Fuel source shift or cost reduction: Context-dependent adaptation strategies in closely related Neodon fuscus and Lasiopodomys brandtii against hypoxia

Respiratory failure is a major cause of mortality during septic shock and is due in part to decreased ventilatory muscle contraction. Ventilatory muscles have high energy demands; fatty acid (FA) oxidation is an important source of ATP. FA oxidation is regulated by nuclear hormone receptors; studies have shown that the expression of these receptors is decreased in liver, heart, and kidney during sepsis. Here, we demonstrate that lipopolysaccharide (LPS) decreases FA oxidation and the expression of lipoprotein lipase (LPL), FA transport protein 1 (FATP-1), CD36, carnitine palmitoyltransferase beta, medium chain acyl-CoA dehydrogenase (MCAD), and acyl-CoA synthetase, key proteins required for FA uptake and oxidation, in the diaphragm. LPS also decreased mRNA levels of PPARalpha and beta/delta, RXRalpha, beta, and gamma, thyroid hormone receptor alpha and beta, and estrogen related receptor alpha (ERRalpha) and their coactivators PGC-1alpha, PGC-1beta, SRC1, SRC2, Lipin 1, and CBP. Zymosan resulted in similar changes in the diaphragm. Finally, in PPARalpha deficient mice, baseline CPT-1beta and FATP-1 levels were markedly decreased and were not further reduced by LPS suggesting that a decrease in the PPARalpha signaling pathway plays an important role in inducing some of these changes. The decrease in FA oxidation in the diaphragm may be detrimental, leading to decreased diaphragm contraction and an increased risk of respiratory failure during sepsis.

Oxygen is essential for most life forms. An insufficient oxygen supply can disrupt homeostasis and compromise the survival of organisms, and hypoxia-induced cardiovascular failure is fatal in many animals, including humans. Some species have adapted to hypoxic environments and evolved to endure such conditions, making them good models for studying the regulatory mechanisms involved in the cardiovascular system in response to hypoxia. To explore the coping mechanisms of cardiovascular system in hypoxic adaptation species with different life histories, we investigated the physiological and molecular responses of the cardiovascular systems of two closely related rodents, Qinghai vole (Neodon fuscus) and Brandt’s vole (Lasiopodomys brandtii), exposed to hypoxic (10% O2 for 48 h) and normoxic (20.9% O2 for 48 h) conditions. Kunming mouse (Mus musculus) was used as a comparison.

Mitochondria are central to cellular metabolism. The mitochondria’s metabolic pathways include fatty acid oxidation, glucose oxidation and glutaminolysis. The initial step in glucose metabolism occurs in the cytosol, where glycolysis converts glucose to pyruvate1 (Figure 1). Figure 1 Mechanism of impaired glucose oxidation and enhanced aerobic glycolysis in PAH. Changes in redox signaling, such as downregulation of SOD2 and the resultant decrease in H2O2 signaling, can activate transcription factors (i.e. HIF-1α) which in ... Normally, glycolysis is coupled to glucose oxidation, meaning that the pyruvate is transported into the mitochondria where it serves as a substrate for pyruvate dehydrogenase (PDH)3. Under pathologic conditions, such as inhibition of PDH, glycolysis may be uncoupled from glucose oxidation and remain a wholly cytosolic reaction that terminates in the generation of lactate. Metabolism is quite plastic and the relative importance of each pathway can change in response to environmental stimuli, such as substrate availability, the organism’s developmental stage, and pathologic stimuli, such as hypoxia, shear stress, pressure overload, ischemia and hypertrophy. In addition, the activity of one metabolic pathway alters the activity of competing pathways. Examples of this metabolic crosstalk include the reciprocal relationship between fatty acid and glucose oxidation. Fatty acid oxidation suppresses glucose oxidation, through a mechanism called the Randle cycle (Figure 2), named after Phillip Randle who first described the phenomenon3. Another example of metabolic plasticity is the uncoupling of glycolysis from glucose oxidation, so called aerobic glycolysis. Aerobic glycolysis is also called the Warburg effect, in honor of Otto Warburg who first described the phenomenon in cancer cells5. Warburg noted that this shift to glycolysis contributed to the growth and survival advantage of cancer cells5. He also observed, but could not explain, accumulation of ammonia in his cancer tissue culture. Ultimately this proved to relate to a concomitant upregulation of glutaminolysis in cancer cells. Aerobic glycolysis results in a reliance on glycolysis to produce ATP despite the presence of sufficient oxygen to have allowed pyruvate generation and mitochondrial glucose oxidation. Aerobic glycolysis usually reflects active inhibition of one or more mitochondrial enzymes, notably inhibition of PDH by pyruvate dehydrogenase kinases (PDK). These acquired changes in metabolism alter the cell’s bioenergetics status, susceptibility to hypertrophy and fibrosis, rates of proliferation and apoptosis, angiogenesis and contractility. Importantly, the cell’s metabolic choices can be pharmacologically manipulated, offering the potential for metabolic therapies. Figure 2 Manipulating fatty acid and glucose oxidation in PAH: The Randle’s cycle. Randle’s cycle is the reciprocal relationship between glucose oxidation and fatty acid oxidation. Note how the acetyl CoA and citrate produced by β-oxidation ... In addition to generating adenosine triphosphate (ATP), mitochondria are constantly dividing and joining together6. These highly conserved and regulated processes are called fission and fusion, respectively7. These non-canonical mitochondrial functions (fission, fusion), as well as migration, are called mitochondrial dynamics.8 Mitochondrial dynamics are important in physiology, participating in oxygen sensing9 and the distribution of mitochondria to daughter cells during mitosis10. Mitochondrial dynamics are also involved in cellular quality control, notably participating in mitophagy and apoptosis. Acquired and inherited disorders of mitochondrial dynamics are involved in diseases, including pulmonary arterial hypertension (PAH), cancer, and cardiac ischemia reperfusion injury7. Both metabolic plasticity and mitochondrial dynamics are relevant to the pathogenesis of PAH and offer new therapeutic targets in the pulmonary vasculature and the right ventricle.

Peroxisome proliferator-activated receptor alpha (PPARalpha) is a nuclear receptor transcription factor that has an important role in controlling cardiac metabolic gene expression. We determined whether mice lacking PPARalpha (PPARalpha (-/-) mice) have alterations in cardiac energy metabolism. Rates of palmitate oxidation were significantly decreased in isolated working hearts from PPARalpha (-/-) hearts compared with hearts from age-matched wild type mice (PPARalpha (+/+) mice), (62 +/- 12 versus 154 +/- 65 nmol/g dry weight/min, respectively, p < 0.05). This was compensated for by significant increases in the rates of glucose oxidation and glycolysis. The decreased fatty acid oxidation in PPARalpha (-/-) hearts was associated with increased levels of cardiac malonyl-CoA compared with PPARalpha (+/+) hearts (15.15 +/- 1.63 versus 7.37 +/- 1.31 nmol/g, dry weight, respectively, p < 0.05). Since malonyl-CoA is an important regulator of cardiac fatty acid oxidation, we also determined if the enzymes that control malonyl-CoA levels in the heart are under transcriptional control of PPARalpha. Expression of both mRNA and protein as well as the activity of malonyl-CoA decarboxylase, which degrades malonyl-CoA, were significantly decreased in the PPARalpha (-/-) hearts. In contrast, the expression and activity of acetyl-CoA carboxylase, which synthesizes malonyl-CoA and 5'-AMP-activated protein kinase, which regulates acetyl-CoA carboxylase, were not altered. Glucose transporter expression (GLUT1 and GLUT4) was not different between PPARalpha (-/-) and PPARalpha (+/+) hearts, suggesting that the increase in glycolysis and glucose oxidation in the PPARalpha null mice was not due to direct effects on glucose uptake but rather was occurring secondary to the decrease in fatty acid oxidation. This study demonstrates that PPARalpha is an important regulator of fatty acid oxidation in the heart and that this regulation of fatty acid oxidation may in part occur due to the transcriptional control of malonyl-CoA decarboxylase.

Laboratory investigations into preserving viability of the ischemic myocardium or to promote recovery during reperfusion have often focused on the intermediary pathways of energy metabolism. However, in the clinical treatment of angina, the application of metabolic therapies has generally lagged behind or has been incidental to other approaches, such as a vasodilators, calcium antagonists, and negative inotropes. A study published in this issue of Circulation Research has demonstrated that the antianginal agent trimetazidine (1-[2,3,4-trimethoxybenzyl] piperazine dihydrochloride [TMZ]) inhibits the activity of one of the enzymes of the β-oxidation pathway in cardiac mitochondria with direct increases in glucose oxidation.1 These findings confirm in an intact, functioning heart model the well-documented, anti-ischemic properties of TMZ2 3 4 and the inhibitory effects of TMZ on long-chain fatty acid oxidation5 with reciprocal enhancement of glucose uptake.6 The study localizes the inhibition of β-oxidation to a specific enzyme, the mitochondrial long-chain 3-ketoacyl coenzyme A (CoA) thiolase. The suggestion by the authors is that the effectiveness of TMZ as an antianginal agent is directly linked to this inhibitory effect on long-chain fatty acid oxidation. Although studies on the isolated heart preparation can neither specifically nor conclusively identify an antianginal mechanism, the findings of the University of Alberta group1 are consistent with the known effectiveness of TMZ as an antianginal agent7 8 9 that reduces long-chain fatty acid oxidation, while lacking both vasodilator activity and negative inotropic effects.9 The inhibitory effects of TMZ on long-chain fatty acid transport into rat heart mitochondria, via inhibition of carnitine palmitoyltransferase 1 (CPT 1) enzyme, have already been demonstrated, but TMZ was also found to be much less potent than two other proven antianginal drugs, perhexiline and amiodarone.5 10 However, TMZ does not induce the confounding vasoactive, …

Ranolazine is a novel antianginal agent that may reduce symptoms without affecting hemodynamics and has shown cardiac antiischemic effects in in vivo and in vitro models. In one study it increased active pyruvate dehydrogenase (PDHa). Other agents that increase PDHa and so increase glucose and decrease fatty acid (FA) oxidation are beneficial in ischemic-reperfused hearts. Effects of ranolazine on glucose and palmitate oxidation and glycolysis were assessed in isolated rat hearts. Working hearts were perfused with Krebs-Henseleit buffer plus 3% albumin under normoxic conditions and on reperfusion after 30-minute no-flow ischemia and under conditions designed to give either low [low (Ca) (1.25 mmol/L), high [FA] (1.2 mmol/L palmitate; with/without insulin] or high (2.5 mmol/L Ca, 0.4 mmol/L palmitate; with/without pacing) glucose oxidation rates; Langendorff-perfused hearts (high Ca, low FA) were subjected to varying degrees of low-flow ischemia. Glycolysis and glucose oxidation were measured with the use of [5-3H/U-14C]-glucose and FA oxidation with the use of [1-14C]- or [9,10-3H]-palmitate. In working hearts, 10 micromol/L ranolazine significantly increased glucose oxidation 1.5-fold to 3-fold under conditions in which the contribution of glucose to overall ATP production was low (low Ca, high FA, with insulin), high (high Ca, low Fa, with pacing), or intermediate. In some cases, reductions in FA oxidation were seen. No substantial changes in glycolysis were noted with/without ranolazine; rates were approximately 10-fold glucose oxidation rates, suggesting that pyruvate supply was not limiting. Insulin increased basal glucose oxidation and glycolysis but did not alter ranolazine responses. In normoxic Langendorff hearts (high Ca, low FA; 15 mL/min), all basal rates were lower compared with working hearts, but 10 micromol/L ranolazine similarly increased glucose oxidation; ranolazine also significantly increased it during flow reduction to 7, 3, and 0.5 mL/min. Ranolazine did not affect baseline contractile or hemodynamic parameters or O2 use. In reperfused ischemic working hearts, ranolazine significantly improved functional outcome, which was associated with significant increases in glucose oxidation, a reversal of the increased FA oxidation seen in control reperfusions (versus preischemic), and a smaller but significant increase in glycolysis. Beneficial effects of ranolazine in cardiac ischemia/reperfusion may be due, at least in part, to a stimulation of glucose oxidation and a reduction in FA oxidation, allowing improved ATP/O2 and reduction in the buildup of H+, lactate, and harmful fatty acyl intermediates.

Emerging evidence documents a key function for the forkhead transcription factor FoxO1 in cellular metabolism. Here, we investigate the role of FoxO1 in the regulation of fatty acid (FA) metabolism in muscle cells. C2C12 cells expressing an inducible construct with either wild type FoxO1 or a mutant form (FoxO1/TSS) refractory to the protein kinase B inhibitory effects were generated. FoxO1 activation after myotube formation altered the expression of several genes of FA metabolism. Acyl-CoA oxidase and peroxisome proliferator-activated receptor delta mRNA levels increased 2.2-fold and 1.4-fold, respectively, whereas mRNA for acetyl-CoA carboxylase decreased by 50%. Membrane uptake of oleate increased 3-fold, and oleate oxidation increased 2-fold. Cellular triglyceride content was also increased. The enhanced FA utilization induced by FoxO1 was mediated by a severalfold increase in plasma membrane level of the fatty acid translocase FAT/CD36 and eliminated by cell treatment with the CD36 inhibitor sulfo-N-succinimidyl-oleate. We conclude that FoxO1 activation induces coordinate increases in FA uptake and oxidation and that these effects are mediated, at least in part, by membrane enrichment in CD36. The data suggest that FoxO1 contributes to preparing the muscle cell for the increased reliance on FA metabolism that is characteristic of fasting. Dysregulation of FoxO1 in muscle could contribute to intramuscular lipid accumulation and insulin resistance by maintaining activation of FA uptake.

The early initiation phase of acute inflammation is anabolic and primarily requires glycolysis with reduced mitochondrial glucose oxidation for energy, whereas the later adaptation phase is catabolic and primarily requires fatty acid oxidation for energy. We reported previously that switching from the early to the late acute inflammatory response following TLR4 stimulation depends on NAD(+) activation of deacetylase sirtuin 1 (SirT1). Here, we tested whether NAD(+) sensing by sirtuins couples metabolic polarity with the acute inflammatory response. We found in TLR4-stimulated THP-1 promonocytes that SirT1 and SirT 6 support a switch from increased glycolysis to increased fatty acid oxidation as early inflammation converts to late inflammation. Glycolysis enhancement required hypoxia-inducing factor-1α to up-regulate glucose transporter Glut1, phospho-fructose kinase, and pyruvate dehydrogenase kinase 1, which interrupted pyruvate dehydrogenase and reduced mitochondrial glucose oxidation. The shift to late acute inflammation and elevated fatty acid oxidation required peroxisome proliferator-activated receptor γ coactivators PGC-1α and β to increase external membrane CD36 and fatty acid mitochondrial transporter carnitine palmitoyl transferase 1. Metabolic coupling between early and late responses also required NAD(+) production from nicotinamide phosphoryltransferase (Nampt) and activation of SirT6 to reduce glycolysis and SirT1 to increase fatty oxidation. We confirmed similar shifts in metabolic polarity during the late immunosuppressed stage of human sepsis blood leukocytes and murine sepsis splenocytes. We conclude that NAD(+)-dependent bioenergy shifts link metabolism with the early and late stages of acute inflammation.

Diverse energy metabolism patterns in females in Neodon fuscus, Lasiopodomys brandtii, and Mus musculus revealed by comparative transcriptomics under hypoxic conditions

Lipin-1 is the major phosphatidate phosphatase (PAP) in the heart and a transcriptional coactivator that regulates fatty acid (FA) oxidation in the liver. As the control of FA metabolism is essential for maintaining cardiac function, we investigated whether lipin-1 deficiency affects cardiac metabolism and performance. Cardiac PAP activity in lipin-1 deficient [fatty liver dystrophy (fld)] mice was decreased by >80% compared with controls. Surprisingly, oleate oxidation and incorporation in triacylglycerol (TG), as well as glucose oxidation, were not significantly different in perfused working fld hearts. Despite this, [³H]oleate accumulation in phosphatidate and phosphatidylinositol was increased in fld hearts, reflecting the decreased PAP activity. Phosphatidate accumulation was linked to increased cardiac mammalian target of rapamycin complex 1 (mTORC1) signaling and endoplasmic reticulum (ER) stress. Transthoracic echocardiography showed decreased cardiac function in fld mice; however, cardiac dysfunction was not observed in ex vivo perfused working fld hearts. This showed that changes in systemic factors due to the global absence of lipin-1 could contribute to the decreased cardiac function in vivo. Collectively, this study shows that fld hearts exhibit unchanged oleate esterification, as well as oleate and glucose oxidation, despite the absence of lipin-1. However, lipin-1 deficiency increases the accumulation of newly synthesized phosphatidate and induces aberrant cell signaling.

the heart has continuous high-energy demands required to sustain efficient contraction. This is met by the metabolism of major circulating substrates (e.g., glucose, lactate, or lipids), according to availability, since the heart has a limited capacity for nutrient storage (reviewed in Ref. [16][1

Hypoxic response patterns in lung tissue: An integrated analysis of comparative physiological and transcriptomic studies from Neodon fuscus and Lasiopodomys brandtii

Glucose Metabolism in Cardiac Hypertrophy and Heart Failure.

5-Amino-4-imidazolecarboxamide riboside (AICAR), a pharmacological activator of AMP-activated protein kinase (AMPK), acutely stimulates glucose uptake and fatty acid (FA) oxidation in skeletal muscle. However, it is not fully understood whether AICAR-induced changes in glucose oxidation are secondary to changes in FA oxidation (i.e. glucose fatty acid cycle), or what role AMPK may be playing in the regulation of intramuscular triacylglycerol (TAG) esterification and hydrolysis. We examined the acute (60 min) effects of AICAR (2 mm) on FA metabolism, glucose oxidation and pyruvate dehydrogenase (PDH) activation in isolated resting rat soleus muscle strips exposed to two different FA concentrations (low fatty acid, LFA, 0.2 mm; high fatty acid, HFA, 1 mm). AICAR significantly increased AMPK alpha2 activity (+192%; P<0.05) over 60 min, and simultaneously increased both FA (LFA: +33%, P<0.05; HFA: +36%, P<0.05) and glucose (LFA: +105%, P<0.05; HFA: +170, P<0.001) oxidation regardless of FA availability. While there were no changes in TAG esterification, AICAR did increase the ratio of FA partitioned to oxidation relative to TAG esterification (LFA: +15%, P<0.05; HFA: +49%, P<0.05). AICAR had no effect on endogenous TAG hydrolysis and oxidation in resting soleus. The stimulation of glucose oxidation with AICAR was associated with an increase in PDH activation (+126%; P<0.05) but was without effect on pyruvate, an allosteric activator of the PDH complex, suggesting that AMPK may stimulate PDH directly. In conclusion, AMPK appears to be an important regulator of both FA metabolism and glucose oxidation in resting skeletal muscle.

Mammals dwelling at different altitudes exhibit distinct molecular mechanisms to adapt to low-oxygen environments owing to habitat-specific oxygen levels. Notably, these adaptations include energy metabolism patterns, which fundamentally sustain vital physiological functions. Skeletal muscle, a pivotal contributor to systemic energy metabolism, facilitates vertebrate body movement through the contraction and relaxation of muscle fibers and is highly dependent on mitochondrial substrate oxidation for energy production. This study focused on three rodent species inhabiting different altitudes: the Qinghai vole (Neodon fuscus), Brandt’s vole (Lasiopodomys brandtii), and Kunming mouse (Mus musculus). Using transcriptomics and quasi-targeted metabolomics, we systematically analyzed the differences in skeletal muscle metabolic regulation among the three rodent species before and after exposure to hypoxia, thereby revealing the underlying molecular mechanisms. In summary, N. fuscus, native to high-altitude environments, tended to sustain energy supplies through regulating fatty acid oxidation under low-oxygen conditions. Conversely, L. brandtii and M. musculus, acclimatized to middle- and low-altitude habitats, relied on aerobic oxidation and anaerobic glycolysis of glucose, respectively, for energy maintenance under hypoxic conditions. In addition to their differential metabolic preferences under hypoxic conditions, these three rodent species showed species-specific responses related to oxygen utilization, antioxidant defense mechanisms, and anti-inflammatory processes. This study provides insights into the metabolic response patterns of mammalian skeletal muscle under hypoxic conditions, thereby establishing a basis for future investigations on transcriptional–metabolic associations.Graphical abstractSupplementary InformationThe online version contains supplementary material available at 10.1186/s12983-025-00582-2.