Nitric oxide-induced autophagy and the activation of activated protein kinase pathway protect against apoptosis in human dental pulp cells

Sinomenine promotes flap survival by upregulating eNOS and eNOS-mediated autophagy via PI3K/AKT pathway

Large skin defects and surgical tissue reconstructions are frequently covered utilizing random flaps. The flap has the advantage of being designed according to the size and shape of a surgical wound. However, the necrosis of the distal part of the flap restricts the clinical application of flaps. Sinomenine (SIN) is the major active component of sinomenium acutum. SIN has been demonstrated to inhibit oxidative stress and stimulate autophagy in a cell, animal, and clinical studies. The protective and proliferative effects of sinomenium on HUVECs were evaluated by scratched test, CCK-8, and EDU assays. For the flap survival, we established a mouse random pattern flap model and observed the effects of SIN injected intraperitoneally. The survival area and blood flow intensity of the flap in sinomenium group were significantly increased compared to the control group. Our results demonstrate that SIN promotes flap survival. Sinomenium enhances eNOS expression in the flap and reduces the level of oxidative stress, promotes autophagy flux increase, reduces apoptosis, and promotes angiogenesis. Having a therapeutic benefit of SIN, Autophagy inhibitor 3-MA shows its critical role by reversing the beneficial effects of SIN, and the nitric oxide synthase inhibitor l-NAME both stimulated HUVECs that explore the relationship between autophagy flux and nitric oxide synthase. Furthermore, the mechanism in our study reveals the changes in the signal pathway of PI3K/AKT, the protective effect of SIN during antioxidant activity, the activation of eNOS through PI3K/AKT signaling pathway affects autophagy through the eNOS system, and promote the random flap survival.

Selenium deficiency aggravates bisphenol A-induced autophagy in chicken kidney through regulation of nitric oxide and adenosine monophosphate activated protein kinase/mammalian target of rapamycin signaling pathway

Bisphenol A (BPA), a phenolic compound, is harmful to humans and animals as its residue in the water threatens multiple organs, especially the kidney. Low selenium (Se) diets are consumed in many regions of the world, and poor Se status has exacerbating effect on toxicity of several environmental chemicals. Here, we described the discovery path of Se deficiency aggravation on autophagy in BPA treated chicken kidney through regulating nitric oxide (NO) and adenosine monophosphate activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) signaling pathways. The actual dietary Se intake for chickens was 0.30 mg/kg in control group and 0.03 mg/kg in Low-Se group, and BPA exposure concentration for chickens was 0.05 g/kg. Chicken embryo kidney (CEK) cells were used in vitro and the BPA exposure concentration for CEK cells was 150 nM. We found that BPA significantly increased levels of NO and inducible nitric oxide synthase, activated AMPK/mTOR signaling pathways, thereby triggering p62/LC3/Beclin1 signaling, resulting in formations of autophagosome and autolysosome, and finally stimulating autophagy in the chicken kidney. Additionally, Se deficiency promoted the occurrence of autophagy in BPA-treated kidneys. Altogether, our findings showed that Se deficiency exacerbates BPA-induced renal autophagy in chickens via regulation of NO and AMPK/mTOR signaling pathways. These findings will improve our understandings of the mechanisms of nephrotoxicity of BPA and detoxification by Se in chickens. In addition, further work is required to determine if Se status of exposed populations needs to be considered in future epidemiological assessments.

Ferulic acid ameliorates acetaminophen-induced acute liver injury by promoting AMPK-mediated protective autophagy

Acetaminophen (APAP), one of the most widely used antipyretics and analgesics, principally results in acute liver injury (ALI) in developed countries when taken overdose. Ferulic acid (FA) is a natural polyphenol compound existing in many plants that has free radical scavenging, anti-inflammatory and liver-protective properties. However, the effect and underlying mechanism of FA in treating APAP-induced ALI have not been fully elucidated. Herein, we established a mouse model of APAP-induced ALI and used APAP-stimulated mouse primary hepatocytes for biochemical assessment of molecular parameters. After constructing networks and obtaining predicted targets from public databases, we further verified the putative pathways using immune-blotting assays both in vivo and in vitro. The reign of liver necrosis, serum levels of ALT and AST and oxidative stress in livers significantly elevated after APAP treatment, which were almost recovered back to normal levels by FA administration. In addition, FA significantly upregulated the APAP-induced downregulation of hepatic specific markers, including HNF4a, Foxa2 and ALB. Then, the results of functional enrichment indicated the possible signaling pathways of FA against APAP challenge, mainly including AMPK, autophagy, apoptosis and other metabolic process. Furthermore, FA markedly reversed the APAP-induced decline of mitochondria membrane potential, increased ratio of BAX/BCL2 and CASPASE 3 expression, and promoted autophagy flux of hepatocytes by upregulating AMPK phosphorylation, which were abrogated by a specific AMPK inhibitor, compound C. Overall, the hepatoprotective effect of FA on APAP-induced ALI might be associated with anti-oxidant and anti-apoptosis, which were at least partly attributed to AMPK-mediated protective autophagy.

Graphene quantum dot antioxidant and proautophagic actions protect SH-SY5Y neuroblastoma cells from oxidative stress-mediated apoptotic death

We investigated the ability of graphene quantum dot (GQD) nanoparticles to protect SH-SY5Y human neuroblastoma cells from oxidative/nitrosative stress induced by iron-nitrosyl complex sodium nitroprusside (SNP). GQD reduced SNP cytotoxicity by preventing mitochondrial depolarization, caspase-2 activation, and subsequent apoptotic death. Although GQD diminished the levels of nitric oxide (NO) in SNP-exposed cells, NO scavengers displayed only a slight protective effect, suggesting that NO quenching was not the main protective mechanism of GQD. GQD also reduced SNP-triggered increase in the intracellular levels of hydroxyl radical (^•OH), superoxide anion (O₂^•-), and lipid peroxidation. Nonselective antioxidants, ^•OH scavenging, and iron chelators, but not superoxide dismutase, mimicked GQD cytoprotective activity, indicating that GQD protect cells by neutralizing ^•OH generated in the presence of SNP-released iron. Cellular internalization of GQD was required for optimal protection, since a removal of extracellular GQD by extensive washing only partly diminished their protective effect. Moreover, GQD cooperated with SNP to induce autophagy, as confirmed by the inhibition of autophagy-limiting Akt/PRAS40/mTOR signaling and increase in autophagy gene transcription, protein levels of proautophagic beclin-1 and LC3-II, formation of autophagic vesicles, and degradation of autophagic target p62. The antioxidant activity of GQD was not involved in autophagy induction, as antioxidants N-acetylcysteine and dimethyl sulfoxide failed to stimulate autophagy in SNP-exposed cells. Pharmacological inhibitors of early (wortmannin, 3-methyladenine) or late stages of autophagy (NH₄Cl) efficiently reduced the protective effect of GQD. Therefore, the ability of GQD to prevent the in vitro neurotoxicity of SNP depends on both ^•OH/NO scavenging and induction of cytoprotective autophagy.

Autophagy upregulates inflammatory cytokines in gingival tissue of patients with periodontitis and lipopolysaccharide-stimulated human gingival fibroblasts

Background

Periodontitis is an inflammatory disease caused by multiple disease‐associated bacterial species in periodontal tissues. Autophagy is known to modulate various inflammation‐driven diseases and inflammatory responses, but the role of autophagy related to the pathogenesis of periodontitis is not fully established. We investigated whether autophagic flux regulated the expression of inflammatory cytokines in the gingiva of periodontitis patients and lipopolysaccharide (LPS)‐stimulated human gingival fibroblasts (HGFs) and the underlying mechanism.

Methods

The mRNA and protein expression of proinflammatory cytokines was assessed in human gingival tissues collected from patients with periodontitis and HGFs treated with LPS. The expression of signaling molecules related to autophagy was evaluated by immunofluorescence and Western blot analyses.

Results

The expression of interleukin (IL)‐6, tumor necrosis factor‐α (TNF‐α), cyclooxygenase‐2 (COX‐2), and intercellular adhesion molecule‐1 (ICAM‐1) was increased in the gingival tissues of patients with periodontitis. LC3B‐positive cells, a typical autophagic marker, were increased in the gingival tissues of periodontitis patients and LPS‐treated HGFs. The conversion ratio of LC3‐I to LC3‐II was higher in the gingival tissues associated with periodontitis and LPS‐treated HGFs compared to the controls. The autophagy inhibitor 3‐methyladenine (3MA) significantly abrogated the LPS‐sustained inflammatory effect by reducing the expression of IL‐6, TNF‐α, COX‐2, and ICAM‐1 in HGFs. The phosphorylation of protein kinase B (AKT) and protein S6K1 (S6), signals involved in the mTOR‐dependent mechanism, was decreased in gingiva derived from periodontitis patients and LPS‐treated HGFs.

Conclusions

Autophagy augmented the production of inflammatory cytokines by mTOR inactivation via the AKT signaling pathway in the gingival tissues of patients with periodontitis and LPS‐stimulated HGFs. These findings would provide a better understanding of the mechanism by which autophagy regulates the inflammatory response associated with periodontal pathogenesis.

Autophagy in tooth: Physiology, disease and therapeutic implication

Autophagy is an evolutionarily conserved cellular process, in which damaged organelles and proteins are engulfed in autophagic vesicles and subsequently fuse with lysosomes for degradation. Autophagy is widely involved in different physiologic or pathologic processes in human. Accumulating evidence indicates that autophagy operates as a critical quality control mechanism to maintain pulp homeostasis and structural integrity of the dentin-pulp complex. Autophagy is activated during stresses and is involved in the pathogenesis of pulpitis and periapical infection. Recent discoveries have also provided intriguing insights into the roles of autophagy in tooth development, pulp aging and stress adaptation. In this review, we provide an update on the multifaceted functions of autophagy in physiology and pathophysiology of tooth. We also discuss the therapeutic implications of autophagy modulation in diseases and the regeneration of dentin-pulp complex.

Nitric Oxide Alleviated High Salt-Induced Cardiomyocyte Apoptosis and Autophagy Independent of Blood Pressure in Rats

The present study aimed to explore whether high-salt diet (HSD) could cause cardiac damage independent of blood pressure, and whether nitric oxide (NO) could alleviate high-salt–induced cardiomyocyte apoptosis and autophagy in rats. The rats received 8% HSD in vivo. H9C2 cells or primary neonatal rat cardiomyocytes (NRCM) were treated with sodium chloride (NaCl) in vitro. The levels of cleaved-caspase 3/caspase 3, cleaved-caspase 8/caspase 8, Bax/Bcl2, LC3 II/LC3 I, Beclin-1 and autophagy related 7 (ATG7) were increased in the heart of HSD rats with hypertension (HTN), and in hypertension-prone (HP) and hypertension-resistant (HR) rats. Middle and high doses (50 and 100 mM) of NaCl increased the level of cleaved-caspase 3/caspase 3, cleaved-caspase 8/caspase 8, Bax/Bcl2, LC3 II/LC3 I, Beclin-1, and ATG7 in H9C2 cells and NRCM. The endothelial NO synthase (eNOS) level was increased, but p-eNOS level was reduced in the heart of HSD rats and H9C2 cells treated with 100 mM NaCl. The level of NO was reduced in the serum and heart of HSD rats. NO donor sodium nitroprusside (SNP) reversed the increases of cleaved-caspase 3/caspase 3, cleaved-caspase 8/caspase 8, Bax/Bcl2 induced by NaCl (100 mM) in H9C2 cells and NRCM. SNP treatment attenuated the increases of cleaved-caspase 3/caspase 3, Bax/Bcl2, LC3 II/LC3 I, Beclin-1, and ATG7 in the heart, but had no effect on the blood pressure of HSD rats with HR. These results demonstrated that HSD enhanced cardiac damage independently of blood pressure. Exogenous NO supplementarity could alleviate the high salt–induced apoptosis and autophagy in cardiomyocytes.

Complex interplay between autophagy and oxidative stress in the development of pulmonary disease

The autophagic pathway involves the encapsulation of substrates in double-membraned vesicles, which are subsequently delivered to the lysosome for enzymatic degradation and recycling of metabolic precursors. Autophagy is a major cellular defense against oxidative stress, or related conditions that cause accumulation of damaged proteins or organelles. Selective forms of autophagy can maintain organelle populations or remove aggregated proteins. Dysregulation of redox homeostasis under pathological conditions results in excessive generation of reactive oxygen species (ROS), leading to oxidative stress and the associated oxidative damage of cellular components. Accumulating evidence indicates that autophagy is necessary to maintain redox homeostasis. ROS activates autophagy, which facilitates cellular adaptation and diminishes oxidative damage by degrading and recycling intracellular damaged macromolecules and dysfunctional organelles. The cellular responses triggered by oxidative stress include the altered regulation of signaling pathways that culminate in the regulation of autophagy. Current research suggests a central role for autophagy as a mammalian oxidative stress response and its interrelationship to other stress defense systems. Altered autophagy phenotypes have been observed in lung diseases such as chronic obstructive lung disease, acute lung injury, cystic fibrosis, idiopathic pulmonary fibrosis, and pulmonary arterial hypertension, and asthma. Understanding the mechanisms by which ROS regulate autophagy will provide novel therapeutic targets for lung diseases. This review highlights our current understanding on the interplay between ROS and autophagy in the development of pulmonary disease.

Nitric Oxide in Dental Pulp Tissue: From Molecular Understanding to Clinical Application in Regenerative Endodontic Procedures

Nitric oxide (NO), which is synthesized by the enzyme NO synthase (NOS), is a versatile endogenous molecule with multiple biological effects on many tissues and organs. In dental pulp tissue, NO has been found to play multifaceted roles in regulating physiological activities, inflammation processes, and tissue repair events, such as cell proliferation, neuronal degeneration, angiogenesis, and odontoblastic differentiation. However, there is a deficiency of detailed discussion on the NO-mediated interactions between inflammation and reparative/regenerative responses in wounded dental pulp tissue, which is a central determinant of ultimate clinical outcomes. Thus, the purpose of this review is to outline the current molecular understanding on the roles of Janus-faced molecule NO in dental pulp physiology, inflammation, and reparative activities. Based on this knowledge, advanced physicochemical techniques designed to manipulate the therapeutic potential of NOS and NO production in endodontic regeneration procedures are further discussed. Impact statement The interaction between inflammation and reparative/regenerative responses is very important for regenerative endodontic procedures, which are biologically based approaches intended to replace damaged tissues. Inside dental pulp tissue, endogenous nitric oxide (NO) is generated mainly by immunocompetent cells and dental pulp cells and mediates not only inflammatory/immune activities but also signaling cascades that regulate tissue repair and reconstruction, indicating its involvement in both tissue destruction and regeneration. Thus, it is feasible that NO acts as one of the indicators and modulators in dental pulp repair or regeneration under physiological and pathological conditions.

Biglycan protects human neuroblastoma cells from nitric oxide-induced death by inhibiting AMPK-mTOR mediated autophagy and intracellular ROS level

The ubiquitous proteoglycan, biglycan (BGN) acts as an important modulator, regulating key molecular pathways of metabolism and brain function. Autophagy is documented as a defining feature of neurodegeneration in Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD). In the present study, we found that BGN protected neuronal cells from nitric oxide (NO)-induced cell apoptosis. However, it is still unclear that whether the neuroprotective effect of BGN relates to autophagy. Here, we discovered that an NO donor, sodium nitroprusside (SNP) induced autophagy in human SH-SY5Y neuroblastoma cells, including activating LC3B and inhibiting p62. Inhibiting autophagy by 3MA aggravated NO-induced cell death, otherwise promoting autophagy by Rapamycin rescued NO-triggered cell death. Notably, BGN downregulated by NO, significantly protected SH-SY5Y cells against NO-induced neurotoxicity by inhibiting the activation of autophagy-dependent AMPK signaling pathway. Moreover, BGN overexpression also diminished NO-induced the elevation of intracellular reactive oxygen species (ROS) level, but not NO content. These findings suggest that BGN protects neuroblastoma cells from NO-induced death by suppressing autophagy-dependent AMPK-mTOR signaling and intracellular ROS level.

Sevoflurane postconditioning protects against myocardial ischemia/reperfusion injury by restoring autophagic flux via an NO-dependent mechanism

Volatile anesthetics improve postischemic cardiac function and reduce infarction even when administered for only a brief time at the onset of reperfusion. A recent study showed that sevoflurane postconditioning (SPC) attenuated myocardial reperfusion injury, but the underlying mechanisms remain unclear. In this study, we examined the effects of sevoflurane on nitric oxide (NO) release and autophagic flux during the myocardial ischemia/reperfusion (I/R) injury in rats in vivo and ex vivo. Male rats were subjected to 30 min ischemia and 2 h reperfusion in the presence or absence of sevoflurane (1.0 minimum alveolar concentration) during the first 15 min of reperfusion. We found that SPC significantly improved hemodynamic performance after reperfusion, alleviated postischemic myocardial infarction, reduced nicotinamide adenine dinucleotide content loss, and cytochrome c release in heart tissues. Furthermore, SPC significantly increased the phosphorylation of endothelial nitric oxide synthase (NOS) and neuronal nitric oxide synthase, and elevated myocardial NOS activity and NO production. All these effects were abolished by treatment with an NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg, i.v.). We also observed myocardial I/R-induced accumulation of autophagosomes in heart tissues, as evidenced by increased ratios of microtubule-associated protein 1 light chain 3 II/I, up-regulation of Beclin 1 and P62, and reduced lysosome-associated membrane protein-2 expression. SPC significantly attenuated I/R-impaired autophagic flux, which were blocked by L-NAME. Moreover, pretreatment with the autophagic flux blocker chloroquine (10 mg/kg, i.p.) increased autophagosome accumulation in SPC-treated heart following I/R and blocked SPC-induced cardioprotection. The same results were also observed in a rat model of myocardial I/R injury ex vivo, suggesting that SPC protects rat hearts against myocardial reperfusion injury by restoring I/R-impaired autophagic flux via an NO-dependent mechanism.

Distinct role of autophagy on angiogenesis: highlights on the effect of autophagy in endothelial lineage and progenitor cells

Autophagy plays a critical role in the dynamic growth of each cell through different conditions. It seems that this intracellular mechanism acts as a two-edged sword against the numerous cell insults. Previously, autophagy was described in the context of cell activity and behavior, but little knowledge exists related to the role of autophagy in endothelial cells, progenitors, and stem cells biology from different tissues. Angiogenic behavior of endothelial lineage and various stem cells are touted as an inevitable feature in the restoration of different damaged tissues and organs. This capacity was found to be dictated by autophagy signaling pathway. This review article highlights the fundamental role of cell autophagic response in endothelial cells function, stem cells dynamic, and differentiation rate. It seems that elucidation of the mechanisms related to pro- and/or anti-angiogenic potential of autophagy inside endothelial cells and stem cells could help us to modulate stem cell therapeutic feature post-transplantation.

Schisandrin C enhances odontoblastic differentiation through autophagy and mitochondrial biogenesis in human dental pulp cells

OBJECTIVE

To investigate the role of Schisandrin C in odontoblastic differentiation, and its relations between autophagy and mitochondrial biogenesis in human dental pulp cells (HPDCs).

DESIGN

Fresh third molars were used, and cultured for HDPCs. Western blotting technique, Alizarin red S staining, alkaline phosphatase (ALP) activity, and confocal microscopy were used to detect autophagy, mitochondrial biogenesis, and odontoblastic differentiation. To understand the mechanism of Schisandrin C, the HDPCs were treated with lipopolysaccharide (LPS), autophagy and heme oxygenase-1 (HO-1) inhibitors: 3-Methyladenine (3-MA) and Zinc protoporphyrin IX (ZnPP), respectively.

RESULTS

LPS decreased the expression of autophagy molecules [autophagy protein 5 (ATG-5), beclin-1, and microtubule-associated protein 1A/1B light chain 3 (LC3-I/II)] and mitochondrial biogenesis molecules [heme oxygenase-1 (HO-1) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α)], and disrupted odontoblastic differentiation. The down-regulation of autophagy and mitochondrial biogenesis with 3-MA and ZnPP inhibited odontoblastic differentiation. However, Schisandrin C restored the expression of all the above molecules, even with LPS and inhibitor treatment. This result demonstrates that autophagy and mitochondrial biogenesis plays an essential role in odontoblastic differentiation, and Schisandrin C activates these systems to promote odontoblastic differentiation of HDPCs.

CONCLUSION

Schisandrin C has potential characters to regulate odontoblastic differentiation, and may be recommended for use as a compound for pulp homeostasis.

Crosstalk of ROS/RNS and autophagy in silibinin-induced apoptosis of MCF-7 human breast cancer cells in vitro

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) play important roles in regulating cell survival and death. Silibinin is a natural polyphenolic flavonoid isolated from milk thistle with anti-tumor activities, but it was found to induce cytoprotective ROS/RNS in human breast cancer MCF-7 cells. Furthermore, treatment with silibinin down-regulates ERα expression in MCF-7 cells, and inducing both autophagy and apoptosis. In this study we explored the relationship between ER-associated pathways and RNS/ROS in MCF-7 cells. We also investigated the molecular mechanisms underlying the reciprocal regulation between ROS/RNS levels and autophagy in the death signaling pathways in silibinin-treated MCF-7 cells. Silibinin (100-300 μmol/L) dose-dependently increased ROS/RNS generation in MCF-7 cells (with high expression of ERα and low expression of ERβ) and MDA-MB-231 cells (with low expression of ERα and high expression of ERβ). Scavenging ROS/RNS significantly enhanced silibinin-induced death of MCF-7 cells, but not MDA-MB231 cells. Pharmacological activation or blockade of ERα in MCF-7 cells significantly enhanced or decreased, respectively, silibinin-induced ROS/RNS generation, whereas activation or block of ERβ had no effect. In silibinin-treated MCF-7 cells, exposure to the ROS/RNS donators decreased the autophagic levels, whereas inhibition of autophagy with 3-MA significantly increased ROS/RNS levels. We further showed that increases in ROS/RNS generation, ERα activation or autophagy down-regulation had protective roles in silibinin-treated MCF-7 cells. Under a condition of ERα activation, scavenging ROS/RNS or stimulating autophagy enhanced the cytotoxicity of silibinin. These results demonstrate the existence of two conflicting pathways in silibinin-induced death of MCF-7 cells: one involves the down-regulation of ERα and thereby augmenting the pro-apoptotic autophagy downstream, leading to cell death; the other involves the up-regulation of pro-survival ROS/RNS; and that the generation of ROS/RNS and autophagy form a negative feedback loop whose balance is regulated by ERα.

Enhanced nitric oxide-mediated autophagy contributes to the hepatoprotective effects of ischemic preconditioning during ischemia and reperfusion

Ischemic preconditioning (IPC) protects against liver ischemia/reperfusion (I/R) injury. Autophagy is an essential cytoprotective system that is rapidly activated by multiple stressors. Nitric oxide (NO) acts as an inducer of IPC. We examined the impact of autophagy in liver IPC and its regulation by NO. Male C57BL/6 mice were subjected to 60 min of hepatic ischemia followed by 6 h of reperfusion. IPC was achieved for 10 min of ischemia followed by 10 min of reperfusion prior to sustained ischemia. N(ω)-Nitro-l-arginine methyl ester (L-NAME, 15 mg/kg, i.v., all NOS inhibitor) and aminoguanidine (AG, 10 mg/kg, i.v., iNOS inhibitor) were injected 10 min before IPC. SB203580 (10 mg/kg, i.p., p38 inhibitor) was injected 30 min before IPC. I/R increased serum alanine aminotransferase activity. IPC attenuated this increase, which was abolished by L-NAME, but not AG. Microtubule-associated protein-1 light chain 3-II levels increased and p62 protein levels decreased after I/R; these changes were augmented by IPC and abolished by L-NAME. I/R increased liver protein expression of autophagy-related protein (Atg)12-Atg5 complex and lysosome-associated membrane protein-2. IPC augmented the expression of these proteins, which were abolished by L-NAME, but not AG. IPC also augmented the level of phosphorylated p38 MAPK induced by I/R and this phosphorylation was abolished by L-NAME. Our findings suggest that IPC-mediated NO protects against I/R-induced liver injury by enhancing autophagic flux.