Structural basis of respiratory complex adaptation to cold temperatures.

In response to cold, mammals activate brown fat for respiratory-dependent thermogenesis reliant on the electron transport chain. Yet, the structural basis of respiratory complex adaptation upon cold exposure remains elusive. Herein, we combined thermoregulatory physiology and cryoelectron microscopy (cryo-EM) to study endogenous respiratory supercomplexes from mice exposed to different temperatures. A cold-induced conformation of CI:III2 (termed type 2) supercomplex was identified with a ∼25° rotation of CIII2 around its inter-dimer axis, shortening inter-complex Q exchange space, and exhibiting catalytic states that favor electron transfer. Large-scale supercomplex simulations in mitochondrial membranes reveal how lipid-protein arrangements stabilize type 2 complexes to enhance catalytic activity. Together, our cryo-EM studies, multiscale simulations, and biochemical analyses unveil the thermoregulatory mechanisms and dynamics of increased respiratory capacity in brown fat at the structural and energetic level.

A lipid synthase maintains metabolic flux for jasmonate synthesis to regulate root growth and phosphate homeostasis.

Plants require phosphate (Pi) for proper growth and development but often face scarcity of this vital nutrient in the soil. Pi-starvation triggers membrane lipid remodeling to utilize the membrane phospholipid-bound Pi in plants. In this process, phospholipids are replaced by non-Pi-containing galactolipids (MGDG, DGDG) and sulfolipids. The galactolipids ratio (MGDG:DGDG) is suggested to influence jasmonic acid (JA) biosynthesis. However, how the MGDG:DGDG ratio, JA levels, and root growth are coordinated under Pi deficiency in rice (Oryza sativa) remains unknown. Here, we characterized DGDG synthase 1 (OsDGD1) for its role in regulating root development by maintaining metabolic flux for JA biosynthesis. We showed that OsDGD1 is responsive under low Pi and is under the direct control of Phosphate Starvation Response 2 (OsPHR2), the master regulator of low Pi adaptations. Further, OsDGD1 knockout (KO) lines showed marked phenotypic differences compared to the wild type (WT), including a significant reduction in root length and biomass, leading to reduced Pi uptake. Further, lipidome analyses revealed reduced DGDG levels in the KO line, leading to reduced membrane remodeling, thus affecting P utilization efficiency. We also observed an increase in the MGDG: DGDG ratio in KO lines, which enhanced the endogenous JA levels and signaling. This imbalance of JA in KO plants led to changes in auxin levels, causing drastic root growth inhibition. These findings indicate the critical role of OsDGD1 in maintaining optimum levels of JA during Pi deficiency for conducive root growth. Besides acting as signaling molecules and structural components, our study widens the role of lipids as metabolic flux controllers for phytohormone biosynthesis.

Biochemical Pathways Delivering Distinct Glycosphingolipid Patterns in MDA-MB-231 and MCF-7 Breast Cancer Cells.

The complex structure of glycosphingolipids (GSLs) supports their important role in cell function as modulators of growth factor receptors and glutamine transporters in plasma membranes. The aberrant composition of clustered GSLs within signaling platforms, so-called lipid rafts, inevitably leads to tumorigenesis due to disturbed growth factor signal transduction and excessive uptake of glutamine and other molecules needed for increased energy and structural molecule cell supply. GSLs are also involved in plasma membrane processes such as cell adhesion, and their transition converts cells from epithelial to mesenchymal with features required for cell migration and metastasis. Glutamine activates the mechanistic target of rapamycin complex 1 (mTORC1), resulting in nucleotide synthesis and proliferation. In addition, glutamine contributes to the cancer stem cell GD2 ganglioside-positive phenotype in the triple-negative breast cancer cell line MDA-MB-231. Thieno[2,3-b]pyridine derivative possesses higher cytotoxicity against MDA-MB-231 than against MCF-7 cells and induces a shift to aerobic metabolism and a decrease in S(6)nLc4Cer GSL-positive cancer stem cells in the MDA-MB-231 cell line. In this review, we discuss findings in MDA-MB-231, MCF-7, and other breast cancer cell lines concerning their differences in growth factor receptors and recent knowledge of the main biochemical pathways delivering distinct glycosphingolipid patterns during tumorigenesis and therapy.

Non-specific phospholipases C2 and C6 redundantly function in pollen tube growth via triacylglycerol production in Arabidopsis.

Non-specific phospholipase Cs (NPCs) are responsible for membrane lipid remodeling that involves hydrolysis of the polar head group of membrane phospholipids. Arabidopsis NPC2 and NPC6 are essential in gametogenesis, but their underlying role in the lipid remodeling remains elusive. Here, we show that these NPCs are required for triacylglycerol (TAG) production in pollen tube growth. NPC2 and NPC6 are highly expressed in developing pollen tubes and are localized at the endoplasmic reticulum. Mutants of NPC2 and NPC6 showed reduced rate of pollen germination, length of pollen tube and amount of lipid droplets (LDs). Overexpression of NPC2 or NPC6 induced LD accumulation, which suggests that these NPCs are involved in LD production. Furthermore, mutants defective in the biosynthesis of TAG, a major component of LDs, showed defective pollen tube growth. These results suggest that NPC2 and NPC6 are essential in gametogenesis for a role in hydrolyzing phospholipids and producing TAG required for pollen tube growth. Thus, lipid remodeling from phospholipids to TAG during pollen tube growth represents an emerging role for the NPC family in plant developmental control.

The phospho-base N-methyltransferases PMT1 and PMT2 produce phosphocholine for leaf growth in phosphorus-starved Arabidopsis.

Phosphorus (P) is an essential nutrient for plants. Membrane lipid remodeling is an adaptive mechanism for P-starved plants that replaces membrane phospholipids with non-P galactolipids, presumably to retrieve scarce P sources and maintain membrane integrity. Whereas metabolic pathways to convert phospholipids to galactolipids are well-established, the mechanism by which phospholipid biosynthesis is involved in this process remains elusive. Here, we report that phospho-base N-methyltransferases 1 and 2 (PMT1 and PMT2), which convert phosphoethanolamine to phosphocholine (PCho), are transcriptionally induced by P starvation. Shoots of seedlings of pmt1 pmt2 double mutant showed defective growth upon P starvation; however, membrane lipid profiles were unaffected. We found that P-starved pmt1 pmt2 with defective leaf growth had reduced PCho content, and the growth defect was rescued by exogenous supplementation of PCho. We propose that PMT1 and PMT2 are induced by P starvation to produce PCho mainly for leaf growth maintenance, rather than for phosphatidylcholine biosynthesis, in membrane lipid remodeling.

Recent insights into the metabolic adaptations of phosphorus-deprived plants.

Inorganic phosphate (Pi) is an essential macronutrient required for many fundamental processes in plants, including photosynthesis and respiration, as well as nucleic acid, protein, and membrane phospholipid synthesis. The huge use of Pi-containing fertilizers in agriculture demonstrates that the soluble Pi levels of most soils are suboptimal for crop growth. This review explores recent advances concerning the understanding of adaptive metabolic processes that plants have evolved to alleviate the negative impact of nutritional Pi deficiency. Plant Pi starvation responses arise from complex signaling pathways that integrate altered gene expression with post-transcriptional and post-translational mechanisms. The resultant remodeling of the transcriptome, proteome, and metabolome enhances the efficiency of root Pi acquisition from the soil, as well as the use of assimilated Pi throughout the plant. We emphasize how the up-regulation of high-affinity Pi transporters and intra- and extracellular Pi scavenging and recycling enzymes, organic acid anion efflux, membrane remodeling, and the remarkable flexibility of plant metabolism and bioenergetics contribute to the survival of Pi-deficient plants. This research field is enabling the development of a broad range of innovative and promising strategies for engineering phosphorus-efficient crops. Such cultivars are urgently needed to reduce inputs of unsustainable and non-renewable Pi fertilizers for maximum agronomic benefit and long-term global food security and ecosystem preservation.

Arabidopsis PECP1 and PS2 are phosphate starvation-inducible phosphocholine phosphatases.

Phosphate-starved plants reduce phosphatidylcholine content presumably to provide an internal phosphate source while replacing membrane phospholipids by galactolipids, a process termed membrane lipid remodeling. However, whether the metabolic fate of released phosphocholine is a phosphate source remains elusive because primary phosphocholine phosphatases in vivo are unknown in seed plants. Here, we show that PECP1 and PS2 are the primary phosphocholine phosphatases in Arabidopsis and function redundantly under phosphate starvation. Under phosphate starvation, the double knockout mutant of PECP1 and PS2 showed reduced content of choline but no severe growth phenotype, which suggests that phosphocholine dephosphorylation is not likely a major source of internal phosphate reserve. We identified primary phosphocholine phosphatases, demonstrated their involvement under phosphate starvation, and updated the metabolic map of membrane lipid remodeling.

Lipid metabolism in malignant tumor brain metastasis: reprogramming and therapeutic potential.

INTRODUCTION: Brain metastasis is a highly traumatic event in the progression of malignant tumors, often symbolizing higher mortality. Metabolic alterations are hallmarks of cancer, and the mask of lipid metabolic program rearrangement in cancer progression is gradually being unraveled. AREAS COVERED: In this work, we reviewed clinical and fundamental studies related to lipid expression and activity changes in brain metastases originating from lung, breast, and cutaneous melanomas, respectively. Novel roles of lipid metabolic reprogramming in the development of brain metastasis from malignant tumors were identified and its potential as a therapeutic target was evaluated. Published literature and clinical studies in databases consisting of PubMed, Embase, Scopus and www.ClinicalTrials.gov from 1990 to 2022 were searched. EXPERT OPINION: Lipid metabolic reprogramming in brain metastasis is involved in de novo lipid synthesis within low lipid availability environments, regulation of lipid uptake and storage, metabolic interactions between brain tumors and the brain microenvironment, and membrane lipid remodeling, in addition to being a second messenger for signal transduction. Although some lipid metabolism modulators work efficiently in preclinical models, there is still a long way to go from laboratory to clinic. This area of research holds assurance for the organ-targeted treatment of brain metastases through drug-regulated metabolic targets and dietary interventions.

Inhibition of monogalactosyldiacylglycerol synthesis by down-regulation of MGD1 leads to membrane lipid remodeling and enhanced triacylglycerol biosynthesis in Chlamydomonas reinhardtii.

BACKGROUND: Membrane lipid remodeling involves regulating the physiochemical modification of cellular membranes against abiotic stress or senescence, and it could be a trigger to increase neutral lipid content. In algae and higher plants, monogalactosyldiacylglycerol (MGDG) constitutes the highest proportion of total membrane lipids and is highly reduced as part of the membrane lipid remodeling response under several abiotic stresses. However, genetic regulation of MGDG synthesis and its influence on lipid synthesis has not been studied in microalgae. For development of an industrial microalgae strain showing high accumulation of triacylglycerol (TAG) by promoting membrane lipid remodeling, MGDG synthase 1 (MGD1) down-regulated mutant of Chlamydomonas reinhardtii (Cr-mgd1) was generated and evaluated for its suitability for biodiesel feedstock. RESULTS: The Cr-mgd1 showed a 65% decrease in CrMGD1 gene expression level, 22% reduction in MGDG content, and 1.39 and 5.40 times increase in diacylglyceryltrimethylhomoserines (DGTS) and TAG, respectively. The expression levels of most genes related to the decomposition of MGDG (plastid galactoglycerolipid degradation1) and TAG metabolism (diacylglycerol O-acyltransferase1, phospholipid:diacylglycerol acyltransferase, and major lipid droplet protein) were increased. The imbalance of DGDG/MGDG ratio in Cr-mgd1 caused reduced photosynthetic electron transport, resulting in less light energy utilization and increased reactive oxygen species levels. In addition, endoplasmic reticulum stress was induced by increased DGTS levels. Thus, accelerated TAG accumulation in Cr-mgd1 was stimulated by increased cellular stress as well as lipid remodeling. Under high light (HL) intensity (400 µmol photons/m2/s), TAG productivity in Cr-mgd1-HL (1.99 mg/L/d) was 2.71 times higher than that in wild type (WT-HL). Moreover, under both nitrogen starvation and high light intensity, the lipid (124.55 mg/L/d), TAG (20.03 mg/L/d), and maximum neutral lipid (56.13 mg/L/d) productivity were the highest. CONCLUSIONS: By inducing lipid remodeling through the mgd1 gene expression regulation, the mutant not only showed high neutral lipid content but also reached the maximum neutral lipid productivity through cultivation under high light and nitrogen starvation conditions, thereby possessing improved biomass properties that are the most suitable for high quality biodiesel production. Thus, this mutant may help understand the role of MGD1 in lipid synthesis in Chlamydomonas and may be used to produce high amounts of TAG.

Intracellular phosphate recycling systems for survival during phosphate starvation in plants.

Phosphorus (P) is an essential nutrient for plant growth and plants use inorganic phosphate (Pi) as their P source, but its bioavailable form, orthophosphate, is often limited in soils. Hence, plants have several mechanisms for adaptation to Pi starvation. One of the most common response strategies is "Pi recycling" in which catabolic enzymes degrade intracellular constituents, such as phosphoesters, nucleic acids and glycerophospholipids to salvage Pi. Recently, several other intracellular degradation systems have been discovered that salvage Pi from organelles. Also, one of sphingolipids has recently been identified as a degradation target for Pi recycling. So, in this mini-review we summarize the current state of knowledge, including research findings, about the targets and degradation processes for Pi recycling under Pi starvation, in order to further our knowledge of the whole mechanism of Pi recycling.

Physiology of microalgae and their application to sustainable agriculture: A mini-review.

Concern that depletion of fertilizer feedstocks, which are a finite mineral resource, threatens agricultural sustainability has driven the exploration of sustainable methods of soil fertilization. Given that microalgae, which are unicellular photosynthetic organisms, can take up nutrients efficiently from water systems, their application in a biological wastewater purification system followed by the use of their biomass as a fertilizer alternative has attracted attention. Such applications of microalgae would contribute to the accelerated recycling of nutrients from wastewater to farmland. Many previous reports have provided information on the physiological characteristics of microalgae that support their utility. In this review, we focus on recent achievements of studies on microalgal physiology and relevant applications and outline the prospects for the contribution of microalgae to the establishment of sustainable agricultural practices.

Specific galactolipids species correlate with rice genotypic variability for phosphate utilization efficiency.

Membrane lipid remodeling helps in the efficient utilization of phosphorus (P) by replacing phospholipids with galactolipids during P deficiency. Previous studies have shown lipid remodeling in rice under P deficiency; however, main lipid classes did not show association with superior P-use-efficiency in rice genotypes. Here, diverse rice genotypes were extensively phenotyped in normal (NP) and low P (LP) conditions. Based on the phenotypic response to P deficiency, genotypes were identified as tolerant and sensitive. Further, bulks were generated differing in their physiological P-use-efficiency (PPUE) during LP condition. Shoot lipidome profiling of genotypes was performed and used to correlate the abundance of various lipid classes and their constituent species with the PPUE of the genotypes. Lipid remodeling was observed as a P-starvation-induced response in all the genotypes. However, neither total galacto- and phospholipids nor the lipid classes correlated with PPUE during P deficiency. However, the difference in PPUE in the two bulks correlated with specific lipid species of galactolipids (DGDG, MGDG). Further, DGDG34:3 had the highest Mol% among the differentially accumulated lipid species between the two bulks. Our study reveals the importance of specific galactolipids species in rice adaptation to P deficient soils and thus opens new targets for future research.

An Advanced Lipid Metabolism System Revealed by Transcriptomic and Lipidomic Analyses Plays a Central Role in Peanut Cold Tolerance.

Cold stress restricts peanut (Arachis hypogaea L.) growth, development, and yield. However, the specific mechanism of cold tolerance in peanut remains unknown. Here, the comparative physiological, transcriptomic, and lipidomic analyses of cold tolerant variety NH5 and cold sensitive variety FH18 at different time points of cold stress were conducted to fill this gap. Transcriptomic analysis revealed lipid metabolism including membrane lipid and fatty acid metabolism may be a significant contributor in peanut cold tolerance, and 59 cold-tolerant genes involved in lipid metabolism were identified. Lipidomic data corroborated the importance of membrane lipid remodeling and fatty acid unsaturation. It indicated that photosynthetic damage, resulted from the alteration in fluidity and integrity of photosynthetic membranes under cold stress, were mainly caused by markedly decreased monogalactosyldiacylglycerol (MGDG) levels and could be relieved by increased digalactosyldiacylglycerol (DGDG) and sulfoquinovosyldiacylglycerol (SQDG) levels. The upregulation of phosphatidate phosphatase (PAP1) and phosphatidate cytidylyltransferase (CDS1) inhibited the excessive accumulation of PA, thus may prevent the peroxidation of membrane lipids. In addition, fatty acid elongation and fatty acid ß-oxidation were also worth further studied in peanut cold tolerance. Finally, we constructed a metabolic model for the regulatory mechanism of peanut cold tolerance, in which the advanced lipid metabolism system plays a central role. This study lays the foundation for deeply analyzing the molecular mechanism and realizing the genetic improvement of peanut cold tolerance.

A global metabolomic insight into the oxidative stress and membrane damage of copper oxide nanoparticles and microparticles on microalga Chlorella vulgaris.

To compare aquatic organisms' responses to the toxicity of copper oxide (CuO) nanoparticles (NPs) with those of CuO microparticles (MPs) and copper (Cu) ions, a global metabolomics approach was employed to investigate the changes of both polar and nonpolar metabolites in microalga Chlorella vulgaris after 5-day exposure to CuO NPs and MPs (1 and 10 mg/L), as well as the corresponding dissolved Cu ions (0.08 and 0.8 mg/L). Unchanged growth, slight reactive oxygen species production, and significant membrane damage (at 10 mg/L CuO particles) in C. vulgaris were demonstrated. A total of 75 differentiated metabolites were identified. Most metabolic pathways perturbed after CuO NPs exposure were shared by those after CuO MPs and Cu ions exposure, including accumulation of chlorophyll intermediates (max. 2.4-5.2 fold), membrane lipids remodeling for membrane protection (decrease of phosphatidylethanolamines (min. 0.6 fold) and phosphatidylcholines (min. 0.2-0.7 fold), as well as increase of phosphatidic acids (max. 1.5-2.9 fold), phosphatidylglycerols (max. 2.2-2.3 fold), monogalactosyldiacylglycerols (max. 1.2-1.4 fold), digalactosylmonoacylglycerols (max. 1.9-3.8 fold), diacylglycerols (max. 1.4 fold), lysophospholipids (max. 1.8-3.0 fold), and fatty acids (max. 3.0-6.2 fold)), perturbation of glutathione metabolism induced by oxidative stress, and accumulation of osmoregulants (max. 1.3-2.6 fold) to counteract osmotic stress. The only difference between metabolic responses to particles and those to ions was the accumulation of fatty acids oxidation products: particles caused higher fold changes (particles/ions ratio 1.9-3.0) at 1 mg/L and lower fold changes (particles/ions ratio 0.4-0.7) at 10 mg/L compared with ions. Compared with microparticles, there was no nanoparticle-specific pathway perturbed. These results confirm the predominant role of dissolved Cu ions on the toxicity of CuO NPs and MPs, and also reveal particle-specific toxicity from a metabolomics perspective.

Expression Profiles of 2 Phosphate Starvation-Inducible Phosphocholine/Phosphoethanolamine Phosphatases, PECP1 and PS2, in Arabidopsis.

Phosphorus is essential for plant viability. Phosphate-starved plants trigger membrane lipid remodeling to replace membrane phospholipids by non-phosphorus galactolipids presumably to acquire scarce phosphate source. Phosphoethanolamine/phosphocholine phosphatase 1 (PECP1) and phosphate starvation-induced gene 2 (PS2) belong to an emerging class of phosphatase induced by phosphate starvation and dephosphorylates phosphocholine and phosphoethanolamine (PEtn) in vivo. However, detailed spatiotemporal expression pattern as well as subcellular localization has not been investigated yet. Here, by constructing transgenic plants harboring functional translational promoter-reporter fusion system, we showed the expression pattern of PECP1 and PS2 in different tissues and in response to phosphate starvation. Besides, the Venus fluorescent reporter revealed that both are localized at the ER. Characterization of transgenic plants that overexpress PECP1 or PS2 showed that their activity toward PEtn may be different in vivo. We suggest that PECP1 and PS2 are ER-localized phosphatases that show similar expression pattern yet have a distinct substrate specificity in vivo.

Oncogene Amplification in Growth Factor Signaling Pathways Renders Cancers Dependent on Membrane Lipid Remodeling.

Advances in DNA sequencing technologies have reshaped our understanding of the molecular basis of cancer, providing a precise genomic view of tumors. Complementary biochemical and biophysical perspectives of cancer point toward profound shifts in nutrient uptake and utilization that propel tumor growth and major changes in the structure of the plasma membrane of tumor cells. The molecular mechanisms that bridge these fundamental aspects of tumor biology remain poorly understood. Here, we show that the lysophosphatidylcholine acyltransferase LPCAT1 functionally links specific genetic alterations in cancer with aberrant metabolism and plasma membrane remodeling to drive tumor growth. Growth factor receptor-driven cancers are found to depend on LPCAT1 to shape plasma membrane composition through enhanced saturated phosphatidylcholine content that is, in turn, required for the transduction of oncogenic signals. These results point to a genotype-informed strategy that prioritizes lipid remodeling pathways as therapeutic targets for diverse cancers.