bXanthine oxidase (XO), also known as xanthine oxidoreductase, has long been considered an important host defense molecule in the intestine and in breastfed infants. Here, we present evidence that XO is released from and active in intestinal tissues and fluids in response to infection with enteropathogenic Escherichia coli (EPEC) and Shiga-toxigenic E. coli (STEC), also known as enterohemorrhagic E. coli (EHEC). XO is released into intestinal fluids in EPEC and STEC infection in a rabbit animal model. XO activity results in the generation of surprisingly high concentrations of uric acid in both cultured cell and animal models of infection. Hydrogen peroxide (H 2 O 2 ) generated by XO activity triggered a chloride secretory response in intestinal cell monolayers within minutes but decreased transepithelial electrical resistance at 6 to 22 h. H 2 O 2 generated by XO activity was effective at killing laboratory strains of E. coli, commensal microbiotas, and anaerobes, but wild-type EPEC and STEC strains were 100 to 1,000 times more resistant to killing or growth inhibition by this pathway. Instead of killing pathogenic bacteria, physiologic concentrations of XO increased virulence by inducing the production of Shiga toxins from STEC strains. In vivo, exogenous XO plus the substrate hypoxanthine did not protect and instead worsened the outcome of STEC infection in the rabbit ligated intestinal loop model of infection. XO released during EPEC and STEC infection may serve as a virulence-inducing signal to the pathogen and not solely as a protective host defense. Xanthine oxidase (XO), also known as xanthine oxidoreductase (XOR) and xanthine dehydrogenase (XDH), has long been considered an important host defense molecule in the liver, intestine, and breastfed infants (1-3). In this report, we will use the traditional name xanthine oxidase (XO), intending this name to encompass all the various chemical reactions this enzyme can catalyze. XO is expressed in epithelial cells of the gastrointestinal (GI) tract and is secreted in large amounts in milk, where it is localized to the external surface of fat globules. XO is also abundant in liver and expressed in the cornea. XO is not abundant in lung or brain and is present in serum at low levels except after liver or intestinal injury.We previously showed that enteropathogenic Escherichia coli (EPEC) infection triggers the release of ATP from host cells and that this ATP is broken down to ADP, AMP, and adenosine. We wished to determine if the catabolic pathway extended to produce inosine and purines such as hypoxanthine, xanthine, and uric acid (Fig. 1). In our initial experiments with cultured T84 cells, we were surprised to observe that infection with EPEC, but not EPEC mutants or commensal E. coli, triggered release of uric acid into the culture supernatants, achieving uric acid concentrations up to 200 M. Later, we observed similar high levels of uric acid in intestinal fluids recovered from rabbits infected with EPEC and Shigatoxigenic E. coli (STEC) using the ligated in...

Chronic demyelination in the human CNS is characterized by an inhibitory microenvironment that impairs recruitment and differentiation of oligodendrocyte progenitor cells (OPCs) leading to failed remyelination and axonal atrophy. By network-based transcriptomics, we identified sulfatase 2 (Sulf2) mRNA in activated human primary OPCs. Sulf2, an extracellular endosulfatase, modulates the signaling microenvironment by editing the pattern of sulfation on heparan sulfate proteoglycans. We found that Sulf2 was increased in demyelinating lesions in multiple sclerosis and was actively secreted by human OPCs. In experimental demyelination, elevated OPC Sulf1/2 expression directly impaired progenitor recruitment and subsequent generation of oligodendrocytes thereby limiting remyelination. Sulf1/2 potentiates the inhibitory microenvironment by promoting BMP and WNT signaling in OPCs. Importantly, pharmacological sulfatase inhibition using PI-88 accelerated oligodendrocyte recruitment and remyelination by blocking OPC-expressed sulfatases. Our findings define an important inhibitory role of Sulf1/2 and highlight the potential for modulation of the heparanome in the treatment of chronic demyelinating disease.

The proinflammatory cytokine IFN-γ, which is chronically elevated in multiple sclerosis, induces pathologic quiescence in human oligodendrocyte progenitor cells (OPCs) via upregulation of the transcription factor PRRX1. In this study using animals of both sexes, we investigated the role of heparan sulfate proteoglycans in the modulation of IFN-γ signaling following demyelination. We found that IFN-γ profoundly impaired OPC proliferation and recruitment following adult spinal cord demyelination. IFN-γ-induced quiescence was mediated by direct signaling in OPCs as conditional genetic ablation ofIFNγR1(Ifngr1) in adult NG2+OPCs completely abrogated these inhibitory effects. Intriguingly, OPC-specific IFN-γ signaling contributed to failed oligodendrocyte differentiation, which was associated with hyperactive Wnt/Bmp target gene expression in OPCs. We found that PI-88, a heparan sulfate mimetic, directly antagonized IFN-γ to rescue human OPC proliferation and differentiationin vitroand blocked the IFN-γ-mediated inhibitory effects on OPC recruitmentin vivo. Importantly, heparanase modulation by PI-88 or OGT2155 in demyelinated lesions rescued IFN-γ-mediated axonal damage and demyelination. In addition to OPC-specific effects, IFN-γ-augmented lesions were characterized by increased size, reactive astrogliosis, and proinflammatory microglial/macrophage activation along with exacerbated axonal injury and cell death. Heparanase inhibitor treatment rescued many of the negative IFN-γ-induced sequelae suggesting a profound modulation of the lesion environment. Together, these results suggest that the modulation of the heparanome represents a rational approach to mitigate the negative effects of proinflammatory signaling and rescuing pathologic quiescence in the inflamed and demyelinated human brain.SIGNIFICANCE STATEMENTThe failure of remyelination in multiple sclerosis contributes to neurologic dysfunction and neurodegeneration. The activation and proliferation of oligodendrocyte progenitor cells (OPCs) is a necessary step in the recruitment phase of remyelination. Here, we show that the proinflammatory cytokine interferon-γ directly acts on OPCs to induce pathologic quiescence and thereby limit recruitment following demyelination. Heparan sulfate is a highly structured sulfated carbohydrate polymer that is present on the cell surface and regulates several aspects of the signaling microenvironment. We find that pathologic interferon-γ can be blocked by modulation of the heparanome following demyelination using either a heparan mimetic or by treatment with heparanase inhibitor. These studies establish the potential for modulation of heparanome as a regenerative approach in demyelinating disease.

In previous work, we identified xanthine oxidase (XO) as an important enzyme in the interaction between the host and enteropathogenic Escherichia coli (EPEC) and Shiga-toxigenic E. coli (STEC). Many of the biological effects of XO were due to the hydrogen peroxide produced by the enzyme. We wondered, however, if uric acid generated by XO also had biological effects in the gastrointestinal tract. Uric acid triggered inflammatory responses in the gut, including increased submucosal edema and release of extracellular DNA from host cells. While uric acid alone was unable to trigger a chloride secretory response in intestinal monolayers, it did potentiate the secretory response to cyclic AMP agonists. Uric acid crystals were formed in vivo in the lumen of the gut in response to EPEC and STEC infections. While trying to visualize uric acid crystals formed during EPEC and STEC infections, we noticed that uric acid crystals became enmeshed in the neutrophilic extracellular traps (NETs) produced from host cells in response to bacteria in cultured cell systems and in the intestine in vivo. Uric acid levels in the gut lumen increased in response to exogenous DNA, and these increases were enhanced by the actions of DNase I. Interestingly, addition of DNase I reduced the numbers of EPEC bacteria recovered after a 20-h infection and protected against EPEC-induced histologic damage. Xanthine oxidase (XO), also known as xanthine oxidoreductase (XOR), has been hailed as an important host defense against enteric pathogens for decades (1, 2). In a recent study, however, we found that XO could have deleterious as well as beneficial effects in the context of infection with Shiga-toxigenic Escherichia coli (STEC) (3). One of the deleterious effects of XO was its ability to induce production of the Shiga toxins (Stx) from STEC bacteria. Low to intermediate amounts of XO activity generated enough H 2 O 2 to induce Stx but not enough to actually kill STEC or enteropathogenic E. coli (EPEC) bacteria, resulting in an "uncanny valley" of worsened disease outcome.In addition to H 2 O 2 , XO also generates uric acid as a product. While uric acid used to be viewed as an inert waste product of purine metabolism, recent advances have highlighted the biological roles of uric acid in inflammation and innate immunity (4, 5). Although monosodium urate (MSU) is the technically more accurate term, we will use "uric acid" here, since the latter term is deeply entrenched in the biomedical literature. In a previous study, we found that uric acid crystals were formed in vivo in response to EPEC and STEC infection in the lumen of the gastrointestinal (GI) tract (6). In the present study, we focused on determining the biological effects of uric acid, as opposed to H 2 O 2 , produced by XO. We investigated the effects of uric acid on inflammatory responses, as well as secretory responses, in intestinal tissues and found that uric acid acted as a potentiator or modulator of proinflammatory or prosecretory agonists and that its crystals became enmeshed in the...

Endogenous remyelination in demyelinating diseases such as multiple sclerosis is contingent upon the successful differentiation of oligodendrocyte progenitor cells (OPCs). Signaling via the Gαq-coupled muscarinic receptor (M1/3R) inhibits human OPC differentiation and impairs endogenous remyelination in experimental models. We hypothesized that calcium release following Gαq-coupled receptor (GqR) activation directly regulates human OPC (hOPC) cell fate. In this study, we show that specific GqR agonists activating muscarinic and metabotropic glutamate receptors induce characteristic oscillatory calcium release in hOPCs and that these agonists similarly block hOPC maturation in vitro. Both agonists induce calcium release from endoplasmic reticulum (ER) stores and store operated calcium entry (SOCE) likely via STIM/ORAI-based channels. siRNA mediated knockdown (KD) of obligate calcium sensors STIM1 and STIM2 decreased the magnitude of muscarinic agonist induced oscillatory calcium release and attenuated SOCE in hOPCs. In addition, STIM2 expression was necessary to maintain the frequency of calcium oscillations and STIM2 KD reduced spontaneous OPC differentiation. Furthermore, STIM2 siRNA prevented the effects of muscarinic agonist treatment on OPC differentiation suggesting that SOCE is necessary for the anti-differentiative action of muscarinic receptor-dependent signaling. Finally, using a gain-of-function approach with an optogenetic STIM lentivirus, we demonstrate that independent activation of SOCE was sufficient to significantly block hOPC differentiation and this occurred in a frequency dependent manner while increasing hOPC proliferation. These findings suggest that intracellular calcium oscillations directly regulate hOPC fate and that modulation of calcium oscillation frequency may overcome inhibitory Gαq-coupled signaling that impairs myelin repair.