title: Converging evidence of mitochondrial dysfunction in a yeast model of homocysteine metabolism imbalance.
abstract: An elevated level of homocysteine, a thiol amino acid, is associated with various complex disorders. The cellular effects of homocysteine and its precursors S-adenosylhomocysteine (AdoHcy) and S-adenosylmethionine (AdoMet) are, however, poorly understood. We used Saccharomyces cerevisiae as a model to understand the basis of pathogenicity induced by homocysteine and its precursors. Both homocysteine and AdoHcy but not AdoMet inhibited the growth of the str4Δ strain (which lacks the enzyme that converts homocysteine to cystathionine-mimicking vascular cells). Addition of AdoMet abrogated the inhibitory effect of AdoHcy but not that of homocysteine indicating that an increase in the AdoMet/AdoHcy ratio is sufficient to overcome the AdoHcy-mediated growth defect but not that of homocysteine. Also, the transcriptomic profile of AdoHcy and homocysteine showed gross dissimilarity based on gene enrichment analysis. Furthermore, compared with homocysteine, AdoHcy treatment caused a higher level of oxidative stress in the cells. However, unlike a previously reported response in wild type (Kumar, A., John, L., Alam, M. M., Gupta, A., Sharma, G., Pillai, B., and Sengupta, S. (2006) Biochem. J. 396, 61-69), the str4Δ strain did not exhibit an endoplasmic reticulum stress response. This suggests that homocysteine induces varied response depending on the flux of homocysteine metabolism. We also observed altered expression of mitochondrial genes, defective membrane potential, and fragmentation of the mitochondrial network together with the increased expression of fission genes indicating that the imbalance in homocysteine metabolism has a major effect on mitochondrial functions. Furthermore, treatment of cells with homocysteine or AdoHcy resulted in apoptosis as revealed by annexin V staining and TUNEL assay. Cumulatively, our results suggest that elevated levels of homocysteine lead to mitochondrial dysfunction, which could potentially initiate pro-apoptotic pathways, and this could be one of the mechanisms underlying homocysteine-induced pathogenicity.
authors.affiliation: Institute of Genomics and Integrative Biology, Council of Scientific and Industrial Research, Mall Road, Delhi-110007, India.
authors.forename: Arun
authors.initials: A
authors.lastname: Kumar
authors.forename: Lijo
authors.initials: L
authors.lastname: John
authors.forename: Shuvadeep
authors.initials: S
authors.lastname: Maity
authors.forename: Mini
authors.initials: M
authors.lastname: Manchanda
authors.forename: Abhay
authors.initials: A
authors.lastname: Sharma
authors.forename: Neeru
authors.initials: N
authors.lastname: Saini
authors.forename: Kausik
authors.initials: K
authors.lastname: Chakraborty
authors.forename: Shantanu
authors.initials: S
authors.lastname: Sengupta
mesh_terms: D017304:Annexin A5 / Q000737:chemistry; D002843:Chromatin / Q000737:chemistry; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D006710:Homocysteine / Q000737:chemistry / Q000378:metabolism*; D020287:In Situ Nick-End Labeling; D008564:Membrane Potentials; D008954:Models, Biological; D009693:Nucleic Acid Hybridization; D018384:Oxidative Stress; D011489:Protein Denaturation; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D017304:Annexin A5; D002843:Chromatin; D005656:Fungal Proteins; D006710:Homocysteine