Inhibition of autophagy modulates astaxanthin and total fatty acid biosynthesis in Chlorella zofingiensis under nitrogen starvation

Microalgae-derived astaxanthin: bioactivities, biotechnological approaches and industrial technologies for its production

Microalgae are rich sources of astaxanthin well recognized for their potent bioactivities such as antioxidant, anti-cancer, and anti-inflammatory activities. Recent interests focused on the bioactivities of microalgae-derived astaxanthin on treating or preventing cancers mediated by their antioxidant and anti-inflammatory properties. This is due to the special structural configuration of microalgae-derived astaxanthin in terms of unsaturation (conjugated double bonds), stereochemical isomerism (3S,3'S optical isomer) and esterification (monoester), which display more potent bioactivities, compared with those from the other natural sources such as yeasts and higher plants, as well as synthetic astaxanthin. This review focuses on the recent advances on the bioactivities of microalgae-derived astaxanthin in association with cancers and immune diseases, with emphasis on their potential applications as natural antioxidants. Various well-developed biotechnological approaches for inducing astaxanthin production from microalgal culture, along with the proven and emerging industrial technologies to commercialize astaxanthin products in a large-scale manner, are also critically reviewed. These would facilitate the manufacture of bioactive microalgae-derived astaxanthin products to be applied in the food and pharmaceutical industries as salutary nutraceuticals.

Exploiting synergy of dopamine and stressful conditions in enhancing Haematococcus lacustris biomass and astaxanthin yield

Dopamine (DA) has attracted attention because of its effects on Haematococcus lacustris biomass, astaxanthin production, and physiological responses. The alga treated with 25 μM DA combined with 1 g L-1 sodium chloride exhibited 7.63 %, 41.25 %, and 52.04 % increases in biomass (1.41 g L-1), astaxanthin content (32.37 mg/g), and astaxanthin productivity (3.51 mg L-1 d-1) respectively, compared with the salinity stress and high light. Exogenous DA treatment promoted lipid synthesis while reducing carbohydrate and protein contents. Moreover, carotenogenesis and lipogenesis-associated genes were upregulated under DA induction. Inhibition of reactive oxygen species and autophagy, along with mitogen-activated protein kinase activation, promoted astaxanthin accumulation under DA. Furthermore, DA application boosted astaxanthin biosynthesis by regulating the levels of respiratory metabolic intermediates, the γ-aminobutyric acid shunt, and important phytohormones. These findings present a potential and successful biotechnological approach for enhancing biomass and astaxanthin production in H. lacustris under stressful conditions.

High biomass yields of Chlorella protinosa with efficient nitrogen removal from secondary effluent in a membrane photobioreactor

Further treatment of secondary effluents before their discharge into the receiving water bodies could alleviate water eutrophication. In this study, the Chlorella proteinosa was cultured in a membrane photobioreactor to further remove nitrogen from the secondary effluents. The effect of hydraulic retention time (HRT) on microalgae biomass yields and nutrient removal was studied. The results showed that soluble algal products concentration reduced in the suspension at low HRT, thereby alleviating microalgal growth inhibition. In addition, the lower HRT reduced the nitrogen limitation for Chlorella proteinosa's growth through the phase-out of nitrogen-related functional bacteria. As a result, the productivity for Chlorella proteinosa increased from 6.12 mg/L/day at an HRT of 24 hr to 20.18 mg/L/day at an HRT of 8 hr. The highest removal rates of 19.7 mg/L/day, 23.8 mg/L/day, and 105.4 mg/L/day were achieved at an HRT of 8 hr for total nitrogen (TN), ammonia, and chemical oxygen demand (COD), respectively. However, in terms of removal rate, TN and COD were the largest when HRT is 24 hr, which were 74.5% and 82.6% respectively. The maximum removal rate of ammonia nitrogen was 99.2% when HRT was 8 hr.

Regulatory mechanisms of autophagy on DHA and carotenoid accumulation in Crypthecodinium sp. SUN

BACKGROUND

Autophagy is a crucial process of cellular self-destruction and component reutilization that can affect the accumulation of total fatty acids (TFAs) and carotenoids in microalgae. The regulatory effects of autophagy process in a docosahexaenoic acid (DHA) and carotenoids simultaneously producing microalga, Crypthecodinium sp. SUN, has not been studied. Thus, the autophagy inhibitor (3-methyladenine (MA)) and activator (rapamycin) were used to regulate autophagy in Crypthecodinium sp. SUN.

RESULTS

The inhibition of autophagy by 3-MA was verified by transmission electron microscopy, with fewer autophagy vacuoles observed. Besides, 3-MA reduced the glucose absorption and intracellular acetyl-CoA level, which resulting in the decrease of TFA and DHA levels by 15.83 and 26.73% respectively; Surprisingly, 3-MA increased intracellular reactive oxygen species level but decreased the carotenoids level. Comparative transcriptome analysis showed that the downregulation of the glycolysis, pentose phosphate pathway and tricarboxylic acid cycle may underlie the decrease of acetyl-CoA, NADPH and ATP supply for fatty acid biosynthesis; the downregulation of PSY and HMGCR may underlie the decreased carotenoids level. In addition, the class I PI3K-AKT signaling pathway may be crucial for the regulation of carbon and energy metabolism. At last, rapamycin was used to activate autophagy, which significantly enhanced the cell growth and TFA level and eventually resulted in 1.70-fold increase in DHA content.

CONCLUSIONS

Our findings indicate the mechanisms of autophagy in Crypthecodinium sp. SUN and highlight a way to manipulate cell metabolism by regulating autophagy. Overall, this study provides valuable insights to guide further research on autophagy-regulated TFA and carotenoids accumulation in Crypthecodinium sp. SUN.

Melatonin, a phytohormone for enhancing the accumulation of high-value metabolites and stress tolerance in microalgae: Applications, mechanisms, and challenges

High-value metabolites, such as carotenoids, lipids, and proteins, are synthesized by microalgae and find applications in various fields, including food, health supplements, and cosmetics. However, the potential of the microalgal industry to serve these sectors is constrained by low productivity and high energy consumption. Environmental stressors can not only stimulate the accumulation of secondary metabolites in microalgae but also induce oxidative stress, suppressing cell growth and activity, thereby resulting in a decrease in overall productivity. Using melatonin (MT) under stressful conditions is an effective approach to enhance the productivity of microalgal metabolites. This review underscores the role of MT in promoting the accumulation of high-value metabolites and enhancing stress resistance in microalgae under stressful and wastewater conditions. It discusses the underlying mechanisms whereby MT enhances metabolite synthesis and improves stress resistance. The review also offers new perspectives on utilizing MT to improve microalgal productivity and stress resistance in challenging environments.

Salicylic acid enhances cell growth, fatty acid and astaxanthin production in heterotrophic Chromochloris zofingiensis without reactive oxygen species elevation

BACKGROUND

The induction of lipid and astaxanthin accumulation in microalgae is often achieved through abiotic stress. However, this approach usually leads to oxidative stress, which results in relatively low growth rate. Phytohormones, as important small molecule signaling substances, not only affect the growth and metabolism of microalgae but also influence the intracellular reactive oxygen species level. This study aimed to screen phytohormones that could promote the fatty acids and astaxanthin yield of heterotrophic Chromochloris zofingiensis without causing oxidative damage, and further investigate the underlying mechanisms.

RESULTS

In the present study, among all the selected phytohormones, the addition of exogenous salicylic acid (SA) could effectively promote cell growth along with the yield of total fatty acids (TFA) and astaxanthin in heterotrophic C. zofingiensis. Notably, the highest yields of TFA and astaxanthin were achieved at 100 μM SA, 43% and 97.2% higher compared with the control, respectively. Interestingly, the intracellular reactive oxygen species (ROS) levels, which are usually increased with elevated TFA content under abiotic stresses, were significantly decreased by SA treatment. Comparative transcriptome analysis unveiled significant alterations in overall carbon metabolism by SA. Specifically, the upregulation of fatty acid synthesis pathway, upregulation of β-carotene-4-ketolase (BKT) in carotenoid synthesis aligned with biochemical findings. Weighted gene co-expression network analysis highlighted ABC transporters and GTF2B-like transcription factor as potential key regulators.

CONCLUSION

This study found that salicylic acid can serve as an effective regulator to promote the celling growth and accumulation of fatty acids and astaxanthin in heterotrophic C. zofingiensis without ROS elevation, which provides a promising approach for heterotrophic production of TFA and astaxanthin without growth inhibition.

Metabolite analysis of soybean oil on promoting astaxanthin production of Phaffia rhodozyma

BACKGROUND

Astaxanthin is a carotenoid with strong antioxidant property. In addition, it has anti-cancer, anti-tumor, anti-inflammatory and many other functions. The micro-organisms that mainly produce astaxanthin are Haematococcus pluvialis and Phaffia rhodozyma. Compared with H. pluvialis, P. rhodozyma has shorter fermentation cycle and easier to control culture conditions, but the yield of astaxanthin in P. rhodozyma is low. This article studied how to improve the astaxanthin production of P. rhodozyma.

RESULTS

The results showed that when 10 mL L^-1 soybean oil was added to the culture medium, astaxanthin production increased significantly, reaching 7.35 mg L^-1 , which was 1.4 times that of the control group, and lycopene and β-carotene contents also increased significantly. Through targeted metabolite analysis, the fatty acids in P. rhodozyma significantly increased under the soybean oil stimulation, especially the fatty acids closely related to the formation of astaxanthin esters, included palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1n9), linoleic acid (C18:2n6), α-linolenic acid (C18:3n3) and γ-linolenic acid (C18:3n6), thereby increasing the astaxanthin esters content.

CONCLUSION

It showed that the addition of soybean oil can promote the accumulation of astaxanthin by promoting the increase of astaxanthin ester content. © 2022 Society of Chemical Industry.

Fourth generation biofuel from genetically modified algal biomass for bioeconomic development

Biofuels from microalgae have promising potential for a sustainable bioeconomy. Algal strains' oil content and biomass yield are the most influential cost drivers in the fourth generation biofuel (FGB) production. Genetic modification is the key to improving oil accumulation and biomass yield, consequently developing the bioeconomy. This paper discusses current practices, new insights, and emerging trends in genetic modification and their bioeconomic impact on FGB production. It was demonstrated that enhancing the oil and biomass yield could significantly improve the probability of economic success and the net present value of the FGB production process. The techno-economic and socioeconomic burden of using genetically modified (GM) strains and the preventive control strategies on the bioeconomy of FGB production is reviewed. It is shown that the fully lined open raceway pond could cost up to 25% more than unlined ponds. The cost of a plastic hoop air-supported greenhouse covering cultivation ponds is estimated to be US 60,000$ /ha. The competitiveness and profitability of large-scale cultivation of GM biomass are significantly locked to techno-economic and socioeconomic drivers. Nonetheless, it necessitates further research and careful long-term follow-up studies to understand the mechanism that affects these parameters the most.

Autophagy: a game changer for plant development and crop improvement

Manipulation of autophagic pathway represents a tremendous opportunity for designing climate-smart crops with improved yield and better adaptability to changing environment. For exploiting autophagy to its full potential, identification and comprehensive characterization of adapters/receptor complex and elucidation of its regulatory network in crop plants is highly warranted.  Autophagy is a major intracellular trafficking pathway in eukaryotes involved in vacuolar degradation of cytoplasmic constituents, mis-folded proteins, and defective organelles. Under optimum conditions, autophagy operates at a basal level to maintain cellular homeostasis, but under stressed conditions, it is induced further to provide temporal stress relief. Our understanding of this highly dynamic process has evolved exponentially in the past few years with special reference to several plant-specific roles of autophagy. Here, we review the most recent advances in the field of autophagy in plants and discuss its potential implications in designing crops with improved stress and disease-tolerance, enhanced yield potential, and improved capabilities for producing metabolites of high economic value. We also assess the current knowledge gaps and the possible strategies to develop a robust module for biotechnological application of autophagy to enhance bioeconomy and sustainability of agriculture.

The Anticancer Potential of Plant-Derived Nutraceuticals via the Modulation of Gene Expression

Current studies show that approximately one-third of all cancer-related deaths are linked to diet and several cancer forms are preventable with balanced nutrition, due to dietary compounds being able to reverse epigenetic abnormalities. An appropriate diet in cancer patients can lead to changes in gene expression and enhance the efficacy of therapy. It has been demonstrated that nutraceuticals can act as powerful antioxidants at the cellular level as well as anticarcinogenic agents. This review is focused on the best studies on worldwide-available plant-derived nutraceuticals: curcumin, resveratrol, sulforaphane, indole-3-carbinol, quercetin, astaxanthin, epigallocatechin-3-gallate, and lycopene. These compounds have an enhanced effect on epigenetic changes such as histone modification via HDAC (histone deacetylase), HAT (histone acetyltransferase) inhibition, DNMT (DNA methyltransferase) inhibition, and non-coding RNA expression. All of these nutraceuticals are reported to positively modulate the epigenome, reducing cancer incidence. Furthermore, the current review addresses the issue of the low bioavailability of nutraceuticals and how to overcome the drawbacks related to their oral administration. Understanding the mechanisms by which nutraceuticals influence gene expression will allow their incorporation into an “epigenetic diet” that could be further capitalized on in the therapy of cancer.

Critical assessment of protozoa contamination and control measures in mass culture of the diatom Phaeodactylum tricornutum

The diatom Phaeodactylum tricornutum is considered a promising "cell factory" for high-value products fucoxanthin and EPA. But its potential has not been realized due largely to microbial contamination. In this study, seven protozoan strains were identified, of which a heterolobosean amoeba was identified as the most frequently occurring and destructive predator in P. tricornutum culture. The addition of 400 mg L^-1 NH₄HCO₃ inhibited amoeba proliferation with little impact on algal growth. Halting culture mixing at night induced a hypoxia environment that further inhibited amoeba growth. Regardless of culture systems employed, a periodical supply of proper amounts of NH₄HCO₃ alone or in combination with halting culture mixing at night may prevent or treat protozoa contamination in mass culture of P. tricornutum.

The associative induction of succinic acid and hydrogen sulfide for high-producing biomass, astaxanthin and lipids in Haematococcus pluvialis

To obtain higher yield of natural astaxanthin, the present study aims to develop a viable and economic induction strategy for astaxanthin production comprising succinic acid (SA) combined with sodium hydrosulfide (NaHS). The biomass (1.33 g L^-1), astaxanthin concentration (44.96 mg L^-1), astaxanthin content (163.55 pg cell^-1), and lipid content (55.34%) were achieved under 1.0 mM SA and 100 μM NaHS treatment. These results were concomitant with enhanced hydrogen sulfide (H₂S) but diminished reactive oxide species (ROS). Further study discovered that endogenous H₂S could improve astaxanthin and lipid coproduction under SA induction by mediating related gene transcript levels and ROS signalling. Additionally, the concentrations of biomass and astaxanthin increased to 2.14 g L^-1 and 66.25 mg L^-1, respectively, under the induction of SA and NaHS in a scaled-up bioreactor. Briefly, the work proposed a novel feasible strategy for high yields of biomass and astaxanthin by H. pluvialis.

Gamma-aminobutyric acid coupled with copper ion stress stimulates lipid production of green microalga Monoraphidium sp. QLY-1 through multiple mechanisms

Induction of copper ion (Cu²⁺) stress is a method used to increase lipid accumulation in microalgae, but it decreases cell growth. In this work, the impacts of gamma-aminobutyric acid (GABA) coupled with Cu²⁺ stress on the biomass and oil yield in Monoraphidium sp. QLY-1 were investigated. Results suggested that the combined treatment of GABA and Cu²⁺ resulted in a higher lipid content (55.13%) than Cu²⁺ treatment (48.43%). Furthermore, GABA addition upregulated the levels of lipid-relevant genes, cellular GABA, ethylene (ETH), and antioxidant enzyme activities and alleviated oxidative damage caused by Cu²⁺ stress. The autophagy-relevant gene atg8 was also upregulated by GABA treatment. Further exploration indicated that cell autophagy induced the lipid content up to 58.09% with GABA and Cu²⁺ stress treatment. This investigation demonstrates that the coupling strategy can stimulate lipid production and shed light on the underlying mechanisms in lipid biosynthesis, cell autophagy, and stress response of microalgae.

A joint strategy comprising melatonin and 3-methyladenine to concurrently stimulate biomass and astaxanthin hyperaccumulation by Haematococcus pluvialis

Haematococcus pluvialis is a commercial microalgae used for natural astaxanthin production. This study aims to investigate the roles of melatonin (MT) and 3-methyladenine (3-MA) in regulating the cell growth and biosynthesis of astaxanthin and fatty acids under adverse conditions by H. pluvialis. Upon the dual treatments, the maximum astaxanthin concentration (46.78 mg L^-1) was 2.39- and 1.35-fold higher compared with the control and MT treatments, respectively. Concomitantly, the combined application of MT and 3-MA suppressed autophagy but promoted the production of biomass and lipids and upregulated carotenogenesis, lipogenesis and antioxidant enzyme-related genes at the transcriptional level, which were linked with astaxanthin and lipid biosynthesis and oxidative stress. Additionally, astaxanthin exhibited a noticeable increase under MT coupled with 3-MA in the other two strains of H. pluvialis. This study proposed a potential method for astaxanthin induction and provided insights into the function of autophagy in modulating cell growth and astaxanthin synthesis.

Sunscreen Effect Exerted by Secondary Carotenoids and Mycosporine-like Amino Acids in the Aeroterrestrial Chlorophyte Coelastrella rubescens under High Light and UV-A Irradiation

The microalga Coelastrella rubescens dwells in habitats with excessive solar irradiation; consequently, it must accumulate diverse compounds to protect itself. We characterized the array of photoprotective compounds in C. rubescens. Toward this goal, we exposed the cells to high fluxes of visible light and UV-A and analyzed the ability of hydrophilic and hydrophobic extracts from the cells to absorb radiation. Potential light-screening compounds were profiled by thin layer chromatography and UPLC-MS. Coelastrella accumulated diverse carotenoids that absorbed visible light in the blue-green part of the spectrum and mycosporine-like amino acids (MAA) that absorbed the UV-A. It is the first report on the occurrence of MAA in Coelastrella. Two new MAA, named coelastrin A and coelastrin B, were identified. Transmission electron microscopy revealed the development of hydrophobic subcompartments under the high light and UV-A exposition. We also evaluate and discuss sporopollenin-like compounds in the cell wall and autophagy-like processes as the possible reason for the decrease in sunlight absorption by cells, in addition to inducible sunscreen accumulation. The results suggested that C. rubescens NAMSU R1 accumulates a broad range of valuable photoprotective compounds in response to UV-A and visible light irradiation, which indicates this strain as a potential producer for biotechnology.

Reactive oxygen species and their applications toward enhanced lipid accumulation in oleaginous microorganisms

Oleaginous microorganisms are among the most promising alternative sources of lipids for oleochemicals and biofuels. However, in the course of lipid production, reactive oxygen species (ROS) are generated inevitably as byproducts of aerobic metabolisms. Although excessive accumulation of ROS leads to lipid peroxidation, DNA damage, and protein denaturation, ROS accumulation has been suggested to enhance lipid synthesis in these microorganisms. There are many unresolved questions concerning this dichotomous view of ROS influence on lipid accumulation. These include what level of ROS triggers lipid overproduction, what mechanisms and targets are vital and whether ROS act as toxic byproducts or cellular messengers in these microorganisms? Here we review the current state of knowledge on ROS generation, antioxidative defense system, the dual effects of ROS on microbial lipid production, and ROS-induced lipid peroxidation and accumulation mechanisms. Toward the end, the review summarizes strategies that enhance lipid production based on ROS manipulation.

Enhancement of linoleic acid content stimulates astaxanthin esterification in Coelastrum sp

Most natural astaxanthin is fatty acid-esterified in microalgae to prevent oxidation. However, the factors influencing astaxanthin esterification (AE) are poorly understood. In this study, obstacles to AE in Coelastrum sp. HA-1 were investigated. Only half of the astaxanthin molecules in HA-1 were esterified, but AE was stimulated with exogenous linoleic acid (LA) and ethanol treatment. Astaxanthin esters and total astaxanthin (TA) with exogenous LA were elevated to 3.82-fold and 2.18-fold of control levels, respectively. Treatment with 3% (v/v) ethanol enhanced transcription of the Δ12 fatty acid desaturase gene, which caused more oleic acid (OA) to be converted to LA. Furthermore, the contents of astaxanthin esters and TA were 2.42-fold and 1.61-fold control levels, respectively. These findings confirmed that AE was upregulated by increasing LA content. Thus, a large concentration of OA alone does not increase astaxanthin accumulation in HA-1, and a certain amount of LA was necessary for AE.

Enhancement of β-carotene production by regulating the autophagy-carotenoid biosynthesis seesaw in Chlamydomonas reinhardtii

This work aimed to demonstrate a new strategy for enhancing the production of carotenoids through the regulation of seesaw cross-talk between autophagy and carotenoid biosynthesis pathways in Chlamydomonas reinhardtii. Autophagy-related ATG1 and ATG8 genes were first silenced using artificial microRNA, which in turn reduced the mRNA expression of ATG1 and ATG8 by 84.4% and 74.3%, respectively. While ATG1 kinase controls early step in autophagy induction and ATG8 is an essential factor for the downstream formation of autophagosome membranes, the decreased expression of these genes led to a 2.34-fold increase in the amount of β-carotene content (i.e., 23.75 mg/g DCW). Furthermore, all mutants seemed to exhibit greater biodiesel properties than that of wild-type due to increased accumulation of saturated and monounsaturated fatty acids. These results support the role of autophagy in regulating the production of valuable metabolites, which could contribute to uplifting the economic outlook of nascent algal biorefinery.

Ethanol induced jasmonate pathway promotes astaxanthin hyperaccumulation in Haematococcus pluvialis

Haematococcus pluvialis is a main biological resource for the antioxidant astaxanthin production, however, potential modulators and molecular mechanisms underpinning astaxanthin accumulation remain largely obscured. We discovered that provision of ethanol (0.4%) significantly triggered the cellular astaxanthin content up to 3.85% on the 4th day of treatment. Amongst, 95% of the accumulated astaxanthin was esterified, particularly enriched with monoesters. Ultrastructural analysis revealed that ethanol altered cell wall structure and physiological properties. Antioxidant analyses revealed that astaxanthin accumulation offset the ethanol induced oxidative stress. Ethanol treatment reduced carbohydrates while increased lipids and jasmonic acid production. Transcriptomic analysis uncovered that ethanol orchestrated the expression of crucial genes involved in carotenogenesis, e.g. PSY, BKT and CRTR-b were significantly upregulated. Moreover, methyl jasmonic acid synthesis was induced and played a major role in regulating the carotenogenic genes. The findings uncovered the novel viewpoint in the intricate transcriptional regulatory mechanisms of astaxanthin biosynthesis.

Light induces carotenoids accumulation in a heterotrophic docosahexaenoic acid producing microalga, Crypthecodinium sp. SUN

In the present study, the effect of various light conditions on carotenoid accumulation in a novel heterotrophic microalga, Crypthecodinium sp. SUN was investigated. The results showed that C. sp. SUN mainly produced γ-carotene and β-carotene. The total carotenoid content could reach to 12.8 mg g^-1 dry weight under high light intensity (100 μmol m^-2 s^-1), which was >100-fold higher than that under dark condition. Besides, along with the light intensity increased, the ROS level in vivo was decreased at 48 h and 72 h. Further study showed that, light could efficiently promote the gene expression of PSY and LCYb, which explain the molecular mechanisms of carotenoids accumulation under light conditions. Meanwhile, slightly inhibited fatty acids accumulation could promote the carotenoids yield. The present work proposed that C. sp. SUN could be a potential carotenoid producer, and provided valuable insight for carotenoids biosynthesis.

Coupling of abiotic stresses and phytohormones for the production of lipids and high-value by-products by microalgae: A review

Microalgae can produce lipids and high-value by-products under abiotic stress conditions, including nutrient starvation, high light intensity, extreme temperature, high salinity and the presence of heavy metals. However, the growth and development of microalgae and the accumulation of metabolites may be inhibited by adverse stresses. In recent years, phytohormones have emerged as a topic of intense focus in microalgae research. Phytohormones could sustain the growth of microalgae under abiotic stress conditions. In addition, the combination of plant hormones and abiotic stresses could further promote the biosynthesis of metabolites and improve the ability of microalgae to tolerate abiotic stresses. This review primarily focuses on the regulatory effects of exogenous phytohormones on the biosynthesis of metabolites by microalgae under adverse environmental conditions and discusses the mechanisms of phytohormone-mediated cell growth, stress tolerance and lipid biosynthesis in microalgae under abiotic stress conditions.

Metabolic profiling associated with autophagy of human placenta-derived mesenchymal stem cells by chemical isotope labeling LC-MS

Autophagy has been reported to have a pivotal role in maintaining stemness, regulating immunomodulation and enhancing the survival of mesenchymal stem cells (MSCs). However, the effect of autophagy on MSC metabolism is largely unknown. Here, we report a workflow for examining the impact of autophagy on human placenta-derived MSC (hPMSC) metabolome profiling with chemical isotope labeling (CIL) LC-MS. Rapamycin or 3-methyladenine was successfully used to induce or inhibit autophagy, respectively. Then, 12C- and 13C-dansylation labeling LC-MS were used to profile the amine/phenol submetabolome. A total of 935 peak pairs were detected and 50 metabolites were positively identified using the dansylation metabolite standards library, and 669 metabolites were putatively identified based on an accurate mass match in metabolome databases. 12C/13C-p-dimethylaminophenacyl bromide labeling LC-MS was used to analyze the carboxylic acid submetabolome; 4736 peak pairs were detected, among which 33 metabolites were positively identified in the dimethylaminophenacyl metabolite standards library, and 3007 metabolites were putatively identified. PCA/OPLS-DA analysis combined with volcano plots and Venn diagrams was used to determine the significant metabolites. Metabolites pathway analysis demonstrated that hPMSCs appeared to generate more ornithine with the arginine and proline metabolism pathway and utilized more pantothenic acid to synthesize acetyl-CoA in the beta-alanine metabolism pathway when autophagy was activated. Meanwhile, acetyl-CoA conversion to fatty acids led to accumulation in the fatty acid biosynthesis pathway. In contrast, when autophagy was suppressed, a reduction in metabolites demonstrated weakened metabolic activity in these metabolic pathways. Our research provides a more comprehensive understanding of hPMSC metabolism associated with autophagy.

Effects of Astaxanthin on the Proliferation and Migration of Breast Cancer Cells In Vitro

Astaxanthin (ASX) is a marine-based ketocarotenoid; an accessory pigment in plants in that it has many different potential functions. ASX is an antioxidant that is notably more potent than many other antioxidants. Antioxidants have anti-inflammatory and oxidative stress-reducing properties to potentially reduce the incidence of cancer or inhibit the expansion of tumor cells. In this study, we tested the hypothesis that ASX would inhibit proliferation and migration of breast cancer cells in vitro. We found that application of ASX significantly reduced proliferation rates and inhibited breast cancer cell migration compared to control normal breast epithelial cells. Based on these results, further investigation of the effects of ASX on not only breast cancer cells, but other forms of tumor cells, should be carried out.

Melatonin: A Multifunctional Molecule That Triggers Defense Responses against High Light and Nitrogen Starvation Stress in Haematococcus pluvialis

Melatonin (MLT), a ubiquitously distributed small molecule, functions in plant responses to various biotic and abiotic stresses. However, the interactions between melatonin and other important molecules in Haematococcus pluvialis response stresses are largely unknown. In the present study, exogenous melatonin improved H. pluvialis resistance to nitrogen starvation and high light. We concluded that exogenous melatonin treatment prevented the reactive oxygen species (ROS) burst and limited cell damage induced by abiotic stress through activation of antioxidant enzymes and antioxidants. Astaxanthin, a major antioxidant in H. pluvialis cells, exhibited a 2.25-fold increase in content after treatment with melatonin. The maximal astaxanthin content was 32.4 mg g^-1. The functional roles of the nitric oxide (NO)-mediated mitogen activated protein kinase (MAPK) signaling pathway and cyclic adenosine monophosphate (cAMP) signaling pathway induced by melatonin were also evaluated. The results clearly indicate that cAMP signaling pathways are positively associated with microalgal astaxanthin biosynthesis. Additionally, the NO-dependent MAPK signaling cascade is activated in response to astaxanthin accumulation induced by melatonin, confirming that MAPK is a target of NO action in physiological processes. This work is the first to use H. pluvialis as in vivo model and documents the influence of melatonin on the physiological response to abiotic stress in this microalgae.

Lipid catabolism in microalgae

Lipid degradation processes are important in microalgae because survival and growth of microalgal cells under fluctuating environmental conditions require permanent remodeling or turnover of membrane lipids as well as rapid mobilization of storage lipids. Lipid catabolism comprises two major spatially and temporarily separated steps, namely lipolysis, which releases fatty acids and head groups and is catalyzed by lipases at membranes or lipid droplets, and degradation of fatty acids to acetyl-CoA, which occurs in peroxisomes through the β-oxidation pathway in green microalgae, and can sometimes occur in mitochondria in some other algal species. Here we review the current knowledge on the enzymes and regulatory proteins involved in lipolysis and peroxisomal β-oxidation and highlight gaps in our understanding of lipid degradation pathways in microalgae. Metabolic use of acetyl-CoA products via glyoxylate cycle and gluconeogenesis is also reviewed. We then present the implication of various cellular processes such as vesicle trafficking, cell cycle and autophagy on lipid turnover. Finally, physiological roles and the manipulation of lipid catabolism for biotechnological applications in microalgae are discussed.