Jie Cheng

Inhibition of voltage-gated sodium channels by bisphenol A in mouse dorsal root ganglion neurons.

Bisphenol A (BPA), an estrogenic compound, is contained in cans, polycarbonate bottles, and some dental sealants. Exposure to BPA might have potential toxicological effects on the nervous system. Previous studies have demonstrated that BPA may affect ion channel function, but the effects of BPA on voltage-gated sodium channels are unknown. Herein, we report the effects of BPA on TTX-sensitive (TTX-S) and TTX-resistant (TTX-R) Na+ currents, using a conventional whole-cell patch clamp technique from acutely isolated mouse dorsal root ganglion neurons. BPA inhibited TTX-S Na+ currents and TTX-R Na+ currents, the effects of BPA were rapid, reversible and in a concentration-dependent manner. Moreover, BPA could shift the voltage-gated activation curve for TTX-S Na+ channel in the hyperpolarizing direction without changing that for TTX-R Na+ channel; shift the steady-state inactivation curve for TTX-S Na+ channel in the depolarizing direction without changing that for TTX-R Na+ channel; and lengthen the time course of recovery from inactivation for both TTX-S Na+ current and TTX-R Na+ current. We also found that PKC inhibitor GÖ-6983 and PKA inhibitor H-89 blocked the BPA-induced inhibition of Na+ currents. Considering its complex modulatory effects on voltage-gated sodium channels, BPA might have potential toxicological effects on the nervous system and lead to a change in excitability of nociceptive afferent fibers.

The toxic effects of Bisphenol A on the mouse spermatocyte GC-2 cell line: the role of the Ca2+-calmodulin-Ca2+/calmodulin-dependent protein kinase II axis.

Bisphenol A (BPA), an endocrine‐disrupting chemical (EDC), is known to induce male reproductive toxicity in rodents. However, its toxic effects on the germ cells are still poorly understood. It has been proposed that Ca2+ homeostasis and Ca2+ sensors, including calmodulin (CaM) and calmodulin‐dependent protein kinase II (CaMKII), play critical roles in spermatogenesis. Therefore, in the present study, we aimed to investigate whether a perturbation in Ca2+‐CaM‐CaMKII signaling was involved in the BPA‐induced injury to mouse spermatocyte GC‐2spd (ts) (GC‐2) cells. Our results showed that BPA (range from 0.2 to 20 μM) induced obvious GC‐2 cell injury, including decreased cell viability, the release of mitochondrial cytochrome c and the activation of caspase‐3. However, these processes could be partially abrogated by pretreatment with a Ca2+ chelator (BAPTA/AM), a CaM antagonist (W7) or a CaMKII inhibitor (KN93). These results, taken together, indicate that BPA exposure contributes to male germ cell injury, which may be partially mediated through a perturbation in Ca2+/CaM/CaMKII signaling and the mitochondrial apoptotic process. Copyright

Effects of Raloxifene on Voltage- Dependent T-Type Ca2+ Channels in Mouse Spermatogenic Cells

Voltage-dependent T-type Ca2+ channels have eminent roles in sperm function. In the present study, we investigated the effects of raloxifene, a selective estrogen receptor modulator, on T-type Ca2+ channels in mouse spermatogenic cells by using both electrophysiological and molecular techniques. We found that T-type calcium currents (IT-Ca) were inhibited by raloxifene in a concentration-dependent manner with an IC50 of 2.97 µM, as assessed with the patch clamp technique. Application of raloxifene at 2 µM inhibited IT-Ca by 54.9 ± 2.1% at –20 mV (n = 10, p < 0.05). Furthermore, raloxifene-induced inhibition of IT-Ca was associated with a negative shift of both the activation and the steady-state inactivation properties. The time constants of activation and inactivation were decreased, the time constant of deactivation was increased, but the time constant of recovery was not affected. In addition, the inhibitory effects of raloxifene and 17β-estradiol on IT-Ca were unaffected by the estrogen receptor antagonist ICI 182,780. We also found that raloxifene treatment decreased the mRNA expression of CaV3.2 and CaV3.3, but not CaV3.1 in GC-2spd (ts) cells (mouse spermatocyte cell line), as assessed by real-time RT-PCR. Taken together, these data indicate that in mouse spermatogenic cells, raloxifene decreases IT-Ca independent of classical estrogen, and the mRNA expression of T-type calcium channels and therefore may affect male reproductive function.

Fenvalerate-induced Ca2+ transients via both intracellular and extracellular way in mouse GC-2spd (ts) cells.

Fenvalerate (Fen) is a widely used synthetic pyrethroid insecticide which is considered to impede the male reproductive function. However, little is known about its underlying mechanism. In this study, we found that fenvalerate affected the Ca(2+) homeostasis, inducing Ca(2+) transients via both intracellular Ca(2+) release and extracellular Ca(2+) influx. Ca(2+) influx was via store-operated channel (SOC). Therefore, the effects of fenvalerate on Ryanodine receptors (RyRs) and Inositol (1,4,5)-trisphosphate receptors (IP(3)Rs) which involved in forming Ca(2+) transient was assessed by pharmacological way. We also demonstrated that fenvalerate affected the expression of both receptors and hindered cell proliferation as well. In addition, we discovered that 2-APB, an antagonist of IP(3)Rs, inhibited GC-2spd (ts) cells (GC-2 cells) proliferation. Cell cycle analysis of GC-2 cells treated with fenvalerate and 2-APB indicated that both of which showed a slight S-phase accumulation. In conclusion, our results demonstrate that fenvalerate-induced Ca(2+) transients from both calcium release through RyRs or IP(3)Rs and calcium influx via SOC. IP(3)Rs seem to serve a predominant role in triggering Ca(2+) transients which could participate to the regulation of GC-2 cell proliferation.

Pharmacological effect of deoxypodophyllotoxin: A medicinal agent of plant origin, on mammalian neurons

Deoxypodophyllotoxin (DOP) is a natural product that can be isolated from a variety of medicinal herb plants. It is well known for its antitumor, antiviral, and anti-inflammatory activities. However, there are few investigations that address neurotoxic effect of DOP in animal nervous system. In this study, whole-cell patch clamp and calcium imaging techniques were employed to investigate effects of DOP on electrophysiological properties and calcium regulation of rat dorsal root ganglion (DRG) neurons. DOP inhibited both TTX-S (tetrodotoxin-sensitive) and TTX-R (tetrodotoxin-resistant) sodium currents in voltage clamp recording and caused a decrease in the number of action potentials (APs) in current clamp experiment. Suppressive and unfavorable effects of DOP on the kinetics of sodium currents in terms of excitability of DRG neurons may greatly contribute to its antitumor and anti-inflammatory activities. Moreover, DOP evoked increase of intracellular Ca(2+) concentrations ([Ca(2+)](i)) in DRG neurons, and this effect may lead to neuronal cytotoxicity.

Involvement of Insulin Signaling Disturbances in Bisphenol A-Induced Alzheimer’s Disease-like Neurotoxicity

Bisphenol A (BPA), a member of the environmental endocrine disruptors (EDCs), has recently received increased attention because of its effects on brain insulin resistance. Available data have indicated that brain insulin resistance may contribute to neurodegenerative diseases. However, the associated mechanisms that underlie BPA-induced brain-related outcomes remain largely unknown. In the present study, we identified significant insulin signaling disturbances in the SH-SY5Y cell line that were mediated by BPA, including the inhibition of physiological p-IR Tyr1355 tyrosine, p-IRS1 tyrosine 896, p-AKT serine 473 and p-GSK3α/β serine 21/9 phosphorylation, as well as the enhancement of IRS1 Ser307 phosphorylation; these effects were clearly attenuated by insulin and rosiglitazone. Intriguingly, Alzheimer’s disease (AD)-associated pathological proteins, such as BACE-1, APP, β-CTF, α-CTF, Aβ 1–42 and phosphorylated tau proteins (S199, S396, T205, S214 and S404), were substantially increased after BPA exposure, and these effects were abrogated by insulin and rosiglitazone treatment; these findings underscore the specific roles of insulin signaling in BPA-mediated AD-like neurotoxicity. Thus, an understanding of the regulation of insulin signaling may provide novel insights into potential therapeutic targets for BPA-mediated AD-like neurotoxicity.

Insulin signaling disruption in male mice due to perinatal bisphenol A exposure: Role of insulin signaling in the brain

Bisphenol A (BPA), an environmental estrogenic endocrine disruptor, is widely used for producing polycarbonate plastics and epoxy resins. Available data have shown that perinatal exposure to BPA contributes to peripheral insulin resistance, while in the present study, we aimed to investigate the effects of perinatal BPA exposure on insulin signaling and glucose transport in the cortex of offspring mice. The pregnant mice were administrated either vehicle or BPA (100 μg/kg/day) at three perinatal stages. Stage I: from day 6 of gestation until parturition (P6-PND0 fetus exposure); Stage II: from lactation until delactation (PND0-PND21 newborn exposure) and Stage III: from day 6 of pregnancy until delactation (P6-PND21 fetus and newborn exposure). At 8 months of age for the offspring mice, the insulin signaling pathways and glucose transporters (GLUTs) were detected. Our data indicated that the insulin signaling including insulin, phosphorylated insulin receptor (IR), phosphorylated protein kinase B (p-AKT), phosphorylated glycogen synthase kinase 3β (p-GSK3β) and phosphorylated extracellular signal regulated protein kinase (p-ERK) were significantly decreased in the brain. In parallel, GLUTs (GLUT1/3/4) were obviously decreased as well in BPA-treated group in mice brain. Noteworthily, the phosphorylated tau (p-tau) and amyloid precursor protein (APP) were markedly up-regulated in all BPA-treated groups. These results, taken together, suggest the adverse effects of BPA on insulin signaling and GLUTs, which might subsequently contribute to the increment of p-tau and APP in the brain of adult offspring. Therefore, perinatal BPA exposure might be a risk factor for the long-term neurodegenerative changes in offspring male mice.

Involvement of the delayed rectifier outward potassium channel Kv2.1 in methamphetamine-induced neuronal apoptosis via the p38 mitogen-activated protein kinase signaling pathway: Kv2.1 in meth-induced neuronal apoptosis via the p38 MAPK signaling

Methamphetamine (Meth) is an illicit psychostimulant with high abuse potential and severe neurotoxicity. Recent studies have shown that dysfunctions in learning and memory induced by Meth may partially reveal the mechanisms of neuronal channelopathies. Kv2.1, the primary delayed rectifying potassium channel in neurons, is responsible for mediating apoptotic current surge. However, whether Kv2.1 is involved in Meth‐mediated neural injury remains unknown. In the present study, the treatment of primary cultured hippocampal neurons with Meth indicated that Meth induced a time‐ and dose‐dependent augmentation of Kv2.1 protein expression, accompanied by elevated cleaved‐caspase 3 and declined bcl‐2/bax ratio. The blockage of Kv2.1 with the inhibitor GxTx‐1E or the knockdown of the channel noticeably abrogated the pro‐apoptotic effects mediated by Meth, demonstrating the specific roles of Kv2.1 in Meth‐mediated neural damage. Additionally, the p38 mitogen‐activated protein kinase (MAPK) signaling was demonstrated to be involved in Meth‐mediated Kv2.1 upregulation and in the subsequent pro‐apoptotic effects, as treatment with a p38 MAPK inhibitor significantly attenuated Meth‐mediated Kv2.1 upregulation and cell apoptosis. Of note, PRE‐084, a sigma‐1 receptor agonist, obviously attenuated Meth‐induced upregulation of Kv2.1 expression, neural apoptosis and p38 MAPK activation. Taken together, these results reveal a novel mechanism involved in Meth‐induced neural death with implications for therapeutic interventions for Meth users.

Effects of BmKNJX11, a bioactive polypeptide purified from Buthus martensi Karsch, on sodium channels in rat dorsal root ganglion neurons.

A long-chain polypeptide BmKNJX11 was purified from the venom of Asian scorpion Buthus martensi Karsch (BmK) by a combination of gel filtration, ion-exchange chromatography, and reverse-phase high-performance liquid chromatography. The molecular mass was found to be 7036.85 Da by electrospray ionization mass spectrometry. The first 15 N-terminal amino acid sequence of BmKNJX11 was determined to be GRDAY IADSE NCTYT by Edman degradation. With whole cell recording, BmKNJX11 inhibited tetrodotoxin-sensitive voltage-gated sodium channels (TTX-S VGSC) in freshly isolated rat dorsal root ganglion (DRG) neurons in a concentration- and voltage-dependent manner. At a concentration of 40 μg/ml BmKNJX11 lowered the activation threshold and produced negative shifting of TTX-S sodium current (I Na) activation curve. In addition, BmKNJX11 induced shifting of the steady-state inactivation curve to the left, delayed the recovery of TTX-S I Na from inactivation, and also reduced the fraction of available sodium channels. These results suggested that BmKNJX11 might exert effects on VGSC by binding to a specific site. Considering that TTX-S VGSC expressed in DRG neurons play a critical role in nociceptive transmission, the interaction of BmKNJX11 with TTX-S VGSC might lead to a change in excitability of nociceptive afferent fibers, which may be involved in the observed peripheral pain expression.

Involvement of insulin signalling pathway in methamphetamine-induced hyperphosphorylation of Tau

Methamphetamine (METH), an amphetamine-like drug, is one of the most commonly used central nervous system psychostimulants worldwide. METH abuse frequently leads to cognitive decline and dementia-like changes, but the mechanisms remain poorly understood. In the present study, the mechanisms of METH-induced changes in Alzheimers disease-like pathological protein in Neuro2A cells were explored. Our results indicated that METH exposure significantly increased the expression of the pathological protein hyperphosphorylated tau (p-tau). Further analysis revealed that METH exposure obviously disrupted insulin signalling, resulted in brain insulin resistance, which manifested as downregulation of the insulin receptor substrate-1, AKTser 473, and GSK3β activation. Notably, the linkage between p-tau expression and insulin signalling can be partially verified by treatment with the insulin-sensitizing drug rosiglitazone and GSK3β inhibitor TWS119 which specifically reversed METH-induced hyperphosphorylation of tau. Our results indicate that insulin signalling can be therapeutically exploited for attenuating METH-induced upregulation of p-tau.