Nyosha Alikhani

Columbia University, New York City, NY, United States

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Publications (10)30.76 Total impact

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    ABSTRACT: Mitochondrial presequences and other unstructured peptides are degraded inside mitochondria by presequence proteases (PrePs) identified in Arabidopsis thaliana (AtPreP), humans (hPreP), and yeast (Cym1/Mop112). The presequences of A. thaliana and human PreP are predicted to consist of 85 and 29 amino acids, respectively, whereas the Saccharomyces cerevisiae Cym1/Mop112 presequence contains only 7 residues. These differences may explain the reported targeting of homologous proteins to different mitochondrial subcompartments. Here we have investigated the targeting capacity of the PreP homologues' presequences. We have produced fusion constructs containing N-terminal portions of AtPreP(1-125), hPreP(1-69), and Cym1(1-40) coupled to green fluorescent protein (GFP) and studied their import into isolated plant, mammalian, and yeast mitochondria, followed by mitochondrial subfractionation. Whereas the AtPreP presequence has the capacity to target GFP into the mitochondrial matrix of all three species, the hPreP presequence only targets GFP to the matrix of mammalian and yeast mitochondria. The Cym1/Mop112 presequence has an overall much weaker targeting capacity and only ensures mitochondrial sorting in its host species yeast. Revisiting the submitochondrial localization of Cym1 revealed that endogenous Cym1/Mop112 is localized to the matrix space, as has been previously reported for the plant and human homologues. Moreover, complementation studies in yeast show that native AtPreP restores the growth phenotype of yeast cells lacking Cym1, demonstrating functional conservation.
    Journal of Molecular Biology 07/2011; 410(3):400-10. · 3.91 Impact Factor
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    ABSTRACT: Accumulation of amyloid-β peptide (Aβ), the neurotoxic peptide implicated in the pathogenesis of Alzheimer's disease (AD), has been shown in brain mitochondria of AD patients and of AD transgenic mouse models. The presence of Aβ in mitochondria leads to free radical generation and neuronal stress. Recently, we identified the presequence protease, PreP, localized in the mitochondrial matrix in mammalian mitochondria as the novel mitochondrial Aβ-degrading enzyme. In the present study, we examined PreP activity in the mitochondrial matrix of the human brain's temporal lobe, an area of the brain highly susceptible to Aβ accumulation and reactive oxygen species (ROS) production. We found significantly lower hPreP activity in AD brains compared with non-AD age-matched controls. By contrast, in the cerebellum, a brain region typically spared from Aβ accumulation, there was no significant difference in hPreP activity when comparing AD samples to non-AD controls. We also found significantly reduced PreP activity in the mitochondrial matrix of AD transgenic mouse brains (Tg mAβPP and Tg mAβPP/ABAD) when compared to non-transgenic aged-matched mice. Furthermore, mitochondrial fractions isolated from AD brains and Tg mAβPP mice had higher levels of 4-hydroxynonenal, an oxidative product, as compared with those from non-AD and nonTg mice. Accordingly, activity of cytochrome c oxidase was significantly reduced in the AD mitochondria. These findings suggest that decreased PreP proteolytic activity, possibly due to enhanced ROS production, contributes to Aβ accumulation in mitochondria leading to the mitochondrial toxicity and neuronal death that is exacerbated in AD. Clearance of mitochondrial Aβ by PreP may thus be of importance in the pathology of AD.
    Journal of Alzheimer's disease: JAD 07/2011; 27(1):75-87. · 4.17 Impact Factor
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    Elzbieta Glaser, Nyosha Alikhani
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    ABSTRACT: The novel peptidasome, called presequence protease, PreP, was originally identified and characterized in Arabidopsis thaliana as a mitochondrial matrix and chloroplast stroma localized metalloprotease. PreP has a function as the organellar peptide clearing protease and is responsible for degrading free targeting peptides and also other unstructured peptides up to 65 amino acid residues that might be toxic to organellar functions. PreP contains an inverted Zn-binding motif and belongs to the pitrilysin protease family. The crystal structure of AtPreP refined at 2.1 A demonstrated a unique totally enclosed large cavity of 10000 A3 that opens and closes in response to peptide binding, revealing a novel catalytic mechanism for proteolysis. Homologues of PreP have been found in yeast and human mitochondria. Interestingly, the human PreP, hPreP, is the protease that is responsible for clearing the human brain mitochondria from the toxic amyloid-beta peptide (Abeta) associated with Alzheimer's disease (AD). Accumulation of Abeta has been shown in the brain mitochondria from AD patients and mutant transgenic mice overexpressing Abeta. Here, we present a review of our present knowledge on structural and functional characteristics of PreP and discuss its mitochondrial Abeta-degrading activity in the human brain mitochondria in relation to AD.
    Biochimica et Biophysica Acta 01/2010; 1797(6-7):1076-80. · 4.66 Impact Factor
  • Alzheimers & Dementia - ALZHEIMERS DEMENT. 01/2010; 6(4).
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    ABSTRACT: Several studies suggest mitochondrial dysfunction as a possible mechanism underlying the development of Alzheimer disease (AD). There is data showing that amyloid-beta (A beta) peptide is present in AD brain mitochondria. The human presequence protease (hPreP) was recently shown to be the major mitochondrial A beta-degrading enzyme. We investigated if there is an increased susceptibility to AD, which can be attributed to genetic variation in the hPreP gene PITRM1 and if the proteolytic efficiency of recombinant hPreP variants is affected. When a total of 673 AD cases and 649 controls were genotyped for 18 single nucleotide polymorphisms (SNPs), no genetic association between any of the SNPs and the risk for AD was found. In contrast, functional analysis of four non-synonymous SNPs in hPreP revealed a decreased activity compared to wild type hPreP. Using A beta, the presequence of ATP synthase F(1)beta subunit and a fluorescent peptide as substrates, the lowest activity was observed for the hPreP(A525D) variant, corresponding to rs1224893, which displayed only 20-30% of wild type activity. Furthermore, the activity of all variants was restored by the addition of Mg(2+), suggesting an important role for this metal during proteolysis. In conclusion, our data suggest that genetic variation in the hPreP gene PITRM1 may potentially contribute to mitochondrial dysfunctions.
    Neuroscience Letters 12/2009; 469(2):204-8. · 2.03 Impact Factor
  • Nyosha Alikhani, Maria Ankarcrona, Elzbieta Glaser
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    ABSTRACT: Several lines of evidence suggest mitochondrial dysfunction as a possible underlying mechanism of Alzheimer's disease (AD). Accumulation of the amyloid-beta peptide (Abeta), a neurotoxic peptide implicated in the pathogenesis of AD, has been detected in brain mitochondria of AD patients and AD transgenic mouse models. In vitro evidence suggests that the Abeta causes mitochondrial dysfunction e.g. oxidative stress, mitochondrial fragmentation and decreased activity of cytochrome c oxidase and TCA cycle enzymes. Here we review the link between mitochondrial dysfunctions and AD. In particular we focus on the mechanism for Abeta uptake by mitochondria and on the recently identified Abeta degrading protease in human brain mitochondria.
    Journal of Bioenergetics 10/2009; 41(5):447-51. · 1.60 Impact Factor
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    ABSTRACT: The amyloid beta-peptide (Abeta) has been suggested to exert its toxicity intracellularly. Mitochondrial functions can be negatively affected by Abeta and accumulation of Abeta has been detected in mitochondria. Because Abeta is not likely to be produced locally in mitochondria, we decided to investigate the mechanisms for mitochondrial Abeta uptake. Our results from rat mitochondria show that Abeta is transported into mitochondria via the translocase of the outer membrane (TOM) machinery. The import was insensitive to valinomycin, indicating that it is independent of the mitochondrial membrane potential. Subfractionation studies following the import experiments revealed Abeta association with the inner membrane fraction, and immunoelectron microscopy after import showed localization of Abeta to mitochondrial cristae. A similar distribution pattern of Abeta in mitochondria was shown by immunoelectron microscopy in human cortical brain biopsies obtained from living subjects with normal pressure hydrocephalus. Thus, we present a unique import mechanism for Abeta in mitochondria and demonstrate both in vitro and in vivo that Abeta is located to the mitochondrial cristae. Importantly, we also show that extracellulary applied Abeta can be internalized by human neuroblastoma cells and can colocalize with mitochondrial markers. Together, these results provide further insight into the mitochondrial uptake of Abeta, a peptide considered to be of major significance in Alzheimer's disease.
    Proceedings of the National Academy of Sciences 10/2008; 105(35):13145-50. · 9.74 Impact Factor
  • Alzheimers & Dementia - ALZHEIMERS DEMENT. 01/2008; 4(4).
  • Nyosha Alikhani, Maria Ankarcrona, Elzbieta Glaser
    Alzheimers & Dementia - ALZHEIMERS DEMENT. 01/2008; 4(4).
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    ABSTRACT: Recently we have identified the novel mitochondrial peptidase responsible for degrading presequences and other short unstructured peptides in mitochondria, the presequence peptidase, which we named PreP peptidasome. In the present study we have identified and characterized the human PreP homologue, hPreP, in brain mitochondria, and we show its capacity to degrade the amyloid beta-protein (Abeta). PreP belongs to the pitrilysin oligopeptidase family M16C containing an inverted zinc-binding motif. We show that hPreP is localized to the mitochondrial matrix. In situ immuno-inactivation studies in human brain mitochondria using anti-hPreP antibodies showed complete inhibition of proteolytic activity against Abeta. We have cloned, overexpressed, and purified recombinant hPreP and its mutant with catalytic base Glu(78) in the inverted zinc-binding motif replaced by Gln. In vitro studies using recombinant hPreP and liquid chromatography nanospray tandem mass spectrometry revealed novel cleavage specificities against Abeta-(1-42), Abeta-(1-40), and Abeta Arctic, a protein that causes increased protofibril formation an early onset familial variant of Alzheimer disease. In contrast to insulin degrading enzyme, which is a functional analogue of hPreP, hPreP does not degrade insulin but does degrade insulin B-chain. Molecular modeling of hPreP based on the crystal structure at 2.1 A resolution of AtPreP allowed us to identify Cys(90) and Cys(527) that form disulfide bridges under oxidized conditions and might be involved in redox regulation of the enzyme. Degradation of the mitochondrial Abeta by hPreP may potentially be of importance in the pathology of Alzheimer disease.
    Journal of Biological Chemistry 10/2006; 281(39):29096-104. · 4.65 Impact Factor