Mechanistic target of rapamycin (mTOR) is essential for cardiac development, growth, and function, but the role of mTOR in the regulation of cardiac metabolism and mitochondrial respiration is not well established. This study sought to determine cardiac metabolism and mitochondrial bioenergetics in mice with inducible deletion of mTOR in the adult heart. Doxycycline-inducible and cardiac-specific mTOR-deficient mice were generated by crossing cardiac-specific doxycycline-inducible tetO-Cre mice with mice harboring mTOR floxed alleles. Deletion of mTOR reduced mTORC1 and mTORC2 signaling after in vivo insulin stimulation. Maximum and minimum dP/dt measured by cardiac catheterization in vivo under anesthesia and cardiac output, cardiac power, and aortic pressure in ex vivo working hearts were unchanged, suggesting preserved cardiac function 4 wk after doxycycline treatment. However, myocardial palmitate oxidation was impaired, whereas glucose oxidation was increased. Consistent with reduced palmitate oxidation, expression of fatty acid metabolism genes fatty acid-binding protein 3, medium-chain acyl-CoA dehydrogenase, and hydroxyacyl-CoA dehydrogenase/3-ketoacyl-CoA thiolase/enoyl-CoA hydratase (trifunctional protein)-α and -β was reduced, and carnitine palmitoyl transferase-1 and -2 enzymatic activity was decreased. Mitochondrial palmitoyl carnitine respiration was diminished. However, mRNA for peroxisome proliferator-activated receptor-γ coactivator (PGC)-1α and -1β, protein levels of PGC-1α, and electron transport chain subunits, mitochondrial DNA, and morphology were unchanged. Also, pyruvate-supported and FCCP-stimulated respirations were unchanged, suggesting that mTOR deletion induces a specific defect in fatty acid utilization. In conclusion, mTOR regulates mitochondrial fatty acid utilization but not glucose utilization in the heart via mechanisms that are independent of changes in PGC expression.

GPR55, an orphan G-protein coupled receptor, is activated by lysophosphatidylinositol (LPI) and the endocannabinoid anandamide, as well as by other compounds including THC. Such signaling molecules are capable of modulating synaptic plasticity. LPI is a potent endogenous ligand of GPR55 and neither GPR55 nor LPIs’ functions in the brain are well understood. While endocannabinoids are well known to modulate brain synaptic plasticity, the potential role LPI could have on brain plasticity has never been demonstrated. Therefore, we examined not only GPR55 expression, but also the role its endogenous ligand could play in long-term potentiation, a common form of synaptic plasticity. Using quantitative RT-PCR, electrophysiology, and behavioral assays, we examined hippocampal GPR55 expression and function. qRT-PCR results indicate that GPR55 is expressed in hippocampi of both rats and mice. Immunohistochemistry and single cell PCR demonstrates GPR55 protein in pyramidal cells of CA1 and CA3 layers in the hippocampus. Application of the GPR55 endogenous agonist LPI to hippocampal slices of GPR55+/+ mice significantly enhanced CA1 LTP. This effect was absent in GPR55−/− mice, and blocked by the GPR55 antagonist CID 16020046. We also examined paired-pulse ratios of GPR55−/− and GPR55+/+ mice with or without LPI and noted significant enhancement in paired-pulse ratios by LPI in GPR55+/+ mice. Behaviorally, GPR55−/− and GPR55+/+ mice did not differ in memory tasks including novel object recognition, radial arm maze, or Morris water maze. However, performance on radial arm maze and elevated plus maze task suggests GPR55−/− mice have a higher frequency of immobile behavior. This is the first demonstration of LPI involvement in hippocampal synaptic plasticity.

Oxidative stress plays a central role in age‐related macular degeneration (AMD). Iron, a potent generator of hydroxyl radicals through the Fenton reaction, has been implicated in AMD. One easily oxidized molecule is docosahexaenoic acid (DHA), the most abundant polyunsaturated fatty acid in photoreceptor membranes. Oxidation of DHA produces toxic oxidation products including carboxyethylpyrrole (CEP) adducts, which are increased in the retinas of AMD patients. In this study, we hypothesized that deuterium substitution on the bis‐allylic sites of DHA in photoreceptor membranes could prevent iron‐induced retinal degeneration by inhibiting oxidative stress and lipid peroxidation. Mice were fed with either DHA deuterated at the oxidation‐prone positions (D‐DHA) or control natural DHA and then given an intravitreal injection of iron or control saline. Orally administered D‐DHA caused a dose‐dependent increase in D‐DHA levels in the neural retina and retinal pigment epithelium (RPE) as measured by mass spectrometry. At 1 week after iron injection, D‐DHA provided nearly complete protection against iron‐induced retinal autofluorescence and retinal degeneration, as determined by in vivo imaging, electroretinography, and histology. Iron injection resulted in carboxyethylpyrrole conjugate immunoreactivity in photoreceptors and RPE in mice fed with natural DHA but not D‐DHA. Quantitative PCR results were consistent with iron‐induced oxidative stress, inflammation, and retinal cell death in mice fed with natural DHA but not D‐DHA. Taken together, our findings suggest that DHA oxidation is central to the pathogenesis of iron‐induced retinal degeneration. They also provide preclinical evidence that dosing with D‐DHA could be a viable therapeutic strategy for retinal diseases involving oxidative stress.