Inflammasome involvement in Rett syndrome subclinical inflammation

Mutations in X-linked MECP2 gene cause most cases of Rett syndrome (RTT), a rare neurodevelopmental disorder typically affecting girls. Although RTT is mainly a neurological disorder, affected patients show many systemic abnormalities including redox imbalance, mitochondrial dysfunctions, metabolic alterations, gastrointestinal disorders, breathing disturbances and recurrent infections. Growing evidence highlights the importance of inflammation and immune system dysregulation in RTT pathophysiological mechanisms. Inflammasomes, cytoplasmic multi-protein complexes, regulate host immune response against pathogen infections and cellular stress. Assembly of NLRP3/ASC inflammasome leads to pro-caspase-1 activation and subsequent IL-1β and IL-18 maturation and secretion. Inflammasome dysregulation drives pathological conditions in a wide variety of human diseases. To investigate the possible role of inflammasome in the persistent and subclinical inflammatory status observed in RTT patients, we treated primary dermal fibroblasts from RTT and control subjects with LPS followed by ATP Analysis of confocal immunofluorescence showed a significant increased colocalization for NLRP3 and ASC signals in unstimulated RTT fibroblasts. This result parallels with a higher level of ASC-b isoform in untreated RTT cells, as determined by immunoblotting. Interestingly, while control fibroblasts responded to LPS/ATP with increased NLRP3/ASC colocalization, RTT fibroblasts appeared to be unresponsive to the treatment, showing a decreased NLRP3/ASC colocalization and no change in ASC-b levels. In addition, procaspase-1 and caspase-1 protein levels were significantly lower in unstimulated RTT, but casp-1/procasp-1 ratio was higher in RTT than control fibroblasts. Finally, IL-1β gene expression was higher in unstimulated RTT cells, but showing no change after LPS/ATP treatment. Taken together, our results suggest a possible basal activation of inflammasome in RTT cells that, on the other hand, appear to be unable to respond properly at the inflammatory stimulus. The dysregulated inflammasome activity could contribute to the subclinical inflammatory status of RTT, thereby identifying a new potential target for therapeutic intervention.