animals show a progressive loss confined to the epidermis. At day 6 after birth, the mtDNA-encoded subunit II of cytochrome oxidase is not detectable any more. The epidermis gradually gets thinner, its epidermal stem cell compartment, the basal layer, is disordered and hair follicles fail to develop normally. The knockout mice stop gaining weight at day 3 and die between day 4 and day 7. The tongue epithelium is also disordered and papillae show a progressive degradation from day 0 to day 6. The animals develop an ulceration at the back of the tongue, the resulting pain probably inhibiting food intake, leading to the observed weight loss and ultimately death. Considering the proposal by some authors that the epidermis is a physiologically anaerobic tissue [4], the drastic effect of ablating respiratory chain activity in keratinocytes is even more striking. These results show that an intact mitochondrial respiratory chain is essential for cellular proliferation in vitro and proliferation and differentiation in vitro and in vivo.

1.  Ekstrand MI, Falkenberg M, Rantanen A, Park CB, Gaspari M, Hultenby K, Rustin P, Gustafsson CM, Larsson NG (2004) Mitochondrial transcription factor A regulates mtDNA copy number in mammals. Hum. Mol. Genet. 13: 935-944.

2.  Larsson NG, Wang J, Wilhelmsson H, Oldfors A, Rustin P, Lewandoski M, Barsh GS, Clayton DA (1998) Mitochondrial transcription factor A is necessary for mtDNA maintenance and embryogenesis in mice. Nat. Genet. 18: 231-236.

3.  Maniura-Weber K, Goffart S, Garstka HL, Montoya J, Wiesner RJ (2004) Transient overexpression of mitochondrial transcription factor A (TFAM) is sufficient to stimulate mitochondrial DNA transcription, but not sufficient to increase mtDNA copy number in cultured cells. Nucleic Acids Res. 32: 6015-6027.

4.  Ronquist G, Andersson A, Bendsoe N, Falck B (2003) Human epidermal energy metabolism is functionally anaerobic. Exp. Dermatol. 12: 572-579.


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