OXPHOS capacity is diminished and the phosphorylation system inhibited during diapause in an extremophile, embryos of Artemia franciscana

• Published in: Journal of experimental biology Vol. 227; no. 2
• Main Authors: Patil, Yuvraj N, Gnaiger, Erich, Landry, Alexander P, Leno, Zachary J, Hand, Steven C
• Format: Journal Article
• Language: English
• Published: England 15.01.2024
• Subjects: Long chain acyl-CoA esters; Mitochondria; Brine shrimp; Oxidative phosphorylation; Metabolic inhibition; Diapause
• ISSN: 0022-0949; 1477-9145; 1477-9145
• DOI: 10.1242/jeb.245828

Diapause exhibited by embryos of Artemia franciscana is accompanied by severe arrest of respiration. A large fraction of this depression is attributable to downregulation of trehalose catabolism that ultimately restricts fuel to mitochondria. This article now extends the mechanism by revealing metabolic depression is heightened by inhibitions within mitochondria. Compared to embryo lysates during post-diapause, OXPHOS capacity P is depressed during diapause when either NADH-linked substrates (pyruvate and malate) for electron transfer (ET capacity, E) through respiratory Complex I or the Complex II substrate succinate are used. When pyruvate, malate and succinate are combined, respiratory inhibition by the phosphorylation system in diapause lysates was discovered as judged by P/E flux control ratios (two-way ANOVA; F1,24=38.78; p<0.0001). Inhibition is eliminated as the diapause extract is diluted (significant interaction term; F2,24=9.866; p=0.0007), consistent with the presence of a diffusible inhibitor. One candidate is long-chain acyl CoA esters known to inhibit the adenine nucleotide translocator. Addition of oleoyl-CoA to post-diapause lysates markedly decreases the P/E ratio to 0.40±0.07 (mean±SD; p=0.002) compared to 0.79±0.11 without oleoyl-CoA. Oleoyl-CoA inhibits the phosphorylation system and may be responsible for the depressed P/E in lysates from diapause embryos. With isolated mitochondria, depression of P/E by oleoyl-CoA is fully reversed by addition of L-carnitine (control versus recovery with L-carnitine, p=0.338), which facilitates oleoyl-CoA transport into the matrix and elimination by β-oxidation. In conclusion, severe metabolic arrest during diapause promoted by restricting glycolytic carbon to mitochondria is reinforced by depression of OXPHOS capacity and the phosphorylation system.