Temperature increase exacerbates apoptotic neuronal death in chemically-induced ischemia

Phosphatidylinositol (4, 5)-bisphosphate targets double C2 domain protein B to the plasma membrane

Double C2 domain protein B (DOC2B) is a high-affinity Ca²⁺ sensor that translocates from the cytosol to the plasma membrane (PM) and promotes vesicle priming and fusion. However, the molecular mechanism underlying its translocation and targeting to the PM in living cells is not completely understood. DOC2B interacts in vitro with the PM components phosphatidylserine, phosphatidylinositol (4, 5)-bisphosphate [PI(4, 5)P₂ ] and target SNAREs (t-SNAREs). Here, we show that PI(4, 5)P₂ hydrolysis at the PM of living cells abolishes DOC2B translocation, whereas manipulations of t-SNAREs and other phosphoinositides have no effect. Moreover, we were able to redirect DOC2B to intracellular membranes by synthesizing PI(4, 5)P₂ in those membranes. Molecular dynamics simulations and mutagenesis in the calcium and PI(4, 5)P₂ -binding sites strengthened our findings, demonstrating that both calcium and PI(4, 5)P₂ are required for the DOC2B-PM association and revealing multiple PI(4, 5)P₂ -C2B interactions. In addition, we show that DOC2B translocation to the PM is ATP-independent and occurs in a diffusion-like manner. Our data suggest that the Ca²⁺ -triggered translocation of DOC2B is diffusion-driven and aimed at PI(4, 5)P₂ -containing membranes.

Unfavorable effect of levetiracetam on cultured hippocampal neurons after hyperthermic injury

BACKGROUND

The aim of this study was to examine the viability of neurons and the putative neuroprotective effects of second-generation antiepileptic drug, levetiracetam (LEV), on cultured hippocampal neurons injured by hyperthermia.

METHODS

Primary cultures of rat's hippocampal neurons at 7 day in vitro (DIV) were incubated in the presence or absence of LEV in varied concentrations under hyperthermic conditions. Cultures were heated in a temperature of 40 °C for 24 h or in a temperature of 41 °C for 6 h. Flow cytometry with Annexin V/PI staining as well as fluorescent microscopy assay were used for counting and establishing neurons as viable, necrotic or apoptotic. Additionally, the release of lactate dehydrogenase (LDH) to the culture medium, as a marker of cell death, was evaluated. Assessment was performed after 9DIV and 10 DIV.

RESULTS

Incubation of hippocampal cultures in hyperthermic conditions resulted in statistically significant increase in the number of injured neurons when compared with non-heated control cultures. Intensity of neuronal destruction was dependent on temperature-value. When incubation temperature 40 °C was used, over 80% of the population of neurons remained viable after 10 DIV. Under higher temperature 41 °C, only less than 60% of neurons were viable after 10 DIV. Both apoptotic and necrotic pathways of neuronal death induced by hyperthermia were confirmed by Annexin V/PI staining.

CONCLUSIONS

LEV showed no neuroprotective effects in the current model of hyperthermia in vitro. Moreover, drug, especially when used in higher concentrations, exerted unfavorable intensification of aponecrosis of cultured hippocampal neurons.

Targeted Intracellular Heat Transfer in Cancer Therapy: Assessment of Asparagine-laminated Gold Nanoparticles in Cell Model of T cell Leukemia

BACKGROUND

High temperatures have destructive effects on cancer cells by damaging proteins and structures within cells. Gold nanoparticles (AuNPs) can act as drug delivery vehicles, especially for cancer therapy. Due to the selective intake of asparagine molecules into malignant cells, AuNPs were coated with asparagine; and CCRF-CEM human T-cell leukemia cells were treated with the new combination, Asn-AuNPs, at 39 °C.

METHODS

The co-authors from a number of collaborative labs located at Tehran University of Medical Sciences, Tehran, Iran, have initiated the idea and preliminary design of this study in 2011. Hydroxyl surfaced AuNPs were preliminary prepared by tannin free ethanol extract of black tea leaves. These biogenic AuNPs were further capped with asparagines to form asparagine-gold nanoparticle conjugates (Asn-AuNP conjugates). Then CCRF-CEM human T-cell leukemia cells were separately treated with different concentrations of AuNPs and Asn-AuNP conjugates (3, 30, 300 μg/mL). MTT assay and zymography analysis were carried out, and the apoptotic and necrotic effects of Asn-AuNPs were determined in comparison with AuNPs, using flow cytometry assay.

RESULTS

Asn-AuNP conjugates at 300 μg/mL significantly inhibited MMPs at 39 °C, compared to AuNPs. In terms of cytotoxicity, a remarkable decrease was observed in the percentage of viable cells treated with Asn-AuNP conjugates, rather than AuNPs. Moreover, the AuNPs and Asn-AuNP conjugates enhanced the level of apoptosis at almost similar rates.

CONCLUSION

AuNPs are coated with asparagine molecules and the temperature is slightly increased by 2 °C, the apoptosis is not only enhanced among cells but also shifts to necrosis in higher concentrations of Asn-AuNP conjugates. More investigations should be carried out to explain the exact mechanism underlying the necrotic effects of Asn-AuNPs.

Short Chemical Ischemia Triggers Phosphorylation of eIF2α and Death of SH-SY5Y Cells but not Proteasome Stress and Heat Shock Protein Response in both SH-SY5Y and T98G Cells

Both translation arrest and proteasome stress associated with accumulation of ubiquitin-conjugated protein aggregates were considered as a cause of delayed neuronal death after transient global brain ischemia; however, exact mechanisms as well as possible relationships are not fully understood. The aim of this study was to compare the effect of chemical ischemia and proteasome stress on cellular stress responses and viability of neuroblastoma SH-SY5Y and glioblastoma T98G cells. Chemical ischemia was induced by transient treatment of the cells with sodium azide in combination with 2-deoxyglucose. Proteasome stress was induced by treatment of the cells with bortezomib. Treatment of SH-SY5Y cells with sodium azide/2-deoxyglucose for 15 min was associated with cell death observed 24 h after treatment, while glioblastoma T98G cells were resistant to the same treatment. Treatment of both SH-SY5Y and T98G cells with bortezomib was associated with cell death, accumulation of ubiquitin-conjugated proteins, and increased expression of Hsp70. These typical cellular responses to proteasome stress, observed also after transient global brain ischemia, were not observed after chemical ischemia. Finally, chemical ischemia, but not proteasome stress, was in SH-SY5Y cells associated with increased phosphorylation of eIF2α, another typical cellular response triggered after transient global brain ischemia. Our results showed that short chemical ischemia of SH-SY5Y cells is not sufficient to induce both proteasome stress associated with accumulation of ubiquitin-conjugated proteins and stress response at the level of heat shock proteins despite induction of cell death and eIF2α phosphorylation.