Mimicking disruption of brain-immune system-joint communication results in collagen type II-induced arthritis in non-susceptible PVG rats.

The brain-immune system-joint communication is disrupted during collagen type II (CII) arthritis in DA rats. Since PVG rats are not susceptible to arthritis induction, comparison of hypothalamic and peripheral neuro-endocrine and immune responses between immunized DA and PVG rats might help to explain their different susceptibility to develop the disease. PVG and DA rats were immunized with CII. Corticosterone, neurotransmitters, anti-CII antibodies, and cytokine concentrations in plasma, and hypothalamic neurotransmitters and cytokines were determined by ELISA, Luminex, HPLC and RT-qPCR. Adrenalectomy or sham-operation was performed in PVG and DA rats 14 days before immunization. Basal plasma corticosterone and adrenaline concentrations were significantly higher, and plasma cytokines and hypothalamic noradrenaline were lower in PVG rats than in DA rats. While DA rats developed severe arthritis upon immunization (maximum score 16), only 12 out of 28 PVG rats showed minimal symptoms (score 1-2). The density of sympathetic nerve fibers in arthritic joints of DA rats markedly decreased, but it remained stable in immunized PVG rats. The ratio corticosterone to IL-1ß levels in plasma was markedly higher in immunized PVG rats than in arthritic DA rats. Adrenalectomy resulted in severe arthritis in PVG rats upon immunization with CII. While DA rats show an altered immune-brain communication that favors the development of arthritis, PVG rats express a protective neuro-endocrine milieu, particularly linked to the basal tone of the HPA axis. Mimicking disruption of this axis elicits arthritis in non-susceptible PVG rats.

A cytokine network involving brain-borne IL-1ß, IL-1ra, IL-18, IL-6, and TNFα operates during long-term potentiation and learning.

We have previously shown that long-term potentiation (LTP) induces hippocampal IL-1ß and IL-6 over-expression, and interfering their signalling either inhibits or supports, respectively, LTP maintenance. Consistently, blockade of endogenous IL-1 or IL-6 restricts or favours hippocampal-dependent memory, effects that were confirmed in genetically manipulated mice. Since cytokines are known for their high degree of mutual crosstalk, here we studied whether a network of cytokines with known neuromodulatory actions is activated during LTP and learning. We found that, besides IL-1ß and IL-6, also IL-1 receptor antagonist (IL-1ra) and IL-18, but not TNFα are over-expressed during LTP maintenance in freely moving rats. The increased expression of these cytokines is causally related to an increase in synaptic strength since it was abrogated when LTP was interfered by blockade of NMDA-glutamate receptors. Likewise, IL-1 and IL-6 were found to be over-expressed in defined regions of the hippocampus during learning a hippocampus-dependent task. However, during learning, changes in IL-18 were restricted to the dorsal hippocampus, and no differences in TNFα and IL1-ra expression were noticed in the hippocampus. Noticeably, IL-1ra transcripts were significantly reduced in the prefrontal cortex. The relation between cytokine expression and learning was causal because such changes were not observed in animals from a pseudo-trained group that was subject to the same manipulation but could not learn the task. Taken together with previous studies, we conclude that activation of a cytokine network in the brain is a physiologic relevant phenomenon not only for LTP maintenance but also for certain types of learning.

Chronic neuropathic pain-like behavior correlates with IL-1ß expression and disrupts cytokine interactions in the hippocampus.

We have proposed that neuropathic pain engages emotional learning, suggesting the involvement of the hippocampus. Because cytokines in the periphery contribute to induction and maintenance of neuropathic pain but might also participate centrally, we used 2 neuropathic pain models, chronic constriction injury (CCI) and spared nerve injury (SNI), to investigate the temporal profile of hippocampal cytokine gene expression in 2 rat strains that show different postinjury behavioral threshold sensitivities. SNI induced long-lasting allodynia in both strains, while CCI induced allodynia with time-dependent recovery in Sprague Dawley (SD) and no allodynia in Wistar Kyoto (WK) rats. In WK rats, only SNI induced sustained upregulation of hippocampal interleukin (IL)-1ß, while IL-6 expression was transiently increased and no significant changes in IL-1ra expression were detected. Conversely, in SD rats, SNI resulted in sustained and robust increased hippocampal IL-1ß expression, which was only transient in rats with CCI. In this strain, IL-6 expression was not affected in any of the 2 injury models and IL-1ra expression was significantly increased in rats with SNI or CCI at late phases. We found that the degree and development of neuropathic pain depend on the specific nerve injury model and rat strain; that hippocampal IL-1ß mRNA levels correlate with neuropathic pain behavior; that, in contrast to sham-operated animals, there are no correlations between hippocampal IL-1ß and IL-1ra or IL-6 in neuropathic rats; and that alterations in cytokine expression are restricted to the hippocampus contralateral to the injury side, again implying that the observed changes reflect nociception.

When immune-neuro-endocrine interactions are disrupted: experimentally induced arthritis as an example.

We studied whether, in parallel to the activity of the hypothalamus-pituitary-adrenal axis and the sympathetic nervous system, hypothalamic cytokine expression and monoaminergic neurotransmitter concentrations are affected during the development and chronification of arthritis induced by immunization of rats with type II collagen. Corticosterone levels were increased only transiently, and were even below the normal range as the disease progressed. Increased adrenaline blood levels and hypothalamic IL-1beta and IL-6 overexpression were observed only during the induction phase of the disease. The increase in hypothalamic noradrenaline content during the symptomatic phase was paralleled by a gradual loss of sympathetic fibers in the joints. Depletion of hypothalamic noradrenergic neurons at this time did not affect the symptomatology. Contrary to observations in healthy animals, no correlation between hypothalamic IL-1beta expression and noradrenaline content was observed in rats with arthritis. The dissociation between hypothalamic cytokine gene expression and noradrenergic neuronal activity, the lack of sustained stimulation of the stress axes, and the loss of sympathetic signals in the joints indicate that the communication between afferent immune messages to the central nervous system and two main efferent anti-inflammatory pathways under control of the brain are disrupted during experimental arthritis.

Re-exposure to endotoxin induces differential cytokine gene expression in the rat hypothalamus and spleen.

This study was designed to investigate whether the pattern of hypothalamic and splenic cytokine expression induced by peripheral administration of a bacterial lipopolysaccharide (LPS) is affected by prior exposure to LPS derived from another bacterial strain. Injection of LPS from Salmonella enteritidis (LPS(2)) alone resulted in increased hypothalamic gene expression of IL-1beta, IL-6, TNFalpha, IL-1ra and IL-10. However, pre-exposure to LPS derived from Escherichia coli (LPS(1)) 3 weeks before, significantly attenuated hypothalamic IL-1ra, IL-6 and IL-10 expression. IL-1beta expression also tended to be lower. This pattern contrasted with the robust cytokine expression in the spleen of LPS(2)-treated rats previously exposed to LPS(1), since pre-treatment with endotoxin resulted in a significantly greater response of IL-1beta and IL-1ra to LPS(2). Expression of TNFalpha and IL-10 also tended to be higher. Pre-treatment with LPS(1) did not significantly affect the marked increase in corticosterone and adrenaline blood levels induced by LPS(2). Thus, while endotoxin pre-exposure seemed not to induce a "tolerant" state in the periphery as judged by the immune and endocrine parameters evaluated upon re-stimulation, expression of four of the six cytokines measured was decreased in the hypothalamus. This is the first demonstration that endotoxin priming can differentially affect cytokine expression in the central nervous system and peripheral tissues when a host is confronted with a second, acute, pro-inflammatory stimulus. These results may provide new evidence for the involvement of cytokine pathways in the central nervous system in modulating peripheral inflammation and mediating cognitive and behavioural alterations during inflammatory diseases.

Disrupted brain-immune system-joint communication during experimental arthritis.

OBJECTIVE: To explore the hypothesis that, in parallel with alterations in the hypothalamus-pituitary-adrenal axis and the sympathetic nervous system, hypothalamic cytokine expression and monoaminergic neurotransmitter concentrations are affected during the course of arthritis development induced by type II collagen. This hypothesis was based on evidence that acute inflammatory processes induce cytokine expression in the brain and affect neuronal activity. We also studied whether depletion of hypothalamic noradrenaline can affect peripheral joint disease. METHODS: Hypothalamic cytokine gene expression and neurotransmitter concentration, parameters of inflammation, and joint innervation were evaluated during arthritis development in rats induced by injection of type II collagen in Freund's incomplete adjuvant. Noradrenergic neurons in the brain were depleted with 6-hydroxydopamine. RESULTS: Transiently increased corticosterone levels, followed by increased adrenaline levels and hypothalamic interleukin-1beta (IL-1beta) and IL-6 overexpression were observed only during the induction phase of the disease. Hypothalamic noradrenaline content was increased during the symptomatic phase and was paralleled by a gradual loss of noradrenergic fibers in the joints. The positive correlation between hypothalamic IL-1beta expression and noradrenaline content in control groups was not observed in rats in which arthritis developed. Depletion of hypothalamic noradrenergic neurons when arthritis was established did not affect the course of the disease. CONCLUSION: The dissociation between hypothalamic cytokine gene expression and noradrenergic neuronal activity, the lack of sustained stimulation of the stress axes, and the loss of sympathetic signals in the joints indicate a disruption in communication between afferent immune messages to the central nervous system and 2 main efferent antiinflammatory pathways under control of the brain during collagen-induced arthritis.

IL-1 resets glucose homeostasis at central levels.

Administration of IL-1beta results in a profound and long-lasting hypoglycemia. Here, we show that this effect can be elicited by endogenous IL-1 and is related to not only the capacity of the cytokine to increase glucose uptake in peripheral tissues but also to mechanisms integrated in the brain. We show that (i) blockade of IL-1 receptors in the brain partially counteracted IL-1-induced hypoglycemia; (ii) peripheral administration or induction of IL-1 production resulted in IL-1beta gene expression in the hypothalamus of normal and insulin-resistant, leptin receptor-deficient, diabetic db/db mice; (iii) IL-1-treated normal and db/db mice challenged with glucose did not return to their initial glucose levels but remained hypoglycemic for several hours. This effect was largely antagonized by blockade of IL-1 receptors in the brain; and (iv) when animals with an advanced Type II diabetes were treated with IL-1 and challenged with glucose, they died in hypoglycemia. However, when IL-1 receptors in the brains of these diabetic mice were blocked, they survived, and glucose blood levels approached those that these mice had before IL-1 administration. The prolonged hypoglycemic effect of IL-1 is insulin-independent and develops against increased levels of glucocorticoids, catecholamines, and glucagon. These findings, together with the present demonstration that this effect is integrated in the brain and is paralleled by IL-1beta expression in the hypothalamus, indicate that this cytokine can reset glucose homeostasis at central levels. Such reset, along with the peripheral actions of the cytokine, would favor glucose uptake by immune cells during inflammatory/immune processes.

Expression of IL-1beta in supraspinal brain regions in rats with neuropathic pain.

We examined mRNA expression of the pro-inflammatory cytokine IL-1beta in the brainstem, thalamus, and prefrontal cortex in two rat models of neuropathic pain. Rats received a neuropathic injury: spared nerve injury (SNI) or chronic constriction injury (CCI), sham injury, or were minimally handled (control). Neuropathic pain-like behavior was monitored by tracking tactile thresholds. SNI-injured animals showed a robust decrease in tactile thresholds of the injured foot, while CCI-injured animals did not show tactile threshold changes. Ten or 24 days after nerve injury, IL-1beta gene expression in the brain was determined by RT-PCR. IL-1beta expression changes were observed mainly at 10 days after injury in the SNI animals, contralateral to the injury side, with increased expression in the brainstem and prefrontal cortex. The results indicate that neuro-immune activation in neuropathic pain conditions includes supraspinal brain regions, suggesting cytokine modulation of supraspinal circuitry of pain in neuropathic conditions.

A reconstituted replication and transcription system for Ebola virus Reston and comparison with Ebola virus Zaire.

The only known filovirus, which presumably is not pathogenic for humans, is Ebola virus (EBOV) Reston. When EBOV Reston and the highly pathogenic EBOV Zaire were grown in cell culture, comparison of the replication kinetics showed a clear growth impairment of EBOV Reston, indicating that the replication cycle of EBOV Reston might be delayed. In addition, the cytopathic effect caused by the virus was much milder with EBOV Reston than with EBOV Zaire. To compare replication and transcription of EBOV Reston and Zaire, a reconstituted minigenomic replication and transcription system based on reverse genetics has been established for EBOV Reston. This system was used to exchange the EBOV Zaire and EBOV Reston nucleocapsid (NC) proteins NP, VP35, VP30, and L, which catalyze replication and transcription. Furthermore, chimeric minigenomes were constructed containing the cis-acting replication signals of EBOV Zaire combined with those of EBOV Reston. Surprisingly, the cis-acting signals as well as almost all NC proteins could be exchanged between EBOV Reston and Zaire, suggesting a high degree of functional homology of the replication/transcription complexes of EBOV Zaire and EBOV Reston. Only the combination of EBOV Zaire VP35 and EBOV Reston L did not result in replication and transcription activity. Although these two proteins did not constitute an active polymerase complex, it was shown by immunofluorescence analysis that they were still able to interact.