Amyloid β1-42 Oligomers Induce Galectin-1S8 O-GlcNAcylation Leading to Microglia Migration

Protein O-GlcNAcylation has been associated with neurodegenerative diseases such as Alzheimer's disease (AD). The O-GlcNAcylation of the Amyloid Precursor Protein (APP) regulates both the trafficking and the processing of the APP through the amyloidogenic pathway, resulting in the release and aggregation of the Aβ_1-42 peptide. Microglia clears Aβ aggregates and dead cells to maintain brain homeostasis. Here, using LC-MS/MS, we revealed that the Aβ_1-42 oligomers modify the microglia O-GlcNAcome. We identified 55 proteins, focusing our research on Galectin-1 protein since it is a very versatile protein from a functional point of view. Combining biochemical with genetic approaches, we demonstrated that Aβ_1-42 oligomers specifically target Galectin-1^S8 O-GlcNAcylation via OGT. In addition to this, the Gal-1-O-GlcNAcylated form, in turn, controls human microglia migration. Given the importance of microglia migration in the progression of AD, this study reports the relationship between the Aβ_1-42 oligomers and Serine 8-O-GlcNAcylation of Galectin-1 to drive microglial migration.

Small GTPases of the Ras and Rho Families Switch on/off Signaling Pathways in Neurodegenerative Diseases

Small guanosine triphosphatases (GTPases) of the Ras superfamily are key regulators of many key cellular events such as proliferation, differentiation, cell cycle regulation, migration, or apoptosis. To control these biological responses, GTPases activity is regulated by guanine nucleotide exchange factors (GEFs), GTPase activating proteins (GAPs), and in some small GTPases also guanine nucleotide dissociation inhibitors (GDIs). Moreover, small GTPases transduce signals by their downstream effector molecules. Many studies demonstrate that small GTPases of the Ras family are involved in neurodegeneration processes. Here, in this review, we focus on the signaling pathways controlled by these small protein superfamilies that culminate in neurodegenerative pathologies, such as Alzheimer's disease (AD) and Parkinson's disease (PD). Specifically, we concentrate on the two most studied families of the Ras superfamily: the Ras and Rho families. We summarize the latest findings of small GTPases of the Ras and Rho families in neurodegeneration in order to highlight these small proteins as potential therapeutic targets capable of slowing down different neurodegenerative diseases.

Small GTPases of the Ras superfamily and glycogen phosphorylase regulation in T cells

Small GTPases, together with their regulatory and effector molecules, are key intermediaries in the complex signalling pathways that control almost all cellular processes, working as molecular switches to transduce extracellular cues into cellular responses that drive vital functions, such as intracellular transport, biomolecule synthesis, gene activation and cell survival. How all of these networks are linked to metabolic pathways is a subject of intensive study. Because any response to cellular action requires some form of energy input, elucidating how cells coordinate the signals that lead to a tangible response involving metabolism is central to understand cellular activities. In this review, we summarize recent advances in our understanding of the molecular basis of the crosstalk between small GTPases of the Ras superfamily, specifically Rac1 and Ras/Rap1, and glycogen phosphorylase in T lymphocytes. Abbreviations: ADCY: adenylyl cyclase; ADCY6: adenylyl cyclase 6; BCR: B cell receptor; cAMP: 3',5'-cyclic adenosine monophosphate; CRIB: Cdc42/Rac binding domain; DLPFC: dysfunction of the dorsolateral prefrontal cortex; EGFR: epidermal growth factor receptor; Epac2: exchange protein directly activated by cAMP; GDP: guanodine-5'-diphosphate; GPCRs: G protein-coupled receptors; GTP: guanodin-5'-triphosphate; IL2: interleukin 2; IL2-R: interleukin 2 receptor; JAK: janus kinases; MAPK: mitogen-activated protein kinase; O-GlcNAc: O-glycosylation; PAK1: p21 activated kinase 1; PI3K: phosphatidylinositol 3-kinase; PK: phosphorylase kinase; PKA: cAMP-dependent protein kinase A; PKCθ: protein kinase Cθ; PLCγ: phospholipase Cγ; Src: proto-oncogene tyrosine-protein kinase c; STAT: signal transducer and activator of transcription proteins.

Epidermal growth factor receptor controls glycogen phosphorylase in T cells through small GTPases of the RAS family

We recently uncovered a regulatory pathway of the muscle isoform of glycogen phosphorylase (PYGM) that plays an important role in regulating immune function in T cells. Here, using various enzymatic, pulldown, and immunoprecipitation assays, we describe signaling cross-talk between the small GTPases RAS and RAP1A, member of RAS oncogene family (RAP1) in human Kit 225 lymphoid cells, which, in turn, is regulated by the epidermal growth factor receptor (EGFR). We found that this communication bridge is essential for glycogen phosphorylase (PYG) activation through the canonical pathway because this enzyme is inactive in the absence of adenylyl cyclase type 6 (ADCY6). PYG activation required stimulation of both exchange protein directly activated by cAMP 2 (EPAC2) and RAP1 via RAS and ADCY6 phosphorylation, with the latter being mediated by Raf-1 proto-oncogene, Ser/Thr kinase (RAF1). Consistent with this model, PYG activation was EGFR-dependent and may be initiated by the constitutively active form of RAS. Consequently, PYG activation in Kit 225 T cells could be blocked with specific inhibitors of RAS, EPAC, RAP1, RAF1, ADCY6, and cAMP-dependent protein kinase. Our results establish a new paradigm for the mechanism of PYG activation, which depends on the type of receptor involved.

A damping circadian clock drives weak oscillations in metabolism and locomotor activity of aphids (Acyrthosiphon pisum)

Timing seasonal events, like reproduction or diapause, is crucial for the survival of many species. Global change causes phenologies worldwide to shift, which requires a mechanistic explanation of seasonal time measurement. Day length (photoperiod) is a reliable indicator of winter arrival, but it remains unclear how exactly species measure day length. A reference for time of day could be provided by a circadian clock, by an hourglass clock, or, as some newer models suggest, by a damped circadian clock. However, damping of clock outputs has so far been rarely observed. To study putative clock outputs of Acyrthosiphon pisum aphids, we raised individual nymphs on coloured artificial diet, and measured rhythms in metabolic activity in light-dark illumination cycles of 16:08 hours (LD) and constant conditions (DD). In addition, we kept individuals in a novel monitoring setup and measured locomotor activity. We found that A. pisum is day-active in LD, potentially with a bimodal distribution. In constant darkness rhythmicity of locomotor behaviour persisted in some individuals, but patterns were mostly complex with several predominant periods. Metabolic activity, on the other hand, damped quickly. A damped circadian clock, potentially driven by multiple oscillator populations, is the most likely explanation of our results.