Revisiting the role of IL-1 signaling in the development of apical periodontitis

Apical periodontitis (AP) develops as a result of an immune response to pulpal bacterial infection, and various cytokines are involved in the pathogenesis of AP, with Interleukin (IL)-1 being considered a key cytokine. The role of IL-1 in the pathogenesis of AP has been well studied. It is known that IL-1 expression in periapical lesions correlates closely with the development of AP. IL-1 is a potent bone-resorptive cytokine that induces osteoclast formation and activation. Hence, inhibiting its signaling with IL-1 receptor antagonist (IL-1RA) results in a reduction in periapical lesion size. On the other hand, IL-1 is also a central cytokine that combats bacterial infection by activating innate immune responses. Therefore, a complete loss of IL-1 signaling leads to a failure to limit bacterial dissemination and consequently exacerbates AP. In vivo, IL-1 expression is tightly regulated and its signaling is modulated to optimize the immune response. Obesity causes systemic low-grade chronic inflammation and increases the risk of cardiovascular, renal, and other disorders. In experimentally induced AP, obesity significantly increases periapical bone loss, albeit the underlying mechanism remains unclear. Recent technological innovations have enabled more comprehensive and detailed analyses than previously, leading to new insights into the role of IL-1RA in regulating IL-1 signaling, and modulating apical lesion progression in obesity. In this review, we provide a brief overview of the function of IL-1 in AP development, with special emphasis on the latest findings in normal weight and obese states.

Single-Cell Analysis of Multiple Steps of Dynamic NF-κB Regulation in Interleukin-1α-Triggered Tumor Cells Using Proximity Ligation Assays

The frequently occurring heterogeneity of cancer cells and their functional interaction with immune cells in the tumor microenvironment raises the need to study signaling pathways at the single cell level with high precision, sensitivity, and spatial resolution. As aberrant NF-κB activity has been implicated in almost all steps of cancer development, we analyzed the dynamic regulation and activation status of the canonical NF-κB pathway in control and IL-1α-stimulated individual cells using proximity ligation assays (PLAs). These systematic experiments allowed the visualization of the dynamic dissociation and re-formation of endogenous p65/IκBα complexes and the nuclear translocation of NF-κB p50/p65 dimers. PLA combined with immunostaining for p65 or with NFKBIA single molecule mRNA-FISH facilitated the analysis of (i) further levels of the NF-κB pathway, (i) its functionality for downstream gene expression, and (iii) the heterogeneity of the NF-κB response in individual cells. PLA also revealed the interaction between NF-κB p65 and the P-body component DCP1a, a new p65 interactor that contributes to efficient p65 NF-κB nuclear translocation. In summary, these data show that PLA technology faithfully mirrored all aspects of dynamic NF-κB regulation, thus allowing molecular diagnostics of this key pathway at the single cell level which will be required for future precision medicine.

Interleukin-1 receptor accessory proteins are required for normal homeostatic responses to sleep deprivation

Interleukin-1β (IL1) is a sleep regulatory substance. The IL1/IL1 type 1 receptor complex requires a receptor accessory protein (AcP) to signal. There are three isoforms of AcP. In the current experiments, mice lacking a neuron-specific isoform, called AcPb knockout (AcPb KO), or mice lacking AcP + AcPb isoforms (AcP KO) or wild-type (WT) mice were used. Spontaneous sleep and sleep responses to sleep deprivation (SD) between zeitgeber time (ZT) 20-ZT4 and ZT8-ZT16 were characterized. Furthermore, somatosensory cortical protein extracts were examined for phosphorylated (p) proto-oncogene tyrosine-protein kinase sarcoma (Src) and p38MAPK levels at ZT4 and ZT16 and after SD. Spontaneous sleep was similar in the three strains, except rapid eye movement sleep (REMS) duration between ZT12-ZT16 was greater in AcP KO than WT mice. After SD at ZT4, only WT mice had non-REMS (NREMS) rebounds. All mouse strains lacked an NREMS rebound after SD at ZT16. All strains after both SD periods had REMS rebounds. AcPb KO mice, but not AcP KO mice, had greater EEG delta wave (0.5-4 Hz) power during NREMS than WT mice. p-Src was very low at ZT16 but high at ZT4, whereas p-p38MAPK was low at ZT4 and high at ZT16. p-p38MAPK levels were not sensitive to SD. In contrast, p-Src levels were less after SD at the P = 0.08 level of significance in the strains lacking AcPb. We conclude that AcPb is required for NREMS responses to sleep loss, but not for SD-induced EEG delta wave or REMS responses.NEW & NOTEWORTHY Interleukin-1β (IL1), a well-characterized sleep regulatory substance, requires an IL1 receptor accessory protein (AcP); one of its isoforms is neuron-specific (called AcPb). We showed that in mice, AcPb is required for nonrapid eye movement sleep responses following 8 h of sleep loss ending 4 h after daybreak but did not affect rapid eye movement sleep rebound. Sleep loss reduced phosphorylation of proto-oncogene tyrosine-protein kinase sarcoma but not of the less sensitive p38MAPK, downstream IL1 signaling molecules.