Cryo-EM structure of a eukaryotic zinc transporter at a low pH suggests its Zn2+-releasing mechanism.

Zinc transporter 8 (ZnT8) is mainly expressed in pancreatic islet ß cells and is responsible for H+-coupled uptake (antiport) of Zn2+ into the lumen of insulin secretory granules. Structures of human ZnT8 and its prokaryotic homolog YiiP have provided structural basis for constructing a plausible transport cycle for Zn2+. However, the mechanistic role that protons play in the transport process remains unclear. Here we present a lumen-facing cryo-EM structure of ZnT8 from Xenopus tropicalis (xtZnT8) in the presence of Zn2+ at a luminal pH (5.5). Compared to a Zn2+-bound xtZnT8 structure at a cytosolic pH (7.5), the low-pH structure displays an empty transmembrane Zn2+-binding site with a disrupted coordination geometry. Combined with a Zn2+-binding assay our data suggest that protons may disrupt Zn2+ coordination at the transmembrane Zn2+-binding site in the lumen-facing state, thus facilitating Zn2+ release from ZnT8 into the lumen.

Novel QTL Conferring Phosphorus Acquisition and Utilization Efficiencies in Barley.

Phosphorus (P) deficiency in agricultural soil is a major constraint for crop production and increasing P acquisition efficiency (PAE) of plants is considered as one of the most cost-effective solutions for yield increase. The objective of this study was to detect quantitative trait loci (QTL) controlling (PAE) and P utilization efficiency (PUE) in barley under applied (+P) and non-applied P (-P) conditions. Based on the analysis of a recombinant inbred lines (RILs) population derived from a cross between a malting barley variety and a wild barley accession, 17 QTL controlling PAE, PUE and yield traits were detected. The phenotypic variation explained by each of these QTL ranges from 11.0 to 24.7%. Significant correlation was detected between most of P-related traits and yield traits. Five QTL clusters were identified on four different chromosomes (1H, 3H, 5H, and 7H). Two of the QTL clusters, located on chromosome 1H (for GPUP/PUP) and 7H (for SPUE/SPC), respectively, are novel. Fourteen genes located in the interval harboring the major QTL were identified as candidates associated with P efficiency. The stable QTL for PAE, PUE and yield-related traits could be important for breeding P-efficient barley varieties.

Hydrogen sulfide ameliorates disorders in the parafacial respiratory group region of neonatal rats caused by prenatal cigarette smoke exposure via an antioxidative effect.

We previously found that hydrogen sulfide (H2S) ameliorated the dysfunction of central chemoreception caused by prenatal cigarette smoke exposure (CSE). In the present study, we further explored whether the parafacial respiratory group (pFRG) is involved in the protection of central chemoreception by H2S against prenatal CSE-induced injury. We found that NaHS, a donor of H2S, restored the expression of Phox2b, which was downregulated by prenatal CSE, in the pFRG region of neonatal rats. NaHS also relieved the prenatal CSE-induced excitatory synapse disturbance in the pFRG region of neonatal rats. Additionally, NaHS prevented the increase in the malondialdehyde level and suppression of antioxidase activity in the pFRG region of neonatal rats induced by prenatal CSE. Furthermore, NaHS prevented the downregulation of the expression of antioxidases and Nrf2 in the pFRG region of neonatal rats with prenatal CSE. These results suggest that H2S can protect the pFRG of neonatal rats against prenatal CSE-induced injury via an antioxidative effect.

Protective Effects of Hydrogen Sulfide Against Cigarette Smoke Exposure-Induced Placental Oxidative Damage by Alleviating Redox Imbalance via Nrf2 Pathway in Rats.

BACKGROUND/AIMS: Cigarette smoke exposure (CSE) during pregnancy is a well-recognized health hazard that causes placental damage. Hydrogen sulfide (H2S) has been reported to protect multiple organs from injury. However, the protective effects of H2S have not been tested in the placenta. This study aimed to explore the potential of H2S in protecting placenta against oxidative injury induced by CSE during pregnancy and the possible underlying mechanisms. METHODS: Pregnant SD rats were randomly divided into 4 groups: NaCl, NaHS (a donor of H2S), CSE and CSE+NaHS. Placental oxidative damage was detected by 8-hydroxy-2-deoxyguanosine (8-OHdG) stain and malondialdehyde (MDA) assay. Placental redox status was assessed by measuring reactive oxygen species (ROS), total antioxidant capacity (T-AOC) and glutathione (GSH) levels, as well as copper/zinc SOD (SOD1), manganese SOD (SOD2), catalase (CAT) and glutathione peroxidase (GPx) activities and expressions. Meanwhile, nuclear factor erythroid 2-related factor 2 (Nrf2) was analyzed by immunohistochemistry, real-time PCR and Western blot. RESULTS: We found that NaHS markedly reduced the elevated levels of 8-OHdG and MDA induced by CSE. Further, NaHS treatment effectively mitigated CSE-induced placental redox imbalance by inhibiting ROS production, restoring T-AOC level, increasing GSH/GSSG ratio, and augmenting SOD1 SOD2, CAT and GPx activities and expressions. More notably, NaHS administration also reversed the aberrant decrease of Nrf2 due to CSE in rat placentas. CONCLUSION: Our data demonstrate that H2S can protect against CSE-induced placental oxidative damage probably by alleviating redox imbalance via Nrf2 pathway.

Hydrogen sulfide alleviates placental injury induced by maternal cigarette smoke exposure during pregnancy in rats.

Maternal cigarette smoke exposure (CS) during pregnancy is a well recognized causative factor for placental injury. Hydrogen sulfide (H2S), a gaseous signal molecule, has been shown to exert a protective effect against tissue injury in many organs. This study aimed to investigate whether H2S could alleviate CS-induced placental injury in rats. Pregnant SD rats were randomly divided into 4 groups: NaCl, CS, CS + NaHS (a donor of H2S) and NaHS. On gestational day 21, placental and fetal weights were measured. Placental H2S content was assessed by methylene blue method. Placental histological changes were examined by light microscopy and transmission electron microscopy. The results showed that administration of NaHS significantly attenuated CS-induced decrease in placental and fetal weights. Moreover, NaHS injection markedly alleviated CS-induced reduction in placental H2S content. Meanwhile, NaHS treatment obviously improved CS-induced morphological changes of placental junctional and labyrinthine zones. More notably, NaHS administration in CS rats was also found to ameliorate placental ultrastructural alterations, as indicated by decrease in the thickness of placental barrier, prevention of apical microvilli loss, alleviation of endoplasmic reticulum swelling and reduction in the number of vacuoles in trophoblast cells. Taken together, these findings demonstrate that administration of NaHS can alleviate CS-induced placental injuries in rats, suggesting that H2S may have therapeutic potential for treatment of placental injury caused by CS.

Hydrogen sulfide ameliorates prenatal cigarette smoke exposure-induced impairment of respiratory responses to hypercapnia in neonatal rats.

The present study was designed to investigate whether H2S could improve the respiratory responses to hypercapnia blunted by prenatal CSE in neonatal rats in vivo. Respiratory activities were recorded with head-out body plethysmography. The results showed that during baseline, respiratory frequency (FR), tidal volume (VT) and minute ventilation (VE) were similar among tested groups; frequency of spontaneous apnea (FSA), not post-sigh apnea (FPA), was significantly elevated by prenatal CSE. During hypercapnia, the increases in FR and VE were significantly reduced, but VT was not markedly different, in CSE group; both FSA and FPA were decreased, although FSA remained higher in CSE group. All the aforementioned effects induced by CSE on respiratory activities were relieved by NaHS (donor of H2S, 56µmol/kg by intraperitoneal injection). These data indicate that H2S could ameliorate the disruption of respiratory responses to hypercapnia induced by prenatal CSE in neonatal rats.

Impairment of Central Chemoreception in Neonatal Rats Induced by Maternal Cigarette Smoke Exposure during Pregnancy.

It has been postulated that prenatal cigarette smoke exposure (CSE) increases the risk for sudden infant death syndrome. The victims of infant death syndrome suffer from respiratory abnormalities, such as central apnea, diminished chemoreflex and alteration in respiratory pattern during sleep. However, no experimental evidence on CSE model exists to confirm whether prenatal CSE gives rise to reduction of neonatal central chemoreception in in vitro preparations in absence of peripheral sensory feedback. The aim of the present study was to test the hypothesis that maternal CSE during pregnancy depresses central chemoreception of the neonatal rats. The pregnant rats were divided into two groups, control (n = 8) and CSE (n = 8). Experiments were performed on neonatal (0-3days) rat pups. Fictive respiratory activity was monitored by recording the rhythmic discharge from the hypoglossal rootlets of the medullary slices obtained from the neonatal rats. The burst frequency (BF) and integrated amplitude (IA) of the discharge were analyzed. Their responses to acidified artificial cerebrospinal fluid (aCSF) were tested to indicate the change of the central chemosensitivity. Under condition of perfusing with standard aCSF (pH 7.4), no significant difference was detected between the two groups in either BF or IA (P>0.05). Under condition of perfusing with acidified aCSF (pH 7.0), BF was increased and IA was decreased in both groups (P<0.01). However, their change rates in the CSE group were obviously smaller than that in the control group, 66.98 ± 10.11% vs. 143.75 ± 15.41% for BF and -22.38 ± 2.51% vs. -44.90 ± 3.92% for IA (P<0.01). In conclusion, these observations, in a prenatal CSE model, provide important evidence that maternal smoking during pregnancy exerts adverse effects on central chemoreception of neonates.