Biology subjects

Pyles, K. D.

Publications and source records attributed to Pyles, K. D..

5 recordsLinked to original sources

bioRxiv2024

Ketone Body Metabolism is Not Required for Improvement of Heart Failure by Ketogenic Diet in Mice

Failing hearts increasingly metabolize ketone bodies, and enhancing ketosis improves heart failure (HF) remodeling. Circulating ketones are elevated by fasting/starvation, which is mimicked with a high-fat, low-carbohydrate "ketogenic diet" (KD). While speculated that KD improves HF through increased ketone oxidation, some evidence suggests KD paradoxically downregulates cardiac ketone oxidation despite increased ketone delivery. We sought to clarify the significance of cardiac ketone metabolism during KD in HF. Mice were subjected to transverse aortic constriction with apical myocardial infarction (TAC-MI) and fed either low-fat (LF) control or KD. Cardiac-specific mitochondrial pyruvate carrier 2 (csMPC2-/-) mice were used as a second model of heart failure. In both mice, feeding a KD improved HF, determined by echocardiography, heart weights, and gene expression analyses. Although KD increases plasma ketone bodies, gene expression for ketone metabolic genes is decreased in the hearts of KD-fed mice. Cardiac-specific {beta}-hydroxybutyrate dehydrogenase 1 (csBDH1-/-), the first enzyme in ketone catabolism, mice were also studied and crossed with the csMPC2-/-mice to create double knockout (DKO) mice. These mice were aged to 16 weeks and switched to LF or KD, and KD was able to completely normalize the hearts of both csMPC2-/- and DKO mice, suggesting that ketone metabolism is unnecessary for improving heart failure with ketogenic diet. These studies were then repeated, and mice injected with U-13C-{beta}-hydroxybutyrate to evaluate ketone metabolism. KD feeding significantly decreased the enrichment of the TCA cycle from ketone body carbons, as did the BDH1-deletion in DKO mice. Gene expression and respirometry suggests that KD instead increases cardiac fat oxidation. In conclusion, these results suggest that ketogenic diet decreases cardiac ketone metabolism and does not require ketone metabolism to improve heart failure.

physiology↗

bioRxiv2024

Loss of mitochondrial pyruvate transport initiates cardiac glycogen accumulation and heart failure

Heart failure involves metabolic alterations including increased glycolysis despite unchanged or decreased glucose oxidation. The mitochondrial pyruvate carrier (MPC) regulates pyruvate entry into the mitochondrial matrix, and cardiac deletion of the MPC in mice causes heart failure. How MPC deletion results in heart failure is unknown. We performed targeted metabolomics and isotope tracing in wildtype (fl/fl) and cardiac-specific Mpc2-/- (CS-Mpc2-/-) hearts after in vivo injection of U-13C-glucose. Failing CS-Mpc2-/- hearts contained normal levels of ATP and phosphocreatine, yet these hearts displayed increased enrichment from U-13C-glucose and increased glycolytic metabolite pool sizes. 13C enrichment and pool size was also increased for the glycogen intermediate UDP-glucose, as well as increased enrichment of the glycogen pool. Glycogen levels were increased [~]6-fold in the failing CS-Mpc2-/- hearts, and glycogen granules were easily detected by electron microscopy. In young, non-failing CS-Mpc2-/- hearts, increased glycolytic 13C enrichment occurred, but glycogen levels remained low and unchanged compared to fl/fl hearts. Inhibiting glycogen synthase with MZ-101 reduced cardiac glycogen levels and improved heart failure. Feeding a ketogenic diet to CS-Mpc2-/- mice reversed the heart failure and normalized the cardiac glycogen and glycolytic metabolite accumulation. Cardiac glycogen levels were also elevated in mice infused with angiotensin-II, and both the cardiac hypertrophy and glycogen levels were improved by ketogenic diet. Thus, loss of MPC in the heart causes glycogen accumulation and heart failure, while inhibition of glycogen synthesis or a ketogenic diet can reverse both the glycogen accumulation and heart failure.

physiology↗

bioRxiv2022

Enhancing Hepatic MBOAT7 Expression Does Not Improve Nonalcoholic Steatohepatitis in Mice

Background & AimsGenetic analyses of human NASH have revealed polymorphisms near the membrane bound O-acyl transferase domain containing 7 (MBOAT7) gene associated with worsened liver injury. NAFLD/NASH also appears to decrease MBOAT7 expression or activity independent of these polymorphisms. Thus, we hypothesized that enhancing MBOAT7 function in NASH would improve pathology. Approach & ResultsMale C57BL6/J mice were infected with adeno-associated virus 8 (AAV8) expressing MBOAT7 under control of the hepatocyte-specific thyroid hormone-binding globulin promoter, or control virus expressing green fluorescent protein (GFP). Mice were infected after NASH induction with either choline-deficient high-fat diet or Gubra Amylin NASH diet and compared to low-fat fed control mice. Both NASH diets increased liver weights, liver triglycerides, and plasma alanine and aspartate aminotransferase (ALT and AST) markers of liver injury, which were modestly yet significantly improved by MBOAT7 overexpression. However, NASH liver histology assessed by categorical scoring was not substantially improved by MBOAT7 overexpression. MBOAT7 regulates the formation of phosphatidylinositol (PI) predominantly by arachidonoylation of lysophosphatidylinositol (LPI). Shotgun lipidomics of NASH GFP-control livers suggested decreased MBOAT7 activity in that LPI content was elevated, and both total and arachidonoylated-PI were reduced. Surprisingly, MBOAT7 overexpression did not rescue the content of most arachidonoylated PI species but did normalize or increase the abundance of several oleate and linoleate-containing PI species. Free arachidonic acid was elevated but the MBOAT7 substrate arachidonoyl-CoA was found to be low in all NASH livers compared to low-fat fed mice, likely due to decreased expression of both long-chain acyl-CoA synthetases (ACSL) 1 and 4 in NASH livers compared to controls. ConclusionsThese results suggest MBOAT7 overexpression fails to measurably improve NASH pathology potentially due to insufficient abundance of its arachidonoyl-CoA substrate in fatty livers.

pathology↗

bioRxiv2020

MSDC-0602K, A Novel Insulin-Sensitizer Improves Insulinemia and Fatty Liver Disease Alone and in Addition to Liraglutide in Mice

Aims/hypothesisInsulin sensitizers and incretin mimetics are antidiabetic agents with vastly different mechanisms of action. Additionally, while thiazolidinedione (TZD) insulin sensitizers are associated with the side-effect of weight gain, glucagon-like peptide-1 receptor agonists (GLP-1RAs) can induce weight loss. We hypothesized that combination therapy with a novel TZD insulin sensitizer and the GLP-1RA Liraglutide would more significantly improve mouse models of diabetes and nonalcoholic steatohepatitis (NASH) compared to individual therapy. Methodsdb/db mice were treated with the novel TZD MSDC-0602K by oral gavage, Liraglutide (Lira) by s.c. injection, combination 0602K+Lira, or both vehicle solutions. Vehicle-treated db/+ mice were included as non-obese controls. To assess treatment effects on nonalcoholic fatty liver disease, MS-NASH mice were similarly treated with vehicle, either drug individually, or in combination. Lastly, islets were isolated from C57BL/6J mice to assess glucose-stimulated insulin secretion (GSIS). Results0602K-treated db/db mice displayed slight weight gain but completely corrected glycemia and markedly improved glucose tolerance. Lira slightly reduced body weights and modestly improved glycemia. 0602K+Lira combination still induced slight weight gain but completely corrected glycemia and improved glucose tolerance beyond lean db/+ levels. As expected, 0602K resulted in reduced plasma insulin, whereas Lira further increased the hyperinsulinemia of db/db mice. Surprisingly, 0602K+Lira treatment reduced plasma insulin and C-peptide to the same extent as mice treated with 0602K alone. 0602K did not directly reduce GSIS in isolated islets, thus the reduced insulinemia with 0602K is likely compensatory due to improved insulin action. In the MS-NASH mouse model, both 0602K or Lira alone improved plasma ALT and AST, and liver histology, but more significant improvements were observed with 0602K+Lira combination therapy. 0602K or 0602K+Lira also increased pancreatic insulin content in both db/db and MS-NASH mice. ConclusionsMSDC-0602K corrected glycemia and reduced insulinemia when given alone, or in combination with Lira. However, 0602K+Lira combination more significantly improved glucose tolerance in db/db mice, and more significantly improved liver histology in MS-NASH mice.

pharmacology and toxicology↗

bioRxiv2020

Ketogenic Diet Prevents Heart Failure from Defective Mitochondrial Pyruvate Metabolism

The myocardium is metabolically flexible and can use fatty acids, glucose, lactate/pyruvate, ketones, or amino acids to fuel mechanical work. However, impaired metabolic flexibility is associated with cardiac dysfunction in conditions including diabetes and heart failure. The mitochondrial pyruvate carrier (MPC) is required for pyruvate metabolism and is composed of a hetero-oligomer of two proteins known as MPC1 and MPC2. Interestingly, MPC1 and MPC2 expression is downregulated in failing human hearts and in a mouse model of heart failure. Mice with cardiac-specific deletion of MPC2 (CS-MPC2-/-) exhibited loss of both MPC2 and MPC1 proteins and reduced pyruvate-stimulated mitochondrial respiration. CS-MPC2-/- mice exhibited normal cardiac size and function at 6-weeks old, but progressively developed cardiac dilation and contractile dysfunction thereafter. Feeding CS-MPC2-/- mice a ketogenic diet (KD) completely prevented or reversed the cardiac remodeling and dysfunction. Other diets with higher fat content and enough carbohydrate to limit ketosis also improved heart failure in CS-MPC2-/- mice, but direct ketone body provisioning provided only minor improvements in cardiac remodeling. Finally, KD was also able to prevent further remodeling in an ischemic, pressure-overload mouse model of heart failure. In conclusion, loss of mitochondrial pyruvate utilization leads to dilated cardiomyopathy that can be corrected by a ketogenic diet.

physiology↗