Modulation of expression of Na+/Ca2+ exchanger in heart of rat and mouse under stress

Effects of exposure to sediment-associated fipronil on cardiac function of Neotropical armored catfish Hypostomus regani

Fipronil is widely used as a broad-spectrum insecticide in agriculture, urban environments, and veterinary medicine. Fipronil can enter aquatic ecosystems and spread to sediment and organic matter, representing a risk to non-target species. This study aimed to evaluate the effects of short-term (96 h) exposure to a low and realistic concentration of sediment-associated fipronil (4.2 µg.kg^-1 of Regent® 800 WG) on myocardial contractility of armored catfish Hypostomus regain, a benthic fish species. Fipronil exposure induced increased inotropism and acceleration of contractile kinetics, although no alterations in the relative ventricular mass were observed. This better cardiac function was associated with an elevated expression and/or function of the Na⁺/Ca²⁺ exchanger and its marked contribution to contraction and relaxation, probably due to a stress-induced adrenergic stimulation. Ventricle strips of exposed fish also exhibited a faster relaxation and a higher cardiac pumping capacity, indicating that armored catfish were able to perform cardiac adjustments to face the exposure. However, a high energetic cost to maintain an increased cardiac performance can make fish more susceptible to other stressors, impairing developmental processes and/or survival. These findings highlight the need for regulations of emerging contaminants, such as fipronil, to ensure adequate protection of the aquatic system.

MicroRNA signatures of perioperative myocardial injury after elective noncardiac surgery: a prospective observational mechanistic cohort study

BACKGROUND

Elevated plasma or serum troponin, indicating perioperative myocardial injury (PMI), is common after noncardiac surgery. However, underlying mechanisms remain unclear. Acute coronary syndrome (ACS) is associated with the early appearance of circulating microRNAs, which regulate post-translational gene expression. We hypothesised that if PMI and ACS share pathophysiological mechanisms, common microRNA signatures should be evident.

METHODS

We performed a nested case control study of samples obtained before and after noncardiac surgery from patients enrolled in two prospective observational studies of PMI (postoperative troponin I/T>99th centile). In cohort one, serum microRNAs were compared between patients with or without PMI, matched for age, gender, and comorbidity. Real-time polymerase chain reaction quantified (qRT-PCR) relative microRNA expression (cycle quantification [Cq] threshold <37) before and after surgery for microRNA signatures associated with ACS, blinded to PMI. In cohort two, we analysed (EdgeR) microRNA from plasma extracellular vesicles using next-generation sequencing (Illumina HiSeq 500). microRNA-messenger RNA-function pathway analysis was performed (DIANA miRPath v3.0/TopGO).

RESULTS

MicroRNAs were detectable in all 59 patients (median age 67 yr [61-75]; 42% male), who had similar clinical characteristics independent of developing PMI. In cohort one, serum microRNA expression increased after surgery (mean fold-change) hsa-miR-1-3p: 3.99 (95% confidence interval [CI: 1.95-8.19]; hsa-miR-133-3p: 5.67 [95% CI: 2.94-10.91]; P<0.001). These changes were not associated with PMI. Bioinformatic analysis of differentially expressed microRNAs from cohorts one (n=48) and two (n=11) identified pathways associated with adrenergic stress and calcium dysregulation, rather than ischaemia.

CONCLUSIONS

Circulating microRNAs associated with cardiac ischaemia were universally elevated in patients after surgery, independent of development of myocardial injury.

Detection of heat shock protein 27, 70, 90 expressions in primary parenchymatous organs of goats after transport stress by real-time PCR and ELISA

Transport stress causes a series of problems to goat production, such as tissue injury and immunity damage. As a pro‐survival pathway, the heat shock response protects healthy cells of goat from stressors. To evaluate the effects of transport stress on heat shock protein (HSPs) expression on goat primary parenchymatous organs, a total of three batches of goats were treated in this study. For each batch, 12 healthy adult male goats were randomly and averagely divided into three groups: Control group (non‐transported group), 2 hr transported group and 6 hr transported group. Real‐time PCR results indicated that the mRNA expression level of heat shock protein 27 (HSP27) in all examined organs of 2 hr transport‐treated goats were upregulated (p < .05) except lung, and heat shock protein 70 (HSP70; except spleen) and heat shock protein 90 (HSP90; except liver and lung) were also increased (p < .05). In 6 hr transported group, the transcription levels of HSP27 (except heart and kidney), HSP70 (except heart, liver and lymph nodes) and HSP90 (except heart and spleen) were all backed to the original levels or even reduced (p < .05). Enzyme‐linked immunosorbent assay (ELISA) results showed that the protein levels of HSP27 (except lymph nodes), HSP70 (except spleen) and HSP90 (except liver and lung) were all increased after 2 hr transport (p < .05). After 6 hr transport, HSP27 only in kidney and HSP70 only in heart and liver were upregulated (p < .05), while HSP90 in all the examined organs except liver and lung were also maintained in relatively high levels (p < .05). Taken together, these results suggested that the expression of HSPs in goat primary parenchymatous organs may be regulated by transport stress time. Moreover, this study also provides some new data to advocate reducing transport stress of goats and improving animal welfare.

Type 1 Sodium Calcium Exchanger Forms a Complex with Carbonic Anhydrase IX and Via Reverse Mode Activity Contributes to pH Control in Hypoxic Tumors

Hypoxia and acidosis are among the key microenvironmental factors that contribute to cancer progression. We have explored a possibility that the type 1Na⁺/Ca²⁺ exchanger (NCX1) is involved in pH control in hypoxic tumors. We focused on changes in intracellular pH, co-localization of NCX1, carbonic anhydrase IX (CA IX), and sodium proton exchanger type 1 (NHE1) by proximity ligation assay, immunoprecipitation, spheroid formation assay and migration of cells due to treatment with KB-R7943, a selective inhibitor of the reverse-mode NCX1. In cancer cells exposed to hypoxia, reverse-mode NCX1 forms a membrane complex primarily with CA IX and also with NHE1. NCX1/CA IX/NHE1 assembly operates as a metabolon with a potent ability to extrude protons to the extracellular space and thereby facilitate acidosis. KB-R7943 prevents formation of this metabolon and reduces cell migration. Thus, we have shown that in hypoxic cancer cells, NCX1 operates in a reverse mode and participates in pH regulation in hypoxic tumors via cooperation with CAIX and NHE1.

Cardiac sigma receptors - an update

More than four decades passed since sigma receptors were first mentioned. Since then, existence of at least two receptor subtypes and their tissue distributions have been proposed. Nowadays, it is clear, that sigma receptors are unique ubiquitous proteins with pluripotent function, which can interact with so many different classes of proteins. As the endoplasmic resident proteins, they work as molecular chaperones - accompany various proteins during their folding, ensure trafficking of the maturated proteins between cellular organelles and regulate their functions. In the heart, sigma receptor type 1 is more dominant. Cardiac sigma 1 receptors regulate response to endoplasmic reticulum stress, modulates calcium signaling in cardiomyocyte and can affect function of voltage-gated ion channels. They contributed in pathophysiology of cardiac hypertrophy, heart failure and many other cardiovascular disorders. Therefore, sigma receptors are potential novel targets for specific treatment of cardiovascular diseases.

Sodium/calcium exchanger is upregulated by sulfide signaling, forms complex with the β1 and β3 but not β2 adrenergic receptors, and induces apoptosis

Hydrogen sulfide (H2S) as a novel gasotransmitter regulates variety of processes, including calcium transport systems. Sodium calcium exchanger (NCX) is one of the key players in a regulation calcium homeostasis. Thus, the aims of our work were to determine effect of sulfide signaling on the NCX type 1 (NCX1) expression and function in HeLa cells, to investigate the relationship of β-adrenergic receptors with the NCX1 in the presence and/or absence of H2S, and to determine physiological importance of this potential communication. As a H2S donor, we used morpholin-4-ium-4-methoxyphenyl(morpholino) phosphinodithioate-GYY4137. We observed increased levels of the NCX1 mRNA, protein, and activity after 24 h of GYY4137 treatment. This increase was accompanied by elevated cAMP due to the GYY4137 treatment, which was completely abolished, when NCX1 was silenced. Increased cAMP levels would point to upregulation of β-adrenergic receptors. Indeed, GYY4137 increased expression of β1 and β3 (but not β2) adrenergic receptors. These receptors co-precipitated, co-localized with the NCX1, and induced apoptosis in the presence of H2S. Our results suggest that sulfide signaling plays a role in regulation of the NCX1, β1 and β3 adrenergic receptors, their co-localization, and stimulation of apoptosis, which might be of a potential importance in cancer treatment.

Stress and chewing affect blood flow and oxygen levels in the rat brain

OBJECTIVE

Mastication, including chewing, would be of great importance not only for food intake, but also for the mental, physical and physiological functioning of the body. Our study showed that mastication, especially chewing, suppresses the stress response and was regarded as a biological response to defend against various stresses. Although mastication altered brain function during stress, the underlying mechanisms have not been elucidated.

METHODS

The effects of chewing during restraint stress on blood flow and oxygen partial pressure (PO(2)) levels in the rat amygdala and hypothalamus were measured using laser Doppler flowmetry and O(2)-selective electrodes.

RESULTS

Amygdaloidal and hypothalamic blood flow were not affected by restraint stress, but PO(2) levels were significantly reduced by restraint stress for 180 min compared to unrestrained control rats. The decrease in amygdaloidal and hypothalamic PO(2) levels during restraint stress was reduced after chewing for 30 min.

CONCLUSION

These results suggested that it is possible to evaluate hypothalamic and amygdaloidal blood flow and PO(2) levels in rat brains during restraint stress. Restraint stress reduced cerebral PO(2) levels. In addition, chewing would lead to increased blood flow and to recover cerebral PO(2) levels.

Analysis of Na(+)/Ca (2+) exchanger (NCX) function and current in murine cardiac myocytes during heart failure

Na(+)/Ca(2+) exchanger (NCX) plays important roles in cardiac electrical activity and calcium homeostasis. NCX current (I(NCX)) shows transmural gradient across left ventricle in many species. Previous studies demonstrated that NCX expression was increased and transmural gradient of I(NCX) was disrupted in failing heart, but the mechanisms underlying I(NCX) remodeling still remain unknown. In present study, we used patch clamp technique to record I(NCX) from subepicardial (EPI) myocytes and subendocardial (ENDO) myocytes isolated from sham operation (SO) mice and heart failure (HF) mice. Our results showed that I(NCX) was higher in normal EPI cells compared with that in ENDO, whatever for forward mode or reverse mode. In HF group, I(NCX) was significantly up-regulated, but EPI-ENDO difference was disrupted because of a more increase of I(NCX) in ENDO myocytes. In order to explore the molecular mechanism underlying remodeling of I(NCX) in failing heart, we detected the protein expression of NCX1 and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) by Western blot. We found that CaMKII activity was dramatically enhanced and parallel with the expression of NCX1 in failing heart. Our study demonstrated that transmural gradient of I(NCX) existed in murine left ventricle, and increased activity of CaMKII should account for I(NCX) remodeling in failing heart.

Modulation of the sodium-calcium exchanger in the rat kidney by different sequential stressors

Stress, if exaggerated, modulates a variety of metabolic pathways and results in development of serious health consequences. The cell membrane sodium-calcium exchanger (NCX) is a major calcium extrusion system and is also modulated by stress. It has been shown previously that mRNA, protein levels and activity of the type 1 NCX (NCX1) in the left ventricle of the rat heart are increased by stressors, such as immobilization or hypoxia. In this study we investigated whether exposure to a subsequent different stressor can affect gene expression, protein level and activity of the NCX1 in rat kidney compared to exposure to only one type of stressor. In these experiments, we used immobilization and cold as the model stressors.We found that cold exposure at 4 degrees C for 24 h, when applied after immobilization repeated seven times, completely abolished the immobilization-induced increase in NCX mRNA level and after 7 days cold exposure the increases in NCX1 protein and activity in rat kidney were also abolished. Permanently increased NCX1 expression can result in imbalance of cellular calcium homeostasis and thus contribute to kidney dysfunction. Based on our results, we conclude that exposure to a cold stressor can have a protective effect on the kidney in rats exposed previously to repeated immobilization stress. This might be explained by differential stimulation of sympathetic neural and adrenal medullary responses by these different stressors.