Metabolic engineering of cofactor flavin adenine dinucleotide (FAD) synthesis and regeneration in Escherichia coli for production of α-keto acids.

Cofactor flavin adenine dinucleotide (FAD) plays a vital role in many FAD-dependent enzymatic reactions; therefore, how to efficiently accelerate FAD synthesis and regeneration is an important topic in biocatalysis and metabolic engineering. In this study, a system involving the synthesis pathway and regeneration of FAD was engineered in Escherichia coli to improve α-keto acid production-from the corresponding l-amino acids-catalyzed by FAD-dependent l-amino acid deaminase (l-AAD). First, key genes, ribH, ribC, and ribF, were overexpressed and fine-tuned for FAD synthesis. In the resulting E. coli strain PHCF7, strong overexpression of pma, ribC, and ribF and moderate overexpression of ribH yielded a 90% increase in phenylpyruvic acid (PPA) titer: 19.4 ± 1.1 g · L-1 . Next, formate dehydrogenase (FDH) and NADH oxidase (NOX) were overexpressed to strengthen the regeneration rate of cofactors FADH2 /FAD using FDH for FADH2 /FAD regeneration and NOX for NAD+ /NADH regeneration. The resulting E. coli strain PHCF7-FDH-NOX yielded the highest PPA production: 31.4 ± 1.1 g · L-1 . Finally, this whole-cell system was adapted to production of other α-keto acids including α-ketoglutaric acid, α-ketoisocaproate, and keto-γ-methylthiobutyric acid to demonstrate the broad utility of strengthening of FAD synthesis and FADH2 /FAD regeneration for production of α-keto acids. Notably, the strategy reported herein may be generally applicable to other flavin-dependent biocatalysis reactions and metabolic pathway optimizations. Biotechnol. Bioeng. 2017;114: 1928-1936. © 2017 Wiley Periodicals, Inc.

The Potential for microRNA Therapeutics and Clinical Research.

As FDA-approved small RNA drugs start to enter clinical medicine, ongoing studies for the microRNA (miRNA) class of small RNAs expand its preclinical and clinical research applications. A growing number of reports suggest a significant utility of miRNAs as biomarkers for pathogenic conditions, modulators of drug resistance, and/or as drugs for medical intervention in almost all human health conditions. The pleiotropic nature of this class of nonprotein-coding RNAs makes them particularly attractive drug targets for diseases with a multifactorial origin and no current effective treatments. As candidate miRNAs begin to proceed toward initiation and completion of potential phase 3 and 4 trials in the future, the landscape of both diagnostic and interventional medicine will arguably continue to evolve. In this mini-review, we discuss miRNA drug discovery development and their current status in clinical trials.

Peroxynitrite causes endoplasmic reticulum stress and apoptosis in human vascular endothelium: implications in atherogenesis.

OBJECTIVE: Peroxynitrite, a potent oxidant generated by the reaction of NO with superoxide, has been implicated in the promotion of atherosclerosis. We designed this study to determine whether peroxynitrite induces its proatherogenic effects through induction of endoplasmic reticulum (ER) stress. METHODS AND RESULTS: Human vascular endothelial cells treated with Sin-1, a peroxynitrite generator, induced the expression of the ER chaperones GRP78 and GRP94 and increased eIF2alpha phosphorylation. These effects were inhibited by the peroxynitrite scavenger uric acid. Sin-1 caused the depletion of ER-Ca2+, an effect known to induce ER stress, resulting in the elevation of cytosolic Ca2+ and programmed cell death (PCD). Sin-1 treatment was also found, via 3-nitrotyrosine and GRP78 colocalization, to act directly on the ER. Adenoviral-mediated overexpression of GRP78 in endothelial cells prevented Sin-1-induced PCD. Consistent with these in vitro findings, 3-nitrotyrosine was observed and colocalized with GRP78 in endothelial cells of early atherosclerotic lesions from apolipoprotein E-deficient mice. CONCLUSIONS: Peroxynitrite is an ER stress-inducing agent. Its effects include the depletion of ER-Ca2+, a known mechanism of ER stress induction. The observation that 3-nitrotyrosine-containing proteins colocalize with markers of ER stress within early atherosclerotic lesions suggests that peroxynitrite contributes to atherogenesis through a mechanism involving ER stress.

Association of multiple cellular stress pathways with accelerated atherosclerosis in hyperhomocysteinemic apolipoprotein E-deficient mice.

BACKGROUND: A causal relation between hyperhomocysteinemia (HHcy) and accelerated atherosclerosis has been established in apolipoprotein E-deficient (apoE-/-) mice. Although several cellular stress mechanisms have been proposed to explain the atherogenic effects of HHcy, including oxidative stress, endoplasmic reticulum (ER) stress, and inflammation, their association with atherogenesis has not been completely elucidated. METHODS AND RESULTS: ApoE-/- mice were fed a control or a high-methionine (HM) diet for 4 (early lesion group) or 18 (advanced lesion group) weeks to induce HHcy. Total plasma homocysteine levels and atherosclerotic lesion size were significantly increased in early and advanced lesion groups fed the HM diet compared with control groups. Markers of ER stress (GRP78/94, phospho-PERK), oxidative stress (HSP70), and inflammation (phospho-IkappaB-alpha) were assessed by immunohistochemical staining of these atherosclerotic lesions. GRP78/94, HSP70, and phospho-IkappaB-alpha immunostaining were significantly increased in the advanced lesion group fed the HM diet compared with the control group. HSP47, an ER-resident molecular chaperone involved in collagen folding and secretion, was also increased in advanced lesions of mice fed the HM diet. GRP78/94 and HSP47 were predominantly localized to the smooth muscle cell-rich fibrous cap, whereas HSP70 and phospho-IkappaB-alpha were observed in the lipid-rich necrotic core. Increased HSP70 and phospho-IkappaB-alpha immunostaining in advanced lesions of mice fed the HM diet are consistent with enhanced carotid artery dihydroethidium staining. Interestingly, GRP78/94 and phospho-PERK were markedly increased in macrophage foam cells from early lesions of mice fed the control or the HM diet. CONCLUSIONS: Multiple cellular stress pathways, including ER stress, are associated with atherosclerotic lesion development in apoE-/- mice.

Deficiency of TDAG51 protects against atherosclerosis by modulating apoptosis, cholesterol efflux, and peroxiredoxin-1 expression.

BACKGROUND: Apoptosis caused by endoplasmic reticulum (ER) stress contributes to atherothrombosis, the underlying cause of cardiovascular disease (CVD). T-cell death-associated gene 51 (TDAG51), a member of the pleckstrin homology-like domain gene family, is induced by ER stress, causes apoptosis when overexpressed, and is present in lesion-resident macrophages and endothelial cells. METHODS AND RESULTS: To study the role of TDAG51 in atherosclerosis, male mice deficient in TDAG51 and apolipoprotein E (TDAG51(-/-)/ApoE(-/-)) were generated and showed reduced atherosclerotic lesion growth (56 ± 5% reduction at 40 weeks, relative to ApoE(-/-) controls, P<0.005) and necrosis (41 ± 4% versus 63 ± 8% lesion area in TDAG51(-/-)/ApoE(-/-) and ApoE(-/-), respectively; P<0.05) without changes in plasma levels of lipids, glucose, and inflammatory cytokines. TDAG51 deficiency caused several phenotypic changes in macrophages and endothelial cells that increase cytoprotection against oxidative and ER stress, enhance PPARγ-dependent reverse cholesterol transport, and upregulate peroxiredoxin-1 (Prdx-1), an antioxidant enzyme with antiatherogenic properties (1.8 ± 0.1-fold increase in Prdx-1 protein expression, relative to control macrophages; P<0.005). Two independent case-control studies found that a genetic variant in the human TDAG51 gene region (rs2367446) is associated with CVD (OR, 1.15; 95% CI, 1.07 to 1.24; P=0.0003). CONCLUSIONS: These findings provide evidence that TDAG51 affects specific cellular pathways known to reduce atherogenesis, suggesting that modulation of TDAG51 expression or its activity may have therapeutic benefit for the treatment of CVD.

TDAG51 is induced by homocysteine, promotes detachment-mediated programmed cell death, and contributes to the cevelopment of atherosclerosis in hyperhomocysteinemia.

Hyperhomocysteinemia is an independent risk factor for cardiovascular disease and accelerates atherosclerosis in apoE-/- mice. Despite the observations that homocysteine causes endoplasmic reticulum (ER) stress and programmed cell death (PCD) in cultured human vascular endothelial cells, the cellular factors responsible for this effect and their relevance to atherogenesis have not been completely elucidated. We report here that homocysteine induces the expression of T-cell death-associated gene 51 (TDAG51), a member of the pleckstrin homology-related domain family, in cultured human vascular endothelial cells. This effect was observed for other ER stress-inducing agents, including dithiothreitol and tunicamycin. TDAG51 expression was attenuated in homozygous A/A mutant eukaryotic translation initiation factor 2 alpha mouse embryonic fibroblasts treated with homocysteine or tunicamycin, suggesting that ER stress-induced phosphorylation of eukaryotic translation initiation factor 2 alpha is required for TDAG51 transcriptional activation. Transient overexpression of TDAG51 elicited significant changes in cell morphology, decreased cell adhesion, and promoted detachment-mediated PCD. In support of these in vitro findings, TDAG51 expression was increased and correlated with PCD in the atherosclerotic lesions from apoE-/- mice fed hyperhomocysteinemic diets, compared with mice fed a control diet. Collectively, these findings provide evidence that TDAG51 is induced by homocysteine, promotes detachment-mediated PCD, and contributes to the development of atherosclerosis observed in hyperhomocysteinemia.