Rapamycin Ameliorates Age-Dependent Obesity Associated with Increased mTOR Signaling in Hypothalamic POMC Neurons

The prevalence of obesity in older people is the leading cause of metabolic syndromes. Central neurons serving as homeostatic sensors for body-weight control include hypothalamic neurons that express pro-opiomelanocortin (POMC) or neuropeptide-Y (NPY) and agouti-related protein (AgRP). Here, we report an age-dependent increase of mammalian target of rapamycin (mTOR) signaling in POMC neurons that elevates the ATP-sensitive potassium (K(ATP)) channel activity cell-autonomously to silence POMC neurons. Systemic or intracerebral administration of the mTOR inhibitor rapamycin causes weight loss in old mice. Intracerebral rapamycin infusion into old mice enhances the excitability and neurite projection of POMC neurons, thereby causing?a reduction of food intake and body weight. Conversely, young mice lacking the mTOR-negative regulator TSC1 in POMC neurons, but not those lacking TSC1 in NPY/AgRP neurons, were obese. Our study reveals that an increase in mTOR signaling in hypothalamic POMC neurons contributes to age-dependent obesity. VIDEO ABSTRACT:     

Glucose Regulates Hypothalamic Long-chain Fatty Acid Metabolism via AMP-activated Kinase (AMPK) in Neurons and Astrocytes

Hypothalamic controls of energy balance rely on the detection of circulating nutrients such as glucose and long-chain fatty acids (LCFA) by the mediobasal hypothalamus (MBH). LCFA metabolism in the MBH plays a key role in the control of food intake and glucose homeostasis, yet it is not known if glucose regulates LCFA oxidation and esterification in the MBH and, if so, which hypothalamic cell type(s) and intracellular signaling mechanisms are involved. The aim of this study was to determine the impact of glucose on LCFA metabolism, assess the role of AMP-activated Kinase (AMPK), and to establish if changes in LCFA metabolism and its regulation by glucose vary as a function of the kind of LCFA, cell type, and brain region. We show that glucose inhibits palmitate oxidation via AMPK in hypothalamic neuronal cell lines, primary hypothalamic astrocyte cultures, and MBH slices ex vivo but not in cortical astrocytes and slice preparations. In contrast, oleate oxidation was not affected by glucose or AMPK inhibition in MBH slices. In addition, our results show that glucose increases palmitate, but not oleate, esterification into neutral lipids in neurons and MBH slices but not in hypothalamic astrocytes. These findings reveal for the first time the metabolic fate of different LCFA in the MBH, demonstrate AMPK-dependent glucose regulation of LCFA oxidation in both astrocytes and neurons, and establish metabolic coupling of glucose and LCFA as a distinguishing feature of hypothalamic nuclei critical for the control of energy balance.     

Involvement of the S100B in cAMP-Induced Cytoskeleton Remodeling in Astrocytes: A Study Using TRTK-12 in Digitonin-Permeabilized Cells

1. Stellation of astrocytes in culture involves a complex rearrangement of microfilaments, intermediate filaments, and microtubules, which reflects in part the plasticity of these cells observed during development or after injury.2. An astrocytic calcium-binding protein, S100B, has been implicated in the regulation of plasticity due to its ability to interact with cytoskeletal proteins.3. We used digitonin-permeabilized astrocytes to introduce TRTK-12, a peptide that binds to the C-terminal of S100B and blocks its interaction with cytoskeletal proteins.4. TRTK-12 was able to block cAMP-induced astrocyte stellation and this effect was dependent on the concentration of the peptide. These results support the idea that S100B has a modulatory role on astrocyte morphology.     

Metabolic Plasticity of Astrocytes

Journal of Evolutionary Biochemistry and Physiology - Astrocytes are most abundant glial cells in the central nervous system that reside between the microvascular network of the brain and neuronal...     

Astrocytes and Epilepsy

Neurochemical Research - Changes in astrocyte channels, transporters, and metabolism play a critical role in seizure generation and epilepsy. In particular, alterations in astrocyte potassium,...     

Neurochemical effects of choline supplementation

Whether or not the brain can use supplemental choline to enhance the synthesis of acetylcholine (ACh) is an important consideration for assessing the merits of using choline or phosphatidylcholine (lecithin) for the treatment of neuropsychiatric disorders postulated to involve hypocholinergic activity. While it is well documented that administered choline is incorporated into ACh, the ability of supplemental choline to increase the synthesis and release of ACh has been questionable. Studies in my laboratory have demonstrated that acute or chronic choline supplementation does not, by itself, enhance the levels of ACh in brain under normal biochemical and physiological conditions. However, supplemental choline prevents the depletion of ACh in brain induced by numerous pharmacological agents that increase the firing of cholinergic neurons. Since the levels of free choline in brains from supplemented rats were not different from controls prior to drug challenge, evidence suggested that the observed effects of choline were mediated by alterations in the mobilization of choline from choline-containing compounds. Studies investigating the release of choline from brain indicated that more choline was released per unit time in tissues from choline-supplemented rats than from controls. In addition, brain tissue from choline-supplemented rats had increased concentrations of total lipid phosphorus as compared with controls. Hence, although choline supplementation does not alter the levels of ACh in brain under normal conditions, it does appear to support ACh synthesis during drug-induced increases in neuronal activity, an effect most likely mediated by alterations in the metabolism of choline-containing phospholipids.     

Neurochemical effects ofl-pyroglutamic acid

The effect ofl-pyroglutamic acid, a metabolite that accumulates in pyroglutamic aciduria, on different neurochemical parameters was investigated in adult male Wistar rats. Glutamate binding, adenylate cyclase activity and G protein coupling to adenylate cyclase were assayed in the presence of the acid.l-pyroglutamic acid decreased Na⁺-dependent and Na⁺-independent glutamate binding Basal and GMP-PNP stimulated adenylate cyclase activity were not affected by the acid. Furthermore, rats received unilateral intrastriatal injections of 10–300 nmol of bufferedl-pyroglutamic acid. Vehicle (0.25 M Tris-Cl, pH 7.35–7.4) was injected into the contralateral striatum. Neurotoxic damage was assessed seven days after the injection by histological examination and by weighing both cerebral hemispheres. No difference in histology or weight could be identified between hemispheres. These results suggest that, although capable of interfering with glutamate binding, pyroglutamate did not cause a major lesion in the present model of neurotoxicity.     

Neurochemical correlates of spasticity.

Dogs were made paraplegic by complete mid-thoracic spinal cord transection. The content of glycine, glutamate, aspartate, and γ-aminobutyric acid were determined in ventral and central grey matter from the lumbar enlargement of the spinal cord at 1, 3 and 8 weeks after transection. A rapid decrease in the content of aspartate and glycine accompanied the onset of spasticity. By the eight week post-transection, aspartate and glycine had decreased to less than 50% of control levels.     

Age-Dependent Impairment of Mitochondrial Function in Primate Brain

Abstract: It has been hypothesized that some of the functional impairments associated with aging are the result of increasing oxidative damage to mitochondrial DNA that produces defects in oxidative phosphorylation. To test this hypothesis, we examined the enzymes that catalyze oxidative phosphorylation in crude mitochondrial preparations from frontoparietal cortex of 20 rhesus monkeys (5-34 years old). Samples were assayed for complex I, complex II-III, complex IV, complex V, and citrate synthase activities. When enzyme activities were corrected for citrate synthase activities (to account for variable degrees of mitochondrial enrichment), linear regression analysis demonstrated a significant negative correlation of the activities of complex I (p < 0.002) and complex IV (p < 0.03) with age but no significant change in complex II-III or complex V activities. Relative to animals 6.9 ± 0.9 years old (n = 7), the citrate synthase-corrected activity of complex I was reduced by 17% in animals 22.5 ± 0.9 years old (n = 6) (p < 0.05) and by 22% in animals 30.7 ± 0.9 years old (n = 7) (p < 0.01). Similar age-related reductions in the activities of complexes I and IV were obtained when enzyme activities were corrected for complex II-III activity. These findings show an age-associated progressive impairment of mitochondrial complex I and complex IV activities in cerebral cortices of primates.