Activation of PI3-K/Akt pathway for thermal preconditioning to protect cultured cerebellar granule neurons against low potassium-induced apoptosis

PI3K/AKT pathway modulation and cold acclimation alleviation concerning apoptosis and necroptosis in broiler thymus

Moderate cold stimulation regulates the thymus's growth and function and facilitates cold acclimatization in broilers. However, the underlying mechanism remains unknown. To explore the possible mechanism of the thymus in cold-acclimated broilers against cold stress, 240 one-day-old Arbor Acres (AA) broilers were assigned to 2 groups randomly. The control group (C) was housed at conventional temperatures. The temperature during the first week was 33°C to 34°C. Between the ages of 8 and 32 d, the temperature was lowered by 1°C every 2 d, i.e., gradually from 32°C to 20°C, and then maintained at 20°C until 42 d of age. The cold-acclimated group (C-3) was housed at the same temperature as C from 1 to 7 d after birth. Between 8 and 42 d, the temperature of C-3 was 3°C colder than C. After 24 h exposure to acute cold stress (ACS) at 42 d, C and C-3 were named as S and S-3. The results showed that ACS was able to induce oxidation stress, modulate PI3K/AKT signal, and cause necroptosis and apoptosis in broiler thymus. By contrast, cold acclimation could alleviate apoptosis and necroptosis induced by cold stress via alleviating oxidative stress, efficiently activating the PI3K/AKT signal, as well as decreasing apoptotic and necrotic genes' levels. This study offers a novel theoretical basis for cold acclimation to improve the body's cold tolerance.

Integrated metabolomic and transcriptomic responses to heat stress in a high-altitude fish, Triplophysa siluroides

Species in Triplophysa display strong adaptability to the extreme environment of the plateau, thus offering an ideal model to study the molecular mechanism of fish adaptation to environmental stress. In the present study, we conducted integrated analysis of the transcriptome and metabolism of liver tissue in Triplophysa siluroides under heat stress (28 °C) and control (10 °C) conditions to identify heat stress-induced genes, metabolites and pathways. RNA-Seq identified 2373 differentially expressed genes, which consisted of 1360 upregulated genes and 1013 downregulated genes, in the heat stress group vs. the control group. Genes in the heat shock protein (Hsp) family, including Hsp40, Hsp70, Hsp90 and other Hsps, were strongly upregulated by heat stress. Pathway enrichment analysis revealed that the PI3K/AKT/mTOR and protein processing in the endoplasmic reticulum (ER) pathways were significantly affected by heat stress. Metabolism sequencing identified a total of 155 differentially abundant metabolites, including 118 significantly upregulated metabolites and 37 downregulated metabolites. Combined analysis of the transcriptome and metabolism results showed that ubiquitin-dependent proteolysis and purine metabolism pathways were enhanced in response to acute heat stress to protect cells from damage under stress conditions. The results of this study may contribute to our understanding of the underlying molecular mechanism of the heat stress response in cold-water fish.

Long-read RNA sequencing of Pacific abalone Haliotis discus hannai reveals innate immune system responses to environmental stress

Haliotis discus hannai is a commercially important mollusk species, and the abalone aquaculture sector has been jeopardized by deteriorating environmental circumstances such as bacterial infection and thermal stress during the hot summers. However, due to a paucity of genetic information, such as transcriptome resources, our understanding of their stress adaptation is restricted. In this research, using single-molecule long-read (SMRT) sequencing technology, a library composed of ten tissues (i.e., haemocytes, gills, muscle, hepatopancreas, digestive tract, mantle, mucous gland, ovary, testis and head) was constructed and sequenced. In all, 41,855 high-quality unique transcripts, among which 24,778 were successfully annotated. Additionally, 13,463 SSRs, 1,169 transcription factors, and 18,124 lncRNAs were identified in H. discus hannai transcriptome. Furthermore, multiple immune-related transcripts were identified according to KEGG annotation, and a portion of these transcripts were mapped into several classical immune-related pathways, including the PI3K-AKT signaling pathway and Toll-like receptor signaling pathway. Additionally, 24 typical sequences related to the immunity pathway were detected by RT-PCR; the results showed that most of the immune-related genes showed significantly high expression at 72 h after bacterial challenges and thermal stress, especially the expression level of genes in gills was significantly higher than that in haemocytes under V. parahaemolyticus stress at 24 h. At the same time. The analysis of alternative splicing identified several innate immunity-related functions genes, including CD109 and caspase 2. These results suggest that the complex immune system, particularly the powerful innate immunity system, was crucial for H. discus hannai response to numerous environmental challenges.

PI3K-AKT signaling pathway is involved in hypoxia/thermal-induced immunosuppression of small abalone Haliotis diversicolor

The PI3K-AKT signal pathway has been found to be involved in many important physiological and pathological processes of the innate immune system of vertebrates and invertebrates. In this study, the AKT (HdAKT) and PI3K (HdPI3K) gene of small abalone Haliotis diversicolor were cloned and characterized for the important status of PI3K and AKT protein in PI3K-AKT signaling pathway. The full length cDNAs of HdAKT and HdPI3K are 2126 bp and 6052 bp respectively, encoding proteins of 479 amino acids and 1097 amino acids, respectively. The mRNA expression level of fourteen genes in the PI3K-AKT signaling pathway were detected by quantitative real-time PCR. The results showed that all these fourteen genes were ubiquitously expressed in seven selected tissues. Meanwhile, HdAKT was expressed in haemocytes with the highest expression level (p < 0.05) next in hepatopancreas (p < 0.05). On the other hand, the expression level of HdPI3K in haemocytes was higher than other tissues. Under normal condition, the gene expression level of HdAKT, HdPI3K, and other PI3K-AKT signaling pathway members were significantly up-regulated by Vibrio parahaemolyticus infection which demonstrated that HdAKT, HdPI3K, and other PI3K-AKT signaling pathway members play a role in the innate immune system of abalone. The mRNA expression of these genes in gills, haemocytes and hepatopancreas was significantly down-regulated after the Vibrio parahaemolyticus stimulation with environment stimulation (thermal, hypoxia and thermal & hypoxia). These results indicate that the dual/multiple stresses defeat the immune system and lead to immunosuppression in abalone. PI3K-AKT signaling pathway may be involved in hypoxia/thermal-induced immunosuppression of small abalone Haliotis diversicolor.

HSF1 protects neurons through a novel trimerization- and HSP-independent mechanism

Heat shock factor 1 (HSF1) protects neurons from death caused by the accumulation of misfolded proteins. It is believed that this protective effect is mediated by the transcriptional stimulation of genes encoding heat shock proteins (HSPs), a family of chaperones that refold or degrade misfolded proteins. Whether HSF1 is protective when neuronal death is not caused by protein misfolding has not been studied. Here, we report that HSF1 expression is necessary for the survival of rat neurons and that HSF1 mRNA and protein expression is reduced in neurons primed to die. Knock-down of HSF1 induces death of otherwise healthy neurons, whereas reestablishment of elevated levels of HSF1 protects neurons even when death is not due to accumulation of misfolded proteins. Neuroprotection by HSF1 does not require its trimerization, an event obligatory for the binding of HSF1 to heat shock elements within HSP gene promoters. Moreover, knock-down of HSP70 or blockade of HSP90 signaling does not reduce neuroprotection by HSF1. Although several neuroprotective molecules and signaling pathways, including CaMK, PKA, Casein kinase-II, and the Raf-MEK-ERK and PI-3K-Akt pathways, are not required for HSF1-mediated neuroprotection, protection is abrogated by inhibition of classical histone deacetylases (HDACs). We report that the novel mechanism of neuroprotection by HSF1 involves cooperation with SIRT1, an HDAC with well documented neuroprotective effects. Using a cell culture model of Huntington's disease, we show that HSF1 trimerization is not required for protection against mutant huntingtin-induced neurotoxicity, suggesting that HSF1 can protect neurons against both proteinopathic and nonproteinopathic death through a noncanonical pathway.

Protective actions of epoxyeicosatrienoic acid: dual targeting of cardiovascular PI3K and KATP channels

Epoxyeicosatrienoic acid(s) (EETs) have been shown to protect cardiovascular tissue against apoptosis dependent on activation of targets such as ATP-sensitive K+ (KATP) channels (sarcolemmal and mitochondrial), calcium-activated K+ channels, extracellular signal-regulated kinase or phosphoinositide 3-kinase (PI3K). We tested if EETs protect human atrial tissue ex vivo from hypoxia/reoxygenation (H/R) injury, and compared our results with myocardium from two rodent species, rats and mice. EETs reduced myocardial caspase 3 activity in all three species and protected against loss of mitochondrial membrane potential in primary cultures of neonatal rat ventricular myocytes submitted to H/R. In addition, EETs protected mouse pulmonary arteries ex vivo exposed to H/R. Myocardium and pulmonary arteries from genetically engineered mice having elevated plasma levels of EETs (Ephx2-/-) exhibited protection from H/R-induced injury over that of wild type controls, suggesting that endogenously produced EETs may have pro-survival effects. Electrophysiological studies in myocytes demonstrated that EETs can stimulate KATP currents even when PI3K is inhibited. Similarly, activation of PI3K/Akt occurred in the presence of the KATP channel blocker glibenclamide. Based upon loss of protection with EETs in the presence of either wortmannin (a PI3K inhibitor) or glibenclamide, simultaneous activation of at least 2 pathways, PI3K and KATP channels respectively, appears to be required for protection. In conclusion, we demonstrate that exogenous and endogenous EETs have powerful pro-survival effects in cardiovascular tissues including diseased human myocardium, mediated by activation of not only one but at least two pathways, PI3K and KATP channels.

Akt phosphorylation is required for heat acclimation-induced neuroprotection

Long-term heat exposure, known as heat acclimation (HA; 30 days at 34 +/- 1 degrees C) is neuroprotective against traumatic brain injury. Acclimated mice were previously found to display improved functional recovery as well as an increase in the levels of the specific erythropoietin receptor. As the activation of this receptor is known to facilitate functional recovery on one hand and the phosphorylation and activation of Akt, an intracellular kinase which regulates anti-apoptotic pathways on the other, in this study we investigated whether HA affects Akt phosphorylation prior to and following injury and whether this step is required for development of HA-induced neuroprotection. Akt phosphorylation was blocked using Triciribine (TCN), a compound shown to block the phosphorylation process without affecting upstream effectors of this kinase, and several post-injury functional end-point measures were subsequently evaluated. Acclimation led to a post-injury increase in the levels of phosphorylated Akt, resulting in higher levels when compared with normothermic controls at 4 h post-injury (63.6 +/- 5.2% and 42.7 +/- 3.7%, respectively, p </= 0.05). This increase was diminished following TCN administration. Post-injury TCN treatment abolished the HA-induced functional benefits, including effects on motor and cognitive functions as well as the attenuation of edema formation. We therefore suggest that Akt phosphorylation is essential for HA-induced neuroprotection after traumatic brain injury.