FASN-dependent de novo lipogenesis is required for brain development

Fate and behavior of neural progenitor cells are tightly regulated during mammalian brain development. Metabolic pathways, such as glycolysis and oxidative phosphorylation, that are required for supplying energy and providing molecular building blocks to generate cells govern progenitor function. However, the role of de novo lipogenesis, which is the conversion of glucose into fatty acids through the multienzyme protein fatty acid synthase (FASN), for brain development remains unknown. Using Emx1Cre-mediated, tissue-specific deletion of Fasn in the mouse embryonic telencephalon, we show that loss of FASN causes severe microcephaly, largely due to altered polarity of apical, radial glia progenitors and reduced progenitor proliferation. Furthermore, genetic deletion and pharmacological inhibition of FASN in human embryonic stem cell–derived forebrain organoids identifies a conserved role of FASN-dependent lipogenesis for radial glia cell polarity in human brain organoids. Thus, our data establish a role of de novo lipogenesis for mouse and human brain development and identify a link between progenitor-cell polarity and lipid metabolism.

Acetyl-CoA mediated autoacetylation of fatty acid synthase in de novo lipogenesis

De novo lipogenesis (DNL) is a highly regulated metabolic process, which is known to be activated through transcriptional regulation of lipogenic genes, including fatty acid synthase (FASN). Unexpectedly, we find that the expression of FASN protein remains unchanged during Drosophila larval development when lipogenesis is hyperactive. Instead, acetylation modification of FASN is highly upregulated in fast-growing larvae. We further show that lysine K813 is highly acetylated in developing larvae, and its acetylation is required for upregulated FASN activity, body fat accumulation, and normal development. Intriguingly, K813 is rapidly autoacetylated by acetyl-CoA in a dosage-dependent manner, independent of known acetyltransferases. Furthermore, the autoacetylation of K813 is mediated by a conserved P-loop-like motif (N-xx-G-x-A). In summary, this work uncovers a novel role of acetyl-CoA-mediated autoacetylation of FASN in developmental lipogenesis and reveals a self-regulatory system that controls metabolic homeostasis by linking acetyl-CoA, lysine acetylation, and DNL.

PPARα−ACOT12 axis is responsible for maintaining cartilage homeostasis through modulating de novo lipogenesis

Here, in Ppara−/− mice, we found that an increased DNL stimulated the cartilage degradation and identified ACOT12 as a key regulatory factor. Suppressed level of ACOT12 was observed in cartilages of OA patient and OA-induced animal. To determine the role and association of ACOT12 in the OA pathogenesis, we generated Acot12 knockout (KO) (Acot12−/−) mice using RNA-guided endonuclease. Acot12−/− mice displayed the severe cartilage degradation with the stimulation of matrix MMPs and chondrocyte apoptosis through the accumulation of acetyl CoA. Delivery of acetyl CoA-conjugated chitosan complex into cartilage stimulated DNL and cartilage degradation. Moreover, restoration of ACOT12 into human OA chondrocytes and OA-induced mouse cartilage effectively rescued the pathophysiological features of OA by regulating DNL. Taken together, our study suggested ACOT12 as a novel regulatory factor in maintaining cartilage homeostasis and targeting ACOT12 could contribute to developing a new therapeutic strategy for OA.

Metabolically-Incorporated Deuterium in Myelin Localized by Neutron Diffraction and Identified by Mass Spectrometry

Myelin is a natural and dynamic multilamellar membrane structure that continues to be of significant biological and neurological interest, especially its biosynthesis and assembly in the context of its normal formation and renewal, and pathological breakdown. To explore further the usefulness of neutron diffraction in the structural analysis of myelin, we investigated the use of in vivo labeling by metabolically incorporating via drinking water nontoxic levels of deuterium (2H; D) into pregnant dams and their developing embryos. All of the mice were sacrificed when the pups were about 60 days old. Myelinated nerves were dissected, fixed in glutaraldehyde and examined by neutron diffraction. Parallel samples that were unfixed were frozen for mass spectrometry (MS). Analysis of the neutron diffraction patterns of the sciatic nerves from deuterium-fed mice (D mice) versus the controls (H mice) showed no appreciable differences in myelin periodicity, but major differences in the intensities of the Bragg peaks. The neutron scattering density profiles showed an appreciable increase in density at the center of the membrane bilayer in the D mice, particularly in the pups. MS analysis of the lipids isolated from the trigeminal nerves demonstrated that the level of D was greater in the pups compared to their mother: 97.6% +/- 2.0% (n=54; range 89.6% to 99.6%) versus 60.6% +/- 26.4% (n=27; range 11.4% to 97.3%). Deuteration in the mother also varied by lipid species, and among lipid subspecies. Three molecular species of phosphatidylcholine (PC), phosphatidylinositol (PI), and diglycerol (DG) were the most deuterated lipids, and sulfatide (SHexCer), one species of sphingomyelin (SM), and triacylglycerol (TG) were the least deuterated. The distribution pattern of deuterium in the D pups was always bell-shaped, and the average number of D atoms ranged from a low of ~4 in fatty acid (FA), to a high of ~9 in cerebroside (HexCer). By contrast, in D dam only about one third of the lipids had symmetric bell-shaped distributions; most had more complex, overlapping distributions that were weighted toward a lower average number of D atom labels. The average number of D atoms ranged from a low of ~3 to 4 in FA and in one species of SHexCer, to a high of 6 to 7 in HexCer and SM. In D pups, the consistently high level of deuteration can be attributed to their de novo lipogenesis during gestation and continuation of rapid myelination postnatally. In D dam, the widely varying levels of deuteration of lipids likely depends on the relative metabolic stability of the particular lipid species during myelin maintenance in the mature animal. Our current findings demonstrate that stably-incorporated D label can be detected and localized using neutron diffraction in a complex tissue such as myelin; and moreover, that MS can be used to screen a broad range of deuterated lipid species to monitor differential rates of lipid turnover. In addition to helping to develop a comprehensive understanding of the de novo synthesis and turnover of specific lipids in normal and abnormal myelin, our results also suggest application to myelin proteins, as well as more broadly to the molecular constituents of other biological tissues.

USP14 Regulates Cancer Cell Growth in a Fatty Acid Synthase-Independent Manner

Fatty acid synthase (FASN) plays an important role in cancer development, providing excess lipid sources for cancer growth by participating in de novo lipogenesis. Although several inhibitors of FASN have been developed, there are many limitations to using FASN inhibitors alone as cancer therapeutics. We therefore attempted to effectively inhibit cancer cell growth by using a FASN inhibitor in combination with an inhibitor of a deubiquitinating enzyme USP14, which is known to maintain FASN protein levels in hepatocytes. However, when FASN and USP14 were inhibited together, there were no synergistic effects on cancer cell death compared to inhibition of FASN alone. Surprisingly, USP14 rather reduced the protein levels and activity of FASN in cancer cells, although it slightly inhibited the ubiquitination of FASN. Indeed, treatment of an USP14 inhibitor IU1 did not significantly affect FASN levels in cancer cells. Furthermore, from an analysis of metabolites involved in lipid metabolism, metabolite changes in IU1-treated cells were significantly different from those in cells treated with a FASN inhibitor, Fasnall. These results suggest that FASN may not be a direct substrate of USP14 in the cancer cells. Consequently, we demonstrate that USP14 regulates proliferation of the cancer cells in a fatty acid synthase-independent manner, and targeting USP14 in combination with FASN may not be a viable method for effective cancer treatment.

Raphani Semen (Raphanus sativus L.) Ameliorates Alcoholic Fatty Liver Disease by Regulating De Novo Lipogenesis

In this study, we investigated the pharmacological effect of a water extract of Raphani Semen (RSWE) on alcoholic fatty liver disease (AFLD) using ethanol-induced AFLD mice (the NIAAA model) and palmitic acid (PA)-induced steatosis HepG2 cells. An RSWE supplement improved serum and hepatic triglyceride (TG) levels of AFLD mice, as well as their liver histological structure. To explore the molecular action of RSWE in the improvement of AFLD, we investigated the effect of RSWE on four major pathways for lipid homeostasis in the liver: free fatty acid transport, lipogenesis, lipolysis, and β-oxidation. Importantly, RSWE decreased the mRNA expression of de novo lipogenesis-related genes, such as Srebf1, Cebpa, Pparg, and Lpin1, as well as the protein levels of these factors, in the liver of AFLD mice. That these actions of RSWE affect lipogenesis was confirmed using PA-induced steatosis HepG2 cells. Overall, our findings suggest that RSWE has the potential for improvement of AFLD by inhibiting de novo lipogenesis.