Emre Tarakcioglu

Microglia play a crucial role in maintaining the health of the central nervous system (CNS) through synaptic pruning, debris clearance, and pathogen elimination; however, sustained microglial inflammation can lead to neuronal damage. The NLRP3 inflammasome, a key regulator of inflammatory responses, has been implicated in various CNS diseases. Perineuronal nets (PNNs) are specialized structures that encase neuron somas, protect neurons from oxidative stress, and stabilize synaptic connections. While inflammatory microglia can degrade PNNs, the specific role of inflammasomes in this degradation process remains unclear. To investigate the role of inflammasomes in degradation of PNNs, neurons were derived from the murine Neuro-2a cell line using retinoic acid. Subsequently, we induced the NLRP3 inflammasome in the murine N9 microglial cell line via exposure to lipopolysaccharide and ATP. The effect of NLRP3 activation on degradation of PNNs was examined by coculturing neurons and microglia with and without NLRP3 inhibition for 24 h. PNNs were quantified using immunofluorescence staining with Wisteria floribunda agglutinin and neurocan antibodies, both of which bind to PNNs. Our findings demonstrate that coculture with NLRP3-activated microglia reduces the percentage of WFA- and neurocan-positive neurons whereas the inhibition of NLRP3 reverses this effect. Our findings highlight the significant role of the NLRP3 inflammasome in the degradation of PNNs in inflammatory states. Moreover, our research suggests that targeting the NLRP3 inflammasome could protect PNN-positive neurons from the damaging effects of inflammation. These findings might provide insight into the inflammatory mechanisms underlying loss of PNNs. Not applicable.

NLRP3 inflammasome is a part of the innate immune system and responsible for the rapid identification and eradication of pathogenic microbes, metabolic stress products, reactive oxygen species, and other exogenous agents. NLRP3 inflammasome is overactivated in several neurodegenerative, cardiac, pulmonary, and metabolic diseases. Therefore, suppression of inflammasome activation is of utmost clinical importance. Melatonin is a ubiquitous hormone mainly produced in the pineal gland with circadian rhythm regulatory, antioxidant, and immunomodulatory functions. Melatonin is a natural product and safer than most chemicals to use for medicinal purposes. Many in vitro and in vivo studies have proved that melatonin alleviates NLRP3 inflammasome activity via various intracellular signaling pathways. In this review, the effect of melatonin on the NLRP3 inflammasome in the context of diseases will be discussed.

Neuronal senescence, triggered by telomere shortening, oncogene activation, DNA damage, or oxidative stress, has been associated with neurodegenerative diseases’ pathogenesis. Therefore, preventing neuronal senescence could be a novel treatment strategy for neurodegenerative diseases. Lithium (Li), the first-line treatment against bipolar disorder, has been shown to have neuroprotective effects in clinical, pre-clinical, and in vitro studies. Li can protect cells from senescence, and its effect on neuronal senescence was investigated in our study. Furthermore, we also investigated the effects of Li on the senescence-associated miR-34a/Sirt1/p53 pathway. In this study, hydrogen peroxide was used as an inducer for the “stress-induced premature senescence” model. In the senescence model, we have assessed Li’s effects on senescence by analyzing β-galactosidase activity, Sudan Black B, and senescence-associated heterochromatin foci (SAHF) stainings, and on cell cycle arrest by BrdU staining. Furthermore, expression levels of senescence and cell cycle arrest-related proteins (p53, p21, p16INK4a, and SIRT1) by western blotting. Finally, the effects of Li on senescence-associated miR-34a levels were measured by quantitative PCR. We show via Sudan Black B staining, β-Gal activity assay, and by detecting SAHF, Li protects against senescence in neuronal cells. Then, Li’s effect on signaling has also been determined on pathways involved in senescence and cell cycle arrest. Moreover, we have observed that Li has a modulatory effect on miR-34a expression. Therefore, we posit that Li suppresses senescence in neuronal cells and that this effect is mediated through miR-34a/Sirt1/p53 axis.