Astroglial S100B Secretion Is Mediated by Ca2+ Mobilization from Endoplasmic Reticulum: A Study Using Forskolin and DMSO as Secretagogues

S100B, a homodimeric Ca2+-binding protein, is produced and secreted by astrocytes, and its extracellular levels have been used as a glial marker in brain damage and neurodegenerative and psychiatric diseases; however, its mechanism of secretion is elusive. We used primary astrocyte cultures and calcium measurements from real-time fluorescence microscopy to investigate the role of intracellular calcium in S100B secretion. In addition, the dimethyl sulfoxide (DMSO) effect on S100B was investigated in vitro and in vivo using Wistar rats. We found that DMSO, a widely used vehicle in biological assays, is a powerful S100B secretagogue, which caused a biphasic response of Ca2+ mobilization. Our data show that astroglial S100B secretion is triggered by the increase in intracellular Ca2+ and indicate that this increase is due to Ca2+ mobilization from the endoplasmic reticulum. Also, blocking plasma membrane Ca2+ channels involved in the Ca2+ replenishment of internal stores decreased S100B secretion. The DMSO-induced S100B secretion was confirmed in vivo and in ex vivo hippocampal slices. Our data support a nonclassic vesicular export of S100B modulated by Ca2+, and the results might contribute to understanding the mechanism underlying the astroglial release of S100B.

The effect of social deprivation on the dynamic of the SARS-CoV-2 infection in France

Background

The association between health inequalities and the SARS-CoV-2 infection dynamic remains to be studied in France. The objective of this study was to analyse the relationship between an area-based deprivation indicator and SARS-CoV-2 infection indicators, during four epidemic waves running from August 4th 2020 to January 27th 2021 (second wave), January 28th to June 24th 2021 (third wave), June 25th to October 28th 2021 (fourth wave), and October 29th 2021 to March 29th 2022 (fifth wave).

Methods

We analysed weekly indicators of SARS-CoV-2 infection, extracted from the national testing information system: incidence, positivity and testing rates. The associations of these outcomes with the European Deprivation Index (EDI) quintiles were estimated with negative binomial generalized additive models adjusted for epidemic waves, population density (sparsely, moderately, densely populated), region (random effect) and interactions between epidemic waves and the variables EDI, population density, and region.

Results

The most deprived areas had a higher positivity rate than the least deprived ones during the second, third and fourth waves, but a lower rate during the fifth wave. They also had higher incidence during the third and fourth waves, but a similar incidence than the least deprived areas during the second wave, and even a lower rate during the fifth wave. The testing rate was lower in the most deprived areas than elsewhere, irrespective of the epidemic waves.

Conclusions

People living in the most deprived areas were less likely to be tested and more likely to test positive than people living in less deprived areas. The lower incidence, positivity and testing rates during the fifth wave in the most deprived areas may be explained by the enacted change in policy whereby screening tests were no longer free. These findings may reflect structural differences in access to care and lower capacity to benefit from prevention measures by deprived populations.

Key messages

• People living in the most deprived areas were less likely to be tested for COVID-19 irrespective of the epidemic waves.

• Health authorities should address the issues of social inequalities more rapidly and target prevention strategy to disadvantaged populations.

PKR and GCN2 stress kinases promote an ER stress-independent eIF2α phosphorylation responsible for calreticulin exposure in melanoma cells

The immunogenic cell death (ICD) process represents a novel therapeutic approach to treat tumours, in which cytotoxic compounds promote both cancer cell death and the emission of damage-associated molecular patterns (DAMPs) from dying cells, to activate the immune system against the malignancy. Therefore, we explored the possibility to stimulate the key molecular players with a pivotal role in the execution of the ICD program in melanoma cells. To this aim, we used the pro-ICD agents mitoxantrone and doxorubicin and found that both agents could induce cell death and stimulate the release/exposure of the strictly required DAMPs in melanoma cells: i) calreticulin (CRT) exposure on the cell membrane; ii) ATP secretion; iii) type I IFNs gene up-regulation and iv) HMGB1 secretion, highlighting no interference by oncogenic BRAF. Importantly, although the ER stress-related PERK activation has been linked to CRT externalization, through the phosphorylation of eIF2α, we found that this stress pathway together with PERK were not involved in melanoma cells. Notably, we identified PKR and GCN2 as key mediators of eIF2α phosphorylation, facilitating the translocation of CTR on melanoma cells surface, under pro-ICD drugs stimulation. Therefore, our data indicate that pro-ICD drugs are able to stimulate the production/release of DAMPs in melanoma cells at least in vitro, indicating in this approach a potential new valuable therapeutic strategy to treat human skin melanoma malignancy.

Fasting boosts sensitivity of human skin melanoma to cisplatin-induced cell death

Melanoma is one of leading cause of tumor death worldwide. Anti-cancer strategy includes combination of different chemo-therapeutic agents as well as radiation; however these treatments have limited efficacy and induce significant toxic effects on healthy cells. One of most promising novel therapeutic approach to cancer therapy is the combination of anti-cancer drugs with calorie restriction. Here we investigated the effect Cisplatin (CDDP), one of the most potent chemotherapeutic agent used to treat tumors, in association with fasting in wild type and mutated BRAFV600E melanoma cell lines. Here we show that nutrient deprivation can consistently enhance the sensitivity of tumor cells to cell death induction by CDDP, also of those malignancies particularly resistant to any treatment, such as oncogenic BRAF melanomas. Mechanistic studies revealed that the combined therapy induced cell death is characterized by ROS accumulation and ATF4 in the absence of ER-stress. In addition, we show that autophagy is not involved in the enhanced sensitivity of melanoma cells to combined CDDP/EBSS-induced apoptosis. While, the exposure to 2-DG further enhanced the apoptotic rate observed in SK Mel 28 cells upon treatment with both CDDP and EBSS.

Calcium and cell death signaling in neurodegeneration and aging

Transient increase in cytosolic (Cac2+) and mitochondrial Ca2+ (Ca m2+) are essential elements in the control of many physiological processes. However, sustained increases in Ca c2+ and Ca m2+ may contribute to oxidative stress and cell death. Several events are related to the increase in Ca m2+, including regulation and activation of a number of Ca2+ dependent enzymes, such as phospholipases, proteases and nucleases. Mitochondria and endoplasmic reticulum (ER) play pivotal roles in the maintenance of intracellular Ca2+ homeostasis and regulation of cell death. Several lines of evidence have shown that, in the presence of some apoptotic stimuli, the activation of mitochondrial processes may lead to the release of cytochrome c followed by the activation of caspases, nuclear fragmentation and apoptotic cell death. The aim of this review was to show how changes in calcium signaling can be related to the apoptotic cell death induction. Calcium homeostasis was also shown to be an important mechanism involved in neurodegenerative and aging processes.

The negative inotropic action of canrenone is mediated by L-type calcium current blockade and reduced intracellular calcium transients

BACKGROUND AND PURPOSE

Adding spironolactone to standard therapy in heart failure reduces morbidity and mortality, but the underlying mechanisms are not fully understood. We analysed the effect of canrenone, the major active metabolite of spironolactone, on myocardial contractility and intracellular calcium homeostasis.

EXPERIMENTAL APPROACH

Left ventricular papillary muscles and cardiomyocytes were isolated from male Wistar rats. Contractility of papillary muscles was assessed with force transducers, Ca(2+) transients by fluorescence and Ca(2+) fluxes by electrophysiological techniques.

KEY RESULTS

Canrenone (300-600 micromol L(-1)) reduced developed tension, maximum rate of tension increase and maximum rate of tension decay of papillary muscles. In cardiomyocytes, canrenone (50 micromol L(-1)) reduced cell shortening and L-type Ca(2+) channel current, whereas steady-state activation and inactivation, and reactivation curves were unchanged. Canrenone also decreased the Ca(2+) content of the sarcoplasmic reticulum, intracellular Ca(2+) transient amplitude and intracellular diastolic Ca(2+) concentration. However, the time course of [Ca(2+)](i) decline during transients evoked by caffeine was not affected by canrenone.

CONCLUSION AND IMPLICATIONS

Canrenone reduced L-type Ca(2+) channel current, amplitude of intracellular Ca(2+) transients and Ca(2+) content of sarcoplasmic reticulum in cardiomyocytes. These changes are likely to underlie the negative inotropic effect of canrenone.

Effect of withdrawal from long-term nifedipine administration on open-field habituation in the rat

The effects of withdrawal from long-term administration of nifedipine (2.5 mg/kg, ip, twice daily for 30 days) on open-field habituation were evaluated in 3-month old male Wistar rats (13-14 animals per group). Habituation was evaluated by the ratio between locomotion or rearing frequencies obtained in the second and the first open-field session for each animal. Nifedipine treatment did not modify the locomotion ratio (with a mean +/- SEM ratio of 0.66 +/- 0.12 for control and 0.45 +/- 0.08 for nifedipine-treated group) nor the rearing ratio (with a mean +/- SEM ratio of 0.51 +/- 0.12 for control and 0.62 +/- 0.18 for nifedipine-treated group). The possible factors underlying the discrepancy between the present results and the commonly reported positive effects of calcium channel blockers on memory are discussed.

Effects of single and long-term administration of nifedipine on nociception and stereotyped behavior of rats

In the present investigation, nociception and stereotyped behavior were evaluated in 3-month old male Wistar rats after a single nifedipine dose (2.5 and 5.0 mg/kg, ip, 1 h before testing, 6-7 rats per group for stereotypy studies and 15 animals per group for nociception experiments) or after long-term nifedipine treatment (2.5 mg/kg, ip, twice daily for 30 days, with testing performed 72 or 96 h after the last injection, 7 rats per group for stereotypy studies and 14-16 animals per group for nociception experiments). Stereotypy was induced with 2.5 mg/kg amphetamine, ip, and nociception was measured by the tail-immersion test. Administration of a single nifedipine dose did not modify nociception or amphetamine-induced stereotypy (with a mean +/- SEM tail-withdrawal latency of 4.5 +/- 0.5 s for control, 4.4 +/- 0.3 s for 2.5 mg/kg nifedipine and 4.7 +/- 0.7 s for 5.0 mg/kg nifedipine and with mean +/- SEM sum of stereotypy scores of 32.5 +/- 1.6 for control, 29.1 +/- 1.0 for 2.5 mg/kg nifedipine and 29.1 +/- 1.6 for 5.0 mg/kg nifedipine). Withdrawal from long-term nifedipine treatment did not affect stereotyped behavior (with mean +/- SEM sum of stereotypy scores of 28.7 +/- 1.6 for control and 30.7 +/- 1.3 for nifedipine-treated rats) but significantly increased tail-withdrawal latencies (with a mean +/- SEM tail-withdrawal latency of 4.1 +/- 0.3 s for control and 6.4 +/- 0.6 s for nifedipine-treated rats). Therefore, long-term nifedipine treatment induced plastic modifications in nociception but not in stereotyped behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of single and long-term administration of nifedipine on dopamine-related behaviors

The effects of single (2.5 and 5.0 mg/kg) and long-term (2.5 mg/kg, twice daily, for 30 days) ip administration of nifedipine on open-field and apomorphine-induced stereotyped behavior were evaluated in young male Wistar rats (12-16 animals per group for the open-field studies and 7 animals per group for the stereotypy experiments). Administration of a single dose of nifedipine produced no changes in ambulation or rearing frequencies or in immobility duration in the open-field compared to controls. Similarly, treatment with a single dose of nifedipine did not modify apomorphine-induced stereotypy. Withdrawal from long-term nifedipine administration caused a significant increase only in rearing frequency 24 h after the last drug injection (with a mean +/- SEM frequency of 23.2 +/- 2.8 for the nifedipine group and of 14.7 +/- 2.0 for control rats, after 6-min observation). This enhancement of rearing frequency was no longer observed 48 h after abrupt nifedipine withdrawal (means +/- SEM: 15.0 +/- 2.2 and 19.6 +/- 2.7 for nifedipine-treated and control rats, respectively). The other open-field behavioral parameters and apomorphine-induced stereotypy (which was observed 96 h after nifedipine withdrawal) were not affected by long-term nifedipine treatment; for example, the sum of stereotypy scores (mean +/- SEM) was 26.9 +/- 3.0 for nifedipine-treated rats and 25.5 +/- 2.2 for vehicle-treated animals. The possible mechanisms underlying these results are discussed in light of the changes in dopaminergic neurotransmission induced by dihydropyridine calcium channel blockers.