The enhancement of fat oxidation during the active phase and suppression of body weight gain in glycerol-3-phosphate dehydrogenase 1 deficient mice

Downregulated expression of lactate dehydrogenase in adult oligodendrocytes and its implication for the transfer of glycolysis products to axons

Oligodendrocytes and astrocytes are metabolically coupled to neuronal compartments. Pyruvate and lactate can shuttle between glial cells and axons via monocarboxylate transporters. However, lactate can only be synthesized or used in metabolic reactions with the help of lactate dehydrogenase (LDH), a tetramer of LDHA and LDHB subunits in varying compositions. Here we show that mice with a cell type-specific disruption of both Ldha and Ldhb genes in oligodendrocytes lack a pathological phenotype that would be indicative of oligodendroglial dysfunctions or lack of axonal metabolic support. Indeed, when combining immunohistochemical, electron microscopical, and in situ hybridization analyses in adult mice, we found that the vast majority of mature oligodendrocytes lack detectable expression of LDH. Even in neurodegenerative disease models and in mice under metabolic stress LDH was not increased. In contrast, at early development and in the remyelinating brain, LDHA was readily detectable in immature oligodendrocytes. Interestingly, by immunoelectron microscopy LDHA was particularly enriched at gap junctions formed between adjacent astrocytes and at junctions between astrocytes and oligodendrocytes. Our data suggest that oligodendrocytes metabolize lactate during development and remyelination. In contrast, for metabolic support of axons mature oligodendrocytes may export their own glycolysis products as pyruvate rather than lactate. Lacking LDH, these oligodendrocytes can also "funnel" lactate through their "myelinic" channels between gap junction-coupled astrocytes and axons without metabolizing it. We suggest a working model, in which the unequal cellular distribution of LDH in white matter tracts facilitates a rapid and efficient transport of glycolysis products among glial and axonal compartments.

Glycerol 3-phosphate dehydrogenases (1 and 2) in cancer and other diseases

The glycerol 3-phosphate shuttle (GPS) is composed of two different enzymes: cytosolic NAD+-linked glycerol 3-phosphate dehydrogenase 1 (GPD1) and mitochondrial FAD-linked glycerol 3-phosphate dehydrogenase 2 (GPD2). These two enzymes work together to act as an NADH shuttle for mitochondrial bioenergetics and function as an important bridge between glucose and lipid metabolism. Since these genes were discovered in the 1960s, their abnormal expression has been described in various metabolic diseases and tumors. Nevertheless, it took a long time until scientists could investigate the causal relationship of these enzymes in those pathophysiological conditions. To date, numerous studies have explored the involvement and mechanisms of GPD1 and GPD2 in cancer and other diseases, encompassing reports of controversial and non-conventional mechanisms. In this review, we summarize and update current knowledge regarding the functions and effects of GPS to provide an overview of how the enzymes influence disease conditions. The potential and challenges of developing therapeutic strategies targeting these enzymes are also discussed.

Changes to PUFA-PPAR pathway during mesaconitine induced myocardial coagulative necrosis

Coagulation necrosis is characterized by the denaturation of structural proteins and lysosomal enzymes; its occurrence in myocardium can lead to heart failure. Current studies on myocardial injury primarily focus on inflammation, hypertrophy, and hemorrhage, while those on myocardial coagulation necrosis are still limited. Mesaconitine (MA), a C₁₉ diester diterpenoid alkaloid derived from Aconitum carmichaelii Debx, has strong cardiotoxicity. During this study, the myocardial cells of SD rats showed significant coagulative necrosis after 6 days of oral administration of MA at a dose of 1.2 mg/kg/day. Investigations of its biological mechanism showed abnormal levels of polyunsaturated fatty acids (PUFAs) and Peroxisome proliferator activated receptors Alpha (PPARα) pathway related protein. Moreover, MA affected the PPARα signaling pathway through interactions with proteins such as POR, TFAM and GPD1, indirectly indicating that these above proteins are important targets for blocking myocardial coagulative necrosis. This study thus discusses the effects of the use of cardiotoxic compound, MA, to initiate myocardial coagulative necrosis and its associated toxic mechanisms.

Non-Histone Lysine Crotonylation Is Involved in the Regulation of White Fat Browning

Lysine crotonylation modification is a novel acylation modification that is similar to acetylation modification. Studies have found that protein acetylation plays an important regulatory part in the occurrence and prevention of obesity and is involved in the regulation of glucose metabolism, tricarboxylic acid cycle, white fat browning and fatty acid metabolism. Therefore, we speculate that protein crotonylation may also play a more vital role in regulating the browning of white fat. To verify this conjecture, we identified 7254 crotonyl modification sites and 1629 modified proteins in iWAT of white fat browning model mice by affinity enrichment and liquid chromatography-mass spectrometry (LC-MS/MS). We selected five representative proteins in the metabolic process, namely glycerol-3-phosphate dehydrogenase 1 (GPD1), fatty acid binding protein 4 (FABP4), adenylate kinase 2 (AK2), triosephosphate isomerase 1 (TPI1) and NADH dehydrogenase (ubiquinone) 1 alpha subcomplex 8 (NDUFA8). Through qPCR, Western blotting, immunofluorescence staining, Oil Red O staining and HE staining, we demonstrated that GPD1 and FABP4 inhibited white fat browning, while AK2, TPI1 and NDUFA8 promoted white fat browning. GPD1 and FABP4 proteins were downregulated by crotonylation modification, while AK2, TPI1 and NDUFA8 proteins were upregulated by crotonylation modification. Further detection found that the crotonylation modification of GPD1, FABP4, AK2, TPI1 and NDUFA8 promoted white fat browning, which was consistent with the sequencing results. These results indicate that the protein crotonylation is involved in regulating white fat browning, which is of great significance for controlling obesity and treating obesity-related diseases.