Liraglutide protects palmitate-induced INS-1 cell injury by enhancing autophagy mediated via FoxO1

Docosahexanoic Acid Attenuates Palmitate-Induced Apoptosis by Autophagy Upregulation via GPR120/mTOR Axis in Insulin-Secreting Cells

BACKGRUOUND

Polyunsaturated fatty acids (PUFAs) reportedly have protective effects on pancreatic β-cells; however, the underlying mechanisms are unknown.

METHODS

To investigate the cellular mechanism of PUFA-induced cell protection, mouse insulinoma 6 (MIN6) cells were cultured with palmitic acid (PA) and/or docosahexaenoic acid (DHA), and alterations in cellular signaling and apoptosis were examined.

RESULTS

DHA treatment remarkably repressed caspase-3 cleavage and terminal deoxynucleotidyl transferase-mediated UTP nick end labeling (TUNEL)-positive red dot signals in PA-treated MIN6 cells, with upregulation of autophagy, an increase in microtubule- associated protein 1-light chain 3 (LC3)-II, autophagy-related 5 (Atg5), and decreased p62. Upstream factors involved in autophagy regulation (Beclin-1, unc51 like autophagy activating kinase 1 [ULK1], phosphorylated mammalian target of rapamycin [mTOR], and protein kinase B) were also altered by DHA treatment. DHA specifically induced phosphorylation on S2448 in mTOR; however, phosphorylation on S2481 decreased. The role of G protein-coupled receptor 120 (GPR120) in the effect of DHA was demonstrated using a GPR120 agonist and antagonist. Additional treatment with AH7614, a GPR120 antagonist, significantly attenuated DHA-induced autophagy and protection. Taken together, DHA-induced autophagy activation with protection against PA-induced apoptosis mediated by the GPR120/mTOR axis.

CONCLUSION

These findings indicate that DHA has therapeutic effects on PA-induced pancreatic β-cells, and that the cellular mechanism of β-cell protection by DHA may be a new research target with potential pharmacotherapeutic implications in β-cell protection.

Autophagy, Pyroptosis and Ferroptosis are Rising Stars in the Pathogenesis of Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most common microvascular complications in diabetes and can potentially develop into end-stage renal disease. Its pathogenesis is complex and not fully understood. Podocytes, glomerular endothelial cells (GECs), glomerular mesangial cells (GMCs) and renal tubular epithelial cells (TECs) play important roles in the normal function of glomerulus and renal tubules, and their injury is involved in the progression of DN. Although our understanding of the mechanisms leading to DN has substantially improved, we still need to find more effective therapeutic targets. Autophagy, pyroptosis and ferroptosis are programmed cell death processes that are associated with inflammation and are closely related to a variety of diseases. Recently, a growing number of studies have reported that autophagy, pyroptosis and ferroptosis regulate the function of podocytes, GECs, GMCs and TECs. This review highlights the contributions of autophagy, pyroptosis, and ferroptosis to DN injury in these cells, offering potential therapeutic targets for DN treatment.

FoxO1 as a tissue-specific therapeutic target for type 2 diabetes

Forkhead box O (FoxO) proteins are transcription factors that mediate many aspects of physiology and thus have been targeted as therapeutics for several diseases including metabolic disorders such as type 2 diabetes mellitus (T2D). The role of FoxO1 in metabolism has been well studied, but recently FoxO1's potential for diabetes prevention and therapy has been debated. For example, studies have shown that increased FoxO1 activity in certain tissue types contributes to T2D pathology, symptoms, and comorbidities, yet in other tissue types elevated FoxO1 has been reported to alleviate symptoms associated with diabetes. Furthermore, studies have reported opposite effects of active FoxO1 in the same tissue type. For example, in the liver, FoxO1 contributes to T2D by increasing hepatic glucose production. However, FoxO1 has been shown to either increase or decrease hepatic lipogenesis as well as adipogenesis in white adipose tissue. In skeletal muscle, FoxO1 reduces glucose uptake and oxidation, promotes lipid uptake and oxidation, and increases muscle atrophy. While many studies show that FoxO1 lowers pancreatic insulin production and secretion, others show the opposite, especially in response to oxidative stress and inflammation. Elevated FoxO1 in the hypothalamus increases the risk of developing T2D. However, increased FoxO1 may mitigate Alzheimer's disease, a neurodegenerative disease strongly associated with T2D. Conversely, accumulating evidence implicates increased FoxO1 with Parkinson's disease pathogenesis. Here we review FoxO1's actions in T2D conditions in metabolic tissues that abundantly express FoxO1 and highlight some of the current studies targeting FoxO1 for T2D treatment.

The role of autophagy in the treatment of type II diabetes and its complications: a review

Type II diabetes mellitus (T2DM) is a chronic metabolic disease characterized by prolonged hyperglycemia and insulin resistance (IR). Its incidence is increasing annually, posing a significant threat to human life and health. Consequently, there is an urgent requirement to discover effective drugs and investigate the pathogenesis of T2DM. Autophagy plays a crucial role in maintaining normal islet structure. However, in a state of high glucose, autophagy is inhibited, resulting in impaired islet function, insulin resistance, and complications. Studies have shown that modulating autophagy through activation or inhibition can have a positive impact on the treatment of T2DM and its complications. However, it is important to note that the specific regulatory mechanisms vary depending on the target organ. This review explores the role of autophagy in the pathogenesis of T2DM, taking into account both genetic and external factors. It also provides a summary of reported chemical drugs and traditional Chinese medicine that target the autophagic pathway for the treatment of T2DM and its complications.

The inhibition of FKBP5 protects β-cell survival under inflammation stress via AKT/FOXO1 signaling

The FK506-binding protein 51 (FKBP51, encoded by FKBP5 gene) has emerged as a critical regulator of mammalian endocrine stress responses and as a potential pharmacological target for metabolic disorders, including type 2 diabetes (T2D). However, in β cells, which secrete the only glucose-lowering hormone-insulin, the expression and function of FKBP5 has not been documented. Here, using human pancreatic tissue and primary human islets, we demonstrated the abundant expression of FKBP5 in β cells, which displayed an responsive induction upon acute inflammatory stress mimicked by in vitro treatment with a cocktail of inflammatory cytokines (IL-1β, IFN-γ, and TNF-α). To explore its function, siRNAs targeting FKBP5 and pharmacological inhibitor SAFit2 were applied both in clonal NIT-1 cells and primary human/mice islets. We found that FKBP5 inhibition promoted β-cell survival, improved insulin secretion, and upregulated β-cell functional gene expressions (MAFA and NKX6.1) in acute-inflammation stressed β cells. In primary human and mice islets, which constitutively suffer from inflammation stress during isolation and culture, FKBP5 inhibition also presented decent performance in improving islet function, in accordance with its protective effect against inflammation. Molecular studies found that FKBP5 is an important regulator for FOXO1 phosphorylation at Serine 256, and silencing of FOXO1 abrogated the protective effect of FKBP5 inhibition, suggesting that it is the key downstream effector of FKBP5 in β cells. At last, in situ detection of FKBP5 protein expression on human and mice pancreases revealed a reduction of FKBP5 expression in β cells in human T2D patients, as well as T2D mice model (db/db), which may indicate a FKBP5-inhibition-mediated pro-survival mechanism against the complex stresses in T2D milieus.

β Cell and Autophagy: What Do We Know?

Pancreatic β cells are central to glycemic regulation through insulin production. Studies show autophagy as an essential process in β cell function and fate. Autophagy is a catabolic cellular process that regulates cell homeostasis by recycling surplus or damaged cell components. Impaired autophagy results in β cell loss of function and apoptosis and, as a result, diabetes initiation and progress. It has been shown that in response to endoplasmic reticulum stress, inflammation, and high metabolic demands, autophagy affects β cell function, insulin synthesis, and secretion. This review highlights recent evidence regarding how autophagy can affect β cells' fate in the pathogenesis of diabetes. Furthermore, we discuss the role of important intrinsic and extrinsic autophagy modulators, which can lead to β cell failure.

Dysregulated autophagy: A key player in the pathophysiology of type 2 diabetes and its complications

Autophagy is essential in regulating the turnover of macromolecules via removing damaged organelles, misfolded proteins in various tissues, including liver, skeletal muscles, and adipose tissue to maintain the cellular homeostasis. In these tissues, a specific type of autophagy maintains the accumulation of lipid droplets which is directly related to obesity and the development of insulin resistance. It appears to play a protective role in a normal physiological environment by eliminating the invading pathogens, protein aggregates, and damaged organelles and generating energy and new building blocks by recycling the cellular components. Ageing is also a crucial modulator of autophagy process. During stress conditions involving nutrient deficiency, lipids excess, hypoxia etc., autophagy serves as a pro-survival mechanism by recycling the free amino acids to maintain the synthesis of proteins. The dysregulated autophagy has been found in several ageing associated diseases including type 2 diabetes (T2DM), cancer, and neurodegenerative disorders. So, targeting autophagy can be a promising therapeutic strategy against the progression to diabetes related complications. Our article provides a comprehensive outline of understanding of the autophagy process, including its types, mechanisms, regulation, and role in the pathophysiology of T2DM and related complications. We also explored the significance of autophagy in the homeostasis of β-cells, insulin resistance (IR), clearance of protein aggregates such as islet amyloid polypeptide, and various insulin-sensitive tissues. This will further pave the way for developing novel therapeutic strategies for diabetes-related complications.

Mechanism of GLP-1 Receptor Agonists-Mediated Attenuation of Palmitic Acid-Induced Lipotoxicity in L6 Myoblasts

Methods

Cells were divided into 5 groups-control, high-fat, 10 nmol/L LR + 0.6 mmol/L palmitic acid (PA) (10LR), 100 nmol/L LR + 0.6 mmol/L PA (100LR), and 1000 nmol/L LR + 0.6 mmol/L PA (1000LR). CCK-8 method to detect cell viability, GPO-PAP enzymatic method to detect intracellular triglyceride content, and reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) and western blotting methods to detect fatty acid translocase CD36 (FAT/CD36) and fatty acid binding protein 4 (FABP4) in L6 cells, glucose-regulated protein 78 (GRP78), glucose transporter 4 (GLUT4) expression at the mRNA and protein levels, respectively, were performed.

Results

We found that after PA intervention for 24 h, the cell viability decreased significantly; the cell viability of the LR group was higher than that of the high-fat group (P < 0.01). After PA intervention, compared with those in the high-fat group, GRP-78, FAT/CD36, FABP4 mRNA ((4.36 ± 0.32 vs. 8.15 ± 0.35); (1.00 ± 0.04 vs. 2.46 ± 0.08); (2.88 ± 0.55 vs. 8.29 ± 0.52), P < 0.01) and protein ((3338.13 ± 333.15 vs. 4963.98 ± 277.29); (1978.85 ± 124.24 vs. 2676.07 ± 100.64); (3372.00 ± 219.84 vs. 6083.20 ± 284.70), both P < 0.01) expression decreased in the LR group. The expression levels of GLUT4 mRNA ((0.75 ± 0.04 vs. 0.34 ± 0.03), P < 0.01) and protein ((3443.71 ± 191.89 vs. 2137.79 ± 118.75), P < 0.01) increased.

Conclusion

Therefore, we conclude that LR can reverse PA-induced cell inactivation and lipid deposition, which may be related to the change in GRP-78, FAT/CD36, FABP4, GLUT4, and other factors.

LncRNA MEG3: Potential stock for precision treatment of cardiovascular diseases

The prevalence and mortality rates of cardiovascular diseases are increasing, and new treatment strategies are urgently needed. From the perspective of basic pathogenesis, the occurrence and development of cardiovascular diseases are related to inflammation, apoptosis, fibrosis and autophagy of cardiomyocytes, endothelial cells and other related cells. The involvement of maternally expressed gene 3 (MEG3) in human disease processes has been increasingly reported. P53 and PI3K/Akt are important pathways by which MEG3 participates in regulating cell apoptosis. MEG3 directly or competitively binds with miRNA to participate in apoptosis, inflammation, oxidative stress, endoplasmic reticulum stress, EMT and other processes. LncRNA MEG3 is mainly involved in malignant tumors, metabolic diseases, immune system diseases, cardiovascular and cerebrovascular diseases, etc., LncRNA MEG3 has a variety of pathological effects in cardiomyocytes, fibroblasts and endothelial cells and has great clinical application potential in the prevention and treatment of AS, MIRI, hypertension and HF. This paper will review the research progress of MEG3 in the aspects of mechanism of action, other systemic diseases and cardiovascular diseases, and point out its great potential in the prevention and treatment of cardiovascular diseases. lncRNAs also play a role in endothelial cells. In addition, lncRNA MEG3 has shown biomarker value, prognostic value and therapeutic response measurement in tumor diseases. We boldly speculate that MEG3 will play a role in the emerging discipline of tumor heart disease.

Protective effects of Stevia rebaudiana extracts on beta cells in lipotoxic conditions

AIMS

Stevia rebaudiana Bertoni leaf extracts have gained increasing attention for their potential protection against type 2 diabetes. In this study, we have evaluated the possible beneficial effects of Stevia rebaudiana leaf extracts on beta-cells exposed to lipotoxicity and explored some of the possible mechanisms involved.

METHODS

Extracts, deriving from six different chemotypes (ST1 to ST6), were characterized in terms of steviol glycosides, total phenols, flavonoids, and antioxidant activity. INS-1E beta cells and human pancreatic islets were incubated 24 h with 0.5 mM palmitate with or without varying concentrations of extracts. Beta-cell/islet cell features were analyzed by MTT assay, activated caspase 3/7 measurement, and/or nucleosome quantification. In addition, the proteome of INS-1E cells was assessed by bi-dimensional electrophoresis (2-DE).

RESULTS

The extracts differed in terms of antioxidant activity and stevioside content. As expected, 24 h exposure to palmitate resulted in a significant decrease of INS-1E cell metabolic activity, which was counteracted by all the Stevia extracts at 200 μg/ml. However, varying stevioside only concentrations were not able to protect palmitate-exposed cells. ST3 extract was also tested with human islets, showing an anti-apoptotic effect. Proteome analysis showed several changes in INS-1E beta-cells exposed to ST3, mainly at the endoplasmic reticulum and mitochondrial levels.

CONCLUSIONS

Stevia rebaudiana leaf extracts have beneficial effects on beta cells exposed to lipotoxicity; this effect does not seem to be mediated by stevioside alone (suggesting a major role of the leaf phytocomplex as a whole) and might be due to actions on the endoplasmic reticulum and the mitochondrion.

Autophagy and apoptosis cascade: which is more prominent in neuronal death?

Autophagy and apoptosis are two crucial self-destructive processes that maintain cellular homeostasis, which are characterized by their morphology and regulated through signal transduction mechanisms. These pathways determine the fate of cellular organelle and protein involved in human health and disease such as neurodegeneration, cancer, and cardiovascular disease. Cell death pathways share common molecular mechanisms, such as mitochondrial dysfunction, oxidative stress, calcium ion concentration, reactive oxygen species, and endoplasmic reticulum stress. Some key signaling molecules such as p53 and VEGF mediated angiogenic pathway exhibit cellular and molecular responses resulting in the triggering of apoptotic and autophagic pathways. Herein, based on previous studies, we describe the intricate relation between cell death pathways through their common genes and the role of various stress-causing agents. Further, extensive research on autophagy and apoptotic machinery excavates the implementation of selective biomarkers, for instance, mTOR, Bcl-2, BH3 family members, caspases, AMPK, PI3K/Akt/GSK3β, and p38/JNK/MAPK, in the pathogenesis and progression of neurodegenerative diseases. This molecular phenomenon will lead to the discovery of possible therapeutic biomolecules as a pharmacological intervention that are involved in the modulation of apoptosis and autophagy pathways. Moreover, we describe the potential role of micro-RNAs, long non-coding RNAs, and biomolecules as therapeutic agents that regulate cell death machinery to treat neurodegenerative diseases. Mounting evidence demonstrated that under stress conditions, such as calcium efflux, endoplasmic reticulum stress, the ubiquitin-proteasome system, and oxidative stress intermediate molecules, namely p53 and VEGF, activate and cause cell death. Further, activation of p53 and VEGF cause alteration in gene expression and dysregulated signaling pathways through the involvement of signaling molecules, namely mTOR, Bcl-2, BH3, AMPK, MAPK, JNK, and PI3K/Akt, and caspases. Alteration in gene expression and signaling cascades cause neurotoxicity and misfolded protein aggregates, which are characteristics features of neurodegenerative diseases. Excessive neurotoxicity and misfolded protein aggregates lead to neuronal cell death by activating death pathways like autophagy and apoptosis. However, autophagy has a dual role in the apoptosis pathways, i.e., activation and inhibition of the apoptosis signaling. Further, micro-RNAs and LncRNAs act as pharmacological regulators of autophagy and apoptosis cascade, whereas, natural compounds and chemical compounds act as pharmacological inhibitors that rescue neuronal cell death through inhibition of apoptosis and autophagic cell death.

Autophagy in metabolic disease and ageing

Autophagy is an evolutionarily conserved, lysosome-dependent catabolic process whereby cytoplasmic components, including damaged organelles, protein aggregates and lipid droplets, are degraded and their components recycled. Autophagy has an essential role in maintaining cellular homeostasis in response to intracellular stress; however, the efficiency of autophagy declines with age and overnutrition can interfere with the autophagic process. Therefore, conditions such as sarcopenic obesity, insulin resistance and type 2 diabetes mellitus (T2DM) that are characterized by metabolic derangement and intracellular stresses (including oxidative stress, inflammation and endoplasmic reticulum stress) also involve the accumulation of damaged cellular components. These conditions are prevalent in ageing populations. For example, sarcopenia is an age-related loss of skeletal muscle mass and strength that is involved in the pathogenesis of both insulin resistance and T2DM, particularly in elderly people. Impairment of autophagy results in further aggravation of diabetes-related metabolic derangements in insulin target tissues, including the liver, skeletal muscle and adipose tissue, as well as in pancreatic β-cells. This Review summarizes the role of autophagy in the pathogenesis of metabolic diseases associated with or occurring in the context of ageing, including insulin resistance, T2DM and sarcopenic obesity, and describes its potential as a therapeutic target.

Drosophila melanogaster: A Powerful Tiny Animal Model for the Study of Metabolic Hepatic Diseases

Animal experimentation is limited by unethical procedures, time-consuming protocols, and high cost. Thus, the development of innovative approaches for disease treatment based on alternative models in a fast, safe, and economic manner is an important, yet challenging goal. In this paradigm, the fruit-fly Drosophila melanogaster has become a powerful model for biomedical research, considering its short life cycle and low-cost maintenance. In addition, biological processes are conserved and homologs of ∼75% of human disease-related genes are found in the fruit-fly. Therefore, this model has been used in innovative approaches to evaluate and validate the functional activities of candidate molecules identified via in vitro large-scale analyses, as putative agents to treat or reverse pathological conditions. In this context, Drosophila offers a powerful alternative to investigate the molecular aspects of liver diseases, since no effective therapies are available for those pathologies. Non-alcoholic fatty liver disease is the most common form of chronic hepatic dysfunctions, which may progress to the development of chronic hepatitis and ultimately to cirrhosis, thereby increasing the risk for hepatocellular carcinoma (HCC). This deleterious situation reinforces the use of the Drosophila model to accelerate functional research aimed at deciphering the mechanisms that sustain the disease. In this short review, we illustrate the relevance of using the fruit-fly to address aspects of liver pathologies to contribute to the biomedical area.

Mechanisms of Beta-Cell Apoptosis in Type 2 Diabetes-Prone Situations and Potential Protection by GLP-1-Based Therapies

Type 2 diabetes (T2D) is characterized by chronic hyperglycemia secondary to the decline of functional beta-cells and is usually accompanied by a reduced sensitivity to insulin. Whereas altered beta-cell function plays a key role in T2D onset, a decreased beta-cell mass was also reported to contribute to the pathophysiology of this metabolic disease. The decreased beta-cell mass in T2D is, at least in part, attributed to beta-cell apoptosis that is triggered by diabetogenic situations such as amyloid deposits, lipotoxicity and glucotoxicity. In this review, we discussed the molecular mechanisms involved in pancreatic beta-cell apoptosis under such diabetes-prone situations. Finally, we considered the molecular signaling pathways recruited by glucagon-like peptide-1-based therapies to potentially protect beta-cells from death under diabetogenic situations.