Activation of FXR pathway does not alter glial cell function.

BACKGROUND: The nuclear receptor farnesoid-X-receptor (FXR; NR1H4) is expressed not only in the liver, gut, kidney and adipose tissue but also in the immune cells. FXR has been shown to confer protection in several animal models of inflammation, including experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). FXR agonists are currently tested in clinical trials for treatment of human metabolic diseases. The beneficial effect of FXR agonists in EAE suggests that FXR might represent a potential target in inflammatory-demyelinating CNS diseases, such as MS. In MS, oligodendrocytes not only undergo cell death but also contribute to remyelination. This repair mechanism is impaired due to a differentiation block of oligodendroglial progenitor cells. Activation of other nuclear receptors that heterodimerize with FXR promote oligodendroglial differentiation. Therefore, we wanted to address the functional relevance of FXR for glial cells, especially for oligodendroglial differentiation. METHODS: We isolated primary murine oligodendrocytes from FXR-deficient (FXR Ko) and wild-type (WT) mice and determined the effect of FXR deficiency and activation on oligodendroglial differentiation by analysing markers of oligodendroglial progenitor cells (OPCs) and mature oligodendrocytes (OLs) using qRT-PCR and immunocytochemistry. Additionally, we determined whether FXR activation modulates the pro-inflammatory profile of astrocytes or microglia and whether this may subsequently modulate oligodendroglial differentiation. These in vitro studies were complemented by histological analyses of oligodendrocytes in FXR Ko mice. RESULTS: FXR is expressed by OPCs and mature oligodendrocytes. However, lack of FXR did not affect oligodendroglial differentiation in vitro or in vivo. Furthermore, activation of FXR using the synthetic agonist GW4064 did not affect oligodendroglial differentiation, remyelination in an ex vivo model or the expression of pro-inflammatory molecules in astrocytes or microglia. Concordantly, no effects of supernatants from macrophages cultured in the presence of GW4064 were observed regarding a possible indirect impact on oligodendroglial differentiation. CONCLUSIONS: Our data suggest that FXR is dispensable for oligodendroglial differentiation and that FXR agonists, such as GW4064, represent a potential therapeutic approach for MS which specifically targets peripheral immune cells including macrophages but not brain-resident cells, such as oligodendrocytes, astrocytes or microglia.

Distinct neonatal hyperammonemia and liver synthesis dysfunction: case report of a severe MEGDHEL syndrome.

Background/purpose: MEGDHEL syndrome is a rare autosomal recessive metabolic disorder, which is characterized by 3-methylglutaconic aciduria with deafness-dystonia, hepatopathy, encephalopathy and Leigh-like syndrome. It is caused by biallelic pathogenic variants in the SERAC1 gene. Due to the unspecific symptoms and the diverse manifestations of the clinical phenotype, the diagnosis is challenging. Infantile MEGDHEL syndrome often has a severe disease course with acute liver failure. Differentiation from other metabolic disorders is difficult and requires a multidisciplinary approach. Case presentation: A two-day-old small for gestational age neonate was admitted to our pediatric intensive care unit (PICU) due to severe liver failure with distinct hyperammonemia and hypoglycemia without elevation of transaminases or cholestasis. Due to high ammonia level, continuous hemodialysis was established immediately after admission. In addition, protein intake was stopped, and the patient anabolized with intravenous glucose. Temporary stabilization could be achieved after four days. In the further course, severe neurological and cardiocirculatory complications occurred, which ultimately led to the infant's death. In the metabolic diagnostics, a pronounced lactate acidosis and in urine an increased excretion of 3-methylglutaconic acid as well as other metabolites of mitochondrial energy metabolism has been the leading findings besides the hyperammonemia. Post-mortem trio whole genome analysis detected a homozygous pathogenic variant in SERAC1 with evidence of SERAC1 deficiency leading to the diagnosis of infantile MEGDHEL syndrome. Conclusion: When pediatricians are faced with hepatopathy or even acute liver failure without elevation of transaminases or cholestasis in newborns, SERAC1 deficiency should be considered as a potential differential diagnosis. The initial treatment is based on the recommended management of suspected metabolic disorders. Even while no cure is available yet, patients should be offered proper supportive management through a multidisciplinary team. In addition, genetic confirmation of the diagnosis is important for the families, especially regarding further family planning.If a newborn presents with hyperammonemia, hypoglycemia and impaired liver synthesis function without elevation of transaminases or cholestasis, the possible presence of MEGDHEL syndrome due to a SERAC1 mutation should be considered.