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Parkinson’s disease is a highly prevalent neurological disorder for which there is currently no cure. Therefore, the knowledge of risk factors as well as the development of new putative molecular targets is mandatory. In this sense, peripheral inflammation, especially the originated in the colon, is emerging as a predisposing factor for suffering this disease. We have largely studied the pleiotropic roles of galectin-3 in driving microglia-associated immune responses. However, studies aimed at elucidating the role of galectin-3 in peripheral inflammation in terms of microglia polarization are lacking. To achieve this, we have evaluated the effect of galectin-3 deletion in two different models of acute peripheral inflammation: intraperitoneal injection of lipopolysaccharide or gut inflammation induced by oral administration of dextran sodium sulfate. We found that under peripheral inflammation the number of microglial cells and the expression levels of pro-inflammatory mediators take place specifically in the dopaminergic system, thus supporting causative links between Parkinson’s disease and peripheral inflammation. Absence of galectin-3 highly reduced neuroinflammation in both models, suggesting an important central regulatory role of galectin-3 in driving microglial activation provoked by the peripheral inflammation. Thus, modulation of galectin-3 function emerges as a promising strategy to minimize undesired microglia polarization states., This work was supported by grants from the Spanish Ministerio de Ciencia, Innovación y Universidades (RTI 2018-098830-B-I00), from the Consejería de Economía y Conocimiento of Junta de Andalucía (P18-RT-1372 and US-1264806). MJP, MDVC and PGM were supported by a grant from the Junta de Andalucía (CTS 5884) and AEC by an associated post-doctoral grant.

Summary: Epigenomic mechanisms regulate distinct aspects of the inflammatory response in immune cells. Despite the central role for microglia in neuroinflammation and neurodegeneration, little is known about their epigenomic regulation of the inflammatory response. Here, we show that Ten-eleven translocation 2 (TET2) methylcytosine dioxygenase expression is increased in microglia upon stimulation with various inflammogens through a NF-κB-dependent pathway. We found that TET2 regulates early gene transcriptional changes, leading to early metabolic alterations, as well as a later inflammatory response independently of its enzymatic activity. We further show that TET2 regulates the proinflammatory response in microglia of mice intraperitoneally injected with LPS. We observed that microglia associated with amyloid β plaques expressed TET2 in brain tissue from individuals with Alzheimer’s disease (AD) and in 5xFAD mice. Collectively, our findings show that TET2 plays an important role in the microglial inflammatory response and suggest TET2 as a potential target to combat neurodegenerative brain disorders. : Microglia play a key role in neuroinflammation and neurodegeneration in different neurodegenerative diseases, but little is known about the epigenetic modifying enzymes regulating their inflammatory response. Carrillo-Jimenez et al. identify TET2 as a major regulator of the microglia proinflammatory response and suggest that, by targeting this protein, microglial activation could be impaired. Keywords: microglia, epigenetics, TET2, metabolism, TLR-4, neuroinflammation

Glioma cells recruit and exploit microglia (the resident immune cells of the brain) for their proliferation and invasion ability. The underlying molecular mechanism used by glioma cells to transform microglia into a tumor-supporting phenotype has remained elusive. We found that glioma-induced microglia conversion was coupled to a reduction in the basal activity of microglial caspase-3 and increased S-nitrosylation of mitochondria-associated caspase-3 through inhibition of thioredoxin-2 activity, and that inhibition of caspase-3 regulated microglial tumor-supporting function. Furthermore, we identified the activity of nitric oxide synthase 2 (NOS2, also known as iNOS) originating from the glioma cells as a driving stimulus in the control of microglial caspase-3 activity. Repression of glioma NOS2 expression in vivo led to a reduction in both microglia recruitment and tumor expansion, whereas depletion of microglial caspase-3 gene promoted tumor growth. Our results provide evidence that inhibition of the denitrosylation of S-nitrosylated procaspase-3 mediated by the redox protein Trx2 is a part of the microglial pro-tumoral activation pathway initiated by glioma cancer cells., Supported by the Karolinska Institutet Foundation (X.S. and B.J.), the Swedish Childhood Cancer Foundation (A.M.O., B.J. and K.B.), the Swedish Research Council (M.A.B. and B.J.), the Strategic Research Programme in Cancer (B.J.), the Strategic Research Programme in Neuroscience (K.B.), the Swedish Cancer Foundation (B.J.), Spanish MINECO/FEDER/UE (J.L.V.), the Swedish Cancer Society (B.J.), the Swedish Brain Foundation (B.J.) and Swedish governmental grants for researchers working in healthcare (K.B.).

The impact of systemic inflammation in nigral dopaminergic cell loss remains unclear. Here, we have investigated the role of peripheral inflammation induced by systemic lipopolysaccharide (LPS) administration in the MPTP-based model of Parkinson’s disease. Brain inflammation, microglia and astroglia activation, disruption of the blood–brain barrier (BBB) and integrity of the nigrostriatal dopaminergic system were evaluated in response to i.p. injection of LPS, MPTP or the combination of both. Our results showed that combinative treatment exacerbates microglia activation and enhances (i) the appearance of galectin-3-positive microglia, recently identified as microglial disease-associated phenotypic marker, (ii) the up-regulation of pro-inflammatory cytokines, (iii) the occurrence of A1 neurotoxic astrocytes, (iv) the breakdown of the BBB, and (v) the loss of dopaminergic neurons in the substantia nigra. Microglia activation was triggered earlier than other degenerative events, suggesting that over-activation of microglia (including different polarization states) may induce dopaminergic neuron loss by itself, initiating the endless cycle of inflammation/degeneration. Our study revitalizes the importance of peripheral inflammation as a potential risk factor for Parkinson’s disease and raises the possibility of using new anti-inflammatory therapies to improve the course of neurodegenerative diseases, including those directly aimed at modulating the deleterious activity of disease-associated microglia., This work was supported by a grant from the Spanish Ministerio de Economia y Competitividad SAF2015-64171-R (MINECO/FEDER, EU).

Traumatic brain injury (TBI) is currently a major cause of morbidity and poor quality of life in Western society, with an estimate of 2.5 million people affected per year in Europe, indicating the need for advances in TBI treatment. Within the first 24 h after TBI, several inflammatory response factors become upregulated, including the lectin galectin-3. In this study, using a controlled cortical impact (CCI) model of head injury, we show a large increase in the expression of galectin-3 in microglia and also an increase in the released form of galectin-3 in the cerebrospinal fluid (CSF) 24 h after head injury. We report that galectin-3 can bind to TLR-4, and that administration of a neutralizing antibody against galectin-3 decreases the expression of IL-1β, IL-6, TNFα and NOS2 and promotes neuroprotection in the cortical and hippocampal cell populations after head injury. Long-term analysis demonstrated a significant neuroprotection in the cortical region in the galectin-3 knockout animals in response to TBI. These results suggest that following head trauma, released galectin-3 may act as an alarmin, binding, among other proteins, to TLR-4 and promoting inflammation and neuronal loss. Taking all together, galectin-3 emerges as a clinically relevant target for TBI therapy., A.C.-J. is supported by a pre-doctoral fellowship from Spanish Ministerio de Educación, Cultura y Deporte. This work has been supported by grants from the Spanish Ministerio SAF2015–64171R (MINECO/FEDER, UE), Blizard Research Theme grants, Blizard Institute, Queen Mary University of London. M.A.B has been funded by the Barts Charity Centre for Trauma Sciences (C4TS) and the Wellcome Trust Institutional Strategic Support Fund (ISSF).

In septic patients, the onset of septic shock occurs due to the over-activation of monocytes. We tested the therapeutic potential of directly targeting innate immune cell activation to limit the cytokine storm and downstream phases. We initially investigated whether caspase-8 could be an appropriate target given it has recently been shown to be involved in microglial activation. We found that LPS caused a mild increase in caspase-8 activity and that the caspase-8 inhibitor IETD-fmk partially decreased monocyte activation. Furthermore, caspase-8 inhibition induced necroptotic cell death of activated monocytes. Despite inducing necroptosis, caspase-8 inhibition reduced LPS-induced expression and release of IL-1β and IL-10. Thus, blocking monocyte activation has positive effects on both the pro and anti-inflammatory phases of septic shock. We also found that in primary mouse monocytes, caspase-8 inhibition did not reduce LPS-induced activation or induce necroptosis. On the other hand, broad caspase inhibitors, which have already been shown to improve survival in mouse models of sepsis, achieved both. Thus, given that monocyte activation can be regulated in humans via the inhibition of a single caspase, we propose that the therapeutic use of caspase-8 inhibitors could represent a more selective alternative that blocks both phases of septic shock at the source., This work was supported by grants SAF2012-39029 and SAF2015-64171R (MINECO/FEDER, UE), the Junta of Andalucía (P10-CTS-6494), the Swedish Research Council, the Swedish Childhood Cancer Foundation, the Swedish Cancer Foundation, Swedish Parkinson Foundation and the Swedish Brain Foundation.

The study of monocyte activation and differentiation has great applications in sepsis, chronic inflammatory diseases, and cancer studies. However, despite the existence of well-established protocols for monocyte purification from human blood, the isolation of murine monocytes that can be subsequently activated has not yet been fully optimized. Here we evaluate a recently developed commercial procedure for obtaining monocytes from the bone marrow based on immunomagnetic depletion of non-monocytic cells. Moreover, we compare the advantages and disadvantages of this approach relative to other existing procedures. We found that monocytes isolates generated using this technique had equal purity to those attained via depletion from peripheral blood; however, higher yields were achieved. Furthermore, isolates from this technique have lower levels of macrophage contamination than those reported in samples generated by culturing bone marrow extracts with macrophage colony-stimulating factor (M-CSF). In addition, we demonstrate that the purified monocytes are sensitive to lipopolysaccharide (LPS)-mediated activation and, therefore, are useful for studies aimed at elucidating the molecular mechanisms involved in monocyte activation and differentiation.

Increasing evidence involves sustained pro-inflammatory microglia activation in the pathogenesis of different neurodegenerative diseases, particularly Parkinson's disease (PD). We recently uncovered a completely novel and unexpected role for caspase-8 and its downstream substrates caspase-3/7 in the control of microglia activation and associated neurotoxicity to dopaminergic cells. To demonstrate the genetic evidence, mice bearing a floxed allele of CASP8 were crossed onto a transgenic line expressing Cre under the control of Lysozyme 2 gene. Analysis of caspase-8 gene deletion in brain microglia demonstrated a high efficiency in activated but not in resident microglia. Mice were challenged with lipopolysaccharide, a potent inducer of microglia activation, or with MPTP, which promotes specific dopaminergic cell damage and consequent reactive microgliosis. In neither of these models, CASP8 deletion appeared to affect the overall number of microglia expressing the pan specific microglia marker, Iba1. In contrast, CD16/CD32 expression, a microglial pro-inflammatory marker, was found to be negatively affected upon CASP8 deletion. Expression of additional proinflammatory markers were also found to be reduced in response to lipopolysaccharide. Of importance, reduced pro-inflammatory microglia activation was accompanied by a significant protection of the nigro-striatal dopaminergic system in the MPTP mouse model of PD. España Ministerio de Economía y Competitividad SAF2012-39029 España Andalucía Junta de Andalucia P10-CTS-6494

This review is aimed to highlight the importance of stress and glucocorticoids (GCs) in modulating the inflammatory response of brain microglia and hence its potential involvement in Parkinson’s disease (PD). The role of inflammation in PD has been reviewed extensively in the literature and it is supposed to play a key role in the course of the disease. Historically, GCs have been strongly associated as anti-inflammatory hormones. However, accumulating evidence from the peripheral and central nervous system have clearly revealed that, under specific conditions, GCs may promote brain inflammation including pro-inflammatory activation of microglia. We have summarized relevant data linking PD, neuroinflamamation and chronic stress. The timing and duration of stress response may be critical for delineating an immune response in the brain thus probably explain the dual role of GCs and/or chronic stress in different animal models of PD., The research group is supported by grants from Junta de Andalucía P10-CTS-6494 (Proyecto de Excelencia) and Spanish Ministerio de Economía y Competitividad (SAF2012–39029). AC-J and MJO-M thank Spanish Ministerio de Educación y Ciencia for FPU fellowships.

Research indicates that inflammation and microglial activation are involved in the initiation and progression of Parkinson's disease (PD). Neuroinflammation contributes to the infiltration of peripheral immune cells and blood–brain barrier (BBB) leakage, linking peripheral and central inflammatory events in the pathogenesis of PD. Dopamine (DA) likely plays a role in this process. In the present study, the dopaminergic toxin 6-hydroxydopamine (6-OHDA) was used to damage dopaminergic neurons. Injection of 6-OHDA within the nigrostriatal pathway produced loss of astrocytes, disruption of the BBB, microglia activation and a reduction in osteopontin (OPN) immunoreactivity. Depletion of DA content by alpha-methylparatyrosine (α-MPT, a tyrosine hydroxylase inhibitor) reduced the infiltration of peripheral macrophages as well as the 6-OHDA-induced increase in microglial cells. DA could therefore be relevant in sustaining inflammation and lymphocyte recruitment induced by 6-OHDA, supporting DA implication in the degeneration of dopaminergic neurons induced by inflammatory processes.

DNA damage immediate cellular response requires the activation of p53 by kinases. We found that p53 forms a basal stable complex with VRK1, a Ser-Thr kinase that responds to UV-induced DNA damage by specifically phosphorylating p53. This interaction takes place through the p53 DNA binding domain, and frequent DNA-contact mutants of p53, such as R273H, R248H or R280K, do not disrupt the complex. UV-induced DNA damage activates VRK1, and is accompanied by phosphorylation of p53 at Thr-18 before it accumulates. We propose that the VRK1-p53 basal complex is an early-warning system for immediate cellular responses to DNA damage., I. L.-S. and A.V. have FPI and FPU fellowships respectively from Ministerio de Ciencia e Innovación. M.V.-C., M.S.-G. and A.C. have JAE-CSIC-Fondo Social Europeo fellowships. This work was supported by Grants from Ministerio de Educación, Ciencia e Innovación (SAF2010-14935 and CSD2007-0017) and Kutxa-Fundación Inbiomed to P.A.L.