It has been documented in in vitro studies that zinc oxide nanoparticles (ZnO NPs) are capable of inducing oxidative stress, which plays a crucial role in ZnO NP-mediated apoptosis. However, the underlying molecular mechanism of apoptosis in neurocytes induced by ZnO NP exposure was not fully elucidated. In this study, we investigated the potential mechanisms of apoptosis provoked by ZnO NPs in cultured primary astrocytes by exploring the molecular signaling pathways triggered after ZnO NP exposure. ZnO NP exposure was found to reduce cell viability in MTT assays, increase lactate dehydrogenase (LDH) release, stimulate intracellular reactive oxygen species (ROS) generation, and elicit caspase-3 activation in a dose- and time-dependent manner. Apoptosis occurred after ZnO NP exposure as evidenced by nuclear condensation and poly(ADP-ribose) polymerase-1 (PARP) cleavage. A decrease in mitochondrial membrane potential (MMP) with a concomitant increase in the expression of Bax/Bcl-2 ratio suggested that the mitochondria also mediated the pathway involved in ZnO NP-induced apoptosis. In addition, exposure of the cultured cells to ZnO NPs led to phosphorylation of c-Jun N-terminal kinase (JNK), extracellular signal-related kinase (ERK), and p38 mitogen-activated protein kinase (p38 MAPK). Moreover, JNK inhibitor (SP600125) significantly reduced ZnO NP-induced cleaved PARP and cleaved caspase-3 expression, but not ERK inhibitor (U0126) or p38 MAPK inhibitor (SB203580), indicating that JNK signaling pathway is involved in ZnO NP-induced apoptosis in primary astrocytes.

Airborne fine particulate matter (PM_2.5) can cause pulmonary inflammation and even fibrosis, however, the underlying molecular mechanisms of the pathogenesis of PM_2.5 exposure have not been fully appreciated. In the present study, we explored the dynamics of glycolysis and modification of histone lactylation in macrophages induced by PM_2.5-exposure in both in vivo and in vitro models. Male C57BL/6 J mice were anesthetized and administrated with PM_2.5 by intratracheal instillation once every other day for 4 weeks. Mouse RAW264.7 macrophages and alveolar epithelial MLE-12 cells were treated with PM_2.5 for 24 h. We found that PM_2.5 significantly increased lactate dehydrogenase (LDH) activities and lactate contents, and up-regulated the mRNA expression of key glycolytic enzymes in the lungs and bronchoalveolar lavage fluids of mice. Moreover, PM_2.5 increased the levels of histone lactylation in both PM_2.5-exposed lungs and RAW264.7 cells. The pro-fibrotic cytokines secreted from PM_2.5-treated RAW264.7 cells triggered epithelial-mesenchymal transition (EMT) in MLE-12 cells through activating transforming growth factor-β (TGF-β)/Smad2/3 and VEGFA/ERK pathways. In contrast, LDHA inhibitor (GNE-140) pretreatment effectively alleviated PM_2.5-induced pulmonary inflammation and fibrosis via inhibiting glycolysis and subsequent modification of histone lactylation in mice. Thus, our findings suggest that PM_2.5-induced glycolysis and subsequent modification of histone lactylation play critical role in the PM_2.5-associated pulmonary fibrosis.

Animal and epidemiological studies have suggested that exposure to airborne particulate matter (PM) with an aerodynamic diameter less than 2.5 μm (PM_2.5) is associated with the risk of developing type 2 diabetes. However, the mechanism underlying this risk is poorly understood. In the present study, we investigated the effects of PM_2.5 exposure on glucose homeostasis and related signaling pathways in mice. Wild-type and nuclear factor erythroid 2-related factor 2 (Nrf2) knockout (Nrf2^−/−) C57BL/6 male mice were exposed to either ambient concentrated PM_2.5 or filtered air (FA) for 12 weeks through a whole-body PM exposure system. At the end of the exposure, we assessed liver damage, and performed metabolic studies, gene expressions, as well as molecular signal transductions to determine the signaling pathways involving oxidative responses, insulin signaling, and glucose metabolism. Our results indicated that PM_2.5 exposure for 12 weeks caused significant liver damage as evidenced by elevated levels of aminotransferase (AST) and alanine aminotransferase (ALT). Furthermore, PM_2.5 exposure induced impaired glucose tolerance and inhibited glycogen synthesis, leading to hepatic insulin resistance indicated by higher glucose levels, higher area under the curve (AUC), and homeostasis model assessment of insulin resistance (HOMA-IR) values. We further found that PM_2.5 exposure significantly increased the expressions of Nrf2 and Nrf2-regulated antioxidant genes. Moreover, PM_2.5 exposure activated the c-Jun N-terminal kinase (JNK) signaling pathway and increased insulin receptor substrate-1 (IRS-1) phosphorylation at Ser³⁰⁷, but reduced protein kinase B phosphorylation at Ser⁴⁷³. Taken together, our study demonstrated PM_2.5 exposure triggered Nrf2-mediated oxidative responses and activated the JNK-mediated inhibitory signaling pathway, resulting in hepatic insulin resistance.