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Li S, Mbong EF, John DT, Terasaka T, Li D, Lawson MA. Induction of Stress Signaling In Vitro and Suppression of Gonadotropin Secretion by Free Fatty Acids in Female Mouse Gonadotropes. Endocrinology 2018; 159:1074-1087. [PMID: 29315384 PMCID: PMC5793794 DOI: 10.1210/en.2017-00638] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2017] [Accepted: 12/28/2017] [Indexed: 12/20/2022]
Abstract
An emerging body of evidence supports the concept that the pituitary is a site for integration of multiple physiological and metabolic signals that inform and modulate endocrine pathways. Multiple endocrine mediators of energy balance and adiposity are known to impinge on the neuroendocrine axis regulating reproduction. Observations in humans show that obesity is correlated with decreased gonadotropin secretion, and studies have also suggested that pituitary sensitivity to stimulation by gonadotropin-releasing hormone (GnRH) is decreased in obese individuals. Free fatty acids are a potential mediator of adiposity and energy balance, but their impact as an endocrine modulator of pituitary function has not been closely examined. We evaluated the impact of free fatty acids on a pituitary gonadotrope cell line and in primary pituitary cultures of female mice. We show that increasing physiologically relevant doses of the monounsaturated ω-9 fatty acid oleate induces cellular stress and increases production of reactive oxygen species in a mouse gonadotrope cell line. In contrast, the unsaturated ω-3 α-linolenic and ω-6 linoleic fatty acids do not have this effect. Additionally, oleate can activate immediate-early gene expression independent of GnRH stimulation but has a negative impact on GnRH induction and expression of the gonadotropin subunit gene Lhb. Further, oleate suppresses gonadotropin secretion in response to pulsatile stimulation by GnRH. These results indicate that free fatty acids can directly alter gonadotropin gene expression and secretion in response to GnRH and may provide a link between energy sensing and reproduction.
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Affiliation(s)
- Song Li
- Department of Reproductive Medicine, University of California, San Diego, La Jolla, California 92093
- Neonatal Intensive Care Unit, Dongguan Eighth People’s Hospital, Dongguan 523000, People’s Republic of China
| | - Ekaette F. Mbong
- Department of Reproductive Medicine, University of California, San Diego, La Jolla, California 92093
| | - Denise T. John
- Department of Reproductive Medicine, University of California, San Diego, La Jolla, California 92093
| | - Tomohiro Terasaka
- Department of Reproductive Medicine, University of California, San Diego, La Jolla, California 92093
| | - Danmei Li
- Department of Reproductive Medicine, University of California, San Diego, La Jolla, California 92093
| | - Mark A. Lawson
- Department of Reproductive Medicine, University of California, San Diego, La Jolla, California 92093
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Gierut JJ, Wood LB, Lau KS, Lin YJ, Genetti C, Samatar AA, Lauffenburger DA, Haigis KM. Network-level effects of kinase inhibitors modulate TNF-α-induced apoptosis in the intestinal epithelium. Sci Signal 2015; 8:ra129. [PMID: 26671150 DOI: 10.1126/scisignal.aac7235] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Individual signaling pathways operate in the context of the broader signaling network. Thus, the response of a cell to signals from the environment is affected by the state of the signaling network, such as the clinically relevant example of whether some components in the network are inhibited. The cytokine tumor necrosis factor-α (TNF-α) promotes opposing cellular behaviors under different conditions; the outcome is influenced by the state of the network. For example, in the mouse intestinal epithelium, inhibition of the mitogen-activated protein kinase (MAPK) kinase MEK alters the timing of TNF-α-induced apoptosis. We investigated whether MAPK signaling directly influences TNF-α-induced apoptosis or whether network-level effects secondary to inhibition of the MAPK pathway alter the cellular response. We found that inhibitors of the MAPK kinase kinase Raf, MEK, or extracellular signal-regulated kinase (ERK) exerted distinct effects on the timing and magnitude of TNF-α-induced apoptosis in the mouse intestine. Furthermore, even different MEK inhibitors exerted distinct effects; one, CH5126766, potentiated TNF-α-induced apoptosis, and the others reduced cell death. Computational modeling and experimental perturbation identified the kinase Akt as the primary signaling node that enhanced apoptosis in the context of TNF-α signaling in the presence of CH5126766. Our work emphasizes the importance of integrated network signaling in specifying cellular behavior in response to experimental or therapeutic manipulation. More broadly, this study highlighted the importance of considering the network-level effects of pathway inhibitors and showed the distinct effects of inhibitors that share the same target.
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Affiliation(s)
- Jessica J Gierut
- Cancer Research Institute, Beth Israel Deaconess Cancer Center and Department of Medicine, Harvard Medical School, Boston, MA 02215, USA
| | - Levi B Wood
- Cancer Research Institute, Beth Israel Deaconess Cancer Center and Department of Medicine, Harvard Medical School, Boston, MA 02215, USA.,Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Ken S Lau
- Department of Chemical and Physical Biology, Vanderbilt University Medical Center, Nashville, TN, 37232, USA.,Epithelial Biology Center and Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Yi-Jang Lin
- Cancer Research Institute, Beth Israel Deaconess Cancer Center and Department of Medicine, Harvard Medical School, Boston, MA 02215, USA
| | - Casie Genetti
- Cancer Research Institute, Beth Israel Deaconess Cancer Center and Department of Medicine, Harvard Medical School, Boston, MA 02215, USA
| | | | - Douglas A Lauffenburger
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Kevin M Haigis
- Cancer Research Institute, Beth Israel Deaconess Cancer Center and Department of Medicine, Harvard Medical School, Boston, MA 02215, USA
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Tong M, Longato L, Ramirez T, Zabala V, Wands JR, de la Monte SM. Therapeutic reversal of chronic alcohol-related steatohepatitis with the ceramide inhibitor myriocin. Int J Exp Pathol 2013; 95:49-63. [PMID: 24456332 DOI: 10.1111/iep.12052] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2013] [Accepted: 08/18/2013] [Indexed: 12/13/2022] Open
Abstract
Alcohol-related liver disease (ALD) is associated with steatohepatitis and insulin resistance. Insulin resistance impairs growth and disrupts lipid metabolism in hepatocytes. Dysregulated lipid metabolism promotes ceramide accumulation and oxidative stress, leading to lipotoxic states that activate endoplasmic reticulum (ER) stress pathways and worsen inflammation and insulin resistance. In a rat model of chronic alcohol feeding, we characterized the effects of a ceramide inhibitor, myriocin, on the histopathological and ultrastructural features of steatohepatitis, and the biochemical and molecular indices of hepatic steatosis, insulin resistance and ER stress. Myriocin reduced the severity of alcohol-related steatohepatitis including the abundance and sizes of lipid droplets and mitochondria, inflammation and architectural disruption of the ER. In addition, myriocin-mediated reductions in hepatic lipid and ceramide levels were associated with constitutive enhancement of insulin signalling through the insulin receptor and IRS-2, reduced hepatic oxidative stress and modulation of ER stress signalling mechanisms. In conclusion, ceramide accumulation in liver mediates tissue injury, insulin resistance and lipotoxicity in ALD. Reducing hepatic ceramide levels can help restore the structural and functional integrity of the liver in chronic ALD due to amelioration of insulin resistance and ER stress. However, additional measures are needed to protect the liver from alcohol-induced necroinflammatory responses vis-à-vis continued alcohol abuse.
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Affiliation(s)
- Ming Tong
- Liver Research Center, Division of Gastroenterology, Department of Medicine, Rhode Island Hospital and the Warren Alpert Medical School of Brown University, Providence, RI, USA
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Lizarazo D, Zabala V, Tong M, Longato L, de la Monte SM. Ceramide inhibitor myriocin restores insulin/insulin growth factor signaling for liver remodeling in experimental alcohol-related steatohepatitis. J Gastroenterol Hepatol 2013; 28:1660-8. [PMID: 23802886 PMCID: PMC4551508 DOI: 10.1111/jgh.12291] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 05/19/2013] [Indexed: 12/13/2022]
Abstract
BACKGROUND AND AIM Alcohol-related liver disease (ALD) is mediated in part by insulin resistance. Attendant dysregulation of lipid metabolism increases accumulation of hepatic ceramides that worsen insulin resistance and compromise the structural and functional integrity of the liver. Insulin and insulin growth factor (IGF) stimulate aspartyl-asparaginyl-β-hydroxylase (AAH), which promotes cell motility needed for structural maintenance and remodeling of the liver. AAH mediates its effects by activating Notch, and in ALD, insulin/IGF signaling, AAH, and Notch are inhibited. METHOD To test the hypothesis that in ALD, hepatic ceramide load contributes to impairments in insulin, AAH, and Notch signaling, control and chronic ethanol-fed adult Long-Evans rats were treated with myriocin, an inhibitor of serine palmitoyl transferase. Livers were used to assess steatohepatitis, insulin/IGF pathway activation, and expression of AAH-Notch signaling molecules. RESULTS Chronic ethanol-fed rats had steatohepatitis with increased ceramide levels; impairments in signaling through the insulin receptor, insulin receptor substrate, and Akt; and decreased expression of AAH, Notch, Jagged, Hairy-Enhancer of Split-1, hypoxia-inducible factor 1α, and proliferating cell nuclear antigen. Myriocin abrogated many of these adverse effects of ethanol, particularly hepatic ceramide accumulation, steatohepatitis, and impairments of insulin signaling through Akt, AAH, and Notch. CONCLUSIONS In ALD, the histopathology and impairments in insulin/IGF responsiveness can be substantially resolved by ceramide inhibitor treatments, even in the context of continued chronic ethanol exposure.
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Affiliation(s)
- Diana Lizarazo
- Liver Research Center, Division of Gastroenterology and Department of Medicine, Rhode Island Hospital and the Warren Alpert Medical School of Brown University, Providence, RI, USA
| | - Valerie Zabala
- Liver Research Center, Division of Gastroenterology and Department of Medicine, Rhode Island Hospital and the Warren Alpert Medical School of Brown University, Providence, RI, USA
| | - Ming Tong
- Liver Research Center, Division of Gastroenterology and Department of Medicine, Rhode Island Hospital and the Warren Alpert Medical School of Brown University, Providence, RI, USA
| | - Lisa Longato
- Liver Research Center, Division of Gastroenterology and Department of Medicine, Rhode Island Hospital and the Warren Alpert Medical School of Brown University, Providence, RI, USA
| | - Suzanne M. de la Monte
- Liver Research Center, Divisions of Gastroenterology and Neuropathology and Departments of Medicine, Pathology, Neurology, and Neurosurgery, Rhode Island Hospital and the Warren Alpert Medical School of Brown University, Providence, RI, USA
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Ramirez T, Tong M, Chen WC, Nguyen QG, Wands JR, de la Monte SM. Chronic alcohol-induced hepatic insulin resistance and endoplasmic reticulum stress ameliorated by peroxisome-proliferator activated receptor-δ agonist treatment. J Gastroenterol Hepatol 2013; 28:179-87. [PMID: 22988930 PMCID: PMC4406771 DOI: 10.1111/j.1440-1746.2012.07256.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 08/10/2012] [Indexed: 12/13/2022]
Abstract
BACKGROUND AND AIM Chronic alcoholic liver disease is associated with hepatic insulin resistance, dysregulated lipid metabolism with increased toxic lipid (ceramide) accumulation, lipid peroxidation, and oxidative and endoplasmic reticulum (ER) stress. Peroxisome-proliferator activated receptor (PPAR) agonists are insulin sensitizers that can restore hepatic insulin responsiveness in both alcohol and non-alcohol-related steatohepatitis. Herein, we demonstrate that treatment with a PPAR-δ agonist enhances insulin signaling and reduces the severities of ER stress and ceramide accumulation in an experimental model of ethanol-induced steatohepatitis. METHODS Adult male Long Evans rats were pair fed with isocaloric liquid diets containing 0% or 37% ethanol (caloric) for 8 weeks. After 3 weeks on the diets, rats were treated with vehicle or PPAR-δ agonist twice weekly by i.p. injection. RESULTS Ethanol-fed rats developed steatohepatitis with inhibition of signaling through the insulin and insulin-like growth factor-1 receptors, and Akt activated pathways. Despite continued ethanol exposure, PPAR-δ agonist co-treatments increased Akt activation, reduced multiple molecular indices of ER stress and steatohepatitis. CONCLUSIONS These results suggest that PPAR-δ agonist rescue of chronic alcoholic liver disease is mediated by enhancement of insulin signaling through Akt/metabolic pathways that reduce lipotoxicity and ER stress.
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Affiliation(s)
- Teresa Ramirez
- Liver Research Center and Department of Medicine, Rhode Island Hospital and Warren Alpert Medical School of Brown University, Providence, Rhode Island 02903, USA
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de la Monte SM, Re E, Longato L, Tong M. Dysfunctional pro-ceramide, ER stress, and insulin/IGF signaling networks with progression of Alzheimer's disease. J Alzheimers Dis 2012; 30 Suppl 2:S217-29. [PMID: 22297646 DOI: 10.3233/jad-2012-111728] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
In Alzheimer's disease (AD), brain insulin and insulin-like growth factor (IGF) resistance and deficiency begin early, and worsen with severity of disease. The factors mediating progression of brain insulin/IGF resistance in AD are not well understood. We hypothesize that AD progression is mediated via negative cross-talk that promotes toxic ceramide generation and endoplasmic reticulum (ER) stress. The rationale is that insulin resistance dysregulates lipid metabolism and promotes ceramide accumulation, and thereby increases inflammation and stress. Consequences include disruption of cytoskeletal function and AβPP-Aβ secretion. The present study correlates AD stage with activation of pro-ceramide genes, ceramide levels, and molecular indices of ER stress in postmortem human brain tissue. The results demonstrated that in AD, brain insulin/IGF resistance was associated with constitutive activation of multiple pro-ceramide genes, increased ceramide levels, and increased expression of pro-ER stress pathway genes and proteins. Expression of several pro-ceramide and pro-apoptotic ER stress pathway molecules increased with AD severity and brain insulin/IGF resistance. In contrast, ER stress molecules that help maintain homeostasis with respect to unfolded protein responses were mainly upregulated in the intermediate rather than late stage of AD. These findings support our hypothesis that in AD, a triangulated mal-signaling network initiated by brain insulin/IGF resistance is propagated by the dysregulation of ceramide and ER stress homeostasis, which themselves promote insulin resistance. Therefore, once established, this reverberating loop must be targeted using multi-pronged approaches to disrupt the AD neurodegeneration cascade.
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Affiliation(s)
- Suzanne M de la Monte
- Department of Pathology (Neuropathology), Rhode Island Hospital and The Warren Alpert Medical School of Brown University, Providence, RI, USA. Suzanne DeLaMonte
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Changes in food intake, metabolic parameters and insulin resistance are induced by an isoenergetic, medium-chain fatty acid diet and are associated with modifications in insulin signalling in isolated rat pancreatic islets. Br J Nutr 2012. [PMID: 23182275 DOI: 10.1017/s0007114512004576] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Long-chain fatty acids are capable of inducing alterations in the homoeostasis of glucose-stimulated insulin secretion (GSIS), but the effect of medium-chain fatty acids (MCFA) is poorly elucidated. In the present study, we fed a normoenergetic MCFA diet to male rats from the age of 1 month to the age of 4 months in order to analyse the effect of MCFA on body growth, insulin sensitivity and GSIS. The 45% MCFA substitution of whole fatty acids in the normoenergetic diet impaired whole body growth and resulted in increased body adiposity and hyperinsulinaemia, and reduced insulin-mediated glucose uptake in skeletal muscle. In addition, the isolated pancreatic islets from the MCFA-fed rats showed impaired GSIS and reduced protein kinase Ba (AKT1) protein expression and extracellular signal-related kinase isoforms 1 and 2 (ERK(1/2)) phosphorylation, which were accompanied by increased cellular death. Furthermore, there was a mildly increased cholinergic sensitivity to GSIS. We discuss these findings in further detail, and advocate that they might have a role in the mechanistic pathway leading to the compensatory hyperinsulinaemic status found in this animal model.
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Ramirez T, Longato L, Dostalek M, Tong M, Wands JR, de la Monte SM. Insulin resistance, ceramide accumulation and endoplasmic reticulum stress in experimental chronic alcohol-induced steatohepatitis. Alcohol Alcohol 2012; 48:39-52. [PMID: 22997409 DOI: 10.1093/alcalc/ags106] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
AIMS Chronic alcohol abuse causes steatohepatitis with insulin resistance, which impairs hepatocellular growth, survival and metabolism. However, growing evidence supports the concept that progressive alcohol-related liver injury may be mediated by concurrent mal-signaling through other networks that promote insulin resistance, e.g. pro-inflammatory, pro-ceramide and endoplasmic reticulum (ER) stress cascades. METHODS Using the Long Evans rat model of chronic ethanol feeding, we characterized the histopathologic and ultrastructural features of steatohepatitis in relation to biochemical and molecular indices of tissue injury, inflammation, insulin resistance, dysregulated lipid metabolism and ER stress. RESULTS Chronic steatohepatitis with early chicken-wire fibrosis was associated with enlargement of mitochondria and disruption of ER structure by electron microscopy, elevated indices of lipid storage, lipid peroxidation and DNA damage, increased activation of pro-inflammatory cytokines, impaired signaling through the insulin receptor (InR), InR substrate-1, Akt, ribosomal protein S6 kinase and proline-rich Akt substrate 40 kDa, glycogen synthase kinase 3β activation and constitutive up-regulation of ceramide and ER stress-related genes. Liquid chromatography coupled with tandem mass spectrometry demonstrated altered ceramide profiles with higher levels of C14 and C18, and reduced C16 species in ethanol-exposed livers. CONCLUSION The histopathologic and ultrastructural abnormalities in chronic alcohol-related steatohepatitis are associated with persistent hepatic insulin resistance and pro-inflammatory cytokine activation, dysregulated lipid metabolism with altered ceramide profiles and both ER and oxidative stress. Corresponding increases in lipid peroxidation, DNA damage and protein carbonylation may have contributed to the chronicity and progression of disease. The findings herein suggest that multi-pronged therapeutic strategies may be needed for effective treatment of chronic alcoholic liver disease in humans.
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Affiliation(s)
- Teresa Ramirez
- Liver Research Center, Divisions of Gastroenterology and Neuropathology, Departments of Medicine, Rhode Island Hospital and Warren Alpert Medical School of Brown University, Claverick Street, Providence, RI 02903, USA
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Insulin resistance, ceramide accumulation, and endoplasmic reticulum stress in human chronic alcohol-related liver disease. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2012; 2012:479348. [PMID: 22577490 PMCID: PMC3347750 DOI: 10.1155/2012/479348] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/15/2011] [Revised: 12/28/2011] [Accepted: 01/10/2012] [Indexed: 12/14/2022]
Abstract
Background. Chronic alcohol-related liver disease (ALD) is mediated by insulin resistance, mitochondrial dysfunction, inflammation, oxidative stress, and DNA damage. Recent studies suggest that dysregulated lipid metabolism with accumulation of ceramides, together with ER stress potentiate hepatic insulin resistance and may cause steatohepatitis to progress. Objective. We examined the degree to which hepatic insulin resistance in advanced human ALD is correlated with ER stress, dysregulated lipid metabolism, and ceramide accumulation. Methods. We assessed the integrity of insulin signaling through the Akt pathway and measured proceramide and ER stress gene expression, ER stress signaling proteins, and ceramide profiles in liver tissue. Results. Chronic ALD was associated with increased expression of insulin, IGF-1, and IGF-2 receptors, impaired signaling through IGF-1R and IRS1, increased expression of multiple proceramide and ER stress genes and proteins, and higher levels of the C14, C16, C18, and C20 ceramide species relative to control. Conclusions. In human chronic ALD, persistent hepatic insulin resistance is associated with dysregulated lipid metabolism, ceramide accumulation, and striking upregulation of multiple ER stress signaling molecules. Given the role of ceramides as mediators of ER stress and insulin resistance, treatment with ceramide enzyme inhibitors may help reverse or halt progression of chronic ALD.
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de la Monte SM. Triangulated mal-signaling in Alzheimer's disease: roles of neurotoxic ceramides, ER stress, and insulin resistance reviewed. J Alzheimers Dis 2012; 30 Suppl 2:S231-49. [PMID: 22337830 PMCID: PMC4550324 DOI: 10.3233/jad-2012-111727] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Ceramides are lipid signaling molecules that cause cytotoxicity and cell death mediated by insulin resistance, inflammation, and endoplasmic reticulum (ER) stress. However, insulin resistance dysregulates lipid metabolism, which promotes ceramide accumulation with attendant inflammation and ER stress. Herein, we discuss two major pathways, extrinsic and intrinsic, that converge and often overlap in propagating AD-type neurodegeneration via a triangulated mal-signaling network. First, we review evidence that systemic insulin resistance diseases linked to obesity, type 2 diabetes, and non-alcoholic steatohepatitis promote neurodegeneration. Mechanistically, we propose that toxic ceramides generated in extra-CNS tissues (e.g., liver) get released into peripheral blood, and subsequently transit across the blood-brain barrier into the brain where they induce brain insulin resistance, inflammation, and cell death (extrinsic pathway). Then we discuss the role of the intrinsic pathway of neurodegeneration which is mediated by endogenous or primary brain insulin/IGF resistance, and impairs neuronal and oligodendrocyte survival, energy metabolism, membrane integrity, cytoskeletal function, and AβPP-Aβ secretion. The end result is increased ER stress and ceramide generation, which exacerbate brain insulin resistance, cell death, myelin degeneration, and neuroinflammation. Altogether, the data suggest that the triangulated mal-signaling network mediated by toxic ceramides, ER stress, and insulin resistance should be targeted to disrupt positive feedback loops that drive the AD neurodegeneration cascade.
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Affiliation(s)
- Suzanne M de la Monte
- Department of Pathology (Neuropathology), Rhode Island Hospital and The Warren Alpert Medical School of Brown University, Providence, RI, USA. SuzanneDeLaMonte
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de la Monte SM. Therapeutic targets of brain insulin resistance in sporadic Alzheimer's disease. Front Biosci (Elite Ed) 2012. [PMID: 22201977 DOI: 10.2741/482] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Growing evidence supports roles for brain insulin and insulin-like growth factor (IGF) resistance and metabolic dysfunction in the pathogenesis of Alzheimer's disease (AD). Whether the underlying problem stems from a primary disorder of central nervous system (CNS) neurons and glia, or secondary effects of systemic diseases such as obesity, Type 2 diabetes, or metabolic syndrome, the end-results include impaired glucose utilization, mitochondrial dysfunction, increased oxidative stress, neuroinflammation, and the propagation of cascades that result in the accumulation of neurotoxic misfolded, aggregated, and ubiquitinated fibrillar proteins. This article reviews the roles of impaired insulin and IGF signaling to AD-associated neuronal loss, synaptic disconnection, tau hyperphosphorylation, amyloid-beta accumulation, and impaired energy metabolism, and discusses therapeutic strategies and lifestyle approaches that could be used to prevent, delay the onset, or reduce the severity of AD. Finally, it is critical to recognize that AD is heterogeneous and has a clinical course that fully develops over a period of several decades. Therefore, early and multi-modal preventive and treatment approaches should be regarded as essential.
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Affiliation(s)
- Suzanne M de la Monte
- Department of Neurology, Rhode Island Hospital and Alpert Medical School of Brown University, Providence, RI, USA.
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de la Monte SM, Longato L, Tong M, DeNucci S, Wands JR. The liver-brain axis of alcohol-mediated neurodegeneration: role of toxic lipids. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2009; 6:2055-75. [PMID: 19742171 PMCID: PMC2738898 DOI: 10.3390/ijerph6072055] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/24/2009] [Accepted: 07/16/2009] [Indexed: 12/12/2022]
Abstract
Alcohol abuse causes progressive toxicity and degeneration in liver and brain due to insulin resistance, which exacerbates oxidative stress and pro-inflammatory cytokine activation. Alcohol-induced steatohepatitis promotes synthesis and accumulation of ceramides and other toxic lipids that cause insulin resistance. Ceramides can readily cross the blood-brain barrier, and ceramide exposure causes neurodegeneration with insulin resistance and oxidative stress, similar to the effects of alcohol. Therefore, in addition to its direct neurotoxic effects, alcohol misuse establishes a liver-brain axis of neurodegeneration mediated by toxic lipid trafficking across the blood-brain barrier, leading to progressive white matter degeneration and cognitive impairment.
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Short-term modulation of extracellular signal-regulated kinase 1/2 and stress-activated protein kinase/c-Jun NH2-terminal kinase in pancreatic islets by glucose and palmitate: possible involvement of ceramide. Pancreas 2009; 38:585-92. [PMID: 19295452 DOI: 10.1097/mpa.0b013e31819fef03] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
OBJECTIVES The effect of glucose and palmitate on the phosphorylation of proteins associated with cell growth and survival (extracellular signal-regulated kinase 1/2 [ERK1/2] and stress-activated protein kinase/c-Jun NH2-terminal kinase [SAPK/JNK]) and on the expression of immediate early genes was investigated. METHODS Groups of freshly isolated rat pancreatic islets were incubated in 10-mmol/L glucose with palmitate, LY294002, or fumonisin B1 for the measurement of the phosphorylation and the content of ERK1/2, JNK/SAPK, and v-akt murine thymoma viral oncongene (AKT) (serine 473) by immunoblotting. The expressions of the immediate early genes, c-fos and c-jun, were evaluated by reverse transcription-polymerase chain reaction. RESULTS Glucose at 10 mmol/L induced ERK1/2 and AKT phosphorylations and decreased SAPK/JNK phosphorylation. Palmitate (0.1 mmol/L) abolished the glucose effect on ERK1/2, AKT, and SAPK/JNK phosphorylations. LY294002 caused a similar effect. The inhibitory effect of palmitate on glucose-induced ERK1/2 and AKT phosphorylation changes was not observed in the presence of fumonisin B1. Glucose increased c-fos and decreased c-jun expressions. Palmitate and LY294002 abolished these latter glucose effects. The presence of fumonisin B1 abolished the effect induced by palmitate on c-jun expression. CONCLUSIONS Our results suggest that short-term changes of mitogen-activated protein kinase and AKT signaling pathways and c-fos and c-jun expressions caused by glucose are abolished by palmitate through phosphatidylinositol 3-kinase inhibition via ceramide synthesis.
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