Loss of Drp1 function alters OPA1 processing and changes mitochondrial membrane organization

Silence Therapeutics AG, 13125 Berlin, Germany.
Experimental Cell Research (Impact Factor: 3.25). 06/2009; 315(13):2165-80. DOI: 10.1016/j.yexcr.2009.04.016
Source: PubMed

ABSTRACT RNAi mediated loss of Drp1 function changes mitochondrial morphology in cultured HeLa and HUVEC cells by shifting the balance of mitochondrial fission and fusion towards unopposed fusion. Over time, inhibition of Drp1 expression results in the formation of a highly branched mitochondrial network along with "bulge"-like structures. These changes in mitochondrial morphology are accompanied by a reduction in levels of Mitofusin 1 (Mfn1) and 2 (Mfn2) and a modified proteolytic processing of OPA1 isoforms, resulting in the inhibition of cell proliferation. In addition, our data imply that bulge formation is driven by Mfn1 action along with particular proteolytic short-OPA1 (s-OPA1) variants: Loss of Mfn2 in the absence of Drp1 results in an increase of Mfn1 levels along with processed s-OPA1-isoforms, thereby enhancing continuous "fusion" and bulge formation. Moreover, bulge formation might reflect s-OPA1 mitochondrial membrane remodeling activity, resulting in the compartmentalization of cytochrome c deposits. The proteins Yme1L and PHB2 appeared not associated with the observed enhanced OPA1 proteolysis upon RNAi of Drp1, suggesting the existence of other OPA1 processing controlling proteins. Taken together, Drp1 appears to affect the activity of the mitochondrial fusion machinery by unbalancing the protein levels of mitofusins and OPA1.

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    • "In this study, A549 cells displayed elongated mitochondrial phenotypes basally and hyperfused mitochondria following downregulation of Drp1, consistent with phenotypes observed in cells that are deficient in mitochondrial fission [5], [35]. Additional similarities to cells lacking Drp1 were noted in A549 cells, such as resistance to mitochondrial depolarization and impaired cytochrome c release from the mitochondria [5]. "
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    • "The reductions in OPA1 protein are consistent with previous reports demonstrating enhanced degradation of OPA1 protein (constitutive cleavage) and increased susceptibility to apoptosis (Cipolat et al., 2006; Griparic et al., 2007) with reduced PARL and DRP-1 (Mopert et al., 2009) expression. Therefore, lower OPA1 protein may result from reduced mitochondrial mass or dysfunction as observed in PARL loss-of-function myotubes (see below). "
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