In vitro treatment of 3 T3-L1 adipocytes with recombinant Calcium/calmodulin-dependent Protein Kinase IV (CaMKIV) limits ER stress and improves insulin sensitivity through inhibition of autophagy via the mTOR/CREB signaling pathway

Endoplasmic Reticulum Stress Signaling and Neuronal Cell Death

Besides protein processing, the endoplasmic reticulum (ER) has several other functions such as lipid synthesis, the transfer of molecules to other cellular compartments, and the regulation of Ca²⁺ homeostasis. Before leaving the organelle, proteins must be folded and post-translationally modified. Protein folding and revision require molecular chaperones and a favorable ER environment. When in stressful situations, ER luminal conditions or chaperone capacity are altered, and the cell activates signaling cascades to restore a favorable folding environment triggering the so-called unfolded protein response (UPR) that can lead to autophagy to preserve cell integrity. However, when the UPR is disrupted or insufficient, cell death occurs. This review examines the links between UPR signaling, cell-protective responses, and death following ER stress with a particular focus on those mechanisms that operate in neurons.

Jiedutongluotiaogan formula restores pancreatic function by suppressing excessive autophagy and endoplasmic reticulum stress

CONTEXT

Jiedutongluotiaogan formula (JTTF), a traditional Chinese medicine (TCM), could promote islet function. However, the potential effect of JTTF on endoplasmic reticulum stress (ERS) and autophagy have not been reported.

OBJECTIVE

This study explores the potential effect of JTTF on ERS and autophagy in the pancreas.

MATERIALS AND METHODS

The Zucker diabetic fatty (ZDF) rats were randomised into five groups, control, model, JTTF (1, 3, 5 g/kg/day for 12 weeks). LPS induced pancreatic β-cells were treated with JTTF (50, 100, 200 μg/mL). LPS was used to induce pancreatic β-cell injury, with cell viability and insulin secretion evaluated using MTT, glucose-stimulated insulin secretion (GSIS) assays, and PCR. Intracellular Ca²⁺ concentration was measured using flow cytometry, while ERS and autophagy levels were monitored via Western blotting and/or immunostaining.

RESULTS

Compared with the model group, body weight, FGB, HbA1c, IPGTT, FINs, and HOMA-IR in JTTF treatment groups were significantly reduced. In islets cells treated with JTTF, the pancreatic islet cells in the JTTF group were increased, lipid droplets were reduced, and there was a decrease in Ca²⁺ (16.67%). After JTTF intervention, PERK, p-PERK, IRE1α, p- IRE1α, ATF6, eIF2α, GRP78, p-ULK1, LC3 and p62 expression decreased, whereas Beclin1and p-mTOR expression increased. In addition, the expression of proteins related to apoptosis in the JTTF groups were lower than those in the control group.

DISCUSSION AND CONCLUSIONS

JTTF may alleviate pancreatic β-cell injury by inhibiting ER stress and excessive autophagy in diabetic rats. This provides a new direction for treating diabetes and restoring pancreatic dysfunction by TCM.

ER stress in obesity pathogenesis and management

Given the unprecedented global pandemic of obesity, a better understanding of the etiology of adiposity will be necessary to ensure effective management of obesity and related complications. Among the various potential factors contributing to obesity, endoplasmic reticulum (ER) stress refers to a state of excessive protein unfolding or misfolding that is commonly found in metabolic diseases including diabetes mellitus, insulin resistance (IR), and non-alcoholic fatty liver disease, although its role in obesogenesis remains controversial. ER stress is thought to drive adiposity by dampening energy expenditure, making ER stress a likely therapeutic target for the management of obesity. We summarize the role of ER stress and the ER stress response in the onset and development of obesity, and discuss the underlying mechanisms involved with a view to identifying novel therapeutic strategies for obesity prevention and management.

CREB nuclear transcription activity as a targeting factor in the treatment of diabetes and diabetes complications

Diabetes mellitus is a metabolic disorder diagnosed by elevated blood glucose levels and a defect in insulin production. Blood glucose, an energy source in the body, is regenerated by two fundamental processes: glycolysis and gluconeogenesis. These two processes are the main mechanisms used by humans and many other animals to maintain blood glucose levels, thereby avoiding hypoglycaemia. The released insulin from pancreatic β-cells activates glycolysis. However, the glucagon released from the pancreatic α-cells activates gluconeogenesis in the liver, leading to pyruvate conversion to glucose-6-phosphate by different enzymes such as fructose 1,6-bisphosphatase and glucose 6-phosphatase. These enzymes' expression is controlled by the glucagon/ cyclic adenosine 3',5'-monophosphate (cAMP)/ proteinkinase A (PKA) pathway. This pathway phosphorylates cAMP-response element-binding protein (CREB) in the nucleus to bind it to these enzyme promoters and activate their expression. During fasting, this process is activated to supply the body with glucose; however, it is overactivated in diabetes. Thus, the inhibition of this process by blocking the expression of the enzymes via CREB is an alternative strategy for the treatment of diabetes. This review was designed to investigate the association between CREB activity and the treatment of diabetes and diabetes complications. The phosphorylation of CREB is a crucial step in regulating the gene expression of the enzymes of gluconeogenesis. Many studies have proven that CREB is over-activated by glucagon and many other factors contributing to the elevation of fasting glucose levels in people with diabetes. The physiological function of CREB should be regarded in developing a therapeutic strategy for the treatment of diabetes mellitus and its complications. However, the accessible laboratory findings for CREB activity of the previous research still not strong enough for continuing to the clinical trial yet.

Positive regulation of the CREB phosphorylation via JNK-dependent pathway prevents antimony-induced neuronal apoptosis in PC12 cell and mice brain

Antimony (Sb) is a potentially toxic chemical element abundantly found in the environment. We previously reported that Sb promoted neuronal deathvia reactive oxygen species-dependent autophagy. Here, we assessed the role of cyclic adenosine monophosphate response element-binding protein (CREB) in Sb-induced neuronal damage. We found that Sb treatment induced CREB phosphorylation and neuronal apoptosis both in vitro and in vivo. Interestingly, inhibition of CREB's transcriptional activity with 666-15 dramatically enhanced apoptosis in PC12 cells by downregulating B-cell lymphoma 2 (Bcl-2). Additionally, Sb activated ERK, JNK, and p38 signaling ; however, only JNK promoted CREB phosphorylation. In conclusion, our findings suggest that CREB phosphorylation by JNK attenuates Sb-induced neuronal apoptosis via Bcl-2 upregulation. These data suggest that JNK-dependent CREB activation prevents neurons from Sb-induced apoptosis and guides the development of novel strategies to prevent Sb-induced neurotoxicity.