Changes In Intracellular Homeostasis Research Articles

The Role of Ketamine in Calcium Changes in Intracellular Homeostasis and Mitochondrial Dysfunction

: Ketamine was formerly introduced as an anesthesia drug and known as a non-competitive antagonist of the N-methyl-D-aspartate receptor (NMDAR). As knowledge grows, recent studies reveal the antidepressant effect of the drug. Moreover, a few investigations indicate that ketamine might be responsible for multiple calcium-regulated signaling pathways. Ketamine is thought to affect calcium homeostasis through several of its targets, such as N-Methyl-D-Aspartate (NMDA), α-amino-3-hydroxy-5-methylisoxazole-4-propionate acid receptors (AMPA), and voltage-dependent calcium channels (VDCCs).

Measurements of Physiological Stress Responses in C. Elegans.

Organisms are often exposed to fluctuating environments and changes in intracellular homeostasis, which can have detrimental effects on their proteome and physiology. Thus, organisms have evolved targeted and specific stress responses dedicated to repair damage and maintain homeostasis. These mechanisms include the unfolded protein response of the endoplasmic reticulum (UPRER), the unfolded protein response of the mitochondria (UPRMT), the heat shock response (HSR), and the oxidative stress response (OxSR). The protocols presented here describe methods to detect and characterize the activation of these pathways and their physiological consequences in the nematode, C. elegans. First, the use of pathway-specific fluorescent transcriptional reporters is described for rapid cellular characterization, drug screening, or large-scale genetic screening (e.g., RNAi or mutant libraries). In addition, complementary, robust physiological assays are described, which can be used to directly assess sensitivity of animals to specific stressors, serving as functional validation of the transcriptional reporters. Together, these methods allow for rapid characterization of the cellular and physiological effects of internal and external proteotoxic perturbations.

PERK regulated miR-424(322)-503 cluster fine-tunes activation of IRE1 and ATF6 during Unfolded Protein Response.

The endoplasmic reticulum (ER) responds to changes in intracellular homeostasis through activation of the unfolded protein response (UPR). UPR can facilitate the restoration of cellular homeostasis, via the concerted activation of three ER stress sensors, namely IRE1, PERK and ATF6. Global approaches in several cellular contexts have revealed that UPR regulates the expression of many miRNAs that play an important role in the regulation of life and death decisions during UPR. Here we show that expression of miR-424(322)-503 cluster is downregulated during UPR. IRE1 inhibitor (4 μ8C) and deficiency of XBP1 had no effect on downregulation of miR-424(322)-503 during UPR. Treatment of cells with CCT030312, a selective activator of EIF2AK3/PERK signalling, leads to the downregulation of miR-424(322)-503 expression. The repression of miR-424(322)-503 cluster during conditions of ER stress is compromised in PERK-deficient MEFs. miR-424 regulates the expression of ATF6 via a miR-424 binding site in its 3′ UTR and attenuates the ATF6 transcriptional activity during UPR. Further miR-424 had no effect on IRE1-XBP1 axis but enhanced the regulated IRE1-dependent decay (RIDD). Our results suggest that miR-424 constitutes an obligatory fine-tuning mechanism where PERK-mediated downregulation of miR-424(322)-503 cluster regulates optimal activation of IRE1 and ATF6 during conditions of ER stress.

Endoplasmic Reticulum Stress and Oxidative Stress in Cell Fate Decision and Human Disease

The endoplasmic reticulum (ER) is a specialized organelle for the folding and trafficking of proteins, which is highly sensitive to changes in intracellular homeostasis and extracellular stimuli. Alterations in the protein-folding environment cause accumulation of misfolded proteins in the ER that profoundly affect a variety of cellular signaling processes, including reduction-oxidation (redox) homeostasis, energy production, inflammation, differentiation, and apoptosis. The unfolded protein response (UPR) is a collection of adaptive signaling pathways that evolved to resolve protein misfolding and restore an efficient protein-folding environment. Production of reactive oxygen species (ROS) has been linked to ER stress and the UPR. ROS play a critical role in many cellular processes and can be produced in the cytosol and several organelles, including the ER and mitochondria. Studies suggest that altered redox homeostasis in the ER is sufficient to cause ER stress, which could, in turn, induce the production of ROS in the ER and mitochondria. Although ER stress and oxidative stress coexist in many pathologic states, whether and how these stresses interact is unknown. It is also unclear how changes in the protein-folding environment in the ER cause oxidative stress. In addition, how ROS production and protein misfolding commit the cell to an apoptotic death and contribute to various degenerative diseases is unknown. A greater fundamental understanding of the mechanisms that preserve protein folding homeostasis and redox status will provide new information toward the development of novel therapeutics for many human diseases.

Fine tuning of the UPR by the ubiquitin ligases Siah1/2.

The endoplasmic reticulum (ER) responds to changes in intracellular homeostasis through activation of the unfolded protein response (UPR). Yet, it is not known how UPR-signaling coordinates adaptation versus cell death. Previous studies suggested that signaling through PERK/ATF4 is required for cell death. We show that high levels of ER stress (i.e., ischemia-like conditions) induce transcription of the ubiquitin ligases Siah1/2 through the UPR transducers PERK/ATF4 and IRE1/sXBP1. In turn, Siah1/2 attenuates proline hydroxylation of ATF4, resulting in its stabilization, thereby augmenting ER stress output. Conversely, ATF4 activation is reduced upon Siah1/2 KD in cultured cells, which attenuates ER stress-induced cell death. Notably, Siah1a+/−::Siah2−/− mice subjected to neuronal ischemia exhibited smaller infarct volume and were protected from ischemia-induced death, compared with the wild type (WT) mice. In all, Siah1/2 constitutes an obligatory fine-tuning mechanism that predisposes cells to death under severe ER stress conditions.

Contribution of ?-adrenoceptors to the contractility of the human myocardium in chronic coronary heart disease

The inotropic response of isolated myocardial strips to α1-adrenoceptor stimulation was compared for patients with chronic coronary heart disease (CHD) and patients with WPW syndrome. The α1-adrenoceptors were stimulated with 1 × 10− M phenylephrine after blocking of the β-adrenoceptors with 3 × 10−1 M propranolol. The inotropic activity was recorded in the isometric mode. In the myocardium without signs of ischemic damage, stimulation of the α1-receptors caused a slowly developing single-phase positive inotropic response. The myocardium of the CHD patients was characterized by a three-phase response. The specific features of the inotropic response to α1-adrenoceptor stimulation in the CHD patients were assumed to be determined by changes in intracellular homeostasis of Ca2+. Electromechanical coupling in cardiac myocytes of CHD patients depends on Ca2+ deposited in the sarcoplasmic reticulum to a greater extent than coupling in the intact myocardium. An additional positive inotropic effect is possible upon exogenous calcium influx into cardiac myocytes.

Cellular mechanisms underlying the development of diabetic neuropathies

The data of recent studies of fundamental mechanisms underlying the development of diabetic neuropathies are summarized in the Review. The importance of a sorbitol-polyol pathway of glucose metabolism, as well as the roles of production of peroxide radicals and activation of the processes of non-enzymatic glycosilation in the nerve cells are analyzed. Special attention is paid to the roles of growth factors in morphological modifications of the neuronal structures and to that of intracellular signalization in functional disturbances in the nerve cells. Changes in intracellular homeostasis of Ca ions are of considrable importance for the development of peripheral diabetic neuropathies.