Brain metabolism as a modulator of autophagy in neurodegeneration

Emerging evidence that autophagy serves as a sweeper for toxic materials in the brain gives us new insight into the pathophysiology of neurodegenerative diseases. Autophagy is important for maintaining cellular homeostasis associated with metabolism. Some neurodegenerative diseases such as Alzheimer׳s and Parkinson׳s diseases are accompanied by altered metabolism and autophagy in the brain. In this review, we discuss how hormones and nutrients regulate autophagy in the brain and affect neurodegeneration. This article is part of a Special Issue entitled SI:Autophagy. © 2016 Elsevier B.V.

D-chiro-inositol glycan reduces food intake by regulating hypothalamic neuropeptide expression via AKT-FoxO1 pathway

The regulation of food intake is important for body energy homeostasis. Hypothalamic insulin signaling decreases food intake by upregulating the expression of anorexigenic neuropeptides and downregulating the expression of orexigenic neuropeptides. INS-2, a Mn2+ chelate of 4-O-(2-amino-2-deoxy-β-d-galactopyranosyl)-3-O-methyl-d-chiro-inositol, acts as an insulin mimetic and sensitizer. We found that intracerebroventricular injection of INS-2 decreased body weight and food intake in mice. In hypothalamic neuronal cell lines, INS-2 downregulated the expression of neuropeptide Y (NPY), an orexigenic neuropeptide, but upregulated the expression of proopiomelanocortin (POMC), an anorexigenic neuropeptide, via modulation of the AKT-forkhead box-containing protein-O1 (FoxO1) pathway. Pretreatment of these cells with INS-2 enhanced the action of insulin on downstream signaling, leading to a further decrease in NPY expression and increase in POMC expression. These data indicate that INS-2 reduces food intake by regulating the expression of the hypothalamic neuropeptide genes through the AKT-FoxO1 pathway downstream of insulin. © 2016 Elsevier Inc. All rights reserved.

A translocator protein 18 kDa ligand, Ro5-4864, inhibits ATP-induced NLRP3 inflammasome activation

Ro5-4864 and PK11195, prototypical synthetic ligands of translocator protein 18 kDa (TSPO), have shown anti-inflammatory effects in several models of inflammatory diseases; however, their biochemical mechanisms remain poorly understood. Nod-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome activation as a part of the innate immune system, has been implicated in a variety of inflammatory diseases. Here, we demonstrate for the first time that TSPO ligands, especially Ro5-4864, potently suppressed ATP-induced NLRP3 inflammasome activation in THP-1 and BMDM cells. Detailed action mechanism was further investigated in THP-1 cells. Ro5-4864 efficiently attenuated NLRP3 translocation to mitochondria, inflammasome assembly/oligomerization, activation of caspase-1, and subsequent secretion of the mature forms of interleukin-1β and -18. Ro5-4864 also reduced the production of mitochondrial superoxide and preserved the mitochondrial membrane potential in ATP-treated cells, suggesting that Ro5-4864 may act on mitochondria or more upstream targets in NLRP3 inflammasome signaling. We also observed the distinct effects of the TSPO ligands between THP-1 monocytes and macrophages, which suggested different NLRP3 inflammasome signaling depending on cell type. Collectively, our novel findings demonstrate that Ro5-4864 effectively inhibited ATP-induced NLRP3 inflammasome activation through the prevention of mitochondrial perturbation. Our results indicate Ro5-4864 as a promising candidate for the treatment of NLRP3 inflammasome-related diseases. © 2016 Elsevier Inc. All rights reserved.

Extracts from Dendropanax morbifera Leaves Have Modulatory Effects on Neuroinflammation in Microglia

Dendropanax morbifera (D. morbifera), a species endemic to Korea, is largely distributed throughout the southern part of the country. Its leaves, stems, roots, and seeds have been used as a form of alternative medicine for various diseases and neurological disorders including paralysis, stroke, and migraine. However, the molecular mechanisms that underlie the remedial effects of D. morbifera remain largely unknown. In this paper, extracts from D. morbifera leaves were prepared using ethyl acetate as a solvent (abbreviated as DMLE). The modulatory effects of DMLE on neuroinflammation were studied in a lipopolysaccharide (LPS)-stimulated BV2 murine microglial cell line. Production of pro-inflammatory cytokines, activation of mitogen-activated protein kinases (MAPKs) and nuclear factor-kappa B (NF-κB), and different M1/M2 activation states of microglia were examined. DMLE treatment suppressed the production of pro-inflammatory cytokines including tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and nitric oxide (NO) in LPS-stimulated BV2 cells. DMLE treatment also attenuated the activation of MAPKs and NF-κB. In a novel discovery, we found that DMLE up-regulated the marker genes representing an alternative, anti-inflammatory M2 polarization, while suppressing the expression of the classical, pro-inflammatory M1 activation state genes. Here, we uncovered the cellular mechanisms underlying the beneficial effects of D. morbifera against neuroinflammation using BV2 microglia cells. These results strongly suggest that DMLE was able to counter the effects of LPS on BV2 cells via control of microglia polarization states. Additionally, study results indicated that DMLE may have therapeutic potential as a neuroinflammation-suppressing treatment for neurodegenerative diseases. © 2016 World Scientific Publishing Company.

Calpain Determines the Propensity of Adult Hippocampal Neural Stem Cells to Autophagic Cell Death Following Insulin Withdrawal

Programmed cell death (PCD) has significant effects on the function of neural stem cells (NSCs) during brain development and degeneration. We have previously reported that adult rat hippocampal neural stem (HCN) cells underwent autophagic cell death (ACD) rather than apoptosis following insulin withdrawal despite their intact apoptotic capabilities. Here, we report a switch in the mode of cell death in HCN cells with calpain as a critical determinant. In HCN cells, calpain 1 expression was barely detectable while calpain 2 was predominant. Inhibition of calpain in insulin-deprived HCN cells further augmented ACD. In contrast, expression of calpain 1 switched ACD to apoptosis. The proteasome inhibitor lactacystin blocked calpain 2 degradation and elevated the intracellular Ca2+ concentration. In combination, these effects potentiated calpain activity and converted the mode of cell death to apoptosis. Our results indicate that low calpain activity, due to absence of calpain 1 and degradation of calpain 2, results in a preference for ACD over apoptosis in insulin-deprived HCN cells. On the other hand, conditions leading to high calpain activity completely switch the mode of cell death to apoptosis. This is the first report on the PCD mode switching mechanism in NSCs. The dynamic change in calpain activity through the proteasome-mediated modulation of the calpain and intracellular Ca2+ levels may be the critical contributor to the demise of NSCs. Our findings provide a novel insight into the complex mechanisms interconnecting autophagy and apoptosis and their roles in the regulation of NSC death. © 2015 AlphaMed Press.

Physiological Oxygen Level Is Critical for Modeling Neuronal Metabolism In Vitro

In vitro models are important tools for studying the mechanisms that govern neuronal responses to injury. Most neuronal culture methods employ nonphysiological conditions with regard to metabolic parameters. Standard neuronal cell culture is performed at ambient (21%) oxygen levels, whereas actual tissue oxygen levels in the mammalian brain range from 1% to 5%. In this study, we examined the consequences of oxygen level on the viability and metabolism of primary cultures of cortical neurons. Our results indicate that physiological oxygen level (5% O 2) has a beneficial effect on cortical neuronal survival and mitochondrial function in vitro. Moreover, oxygen level affects metabolic fluxes: glucose uptake and glycolysis was enhanced at physiological oxygen level, whereas glucose oxidation and fatty acid oxidation were reduced. Adenosine monophosphate-activated protein kinase (AMPK) was more activated in 5% O 2 and appears to play a role in these metabolic effects. Inhibiting AMPK activity with compound C decreased glucose uptake, intracellular ATP level, and viability in neurons cultured in 5% O 2. These data indicate that oxygen level is an important parameter to consider when modeling neuronal responses to stress in vitro. © 2011 Wiley Periodicals, Inc.