Phospholipase A2 (PLA2) enzymes are considered the primary source of arachidonic acid for cyclooxygenase (COX)-mediated biosynthesis of prostaglandins. Here, we show that a distinct pathway exists in brain, where monoacylglycerol lipase (MAGL) hydrolyzes the endocannabinoid 2-arachidonoylglycerol to generate a major arachidonate precursor pool for neuroinflammatory prostaglandins. MAGL-disrupted animals show neuroprotection in a parkinsonian mouse model. These animals are spared the hemorrhaging caused by COX inhibitors in the gut, where prostaglandins are instead regulated by cytosolic-PLA2. These findings identify MAGL as a distinct metabolic node that couples endocannabinoid to prostaglandin signaling networks in the nervous system and suggest that inhibition of this enzyme may be a new and potentially safer way to suppress the proinflammatory cascades that underlie neurodegenerative disorders.

Huntington’s disease (HD) is caused by CAG / polyglutamine repeat expansions in the huntingtin (htt) gene, yielding proteins that misfold and resist degradation. HD belongs to a large class of neurodegenerative proteinopathies including Alzheimer’s disease, Parkinson’s disease, and tauopathies. Previous studies demonstrated that mutant htt interferes with transcriptional programs coordinated by PPARγ co-activator 1α (PGC-1α), a regulator of mitochondrial biogenesis and oxidative stress. To test if restoration of PGC-1α could treat HD, we attempted an in vivo genetic rescue in mice. We found that PGC-1α induction ameliorates HD neurodegeneration and virtually eliminates htt protein aggregation, in part by attenuating oxidative stress. Further studies revealed that PGC-1α promotes htt turnover and aggregate elimination by transactivation of TFEB, a master regulator of the autophagy-lysosome pathway, and that TFEB alone is capable of reducing htt aggregation and neurotoxicity, placing PGC-1α upstream of TFEB. PGC-1α and TFEB thus hold great promise as therapies for HD and other neurodegenerative proteinopathies.

BackgroundGrowing evidence suggests that sirtuins, a family of seven distinct NAD-dependent enzymes, are involved in the regulation of neuronal survival. Indeed, SIRT1 has been reported to protect against neuronal death, while SIRT2 promotes neurodegeneration. The effect of SIRTs 3–7 on the regulation of neuronal survival, if any, has yet to be reported.Methodology and Principal FindingsWe examined the effect of expressing each of the seven SIRT proteins in healthy cerebellar granule neurons (CGNs) or in neurons induced to die by low potassium (LK) treatment. We report that SIRT1 protects neurons from LK-induced apoptosis, while SIRT2, SIRT3 and SIRT6 induce apoptosis in otherwise healthy neurons. SIRT5 is generally localized to both the nucleus and cytoplasm of CGNs and exerts a protective effect. In a subset of neurons, however, SIRT5 localizes to the mitochondria and in this case it promotes neuronal death. Interestingly, the protective effect of SIRT1 in neurons is not reduced by treatments with nicotinamide or sirtinol, two pharmacological inhibitors of SIRT1. Neuroprotection was also observed with two separate mutant forms of SIRT1, H363Y and H355A, both of which lack deacetylase activity. Furthermore, LK-induced neuronal death was not prevented by resveratrol, a pharmacological activator of SIRT1, at concentrations at which it activates SIRT1. We extended our analysis to HT-22 neuroblastoma cells which can be induced to die by homocysteic acid treatment. While the effects of most of the SIRT proteins were similar to that observed in CGNs, SIRT6 was modestly protective against homocysteic acid toxicity in HT-22 cells. SIRT5 was generally localized in the mitochondria of HT-22 cells and was apoptotic.Conclusions/SignificanceOverall, our study makes three contributions - (a) it represents the first analysis of SIRT3–7 in the regulation of neuronal survival, (b) it shows that neuroprotection by SIRT1 can be mediated by a novel, non-catalytic mechanism, and (c) that subcellular localization may be an important determinant in the effect of SIRT5 on neuronal viability.

HDAC4 is a Class II histone deacetylase (HDAC) that is highly expressed in the brain but whose functional significance in the brain is not known. We show that forced expression of HDAC4 in cerebellar granule neurons protects them against low potassium-induced apoptosis. HDAC4 also partially protects cultured cortical neurons from 6-hydroxydopamine-induced neurotoxicity and HT22 neuroblastoma cells from death induced by oxidative stress. HDAC4-mediated neuroprotection does not require its HDAC catalytic domain and cannot be inhibited by chemical inhibitors of HDACs. Neuroprotection by HDAC4 also does not require the Raf-MEK-ERK or the PI-3 kinase -Akt signaling pathways, and occurs despite the activation of c-jun, an event that is generally believed to condemn neurons to die. The protective action of HDAC4 occurs in the nucleus and is mediated by a region that contains the nuclear localization signal. HDAC4 inhibits the activity of cyclin-dependent kinase-1 (CDK1) and the progression of proliferating HEK293T and HT22 cells through the cell cycle. Mice lacking HDAC4 have elevated CDK1 activity and display cerebellar abnormalities including a progressive loss of Purkinje neurons postnatally in posterior lobes. Surviving Purkinje neurons in these lobes have duplicated soma. Furthermore, large numbers of cells within these affected lobes incorporate BrdU, indicating cell cycle progression. These abnormalities along with the ability of HDAC4 to inhibit CDK1 and cell cycle progression in cultured cells suggest that neuroprotection by HDAC4 is mediated by preventing abortive cell cycle progression. KeywordsHDAC4; apoptosis; neuronal survival; histone deacetylase; cell cycle Histone deacetylases (HDACs) are the catalytic subunits of multiprotein complexes that deacetylate specific lysines in the tail residues of histones, resulting in the compactation of chromatin into a transcriptionally repressed state (for review, see de Ruijter et al., 2003;Verdin et al., 2003;Yang and Gregoire, 2005). Although best studied for their effects on histones and transcriptional activity, it is now known that HDACs regulate the acetylation status of a number of other non-histone proteins suggesting complex functions of HDACs (for review, see de Ruijter et al., 2003;Verdin et al., 2003). In fact, HDACs have been shown to participate, or have been implicated in a variety of cellular functions including cell transformation, proliferation, senescence, differentiation, survival, and death (for review, see Verdin et al., 2003;Yang and Gregoire, 2005 NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptVertebrates express at least 18 distinct HDACs which have been grouped into four classes based on their similarity with yeast HDACs (for review, see de Ruijter et al., 2003;Verdin et al., 2003;Yang and Gregoire, 2005). Class I HDACs (HDACs 1, 2, 3 and 8) are composed primarily of a catalytic domain. These HDACs are ubiquitously expressed, localized to the nucleus, and serve as transcriptional repressors. Class II HDACs ...

Apoptosis is an essential aspect of normal nervous system development, but when aberrantly activated, apoptosis leads to undesirable neuronal death, and such inappropriate neuronal loss is the hallmark of a variety of neurodegenerative diseases and neurological conditions, such as stroke or traumatic brain injury. The mechanisms underlying the regulation of apoptosis are beginning to be understood. Among the molecules that have recently been implicated are the histone deacetylases (HDACs). HDACs are the catalytic subunits of multiprotein complexes that deacetylate histones (11,42). The action of HDACs is opposed by histone acetyltransferases (HATs) such as CREB-binding protein and p300, which catalyze the transfer of an acetyl moiety from acetyl-coenzyme A to specific lysine residues of histones (25). Acetylation of histones relaxes the chromatin structure to a state that is transcriptionally active, while histone deacetylation transforms chromatin to a transcriptionally repressed state (25). Hence, gene expression is regulated, in part, by the balance of HDAC and HAT activities. Although best studied for their effects on histones and transcriptional activity, it is now known that HDACs and HATs regulate the acetylation of a number of other nonhistone proteins, such as p53, p65/RelA, E2F1, GATA1, and MyoD, suggesting complex functions of HDACs in different cellular processes (11,42). Precisely which cellular functions are involved is currently the subject of intense investigation.Vertebrates express at least 18 distinct HDACs, which have been grouped into three classes based on their similarities with Saccharomyces cerevisiae HDACs (11,42 Class I HDACs consist of little more than a deacetylase domain and function as transcriptional repressors. They generally are nuclear proteins expressed in most tissue and cell types (11,42). On the other hand, members of the class II HDAC subfamily display cell type-restricted patterns of expression and contain a large extended N-terminal extension with which a variety of signaling proteins interact, including MEF2, HP1␣, Bcl6, CtBP, calmodulin,42). Phosphorylation of conserved serine residues in class II HDACs by calcium/calmodulin-dependent kinase (CaMK) or protein kinase D in response to specific stimuli creates docking sites for the 14-3-3 family of protein chaperones (11,28,31,42). Binding of 14-3-3 results in the export of these HDACs from the nucleus and disrupts their interactions with transcriptional corepressor proteins, resulting in derepression of their target genes.Several classes of small-molecule HDAC inhibitors have been identified (11,29 (11,29). Because of their ability to induce the death of transformed cells, HDAC inhibitors are in clinical trials for the treatment of cancers. It is noteworthy, however, that while there are small differences in the sensitivities of individual class I and class II HDACs to different inhibitors, most of the commonly used inhibitors inhibit all HDACs efficiently. The significance of individual HDACs in any biological effect ha...