N‐acetylneuraminic acid (NeuAc) is a common sialic acid that has a wide range of applications in nutraceuticals and pharmaceuticals. However, low production efficiency and high environmental pollution associated with traditional extraction and chemical synthesis methods constrain the supply of NeuAc. Here, a biological approach is developed for food‐grade NeuAc production via whole‐cell biocatalysis by the generally regarded as safe (GRAS) bacterium Bacillus subtilis (B. subtilis). Promoters for controlling N‐acetylglucosamine 2‐epimerase (AGE) and NeuAc adolase (NanA) are optimized, yielding 32.84 g L−1 NeuAc production with a molar conversion rate of 26.55% from N‐acetylglucosamine (GlcNAc). Next, NeuAc production is further enhanced to 46.04 g L−1, which is 40.2% higher than that of the strain with promoter optimization, by expressing NanA from Staphylococcus hominis instead of NanA from Escherichia coli. To enhance the expression level of ShNanA, the N‐terminal coding sequences of genes with high expression levels are fused to the 5′‐end of the ShNanA gene, resulting in 56.82 g L−1 NeuAc production. Finally, formation of the by‐product acetoin from pyruvate is blocked by deleting the alsS and alsD genes, resulting in 68.75 g L−1 NeuAc production with a molar conversion rate of 55.57% from GlcNAc. Overall, a GRAS B. subtilis strain is demonstrated as a whole‐cell biocatalyst for efficient NeuAc production.
Background. Long term high fat diets (HFD) promote skin aging pathogenesis, but detailed mechanisms remain unclear especially for inflammaging, which has recently emerged as a pathway correlating aging and age-related disease with inflammation. p16INK4a (hereafter termed p16) inhibits the cell cycle, with p16 deletion significantly inhibiting inflammaging. We observed that HFD-induced p16 overexpression in the skin. Therefore, we investigated if p16 exacerbated inflammaging in HFD-induced skin and also if p16 deletion exerted protective effects against this process. Methods. Eight-week-old double knockout (KO) ApoE-/-p16-/- mice and ApoE-/- littermates were fed HFD for 12 weeks and their skin phenotypes were analyzed. We measured skin fibrosis, senescence-associated secretory phenotype (SASP) levels, and integrin-inflammasome pathway activation using histopathological, RNA-sequencing (RNA-seq), bioinformatics analysis, and molecular techniques. Results. We found that HFD contributed to inflammaging in the skin by activating the NLRP3 inflammasome pathway, increasing inflammatory infiltration, and promoting apoptosis by balancing expression between proapoptotic and antiapoptotic molecules. p16 knockout, when compared with the ApoE-/- phenotype, inhibited skin fibrosis by ameliorating inflammatory infiltration and proinflammatory factor expression (Interleukin-1β (IL-1β), Interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α)), and also alleviated inflammaging skin progress induced by HFD in the ApoE-/- mouse model. RNA-seq showed that p16 KO mice inhibited both integrin-inflammasome and NF-κB proinflammatory pathway activation. Conclusions. p16 deletion or p16 positive cell clearance could be a novel strategy preventing long term HFD-induced skin aging.
Background Chronic changes caused by a high‐fat diet (HFD) may be associated with weakened lung function in obese patients. However, few studies have focused on the role of senescent cells in HFD‐induced pulmonary fibrosis. This study aimed to determine whether (i) obesity causes the accumulation of aging cells in the lungs, (ii) p16 accumulation in aging epithelial cells or fibroblasts exacerbates long‐term HFD‐induced senescence‐associated pulmonary fibrosis (SAPF) and (iii) p16 deletion or clearance of aging cells ameliorates HFD‐induced SAPF through inactivation of the inflammasome and metabolic remodelling. Methods Twelve‐month old male mice of p16INK4a (hereafter p16) knockout (p16−/−) and wild‐type (WT), ApoE knockout (ApoE−/−) and ApoE−/−p16−/− were fed a HFD to induce obesity, and the effects of treatment with the senolytic drug ABT263 or the SGK1 specific inhibitor EMD638683 on fibrosis, inflammaging, gene expression, integrin‐inflammasome signalling and metabolism were examined. A549 and IMR‐90 cells were transduced with p16‐overexpressing adenovirus, and treated with palmitic and oleic acids (P&O) to induce steatosis in vitro. Results We found that long‐term HFD promoted the expression of p16 and the increase of senescent cells in the lung. P16 knockout or ABT263 treatment alleviated pulmonary fibrosis, the increase of senescent cells and senescence‐associated secretory phenotype (SASP) in HFD‐fed mice, as well as in P&O‐treated A549 and IMR‐90 cells. RNA sequencing and bioinformatics analyses revealed that p16 knockout inhibited activation of the integrin‐inflammasome pathway and cellular glycolysis. Mass spectrometry, co‐immunoprecipitation and GST pull‐down assays demonstrated that p16 bound to the N‐terminal of SGK1, thereby interfering with the interaction between the E3 ubiquitin ligase NEDD4L and SGK1, and subsequently inhibiting K48‐polyubiquitin‐dependent degradation of SGK1 mediated by the NEDD4L–Ubch5 complex. EMD638683 was found to alleviate HFD‐induced pulmonary fibrosis and activation of the integrin‐inflammasome pathway. Conclusion P16 accumulation promoted activation of integrin– inflammasome pathway and cell glycolysis by binding to the N– terminal of SGK1, intefering with the interaction between the E3 ubiquitin ligase NEDD4L and SGK1, thereby inhibiting K48– polyubiquitin– dependent degradation of SGK1 mediated by the NEDD4L–Ubch5 complex. ABT263 or EMD638683 could be used as potential drugs to treat pulmonary fibrosis in obese patients.
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