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Mitochondria are dynamically regulated by fission and fusion processes. Silibinin induces apoptosis of MCF-7 and MDA-MB-231 human breast cancer cells. However, whether or not mitochondria dysfunction is involved in the apoptosis induction with silibinin of both types of the cells remains unknown. We here report that silibinin decreases the mitochondrial mass in terms of MitoTracker Green staining in both breast cancer cells. Silibinin induces morphological changes of mitochondria from oval to truncated or fragmented shapes accordingly. Condensed crests are observed in mitochondria by transmission electron microscopy. Silibinin causes mitochondrial membrane potential reduced. The expression of mitochondrial fission-associated proteins including dynamin-related protein 1 (DRP1) is up-regulated, whereas expression of the mitochondrial fusion-associated proteins, optic atrophy 1 and mitofusin 1, is down-regulated. In addition, silibinin treatment down-regulates ATP content as well as the levels of mitochondrial biogenesis-regulators including mitochondrial transcription factor A, peroxisome proliferator-activated receptor gamma coactivator 1 and nuclear respiratory factor 2. Moreover, treatments with DRP1 inhibitor, mdivi-1, or with DRP1-targetted siRNA efficiently prevent silibinin-induced apoptosis in the breast cancer cells, whereas inhibition of DRP1 phosphorylation with staurosporine increases apoptosis furthermore. Taken together, we conclude that silibinin impairs mitochondrial dynamics and biogenesis, leading to apoptosis of MCF-7 and MDA-MB-123 cells. [ABSTRACT FROM AUTHOR]

Our previous studies showed that silibinin promoted activation of caspases to induce apoptosis in human breast cancer MCF-7 cells by down-regulating the protein expression level of estrogen receptor (ER) α and up-regulating ERβ. Recently, it has been reported that silibinin-induced apoptosis also involved nuclear translocation of apoptosis-inducing factor (AIF). Here we report that silibinin induces nuclear translocation of AIF through the down-regulation of ERα and up-regulation of ERβ in a concentration dependent manner in MCF-7 cells. AIF knockdown with siRNA significantly reverses silibinin-induced apoptosis. The nuclear translocation of AIF is enhanced by treatment with MPP, an ERα antagonist, and blocked with PPT, an ERα agonist. In contrast to ERα activity, the nuclear AIF is increased with an ERβ agonist, DPN and blocked with an ERβ antagonist, PHTPP. Autophagy, negatively regulated by ERα, positively controls AIF-mediated apoptosis, as evidenced by the preventive effect of autophagy inhibitor 3-MA and siRNA targeting LC3, on the nuclear translocation of AIF and cell death induced by silibinin co-treatment with or without MPP. In sum we conclude that AIF in nuclei is involved in silibinin-induced apoptosis, and the nuclear translocation of AIF is increased by down-regulated ERα pathway and/or up-regulated ERβ pathway in MCF-7 cells, accompanying up-regulation of autophagy. Image 1 • Silibinin induces apoptosis-inducing factor-dependent apoptosis in MCF-7 cells. • Estrogen receptor α reduced by silibinin inhibits AIF nuclear translocation. • Estrogen receptor β increased by silibinin promotes AIF nuclear translocation. • Autophagy under the negative control of estrogen receptor α increases nuclear AIF. [ABSTRACT FROM AUTHOR]

Ultraviolet B (UVB) irradiation causes skin inflammation and apoptosis. Mitochondria are highly dynamic and undergo constant fusion and fission that are essential for maintaining physiological functions of cells. Although dysfunction of mitochondria has been implicated in skin damages, little is known about the roles of mitochondrial dynamics in these processes. UVB irradiation increases abnormal mitochondrial content but decreases mitochondrial volume in immortalized human keratinocyte HaCaT cells. UVB irradiation resulted in marked upregulation of mitochondrial fission protein dynamin-related protein 1 (DRP1) and downregulation of mitochondrial outer membrane fusion proteins 1 and 2 (MFN1 and MFN2) in HaCaT cells. Mitochondrial dynamics was discovered to be crucial for NLRP3 inflammasome and cGAS-STING pathway activation, as well as the induction of apoptosis. Inhibition of mitochondrial fission by treatments with a DRP1 inhibitor, mdivi-1, or with DRP1-targeted siRNA, efficiently prevented UVB-induced NLRP3/cGAS-STING mediated pro-inflammatory pathways or apoptosis in the HaCaT cells, whereas inhibition of mitochondrial fusion with MFN1and 2 siRNA increased these pro-inflammatory pathways or apoptosis. The enhanced mitochondrial fission and reduced fusion caused the up-regulation of reactive oxygen species (ROS). Application of an antioxidant, N -acetyl- l -cysteine (NAC), which scavenges excessive ROS, attenuated inflammatory responses through suppressing NLRP3 inflammasome and cGAS-STING pathway activation, and rescued cells from apoptosis caused by UVB-irradiation. Together, our findings revealed the regulation of NLRP3/cGAS-STING inflammatory pathways and apoptosis by mitochondrial fission/fusion dynamics in UVB-irradiated HaCaT cells, providing a new strategy for the therapy of UVB skin injury. [Display omitted] • UVB perturbs mitochondrial fission/fusion dynamics in HaCaT cells. • Disturbed mitochondrial dynamics control the amount of mitochondria. • Disturbed mitochondrial dynamics regulate NLRP3/cGAS-STING mediated pro-inflammatory pathways and apoptosis. • ROS are responsible for pro-inflammatory pathways and apoptosis initiated by the dysregulated mitochondrial dynamics. [ABSTRACT FROM AUTHOR]

Ultraviolet B (UVB) irradiation causes skin damages. In this study, we focus on the involvement of mitochondrial disorders in UVB injury. Surprisingly, UVB irradiation increases the amounts of mitochondria in human immortalized keratinocytes HaCaT. However, further analysis shows that ATP levels decreased by UVB treatment in accordance with the collapse of mitochondrial membrane potential (MMP), suggesting an accumulation of dysfunctional mitochondria in UVB-irradiated HaCaT cells. Mitophagy, mainly mediated by PINK1 and parkin, is critical for the elimination of damaged mitochondria. Western blot results show that the levels of both PINK1 and parkin are decreased in UVB-irradiated cells, indicating the impairment of mitophagy. Silencing the expression of PINK1 or parkin by transfection of siRNA shows essentially the same damage to the cells as UVB irradiation does, including increased mitochondrial amount, decreased MMP and ATP production, and enhanced apoptosis, evidencing that repression of PINK1/parkin-mediated mitophagy plays a primary cause of UVB-caused cells damages. We previously found that HaCaT cells exposed to UVB showed activation of the cGAS-STING pathway and apoptosis. Here, silencing PINK1 or parkin also increases the protein levels of cGAS and STING, facilitates nuclear accumulation of NF-κB, and promotes the transcription of IFNβ, suggesting for the activation of STING pathway. Mitophagy impairment either by UVB-irradiation or by PINK1/parkin silencing initiates caspase-3-mediated apoptosis, as shown by the activation of caspase-3 and cleavage of PARP, as well as the increase of Hoechst-positive stained cells and Annexin V-positive cells. Further studies find that Bax-mediated permeabilization of mitochondrial membrane is critical for cell apoptosis, as well as the cytosolic leakage of mtDNA in UVB-treated cells, which results in cGAS-STING activation, and these processes are negatively-regulated by PINK1/parkin-mediated mitophagy. This study reveals the involvement of dysfunctional mitochondria due to impaired mitophagy in the damaging effect of UVB irradiation on HaCaT cells. Restoring the mitophagy has the potential to be developed as a new strategy to protect skin from UVB damages. [Display omitted] • UVB decreases mitophagy and accumulates dysfunctional mitochondria in HaCaT cells. • UVB reduces PINK1/parkin expression that is involved in mitophagy of damaged mitochondria. • Mitophagy arrest caused by UVB leads to the activation of cGAS-STING/apoptosis pathway. • Mitophagy arrest caused by UVB increases mitochondrial membrane permeability. • Mitophagy arrest caused by UVB results in the mtDNA leakage into cytosol. [ABSTRACT FROM AUTHOR]

We previously reported that silibinin induced a loss of cell viability in breast cancer (MCF-7) cells by ERα down-regulation. But whether this cytotoxicity depends on another estrogen receptor, ERβ, has yet to be elucidated. Therefore, we sought to explore the effects of ERβ modulation on cell viability by using an ERβ-selective agonist (Diarylprepionitrile, DPN) and an antagonist (PHTPP). Our data demonstrated that ERβ served as a growth suppressor in MCF-7 cells, and the incubation of silibinin, elevated ERβ expression, resulting in the tumor growth inhibition. The cytotoxic effect of silibinin was diminished by PHTPP and enhanced by DPN. Silencing of ERβ by siRNA confirmed these results. Apoptotic cascades, including the sequential activation of caspase-9 and -6, and finally the cleavage of caspase substrates, PARP and ICAD, caused by treatment with silibinin, were all repressed by PHTPP pre-treatment but exacerbated by DPN. Unlike ERα, ERβ did not involve autophagic process in the regulation, since neither autophagic inhibitor (3-MA) nor the inducer (rapamycin) affected the cell survival rates regardless ERβ activity. Taken together, silibinin induced apoptosis through mitochondrial pathway by up-regulating ERβ pathways in MCF-7 cells without the involvement of autophagy. [ABSTRACT FROM AUTHOR]

Collagen I is a major component of extracellular matrix in human skin, and is also widely used in a variety of skin-care products. In this study, we investigated the modulatory roles of collagen I on human immortalized keratinocytes HaCaT, especially when cells were irradiated with UVB. Interestingly, the cells grown on plates coated by molecular collagen I, but not fibrillar collagen I, acquired certain resistance against UVB damages, as shown by increased survival and reduced apoptosis. The accumulation of dysfunctional mitochondria in UVB-treated cells was attenuated by molecular collagen I-coating. Interestingly, molecular collagen I rescued the loss of mitochondrial biogenesis in cells treated with UVB. Loss of PINK1/parkin-mediated mitophagy was dominant for the accumulation of dysfunctional mitochondria after UVB irradiation. Of note, cells cultured on molecular collagen I-precoated plates exhibited reserved mitophagy after UVB irradiation, as reflected by the enhanced protein level of PINK1/parkin, increased mitochondrial ubiquitin and the co-localization of lysosomes and mitochondria. Moreover, in UVB-treated cells, inhibiting mitophagy by Cyclosporin A, or by silencing PINK1 or parkin, disturbed the resolution of mitochondrial stress and reduced the protective effect of molecular collagen I, indicating that mitophagy is pivotal for the protection of collagen I against UVB damage in keratinocytes HaCaT. Collectively, this study reveals an unexpected protective role of collagen I, which facilitates mitophagy to rescue cells under UVB irradiation, providing a new direction for clinical application of collagen products. [Display omitted] • Precoating culture plates with collagen I alleviates UVB-induced HaCaT cell apoptosis. • Collagen I inhibits the accumulation of damaged mitochondria in UVB-treated cells. • Arrest of mitophagy accelerates UVB damage by accumulating damaged mitochondria. • UVB protection caused by collagen I depends on rescuing mitophagy. [ABSTRACT FROM AUTHOR]

We reported previously that higher doses (150–250 μM) of silibinin enhanced fission and inhibited fusion of mitochondria, accompanying apoptosis of double-positive breast cancer cell line MCF-7 cells and triple-negative breast cancer cell line MDA-MB-231 cells. We report here three important questions yet unclarified in the previous study; 1) Whether enhanced fission of mitochondria by the treatment of silibinin leads to mitophagy, 2) Whether mitophagy positively contributes to apoptosis and 3) Whether estrogen receptor-positive (ER+) MCF-7 cells and estrogen receptor-negative (ER−) MDA-MB-231 cells are affected in a different way by silibinin treatment, since silibinin often works through ERs signaling pathway. Mitophagy driven by Pink1/Parkin signaling, plays an important role in eliminating damaged mitochondria. Indeed, increased expression of Pink1 and the recruitment of Parkin and LC3-II to mitochondria by the treatment with silibinin account for silibinin induction of mitophagy. In this study, the effects of mitochondrial division inhibitor 1 (mdivi-1) and small interfering RNA targeting dynamin-related protein 1 (DRP1) were examined to reveal the effect of mitochondrial fission on mitophagy. As expected, mdivi-1 or siRNA targeting DRP1 reversed silibinin-induced mitochondrial fission due to down-regulation in the expression of DRP1. Inhibition of mitochondrial fission by mdivi-1 prevented induction of mitophagy as well as autophagy in both MCF-7 and MDA-MB-231 cells, indicating that silibinin-induced mitochondrial fission leads to mitophagy. Inhibition of mitochondrial fission efficiently prevented silibinin-induced apoptosis in MCF-7 and MDA-MB-231 cells in our previous work, and the second point of the present study, inhibition of mitophagy by Pink1 or Parkin knockdown increased silibinin-induced apoptosis of these cells, respectively, suggesting that the mitophagy induced by silibinin treatment serves as a cytoprotective effect, resulting in reduction of apoptosis of cancer cells in both cells. In the third point, we studied whether estrogen receptors (ERs) played a role in silibinin-induced mitophagy and apoptosis in MCF-7 and MDA-MB-231 cells. ERα and ERβ are not involved in silibinin-induced mitophagic process in MCF-7 and MDA-MB-231 cells. These findings demonstrated that silibinin induced mitochondria fission leads to mitophagy, which attenuates silibinin-induced apoptosis not through ERs-Pink1 or -Parkin pathway in MCF-7 and MDA-MB-231. [ABSTRACT FROM AUTHOR]

Ferroptosis, an iron-dependent cell death, is caused by lipid peroxidation. Noteworthily, accumulation of iron and lipid peroxidation are found in the proximity of the neuritic plaque, a hallmark of Alzheimer's disease (AD), but the relationship between ferroptosis and neuroinflammation in AD is unclear. Silibinin, extracted from the Silybum marianum , is possibly developed as an agent for AD treatment from its neuroprotective effect, but the effect of silibinin on sporadic AD that accounts for more than 95% of AD remains unclear. To determine whether silibinin alleviates the pathogenesis of sporadic AD and investigate the underlying mechanisms, STZ-treated HT22 murine hippocampal neurons and intracerebroventricular injection of streptozotocin (ICV-STZ) rats, a sporadic AD model, were used in this study. Results show that silibinin not only promotes survival of STZ-treated HT22 cells, but also ameliorates the cognitive impairment and anxiety/depression-like behavior of ICV-STZ rats. We here demonstrate that silibinin evidently inhibits the protein level of p53 as well as upregulates the protein level of cystine/glutamate antiporter SLC7A11 and ferroptosis inhibitor GPX4, but not p21, leading to the protection against STZ-induced ferroptotic damage. Immunofluorescent staining also shows that accumulation of lipid peroxidation induced by ferroptotic damage leads to increased fluorescence of 8-oxo-deoxyguanosine (8-OHDG), a maker of oxidized DNA. The oxidized DNA then leaks to the cytoplasm and upregulates the expression of the stimulator of interferon gene (STING), which triggers the production of IFN-β and other inflammatory cascades including NF-κB/TNFα and NLRP3/caspase 1/IL-1β. However, the treatment with silibinin blocks the above pathological changes. Moreover, in HT22 cells with/without STZ treatment, GPX4-knockdown increases the protein level of STING, indicating that the ferroptotic damage leads to the activation of STING signaling pathway. These results imply that silibinin exerts neuroprotective effect on an STZ-induced sporadic AD model by downregulating ferroptotic damage and thus the downstream STING-mediated neuroinflammation. [Display omitted] • Silibinin downregulates p53-mediated ferroptosis in STZ-treated HT22 murine hippocampal neurons. • Silibinin ameliorates cognitive deficit and anxiety/depression-like behaviors of ICV-STZ rats. • Silibininreduces STING-mediated neuroinflammation via down-regulating ferroptotic damage both in vitro and in vivo. [ABSTRACT FROM AUTHOR]

Type 2 diabetes (T2DM) is induced by the abundance of glucose and lipids, which causes glucolipotoxicity to the pancreatic β-cells. Silibinin is a natural flavonoid possessing the regulatory activity on insulin production and therapeutic activity in diabetic mice; however, its effect on glucolipotoxicity is not fully explained. This in vitro study investigates the effects of silibinin on palmitic acid (PA) and high glucose (HG)-induced cell loss and ferroptosis of rat insulinoma INS-1 cells. In the cells treated with PA and HG, expressions of glucose transporter 4 (Glut4) and carnitine acyltransferase I (CPT1) for β-oxidation of fatty acids are reduced. Mitochondria are the metabolic organelles for glucose and fatty acids. The mitochondrial membrane potential (MMP) and ATP production were decreased, while the ROS level was elevated in the cells treated with PA and HG, indicating an induction of mitochondrial disorder. Cell loss was partially rescued by ferroptosis inhibition, suggesting an involvement of ferroptosis in the cells treated with PA and HG. More importantly, the increases in total iron, lipid ROS, MDA and COX-2, and the decrease in ferroptosis inhibitory molecules GSH, GPX4 and FSP1 appeared in the cells treated with PA and HG, confirming the occurrence of ferroptosis. Moreover, PINK1/parkin-mediated mitophagy, a vital process for selective elimination of damaged mitochondria, was blocked. Interestingly, silibinin rescued the mitochondria, restricted the ferroptosis and restored the mitophagy. By using the pharmacological stimulator and inhibitor of mitophagy, and si-RNA transfection to silence PINK1 expression, silibinin's protective effect against ferroptosis caused by PA and HG treatment was found to depend on mitophagy. Collectively, our current study reveals the new mechanisms for the protection of silibinin against the injury of INS-1 cells treated with PA and HG, elucidates the participation of ferroptosis in glucolipotoxicity, highlighting the involvement of mitophagy in defense against ferroptotic cell death. [Display omitted] • Silibinin improves the mitochondrial function in INS-1 cells treated with palmitic acid and high glucose. • Silibinin alleviates the reduction of PINK1/parkin-mediated mitophagy in INS-1 cells treated with palmitic acid and high glucose. • Silibinin attenuates ferroptosis in INS-1 cells treated with palmitic acid and high glucose. • Silibinin-induced mitophagy negatively regulates ferroptosis in INS-1 cells treated with palmitic acid and high glucose. [ABSTRACT FROM AUTHOR]