Loss of Drp1 function alters OPA1 processing and changes mitochondrial membrane organization
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 , . 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 . "
ABSTRACT: Evasion of apoptosis is implicated in almost all aspects of cancer progression, as well as treatment resistance. In this study, resistance to apoptosis was identified in tumorigenic lung epithelial (A549) cells as a consequence of defects in mitochondrial and autophagic function. Mitochondrial function is determined in part by mitochondrial morphology, a process regulated by mitochondrial dynamics whereby the joining of two mitochondria, fusion, inhibits apoptosis while fission, the division of a mitochondrion, initiates apoptosis. Mitochondrial morphology of A549 cells displayed an elongated phenotype-mimicking cells deficient in mitochondrial fission protein, Dynamin-related protein 1 (Drp1). A549 cells had impaired Drp1 mitochondrial recruitment and decreased Drp1-dependent fission. Cytochrome c release and caspase-3 and PARP cleavage were impaired both basally and with apoptotic stimuli in A549 cells. Increased mitochondrial mass was observed in A549 cells, suggesting defects in mitophagy (mitochondrial selective autophagy). A549 cells had decreased LC3-II lipidation and lysosomal inhibition suggesting defects in autophagy occur upstream of lysosomal degradation. Immunostaining indicated mitochondrial localized LC3 punctae in A549 cells increased after mitochondrial uncoupling or with a combination of mitochondrial depolarization and ectopic Drp1 expression. Increased inhibition of apoptosis in A549 cells is correlated with impeded mitochondrial fission and mitophagy. We suggest mitochondrial fission defects contribute to apoptotic resistance in A549 cells.PLoS ONE 09/2012; 7(9):e45319. DOI:10.1371/journal.pone.0045319 · 3.23 Impact Factor
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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). "
ABSTRACT: Type 2 diabetes mellitus (T2DM) and aging are characterized by insulin resistance and impaired mitochondrial energetics. In lower organisms, remodeling by the protease pcp1 (PARL ortholog) maintains the function and lifecycle of mitochondria. We examined whether variation in PARL protein content is associated with mitochondrial abnormalities and insulin resistance. PARL mRNA and mitochondrial mass were both reduced in elderly subjects and in subjects with T2DM. Muscle knockdown of PARL in mice resulted in malformed mitochondrial cristae, lower mitochondrial content, decreased PGC1alpha protein levels, and impaired insulin signaling. Suppression of PARL protein in healthy myotubes lowered mitochondrial mass and insulin-stimulated glycogen synthesis and increased reactive oxygen species production. We propose that lower PARL expression may contribute to the mitochondrial abnormalities seen in aging and T2DM.Cell metabolism 05/2010; 11(5):412-26. DOI:10.1016/j.cmet.2010.04.004 · 17.57 Impact Factor
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ABSTRACT: The complex atmospheric and oceanic dynamics within the Greenland, Iceland, and Norwegian Seas (GINS) produce a large portion of the world ocean deep water. Although there are significant interactions between the Arctic Ocean and the GINS which result in the formation of Greenland Sea Deep Water (GSDW), the inflow of Atlantic Water (AW) is also recognized to be a major influence. An extensive historical hydrographic data set for this region has been analyzed using volumetric analysis techniques to determine the mean characteristics of two water classes, the AW and the Arctic Intermediate Water (AIW), on a seasonal basisOCEANS '93. Engineering in Harmony with Ocean. Proceedings; 11/1993