Molecular Association of Glia Maturation Factor with the Autophagic Machinery in Rat Dopaminergic Neurons: a Role for Endoplasmic Reticulum Stress and MAPK Activation

Parkinson's disease (PD) is one of the several neurodegenerative diseases where accumulation of aggregated proteins like α-synuclein occurs. Dysfunction in autophagy leading to this protein build-up and subsequent dopaminergic neurodegeneration may be one of the causes of PD. The mechanisms that impair autophagy remain poorly understood. 1-Methyl-4-phenylpiridium ion (MPP⁺) is a neurotoxin that induces experimental PD in vitro. Our studies have shown that glia maturation factor (GMF), a brain-localized inflammatory protein, induces dopaminergic neurodegeneration in PD and that suppression of GMF prevents MPP⁺-induced loss of dopaminergic neurons. In the present study, we demonstrate a molecular action of GMF on the autophagic machinery resulting in dopaminergic neuronal loss and propose GMF-mediated autophagic dysfunction as one of the contributing factors in PD progression. Using dopaminergic N27 neurons, primary neurons from wild type (WT), and GMF-deficient (GMF-KO) mice, we show that GMF and MPP⁺ enhanced expression of MAPKs increased the mammalian target of rapamycin (mTOR) activation and endoplasmic reticulum stress markers such as phospho-eukaryotic translation initiation factor 2 alpha kinase 3 (p-PERK) and inositol-requiring enzyme 1α (IRE1α). Further, GMF and MPP⁺ reduced Beclin 1, focal adhesion kinase (FAK) family-interacting protein of 200 kD (FIP200), and autophagy-related proteins (ATGs) 3, 5, 7, 16L, and 12. The combined results demonstrate that GMF affects autophagy through autophagosome formation with significantly reduced lysosomal-associated membrane protein 1/2, and the number of autophagic acidic vesicles. Using primary neurons, we show that MPP⁺ treatment leads to differential expression and localization of p62/sequestosome and in GMF-KO neurons, there was a marked increase in p62 staining implying autophagy deficiency with very little co-localization of α-synuclein and p62 as compared with WT neurons. Collectively, this study provides a bidirectional role for GMF in executing dopaminergic neuronal death mediated by autophagy that is relevant to PD.

Vulnerabilities and risks of HIV infection among migrants in the Thane district, India

OBJECTIVES

To explore the vulnerabilities and risks of HIV infection among female migrants compared with male migrants in the Thane district of Maharashtra, India.

STUDY DESIGN

This is a cross-sectional epidemiological study.

METHODS

Data from 35,841 migrants (men 96.2% and women 3.8%) were collected using the web-based 'Migrant Service Delivery System.' The data were then analysed in SPSS, version 23.0. Statistical analysis, including Chi-squared test and multivariate logistic regression, was used to identify factors influencing HIV infection for both male and female migrants.

RESULTS

It was observed that 2.96% of female migrants had HIV infection compared with 0.77% of male migrants. We found that 12.1% of women consumed alcohol compared with 41.9% of men, and access to bars was 1.5% among women and 3.5% in men. We observed an even larger difference between men and women in their previous history of using brothels for sex; only 5.9% of female migrants reported previously having used brothels for sex, compared with 62.9% of male migrants. Approximately 12.3% of married women and 93.6% of married men had sex with someone other than their spouse. We found that 67.0% of married women and 73.9% of married men reported using a condom during their last sexual act compared with 60.9% of unmarried women and 68.1% of unmarried men.

CONCLUSIONS

In Thane, female migrants faced higher vulnerabilities and risks of HIV infection than male migrants. Consequently, innovative strategies are required to address these particular needs of female migrants.

Glia Maturation Factor Dependent Inhibition of Mitochondrial PGC-1α Triggers Oxidative Stress-Mediated Apoptosis in N27 Rat Dopaminergic Neuronal Cells

Parkinson's disease (PD) is a progressive neurodegenerative disease affecting over five million individuals worldwide. The exact molecular events underlying PD pathogenesis are still not clearly known. Glia maturation factor (GMF), a neuroinflammatory protein in the brain plays an important role in the pathogenesis of PD. Mitochondrial dysfunctions and oxidative stress trigger apoptosis leading to dopaminergic neuronal degeneration in PD. Peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α or PPARGC-α) acts as a transcriptional co-regulator of mitochondrial biogenesis and energy metabolism by controlling oxidative phosphorylation, antioxidant activity, and autophagy. In this study, we found that incubation of immortalized rat dopaminergic (N27) neurons with GMF influences the expression of peroxisome PGC-1α and increases oxidative stress, mitochondrial dysfunction, and apoptotic cell death. We show that incubation with GMF reduces the expression of PGC-1α with concomitant decreases in the mitochondrial complexes. Besides, there is increased oxidative stress and depolarization of mitochondrial membrane potential (MMP) in these cells. Further, GMF reduces tyrosine hydroxylase (TH) expression and shifts Bax/Bcl-2 expression resulting in release of cytochrome-c and increased activations of effector caspase expressions. Transmission electron microscopy analyses revealed alteration in the mitochondrial architecture. Our results show that GMF acts as an important upstream regulator of PGC-1α in promoting dopaminergic neuronal death through its effect on oxidative stress-mediated apoptosis. Our current data suggest that GMF is a critical risk factor for PD and suggest that it could be explored as a potential therapeutic target to inhibit PD progression.

Mast Cell Proteases Activate Astrocytes and Glia-Neurons and Release Interleukin-33 by Activating p38 and ERK1/2 MAPKs and NF-κB

Inflammatory mediators released from activated microglia, astrocytes, neurons, and mast cells mediate neuroinflammation. Parkinson's disease (PD) is characterized by inflammation-dependent dopaminergic neurodegeneration in substantia nigra. 1-Methyl-4-phenylpyridinium (MPP⁺), a metabolite of parkinsonian neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), induces inflammatory mediators' release from brain cells and mast cells. Brain cells' interaction with mast cells is implicated in neuroinflammation. However, the exact mechanisms involved are not yet clearly understood. Mouse fetal brain-derived cultured primary astrocytes and glia-neurons were incubated with mouse mast cell protease-6 (MMCP-6) and MMCP-7, and mouse bone marrow-derived mast cells (BMMCs) were incubated with MPP⁺ and brain protein glia maturation factor (GMF). Interleukin-33 (IL-33) released from these cells was quantitated by enzyme-linked immunosorbent assay. Both MMCP-6 and MMCP-7 induced IL-33 release from astrocytes and glia-neurons. MPP⁺ and GMF were used as a positive control-induced IL-33 and reactive oxygen species expression in mast cells. Mast cell proteases and MPP⁺ activate p38 and extracellular signal-regulated kinases 1/2 (ERK1/2), mitogen-activated protein kinases (MAPKs), and transcription factor nuclear factor-kappa B (NF-κB) in astrocytes, glia-neurons, or mast cells. Addition of BMMCs from wt mice and transduction with adeno-GMF show higher chemokine (C-C motif) ligand 2 (CCL2) release. MPP⁺ activated glial cells and reduced microtubule-associated protein 2 (MAP-2) expression indicating neurodegeneration. IL-33 expression increased in the midbrain and striatum of PD brains as compared with age- and sex-matched control subjects. Glial cells and neurons interact with mast cells and accelerate neuroinflammation and these interactions can be explored as a new therapeutic target to treat PD.

Cutting Edge: Mitochondrial Assembly of the NLRP3 Inflammasome Complex Is Initiated at Priming

The NLRP3 inflammasome is activated in response to microbial and danger signals, resulting in caspase-1-dependent secretion of the proinflammatory cytokines IL-1β and IL-18. Canonical NLRP3 inflammasome activation is a two-step process requiring both priming and activation signals. During inflammasome activation, NLRP3 associates with mitochondria; however, the role for this interaction is unclear. In this article, we show that mouse NLRP3 and caspase-1 independently interact with the mitochondrial lipid cardiolipin, which is externalized to the outer mitochondrial membrane at priming in response to reactive oxygen species. An NLRP3 activation signal is then required for the calcium-dependent association of the adaptor molecule ASC with NLRP3 on the mitochondrial surface, resulting in inflammasome complex assembly and activation. These findings demonstrate a novel lipid interaction for caspase-1 and identify a role for mitochondria as supramolecular organizing centers in the assembly and activation of the NLRP3 inflammasome.

Mast Cell Activation in Brain Injury, Stress, and Post-traumatic Stress Disorder and Alzheimer's Disease Pathogenesis

Mast cells are localized throughout the body and mediate allergic, immune, and inflammatory reactions. They are heterogeneous, tissue-resident, long-lived, and granulated cells. Mast cells increase their numbers in specific site in the body by proliferation, increased recruitment, increased survival, and increased rate of maturation from its progenitors. Mast cells are implicated in brain injuries, neuropsychiatric disorders, stress, neuroinflammation, and neurodegeneration. Brain mast cells are the first responders before microglia in the brain injuries since mast cells can release prestored mediators. Mast cells also can detect amyloid plaque formation during Alzheimer's disease (AD) pathogenesis. Stress conditions activate mast cells to release prestored and newly synthesized inflammatory mediators and induce increased blood-brain barrier permeability, recruitment of immune and inflammatory cells into the brain and neuroinflammation. Stress induces the release of corticotropin-releasing hormone (CRH) from paraventricular nucleus of hypothalamus and mast cells. CRH activates glial cells and mast cells through CRH receptors and releases neuroinflammatory mediators. Stress also increases proinflammatory mediator release in the peripheral systems that can induce and augment neuroinflammation. Post-traumatic stress disorder (PTSD) is a traumatic-chronic stress related mental dysfunction. Currently there is no specific therapy to treat PTSD since its disease mechanisms are not yet clearly understood. Moreover, recent reports indicate that PTSD could induce and augment neuroinflammation and neurodegeneration in the pathogenesis of neurodegenerative diseases. Mast cells play a crucial role in the peripheral inflammation as well as in neuroinflammation due to brain injuries, stress, depression, and PTSD. Therefore, mast cells activation in brain injury, stress, and PTSD may accelerate the pathogenesis of neuroinflammatory and neurodegenerative diseases including AD. This review focusses on how mast cells in brain injuries, stress, and PTSD may promote the pathogenesis of AD. We suggest that inhibition of mast cells activation and brain cells associated inflammatory pathways in the brain injuries, stress, and PTSD can be explored as a new therapeutic target to delay or prevent the pathogenesis and severity of AD.

Glia Maturation Factor and Mitochondrial Uncoupling Proteins 2 and 4 Expression in the Temporal Cortex of Alzheimer's Disease Brain

Alzheimer’s disease (AD) is characterized by the presence of neuropathological lesions containing amyloid plaques (APs) and neurofibrillary tangles (NFTs). AD is associated with mitochondrial dysfunctions, neuroinflammation and neurodegeneration in the brain. We have previously demonstrated enhanced expression of the proinflammatory protein glia maturation factor (GMF) in glial cells near APs and NFTs in the AD brains. Parahippocampal gyrus consisting of entorhinal and perirhinal subdivisions of temporal cortex is the first brain region affected during AD pathogenesis. Current paradigm implicates oxidative stress-mediated neuronal damage contributing to the early pathology in AD with mitochondrial membrane potential regulating reactive oxygen species (ROS) production. The inner mitochondrial membrane anion transporters called the uncoupling proteins (UCPs), function as regulators of cellular homeostasis by mitigating oxidative stress. In the present study, we have analyzed the expression of GMF and mitochondrial UCP2 and UCP4 in the parahippocampal gyrus of AD and non-AD brains by immunostaining techniques. APs were detected by thioflavin-S fluorescence staining or immunohistochemistry (IHC) with 6E10 antibody. Our current results suggest that upregulation of GMF expression is associated with down-regulation of UCP2 as well as UCP4 in the parahippocampal gyrus of AD brains as compared to non-AD brains. Further, GMF expression is associated with up-regulation of inducible nitric oxide synthase (iNOS), the enzyme that induces the production of nitric oxide (NO), as well as nuclear factor kB p65 (NF-κB p65) expression. Also, GMF appeared to localize to the mitochondria in AD brains. Based on our current observations, we propose that enhanced expression of GMF down-regulates mitochondrial UCP2 and UCP4 thereby exacerbating AD pathophysiology and this effect is potentially mediated by iNOS and NF-κB. Thus, GMF functions as an activator protein that interferes with the cytoprotective mechanisms in AD brains.

Neuroinflammation Induces Neurodegeneration

Neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and Multiple Sclerosis (MS) are characterized by neuronal degeneration and neuronal death in specific regions of the central nervous system (CNS). In AD, neurons of the hippocampus and entorhinal cortex are the first to degenerate, whereas in PD, dopaminergic neurons in the substantia nigra degenerate. MS patients show destruction of the myelin sheath. Once the CNS neurons are damaged, they are unable to regenerate unlike any other tissue in the body. Neurodegeneration is mediated by inflammatory and neurotoxic mediators such as interleukin-1beta (IL-1β), IL-6, IL-8, IL-33, tumor necrosis factor-alpha (TNF-α), chemokine (C-C motif) ligand 2 (CCL2), CCL5, matrix metalloproteinase (MMPs), granulocyte macrophage colony-stimulating factor (GM-CSF), glia maturation factor (GMF), substance P, reactive oxygen species (ROS), reactive nitrogen species (RNS), mast cells-mediated histamine and proteases, protease activated receptor-2 (PAR-2), CD40, CD40L, CD88, intracellular Ca⁺ elevation, and activation of mitogen-activated protein kinases (MAPKs) and nuclear factor kappa-B (NF-kB). Activated microglia, astrocytes, neurons, T-cells and mast cells release these inflammatory mediators and mediate neuroinflammation and neurodegeneration in a vicious manner. Further, immune and inflammatory cells and inflammatory mediators from the periphery cross the defective blood-brain-barrier (BBB) and augment neuroinflammation. Though inflammation is crucial in the onset and the progression of neurodegenerative diseases, anti-inflammatory drugs do not provide significant therapeutic effects in these patients till date, as the disease pathogenesis is not yet clearly understood. In this review, we discuss the possible factors involved in neuroinflammation-mediated neurodegeneration.

How colonization by microbiota in early life shapes the immune system

Microbial colonization of mucosal tissues during infancy plays an instrumental role in the development and education of the host mammalian immune system. These early-life events can have long-standing consequences: facilitating tolerance to environmental exposures or contributing to the development of disease in later life, including inflammatory bowel disease, allergy, and asthma. Recent studies have begun to define a critical period during early development in which disruption of optimal host-commensal interactions can lead to persistent and in some cases irreversible defects in the development and training of specific immune subsets. Here, we discuss the role of early-life education of the immune system during this "window of opportunity," when microbial colonization has a potentially critical impact on human health and disease.

Akt-mTORC1 signaling regulates Acly to integrate metabolic input to control of macrophage activation

Macrophage activation/polarization to distinct functional states is critically supported by metabolic shifts. How polarizing signals coordinate metabolic and functional reprogramming, and the potential implications for control of macrophage activation, remains poorly understood. Here we show that IL-4 signaling co-opts the Akt-mTORC1 pathway to regulate Acly, a key enzyme in Ac-CoA synthesis, leading to increased histone acetylation and M2 gene induction. Only a subset of M2 genes is controlled in this way, including those regulating cellular proliferation and chemokine production. Moreover, metabolic signals impinge on the Akt-mTORC1 axis for such control of M2 activation. We propose that Akt-mTORC1 signaling calibrates metabolic state to energetically demanding aspects of M2 activation, which may define a new role for metabolism in supporting macrophage activation.

Positive feedback regulation of type I IFN production by the IFN-inducible DNA sensor cGAS

Rapid and robust induction of type I IFN (IFN-I) is a critical event in host antiviral innate immune response. It has been well demonstrated that cyclic GMP-AMP (cGAMP) synthase (cGAS) plays an important role in sensing cytosolic DNA and triggering STING dependent signaling to induce IFN-I. However, it is largely unknown how cGAS itself is regulated during pathogen infection and IFN-I production. In this study, we show that pattern recognition receptor (PRR) ligands, including lipid A, LPS, poly(I:C), poly(dA:dT), and cGAMP, induce cGAS expression in an IFN-I-dependent manner in both mouse and human macrophages. Further experiments indicated that cGAS is an IFN-stimulated gene (ISG), and two adjacent IFN-sensitive response elements (ISREs) in the promoter region of cGAS mediate the induction of cGAS by IFN-I. Additionally, we show that optimal production of IFN-β triggered by poly (dA:dT) or HSV-1 requires IFNAR signaling. Knockdown of the constitutively expressed DNA sensor DDX41 attenuates poly(dA:dT)-triggered IFN-β production and cGAS induction. By analyzing the dynamic expression of poly(dA:dT)-induced IFN-β and cGAS transcripts, we have found that induction of IFN-β is earlier than cGAS. Furthermore, we have provided evidence that induction of cGAS by IFN-I meditates the subsequent positive feedback regulation of DNA-triggered IFN-I production. Thus, our study not only provides a novel mechanism of modulating cGAS expression, but also adds another layer of regulation in DNA-triggered IFN-I production by induction of cGAS.

Positive feedback regulation of type I interferon by the interferon-stimulated gene STING

Stimulator of interferon genes (STING) is an important regulator of the innate immune response to cytoplasmic DNA. However, regulation of STING itself is largely unknown. Here, we show that STING transcription is induced by innate immune activators, such as cyclic dinucleotides (CDNs), through an IFNAR1- and STAT1-dependent pathway. We also identify a STAT1 binding site in the STING promoter that contributes to the activation of STING transcription. Furthermore, we show that induction of STING mediates the positive feedback regulation of CDN-triggered IFN-I. Thus, our study demonstrates that STING is an interferon-stimulated gene (ISG) and its induction is crucial for the IFN-I positive feedback loop.

Regulation of MHC class I expression by Foxp3 and its effect on regulatory T cell function

Expression of MHC class I molecules, which provide immune surveillance against intracellular pathogens, is higher on lymphoid cells than on any other cell types. In T cells, this is a result of activation of class I transcription by the T cell enhanceosome consisting of Runx1, CBFβ, and LEF1. We now report that MHC class I transcription in T cells also is enhanced by Foxp3, resulting in higher levels of class I in CD4(+)CD25(+) T regulatory cells than in conventional CD4(+)CD25(-) T cells. Interestingly, the effect of Foxp3 regulation of MHC class I transcription is cell type specific: Foxp3 increases MHC class I expression in T cells but represses it in epithelial tumor cells. In both cell types, Foxp3 targets the upstream IFN response element and downstream core promoter of the class I gene. Importantly, expression of MHC class I contributes to the function of CD4(+)CD25(+) T regulatory cells by enhancing immune suppression, both in in vitro and in vivo. These findings identify MHC class I genes as direct targets of Foxp3 whose expression augments regulatory T cell function.

Mitochondrial cardiolipin is required for Nlrp3 inflammasome activation

Nlrp3 inflammasome activation occurs in response to numerous agonists but the specific mechanism by which this takes place remains unclear. All previously evaluated activators of the Nlrp3 inflammasome induce the generation of mitochondrial reactive oxygen species (ROS), suggesting a model in which ROS is a required upstream mediator of Nlrp3 inflammasome activation. Here we have identified the oxazolidinone antibiotic linezolid as a Nlrp3 agonist that activates the Nlrp3 inflammasome independently of ROS. The pathways for ROS-dependent and ROS-independent Nlrp3 activation converged upon mitochondrial dysfunction and specifically the mitochondrial lipid cardiolipin. Cardiolipin bound to Nlrp3 directly and interference with cardiolipin synthesis specifically inhibited Nlrp3 inflammasome activation. Together these data suggest that mitochondria play a critical role in the activation of the Nlrp3 inflammasome through the direct binding of Nlrp3 to cardiolipin.

Type I interferon suppresses type II interferon-triggered human anti-mycobacterial responses

Type I interferons (IFN-α and IFN-β) are important for protection against many viral infections, whereas type II interferon (IFN-γ) is essential for host defense against some bacterial and parasitic pathogens. Study of IFN responses in human leprosy revealed an inverse correlation between IFN-β and IFN-γ gene expression programs. IFN-γ and its downstream vitamin D-dependent antimicrobial genes were preferentially expressed in self-healing tuberculoid lesions and mediated antimicrobial activity against the pathogen Mycobacterium leprae in vitro. In contrast, IFN-β and its downstream genes, including interleukin-10 (IL-10), were induced in monocytes by M. leprae in vitro and preferentially expressed in disseminated and progressive lepromatous lesions. The IFN-γ-induced macrophage vitamin D-dependent antimicrobial peptide response was inhibited by IFN-β and by IL-10, suggesting that the differential production of IFNs contributes to protection versus pathogenesis in some human bacterial infections.

Vitamin D is required for IFN-gamma-mediated antimicrobial activity of human macrophages

Control of tuberculosis worldwide depends on our understanding of human immune mechanisms, which combat the infection. Acquired T cell responses are critical for host defense against microbial pathogens, yet the mechanisms by which they act in humans remain unclear. We report that T cells, by the release of interferon-γ (IFN-γ), induce autophagy, phagosomal maturation, the production of antimicrobial peptides such as cathelicidin, and antimicrobial activity against Mycobacterium tuberculosis in human macrophages via a vitamin D-dependent pathway. IFN-γ induced the antimicrobial pathway in human macrophages cultured in vitamin D-sufficient sera, but not in sera from African-Americans that have lower amounts of vitamin D and who are more susceptible to tuberculosis. In vitro supplementation of vitamin D-deficient serum with 25-hydroxyvitamin D3 restored IFN-γ-induced antimicrobial peptide expression, autophagy, phagosome-lysosome fusion, and antimicrobial activity. These results suggest a mechanism in which vitamin D is required for acquired immunity to overcome the ability of intracellular pathogens to evade macrophage-mediated antimicrobial responses. The present findings underscore the importance of adequate amounts of vitamin D in all human populations for sustaining both innate and acquired immunity against infection.

Polyinosinic-polycytidylic acid suppresses acetaminophen-induced hepatotoxicity independent of type I interferons and toll-like receptor 3

Viral infections are often linked to altered drug metabolism in patients; however, the underlying molecular mechanisms remain unclear. Here we describe a mechanism by which activation of antiviral responses by the synthetic double-stranded RNA ligand, polyinosinic-polycytidylic acid (polyI:C), leads to decreased acetaminophen (APAP) metabolism and hepatotoxicity. PolyI:C administration down-regulates expression of retinoic X receptor-α (RXRα) as well as its heterodimeric partner pregnane X receptor (PXR) in mice. This down-regulation results in suppression of downstream cytochrome P450 enzymes involved in conversion of APAP to its toxic metabolite. Although the effects of polyI:C on drug metabolism are often attributed to interferon production, we report that polyI:C can decrease APAP metabolism in the absence of the type I interferon receptor. Furthermore, we demonstrate that polyI:C can attenuate APAP metabolism through both its membrane-bound receptor, Toll-like receptor 3 (TLR3), as well as cytoplasmic receptors.

CONCLUSION

This is the first study to illustrate that in vivo administration of polyI:C affects drug metabolism independent of type I interferon production or in the absence of TLR3 through crosstalk between nuclear receptors and antiviral responses.

Three novel downstream promoter elements regulate MHC class I promoter activity in mammalian cells

BACKGROUND

MHC CLASS I TRANSCRIPTION IS REGULATED BY TWO DISTINCT TYPES OF REGULATORY PATHWAYS: 1) tissue-specific pathways that establish constitutive levels of expression within a given tissue and 2) dynamically modulated pathways that increase or decrease expression within that tissue in response to hormonal or cytokine mediated stimuli. These sets of pathways target distinct upstream regulatory elements, have distinct basal transcription factor requirements, and utilize discrete sets of transcription start sites within an extended core promoter.

METHODOLOGY/PRINCIPAL FINDINGS

We studied regulatory elements within the MHC class I promoter by cellular transfection and in vitro transcription assays in HeLa, HeLa/CIITA, and tsBN462 of various promoter constructs. We have identified three novel MHC class I regulatory elements (GLE, DPE-L1 and DPE-L2), located downstream of the major transcription start sites, that contribute to the regulation of both constitutive and activated MHC class I expression. These elements located at the 3' end of the core promoter preferentially regulate the multiple transcription start sites clustered at the 5' end of the core promoter.

CONCLUSIONS/SIGNIFICANCE

Three novel downstream elements (GLE, DPE-L1, DPE-L2), located between +1 and +32 bp, regulate both constitutive and activated MHC class I gene expression by selectively increasing usage of transcription start sites clustered at the 5' end of the core promoter upstream of +1 bp. Results indicate that the downstream elements preferentially regulate TAF1-dependent, relative to TAF1-independent, transcription.

Mesenchymal stem cells and inflammatory lung diseases

Mesenchymal stem cells (MSCs) are emerging as a therapeutic modality in various inflammatory disease states. A number of ongoing randomized Phase I/II clinical trials are evaluating the effects of allogeneic MSC infusion in patients with multiple sclerosis, graft-versus-host disease, Crohn's disease, and severe chronic myocardial ischemia. MSCs are also being considered as a potential therapy in patients with inflammatory lung diseases. Several studies, including our own, have demonstrated compelling benefits from the administration of MSCs in animal models of lung injury. These studies are leading to growing interest in the therapeutic use of MSCs in inflammatory lung diseases. In this Review, we describe how the immunoregulatory effects of MSCs can confer substantial protection in the setting of lung diseases such as acute lung injury, chronic obstructive pulmonary disease, asthma, and pulmonary hypertension. We also address potential pitfalls related to the therapeutic use of MSCs in fibrotic lung diseases such as idiopathic pulmonary fibrosis. In addition, we identify emerging areas for MSC- based therapies in modulating oxidative stress and in attenuating inflammation in alcohol-related acute lung injury.

Coordinate regulation of sphingosine kinase and actin dynamics

The activation of lipid-modifying enzymes generally involves a physical change in their interactions with the membrane substrate. For sphingosine kinase, a predominantly cytosolic enzyme in resting cells, activation is accompanied by translocation to specific subsets of cellular membranes where catalysis occurs. As all eukaryotic membranes have a tightly associated filamentous actin skeleton, we investigated potential regulatory interactions between sphingosine kinase and actin. Sphingosine kinase 1 (SK1) exhibited constitutive- and stimulus-enhanced association with actin filaments and F-actin-enriched membrane fractions in both intact macrophages and an in vitro reconstitution assay, whereas SK1 bound G-actin only under stimulated conditions. Actin inhibitors disrupted SK1 localization and increased its enzymatic activity. Both the localization and the activity of SK1 were coordinately regulated with the actin cytoskeleton. The association of enzymes with the actin cytoskeleton and how this regulates their activities and functions are subjects of intense interest. Here, we describe the approach we used to investigate regulation of SK1. This provides general methods that can be used to examine the role of actin in regulating enzyme activity in macrophages and other myeloid cells.

The Localization and Activity of Sphingosine Kinase 1 Are Coordinately Regulated with Actin Cytoskeletal Dynamics in Macrophages

The physiologic and pathologic functions of sphingosine kinase (SK) require translocation to specific membrane compartments. We tested the hypothesis that interactions with actin filaments regulate the localization of SK1 to membrane surfaces, including the plasma membrane and phagosome. Macrophage activation is accompanied by a marked increase in association of SK1 with actin filaments. Catalytically-inactive (CI)- and phosphorylation-defective (PD)-SK1 mutants exhibited reductions in plasma membrane translocation, colocalization with cortical actin filaments, membrane ruffling, and lamellipodia formation, compared with wild-type (WT)-SK1. However, translocation of CI- and PD-SK1 to phagosomes were equivalent to WT-SK1. SK1 exhibited constitutive- and stimulus-enhanced association with actin filaments and F-actin-enriched membrane fractions in both intact macrophages and a novel in vitro assay. In contrast, SK1 bound G-actin only under stimulated conditions. Actin inhibitors disrupted SK1 localization and modulated its activity. Conversely, reduction of SK1 levels or activity via RNA interference or specific chemical inhibition resulted in dysregulation of actin filaments. Thus, the localization and activity of SK1 are coordinately regulated with actin dynamics during macrophage activation.