Upregulation of cyclooxygenases by retinoic acid in rat mesangial cells

Role of arachidonic acid metabolism in intervertebral disc degeneration: identification of potential biomarkers and therapeutic targets via multi-omics analysis and artificial intelligence strategies

BACKGROUND

Intervertebral disc degeneration (IVDD) is widely recognized as the primary etiological factor underlying low back pain, often necessitating surgical intervention as the sole recourse in severe cases. The metabolic pathway of arachidonic acid (AA), a pivotal regulator of inflammatory responses, influences the development and progression of IVDD.

METHODS

Initially, a comparative analysis was conducted to investigate the relationship between AA expression patterns and different stages of IVDD using single-cell sequencing (scRNA-seq) data. Additionally, three machine learning methods (LASSO, random forest, and support vector machine recursive feature elimination) were employed to identify hub genes associated with IVDD. Subsequently, a novel artificial intelligence prediction model was developed for IVDD based on an artificial neural network algorithm and validated using an independent dataset. The identified hub genes were further subjected to functional enrichment, immune infiltration, and Connectivity Map analysis. Moreover, external validation was performed using flow cytometry and real-time reverse transcription polymerase chain reaction analysis.

RESULTS

Both scRNA-seq and bulk RNA-seq data revealed a positive correlation between the severity of IVDD and the AA metabolic pathway. They also revealed increased AA metabolic activity in macrophages and neutrophils, as well as enhanced intercellular communication with nucleus pulposus cells. Utilizing advanced machine learning algorithms, five hub genes (AKR1C3, ALOX5, CYP2B6, EPHX2, and PLB1) were identified, and an incipient diagnostic model was developed with an AUC of 0.961 in the training cohort and 0.72 in the validation cohort. An in-depth exploration of the functionality of these hub genes revealed their notable association with inflammatory responses and immune cell infiltration. Lastly, AH6809 was found to delay IVDD by inhibiting AKR1C3.

CONCLUSIONS

This study offers comprehensive insights into potential biomarkers and small molecules associated with the early pathogenesis of IVDD. The identified biomarkers and the developed integrated diagnostic model hold great promise in predicting the onset of early IVDD. AH6809 was established as a therapeutic target for AKR1C3 in the treatment of IVDD, as evidenced by computer simulations and biological experiments.

Aldehyde dehydrogenase 1A1 and 1A3 isoforms - mechanism of activation and regulation in cancer

In some types of human cancer, aldehyde dehydrogenases represent stemness markers and their expression is associated with advanced disease stages and poor prognosis. Although several biological functions are mediated by their product Retinoid acid, the molecular mechanism is tissue-dependent and only partially understood.

In this review, we summarize the current knowledge about the role of ALDH in solid tumours, especially ALDH1A1 and ALDH1A3 isoforms, regarding the molecular mechanism of their transcription and regulation, and their crosstalk with main molecular pathways resulting in the excessive proliferation, chemoresistance, stem cells properties and invasiveness. The recent knowledge of the regulatory effect of lnRNA on ALDH1A1 and ALDH1A3 is discussed too.

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Aldehyde dehydrogenases are important stem cell markers in many human cancer types.

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ALDH1A1 or ALDH1A3 activation participates in tumour progression, chemoresistance, stem-cell properties and invasiveness.

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ALDH1A1 interacts with oncogenic pathways Notch, NRF, CXCR4, Polycomb, MDR, and HOX.

All-trans retinoic acid preconditioning enhances proliferation, angiogenesis and migration of mesenchymal stem cell in vitro and enhances wound repair in vivo

OBJECTIVES

Stem cell therapy is considered to be a suitable alternative in treatment of a number of diseases. However, there are challenges in their clinical application in cell therapy, such as to reduce survival and loss of transplanted stem cells. It seems that chemical and pharmacological preconditioning enhances their therapeutic efficacy. In this study, we investigated effects of all-trans retinoic acid (ATRA) on survival, angiogenesis and migration of mesenchymal stem cells (MSCs) in vitro and in a wound-healing model.

MATERIALS AND METHODS

MSCs were treated with a variety of concentrations of ATRA, and mRNA expression of cyclo-oxygenase-2 (COX-2), hypoxia-inducible factor-1 (HIF-1), C-X-C chemokine receptor type 4 (CXCR4), C-C chemokine receptor type 2 (CCR2), vascular endothelial growth factor (VEGF), angiopoietin-2 (Ang-2) and Ang-4 were examined by qRT-PCR. Prostaglandin E2 (PGE2) levels were measured using an ELISA kit and MSC angiogenic potential was evaluated using three-dimensional tube formation assay. Finally, benefit of ATRA-treated MSCs in wound healing was determined with a rat excisional wound model.

RESULTS

In ATRA-treated MSCs, expressions of COX-2, HIF-1, CXCR4, CCR2, VEGF, Ang-2 and Ang-4 increased compared to control groups. Overexpression of the related genes was reversed by celecoxib, a selective COX-2 inhibitor. Tube formation and in vivo wound healing of ATRA-treated MSCs were also significantly enhanced compared to untreated MSCs.

CONCLUSION

Pre-conditioning of MSCs with ATRA increased efficacy of cell therapy by activation of survival signalling pathways, trophic factors and release of pro-angiogenic molecules.

Detection of retinoic acid catabolism with reporter systems and by in situ hybridization for CYP26 enzymes

Retinoic acid (RA), an active form of vitamin A, is essential for life in vertebrates, owing to its capacity of influencing expression of a sizable fraction of all genes and proteins. It functions via two modes: (1) as controlling ligand for specific transcription factors in the nucleus it stimulates or inhibits gene expression from RA response elements in gene promoters; (2) in non-genomic pathways it activates kinase-signaling cascades that converge with additional influences to regulate gene expression and mRNA translation. RA performs a critical role in morphogenesis of the developing embryo, which is reflected in spatio-temporally changing expression patterns of RA-synthesizing and RA-degrading enzymes and in its biophysical characteristics as a small diffusible lipid. Because its histological localization cannot be directly visualized for technical reasons, its sites of action in vivo are inferred from the locations of the metabolic enzymes and through use of two kinds of RA reporter systems. Here we explain techniques for use of RA reporter cells and RA reporter mice, and we describe in situ hybridization methods for the three major RA-degrading enzymes: CYP26A1, CYP26B1, and CYP26C1. Comparisons of the different indicators for sites of RA signaling demonstrate that local RA peaks and troughs are important for inferring some but not all locations of RA actions. When integrated within cells of living mice, expression of the RA reporter construct is rarely a simple measure of local RA levels, especially in the developing brain, but it appears to provide cues to an RA involvement in site-specific regulatory networks in combination with other spatial determinants.

Transcriptional regulation of cannabinoid receptor-1 expression in the liver by retinoic acid acting via retinoic acid receptor-gamma

Alcoholism can result in fatty liver that can progress to steatohepatitis, cirrhosis, and liver cancer. Mice fed alcohol develop fatty liver through endocannabinoid activation of hepatic CB(1) cannabinoid receptors (CB(1)R), which increases lipogenesis and decreases fatty acid oxidation. Chronic alcohol feeding also up-regulates CB(1)R in hepatocytes in vivo, which could be replicated in vitro by co-culturing control hepatocytes with hepatic stellate cells (HSC) isolated from ethanol-fed mice, implicating HSC-derived mediator(s) in the regulation of hepatic CB(1)R (Jeong, W. I., Osei-Hyiaman, D., Park, O., Liu, J., Bátkai, S., Mukhopadhyay, P., Horiguchi, N., Harvey-White, J., Marsicano, G., Lutz, B., Gao, B., and Kunos, G. (2008) Cell Metab. 7, 227-235). HSC being a rich source of retinoic acid (RA), we tested whether RA and its receptors may regulate CB(1)R expression in cultured mouse hepatocytes. Incubation of hepatocytes with RA or RA receptor (RAR) agonists increased CB(1)R mRNA and protein, the most efficacious being the RARgamma agonist CD437 and the pan-RAR agonist TTNPB. The endocannabinoid 2-arachidonoylglycerol (2-AG) also increased hepatic CB(1)R expression, which was mediated indirectly via RA, because it was absent in hepatocytes from mice lacking retinaldehyde dehydrogenase 1, the enzyme catalyzing the generation of RA from retinaldehyde. The binding of RARgamma to the CB(1)R gene 5' upstream domain in hepatocytes treated with RAR agonists or 2-AG was confirmed by chromatin immunoprecipitation and electrophoretic mobility shift and antibody supershift assays. Finally, TTNPB-induced CB(1)R expression was attenuated by small interfering RNA knockdown of RARgamma in hepatocytes. We conclude that RARgamma regulates CB(1)R expression and is thus involved in the control of hepatic fat metabolism by endocannabinoids.

Role of the molybdoflavoenzyme aldehyde oxidase homolog 2 in the biosynthesis of retinoic acid: generation and characterization of a knockout mouse

The mouse aldehyde oxidase AOH2 (aldehyde oxidase homolog 2) is a molybdoflavoenzyme. Harderian glands are the richest source of AOH2, although the protein is detectable also in sebaceous glands, epidermis, and other keratinized epithelia. The levels of AOH2 in the Harderian gland and skin are controlled by genetic background, being maximal in CD1 and C57BL/6 and minimal in DBA/2, CBA, and 129/Sv strains. Testosterone is a negative regulator of AOH2 in Harderian glands. Purified AOH2 oxidizes retinaldehyde into retinoic acid, while it is devoid of pyridoxal-oxidizing activity. Aoh2(-/-) mice, the first aldehyde oxidase knockout animals ever generated, are viable and fertile. The data obtained for this knockout model indicate a significant role of AOH2 in the local synthesis and biodisposition of endogenous retinoids in the Harderian gland and skin. The Harderian gland's transcriptome of knockout mice demonstrates overall downregulation of direct retinoid-dependent genes as well as perturbations in pathways controlling lipid homeostasis and cellular secretion, particularly in sexually immature animals. The skin of knockout mice is characterized by thickening of the epidermis in basal conditions and after UV light exposure. This has correlates in the corresponding transcriptome, which shows enrichment and overall upregulation of genes involved in hypertrophic responses.

All-trans retinoic acid induces COX-2 and prostaglandin E2 synthesis in SH-SY5Y human neuroblastoma cells: involvement of retinoic acid receptors and extracellular-regulated kinase 1/2

BACKGROUND

Our recent results show that all-trans retinoic acid (ATRA), an active metabolite of vitamin A, induces COX-dependent hyperalgesia and allodynia in rats. This effect was mediated by retinoic acid receptors (RARs) and was associated with increased COX-2 expression in the spinal cord. Since ATRA also up-regulated COX-2 expression in SH-SY5Y human neuroblastoma cells, the current study was undertaken to analyze in these cells the mechanism through which ATRA increases COX activity.

METHODS

Cultured SH-SY5Y neuroblastoma cells were treated with ATRA. COX expression and kinase activity were analyzed by western blot. Transcriptional mechanisms were analyzed by RT-PCR and promoter assays. Pharmacological inhibitors of kinase activity and pan-antagonists of RAR or RXR were used to assess the relevance of these signaling pathways. Production of prostaglandin E2 (PGE2) was quantified by enzyme immunoabsorbent assay. Statistical significance between individual groups was tested using the non-parametric unpaired Mann-Whitney U test.

RESULTS

ATRA induced a significant increase of COX-2 expression in a dose- and time-dependent manner in SH-SY5Y human neuroblastoma cells, while COX-1 expression remained unchanged. Morphological features of differentiation were not observed in ATRA-treated cells. Up-regulation of COX-2 protein expression was followed by increased production of PGE2. ATRA also up-regulated COX-2 mRNA expression and increased the activity of a human COX-2 promoter construct. We next explored the participation of RARs and mitogen-activated peptide kinases (MAPK). Pre-incubation of SH-SY5Y human neuroblastoma cells with either RAR-pan-antagonist LE540 or MAP kinase kinase 1 (MEK-1) inhibitor PD98059 resulted in the abolition of ATRA-induced COX-2 promoter activity, COX-2 protein expression and PGE2 production whereas the retinoid X receptor pan-antagonist HX531, the p38 MAPK inhibitor SB203580 or the c-Jun kinase inhibitor SP600125 did not have any effect. The increase in RAR-beta expression and extracellular-regulated kinase 1/2(ERK1/2) phosphorylation in ATRA-incubated cells suggested that RARs and ERK1/2 were in fact activated by ATRA in SH-SY5Y human neuroblastoma cells.

CONCLUSION

These results highlight the importance of RAR-dependent and kinase-dependent mechanisms for ATRA-induced COX-2 expression and activity.