Search

Mammalian peroxiredoxin class 6 (Prdx6) are bifunctional enzymes. Non-mammalian Prdx6 enzymes display Cys-based peroxidase activity, but to date their putative phospholipase A₂ (PLA₂ activities) has not been experimentally investigated. Initially, we observed that five non-mammalian Prdx6 enzymes (enzymes from Arabidopsis thaliana (AtPER1), Triticum aestivum (TaPER1), Pseudomonas aeruginosa (PaLsfA) and Aspergillus fumigatus (AfPrx1 and AfPrxC)) present features compatible with PLA₂ activities in mammalian Prdx6 by amino acid sequences alignment and tertiary structure modeling. Employing unilamellar liposomes with tracer amounts of [³H]-1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and thin layer chromatography, all the tested non-mammalian Prdx6 enzymes displayed PLA₂ activities, with values ranging from 3.4 to 6.1 nmol/min/mg protein. It was previously shown that Thr177 phosphorylation of human Prdx6 increases its PLA₂ activity, especially at neutral pH. Therefore, we investigated if human Erk2 kinase could also phosphorylate homologous Thr residues in non-mammalian Prdx6 proteins. We observed phosphorylation of the conserved Thr in three out of the five non-mammalian Prdx enzymes by mass spectrometry. In the case of the mitochondrial Prdx6 from A. fumigatus (AfPrxC), we also observed phosphorylation by western blot, and as a consequence, the PLA₂ activity was increased in acidic and neutral conditions by the human Erk2 kinase treatment. The possible physiological meanings of these PLA₂ activities described open new fields for future research.

PurposeTo compare the levels of gene expression for enzymes involved in production and elimination of reactive oxygen/nitrogen species (ROS/RNS) in normal human corneal cells (NL cells) with those in human corneal cells with keratoconus (KC cells) in vitro.MethodsPrimary NL and KC stromal fibroblast cultures were incubated with apocynin (an inhibitor of NADPH oxidase) or N-nitro-L-arginine (N-LLA; an inhibitor of nitric oxide synthase). ROS/RNS levels were measured using an H2 DCFDA fluorescent assay. The RT2 Profiler™ PCR Array for Oxidative Stress and Antioxidant Defense was used for initial screening of the NL and KC cultures. Transcription levels for genes related to production or elimination of ROS/RNS were analyzed using quantitative PCR. Immunohistochemistry was performed on 10 intact human corneas using antibodies against SCARA3 and CPSF3.ResultsArray screening of 84 antioxidant-related genes identified 12 genes that were differentially expressed between NL and KC cultures. Compared with NL cells, quantitative PCR showed that KC cells had decreased expression of antioxidant genes SCARA3 isoform 2 (0.59-fold, P = 0.02) and FOXM1 isoform 1 (0.61-fold, P = 0.03). KC cells also had downregulation of the antioxidant genes SOD1 (0.4-fold, P = 0.0001) and SOD3 (0.37-fold, P = 0.02) but increased expression of SOD2 (3.3-fold, P < 0.0001), PRDX6 (1.47-fold, P = 0.01), and CPSF3 (1.44-fold, P = 0.02).ConclusionThe difference in expression of antioxidant enzymes between KC and NL suggests that the oxidative stress imbalances found in KC are caused by defects in ROS/RNS removal rather than increased ROS/RNS production.

Mammalian peroxiredoxin class 6 (Prdx6) are bifunctional enzymes. Non-mammalian Prdx6 enzymes display Cys-based peroxidase activity, but to date their putative phospholipase A₂ (PLA₂ activities) has not been experimentally investigated. Initially, we observed that five non-mammalian Prdx6 enzymes (enzymes from Arabidopsis thaliana (AtPER1), Triticum aestivum (TaPER1), Pseudomonas aeruginosa (PaLsfA) and Aspergillus fumigatus (AfPrx1 and AfPrxC)) present features compatible with PLA₂ activities in mammalian Prdx6 by amino acid sequences alignment and tertiary structure modeling. Employing unilamellar liposomes with tracer amounts of [³H]-1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and thin layer chromatography, all the tested non-mammalian Prdx6 enzymes displayed PLA₂ activities, with values ranging from 3.4 to 6.1 nmol/min/mg protein. It was previously shown that Thr177 phosphorylation of human Prdx6 increases its PLA₂ activity, especially at neutral pH. Therefore, we investigated if human Erk2 kinase could also phosphorylate homologous Thr residues in non-mammalian Prdx6 proteins. We observed phosphorylation of the conserved Thr in three out of the five non-mammalian Prdx enzymes by mass spectrometry. In the case of the mitochondrial Prdx6 from A. fumigatus (AfPrxC), we also observed phosphorylation by western blot, and as a consequence, the PLA₂ activity was increased in acidic and neutral conditions by the human Erk2 kinase treatment. The possible physiological meanings of these PLA₂ activities described open new fields for future research.

PurposeTo compare the levels of gene expression for enzymes involved in production and elimination of reactive oxygen/nitrogen species (ROS/RNS) in normal human corneal cells (NL cells) with those in human corneal cells with keratoconus (KC cells) in vitro.MethodsPrimary NL and KC stromal fibroblast cultures were incubated with apocynin (an inhibitor of NADPH oxidase) or N-nitro-L-arginine (N-LLA; an inhibitor of nitric oxide synthase). ROS/RNS levels were measured using an H2 DCFDA fluorescent assay. The RT2 Profiler™ PCR Array for Oxidative Stress and Antioxidant Defense was used for initial screening of the NL and KC cultures. Transcription levels for genes related to production or elimination of ROS/RNS were analyzed using quantitative PCR. Immunohistochemistry was performed on 10 intact human corneas using antibodies against SCARA3 and CPSF3.ResultsArray screening of 84 antioxidant-related genes identified 12 genes that were differentially expressed between NL and KC cultures. Compared with NL cells, quantitative PCR showed that KC cells had decreased expression of antioxidant genes SCARA3 isoform 2 (0.59-fold, P = 0.02) and FOXM1 isoform 1 (0.61-fold, P = 0.03). KC cells also had downregulation of the antioxidant genes SOD1 (0.4-fold, P = 0.0001) and SOD3 (0.37-fold, P = 0.02) but increased expression of SOD2 (3.3-fold, P < 0.0001), PRDX6 (1.47-fold, P = 0.01), and CPSF3 (1.44-fold, P = 0.02).ConclusionThe difference in expression of antioxidant enzymes between KC and NL suggests that the oxidative stress imbalances found in KC are caused by defects in ROS/RNS removal rather than increased ROS/RNS production.