Protective effect of nicotine on tunicamycin-induced apoptosis of PC12h cells

Bis(ethylmaltolato)oxidovanadium (IV) alleviates neuronal apoptosis through regulating peroxisome proliferator-activated receptor γ in a triple transgenic animal model of Alzheimer's disease

Endoplasmic reticulum stress (ER stress) plays a critical role in neuronal apoptosis along with the aggravation of Alzheimer's disease (AD). Nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-activated transcription factor that is involved in regulating ER stress in Alzheimer's disease (AD), therefore, this protein could be a promising therapeutic target for AD. Vanadium compounds, such as vanadyl acetylacetonate, sodium metavanadate and bis(maltolato)oxovanadium, are well-known as puissant PPARγ modulators. Thus, we are curious whether bis(ethylmaltolato)oxidovanadium (IV) (BEOV) can ameliorate ER stress and subsequent neuronal apoptosis by regulating PPARγ in AD models. To this end, we determined the effect of BEOV on behavioral performance, ER stress and neuronal apoptosis in the triple transgenic mouse AD model (3×Tg-AD). Our results showed that BEOV improved cognitive abilities and reduced the ER stress- and apoptosis-associated proteins in the brains of 3×Tg-AD mice. In vitro administration of BEOV in primary hippocampal neurons and N2asw cells achieved similar results in repressing ER stress. In addition, cotreatment with GW9662 (an antagonist of PPARγ) effectively blocked these neuroprotective effects of BEOV, which provided strong evidence that PPARγ-dependent signaling plays a key role in protecting against ER stress and neuronal apoptosis in AD. In conclusion, our data demonstrated that BEOV alleviated neuronal apoptosis triggered by ER stress by regulating PPARγ in a 3×Tg-AD model.

Bis(ethylmaltolato)oxidovanadium (IV) mitigates neuronal apoptosis resulted from amyloid-beta induced endoplasmic reticulum stress through activating peroxisome proliferator-activated receptor γ

Neuronal apoptosis caused by amyloid-beta (Aβ) overproduction is one of the most important pathological features in Alzheimer's disease (AD). Endoplasmic reticulum (ER) stress induced by Aβ overload plays a critical role in this process. Bis(ethylmaltolato)oxidovanadium (IV) (BEOV), a vanadium compound which had been regarded as peroxisome proliferator-activated receptor γ (PPARγ) agonist, was reported to exert an antagonistic effect on ER stress. In this study, we tested whether BEOV could ameliorate the Aβ-induced neuronal apoptosis by inhibiting ER stress. It was observed that BEOV treatment ameliorated both tunicamycin-induced and/or Aβ-induced ER stress and neurotoxicity in a dose-dependent manner through downgrading ER stress-associated and apoptosis-associated proteins in primary hippocampal neurons. Consistent with in vitro results, BEOV also reduced ER stress and inhibited neuronal apoptosis in hippocampi and cortexes of transgenic AD model mice. Moreover, by adopting GW9662 and salubrinal, the inhibitor of PPARγ and hyperphosphorylated eukaryotic translation initiation factor 2α, respectively, we further confirmed that BEOV alleviated Aβ-induced ER stress and neuronal apoptosis in primary hippocampal neurons by activating PPARγ. Taken together, these results provided scientific evidences to support the concept that BEOV ameliorates Aβ-induced ER stress and neuronal apoptosis through activating PPARγ.

Expression Changes of Apoptotic Genes in Tissues from Mice Exposed to Nicotine

Objective:

Smoking is the leading preventable cause of various diseases such as lung cancer, chronic obstructive pulmonary disease and cardiovascular disease. Nicotine, one of the major toxic components of tobacco, contributes to the pathogenesis of different diseases.

Methods:

Given the controversy about nicotine toxicity, the present study was conducted to determine apoptotic effects of nicotine on the heart, kidney, lung and liver of male mice. Real-time PCR was performed to identify mRNA expression changes in apoptotic-related genes between nicotine treated and control mice.

Result:

In the heart and lung, nicotine caused significant decrease in P53, Bax and Caspase-3 mRNA expression levels compared to the control group. However, in the kidney and liver, the result was significant increase in Bax, Caspase-2, Caspase-3 and a significant decrease in P53 mRNA expression (p<0.01). DNA fragmentation assays indicated no fragmentation in the heart and lung, but in the kidney and liver of nicotine treated mice, isolated DNA was fragmented.

Conclusion:

Our study provided insight into the molecular mechanisms of nicotine anti-apoptotic effects on the heart and lung as well as pro-apoptotic effects on kidney and liver via a P53-independent pathway.

Overexpression of CREB protein protects from tunicamycin-induced apoptosis in various rat cell types

Endoplasmic reticulum (ER) stress plays an essential role in unfolded protein response induced apoptosis contributing to several pathological conditions. Glycogen synthase kinase-3β (GSK-3β) plays a central role in several apoptotic signaling, including ER stress, as the active form of GSK-3β induces apoptosis. The phosphorylation of cAMP responsive element (CRE) binding protein (CREB) Ser-133 (S133) residue is the end-point of various signaling pathways, like growth factor signaling, while the Ser-129 (S129) residue is phosphorylated by GSK-3β. The significance of the ubiquitously expressed transcription factor CREB is demonstrated in prolonged, tunicamycin (TM)-induced ER stress in this study. In the experiments wild-type (wt) CREB, S129Ala, S133Ala or S129Ala-S133Ala mutant CREB expressing PC12 rat pheochromocytoma cell lines showed increased survival under TM-evoked prolonged ER stress compared to wtPC12 cells. After TM treatment ER stress was activated in all PC12 cell types. Lithium and SB-216763, the selective, well-known inhibitors of GSK-3β, decreased TM-induced apoptosis and promoted cell survival. The proapoptotic BH3-only Bcl-2 family member Bcl-2-interacting mediator of cell death (Bim) level was decreased in the different CREB overexpressing PC12 cells as a result of TM treatment. CREB overexpression also inhibited the sequestration of Bim protein from tubulin molecules, as it was demonstrated in wtPC12 cells. Transient expression of wtCREB diminished TM-induced apoptosis in wtPC12, Rat-1 and primary rat vascular smooth muscle cells. These findings demonstrate a novel role of CREB in different cell types as a potent protector against ER stress.

Protective effects of dibenzocyclooctadiene lignans from Schisandra chinensis against beta-amyloid and homocysteine neurotoxicity in PC12 cells

Aggregated beta-amyloid (Aβ) and elevated plasma levels of homocysteine have been implicated as critical factors in the pathogenesis of Alzheimer's disease. The neuroprotective effects and possible mechanism of four structurally similar dibenzocyclooctadiene lignans (namely schisandrin, schisantherin A, schisandrin B and schisandrin C) isolated from the fruit of Schisandra chinensis (Turcz.) Baill. (Schisandraceae) against Aβ₂₅₋₃₅ and homocysteine toxicity in PC12 cells was studied. Exposure of PC12 cells to 0.5 µm Aβ₂₅₋₃₅ caused significant cell death, increased the number of apoptotic cells, elevated reactive oxygen species, increased the levels of the pro-apoptotic protein Bax and caspase-3 activation. All these effects induced by Aβ₂₅₋₃₅ were markedly reversed by schisandrin B and schisandrin C pretreatment, while schisandrin and schisantherin A had no obvious effects. Meanwhile, schisandrin B and schisandrin C reversed homocysteine-induced cytotoxicity. The results indicated that schisandrin B and schisandrin C protected PC12 cells against Aβ toxicity by attenuating ROS production and modulating the apoptotic signal pathway through Bax and caspase-3. Further structure-activity analysis of Schisandra lignans and evaluations of their neuroprotective effects using AD animal models are warranted.

Inhibition of Toll-like receptor 2-mediated interleukin-8 production in Cystic Fibrosis airway epithelial cells via the alpha7-nicotinic acetylcholine receptor

Cystic Fibrosis (CF) is an inherited disorder characterised by chronic inflammation of the airways. The lung manifestations of CF include colonization with Pseudomonas aeruginosa and Staphylococcus aureus leading to neutrophil-dominated airway inflammation and tissue damage. Inflammation in the CF lung is initiated by microbial components which activate the innate immune response via Toll-like receptors (TLRs), increasing airway epithelial cell production of proinflammatory mediators such as the neutrophil chemokine interleukin-8 (IL-8). Thus modulation of TLR function represents a therapeutic approach for CF. Nicotine is a naturally occurring plant alkaloid. Although it is negatively associated with cigarette smoking and cardiovascular damage, nicotine also has anti-inflammatory properties. Here we investigate the inhibitory capacity of nicotine against TLR2- and TLR4-induced IL-8 production by CFTE29o- airway epithelial cells, determine the role of α7-nAChR (nicotinic acetylcholine receptor) in these events, and provide data to support the potential use of safe nicotine analogues as anti-inflammatories for CF.

Nicotine suppresses tunicamycin-induced, but not thapsigargin-induced, expression of GRP78 during ER stress-mediated apoptosis in PC12 cells

We previously reported that nicotine protected against tunicamycin (Tm)-induced ER stress-mediated apoptosis, but not thapsigargin (Tg)-induced apoptosis in PC12 cells. In the present study, we report that the expression of glucose-regulated protein 78 (GRP78) was suppressed by nicotine in Tm-treated PC12 cells. Interestingly, the GRP78 expression was not changed by nicotine in Tg-treated cells. Moreover, nicotine reduced the activation of caspase-12 in Tm-treated cells, but not in Tg-treated cells. These results suggest that nicotine prevented Tm-induced ER stress-mediated apoptosis by attenuating an early stage of Tm-induced ER stress. It was possible that the suppression of GRP78 expression by nicotine was achieved through the suppression of the Ire1-XBP1 and/or ATF6 pathways. We observed that nicotine suppressed the Tm-induced, but not Tg-induced, splicing of XBP1 mRNA, and also suppressed the Tm-induced, but not Tg-induced, production of cleaved ATF6 in PC12 cells. These results indicate that the suppression of Ire1-XBP1 and ATF6 pathways contributes to the suppression of GRP78 expression by nicotine in Tm-treated PC12 cells, suggesting that nicotine suppresses a common step upstream of both the Ire1-XBP1 and ATF6 pathways which are required for the expression of GRP78 during Tm-induced ER stress.

Nicotine and apoptosis

Cigarette smoking is associated with a plethora of different diseases. Nicotine is the addictive component of cigarette but also acts onto cells of the non-neuronal system, including immune effector cells. Although nicotine itself is usually not referred to as a carcinogen, there is ongoing debate whether nicotine functions as a 'tumor enhancer.' By binding to nicotinic acetylcholine receptors, nicotine deregulates essential biological processes like angiogenesis, apoptosis, and cell-mediated immunity. Apoptosis plays critical roles in a wide variety of physiologic processes during fetal development and in adult tissue and is also a fundamental aspect of the biology of malignant diseases. This review provides an overlook how nicotine influences apoptotic processes and is thus directly involved in the etiology of pathological conditions like cancer and obstructive diseases.

Neuroprotective effect of nicotine against 3-nitropropionic acid (3-NP)-induced experimental Huntington's disease in rats

Nicotinic acetylcholine receptors (nAChRs) are regarded as potential therapeutic targets to control various neurodegenerative diseases. Owing to the relevance of cholinergic neurotransmission in the pathogenesis of Huntington's disease (HD) this investigation was aimed to study the effect of nicotine, a nAChR agonist, on 3-nitropropionic acid (3-NP)-induced neurodegeneration in female Wistar rats. Systemic administration of 3-NP in rats serves as an important model of HD. The animals received subcutaneous injections of nicotine (0, 0.25, 0.50 and 1.00 mg/kg) daily for 7 days. 3-NP (25 mg/kg, i.p.) was administered daily 30 min after nicotine for the same duration. One additional group of rats served as control (vehicle only). On day 8, the animals were observed for neurobehavioral performance (motor activity, inclined plane test, grip strength test, paw test and beam balance). Immediately after behavioral studies, the animals were transcardially perfused with neutral buffered formalin (10%) and brains were fixed for histological studies. Lesions in the striatal dopaminergic neurons were assessed by immunohistochemical method using tyrosine hydroxylase (TH) immunostaining. Treatment of rats with nicotine significantly and dose-dependently attenuated 3-NP-induced behavioral deficits. Administration of 3-NP alone caused significant depletion of striatal dopamine (DA) and glutathione (GSH), which was significantly and dose-dependently attenuated by nicotine. Preservation of striatal dopaminergic neurons by nicotine was also confirmed by immunohistochemical studies. These results clearly showed neuroprotective effect of nicotine in experimental model of HD. The clinical relevance of these findings in HD patients remains unclear and warrants further studies.