Mitochondria form cholesterol-rich contact sites with the nucleus during retrograde response

Desai, R and East, D A and Hardy, L and Crosby, J and Faccenda, D and Alvarex, M S and Mainenti, M and Kuhlman Hussy, L and Bentham, R and Szabadkai, G and Zappulli, V and Dhoot, G and Fleck, R A and Vizcay-Barrena, G and Smith, K and Campanella, M (2018) Mitochondria form cholesterol-rich contact sites with the nucleus during retrograde response. bioRxiv. (In Press)

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Cholesterol metabolism is pivotal to cellular homeostasis, hormones production, and membranes composition. Its dysregulation associates with malignant reprogramming and therapy resistance. Cholesterol is trafficked into the mitochondria for steroidogenesis by the transduceome protein complex, which assembles on the outer mitochondrial membrane (OMM). The highly conserved, cholesterol-binding, stress-reactive, 18kDa translocator protein (TSPO), is a key component of this complex. Here, we modulate TSPO to study the process of mitochondrial retrograde signalling with the nucleus, by dissecting the role played by cholesterol and its oxidized forms. Using confocal and ultrastructural imaging, we describe that TSPO enriched mitochondria, remodel around the nucleus, gathering in cholesterol-enriched domains (or contact sites). This communication is controlled by HMG-CoA reductase inhibitors (statins), molecular and pharmacological regulation of TSPO. The described Nucleus-Associated Mitochondria (NAM) seem to be implementing survival signalling in aggressive forms of breast cancer. This work therefore provides the first evidence for a functional and bio-mechanical tethering between mitochondria and nucleus, as being the basis of pro-survival mechanisms, thus establishing a new paradigm in cross-organelle communication via cholesterol re-distribution.

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