Role ofCNC1gene in TDP-43 aggregation-induced oxidative stress-mediated cell death inS. cerevisiaemodel of ALS

Abstract

TDP-43 is a multi-functional ribonucleoprotein that is also found deposited as hyperphosphorylated and ubiquitinated TDP-43 inclusions in the brain and spinal cord of the patients of the motor neuron diseases, amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Till date, how the cell death ensues is not fully deciphered although several molecular mechanisms of the TDP-43 toxicity such as impairments of endocytosis and chromatin remodelling, mis-regulations of autophagy and proteasome function, mis-localization to the mitochondria and generation of oxidative stress etc., have been proposed. A predominantly nuclear protein, Cyclin C, can regulate the oxidative stress response by affecting the transcription of stress response genes and also by translocation to the cytoplasm for the activation of the mitochondrial fragmentation-dependent cell death pathway. Using the well-established yeast model of TDP-43 aggregation and toxicity, we examined here whether upon TDP-43 aggregation, the cell survival depends on the presence of the CNC1 gene that encodes Cyclin C protein or other genes that encode proteins that function in conjunction with Cyclin C, such as the DNM1, FIS1 and MED13 genes. We found that the TDP-43 toxicity is significantly reduced in the yeast deleted for the CNC1 or DNM1 genes. Importantly, the rescue of TDP-43 toxicity in these yeast deletion backgrounds required the presence of functional mitochondria. Also, the deletion of YBH3 gene, which encodes for a protein involved in the mitochondria-dependent apoptosis, also reduced the TDP-43 toxicity. Furthermore, Cyclin C-YFP was observed to localize from the nucleus to the cytoplasm in response to the TDP-43 co-expression. Also, this cytoplasmic localization of Cyclin C was prevented by the addition of an anti-oxidant molecule, N-acetyl-cysteine.Taken together, our data suggest that Cyclin C, Dnm1 and Ybh3 proteins are important in mediating the TDP-43-induced oxidative stress-mediated cell death in the S. cerevisiae model.3

Mitochondrion-Dependent Cell Death in TDP-43 Proteinopathies

“…However, Ruan et al observed that upon heat shock, a fraction of human TDP-43 could be imported into yeast mitochondria, but these authors did not analyze whether this TDP-43 fraction was cytotoxic [ 50 ]. In a recent paper, TDP-43-triggered cell death in yeast was linked to Cyclin C, the mitochondrial fission factor Dynamin-related protein 1 (Dnm1), and Ybh3, the yeast homolog of human pro-apoptotic BH3-containing factors, such as Bax [ 73 ]. Cyclin C has previously been described to translocate from the nucleus in the cytoplasm to trigger Dnm1- or Drp1-dependent mitochondrial fission and BH3- or BAX-dependent mitochondrial permeabilization in yeast and mammalian cells [ 74 , 75 , 76 ].…”

Where and Why Modeling Amyotrophic Lateral Sclerosis

“…Non-removed intronic lariats act as traps for TDP-43, thus impeding its interference with cellular RNAs and RNA-binding proteins [ 103 , 104 ]. Moreover, a recent report showed that TDP-43-induced cell death is considerably reduced in yeast deleted for CNC1 ( Cyclin C ), DNM1 ( Dynamin-related ) or YBH3 ( Bax inhibitor ) genes, all involved in the oxidative stress response pathway at different levels [ 105 ].…”