Carbon dioxide sensitization delays the postharvest ripening and fatty acids composition of Capsicum fruit by regulating ethylene biosynthesis, malic acid and reactive oxygen species metabolism.

Present study would be significant in the sustenance of quality characters for postharvest storage of Capsicum fruit with CO2-sensitization in biocompatible manner. The present experiment describes effects of CO2 sensitization on delaying postharvest ripening through physiological attributes in Capsicum fruit. The experiment was conducted with acidified bicarbonate-derived CO2 exposure for 2 h on Capsicum fruit, kept under white light at 25 °C through 7 days postharvest storage. Initially, fruits responded well to CO2 as recorded sustenance of greenness and integrity of fruit coat resolved through scanning electron micrograph. Loss of water and accumulation of total soluble solids were marginally increased on CO2-sensitized fruit as compared to non-sensitized (control) fruit. The ethylene metabolism biosynthetic genes like CaACC synthase, CaACC oxidase were downregulated on CO2-sensitization. Accompanying ethylene metabolism cellular respiration was downregulated on CO2 induction as compared to control through 7 days of storage. Fruit coat photosynthesis decarboxylating reaction by NADP malic enzyme was upregulated to maintain the reduced carbon accumulation as recorded on 7 days of storage under the same condition. CO2-sensitization effectively reduced the lipid peroxides as oxidative stress products on ripening throughout the storage. Anti-oxidation reaction essentially downregulates the ROS-induced damages of biomolecules that otherwise are highly required for food preservation during postharvest storage. Thus, the major finding is that CO2-sensitization maintains a higher ratio of unsaturated to saturated fatty acids in fruit coat during storage. Tissue-specific downregulation of ROS also maintained the nuclear stability under CO2 exposure. These findings provide basic as well as applied insights for sustaining Capsicum fruit quality with CO2 exposure under postharvest storage. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-024-01471-4.

Modulation of secondary metabolism and redox regulation by exogenously applied glutathione improves the shelf life of Capsicum annuum L. fruit.

Role of redox homeostasis in fruit ripening of Capsicum annuum L. with oxidative metabolism was studied. The research aims the ability to reduce agents during postharvest storage on fruit for delayed ripening with the regulation of oxidative stress. Thus, we applied 10 mM reduced glutathione (GSH) to fruit as pretreatment followed by 1 mM hydrogen peroxide (H2O2) as ripening-inducing treatment and observed during 7 days of storage at 25 °C. A decrease in total soluble solid and firmness under H2O2, was increased while dehydration in tissue was decreased by GSH pretreatment. Glutathione regulated the turnover of organic acids to reducing sugars with higher activity of NADP malic enzyme that sustained the fruit coat photosynthesis through chlorophyll fluorescence, pigment composition, and photosystem II activity. Malondialdehyde accumulation was inversely correlated with GSH content and antioxidative enzyme activity that reduced loss of cell viability. Conclusively, regulation of oxidative stress with GSH may be effective in the extension of shelf life under postharvest storage.

Single-cell RNA-sequencing provides new insights into the cell-specific expression patterns and transcriptional regulation of photosynthetic genes in bermudagrass leaf blades.

As an important warm-season turfgrass species, bermudagrass (Cynodon dactylon L.) flourishes in warm areas around the world due to the existence of the C4 photosynthetic pathway. However, how C4 photosynthesis operates in bermudagrass leaves is still poorly understood. In this study, we performed single-cell RNA-sequencing on 5296 cells from bermudagrass leaf blades. Eight cell clusters corresponding to mesophyll, bundle sheath, epidermis and vascular bundle cells were successfully identified using known cell marker genes. Expression profiling indicated that genes encoding NADP-dependent malic enzymes (NADP-MEs) were highly expressed in bundle sheath cells, whereas NAD-ME genes were weakly expressed in all cell types, suggesting C4 photosynthesis of bermudagrass leaf blades might be NADP-ME type rather than NAD-ME type. The results also indicated that starch synthesis-related genes showed preferential expression in bundle sheath cells, whereas starch degradation-related genes were highly expressed in mesophyll cells, which agrees with the observed accumulation of starch-filled chloroplasts in bundle sheath cells. Gene co-expression analysis further revealed that different families of transcription factors were co-expressed with multiple C4 photosynthesis-related genes, suggesting a complex transcription regulatory network of C4 photosynthesis might exist in bermudagrass leaf blades. These findings collectively provided new insights into the cell-specific expression patterns and transcriptional regulation of photosynthetic genes in bermudagrass.

Populus euphratica PeNADP-ME interacts with PePLDδ to mediate sodium and ROS homeostasis under salinity stress.

Populus euphratica phospholipase Dδ (PePLDδ) is transcriptionally regulated and mediates reactive oxygen species (ROS) and ion homeostasis under saline conditions. The purpose of this study is to explore the post-transcriptional regulation of PePLDδ in response to salt environment. P. euphratica PePLDδ was shown to interact with the NADP-dependent malic enzyme (NADP-ME) by screening the yeast two-hybrid libraries. The transcription level of PeNADP-ME increased upon salt exposure to NaCl (200 mM) in leaves and roots of P. euphratica. PeNADP-ME had a similar subcellular location with PePLDδ in the cytoplasm, and the interaction between PeNADP-ME and PePLDδ was further verified by GST pull-down and yeast two-hybrid. To clarify whether PeNADP-ME interacts with PePLDδ to enhance salt tolerance, PePLDδ and PeNADP-ME were overexpressed singly or doubly in Arabidopsis thaliana. Dual overexpression of PeNADP-ME and PePLDδ resulted in an even more pronounced improvement in salt tolerance compared with single transformants overexpressing PeNADP-ME or PePLDδ alone. Greater Na+ limitation and Na+ efflux in roots were observed in doubly overexpressed plants compared with singly overexpressed plants with PeNADP-ME or PePLDδ. Furthermore, NaCl stimulation of SOD, APX, and POD activity and transcription were more remarkable in the doubly overexpressed plants. It is noteworthy that the enzymic activity of NADP-ME and PLD, and total phosphatidic acid (PA) concentrations were significantly higher in the double-overexpressed plants than in the single transformants. We conclude that PeNADP-ME interacts with PePLDδ in Arabidopsis to promote PLD-derived PA signaling, conferring Na+ extrusion and ROS scavenging under salt stress.

Overexpression of malic enzyme is involved in breast cancer growth and is correlated with poor prognosis.

Malic enzyme (ME) genes are key functional metabolic enzymes playing a crucial role in carcinogenesis. However, the detailed effects of ME gene expression on breast cancer progression remain unclear. Here, our results revealed ME1 expression was significantly upregulated in breast cancer, especially in patients with oestrogen receptor/progesterone receptor-negative and human epidermal growth factor receptor 2-positive breast cancer. Furthermore, upregulation of ME1 was significantly associated with more advanced pathological stages (p < 0.001), pT stage (p < 0.001) and tumour grade (p < 0.001). Kaplan-Meier analysis revealed ME1 upregulation was associated with poor disease-specific survival (DSS: p = 0.002) and disease-free survival (DFS: p = 0.003). Multivariate Cox regression analysis revealed ME1 upregulation was significantly correlated with poor DSS (adjusted hazard ratio [AHR] = 1.65; 95% CI: 1.08-2.52; p = 0.021) and DFS (AHR, 1.57; 95% CI: 1.03-2.41; p = 0.038). Stratification analysis indicated ME1 upregulation was significantly associated with poor DSS (p = 0.039) and DFS (p = 0.038) in patients with non-triple-negative breast cancer (TNBC). However, ME1 expression did not affect the DSS of patients with TNBC. Biological function analysis revealed ME1 knockdown could significantly suppress the growth of breast cancer cells and influence its migration ability. Furthermore, the infiltration of immune cells was significantly reduced when they were co-cultured with breast cancer cells with ME1 knockdown. In summary, ME1 plays an oncogenic role in the growth of breast cancer; it may serve as a potential biomarker of progression and constitute a therapeutic target in patients with breast cancer.

13C-labeling reveals non-conventional pathways providing carbon for hydroxy fatty acid synthesis in Physaria fendleri.

Physaria fendleri is a member of the Brassicaceae that produces in its embryos hydroxy fatty acids, constituents of oils that are very valuable and widely used by industry for cosmetics, lubricants, biofuels, etc. Free of toxins and rich in hydroxy fatty acids, Physaria provides a promising alternative to imported castor oil and is on the verge of being commercialized. This study aims to identify important biochemical step(s) for oil synthesis in Physaria, which may serve as target(s) for future crop improvement. To advance towards this goal, the endosperm composition was analysed by LC-MS/MS to develop and validate culture conditions that mimic the development of the embryos in planta. Using developing Physaria embryos in culture and 13C-labeling, our studies revealed that: (i) Physaria embryos metabolize carbon into biomass with an efficiency significantly lower than other photosynthetic embryos; (ii) the plastidic malic enzyme provides 42% of the pyruvate used for de novo fatty acid synthesis, which is the highest measured so far in developing 'green' oilseed embryos; and (iii) Physaria uses non-conventional pathways to channel carbon into oil, namely the Rubisco shunt, which fixes CO2 released in the plastid, and the reversibility of isocitrate dehydrogenase, which provides additional carbon for fatty acid elongation.

Dual Roles of Two Malic Enzymes in Lipid Biosynthesis and Salt Stress Response in Dunaliella salina.

Triacylglycerols (TAG) from microalgae can be used as feedstocks for biofuel production to address fuel shortages. Most of the current research has focused on the enzymes involved in TAG biosynthesis. In this study, the effects of malic enzyme (ME), which provides precursor and reducing power for TAG biosynthesis, on biomass and lipid accumulation and its response to salt stress in Dunaliella salina were investigated. The overexpression of DsME1 and DsME2 improved the lipid production, which reached 0.243 and 0.253 g/L and were 30.5 and 36.3% higher than wild type, respectively. The transcript levels of DsME1 and DsME2 increased with increasing salt concentration (0, 1, 2, 3, and 4.5 mol/L NaCl), indicating that DsMEs participated in the salt stress response in D. salina. It was found that cis-acting elements associated with the salt stress response were present on the promoters of two DsMEs. The deletion of the MYB binding site (MBS) on the DsME2 promoter confirmed that MBS drives the expression of DsME2 to participate in osmotic regulation in D. salina. In conclusion, MEs are the critical enzymes that play pivotal roles in lipid accumulation and osmotic regulation.

Abscisic acid priming confers salt tolerance in maize seedlings by modulating osmotic adjustment, bond energies, ROS homeostasis, and organic acid metabolism.

This study aimed at investigating the influence of exogenous abscisic acid (ABA) on salt homeostasis under 100 mM NaCl stress in maize (Zea mays L. cv. Kaveri 50) through 3 and 5 days of exposure. The ratio of Na+ to K+, hydrogen peroxide (H2O2) and superoxide (O2•‒) accumulation, electrolyte leakage were the major determinants for salt sensitivity. Pretreatment with ABA [ABA (+)] had altered the salt sensitivity of plants maximally through 5 days of treatment. Plants controlled well for endogenous ABA level (92% increase) and bond energy minimization of cell wall residues to support salt tolerance proportionately to ABA (+). Salt stress was mitigated through maintenance of relative water content (RWC) (16%), glycine betaine (GB) (26%), proline (28%) and proline biosynthesis enzyme (ΔP5CS) (26%) under the application of ABA (+). Minimization of lipid peroxides (6% decrease), carbonyl content (9% decrease), acid, alkaline phosphatase activities were more tolerated under 100 mM salinity at 5 days duration. Malate metabolism for salt tolerance was dependent on the activity of the malic enzyme, malate dehydrogenase through transcript abundance in real-time manner as a function of ABA (+). Establishment of oxidative stress through days under salinity recorded by NADPH-oxidase activity (39% increase) following ROS generation as detected in tissue specific level. The ABA (+) significantly altered redox homeostasis through ratio of AsA to DHA (21% increase), GSH to GSSG (12% increase) by dehydroascorbate reductase and glutathione reductase respectively, and other enzymes like guaiacol peroxidase, catalase, glutathione reductase activities. The ABA in priming was substantially explained in stress metabolism as biomarker for salinity stress with reference to maize.

High-resolution melting (HRM)-based detection of polymorphisms in the malic enzyme and glucose-6-phosphate isomerase genes for Leishmania infantum genotyping.

BACKGROUND: Leishmaniasis is a zoonotic disease endemic in the Mediterranean region where Leishmania infantum is the causative agent of human and canine infection. Characterization of this parasite at the subspecies level can be useful in epidemiological studies, to evaluate the clinical course of the disease (e.g. resistant strains, visceral and cutaneous forms of leishmaniasis) as well as to identify infection reservoirs. Multilocus enzyme electrophoresis (MLEE), a method currently recognized as the reference method for characterizing and identifying strains of Leishmania, is cumbersome and time-consuming and requires cultured parasites. These disadvantages have led to the development of other methods, such as multilocus microsatellite typing (MLMT) and multilocus sequence typing (MLST), for typing Leishmania parasites; however, these methods have not yet been applied for routine use. In this study, we first used MLST to identify informative polymorphisms on single-copy genes coding for metabolic enzymes, following which we developed two rapid genotyping assays based on high-resolution melting (HRM) analysis to explore these polymorphisms in L. infantum parasites. METHODS: A customized sequencing panel targeting 14 housekeeping genes was designed and MLST analysis was performed on nine L. infantum canine and human strains/isolates. Two quantitative real-time PCR-HRM assays were designed to analyze two informative polymorphisms on malic enzyme (ME) and glucose-6-phosphate isomerase (GPI) genes (390T/G and 1831A/G, respectively). The two assays were applied to 73 clinical samples/isolates from central/southern Italy and Pantelleria island, and the results were confirmed by DNA sequencing in a subset of samples. RESULTS: The MLST analysis, together with sequences available in the Genbank database, enabled the identification of two informative polymorphisms on the genes coding for ME and GPI. The fast screening of these polymorphisms using two HRM-based assays in 73 clinical samples/isolates resulted in the identification of seven genotypes. Overall, genotype 1 (sequence type 390T/1831G) was the most highly represented (45.2%) in the overall sample and correlated with the most common L. infantum zymodemes (MON-1, MON-72). Interestingly, in Pantelleria island, the most prevalent genotype (70.6%) was genotype 6 (sequence type 390T/1831A). CONCLUSIONS: Applying our HRM assays on clinical samples allowed us to identify seven different genotypes without the need for parasite isolation and cultivation. We have demonstrated that these assays could be used as fast, routine and inexpensive tools for epidemiological surveillance of L. infantum or for the identification of new infection reservoirs.

Overexpression of chloroplastic Zea mays NADP-malic enzyme (ZmNADP-ME) confers tolerance to salt stress in Arabidopsis thaliana.

The C4 plants photosynthesize better than C3 plants especially in arid environment. As an attempt to genetically convert C3 plant to C4, the cDNA of decarboxylating C4 type NADP-malic enzyme from Zea mays (ZmNADP-ME) that has lower Km for malate and NADP than its C3 isoforms, was overexpressed in Arabidopsis thaliana under the control of 35S promoter. Due to increased activity of NADP-ME in the transgenics the malate decarboxylation increased that resulted in loss of carbon skeletons needed for amino acid and protein synthesis. Consequently, amino acid and protein content of the transgenics declined. Therefore, the Chl content, photosynthetic efficiency (Fv/Fm), electron transport rate (ETR), the quantum yield of photosynthetic CO2 assimilation, rosette diameter, and biomass were lower in the transgenics. However, in salt stress (150 mM NaCl), the overexpressers had higher Chl, protein content, Fv/Fm, ETR, and biomass than the vector control. NADPH generated in the transgenics due to increased malate decarboxylation, contributed to augmented synthesis of proline, the osmoprotectant required to alleviate the reactive oxygen species-mediated membrane damage and oxidative stress. Consequently, the glutathione peroxidase activity increased and H2O2 content decreased in the salt-stressed transgenics. The reduced membrane lipid peroxidation and lower malondialdehyde production resulted in better preservation, of thylakoid integrity and membrane architecture in the transgenics under saline environment. Our results clearly demonstrate that overexpression of C4 chloroplastic ZmNADP-ME in the C3 Arabidopsis thaliana, although decrease their photosynthetic efficiency, protects the transgenics from salinity stress.

αKG-driven RNA polymerase II transcription of cyclin D1 licenses malic enzyme 2 to promote cell-cycle progression.

Increased metabolic activity usually provides energy and nutrients for biomass synthesis and is indispensable for the progression of the cell cycle. Here, we find a role for α-ketoglutarate (αKG) generation in regulating cell-cycle gene transcription. A reduction in cellular αKG levels triggered by malic enzyme 2 (ME2) or isocitrate dehydrogenase 1 (IDH1) depletion leads to a pronounced arrest in G1 phase, while αKG supplementation promotes cell-cycle progression. Mechanistically, αKG directly binds to RNA polymerase II (RNAPII) and increases the level of RNAPII binding to the cyclin D1 gene promoter via promoting pre-initiation complex (PIC) assembly, consequently enhancing cyclin D1 transcription. Notably, αKG addition is sufficient to restore cyclin D1 expression in ME2- or IDH1-depleted cells, facilitating cell-cycle progression and proliferation in these cells. Therefore, our findings indicate a function of αKG in gene transcriptional regulation and cell-cycle control.

Cytosolic malic enzyme and glucose-6-phosphate dehydrogenase modulate redox balance in NSCLC with acquired drug resistance.

Lung cancer cells often show elevated levels of reactive oxygen species (ROS) and nicotinamide adenine dinucleotide phosphate (NADPH). However, the connections between deregulated redox homeostasis in different subtypes of lung cancer and acquired drug resistance in lung cancer have not yet been fully established. Herein, we analyzed different subtypes of lung cancer data reported in the Cancer Cell Line Encyclopedia (CCLE) database, the Cancer Genome Atlas program (TCGA), and the sequencing data obtained from a gefitinib-resistant non-small-cell lung cancer (NSCLC) cell line (H1975GR). Using flux balance analysis (FBA) model integrated with multiomics data and gene expression profiles, we identified cytosolic malic enzyme 1 (ME1) and glucose-6-phosphate dehydrogenase as the major contributors to the significantly upregulated NADPH flux in NSCLC tissues as compared with normal lung tissues, and gefitinib-resistant NSCLC cell line as compared with the parental cell line. Silencing the gene expression of either of these two enzymes in two osimertinib-resistant NSCLC cell lines (H1975OR and HCC827OR) exhibited strong antiproliferative effects. Our findings not only underscored the pivotal roles of cytosolic ME1 and glucose-6-phosphate dehydrogenase in regulating redox states in NSCLC cells but also provided novel insights into their potential roles in drug-resistant NSCLC cells with disturbed redox states.

An enzyme-centric approach for constructing an amperometric l-malate biosensor with a long and programmable linear range.

l-Malate is a key flavor enhancer and acidulant in the food and beverage industry, particularly winemaking. Enzyme-based amperometric biosensors offer convenience for monitoring its concentration. However, only a small number of off-the-shelf malate-oxidizing enzymes have been used in previous devices. These typically have linear ranges poorly suited for the l-malate concentrations found in fruit processing and winemaking, making it necessary to use precisely diluted samples. Here, we describe a pipeline of database-mining, gene synthesis, recombinant expression, and spectrophotometric assays to characterize previously untested enzymes for their suitability in biosensors. The pipeline yielded a bespoke biocatalyst-the Ascaris suum malic enzyme carrying mutation R181Q [AsME(R181Q)]. Our first prototype with AsME(R181Q) had an ultra-wide linear range of 50-200 mM l-malate, corresponding to concentrations found in undiluted fruit juices (including grape). Changing the dication from Mg2+ to Mn2+ increased sensitivity five-fold and adding citrate (100 mM) increased it another six-fold, albeit decreasing the linear range to 1-10 mM. To our knowledge, this is the first time an l-malate biosensor with a tuneable combination of sensitivity and linear range has been described. The sensor response was also tested in the presence of various molecules abundant in juices and wines, with ascorbate shown to be a potent interferent. Interference was mitigated by the addition of ascorbate oxidase, allowing for differential measurements on an undiluted, untreated wine sample that corresponded well with commercial l-malate testing kits. Overall, this work demonstrates the power of an enzyme-centric approach for designing electrochemical biosensors with improved operational parameters and novel functionality.

The effect of phytoprotectors on the functioning of liver NAD⁺- and NADP⁺-maliс enzymes in rats with alloxan diabetes.

The development of experimental alloxan diabetes in rats was accompanied by the increase the activity of liver NAD⁺- and NADP⁺-dependent malic enzymes (ME; NAD⁺-ME, EC 1.1.1.39 and NADP⁺-ME, 1.1.1.40) associated with an increase in the rate of transcription of genes encoding these enzymes. Oral administration of aqueous extracts of Jerusalem artichoke and olive to diabetic rats caused a noticeable decrease in blood glucose, a decrease in the rate of transcription of the studied genes; and a decrease in ME activity towards normal values. Thus, extracts of Jerusalem artichoke and olive can be used as additives to the standard therapy of diabetes mellitus.

Cellular redox homeostasis maintained by malic enzyme 2 is essential for MYC-driven T cell lymphomagenesis.

T cell lymphomas (TCLs) are a group of rare and heterogeneous tumors. Although proto-oncogene MYC has an important role in driving T cell lymphomagenesis, whether MYC carries out this function remains poorly understood. Here, we show that malic enzyme 2 (ME2), one of the NADPH-producing enzymes associated with glutamine metabolism, is essential for MYC-driven T cell lymphomagenesis. We establish a CD4-Cre; Myc flox/+transgenic mouse mode, and approximately 90% of these mice develop TCL. Interestingly, knockout of Me2 in Myc transgenic mice almost completely suppresses T cell lymphomagenesis. Mechanistically, by transcriptionally up-regulating ME2, MYC maintains redox homeostasis, thereby increasing its tumorigenicity. Reciprocally, ME2 promotes MYC translation by stimulating mTORC1 activity through adjusting glutamine metabolism. Treatment with rapamycin, an inhibitor of mTORC1, blocks the development of TCL both in vitro and in vivo. Therefore, our findings identify an important role for ME2 in MYC-driven T cell lymphomagenesis and reveal that MYC-ME2 circuit may be an effective target for TCL therapy.

Transcriptomic Analysis Reveals the Response of the Bacterium Priestia Aryabhattai SK1-7 to Interactions and Dissolution with Potassium Feldspar.

Potassium feldspar (K2O·Al2O3·6SiO2) is considered to be the most important source of potash fertilizer. The use of microorganisms to dissolve potassium feldspar is a low-cost and environmentally friendly method. Priestia aryabhattai SK1-7 is a strain with a strong ability to dissolve potassium feldspar; it showed a faster pH drop and produced more acid in the medium with potassium feldspar as the insoluble potassium source than in the medium with K2HPO4 as the soluble potassium source. We speculated whether the cause of acid production was related to one or more stresses, such as mineral-induced generation of reactive oxygen species (ROS), the presence of aluminum in potassium feldspar, and cell membrane damage due to friction between SK1-7 and potassium feldspar, and analyzed it by transcriptome. The results revealed that the expression of the genes related to pyruvate metabolism, the two-component system, DNA repair, and oxidative stress pathways in strain SK1-7 was significantly upregulated in potassium feldspar medium. The subsequent validation experiments revealed that ROS were the stress faced by strain SK1-7 when interacting with potassium feldspar and led to a decrease in the total fatty acid content of SK1-7. In the face of ROS stress, strain SK1-7 upregulated the expression of the maeA-1 gene, allowing malic enzyme (ME2) to produce more pyruvate to be secreted outside the cell using malate as a substrate. Pyruvate is both a scavenger of external ROS and a gas pedal of dissolved potassium feldspar. IMPORTANCE Mineral-microbe interactions play important roles in the biogeochemical cycling of elements. Manipulating mineral-microbe interactions and optimizing the consequences of such interactions can be used to benefit society. It is necessary to explore the black hole of the mechanism of interaction between the two. In this study, it is revealed that P. aryabhattai SK1-7 faces mineral-induced ROS stress by upregulating a series of antioxidant genes as a passive defense, while overexpression of malic enzyme (ME2) secretes pyruvate to scavenge ROS as well as to increase feldspar dissolution, releasing K, Al, and Si into the medium. Our research provides a theoretical basis for improving the ability of microorganisms to weather minerals through genetic manipulation in the future.

ME2 Promotes Hepatocellular Carcinoma Cell Migration through Pyruvate.

Cancer metastasis is still a major challenge in clinical cancer treatment. The migration and invasion of cancer cells into surrounding tissues and blood vessels is the primary step in cancer metastasis. However, the underlying mechanism of regulating cell migration and invasion are not fully understood. Here, we show the role of malic enzyme 2 (ME2) in promoting human liver cancer cell lines SK-Hep1 and Huh7 cells migration and invasion. Depletion of ME2 reduces cell migration and invasion, whereas overexpression of ME2 increases cell migration and invasion. Mechanistically, ME2 promotes the production of pyruvate, which directly binds to ß-catenin and increases ß-catenin protein levels. Notably, pyruvate treatment restores cell migration and invasion of ME2-depleted cells. Our findings provide a mechanistic understanding of the link between ME2 and cell migration and invasion.

Malic Enzyme 1 (ME1) Promotes Adiposity and Hepatic Steatosis and Induces Circulating Insulin and Leptin in Obese Female Mice.

Malic Enzyme 1 (ME1) supports lipogenesis, cholesterol synthesis, and cellular redox potential by catalyzing the decarboxylation of L-malate to pyruvate, and the concomitant reduction of NADP to NADPH. We examined the contribution of ME1 to the development of obesity by provision of an obesogenic diet to C57BL/6 wild type (WT) and MOD-1 (lack ME1 protein) female mice. Adiposity, serum hormone levels, and adipose, mammary gland, liver, and small intestine gene expression patterns were compared between experimental groups after 10 weeks on a diet. Relative to WT female mice, MOD-1 female mice exhibited lower body weights and less adiposity; decreased concentrations of insulin, leptin, and estrogen; higher concentrations of adiponectin and progesterone; smaller-sized mammary gland adipocytes; and reduced hepatosteatosis. MOD-1 mice had diminished expression of Lep gene in abdominal fat; Lep, Pparg, Klf9, and Acaca genes in mammary glands; Pparg and Cdkn1a genes in liver; and Tlr9 and Ffar3 genes in the small intestine. By contrast, liver expression of Cdkn2a and Lepr genes was augmented in MOD-1, relative to WT mice. Results document an integrative role for ME1 in development of female obesity, suggest novel linkages with specific pathways/genes, and further support the therapeutic targeting of ME1 for obesity, diabetes, and fatty liver disease.

Melatonin-mediated malic enzyme 2 orchestrates mitochondrial fusion and respiratory functions to promote odontoblastic differentiation during tooth development.

Tooth development is a complex process that is tightly controlled by circadian rhythm. Melatonin (MT) is a major hormonal regulator of the circadian rhythm, and influences dentin formation and odontoblastic differentiation during tooth development; however, the underlying mechanism remains elusive. This study investigated how MT regulates odontoblastic differentiation, with a special focus on its regulation of mitochondrial dynamics. In rat dental papilla cells (DPCs), we found that MT promotes odontoblastic differentiation concurrently with enhanced mitochondrial fusion, while disruption of mitochondrial fusion by depleting optic atrophy 1 (OPA1) impairs MT-mediated differentiation and mitochondrial respiratory functions. Through RNA sequencing, we discovered that MT significantly upregulated malic enzyme 2 (ME2), a mitochondrial NAD(P)+ -dependent enzyme, and identified ME2 as a critical MT downstream effector that orchestrates odontoblastic differentiation, mitochondrial fusion, and respiration functions. By detecting the spatiotemporal expression of ME2 in developing tooth germs, and using tooth germ reconstituted organoids, we also provided in vivo and ex vivo evidence that ME2 promotes dentin formation, indicating a possible involvement of ME2 in MT-modulated tooth development. Collectively, our findings offer novel understandings regarding the molecular mechanism by which MT affects cell differentiation and organogenesis, meanwhile, the critical role of ME2 in MT-regulated mitochondrial functions is also highlighted.