Inflammation in Neuronal Intranuclear Inclusion Disease (NIID): mechanisms, biomarkers, and therapeutic implications

Neuronal intranuclear inclusion disease (NIID) is a group of neurodegenerative diseases caused by GGC repeat expansion and is characterized by diverse clinical manifestations that may characterize a spectrum of underlying pathologies. Extensive inflammatory cell infiltration has been observed in multiple tissues obtained from NIID patients, including the temporal lobe, skin, lungs, colon, kidneys, and fallopian tubes. Intriguingly, eosinophilic intranuclear inclusions have been identified within the nuclei of these infiltrating inflammatory cells, underscoring the central role of inflammation in NIID. The infiltration of immune cells within the brain tissue of NIID patients highlights the critical role of neuroinflammation in disease pathogenesis. Moreover, in patients with NIID, not only is the neutrophil-to-lymphocyte ratio (NLR) markedly elevated but also the peripheral blood cytokine profile substantially altered. Despite the prominent involvement of central and peripheral inflammation in NIID and experimental evidence at the cellular level demonstrating that activation of the NF-κB‒NLRP3 pathway can reduce the burden of intranuclear inclusions and ameliorate phenotypic manifestations, therapeutic strategies targeting inflammation have yet to alter the disease course in human patients. This review presents the latest advancements in the study of inflammatory markers in NIID and the GGC100 cell model. Specifically, it explores the role of inflammatory molecular markers in disease pathogenesis and their correlation with clinical parameters. Furthermore, we summarize the potential applications of certain inflammatory biomarkers as novel therapeutic targets and strategies, which may pave the way for expanded therapeutic interventions in NIID.