PubMed · 15628463
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Masaki Ikemoto. 2004. [Arginase].. https://pubmed.ncbi.nlm.nih.gov/15628463/
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l-Arginine is the common substrate for arginase and nitric oxide synthase (NOS). Arginase converts l-arginine to urea and ornithine, which is the principal precursor for production of polyamines required for cell proliferation. Human placenta expresses endothelial NOS (eNOS) in syncytiotrophoblasts, but the expression of arginase has not been fully elucidated. Our aim was to investigate the expression and distribution patterns of arginase-I (A-I) and arginase-II (A-II) in human placental villi in the first trimester and at term using immunohistochemistry, RT-PCR and Western blot analysis. The arginase enzyme activity in placental villi was also measured. Immunohistochemistry showed different distribution patterns of the arginase isoforms during gestation: A-I was observed only in cytotrophoblasts, while A-II was observed in both cytotrophoblasts and syncytiotrophoblasts. RT-PCR and Western blot analysis showed expression of A-I and A-II in the first trimester and at term in human placental villi. Expression of A-II and arginase activity was greater in the first trimester than at term. Differentiation of cytotrophoblasts into syncytiotrophoblasts may be associated with l-arginine metabolism through modulation of l-arginine availability for eNOS and A-I. And elevated arginase activity in the early gestational period may be responsible for proliferation of trophoblasts by increasing polyamines production. These results suggest that the l-arginine-ornithine-polyamine and l-arginine-nitric oxide pathways play a role in placental growth and development.
Chronic inflammation is accompanied by impaired T-cell immunity. In the mouse, myeloid cell-associated arginase accounts for the suppression of immune reactivity in various models of tumor growth and chronic infections. Here we show that arginase I is liberated from human granulocytes, and very high activities accumulate extracellularly during purulent inflammatory reactions. Human granulocyte arginase induces a profound suppression of T-cell proliferation and cytokine synthesis. This T-cell phenotype is due to arginase-mediated depletion of arginine in the T-cell environment, which leads to CD3zeta chain down-regulation but does not alter T-cell viability. Our study therefore demonstrates that human granulocytes possess a previously unanticipated immunosuppressive effector function. Human granulocyte arginase is a promising pharmacologic target to reverse unwanted immunosuppression.
N. crassa has two forms of arginase. The physiological role of multiple arginases is not understood. The two forms were shown to be differentially expressed from a single locus (aga) and both proteins are localized to the cytoplasm. The 36-kDa protein was expressed in minimal and arginine supplemented medium, whereas the 41-kDa form was detected only in the presence of arginine. In this study we examined developmental expression of the two arginase transcripts and proteins in conidia and during conidial germination. Two novel observations are revealed, storage of both arginase proteins in conidia and temporal expression of aga transcripts during early germination. To better understand the role of arginase in conidia and the nature of the temporal expression, we examined the effects of related metabolites, arginine, ornithine, proline, glutamate and glutamine on protein storage and temporal expression. These metabolites were used as supplements or sole nitrogen sources. Storage of arginase protein was detected in all conidial samples examined except when glutamate was used as the nitrogen source. The aga temporal RNA expression early in germination was abolished when arginine related metabolites were used as nitrogen sources. The exception to this result is observed with glutamate where temporal expression was seen when glutamate was the sole nitrogen source and abolished with glutamate supplementation. The temporal expression result supports a unique role for arginase in glutamate accumulation early in germination whereas the protein storage result supports the existence of a novel pathway utilizing arginase for glutamate synthesis in asexual spore development.