Pharmacological SERCA activation limits diet-induced steatohepatitis and restores liver metabolic function in mice.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common form of liver disease and poses significant health risks to patients who progress to metabolic dysfunction-associated steatohepatitis (MASH). Fatty acid (FA) overload alters endoplasmic reticulum (ER) calcium stores and induces mitochondrial oxidative stress in hepatocytes, leading to hepatocellular inflammation and apoptosis. Obese mice have impaired liver sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) function, which normally maintains intracellular calcium homeostasis by transporting Ca2+ ions from the cytoplasm to ER. We hypothesized that restoration of SERCA activity would improve diet-induced steatohepatitis in mice by limiting ER stress and mitochondrial dysfunction. Wild-type and melanocortin-4 receptor knockout (Mc4r-/-) mice were placed on either chow or Western diet (WD) for 8 weeks. Half of the WD-fed mice were administered CDN1163 to activate SERCA, which reduced liver fibrosis and inflammation. SERCA activation also restored glucose tolerance and insulin sensitivity, improved histological markers of MASH, increased expression of antioxidant enzymes, and decreased expression of oxidative stress and ER stress genes. CDN1163 decreased hepatic citric acid cycle flux and liver pyruvate cycling, enhanced expression of mitochondrial respiratory genes, and shifted hepatocellular [NADH]/[NAD+] and [NADPH]/[NADP+] ratios to a less oxidized state, which was associated with elevated polyunsaturated fatty acid (PUFA) content of liver lipids. In sum, the data demonstrate that pharmacological SERCA activation limits MASLD progression and prevents metabolic dysfunction induced by WD feeding in mice.

Alterations of Lipid Metabolism in the Heart in Spontaneously Hypertensive Rats Precedes Left Ventricular Hypertrophy and Cardiac Dysfunction.

Disturbances in cardiac lipid metabolism are associated with the development of cardiac hypertrophy and heart failure. Spontaneously hypertensive rats (SHRs), a genetic model of primary hypertension and pathological left ventricular (LV) hypertrophy, have high levels of diacylglycerols in cardiomyocytes early in development. However, the exact effect of lipids and pathways that are involved in their metabolism on the development of cardiac dysfunction in SHRs is unknown. Therefore, we used SHRs and Wistar Kyoto (WKY) rats at 6 and 18 weeks of age to analyze the impact of perturbations of processes that are involved in lipid synthesis and degradation in the development of LV hypertrophy in SHRs with age. Triglyceride levels were higher, whereas free fatty acid (FA) content was lower in the LV in SHRs compared with WKY rats. The expression of de novo FA synthesis proteins was lower in cardiomyocytes in SHRs compared with corresponding WKY controls. The higher expression of genes that are involved in TG synthesis in 6-week-old SHRs may explain the higher TG content in these rats. Adenosine monophosphate-activated protein kinase phosphorylation and peroxisome proliferator-activated receptor α protein content were lower in cardiomyocytes in 18-week-old SHRs, suggesting a lower rate of ß-oxidation. The decreased protein content of α/ß-hydrolase domain-containing 5, adipose triglyceride lipase (ATGL) activator, and increased content of G0/G1 switch protein 2, ATGL inhibitor, indicating a lower rate of lipolysis in the heart in SHRs. In conclusion, the present study showed that the development of LV hypertrophy and myocardial dysfunction in SHRs is associated with triglyceride accumulation, attributable to a lower rate of lipolysis and ß-oxidation in cardiomyocytes.

Multitissue 2H/13C flux analysis reveals reciprocal upregulation of renal gluconeogenesis in hepatic PEPCK-C-knockout mice.

The liver is the major source of glucose production during fasting under normal physiological conditions. However, the kidney may also contribute to maintaining glucose homeostasis in certain circumstances. To test the ability of the kidney to compensate for impaired hepatic glucose production in vivo, we developed a stable isotope approach to simultaneously quantify gluconeogenic and oxidative metabolic fluxes in the liver and kidney. Hepatic gluconeogenesis from phosphoenolpyruvate was disrupted via liver-specific knockout of cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C; KO). 2H/13C isotopes were infused in fasted KO and WT littermate mice, and fluxes were estimated from isotopic measurements of tissue and plasma metabolites using a multicompartment metabolic model. Hepatic gluconeogenesis and glucose production were reduced in KO mice, yet whole-body glucose production and arterial glucose were unaffected. Glucose homeostasis was maintained by a compensatory rise in renal glucose production and gluconeogenesis. Renal oxidative metabolic fluxes of KO mice increased to sustain the energetic and metabolic demands of elevated gluconeogenesis. These results show the reciprocity of the liver and kidney in maintaining glucose homeostasis by coordinated regulation of gluconeogenic flux through PEPCK-C. Combining stable isotopes with mathematical modeling provides a versatile platform to assess multitissue metabolism in various genetic, pathophysiological, physiological, and pharmacological settings.

In vivo2H/13C flux analysis in metabolism research.

Identifying the factors and mechanisms that regulate metabolism under normal and diseased states requires methods to quantify metabolic fluxes of live tissues within their physiological milieu. A number of recent developments have expanded the reach and depth of isotope-based in vivo flux analysis, which have in turn challenged existing dogmas in metabolism research. First, minimally invasive techniques of intravenous isotope infusion and sampling have advanced in vivo metabolic tracer studies in animal models and human subjects. Second, recent breakthroughs in analytical instrumentation have expanded the scope of isotope labeling measurements and reduced sample volume requirements. Third, innovative modeling approaches and publicly available software tools have facilitated rigorous analysis of sophisticated experimental designs involving multiple tracers and expansive metabolomics datasets. These developments have enabled comprehensive in vivo quantification of metabolic fluxes in specific tissues and have set the stage for integrated multi-tissue flux assays.