Autophagy Attenuates MnCl2-induced Apoptosis in Human Bronchial Epithelial Cells.

OBJECTIVE: To investigate the role of autophagy in MnCl2-induced apoptosis in human bronchial epithelial 16HBE cells. METHODS: Cell proliferation was measured by MTT assay. Mitochondrial membrane potential (MMP) and apoptosis were measured by flow cytometry. Autophagic vacuoles were detected by fluorescence microscopy. Cellular levels of apoptosis and autophagy-related proteins were measured by western blotting. RESULTS: 16HBE cell proliferation was inhibited by MnCl2 in a dose- and time-dependent manner. MnCl2-induced 16HBE cell growth inhibition was related to MMP depolarization prior to the induction of apoptosis. Our data revealed that MnCl2-induced apoptosis in 16HBE cells was mediated by decreased expression of Bcl-2 and increased levels of cleaved caspase-3. It was observed that when we exposed 16HBE cells to MnCl2 in a dose-dependent manner, the formation of autophagic vacuoles and the levels of LC-3B-II were elevated. RNA interference of LC3B in these MnCl2-exposed cells demonstrated that MMP loss and apoptosis were enhanced. Additionally, the pan-caspase inhibitor Z-VAD-FMK increased the cellular levels of Bcl-2 and decreased apoptosis, but did not affect the cellular levels of LC3B in MnCl2-treated 16HBE cells. CONCLUSION: MnCl2 dose- and time-dependently inhibits 16HBE cell proliferation and induces MMP loss and apoptosis. Autophagy acts in a protective role against MnCl2-induced apoptosis in 16HBE cells.

PINK1/Parkin-mediated mitophagy play a protective role in manganese induced apoptosis in SH-SY5Y cells.

Manganese (Mn) as an environmental risk factor of Parkinson's disease (PD) is considered to cause manganism. Mitophagy is thought to play a key role in elimination the injured mitochondria. The goal of this paper was to explore whether the PINK1/Parkin-mediated mitophagy is activated and its role in Mn-induced mitochondrial dysfunction and cell death in SH-SY5Y cells. Here, we investigated effects of MnCl2 on ROS generation, mitochondrial membrane potential (MMP/ΔΨm) and apoptosis by FACS and examined PINK1/Parkin-mediated mitophagy by western-blotting and the co-localization of mitochondria and acidic lysosomes. Further, we explore the role of mitophagy in Mn-induced apoptosis by inhibition the mitophagy by knockdown Parkin level. Results show that MnCl2 dose-dependently caused ΔΨm decrease, ROS generation and apoptosis of dopaminergic SH-SY5Y cells. Moreover, Mn could induce mitophagy and PINK1/Parkin-mediated pathway was activated in SH-SY5Y cells. Transient transfection of Parkin siRNA knockdown the expressing level of parkin inhibited Mn-induced mitophagy and aggravated apoptosis of SH-SY5Y cells. In conclusion, our study demonstrated that Mn may induce PINK1/Parkin-mediated mitophagy, which may exert significant neuro-protective effect against Mn-induced dopaminergic neuronal cells apoptosis.

S phase cell percentage normalized BrdU incorporation rate, a new parameter for determining S arrest.

In this study, a new parameter, S phase cell percentage (S fraction) normalized BrdU (SFN-BrdU) incorporation rate, was introduced to detect S arrest. The results showed a positive linear correlation between the BrdU incorporation rate and the S fraction in unperturbed 16HBE cells. Theoretical analysis indicated that only S arrest could result in a decrease in the SFN-BrdU incorporation rate. Additionally, the decrease in SFN-BrdU incorporation rate and the activation of DNA damage checkpoints further demonstrated that S arrest was induced by diethyl sulfate treatment of 16HBE cells. In conclusion, SFN-BrdU incorporation rate can be used to detecting S arrest.

Cadmium directly induced the opening of membrane permeability pore of mitochondria which possibly involved in cadmium-triggered apoptosis.

The mitochondrial damage induced by cadmium has been well established, but its mechanism and its relationship with cadmium-induced apoptosis are elusive until now. Our research showed that cadmium could directly lead to the dysfunction of isolated mitochondria from mouse liver, including the inhibition of respiration, the opening of permeability transition pore (PTP), the loss of transmembrane potential, and the release of cytochrome c. These mitochondrial changes were completely suppressed by Bcl-xL and Ruthenium Red (RR). Bongkrekic acid (BK), an inhibitor of the PTP opening directly via adenine nucleotide translocator (ANT), also completely inhibited the PTP opening and loss of transmembrane potential. However, cyclosporin A (CsA), another inhibitor of the PTP opening indirectly via ANT, had not any inhibitory effect. When cadmium being pre-incubated with proteins containing abundant thiol groups, its effect was partially reversed. These results revealed that mitochondria pathway may involve in cadmium-induced apoptosis, and cadmium caused the PTP opening possibly through its binding to thiol groups of ANT. Furthermore, the mechanism of the PTP opening induced by cadmium was probably distinct from that of the calcium-induced PTP opening.

The inhibitory effects of manganese on steroidogenesis in rat primary Leydig cells by disrupting steroidogenic acute regulatory (StAR) protein expression.

Manganese is known to impede the male reproductive function, however, the mechanisms through which the adverse effects are mediated are not clearly elucidated. In order to get insight into those mechanisms, the effects of manganese on the biosynthesis of testosterone by primary rat Leydig cells were examined. Primary Leydig cells were exposed to various concentrations of manganese chloride for different periods of time. Dose and time-dependent reductions of human chorionic gonadotropin (hCG)-stimulated testosterone level were observed in the culture medium. The expression of Steroidogenic Acute Regulatory (StAR) protein and the activities of P450 side-chain cleavage (P450scc) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) enzymes were also detected. The expression of StAR protein stimulated by hCG was suppressed by manganese chloride at all concentrations (0.01, 0.1, 1.0 mM) and time points (2, 4, 24, 48 h) tested. Progesterone productions treated with 22R-hydroxycholesterol or pregnenolone were reduced after treated by manganese chloride for 24 or 48 h, respectively. The manganese exposure effect on cell viability was significant at 1.0 and 1.5 mM at 24 h, while at 48 h it was significant at every concentration tested. The decreasing effect of manganese on mitochondrial membrane potential was significant at every concentration measured and every time point tested. These data suggest that manganese exposure for 2 and 4 h inhibited rat primary Leydig cell steroidogenesis by decreasing StAR protein expression while 24 and 48 h exposure of manganese chloride caused adverse effects on both StAR protein and P450scc and 3beta-HSD enzyme activity to reduce steroidogenesis. Manganese may also disrupt StAR expression and/or function secondary to mitochondrial dysfunction.

The role of thiol reduction in hydroquinone-induced apoptosis in HEK293 cells.

Hydroquinone (HQ) is a chemical used as a reducing agent, antioxidant, polymerization inhibitor, and chemical intermediate. It has a minor use as a bleaching agent in dermatologic preparations. HQ also occurs as a main metabolite of benzene. In the present study, HQ-induced apoptosis was evaluated by cell morphology changes, determination of phosphatidylserine (PS) externalization and analysis of sub-G1 cells. The effect of HQ on intracellular thiol concentration, including glutathione and protein thiol, and the effect of N-acetylcysteine (NAC) and buthionine sulfoximine (BSO) pretreatment on HQ-induced apoptosis were investigated. The results showed that HQ was able to induce typical apoptosis in HEK293 cells (human embryonic kidney cells) in a dose-dependent manner. Intracellular thiol, including glutathione and protein thiol, was decreased following treatment with HQ. NAC, a precursor of intracellular GSH synthesis, significantly inhibited HQ-induced apoptosis. However, BSO, a specific inhibitor of intracellular GSH synthesis, enhanced HQ-induced apoptosis significantly. Taken together, the present study demonstrates that HQ is able to induce apoptosis in HEK293 cells, most probably through depletion of intracellular thiol. The results also suggest that, at least in HEK293 cells, the control of intracellular redox homeostasis has a central role in the regulation of cell death induced by HQ.