Mouse anti-Human NANS monoclonal antibody, clone 4H7

During the last years, compressive sensing by random sampling has received a growing attention due to positive theoretical and experimental results. However, the algorithms used for reconstruction, generally based on L1 norm minimization, are very complex and time consuming. The major effect of random sampling is the appearance of missing pixels. Because inpainting algorithms are able to fill the missing data, we propose to use them as CS reconstruction algorithms. For the case of CS images obtained by random sampling, we propose the inpaint_nans algorithm for reconstruction. We justify our proposal by simulation results and comparisons with L1 norm based CS reconstruction algorithms.

Background: Sialylation of glycoproteins and glycolipids is important for biological processes such as cellular communication, cell migration and protein function. Biosynthesis of CMP-sialic acid, the essential substrate, comprises five enzymatic steps, involving ManNAc and sialic acid and their phosphorylated forms as intermediates. Genetic diseases in this pathway result in different and tissue-restricted phenotypes, which is poorly understood. Methods and results: We aimed to study the mechanisms of sialic acid metabolism in knockouts (KO) of the sialic acid pathway in two independent cell lines. Sialylation of cell surface glycans was reduced by KO of GNE (UDPN-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase), NANS (sialic acid synthase) and CMAS (Nacylneuraminate cytidylyltransferase) genes, but was largely unaffected in NANP (N-acylneuraminate-9-phosphatase) KO, as studied by MAA and PNA lectin binding. NANP is the third enzyme in sialic acid biosynthesis and dephosphorylates sialic acid 9-phosphate to free sialic acid. LC-MS analysis of sialic acid metabolites showed that CMP-sialic acid was dramatically reduced in GNE and NANS KO cells and undetectable in CMAS KO. In agreement with normal cell surface sialylation, CMP-sialic acid levels in NANP KO were comparable to WT cells, even though sialic acid 9-phosphate, the substrate of NANP accumulated. Metabolic flux analysis with C-13(6)-labelled ManNAc showed a lower, but significant conversion of ManNAc into sialic acid. Conclusions: Our data provide evidence that NANP activity is not essential for de novo sialic acid production and point towards an alternative phosphatase activity, bypassing NANP. General significance: This report contributes to a better understanding of sialic acid biosynthesis in humans.