Key Enzymes Of Fatty Acid Synthesis Research Articles

Dysfunction of T Cells from Chronic Lymphocytic Leukemia (CLL) Patients Is Linked to Disturbed Lipid and Fatty Acid Homeostasis

Background: Successful T cell-based anti-cancer therapies require proliferation and longevity of effector cells, features that highly depend on metabolic processes. A key feature of chronic lymphocytic leukemia (CLL) is acquired T cell dysfunction, resulting in impaired proliferative capacity (van Bruggen, et al Blood Adv 2022). T cell lipid metabolism has only recently come into focus as an important source of energy production and at the same time as essential component for the formation of new membranes upon proliferation. Fatty acid (FA) and lipid uptake in T cells requires several membrane proteins, among which the scavenger FA transporter CD36 and the low-density lipoprotein receptor (LDL-R). Specifically CD36-mediated FA transport has been identified to modulate (intratumoral) Treg and cytotoxic CD8+ T cells (Kolonin, et al, 2021 Immunometab). Whether T cell lipid and FA metabolism are affected in CLL is currently unknown. Methods: Peripheral blood mononuclear cells (PBMCs) of untreated CLL patients and, as control, age-matched healthy donors (HD) were studied. T cells were analyzed by transcriptomics, lipidomics and flow cytometry, either directly after thawing or after a 2-day culture with or without αCD3/αCD28 antibodies. Results: Unbiased transcriptomic analyses of patient-derived T cells following αCD3/αCD28 activation showed reduced expression of the master regulators of FA and cholesterol biosynthesis SREBF1 and SREBF2 in the presence of autologous CLL cells. This was associated with significantly reduced protein abundance of downstream targets of the SREBP pathway, including the key enzymes in FA synthesis and saturation FASN and SCD. In accordance with these data, lipidomic analyses highlighted an altered lipid profile in T cells from CLL patients that clearly demarcated them from HD T cells. In short, unbiased analyses revealed disturbed lipid homeostasis in CLL T cells at multiple levels, which led us to investigate lipid and FA metabolic pathways and their related functional consequences. Studying lipid and FA uptake capacity revealed lower expression of the FA transporter CD36 on CLL T cells. Stimulation of HD T cells resulted in upregulation of CD36 and the main receptor for cholesterol uptake LDL-R, accompanied by increased uptake of long chain fatty acids (LCFA) and increased FA-oxidation, concomitantly with induced expression of the activation marker CD25. In contrast, CLL-derived T cells did not increase CD36 or LDL-R expression, LCFA uptake or oxidation (Fig 1 and 2). Because of a recently suggested role for CD36 in T cell function, we next specifically analyzed CD36-expressing T cells (CD36+), and found these to have higher ability for LCFA and glucose uptake, and higher expression of the glucose transporter GLUT-1 than CD36 negative T cells from the same HD. Accordingly, CD36+ cells were also more likely to increase their CD25 expression and mitochondrial mass upon a 48h stimulation. This CD36+ T cell subpopulation, with potential metabolic and functional advantage, was virtually absent in CLL PBMCs. Impact of FA and lipid metabolism on proliferation was further established by the observation that culturing of HD T cells in absence of exogenous lipids resulted in nearly absent proliferative capacity. However, despite decreased expression of lipid and FA transporters, we observed marked accumulation of lipid droplets (LD) in T cells from CLL patients, suggesting an impaired ability to mobilize lipids towards oxidation pathways or as building blocks for membranes. In line with this, we found that in contrast to HD T cells that increased the expression of the rate-limiting enzyme for lipolysis ATGL, CLL T cells failed to do so. Conclusions: We provide the first data showing a disturbed lipid and FA metabolism of CLL T cells that contributes to T cell dysfunction. This includes decreased expression of FA synthesis enzymes as well as FA and cholesterol transporters. CD36+ T cells are metabolically distinct and are largely absent in CLL. We are investigating strategies to increase FA and lipid metabolism in order to rebalance lipid homeostasis. This could ameliorate CLL T cell dysfunction and specifically proliferation defects in CLL. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Study on the Mechanism of Cold Tolerance of the Strain Shewanella putrefaciens WS13 Through Fatty Acid Metabolism

In order to investigate the cold tolerance mechanism of Shewanella, the whole genome of strain Shewanella putrefaciens WS13 was used to study the comparative genome related to cold tolerance of Shewanella . By comparing and analyzing the key enzymes involved in the process of lipid synthesis with those of other psychrophilic and non-psychrophilic bacteria, the results showed that in S. putrefaciens WS13, the genes fabA, fabB, fabD, fabF, fabG, fabH and fabZ, as the key enzymes of fatty acid synthesis, were found in the target strain, but the gene fabI did not exist in the type II fatty acid synthesis pathway. However, due to the absence of the key enzyme fabI gene, the synthesis process of saturated fatty acids will be blocked, and the pathway of unsaturated fatty acid synthesis still exists, which leads to the bacteria Shewanella start to synthesize a large number of unsaturated fatty acids, thus increasing the synthesis of unsaturated fatty acids and reducing the synthesis of saturated fatty acids. It is precisely because unsaturated fatty acids have lower phase transition temperature than that saturated fatty acids have, which can increase the fluidity of biofilm, so that Shewanella has better cold adaptability than that other bacteria have. It is a complex biological process for microorganisms to adapt to the environment, and the biosynthesis of fatty acids is only one aspect. However, the mechanism of cold adaptation of Shewanella in other aspects remains to be further discussed.

MicroRNAs: A new class of regulatory genes affecting metabolism

MicroRNAs (miRNAs) are short noncoding RNAs that regulate gene expression by binding to target mRNAs, which leads to reduced protein synthesis and sometimes decreased steady-state mRNA levels. Although hundreds of miRNAs have been identified, much less is known about their biological function. Several studies have provided evidence that miRNAs affect pathways that are fundamental for metabolic control in higher organisms such as adipocyte and skeletal muscle differentiation. Furthermore, some miRNAs have been implicated in lipid, amino acid, and glucose homeostasis. These studies open the possibility that miRNAs may contribute to common metabolic diseases and point to novel therapeutic opportunities based on targeting of miRNAs.

Synthesis of medium-chain fatty acids and their incorporation into triacylglycerols by cell-free fractions from Cuphea embryos

During their rapid maturation period, seeds of Cuphea wrightii A. Gray mainly accumulate medium-chain fatty acids (C8 to C14) in their storage lipids. The rate of lipid deposition (40-50 mg·d(-1)·(g fresh weight)(-1)) is fourfold higher than in seeds of Cuphea racemosa (L. f.) Spreng, which accumulate long-chain fatty acids (C16 to C18). Measurements of the key enzymes of fatty-acid synthesis in cell-free extracts of seeds of different maturities from Cuphea wrightii show that malonyl-CoA synthesis may be a triggering factor for the observed high capacity for fatty-acid synthesis. Experiments on the incorporation of [1-(14)C]acetate into fatty acids by purified plastid preparations from embryos of Cuphea wrightii have demonstrated that the biosynthesis of medium-chain fatty acids (C8 to C14) is localized in the plastid. Thus, in the presence of cofactors for lipid synthesis (ATP, NADPH, NADH, acyl carrier protein, and sn-glycerol-3-phosphate), purified plastid fractions predominantly synthesized free fatty acids, 30% of which were of medium chain length. Transesterification of the freshly synthesized fatty acids to coenzyme A and recombination with the microsomal fraction of the embryo homogenate induced triacylglycerol synthesis. It also stimulated fatty-acid synthesis by a factor 2-3 and increased the relative amount of medium-chain fatty acids bound to triacylglycerols, which corresponded to about 60-80% in this lipid fraction.