Acute exposure to perfluorooctane sulfonate exacerbates heat-induced oxidative stress in a tropical coral species

Perfluorooctane sulfonate (PFOS) is among the most commonly per- and poly-fluoroalkyl substances (PFAS) found in environmental samples. Nevertheless, the effect of this legacy persistent organic contaminant has never been investigated on corals to date. Corals are the keystone organisms of coral reef ecosystems and sensitive to rising ocean temperatures, but it is not understood how the combination of elevated temperature and PFOS exposure will affect them. Therefore, the aims of the present study were (1) to evaluate the time-dependent bioconcentration and depuration of PFOS in the scleractinian coral Stylophora pistillata using a range of PFOS exposure concentrations, and (2) to assess the individual and combined effects of PFOS exposure and elevated seawater temperature on key physiological parameters of the corals. Our results show that the coral S. pistillata rapidly bioconcentrates PFOS from the seawater and eliminates it 14 days after ceasing the exposure. We also observed an antagonistic effect between elevated temperature and PFOS exposure. Indeed, a significantly reduced PFOS bioconcentration was observed at high temperature, likely due to a loss of symbionts and a higher removal of mucus compared to ambient temperature. Finally, concentrations of PFOS consistent with ranges observed in surface waters were non-lethal to corals, in the absence of other stressors. However, PFOS increased lipid peroxidation in coral tissue, which is an indicator of oxidative stress and enhanced the thermal stress-induced impairment of coral physiology. This study provides valuable insights into the combined effects of PFOS exposure and ocean warming for coral's physiology. PFOS is usually the most prevalent but not the only PFAS defected in reef waters, and thus it will be also important to monitor PFAS mixture concentrations in the oceans and to study their combined effects on aquatic wildlife.

Photophysiology and daily primary production of a temperate symbiotic gorgonian

Gorgonians are one of the most important benthic components of tropical and temperate areas, and play a fundamental role as ecosystem engineers. Although global warming and pollution increasingly threaten them, the acquisition of nutrients, which is a key process in fitness and stress resistance, has been poorly investigated in such species. This study has thus used an advanced in situ incubation chamber for the first time with gorgonians, to assess the daily acquisition of nutrients and the photophysiology of the Mediterranean symbiotic species, Eunicella singularis. The xanthophyll cycle was assessed in parallel. This work has revealed that E. singularis presents a different functioning than the Mediterranean symbiotic corals. This gorgonian indeed relies on both autotrophy and heterotrophy in summer to optimize its energetic budget, while corals mainly shift to autotrophy for their respiratory needs and tissue growth. In addition, although E. singularis lives in the same depths/locations, and harbours the same symbiont genotype than the corals, the photosynthetic performances of their respective symbionts are significantly different. Indeed, E. singularis acquired 2-3 times less autotrophic carbon from its symbionts than corals, but maintained a positive carbon budget by reducing respiration rates, and by presenting maximal photosynthetic rates throughout the day, suggesting a very efficient light utilization. Almost no photoinhibition was observed under very high light levels, because of the induction of a xanthophyll photoprotection process. These results help understanding why gorgonians often dominate many benthic ecosystems.

Canaux ioniques et démyélinisation : les fondements d’un traitement de l’encéphalomyélite autoimmune expérimentale (EAE) par des bloqueurs des canaux potassium

Voltage-gated potassium channels (Kv channels) are ion channels, openings of which provide an outward flow of potassium ions repolarising the cell. In neurons, Kv channels play a crucial role in action potential repolarisation and in shaping neuronal excitability. In non-excitable cells, such as T lymphocytes, Kv channels and calcium-activated K+ channels (KCa channels) determine the driving force for Ca2+ entry. During T cell activation the calcium entry depolarises the cell and increases the cytosolic calcium concentration, which in return activates Kv and KCa channels. K+ channel opening repolarises the cell and drives the membrane potential to a negative voltage. The roles of Kv channels in nervous and immune systems have been investigated here by means of a rat experimental autoimmune disease of the central nervous system, the experimental autoimmune encephalomyelitis (EAE). EAE is characterised clinically by paralysis, and pathologically by inflammatory cell infiltrations into the brain and the spinal cord. Among the inflammatory cells, T lymphocytes play a major role. Hence, EAE can be adoptively transferred into syngenic animals by the injection of T cells reactive to myelin antigens. During adoptive-EAE, somato-sensory evoked potentials recorded along the spinal tracts decrease in amplitude and axonal propagation is disrupted. We have analysed the consequences of Kv channels blockade by peptidyl toxins on central nerve conduction, on T cell activation and on the time course of EAE. In rat optic nerves, Kv channels have been identified up from postnatal day 1. Their blockade by kaliotoxin (a scorpion toxin) or by dendrotoxin-I (a snake toxin) enlarges the compound action potentials, demonstrating the participation of Kv channels to spike repolarisation. This effect disappears at adult age due to the sequestration of Kv channels under the myelin, in the paranodal regions. During acute demyelination by lysophosphatidyl-choline, the surface area of compound action potential decreased probably because conduction block occurred. Demyelination unmasked Kv channels, which are again accessible to toxins. Their blockade by dendrotoxin-I or kaliotoxin favoured a slow delayed conduction suggesting that those Kv channel blockers exert a neurological benefit during demyelinating diseases. In a T-cell line reactive to myelin basic protein antigen, which is used to adoptively transfer experimental autoimmune encephalomyelitis, Kv1.3 channels are constitutively expressed. Their blockade leads to a pronounced reduction of the T cell proliferative response, cytokine production and Ca2+ influx. In the rat, blockade of Kv1.3 inhibits the delayed type hypersensitivity response to myelin basic protein prevents and treats adoptive experimental autoimmune encephalomyelitis. Blockade of Kv channels alone or in combination with KCa channels improves the symptoms of the disease. These results demonstrate that K+ channel blockers displaying high selectivity are potent immunosuppressive agents with beneficial symptomatic effects in experimental autoimmune encephalomyelitis.

Selective blockade of T lymphocyte K(+) channels ameliorates experimental autoimmune encephalomyelitis, a model for multiple sclerosis

Adoptive transfer experimental autoimmune encephalomyelitis (AT-EAE), a disease resembling multiple sclerosis, is induced in rats by myelin basic protein (MBP)-activated CD4(+) T lymphocytes. By patch-clamp analysis, encephalitogenic rat T cells stimulated repeatedly in vitro expressed a unique channel phenotype ("chronically activated") with large numbers of Kv1.3 voltage-gated channels (approximately 1500 per cell) and small numbers of IKCa1 Ca(2+)-activated K(+) channels (approximately 50-120 per cell). In contrast, resting T cells displayed 0-10 Kv1.3 and 10-20 IKCa1 channels per cell ("quiescent" phenotype), whereas T cells stimulated once or twice expressed approximately 200 Kv1.3 and approximately 350 IKCa1 channels per cell ("acutely activated" phenotype). Consistent with their channel phenotype, [(3)H]thymidine incorporation by MBP-stimulated chronically activated T cells was suppressed by the peptide ShK, a blocker of Kv1.3 and IKCa1, and by an analog (ShK-Dap(22)) engineered to be highly specific for Kv1.3, but not by a selective IKCa1 blocker (TRAM-34). The combination of ShK-Dap(22) and TRAM-34 enhanced the suppression of MBP-stimulated T cell proliferation. Based on these in vitro results, we assessed the efficacy of K(+) channel blockers in AT-EAE. Specific and simultaneous blockade of the T cell channels by ShK or by a combination of ShK-Dap(22) plus TRAM-34 prevented lethal AT-EAE. Blockade of Kv1.3 alone with ShK-Dap(22), but not of IKCa1 with TRAM-34, was also effective. When administered after the onset of symptoms, ShK or the combination of ShK-Dap(22) plus TRAM-34 greatly ameliorated the clinical course of both moderate and severe AT-EAE. We conclude that selective targeting of Kv1.3, alone or with IKCa1, may provide an effective new mode of therapy for multiple sclerosis.

Selective blocking of voltage-gated K+ channels improves experimental autoimmune encephalomyelitis and inhibits T cell activation

Kaliotoxin (KTX), a blocker of voltage-gated potassium channels (Kv), is highly selective for Kv1.1 and Kv1.3. First, Kv1.3 is expressed by T lymphocytes. Blockers of Kv1.3 inhibit T lymphocyte activation. Second, Kv1.1 is found in paranodal regions of axons in the central nervous system. Kv blockers improve the impaired neuronal conduction of demyelinated axons in vitro and potentiate the synaptic transmission. Therefore, we investigated the therapeutic properties of KTX via its immunosuppressive and symptomatic neurological effects, using experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. The T line cells used to induce adoptive EAE were myelin basic protein (MBP)-specific, constitutively contained mRNA for Kv1.3. and expressed Kv1.3. These channels were shown to be blocked by KTX. Activation is a crucial step for MBP T cells to become encephalitogenic. The addition of KTX during Ag-T cell activation led to a great reduction in the MBP T cell proliferative response, in the production of IL-2 and TNF, and in Ca(2+) influx. Furthermore, the addition of KTX during T cell activation in vitro led a decreased encephalitogenicity of MBP T cells. Moreover, KTX injected into Lewis rats impaired T cell function such as the delayed-type hypersensitivity. Lastly, the administration of this blocker of neuronal and lymphocyte channels to Lewis rats improved the symptoms of EAE. We conclude that KTX is a potent immunosuppressive agent with beneficial effects on the neurological symptoms of EAE.

Effect of physical exercise on adoptive experimental auto-immune encephalomyelitis in rats

The aim of the study was to determine whether different programmes of exercise influence adoptive monophasic experimental auto-immune encephalomyelitis (adoptive EAE), a paralytic disease mediated by T-cells. Adoptive EAE was induced by the transfer of activated encephalitogenic T-lymphocytes into syngeneic recipients (Lewis rats, n = 85) and its development was followed by two independent observers. The results showed that 2 days of severe exercise (250 and 300 min) performed after the adoptive transfer of EAE slightly delayed the onset of the disease (P <0.008) and the day of its maximal severity (P <0.016) without affecting the overall severity of the disease. When this programme of exercise was performed before the cell transfer, it had no effect (P > 0.05). Two more moderate exercise programmes (5 x 120 min of running at constant speed or 5 x 60 min of running at variable speed, 5 consecutive days) performed between the adoptive transfer and the onset of the disease did not modify the development of the clinical signs of adoptive EAE (P >0.05). These results showed that severe exercise slightly influenced the effector phase of monophasic EAE and confirmed that physical exercise performed before the onset of experimental auto-immune diseases did not exacerbate the clinical signs.

Anergy induction in encephalitogenic T cells by brain microvessel endothelial cells is inhibited by interleukin-1

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory disease of the central nervous system (CNS) which can be induced, in susceptible strains like Lewis rats, by transfer of activated myelin basic protein (MBP)-specific CD4+ T lymphocytes. The role of cerebral endothelium in the onset of EAE, with regard to adhesion, activation and infiltration in the CNS of encephalitogenic T lymphocytes, is not fully understood. When pretreated by interferon-gamma, the immortalized Lewis rat brain microvessel endothelial (RBE4) cells expressed major histocompatibility complex class II molecules and stimulated MBP-specific proliferation and cytolytic activity of the syngeneic encephalitogenic T cell line, designated PAS. However, RBE4-stimulated PAS lymphocytes subsequently entered an unresponsive state, known as anergy. When inoculated in syngeneic animals, anergic PAS cells, although still cytotoxic, failed to induce EAE, and no cell infiltration was detectable within CNS. The addition of interleukin-1 beta (IL-1 beta) during MBP presentation by RBE4 cells prevented T cell anergy induction, and maintained T cell encephalitogenicity, although PAS cells stimulated in these conditions caused delayed and attenuated clinical signs of EAE, with only discrete inflammatory lesions in the CNS, compared with EAE induced by PAS cells fully activated by thymic cells. Altogether, our results indicate that MBP presentation by brain microvessel endothelial cells to encephalitogenic T cells induces T cell anergy and loss of pathogenicity. In addition, IL-1 beta co-stimulation of T cells prevents anergy induction in vitro and at least partially maintains encephalitogenicity in vivo.

Regulation of experimental autoimmune encephalomyelitis: inhibition of adoptive experimental autoimmune encephalomyelitis by 'recovery-associated suppressor cells'

We have previously shown the presence of suppressor cells in Lewis rats at the time of spontaneous recovery from experimental autoimmune encephalomyelitis (EAE). These cells, called 'recovery-associated suppressor cells' (RASC), are capable of preventing active EAE and inhibiting in vitro the specific proliferative response of encephalitogenic anti-MBP T cell line cells. The present investigations were undertaken in order to lend support to the hypothesis that RASC play an active role in the recovery. We found that RASC can prevent adoptive EAE when admixed with already activated, but not resting, anti-MBP T cells or when injected into the recipients separately from the encephalitogenic cells. They can also arrest the course of an ongoing disease when injected after the beginning of the clinical signs. This study provides the first direct demonstration of the downregulation of an ongoing EAE by suppressor cells.

Regulation of experimental autoimmune encephalomyelitis. Specificity of the 'recovery-associated' suppressor cells

We previously reported the presence of suppressor cells in Lewis rats at the very time of spontaneous recovery from experimental autoimmune encephalomyelitis. As these 'recovery-associated' suppressor cells might be implicated in the self-cure process, we investigated their specificity on the in vitro lymphoproliferative responses of a T cell line specific for myelin basic protein (MBP). We report now that these suppressor cells found in the thymus are specific for MBP, and not for T cell receptors, contrasting with the 'post-recovery' suppressor cell specificity reported by others. Furthermore, they do not recognize the encephalitogenic peptide 71-84, suggesting that their specificity involves an epitope outside (or partially out of) the encephalitogenic sequence.