Elovl2-Ablation Leads to Mitochondrial Membrane Fatty Acid Remodeling and Reduced Efficiency in Mouse Liver Mitochondria.

The fatty acid elongase elongation of very long-chain fatty acids protein 2 (ELOVL2) controls the elongation of polyunsaturated fatty acids (PUFA) producing precursors for omega-3, docosahexaenoic acid (DHA), and omega-6, docosapentaenoic acid (DPAn-6) in vivo. Expectedly, Elovl2-ablation drastically reduced the DHA and DPAn-6 in liver mitochondrial membranes. Unexpectedly, however, total PUFAs levels decreased further than could be explained by Elovl2 ablation. The lipid peroxidation process was not involved in PUFAs reduction since malondialdehyde-lysine (MDAL) and other oxidative stress biomarkers were not enhanced. The content of mitochondrial respiratory chain proteins remained unchanged. Still, membrane remodeling was associated with the high voltage-dependent anion channel (VDAC) and adenine nucleotide translocase 2 (ANT2), a possible reflection of the increased demand on phospholipid transport to the mitochondria. Mitochondrial function was impaired despite preserved content of the respiratory chain proteins and the absence of oxidative damage. Oligomycin-insensitive oxygen consumption increased, and coefficients of respiratory control were reduced by 50%. The mitochondria became very sensitive to fatty acid-induced uncoupling and permeabilization, where ANT2 is involved. Mitochondrial volume and number of peroxisomes increased as revealed by transmission electron microscopy. In conclusion, the results imply that endogenous DHA production is vital for the normal function of mouse liver mitochondria and could be relevant not only for mice but also for human metabolism.

Synergistic Effects of DHA and Sucrose on Body Weight Gain in PUFA-Deficient Elovl2 -/- Mice.

The omega-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) is implicated in theregulation of both lipid and carbohydrate metabolism. Thus, we questioned whether dietary DHAand low or high content of sucrose impact on metabolism in mice deficient for elongation of verylong-chain fatty acids 2 (ELOVL2), an enzyme involved in the endogenous DHA synthesis. Wefound that Elovl2 -/- mice fed a high-sucrose DHA-enriched diet followed by the high sucrose, highfat challenge significantly increased body weight. This diet affected the triglyceride rich lipoproteinfraction of plasma lipoproteins and changed the expression of several genes involved in lipidmetabolism in a white adipose tissue. Our findings suggest that lipogenesis in mammals issynergistically influenced by DHA dietary and sucrose content.

Impairment of systemic DHA synthesis affects macrophage plasticity and polarization: implications for DHA supplementation during inflammation.

Docosahexaenoic acid (DHA) is an omega-3 fatty acid obtained from the diet or synthesized from alpha-linolenic acid through the action of fatty acid elongases (ELOVL) and desaturases. DHA plays important roles in the central nervous system as well as in peripheral organs and is the precursor of several molecules that regulate resolution of inflammation. In the present study, we questioned whether impaired synthesis of DHA affected macrophage plasticity and polarization both in vitro and in vivo models. For this we investigated the activation status and inflammatory response of bone marrow-derived M1 and M2 macrophages obtained from mice deficient of Elovl2 (Elovl2-/-), a key enzyme for DHA synthesis in mammals. Although both wild type and Elovl2-/- mice were able to generate efficient M1 and M2 macrophages, M1 cells derived from Elovl2-/- mice showed an increased expression of key markers (iNOS, CD86 and MARCO) and cytokines (IL-6, IL-12 and IL-23). However, M2 macrophages exhibited upregulated M1-like markers like CD80, CD86 and IL-6, concomitantly with a downregulation of their signature marker CD206. These effects were counteracted in cells obtained from DHA-supplemented animals. Finally, white adipose tissue of Elovl2-/- mice presented an M1-like pro-inflammatory phenotype. Hence, impairment of systemic DHA synthesis delineates an alteration of M1/M2 macrophages both in vitro and in vivo, with M1 being hyperactive and more pro-inflammatory while M2 less protective, supporting the view that DHA has a key role in controlling the balance between pro- and anti-inflammatory processes.

Both maternal and offspring Elovl2 genotypes determine systemic DHA levels in perinatal mice.

The molecular details relevant to dietary supplementation of the omega-3 fatty acid DHA in mothers as well as in their offspring are not clear. The PUFA elongase, elongation of very long-chain fatty acid (ELOVL)2, is a critical enzyme in the formation of DHA in mammals. In order to address the question regarding the origin of DHA during perinatal life, we have used DHA-deficient Elovl2-ablated mice as a model system to analyze the maternal impact on the DHA level in their offspring of various genotypes. Elovl2-/- mothers maintained on control diet had significantly lower systemic levels of DHA compared with the Elovl2+/- and Elovl2+/+ mothers. Dietary DHA administration during the pregnancy and lactation periods led to increased DHA accretion in maternal tissues and serum of all genotypes. The proportion of DHA in the liver and serum of the Elovl2-/- offspring was significantly lower than in the Elovl2+/+ offspring. Remarkably, the DHA level in the Elovl2+/- offspring nursed by DHA-free-fed Elovl2-/- mothers was almost as high as in +/+ pups delivered by +/+ mothers, suggesting that endogenous synthesis in the offspring can compensate for maternal DHA deficiency. Maternal DHA supplementation had a strong impact on offspring hepatic gene expression, especially of the fatty acid transporter, Mfsd2a, suggesting a dynamic interplay between DHA synthesis and DHA uptake in the control of systemic levels in the offspring.

Elovl2 ablation demonstrates that systemic DHA is endogenously produced and is essential for lipid homeostasis in mice.

The potential role of endogenously synthesized PUFAs is a highly overlooked area. Elongation of very long-chain fatty acids (ELOVLs) in mammals is catalyzed by the ELOVL enzymes to which the PUFA elongase ELOVL2 belongs. To determine its in vivo function, we have investigated how ablation of ELOVL2, which is highly expressed in liver, affects hepatic lipid composition and function in mice. The Elovl2(-/-) mice displayed substantially decreased levels of 22:6(n-3), DHA, and 22:5(n-6), docosapentaenoic acid (DPA) n-6, and an accumulation of 22:5(n-3) and 22:4(n-6) in both liver and serum, showing that ELOVL2 primarily controls the elongation process of PUFAs with 22 carbons to produce 24-carbon precursors for DHA and DPAn-6 formation in vivo. The impaired PUFA levels positively influenced hepatic levels of the key lipogenic transcriptional regulator sterol-regulatory element binding protein 1c (SREBP-1c), as well as its downstream target genes. Surprisingly, the Elovl2(-/-) mice were resistant to hepatic steatosis and diet-induced weight gain, implying that hepatic DHA synthesis via ELOVL2, in addition to controlling de novo lipogenesis, also regulates lipid storage and fat mass expansion in an SREBP-1c-independent fashion. The changes in fatty acid metabolism were reversed by dietary supplementation with DHA.