Two novel cyanobacterial α-dioxygenases for the biosynthesis of fatty aldehydes

Abstractα-Dioxygenases (α-DOXs) are known as plant enzymes involved in the α-oxidation of fatty acids through which fatty aldehydes, with a high commercial value as flavor and fragrance compounds, are synthesized as products. Currently, little is known about α-DOXs from non-plant organisms. The phylogenic analysis reported here identified a substantial number of α-DOX enzymes across various taxa. Here, we report the functional characterization and Escherichia coli whole-cell application of two novel α-DOXs identified from cyanobacteria: CalDOX from Calothrix parietina and LepDOX from Leptolyngbya sp. The catalytic behavior of the recombinantly expressed CalDOX and LepDOX revealed that they are heme-dependent like plant α-DOXs but exhibit activities toward medium carbon fatty acids ranging from C10 to C14 unlike plant α-DOXs. The in-depth molecular investigation of cyanobacterial α-DOXs and their application in an E. coli whole system employed in this study is useful not only for the understanding of the molecular function of α-DOXs, but also for their industrial utilization in fatty aldehyde biosynthesis.Key points• Two novel α-dioxygenases from Cyanobacteria are reported• Both enzymes prefer medium-chain fatty acids• Both enzymes are useful for fatty aldehyde biosynthesis Graphical abstract

Impaired skin barrier function due to reduced ω- O -acylceramide levels in a mouse model of Sjögren–Larsson syndrome

Sjögren–Larsson syndrome (SLS) is an inherited neurocutaneous disorder whose causative gene encodes the fatty aldehyde dehydrogenase ALDH3A2. To date, the detailed molecular mechanism of the skin pathology of SLS has remained largely unclear. We generated double knockout (DKO) mice for Aldh3a2 and its homolog Aldh3b2 (a pseudogene in humans). These mice showed hyperkeratosis and reduced fatty aldehyde dehydrogenase activity and skin barrier function. The levels of ω- O -acylceramides (acylceramides), which are specialized ceramides essential for skin barrier function, in the epidermis of DKO mice were about 60% of those in wild type mice. In the DKO mice, levels of acylceramide precursors (ω-hydroxy ceramides and triglycerides) were increased, suggesting that the final step of acylceramide production was inhibited. A decrease in acylceramide levels was also observed in human immortalized keratinocytes lacking ALDH3A2 . Differentiated keratinocytes prepared from the DKO mice exhibited impaired long-chain base metabolism. Based on these results, we propose that the long-chain-base–derived fatty aldehydes that accumulate in DKO mice and SLS patients attack and inhibit the enzyme involved in the final step of acylceramide. Our findings provide insight into the pathogenesis of the skin symptoms of SLS, i.e., decreased acylceramide production, and its molecular mechanism.

Nuclear receptors NHR-49 and NHR-79 promote peroxisome proliferation to compensate for aldehyde dehydrogenase deficiency in C. elegans

The intracellular level of fatty aldehydes is tightly regulated by aldehyde dehydrogenases to minimize the formation of toxic lipid and protein adducts. Importantly, the dysregulation of aldehyde dehydrogenases has been implicated in neurologic disorder and cancer in humans. However, cellular responses to unresolved, elevated fatty aldehyde levels are poorly understood. Here, we report that ALH-4 is a C. elegans aldehyde dehydrogenase that specifically associates with the endoplasmic reticulum, mitochondria and peroxisomes. Based on lipidomic and imaging analysis, we show that the loss of ALH-4 increases fatty aldehyde levels and reduces fat storage. ALH-4 deficiency in the intestine, cell-nonautonomously induces NHR-49/NHR-79-dependent hypodermal peroxisome proliferation. This is accompanied by the upregulation of catalases and fatty acid catabolic enzymes, as indicated by RNA sequencing. Such a response is required to counteract ALH-4 deficiency since alh-4; nhr-49 double mutant animals are sterile. Our work reveals unexpected inter-tissue communication of fatty aldehyde levels and suggests pharmacological modulation of peroxisome proliferation as a therapeutic strategy to tackle pathology related to excess fatty aldehydes.

Designed surrogate for high throughput screening of fatty aldehyde reductase engineering

We designed and synthesized a fatty aldehyde surrogate containing a formyl thioester group, which could be reduced by fatty aldehyde reductase (FALR) with a stoichiometric formaldehyde generation. It could be...

Nuclear receptor NHR-49 promotes peroxisome proliferation to compensate for aldehyde dehydrogenase deficiency in C. elegans

The intracellular level of fatty aldehydes is tightly regulated to minimize the formation of toxic aldehyde adducts of cellular components. Accordingly, deficiency of a fatty aldehyde dehydrogenase FALDH causes the neurologic disorder Sjögren-Larsson syndrome (SLS) in humans. However, cellular responses to unresolved, elevated fatty aldehyde levels are poorly understood. Based on lipidomic and imaging analysis, we report that the loss of endoplasmic reticulum-, mitochondria- and peroxisomes-associated ALH-4, the C. elegans FALDH ortholog, increases fatty aldehyde levels and reduces fat storage. ALH-4 deficiency in the intestine, cell-nonautonomously induces NHR-49/NHR-79-dependent hypodermal peroxisome proliferation. This is accompanied by the upregulation of catalases and fatty acid catabolic enzymes, as indicated by RNA sequencing. Such a response is required to counteract ALH-4 deficiency since alh-4; nhr-49 double mutant animals are not viable. Our work reveals unexpected inter-tissue communication of fatty aldehyde levels, and suggests pharmacological modulation of peroxisome proliferation as a therapeutic strategy for SLS.

Myeloperoxidase-Derived 2-Chlorohexadecanal Is Generated in Mouse Heart during Endotoxemia and Induces Modification of Distinct Cardiomyocyte Protein Subsets In Vitro

Sepsis is a major cause of mortality in critically ill patients and associated with cardiac dysfunction, a complication linked to immunological and metabolic aberrations. Cardiac neutrophil infiltration and subsequent release of myeloperoxidase (MPO) leads to the formation of the oxidant hypochlorous acid (HOCl) that is able to chemically modify plasmalogens (ether-phospholipids) abundantly present in the heart. This reaction gives rise to the formation of reactive lipid species including aldehydes and chlorinated fatty acids. During the present study, we tested whether endotoxemia increases MPO-dependent lipid oxidation/modification in the mouse heart. In hearts of lipopolysaccharide-injected mice, we observed significantly higher infiltration of MPO-positive cells, increased fatty acid content, and formation of 2-chlorohexadecanal (2-ClHDA), an MPO-derived plasmalogen modification product. Using murine HL-1 cardiomyocytes as in vitro model, we show that exogenously added HOCl attacks the cellular plasmalogen pool and gives rise to the formation of 2-ClHDA. Addition of 2-ClHDA to HL-1 cardiomyocytes resulted in conversion to 2-chlorohexadecanoic acid and 2-chlorohexadecanol, indicating fatty aldehyde dehydrogenase-mediated redox metabolism. However, a recovery of only 40% indicated the formation of non-extractable (protein) adducts. To identify protein targets, we used a clickable alkynyl analog, 2-chlorohexadec-15-yn-1-al (2-ClHDyA). After Huisgen 1,3-dipolar cycloaddition of 5-tetramethylrhodamine azide (N3-TAMRA) and two dimensional-gel electrophoresis (2D-GE), we were able to identify 51 proteins that form adducts with 2-ClHDyA. Gene ontology enrichment analyses revealed an overrepresentation of heat shock and chaperone, energy metabolism, and cytoskeletal proteins as major targets. Our observations in a murine endotoxemia model demonstrate formation of HOCl-modified lipids in the heart, while pathway analysis in vitro revealed that the chlorinated aldehyde targets specific protein subsets, which are central to cardiac function.

Identification of ALDH3A2 as a novel prognostic biomarker in gastric adenocarcinoma using integrated bioinformatics analysis

Background Extensive research has revealed that genes play a pivotal role in tumor development and growth. However, the underlying involvement of gene expression in gastric carcinoma (GC) remains to be investigated further. Methods In this study, we identified overlapping differentially expressed genes (DEGs) by comparing tumor tissue with adjacent normal tissue using the Gene Expression Omnibus (GEO) and the Cancer Genome Atlas (TCGA) database. Results Our analysis identified 79 up-regulated and ten down-regulated genes. Functional enrichment analysis and prognosis analysis were conducted on the identified genes, and the fatty aldehyde dehydrogenase (FALDH) gene, ALDH3A2, was chosen for more detailed analysis. We performed Gene Set Enrichment Analysis (GSEA) and immunocorrelation analysis (infiltration, copy number alterations, and checkpoints) to elucidate the mechanisms of action of ALDH3A2 in depth. The immunohistochemical (IHC) result based on 140 paraffin-embedded human GC samples indicated that ALDH3A2 was over-expressed in low-grade GC cases and the OS of patients with low expression of ALDH3A2 was significantly shorter than those with high ALDH3A2 expression. In vitro results indicated that the expression of ALDH3A2 was negatively correlated with PDCD1, PDCD1LG2, and CTLA-4. Conclusion We conclude that ALDH3A2 might be useful as a potential reference value for the relief and immunotherapy of GC, and also as an independent predictive marker for the prognosis of GC.

Identification of ALDH3A2 as a novel prognostic biomarker in gastric adenocarcinoma using integrated bioinformatics analysis

Background: Extensive research has revealed that genes play a pivotal role in tumor development and growth. However, the underlying involvement of gene expression in gastric carcinoma (GC) remains to be investigated further. Methods: In this study, we identified overlapping differentially expressed genes (DEGs) by comparing tumor tissue with adjacent normal tissue using the Gene Expression Omnibus (GEO) and the Cancer Genome Atlas (TCGA) database. Results: Our analysis identified 79 up-regulated and ten down-regulated genes. Functional enrichment analysis and prognosis analysis were conducted on the identified genes, and the fatty aldehyde dehydrogenase (FALDH) gene, ALDH3A2, was chosen for more detailed analysis. We performed Gene Set Enrichment Analysis (GSEA) and immunocorrelation analysis (infiltration, copy number alterations, and checkpoints) to elucidate the mechanisms of action of ALDH3A2 in depth. The immunohistochemical (IHC) result based on 140 paraffin-embedded human GC samples indicated that ALDH3A2 was over-expressed in low-grade GC cases and the OS of patients with low expression of ALDH3A2 was significantly shorter than those with high ALDH3A2 expression. In vitro results indicated that the expression of ALDH3A2 was negatively correlated with PDCD1, PDCD1LG2, and CTLA-4. Conclusion: We conclude that ALDH3A2 might be useful as a potential reference value for the relief and immunotherapy of GC, and also as an independent predictive marker for the prognosis of GC.