Fatty acid biosynthesis from glutamate and glutamine is specifically induced in neuronal cells under hypoxia

Abstract

Hypoxia is involved in many neuronal and non-neuronal diseases, and defining the mechanisms for tissue adaptation to hypoxia is critical for the understanding and treatment of these diseases. One mechanism for tissue adaptation to hypoxia is increased glutamine and/or glutamate (Gln/Glu) utilization. To address this mechanism, we determined total Gln/Glu incorporation into lipids and fatty acids in both primary neurons and a neuronal cell line under normoxic and hypoxic conditions and compared this to non-neuronal primary cells and non-neuronal cell lines. Incorporation of Gln/Glu into total lipids was dramatically and specifically increased under hypoxia in neuronal cells including both primary (2.0- and 3.0- fold for Gln and Glu, respectively) and immortalized cultures (3.5- and 8.0- fold for Gln and Glu, respectively), and 90% to 97% of this increase was accounted for by incorporation into fatty acids (FA) depending upon substrate and cell type. All other non-neuronal cells tested demonstrated decreased or unchanged FA synthesis from Gln/Glu under hypoxia. Consistent with these data, total FA mass was also increased in neuronal cells under hypoxia that was mainly accounted for by the increase in saturated and monounsaturated FA with carbon length from 14 to 24. Incorporation of FA synthesized from Gln/Glu was increased in all major lipid classes including cholesteryl esters, TAGs, DAGs, free FA, and phospholipids, with the highest rate of incorporation into TAGs. These results indicate that increased FA biosynthesis from Gln/Glu followed by esterification may be a neuronal specific pathway for adaptation to hypoxia.

Fatty Acid Biosynthesis Inhibition Increases Reduction Potential in Neuronal Cells under Hypoxia

“…The hypoxic treatment was as described earlier (Brose et al, 2014). Briefly, the cells were preconditioned by replacing the growth medium with serum-free minimum essential media (MEM) and incubating in 19% O 2 (Normoxia) or 1% O 2 (Hypoxia) in 5% CO 2 at 37°C using nitrogen gas to purge the oxygen.…”

“…Recently, we have discovered a previously unknown and neuron-specific mechanism for utilizing anaerobic metabolism during hypoxia. We have found that hypoxic-stressed neurons have a unique response of dramatically increased fatty acid (FA) synthesis from glutamine and glutamate (Gln/Glu) (Brose et al, 2014). However, the biochemical significance of this pathway in neuronal adaptation to hypoxia is unknown.…”

“…However, the biochemical significance of this pathway in neuronal adaptation to hypoxia is unknown. Previously, we have hypothesized a few mechanisms to address the importance for activated FA synthesis from Gln/Glu under hypoxia (Brose et al, 2014) including balancing Glu levels, protection against oxidative stress, and maintaining reduction potential with support of anaerobic glycolysis. In the present study, we have tested one of these hypotheses that FA SYNTHESIS supports anaerobic metabolism under hypoxia through accepting hydrogen from reduced cofactors (${\text{NADH}}_2^{+}$, ${\text{NADPH}}_2^{+}$, FADH 2 ), thus maintaining reduction potential.…”

“…To address this hypothesis, we applied a previously validated in-vitro model for neuronal hypoxia using SH-SY5Y cells exposed to 19% (normoxia) or 1% (hypoxia) oxygen levels (Brose et al, 2014). FA synthesis was inhibited at two different steps in the biosynthetic pathway using tetradecyloxy-2-furoic acid (TOFA, inhibits Acetyl-CoA carboxylase Loftus et al, 2000) and cerulenin (inhibits FA synthase, Heiligtag et al, 2002; Lupu and Menendez, 2006).…”

Reduced Glutamatergic Neurotransmission as Possible Indicator of Unfavorable Prognosis

“…Glu has been described as a more "preferred" substrate for fatty acid synthesis than Gln. [56][57][58][59][60] In a pilot study by H. Baran et al, [61 an increase in KYNA level had a direct correlation with the severity of hypoxia. KYNA levels in tissues increased by 44% after 5min of asphyxia and 302% after 20min of asphyxia (the critical time limit of survival).…”