Axonal injury in multiple sclerosis

Tyrphostin A9 protects axons in experimental autoimmune encephalomyelitis through activation of ERKs

AIMS

Small molecule compound tyrphostin A9 (A9), an inhibitor of platelet-derived growth factor (PDGF) receptor, was previously reported by our group to stimulate extracellular signal-regulated kinase 1 (ERK1) and 2 (ERK2) in neuronal cells in a PDGF receptor-irrelevant manner. The study aimed to investigate whether A9 could protect axons in experimental autoimmune encephalomyelitis through activation of ERKs.

MAIN METHODS

A9 treatment on the protection on neurite outgrowth in SH-SY5Y neuroblastoma cells and primary substantia nigra neuron cultures from the neurotoxin MPP+ were analyzed. Then, clinical symptoms as well as ERK1/2 activation, axonal protection induction, and the abundance increases of the regeneration biomarker GAP-43 in the CNS in the relapsing-remitting experimental autoimmune encephalomyelitis (EAE) model were verified.

KEY FINDINGS

A9 treatment could stimulate neurite outgrowth in SH-SY5Y neuroblastoma cells and protect primary substantia nigra neuron cultures from the neurotoxin MPP+. In the relapsing-remitting EAE model, oral administration of A9 successfully ameliorated clinical symptoms, activated ERK1/2, induced axonal protection, and increased the abundance of the regeneration biomarker GAP-43 in the CNS. Interestingly, gene deficiency of ERK1 or ERK2 disrupted the beneficial effects of A9 in MOG-35-55-induced EAE.

SIGNIFICANCE

These results demonstrated that small molecule compounds that stimulate persistent ERK activation in vitro and in vivo may be useful in protective or restorative treatment for neurodegenerative diseases.

Tau Is Elevated in Pediatric Patients on Extracorporeal Membrane Oxygenation

Neurologic injury is a known and feared complication of extracorporeal membrane oxygenation (ECMO). Neurologic biomarkers may have a role in assisting in early identification of such. Axonal biomarker tau has not been investigated in the pediatric ECMO population. The objective of this study is to evaluate plasma levels of tau in pediatric patients supported with ECMO. Eighteen patients requiring ECMO support in a quaternary pediatric intensive care unit at a university-affiliated children's hospital from October 2015 to February 2017 were enrolled. Patients undergoing extracorporeal cardiopulmonary resuscitation or recent history of bypass were excluded. Plasma tau was measured using enzyme-linked immunosorbent assay. Neuroimaging was reviewed for acute neurologic injury, and tau levels were analyzed to assess for correlation. Tau was significantly higher in ECMO patients than in control subjects. Sixty-one percent of subjects had evidence of acute brain injury on neuroimaging, but tau level did not correlate with injury. Subjects with multifocal injury all experienced infarction and had significantly higher tau levels on ECMO day 3 than patients with isolated injury. In addition, peak tau levels of neuro-injured subjects were compared with controls and noninjured ECMO subjects using receiver operating curve analysis. This study demonstrates preliminary evidence of axonal injury in pediatric ECMO patients.

Bioenergetics profile of CD4(+) T cells in relapsing remitting multiple sclerosis subjects

Multiple sclerosis (MS) is a chronic inflammatory autoimmune demyelinating disease of the central nervous system. There are four clinical forms of MS, the most common of which is characterized by a relapsing remitting course (RRMS). The etiology of MS is unknown, but many studies suggested that genetic, environmental and infectious agents may contribute to the development of this disease. In experimental autoimmune encephalomyelitis (EAE), the animal model for MS, it has been shown that CD4(+) T cells play a key role in MS pathogenesis. In fact, these cells are able to cross the blood-brain barrier and cause axonal damage with neuronal death. T cell activation critically depends on mitochondrial ATP synthesis and reactive oxygen species (ROS) production. Interestingly, lots of studies linked the oxidative damage arising from mitochondrial changes to neurodegenerative disorders, such as MS. Based on these evidences, this work focused on the metabolic reprogramming of CD4(+) T cells in MS subjects, being this cell population directly implicated in pathogenesis of disease, paying attention to mitochondrial function and response to oxidative stress. Such aspects, once clarified, may open new opportunities for a therapeutic metabolic modulation of MS disorder.

Discovery of fingolimod, the sphingosine 1-phosphate receptor modulator and its application for the therapy of multiple sclerosis

Fingolimod (FTY720) is a first-in-class, orally active, sphingosine 1-phosphate (S1P)-receptor modulator with a structure closely related to sphingosine. The compound was discovered by chemical modification of a natural product, myriocin. Phosphorylated form of FTY720 acts as a functional antagonist at S1P receptor type 1 (S1P(1)), inhibits lymphocyte egress from secondary lymphoid organs and shows immunomodulating effects. Phase III studies in multiple sclerosis demonstrated that oral FTY720 had superior efficacy compared with intramuscular IFN-β1a (AVONEX(®)) with regard to reducing the rate of relapse and the number of inflammatory lesions in the CNS. FTY720 has been approved as a new therapeutic drug for multiple sclerosis in more than 50 countries, including the USA, Japan and some of those in the EU.

Recombinant T cell receptor ligands: immunomodulatory, neuroprotective and neuroregenerative effects suggest application as therapy for multiple sclerosis

Recombinant T cell receptor (TCR) ligands (RTL) represent the minimal interactive surface with antigen-specific T cell receptors. These novel constructs fold similarly to native four-domain MHC/peptide complexes but deliver suboptimal and qualitatively different signals that cause a 'cytokine switch' to anti-inflammatory factors in targeted encephalitogenic T cells. RTL treatment can reverse clinical and histological signs of experimental autoimmune encephalomyelitis (EAE) and most dramatically can promote myelin and axonal recoveiy in the CNS of mice with chronic disease. These properties of RTL suggest that this novel antigen-specific approach may hold unusual promise as a therapy for multiple sclerosis.

5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside attenuates experimental autoimmune encephalomyelitis via modulation of endothelial-monocyte interaction

Experimental autoimmune encephalomyelitis (EAE) is a model for studying multiple sclerosis (MS), a chronic demyelinating disorder of the CNS. 5-Aminoimidazole-4-carboxamide ribonucleoside (AICAR), an activator of AMP-activated protein kinase (AMPK), has been reported to show antiinflammatory and immunomodulatory effects in various models of inflammation. Recently, we have reported AICAR-mediated attenuation of active and passive EAE in mouse model [Nath et al. (2005) J. Immunol. 175:566-574]. Here we used a rat model of acute EAE to show antiinflammatory effects of AICAR after daily treatment starting at onset of the disease. By maintaining the blood-brain barrier (BBB), AICAR-administered animals showed lower clinical scores compared with untreated EAE animals. AICAR inhibited the infiltration of inflammatory cells across the BBB, resulting in lowered expression of proinflammatory mediators in the CNS and protection from severe demyelination. By using in vitro model of endothelial-leukocyte interaction, we showed that AICAR inhibited adhesion of monocytes to tumor necrosis factor-alpha-activated endothelial cells. One of the mechanisms of this action is through down-regulation of expression of endothelial cell adhesion molecules via modulation of nuclear factor kappaB activation. The data suggest that AICAR attenuates EAE progression by limiting infiltration of leukocytes across the BBB, thereby controlling the consequent inflammatory reaction in the CNS.

Antigen-specific therapy promotes repair of myelin and axonal damage in established EAE

Inflammation results in CNS damage in multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), an animal model of MS. It is uncertain how much repair of injured myelin and axons can occur following highly selective anti-inflammatory therapy in EAE and MS. In this study, SJL/J mice with established EAE were treated successfully with an antigen-specific recombinant T cell receptor ligand (RTL), RTL401, a mouse I-A(s)/PLP-139-151 construct, after the peak of EAE. To define the mechanisms by which late application of RTL401 inhibits EAE, we evaluated mice at different time points to assess the levels of neuroinflammation and myelin and axon damage in their spinal cords. Our results showed that RTL401 administered after the peak of acute EAE induced a marked reduction in inflammation in the CNS, associated with a significant reduction of demyelination, axonal loss and ongoing damage. Electron microscopy showed that RTL-treated mice had reduced pathology compared with mice treated with vehicle and mice at the peak of disease, as demonstrated by a decrease in continued degeneration, increase in remyelinating axons and the presence of an increased number of small, presumably regenerative axonal sprouts. These findings indicate that RTL therapy targeting encephalitogenic T cells may promote CNS neuroregenerative processes.

5-aminoimidazole-4-carboxamide ribonucleoside: a novel immunomodulator with therapeutic efficacy in experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, is a Th1-mediated inflammatory demyelinating disease of the CNS. AMP-activated protein kinase was reported recently to have anti-inflammatory activities by negatively regulating NF-kappaB signaling. In this study, we investigated the prophylactic and therapeutic efficacy of an AMP-activated protein kinase activator, 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), in active and passive EAE induced by active immunization with PLP(139-151) or MOG(35-55) and in adoptive transfer of PLP(139-151)-sensitized T cells, respectively. In vivo treatment with AICAR exerted both prophylactic and therapeutic effects on EAE, attenuating the severity of clinical disease. The anti-inflammatory effects of AICAR were associated with the inhibition of the Ag-specific recall responses and inhibition of the Th1-type cytokines IFN-gamma and TNF-alpha, whereas it induced the production of Th2 cytokines IL-4 and IL-10. Treatment of PLP(139-151)-specific T cells in vitro with AICAR decreased their expression of T-bet in response to IL-12, a Th1 transcription factor, whereas in response to IL-4, it induced the expression and phosphorylation of Th2 transcription factors GATA3 and STAT6, respectively. Moreover, treatment of APCs in vitro with AICAR inhibited their capability to present the proteolipid protein peptide to PLP(139-151)-specific T cells. In an irrelevant Th1-mediated, OT-2 TCR transgenic mouse model, AICAR impaired in vivo Ag-specific expansion of CD4(+) T cells. Together, these findings show for the first time that AICAR is a novel immunomodulator with promising beneficial effects for the treatment of multiple sclerosis and other Th1-mediated inflammatory diseases.

Magnetic resonance spectroscopy in the monitoring of multiple sclerosis

In addition to providing information on tissue structure, magnetic resonance (MR) technology offers the potential to investigate tissue metabolism and function. MR spectroscopy (MRS) offers a wealth of data on the biochemistry of a selected brain tissue volume, which represent potential surrogate markers for the pathology underlying multiple sclerosis (MS). In particular, the N-acetylaspartate peak in an MR spectrum is a putative marker of neuronal and axonal integrity, and the choline peak appears to reflect cell-membrane metabolism. On this basis, a diminished N-acetylaspartate peak is interpreted to represent neuronal/axonal dysfunction or loss, and an elevated choline peak represents heightened cell-membrane turnover, as seen in demyelination, remyelination, inflammation, or gliosis. Therefore, MRS may provide a unique tool to evaluate the severity of MS, establish a prognosis, follow disease evolution, understand its pathogenesis, and evaluate the efficacy of therapeutic interventions, which complements the information obtained from the various forms of assessment made by conventional MR imaging.