High molecular weight hyaluronan reduces lipopolysaccharide mediated microglial activation

Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada Department of Surgery, University of Toronto, Toronto, Ontario, Canada Division of Genetics and Development, Toronto Western Research Institute and Krembil Neuroscience Centre, Toronto Western Hospital, University Health Network, Toronto, Ontario, Canada.
Journal of Neurochemistry (Impact Factor: 4.28). 05/2012; 122(2). DOI: 10.1111/j.1471-4159.2012.07789.x
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J. Neurochem. (2012) 122, 344–355.
Toll-like receptor-4 (TLR4) signaling has been implicated in microglial activation and propagation of inflammation following spinal cord injury (SCI). As such, modulating microglial activation through TLR4 represents an attractive therapeutic approach to treat SCI. High molecular weight hyaluronan (HMW-HA), a polymer with multiple therapeutic uses, has been previously shown to modulate TLR4 activation in macrophages and has shown early promise as a therapeutic agent in SCI. However, the mechanism associated with HMW-HA has not been fully elucidated or tested in microglia, a similar cell type. In the current study, we sought to determine the effects of HMW-HA on TLR4 activation in microglia and to gain insights into the mechanism of action. Rat primary microglial cultures were exposed to lipopolysaccharides (LPS) and HMW-HA, and the extent and mechanisms of inflammation were studied. HMW-HA decreased LPS mediated IL-1β, IL-6, and Tumor necrosis factor-α gene expression and IL-6 and nitric oxide production. This decrease was associated with a reduction in ERK 1/2 and p38 phosphorylation, was dependent on the continued presence of HMW-HA, and activation of Akt and A20 protein expression was reduced by HMW-HA. Together, our results show that HMW-HA can reduce LPS-mediated inflammatory signaling in microglia. We suggest that HA possibly mediates its effects by blocking the induction of inflammatory signaling through an extracellular mechanism.

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Available from: Michael G Fehlings, Apr 09, 2015
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    • "Implantation of a degradationresistant HMW-HA hydrogel into a rat dorsal hemisection lesion reduced macrophage/microglial density, gliosis, and CSPG deposition within the first week post-injury (Khaing et al., 2011). In a separate study, Austin et al. (2012) injected hydrogel containing HMW-HA/ methyl cellulose intrathecally 24 h after a spinal compression injury. This treatment decreased lesion size, reactive gliosis, and IL-1α levels, and improved locomotor recovery. "
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    ABSTRACT: Throughout the body, the extracellular matrix (ECM) provides structure and organization to tissues and also helps regulate cell migration and intercellular communication. In the injured spinal cord (or brain), changes in the composition and structure of the ECM undoubtedly contribute to regeneration failure. Less appreciated is how the native and injured ECM influences intraspinal inflammation and, conversely, how neuroinflammation affects the synthesis and deposition of ECM after CNS injury. In all tissues, inflammation can be initiated and propagated by ECM disruption. Molecules of ECM newly liberated by injury or inflammation include hyaluronan fragments, tenascins, and sulfated proteoglycans. These act as “damage-associated molecular patterns” or “alarmins”, i.e., endogenous proteins that trigger and subsequently amplify inflammation. Activated inflammatory cells, in turn, further damage the ECM by releasing degradative enzymes including matrix metalloproteinases (MMPs). After spinal cord injury (SCI), destabilization or alteration of the structural and chemical compositions of the ECM affects migration, communication, and survival of all cells – neural and non-neural – that are critical for spinal cord repair. By stabilizing ECM structure or modifying their ability to trigger the degradative effects of inflammation, it may be possible to create an environment that is more conducive to tissue repair and axon plasticity after SCI.
    Experimental Neurology 08/2014; 258. DOI:10.1016/j.expneurol.2013.11.020 · 4.70 Impact Factor
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    ABSTRACT: Focal stroke is a disabling disease with lifelong sensory, motor and cognitive impairments. Given the paucity of effective clinical treatments, basic scientists are developing novel options for protection of the affected brain and regeneration of lost tissue. Tissue bioengineering and stem/progenitor cell treatments have both been individually pursued for stroke neural repair therapies, with some benefit in tissue recovery. Emerging directions in stroke neural repair approaches combine these two therapies to use biopolymers with stem/progenitor transplants to promote greater cell survival in the transplant and directed delivery of bioactive molecules to the transplanted cells and the adjacent injured tissue. In this review the background literature on a combined use of neural stem/progenitor cells encapsulated in hyaluronan gels is discussed and the way this therapeutic approach can affect the important processes involved in brain tissue reconstruction, such as angiogenesis, axon regeneration, neural differentiation and inflammation is clarified. The glycosaminoglycan hyaluronan can optimize those processes and be employed in a successful neural tissue engineering approach.
    Biomatter 01/2013; 3(1). DOI:10.4161/biom.23863
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    ABSTRACT: Hyaluronan (HA) is the major glycosaminoglycan in the extracellular matrix. During inflammation, there is an increased breakdown of HA, resulting in the accumulation of low molecular weight (LMW) HA and activation of monocytes and macrophages. Eicosanoids, derived from the cytosolic phospholipase A2 group IVA (cPLA2α) activation, are potent lipid mediators also attributed to acute and chronic inflammation. The aim of this study was to determine the effect of LMW HA on cPLA2α activation, arachidonic acid (AA) release, and subsequent eicosanoid production and to examine the receptors and downstream mechanisms involved in these processes in monocytes and differently polarized macrophages. LMW HA was a potent stimulant of AA release in a time- and dose-dependent manner, induced cPLA2α, ERK1/2, p38, and JNK phosphorylation, as well as activated COX2 expression and prostaglandin (PG) E2 production in primary human monocytes, murine RAW 264.7, and wild-type bone marrow-derived macrophages. Specific cPLA2α inhibitor blocked HA-induced AA release and PGE2 production in all of these cells. Using CD44, TLR4, TLR2, MYD88, RHAMM or STAB2 siRNA-transfected macrophages and monocytes, we found that AA release, cPLA2α, ERK1/2, p38, and JNK phosphorylation, COX2 expression, and PGE2 production were activated by LMW HA through a TLR4/MYD88 pathway. Likewise, PGE2 production and COX2 expression were blocked in Tlr4−/− and Myd88−/− mice, but not in Cd44−/− mice, after LMW HA stimulation. Moreover, we demonstrated that LMW HA activated the M1 macrophage phenotype with the unique cPLA2α/COX2high and COX1/ALOX15/ALOX5/LTA4Hlow gene and PGE2/PGD2/15-HETEhigh and LXA4low eicosanoid profile. These findings reveal a novel link between HA-mediated inflammation and lipid metabolism.
    Journal of Biological Chemistry 12/2013; 289(7). DOI:10.1074/jbc.M113.515106 · 4.57 Impact Factor
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