Figure 5.

The various molecular pathways utilized by M-NPLs result in toxicity: 1. Wnt/ β-Catenin signaling pathway

At the molecular level, when Wnt ligands bind to its cell surface transmembrane receptor, β-catenin will be degraded and then aggregate in the cytoplasm. As β-catenin accumulates to a certain level, it dissociates and possibly undergoes nuclear translocation, thus regulating the expressions of some downstream genes such as α-SMA, fibronectin, and TGF-β, all of which are implicated in fibrogenesis. (1) M-NPLs administration caused an increase in the level of Wnt, β-catenin, p-β-catenin; markers of Wnt/ β-catenin signaling pathway and TGF-β, Collagen I, Collagen III, α-SMA and fibronectin; markers of fibrosis. (2) cGAS/STING Pathway:M-NPLs following interaction with the nucleus and mitochondria causes damage and release of nuclear and mitochondrial DNA fragments into the cytoplasm, which is recognized by the cGAS protein. cGAS protein activates STING protein which in turn causes the internalization of NF-κB. NF-κB causes promote the transcription of pro-inflammatory cytokines. (3) NRF2 signaling pathway:M-NPLs exposure resulted in an increase of intracellular ROS, which caused activation of MAPK proteins (p38 and ERK). These proteins could dissociate Keap-1 from NRF2, resulting in NRF2 translocation into the nucleus and enhanced transcription of antioxidant genes. (4) NF-κB signaling pathway:M-NPLs exposure caused an increase in the level of NFkB protein, which after nuclear translocation, caused an increase in the level of inflammatory, pro-inflammatory cytokines, and M1 polarization.