Fas (APO-1/CD95) in inflammatory CNS diseases: intrathecal release in bacterial meningitis

Fingerprint changes in CSF composition associated with different aetiologies in human neonatal hydrocephalus: inflammatory cytokines

PURPOSE

Hydrocephalus (HC) has a multifactorial and complex picture of pathophysiology due to aetiology, age at and duration since onset. We have previously identified distinctions in markers of cell death associated with different aetiologies. Here, we examined cerebrospinal fluid (CSF) from human HC neonates for cytokines to identify further distinguishing features of different aetiologies.

METHODS

CSF was collected during routine lumbar puncture or ventricular tap from neonates with hydrocephalus, or with no neurological condition (normal controls). Total protein, Fas receptor, Fas ligand, stem cell factor (SCF), hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGF), insulin growth factor-1 (IGF-1), tumour necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) were measured and compared between 8 unaffected and 28 HC neonatal CSF samples.

RESULTS

Total protein was significantly (P < 0.05) raised in late-onset hydrocephalus (LOH). Fas receptor was raised (P < 0.05) in post-haemorrhagic hydrocephalus (PHH) and spina bifida with hydrocephalus (SB/HC), but no difference in Fas ligand was found. SCF was raised (P < 0.05) in SB/HC. HGF was found in all HC and was increased (P < 0.01) in PHH. Increased VEGF was found in PHH (P < 0.01) and SB/HC (P < 0.05). Variable levels of IL-6, TNF-α and IGF-1 were found in all HC groups compared with none in normal.

CONCLUSIONS

LOH was unusual with significantly raised total protein indicating an inflammatory state. Increased Fas receptor, VEGF, IGF-1 and HGF suggest anti-apoptotic and repair mechanism activation. By contrast, elevated TNF-α and IL-6 indicate inflammatory processes in these neonatal brains. Taken with our previous study, these data indicate that different pathophysiology, inflammation and repair are occurring in HC of different aetiologies and that additional treatment strategies may benefit these infants in addition to fluid diversion.

Modulation of hippocampal neuroplasticity by Fas/CD95 regulatory protein 2 (Faim2) in the course of bacterial meningitis

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Fas-apoptotic inhibitory molecule 2 (Faim2) is a neuron-specific membrane protein and a member of the evolutionary conserved lifeguard apoptosis regulatory gene family. Its neuroprotective effect in acute neurological diseases has been demonstrated in an in vivo model of focal cerebral ischemia. Here we show that Faim2 is physiologically expressed in the human brain with a changing pattern in cases of infectious meningoencephalitis.In Faim2-deficient mice, there was increased caspase-associated hippocampal apoptotic cell death and an increased extracellular signal-regulated kinase pattern during acute bacterial meningitis induced by subarachnoid infection with Streptococcus pneumoniae type 3 strain. However, after rescuing the animals by antibiotic treatment, Faim2 deficiency led to increased hippocampal neurogenesis at 7 weeks after infection. This was associated with improved performance of Faim2-deficient mice compared to wild-type littermates in the Morris water maze, a paradigm for hippocampal spatial learning and memory. Thus, Faim2 deficiency aggravated degenerative processes in the acute phase but induced regenerative processes in the repair phase of a mouse model of pneumococcal meningitis. Hence, time-dependent modulation of neuroplasticity by Faim2 may offer a new therapeutic approach for reducing hippocampal neuronal cell death and improving cognitive deficits after bacterial meningitis.

Development of adjunctive therapies for bacterial meningitis and lessons from knockout mice

Bacterial meningitis is a medical emergency and is optimally managed in an intensive care environment. Despite the use of antibiotics, the prognosis of this disease is poor because of central nervous system complications such as brain edema formation, cerebrovascular alterations, intracranial hemorrhage, and hydrocephalus. Effective adjunctive therapies are still missing. Experimental studies with animal models have provided new insights into the pathophysiology during the acute phase of bacterial meningitis. In recent years, knockout mice have become a powerful tool to investigate the role of particular genes and have also been applied in bacterial meningitis research. The use of these mice offered new insights into the role of different cytokines, proteases, and oxidants involved in the inflammatory cascade. Translating this knowledge into new therapies will provide new treatment strategies for this serious disease in the future.

Fas ligand/Fas system in the brain: regulator of immune and apoptotic responses

Apoptosis, also known as programmed cell death, is the major type of cell death involved in normal development, regeneration, proliferation and pathologic degeneration in the central nervous system (CNS). The apoptotic process can be divided further into two pathways depending on the involvement of mitochondria and related biochemical cascades. The internal pathway of apoptosis is initiated by a variety of cytotoxic stimuli and mediated by the release of cytochrome c and subsequent activation of downstream caspases. The external pathway is mainly triggered by ligation of death receptors such as Fas, tumor necrosis factor (TNF)-related apoptosis inducing ligand-R1 (TRAIL-R1), TRAIL-R2 and TNFRp55, and mediated by direct activation of upstream caspases. The Fas-FasL system has been known as a prototypic inducer of extrinsic cell death responsible for cell-mediated cytotoxicity, peripheral immune regulation, immune privilege and "counterattack" of malignant tumor cells against the host immune system. Fas and FasL are expressed in the normal CNS, and expression increases in inflamed and degenerated brains. Like other specialized tissues such as the eye and testis, the Fas-FasL system is thought to be involved in immune suppressed status in the CNS. Expression of Fas and FasL is significantly elevated in a variety of the neurologic disorders, suggesting the possibility that this system may play roles in degenerative and inflammatory responses in the CNS. Therefore, the FasL-Fas system should be considered as a double-edged sword in the CNS: maintaining the immune suppressed status in normal brain and inducing neuronal cell death and inflammation in a variety of neurologic disorders.

Prolonged intrathecal release of soluble Fas following severe traumatic brain injury in humans

The mechanisms underlying cell death following traumatic brain injury (TBI) are not fully understood. Apoptosis is believed to be one mechanism contributing to a marked and prolonged neuronal cell loss following TBI. Recent data suggest a role for Fas (APO-1, CD95), a type I transmembrane receptor glycoprotein of the nerve growth factor/tumor necrosis factor superfamily, and its ligand (Fas ligand, FasL) in apoptotic events in the central nervous system. A truncated form of the Fas receptor, soluble Fas (sFas) may indicate activation of the Fas/FasL system and act as a negative feedback mechanism, thereby inhibiting Fas mediated apoptosis. Soluble Fas was measured in cerebrospinal fluid (CSF) and serum of 10 patients with severe TBI (GCS< or =8) for up to 15 days post-trauma. No sFas was detected in CSF samples from patients without neurological pathologies. Conversely, after TBI 118 out of 120 CSF samples showed elevated sFas concentrations ranging from 56 to 4327 mU/ml. Paired serum samples showed above normal (8.5 U/ml) sFas concentrations in 5 of 10 patients. Serum levels of sFas were always higher than CSF levels. However, there was no correlation between concentrations measured in CSF and in serum (r(2)=0.078, p=0.02), suggesting that the concentrations in the two compartments are independently regulated. Also, no correlation was found between sFas in CSF and blood brain barrier (BBB) dysfunction as assessed by the albumin CSF/serum quotient (Q(A)), and concentrations of the cytotoxic cytokine tumor necrosis factor-alpha in CSF, respectively. Furthermore, there was no correlation with two markers of immune activation (soluble interleukin-2 receptor and neopterin) in CSF. Maximal CSF levels of sFas correlated significantly (r(2)=0.8191, p<0.001) with the early peaks of neuron-specific enolase in CSF (a marker for neuronal cell destruction), indicating that activation of the Fas mediated pathway of apoptosis may be in part the direct result of the initial trauma. However, the prolonged elevation of sFas in CSF may be caused by the ongoing inflammatory response to trauma and delayed apoptotic cell death.

Increased cerebrospinal fluid concentrations of soluble Fas (CD95/Apo-1) in hydrocephalus

BACKGROUND AND AIMS

The ventricular enlargement observed in children with chronically raised intracranial pressure (ICP) causes a secondary loss of brain tissue. In animal studies of hydrocephalus, programmed cell death (apoptosis) has been found as a major mechanism of neuronal injury. One of the regulators of the apoptotic cell death programme is the receptor mediated Fas/Fas ligand interaction.

METHODS

The apoptosis regulating cytokines soluble Fas (sFas) and soluble Fas ligand (sFasL) were studied in the cerebrospinal fluid (CSF) of 31 hydrocephalic children undergoing shunt surgery for symptomatic hydrocephalus and 18 controls.

RESULTS

High concentrations of sFas were observed in children with hydrocephalus (median 252 ng/ml); in controls sFas was below the detection limit (0.5 ng/ml). sFasL was undetectable in all but one sample.

CONCLUSION

High concentrations of sFas in the CSF of children with hydrocephalus suggest intrinsic sFas production, potentially antagonising pressure mediated Fas activation.

Increased TUNEL staining in brains of autoimmune Fas-deficient mice

Profound changes in brain morphology and behavior coincide with the spontaneous development of systemic autoimmune/inflammatory disease in Fas-deficient MRL-lpr mice. The dendrites atrophy, the density of hippocampal and cortical neurons decreases, and an anxious/depressive-like behavior emerges while lymphoid cells infiltrate into the choroid plexus of MRL-lpr mice. We hypothesized that the inherited lack of the Fas-dependent anti-inflammatory mechanism would lead to unsuppressed immune activity, characterized by reduced apoptosis in the MRL-lpr brain. Using the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeled (TUNEL) method as an indicator of apoptosis, a surprisingly high incidence of TUNEL-positive cells was observed in the hippocampus, choroid plexus and periventricular regions of MRL-lpr mice, 5-10-fold higher than that found in the MRL +/+ control brain. Immunostaining with anti-CD3, CD4 and CD8 monoclonal antibodies showed limited overlap between CD-positive and TUNEL-positive cells, suggesting that the dying cells are for the most part (approximately 70%) not T-lymphocytes. Although further characterization of the phenotype of the dying cells and the mechanism of cell death are required, the present results suggest the involvement of a Fas-independent apoptotic process in neurodegeneration induced by systemic autoimmune disease.

Expression of Fas and Fas ligand after experimental traumatic brain injury in the rat

Apoptotic cell death plays an important role in the cascade of neuronal degeneration after traumatic brain injury (TBI), but the underlying mechanisms are not fully understood. However, increasing evidence suggests that expression of Fas and its ligand (FasL) could play a major role in mediating apoptotic cell death in acute and chronic neurologic disorders. To further investigate the temporal pattern of Fas and FasL expression after experimental TBI in the rat, male Sprague Dawley rats were subjected to unilateral cortical impact injury. The animals were killed and examined for Fas and FasL protein expression and for immunohistologic analysis at intervals from 15 minutes to 14 days after injury. Increased Fas and FasL immunoreactivity was seen in the cortex ipsilateral to the injury site from 15 minutes to 72 hours after the trauma, respectively. Immunohistologic investigation demonstrated a differential pattern of Fas and FasL expression in the cortex, respectively: increased Fas immunoreactivity was seen in cortical astrocytes and neurons from 15 minutes to 72 hours after the injury. In contrast, increased expression of FasL was seen in cortical neurons, astrocytes, and microglia from 15 minutes to 72 hours after impact injury. Concurrent double-labeling examinations using terminal deoxynucleotidyl transferase-mediated deoxyuridine-biotin nick end labeling identified Fas- and FasL-immunopositive cells with high frequency in the cortex ipsilateral to the injury site. In contrast, there was no evidence of Fas- and FasL-immunopositive cells in the hippocampus ipsilateral to the injury site up to 14 days after the trauma. Further, Fas and FasL immunoreactivity was absent in the contralateral cortex and hippocampus at all time points investigated. These results reveal induction of Fas and FasL expression in the cortex after TBI in the rat. Further, these data implicate an involvement of Fas and FasL in the pathophysiologic mechanism of apoptotic neurodegeneration after TBI. Last, these data suggest that strategies aimed to repress posttraumatic Fas- and FasL-induced apoptosis may open new perspectives for the treatment of TBI.