Tissue-specific regulation of 3'-nucleotide hydrolysis and nucleolar architecture

CircRNA HLCS regulates lens epithelial cell apoptosis via miR-338-3p/BPNT1 axis

PURPOSE

The purpose of this study was to investigate the effect of circ_HLCS on age-related cataract (ARC).

METHODS

Circ_HLCS, microRNA (miR)-338-3p, and bisphosphate 3'-nucleotidase 1 (BPNT1) were quantified by quantitative real-time polymerase chain reaction or western blot. Cell proliferation and cell viability were assessed by the 5-Ethynyl-2'-deoxyuridinr and cell counting kit-8 assays. Cell apoptosis was detected by flow cytometry. Targeted correlations among circ_HLCS, miR-338-3p, and BPNT1 were verified by the dual-luciferase reporter and RNA pull-down assays.

RESULTS

circ_HLCS was diminished in ARC tissues and UV-treated SRA01/04 cells. Elevated content of circ_HLCS undermined UV-induced cell proliferation inhibition and apoptosis. Mechanistically, circ_HLCS directly targeted miR-338-3p, and circ_HLCS regulated BPNT1 expression through miR-338-3p. Furthermore, reduction of miR-338-3p ameliorated UV-induced SRA01/04 cell damage by increasing BPNT1 expression.

CONCLUSION

Taken together, these data suggested that circ_HLCS inhibited apoptosis of UV-treated SRA01/04 cells by miR-338-3p/BPNT1 axis. Therefore, circ_HLCS might be a potential therapeutic target for ARC.

Diabetic nephropathy associates with deregulation of enzymes involved in kidney sulphur metabolism

Nephropathy is a major chronic complication of diabetes. A crucial role in renal pathophysiology is played by hydrogen sulphide (H₂S) that is produced excessively by the kidney; however, the data regarding H₂S bioavailability are inconsistent. We hypothesize that early type 1 diabetes (T1D) increases H₂S production by a mechanism involving hyperglycaemia‐induced alterations in sulphur metabolism. Plasma and kidney tissue collected from T1D double transgenic mice were subjected to mass spectrometry‐based proteomic analysis, and the results were validated by immunological and gene expression assays.T1D mice exhibited a high concentration of H₂S in the plasma and kidney tissue and histological, showed signs of subtle kidney fibrosis, characteristic for early renal disease. The shotgun proteomic analyses disclosed that the level of enzymes implicated in sulphate activation modulators, H₂S‐oxidation and H₂S‐production were significantly affected (ie 6 up‐regulated and 4 down‐regulated). Gene expression results corroborated well with the proteomic data. Dysregulation of H₂S enzymes underly the changes occurring in H₂S production, which in turn could play a key role in the initiation of renal disease. The new findings lead to a novel target in the therapy of diabetic nephropathy. Mass spectrometry data are available via ProteomeXchange with identifier PXD018053.

Modulation of sulfur assimilation metabolic toxicity overcomes anemia and hemochromatosis in mice

Sulfur assimilation is an essential metabolic pathway that regulates sulfation, amino acid metabolism, nucleotide hydrolysis, and organismal homeostasis. We recently reported that mice lacking bisphosphate 3'-nucleotidase (BPNT1), a key regulator of sulfur assimilation, develop iron-deficiency anemia (IDA) and anasarca. Here we demonstrate two approaches that successfully reduce metabolic toxicity caused by loss of BPNT1: 1) dietary methionine restriction and 2) overproduction of a key transcriptional regulator hypoxia inducible factor 2α (Hif-2a). Reduction of methionine in the diet reverses IDA in mice lacking BPNT1, through a mechanism of downregulation of sulfur assimilation metabolic toxicity. Gaining Hif-2a acts through a different mechanism by restoring iron homeostatic gene expression in BPNT1 deficient mouse intestinal organoids. Finally, as loss of BPNT1 impairs expression of known genetic modifiers of iron-overload, we demonstrate that intestinal-epithelium specific loss of BPNT1 attenuates hepatic iron accumulation in mice with homozygous C282Y mutations in homeostatic iron regulator (HFEC282Y), the most common cause of hemochromatosis in humans. Overall, our study uncovers genetic and dietary strategies to overcome anemia caused by defects in sulfur assimilation and identifies BPNT1 as a potential target for the treatment of hemochromatosis.

Sulfation pathways from red to green

Sulfur is present in the amino acids cysteine and methionine and in a large range of essential coenzymes and cofactors and is therefore essential for all organisms. It is also a constituent of sulfate esters in proteins, carbohydrates, and numerous cellular metabolites. The sulfation and desulfation reactions modifying a variety of different substrates are commonly known as sulfation pathways. Although relatively little is known about the function of most sulfated metabolites, the synthesis of activated sulfate used in sulfation pathways is essential in both animal and plant kingdoms. In humans, mutations in the genes encoding the sulfation pathway enzymes underlie a number of developmental aberrations, and in flies and worms, their loss-of-function is fatal. In plants, a lower capacity for synthesizing activated sulfate for sulfation reactions results in dwarfism, and a complete loss of activated sulfate synthesis is also lethal. Here, we review the similarities and differences in sulfation pathways and associated processes in animals and plants, and we point out how they diverge from bacteria and yeast. We highlight the open questions concerning localization, regulation, and importance of sulfation pathways in both kingdoms and the ways in which findings from these "red" and "green" experimental systems may help reciprocally address questions specific to each of the systems.

The Regulation of Steroid Action by Sulfation and Desulfation

Steroid sulfation and desulfation are fundamental pathways vital for a functional vertebrate endocrine system. After biosynthesis, hydrophobic steroids are sulfated to expedite circulatory transit. Target cells express transmembrane organic anion-transporting polypeptides that facilitate cellular uptake of sulfated steroids. Once intracellular, sulfatases hydrolyze these steroid sulfate esters to their unconjugated, and usually active, forms. Because most steroids can be sulfated, including cholesterol, pregnenolone, dehydroepiandrosterone, and estrone, understanding the function, tissue distribution, and regulation of sulfation and desulfation processes provides significant insights into normal endocrine function. Not surprisingly, dysregulation of these pathways is associated with numerous pathologies, including steroid-dependent cancers, polycystic ovary syndrome, and X-linked ichthyosis. Here we provide a comprehensive examination of our current knowledge of endocrine-related sulfation and desulfation pathways. We describe the interplay between sulfatases and sulfotransferases, showing how their expression and regulation influences steroid action. Furthermore, we address the role that organic anion-transporting polypeptides play in regulating intracellular steroid concentrations and how their expression patterns influence many pathologies, especially cancer. Finally, the recent advances in pharmacologically targeting steroidogenic pathways will be examined.