Reduction of PrP(C) in human cerebrospinal fluid after spinal cord injury

Antibiotics with therapeutic effects on spinal cord injury: a review

Accumulating evidence indicates that a considerable number of antibiotics exert anti-inflammatory and neuroprotective effects in different central and peripheral nervous system diseases including spinal cord injury (SCI). Both clinical and preclinical studies on SCI have found therapeutic effects of antibiotics from different families on SCI. These include macrolides, minocycline, β-lactams, and dapsone, all of which have been found to improve SCI sequels and complications. These antibiotics may target similar signaling pathways such as reducing inflammatory microglial activity, promoting autophagy, inhibiting neuronal apoptosis, and modulating the SCI-related mitochondrial dysfunction. In this review paper, we will discuss the mechanisms underlying therapeutic effects of these antibiotics on SCI, which not only could supply vital information for investigators but also guide clinicians to consider administering these antibiotics as part of a multimodal therapeutic approach for management of SCI and its complications.

The Role of Shed PrPc in the Neuropathogenesis of HIV Infection

HIV-1 enters the CNS soon after peripheral infection and causes chronic neuroinflammation and neuronal damage that leads to cognitive impairment in 40-70% of HIV-infected people. The nonpathogenic cellular isoform of the human prion protein (PrP^c) is an adhesion molecule constitutively expressed in the CNS. Previously, our laboratory showed that shed PrP^c (sPrP^c) is increased in the cerebrospinal fluid of HIV-infected people with cognitive deficits as compared with infected people with no impairment. In this article, we demonstrate that CCL2 and TNF-α, inflammatory mediators that are elevated in the CNS of HIV-infected people, increase shedding of PrP^c from human astrocytes by increasing the active form of the metalloprotease ADAM10. We show that the consequence of this shedding can be the production of inflammatory mediators, because treatment of astrocytes with rPrP^c increased secretion of CCL2, CXCL-12, and IL-8. Supernatants from rPrP^c-treated astrocytes containing factors produced in response to this treatment, but not rPrP^c by itself, cause increased chemotaxis of both uninfected and HIV-infected human monocytes, suggesting a role for sPrP^c in monocyte recruitment into the brain. Furthermore, we examined whether PrP^c participates in glutamate uptake and found that rPrP^c decreased uptake of this metabolite in astrocytes, which could lead to neurotoxicity and neuronal loss. Collectively, our data characterize mediators involved in PrP^c shedding and the effect of this sPrP^c on monocyte chemotaxis and glutamate uptake from astrocytes. We propose that shedding of PrP^c could be a potential target for therapeutics to limit the cognitive impairment characteristic of neuroAIDS.

Characterization of the Antibody Response after Cervical Spinal Cord Injury

The immune system plays a critical and complex role in the pathobiology of spinal cord injury (SCI), exerting both beneficial and detrimental effects. Increasing evidence suggests that there are injury level-dependent differences in the immune response to SCI. Patients with traumatic SCI have elevated levels of circulating autoantibodies against components of the central nervous system, but the role of these antibodies in SCI outcomes remains unknown. In rodent models of mid-thoracic SCI, antibody-mediated autoimmunity appears to be detrimental to recovery. However, whether autoantibodies against the spinal cord are generated following cervical SCI (cSCI), the most common level of injury in humans, remains undetermined. To address this knowledge gap, we investigated the antibody responses following cSCI in a rat model of injury. We found increased immunoglobulin G (IgG) and IgM antibodies in the spinal cord in the subacute phase of injury (2 weeks), but not in more chronic phases (10 and 20 weeks). At 2 weeks post-cSCI, antibodies were detected at the injury epicenter and co-localized with the astroglial scar and neurons of the ventral horn. These increased levels of antibodies corresponded with enhanced activation of immune responses in the spleen. Higher counts of antibody-secreting cells were observed in the spleen of injured rats. Further, increased levels of secreted IgG antibodies and enhanced proliferation of T-cells in splenocyte cultures from injured rats were found. These findings suggest the potential development of autoantibody responses following cSCI in the rat. The impact of the post-traumatic antibody responses on functional outcomes of cSCI is a critical topic that requires further investigation.

Primary blast-induced traumatic brain injury in rats leads to increased prion protein in plasma: a potential biomarker for blast-induced traumatic brain injury

Traumatic brain injury (TBI) is deemed the "signature injury" of recent military conflicts in Afghanistan and Iraq, largely because of increased blast exposure. Injuries to the brain can often be misdiagnosed, leading to further complications in the future. Therefore, the use of protein biomarkers for the screening and diagnosis of TBI is urgently needed. In the present study, we have investigated the plasma levels of soluble cellular prion protein (PrPC) as a novel biomarker for the diagnosis of primary blast-induced TBI (bTBI). We hypothesize that the primary blast wave can disrupt the brain and dislodge extracellular localized PrPC, leading to a rise in concentration within the systemic circulation. Adult male Sprague-Dawley rats were exposed to single pulse shockwave overpressures of varying intensities (15-30 psi or 103.4-206.8 kPa] using an advanced blast simulator. Blood plasma was collected 24 h after insult, and PrPC concentration was determined with a modified commercial enzyme-linked immunosorbent assay (ELISA) specific for PrPC. We provide the first report that mean PrPC concentration in primary blast exposed rats (3.97 ng/mL ± 0.13 SE) is significantly increased compared with controls (2.46 ng/mL ± 0.14 SE; two tailed test p < 0.0001). Furthermore, we report a mild positive rank correlation between PrPC concentration and increasing blast intensity (psi) reflecting a plateaued response at higher pressure magnitudes, which may have implications for all military service members exposed to blast events. In conclusion, it appears that plasma levels of PrPC may be a novel biomarker for the detection of primary bTBI.

Prion Protein Signaling in the Nervous System—A Review and Perspective

Prion protein (PrPC) was originally known as the causative agent of transmissible spongiform encephalopathy (TSE) but with recent research, its true function in cells is becoming clearer. It is known to act as a scaffolding protein, binding multiple ligands at the cell membrane and to be involved in signal transduction, passing information from the extracellular matrix (ECM) to the cytoplasm. Its role in the coordination of transmitters at the synapse, glyapse, and gap junction and in short- and long-range neurotrophic signaling gives PrPC a major part in neural transmission and nervous system signaling. It acts to regulate cellular function in multiple targets through its role as a controller of redox status and calcium ion flux. Given the importance of PrPC in cell physiology, this review considers its potential role in disease apart from TSE. The putative functions of PrPC point to involvement in neurodegenerative disease, neuropathic pain, chronic headache, and inflammatory disease including neuroinflammatory disease of the nervous system. Potential targets for the treatment of disease influenced by PrPC are discussed.

Brain immune interactions and air pollution: macrophage inhibitory factor (MIF), prion cellular protein (PrP(C)), Interleukin-6 (IL-6), interleukin 1 receptor antagonist (IL-1Ra), and interleukin-2 (IL-2) in cerebrospinal fluid and MIF in serum differentiate urban children exposed to severe vs. low air pollution

Mexico City Metropolitan Area children chronically exposed to high concentrations of air pollutants exhibit an early brain imbalance in genes involved in oxidative stress, inflammation, innate and adaptive immune responses along with accumulation of misfolded proteins observed in the early stages of Alzheimer and Parkinson's diseases. A complex modulation of serum cytokines and chemokines influences children's brain structural and gray/white matter volumetric responses to air pollution. The search for biomarkers associating systemic and CNS inflammation to brain growth and cognitive deficits in the short term and neurodegeneration in the long-term is our principal aim. We explored and compared a profile of cytokines, chemokines (Multiplexing LASER Bead Technology) and Cellular prion protein (PrP(C)) in normal cerebro-spinal-fluid (CSF) of urban children with high vs. low air pollution exposures. PrP(C) and macrophage inhibitory factor (MIF) were also measured in serum. Samples from 139 children ages 11.91 ± 4.2 years were measured. Highly exposed children exhibited significant increases in CSF MIF (p = 0.002), IL6 (p = 0.006), IL1ra (p = 0.014), IL-2 (p = 0.04), and PrP(C) (p = 0.039) vs. controls. MIF serum concentrations were higher in exposed children (p = 0.009). Our results suggest CSF as a MIF, IL6, IL1Ra, IL-2, and PrP(C) compartment that can possibly differentiate air pollution exposures in children. MIF, a key neuro-immune mediator, is a potential biomarker bridge to identify children with CNS inflammation. Fine tuning of immune-to-brain communication is crucial to neural networks appropriate functioning, thus the short and long term effects of systemic inflammation and dysregulated neural immune responses are of deep concern for millions of exposed children. Defining the linkage and the health consequences of the brain / immune system interactions in the developing brain chronically exposed to air pollutants ought to be of pressing importance for public health.