Liraglutide protects pancreatic β cells from endoplasmic reticulum stress by upregulating MANF to promote autophagy turnover

Molecular mechanisms of endoplasmic reticulum stress-mediated acute kidney injury in juvenile rats and the protective role of mesencephalic astrocyte-derived neurotrophic factor

OBJECTIVES

This study examined the role of endoplasmic reticulum stress in pediatric acute kidney injury and the therapeutic effect of midbrain astrocyte-derived neurotrophic factor.

METHODS

Two-week-old Sprague-Dawley rats were divided into: Sham, ischemia-reperfusion injury-induced acute kidney injury (AKI), mesencephalic astrocyte-derived neurotrophic factor (MANF)-treated, tauroursodeoxycholic acid (TUDCA)-treated. Analyses were conducted 24 h post-treatment. Serum creatinine, cystatin C, Albumin, MANF levels were measured, cytokine concentrations in serum and renal tissues were determined using a Luminex assay. Histopathology was assessed via light and electron microscopy. Western blotting and RT-qPCR analyzed markers for oxidative stress, apoptosis, endoplasmic reticulum (ER) stress, and autophagy. HK-2 cells underwent hypoxia/reoxygenation (H/R) to simulate AKI and were treated with MANF or TUDCA.

RESULTS

AKI rats had increased serum creatinine, cystatin C, and inflammatory cytokines, along with significant renal damage, and showed loose and swollen ER structures, reduced cell proliferation, and elevated levels of IRE1, PERK, ATF6, CHOP, LC3-II/I, KIM-1, TLR4, JNK, and NF-κB. MANF treatment reduced these biomarkers and protein levels, improved ER structure and cell proliferation, alleviated oxidative stress, apoptosis, ER stress, and inhibited JNK/TLR4/NF-κB signaling. In HK-2 cells, MANF reduced ER stress and inflammation post-H/R exposure.

CONCLUSIONS

MANF treatment alleviates ER stress, oxidative stress, apoptosis, and inflammation in pediatric AKI, improving renal function and morphology.

GLP-1-based therapies for type 2 diabetes: from single, dual and triple agonists to endogenous GLP-1 production and L-cell differentiation

Glucagon-like peptide-1 (GLP-1) is an incretin peptide hormone mainly secreted by enteroendocrine intestinal L-cells. GLP-1 is also secreted by α-cells of the pancreas and the central nervous system (CNS). GLP-1 secretion is stimulated by nutrient intake and exerts its effects on glucose homeostasis by stimulating insulin secretion, gastric emptying confiding the food intake, and β-cell proliferation. The insulinotropic effects of GLP-1, and the reduction of its effects in type 2 diabetes mellitus (T2DM), have made GLP-1 an attractive option for the treatment of T2DM. Furthermore, GLP-1-based medications such as GLP-1 receptor agonists and dipeptidyl peptidase-4 inhibitors, have been shown to improve diabetes control in preclinical and clinical trials with human subjects. Importantly, increasing the endogenous production of GLP-1 by different mechanisms or by increasing the number of intestinal L-cells that tend to produce this hormone may be another effective therapeutic approach to managing T2DM. Herein, we briefly describe therapeutic agents/compounds that enhance GLP-1 function. Then, we will discuss the approaches that can increase the endogenous production of GLP-1 through various stimuli. Finally, we introduce the potential of L-cell differentiation as an attractive future therapeutic approach to increase GLP-1 production as an attractive therapeutic alternative for T2DM.

MANF overexpression ameliorates oxidative stress-induced apoptosis of human nucleus pulposus cells by facilitating mitophagy through promoting MFN2 expression

Intervertebral disc degeneration (IDD) is a degenerative condition associated with impaired mitophagy. MANF has been shown to promote mitophagy in murine kidneys; however, its role in IDD remains unexplored. This study aimed to elucidate the mechanism by which MANF influences IDD development through the regulation of mitophagy. Human nucleus pulposus (NP) cells were exposed to tert-butyl hydroperoxide (TBHP) to establish an oxidative stress-induced cellular model. The expression levels of MANF in NP cells were quantified using quantitative real-time PCR (qPCR) and Western blotting. The impact of MANF on TBHP-induced NP cells was evaluated by assessing cell viability, apoptosis, and the levels of mitophagy-related proteins. The underlying mechanisms were further investigated using RNA-binding protein immunoprecipitation (RIP), dual-luciferase reporter assays, qPCR, and Western blotting. Results indicated that MANF expression was significantly downregulated in both IDD patients and TBHP-induced NP cells. Overexpression of MANF inhibited apoptosis, enhanced cell viability, and promoted mitophagy in TBHP-treated NP cells. MFN2 was identified as a downstream target of MANF, and MANF overexpression upregulated MFN2 expression in NP cells, whereas TBHP markedly suppressed MFN2 expression. Furthermore, knockdown of MFN2 partially reversed the effects of MANF overexpression on apoptosis, cell viability, and mitophagy in TBHP-treated NP cells. Collectively, these findings demonstrate that MANF overexpression enhances mitophagy by upregulating MFN2 expression, thereby mitigating oxidative stress-induced apoptosis in NP cells. These results provide novel insights into the pathogenesis of IDD.

The Impact of SGLT1 Inhibition on Frailty and Sarcopenia: A Mediation Mendelian Randomization Study

BACKGROUND

Although pharmacological effects of SGLT2 inhibitors on the development of frailty and sarcopenia were known, the role of SGLT1 remained less clear. The present study investigated the possible effect of SGLT1 inhibition on these conditions and explored potential mediators.

METHODS

A two-sample Mendelian randomization (MR) analysis was performed to assess the effect of SGLT1 inhibition on frailty index (FI) and low grip strength in individuals aged 60 years and older using both the FNIH and EWGSOP criteria. Subsequently, a two-step MR analysis was conducted to investigate the mediating role of insulin resistance phenotype and identify potential mediators of the effect of SGLT1 inhibition on the FI and low grip strength from 1558 plasma proteins and 1352 metabolites.

RESULTS

Genetically predicted SGLT1 inhibition was associated with decreased FI (β: -0.290 [95% CI: -0.399, -0.181]) and reduced risk of low grip strength in individuals aged 60 years and older under both FNIH (β: -0.796 [95% CI: -1.216, -0.376]) and EWGSOP criteria (β: -0.287 [95% CI: -0.532, -0.041]). The two-step MR analysis demonstrated the role of insulin resistance phenotype in mediating SGTL1 inhibition on alleviating frailty (mediation proportion = 19.56% [95% CI: 8.42%, 30.70%]). After screening, 24 proteins and 16 metabolites were identified as mediators of the impact of SGLT1 inhibition on FI. Additionally, 13 proteins and 16 metabolites were found to mediate the effect of SGLT1 inhibition on low grip strength according to FNIH criteria while 22 proteins and 6 metabolites were shown to mediate the impact of SGLT1 inhibition on low grip strength under EWGSOP criteria.

CONCLUSIONS

SGLT1 inhibition potentially mitigated frailty and sarcopenia through several biological mediators, shedding new light for therapeutic intervention.

Unlocking the promise of MANF in diseases: Mechanistic insights and therapeutic potentials

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is a ubiquitous neurotrophic factor that exhibits a variety of physiological functions and plays a critical role in the exploitation of therapeutic potential across a range of diseases, including cardiovascular disorders, nervous system diseases, metabolic imbalances, and cancers. In the context of cardiac diseases, MANF significantly promotes cardiomyocyte survival and improves cardiac functionality. Furthermore, MANF not only provides neuroprotection by shielding neurons from damage and promoting nerve regeneration in neurological disorders, but also involves in insulin resistance, lipid metabolism disturbances and fat-containing liver lesions. However, the oncogenic or tumor suppressive function of MANF in cancer remains unclear, requiring further investigation to elucidate its precise role in the process of cancer initiation and progression. This review aims to summarize the latest advancements in understanding the molecular pathways, intricate mechanisms, and therapeutic potential of MANF in the prevention and treatment of various diseases, emphasizing its multifaceted contributions to health and disease management.

Key subdomains of mesencephalic astrocyte-derived neurotrophic factor attenuate myocardial ischemia/reperfusion injury by JAK1/STAT1/NF-κB signaling pathway

BACKGROUND

Myocardial ischemia/reperfusion (I/R) injury is a common pathological process in clinical practice. Developing effective therapeutic strategies to reduce or prevent this injury is crucial. The article aimed to investigate the role and mechanism of mesencephalic astrocyte-derived neurotrophic factor (MANF) and its key subdomains in modulating myocardial I/R-induced cardiomyocyte apoptosis.

METHODS

MANF stable knockout cell line and MANF mutant overexpression plasmids were constructed. The effects of MANF and mutants on apoptosis and endoplasmic reticulum (ER) stress related proteins were evaluated in hypoxia/reoxygenation-induced HL-1 cardiomyocytes by western blot, immunofluorescence, Tunel and flow cytometry. Echocardiography, ELISA, TTC and Masson were used to observe the effects of recombinant MANF protein (rMANF) on cardiac function in myocardial I/R mice.

RESULTS

This study observed increased expression of MANF in both myocardial infarction patients and I/R mice. MANF overexpression in cardiomyocytes decreased ER stress-induced apoptosis, while MANF knockout exacerbated it. rMANF improved cardiac function in I/R mice by reducing injury and inflammation. This study specifically demonstrates that mutations in the α-helix of MANF were more effective in reducing ER stress and cardiomyocyte apoptosis. Mechanistically, MANF and the α-helix mutant attenuated I/R injury by inhibiting the JAK1/STAT1/NF-κB signaling pathway in addition to reducing ER stress-induced apoptosis.

CONCLUSION

These findings highlight MANF and its subdomains as critical regulators of myocardial I/R injury, offering promising therapeutic targets with significant clinical implications for I/R-related diseases.

CDNF and MANF in the brain dopamine system and their potential as treatment for Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by gradual loss of midbrain dopamine neurons, leading to impaired motor function. Preclinical studies have indicated cerebral dopamine neurotrophic factor (CDNF) and mesencephalic astrocyte-derived neurotrophic factor (MANF) to be potential therapeutic molecules for the treatment of PD. CDNF was proven to be safe and well tolerated when tested in Phase I-II clinical trials in PD patients. Neuroprotective and neurorestorative effects of CDNF and MANF were demonstrated in animal models of PD, where they promoted the survival of dopamine neurons and improved motor function. However, biological roles of endogenous CDNF and MANF proteins in the midbrain dopamine system have been less clear. In addition to extracellular trophic activities, CDNF/MANF proteins function intracellularly in the endoplasmic reticulum (ER), where they modulate protein homeostasis and protect cells against ER stress by regulating the unfolded protein response (UPR). Here, our aim is to give an overview of the biology of endogenous CDNF and MANF in the brain dopamine system. We will discuss recent studies on CDNF and MANF knockout animal models, and effects of CDNF and MANF in preclinical models of PD. To elucidate possible roles of CDNF and MANF in human biology, we will review CDNF and MANF tissue expression patterns and regulation of CDNF/MANF levels in human diseases. Finally, we will discuss novel findings related to the molecular mechanism of CDNF and MANF action in ER stress, UPR, and inflammation, all of which are mechanisms potentially involved in the pathophysiology of PD.

Altered MANF and RYR2 concentrations associated with hypolipidemia in the serum of patients with schizophrenia

Schizophrenia (SCZ) is associated with abnormal serum lipid profiles, but their relationship is poorly understood. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an important regulator of lipid metabolism. Previous studies have shown its involvement in the pathogenesis of numerous neuropsychiatric disorders, while its role in SCZ is still unknown. Therefore, this study was conducted to examine serum MANF levels in patients with SCZ, and to investigate the potential relationship between MANF, serum lipid levels and SCZ. The results showed that total cholesterol (TC) levels were significantly lower in 225 patients with SCZ than in 233 healthy controls (HCs). According to Ingenuity Pathway Analysis, hypolipidemia is associated with SCZ via MANF/ryanodine receptor 2 (RYR2) pathway. This theory was supported by another sample set, which showed significantly lower MANF levels and higher RYR2 levels in the serum of 170 SCZ patients compared to 80 HCs. Moreover, MANF and RYR2 levels both were significantly correlated with the severity of psychotic symptoms and TC levels. In addition, a model consisting of MANF and RYR2 was found to be effective in distinguishing SCZ patients from HCs. These findings suggested that the MANF/RYR2 pathway might serve as a bridge between hypolipidemia and SCZ, and MANF and RYR2 held promise as biomarkers for SCZ.

Effects of mesencephalic astrocyte-derived neurotrophic factor on sepsis-associated acute kidney injury

BACKGROUND

To determine the protective role of mesencephalic astrocyte-derived neurotrophic factor (MANF) in regulating sepsis-associated acute kidney injury (S-AKI).

METHODS

A total of 96 mice were randomly divided into the control group, control+MANF group, S-AKI group, and S-AKI+MANF group. The S-AKI model was established by injecting lipopolysaccharide (LPS) at 10 mg/kg intraperitoneally. MANF (200 μg/kg) was administered to the control+MANF and S-AKI+MANF groups. An equal dose of normal saline was administered daily intraperitoneally in the control and S-AKI groups. Serum and kidney tissue samples were obtained for biochemical analysis. Western blotting was used to detect the protein expression of MANF in the kidney, and enzyme-linked immunosorbent assay (ELISA) was used to determine expression of MANF in the serum, pro-inflammatory cytokines (tumor necrosis factor-α [TNF-α] and interleukin-6 [IL-6]). Serum creatinine (SCr), and blood urea nitrogen (BUN) were examined using an automatic biochemical analyzer. In addition, the kidney tissue was observed for pathological changes by hematoxylin-eosin staining. The comparison between two groups was performed by unpaired Student's t-test, and statistics among multiple groups were carried out using Tukey's post hoc test following one-way analysis of variance (ANOVA). A P-value <0.05 was considered statistically significant.

RESULTS

At the early stage of S-AKI, MANF in the kidney tissue was up-regulated, but with the development of the disease, it was down-regulated. Renal function was worsened in the S-AKI group, and TNF-α and IL-6 were elevated. The administration of MANF significantly alleviated the elevated levels of SCr and BUN and inhibited the expression of TNF-α and IL-6 in the kidney. The pathological changes were more extensive in the S-AKI group than in the S-AKI+MANF group.

CONCLUSION

MANF treatment may significantly alleviate renal injury, reduce the inflammatory response, and alleviate or reverse kidney tissue damage. MANF may have a protective effect on S-AKI, suggesting a potential treatment for S-AKI.

MANF/EWSR1/ANXA6 pathway might as the bridge between hypolipidemia and major depressive disorder

Major depressive disorder (MDD) involves changes in lipid metabolism, but previous findings are contradictory. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is considered to be a regulator of lipid metabolism. To date, the function of MANF has been studied in many brain disorders, but not in MDD. Therefore, to better understand the role of lipids in MDD, this study was conducted to examine lipid levels in the serum of MDD patients and to investigate the potential function of MANF in MDD. First, the data on total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglyceride (TG) in serum from 354 MDD patients and 360 healthy controls (HCs) were collected and analyzed. The results showed that there were significantly lower concentrations of TC and LDL-C in MDD patients compared with HCs, and TC levels were positively correlated with LDL-C levels. Bioinformatics analysis indicated that MANF/EWSR1/ANXA6 pathway might serve as the connecting bridge through which hypolipidemia played a functional role in MDD. Second, to verify this hypothesis, serum samples were collected from 143 MDD patients, and 67 HCs to measure the levels of MANF, EWSR1, and ANXA6 using ELISA kits. The results showed that compared to HCs, MDD patients had a significantly lower level of MANF and higher levels of ANXA6 and EWSR1, and these molecules were significantly correlated with both TC level and Hamilton Depression Rating Scales (HDRS) score. In addition, a discriminative model consisting of MANF, EWSR1, and ANXA6 was identified. This model was capable of distinguishing MDD subjects from HCs, yielded an area under curve of 0.9994 in the training set and 0.9569 in the testing set. Taken together, our results suggested that MANF/EWSR1/ANXA6 pathway might act as the bridge between hypolipidemia and MDD, and these molecules held promise as potential biomarkers for MDD.

Potential Role of MANF, an ER Stress Responsive Neurotrophic Factor, in Protecting Against Alcohol Neurotoxicity

Alcohol exposure during pregnancy is harmful to the fetus and causes a wide range of long-lasting physiological and neurocognitive impairments, collectively referred to as fetal alcohol spectrum disorders (FASD). The neurobehavioral deficits observed in FASD result from structural and functional damages in the brain, with neurodegeneration being the most destructive consequence. Currently, there are no therapies for FASD. It is exigent to delineate the underlying mechanisms of alcohol neurotoxicity and develop an effective strategy of treatment. ER stress, caused by the accumulation of unfolded/misfolded proteins in the ER, is the hallmark of many neurodegenerative diseases, including alcohol-induced neurodegeneration. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is a newly discovered endoplasmic reticulum (ER) stress responsive neurotrophic factor that regulates diverse neuronal functions. This review summarizes the recent findings revealing the effects of MANF on the CNS and its protective role against neurodegeneration. Particularly, we focus the role of MANF on alcohol-induced ER stress and neurodegeneration and discuss the therapeutic potential of MANF in treating alcohol neurotoxicity such as FASD.

MANF: an emerging therapeutic target for metabolic diseases

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum-resident protein and a secretory factor and has beneficial effects in multiple diseases. Recent evidence shows that its circulating levels in humans are dynamically regulated under various metabolic diseases, including diabetes, obesity, fatty liver, and cardiovascular diseases, suggesting that MANF may play a role in these pathological states. Also, its downregulation in mice impairs glucose homeostasis, promotes lipid accumulation in the liver, reduces energy expenditure, and induces inflammation. Conversely, MANF overexpression prevents or mitigates some of these metabolic disturbances. In particular, systemic MANF administration alleviates dietary obesity and related metabolic disorders in obese mice. We therefore propose that MANF might be a promising target for treating chronic metabolic diseases.

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.

MANF: A Novel Endoplasmic Reticulum Stress Response Protein-The Role in Neurological and Metabolic Disorders

The mesencephalic astrocyte-derived neurotrophic factor (MANF), also named as arginine-rich protein (ARP) or arginine-rich mutated in early-stage tumors (ARMET), is a novel evolutionary conserved protein related to unfolded protein response. Growing evidence suggests that MANF critically involves in many ER stress-related diseases with a protective effect. Here, we review the function of MANF based on its structure in neurological and metabolic disorders and summarize its potential applications in disease diagnosis and therapies.

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.

New insight on the role of liraglutide in alleviating dexamethasone-induced pancreatic cytotoxicity via improving redox status, autophagy flux, and PI3K/Akt/Nrf2 signaling

Chronic glucocorticoids therapy is commonly complicated by steroid diabetes, although the underlying mechanisms are still elusive. Liraglutide, a glucagon-like peptide-1, was initially found to induce glycemic control and recently it was found to have many pleotropic effects; however, its role in pancreas remains unknown. The present study aims to estimate the protective role of liraglutide on dexamethasone-induced pancreatic cytotoxicity and hyperglycemia, highlighting the possible underlying biochemical, molecular, and cellular mechanisms. Twenty-eight male Wistar rats were involved in this study and were randomly divided into four groups. Group III and IV were treated with 1 mg/kg dexamethasone daily for 10 days. Group II and IV were treated with liraglutide in a dose of 0.8 mg/kg per day for 2 weeks. Pancreatic caspase-9, nuclear factor erythroid 2-related factor 2 (Nrf2), phospho-protein kinase-B (pAkt), and sequestrome 1 (p62) levels were assessed by immunoassay. Moreover, phosphoinositide 3-kinase (PI3K) expression by real-time PCR, microtubule-associated protein light chain 3 (LC3B) expression by immunohistochemistry, glycemic status, β-cell function by homoeostasis model assessment (HOMA) β index, and pancreatic redox status were assessed. Liraglutide improved blood glucose level, β-cell function, pancreatic caspase-9 level, redox status, and autophagy. Additionally, it increased pancreatic PI3K, pAkt, and Nrf2 levels. Moreover, preservation of pancreatic histological and the ultrastructural morphological features of β- and α-cells were observed. In conclusion, liraglutide protected against dexamethasone-induced pancreatic injury and hyperglycemia and decelerated the progression towards steroid diabetes via activating PI3K/Akt/Nrf2 signaling and autophagy flux pathways.

The relationship of mesencephalic astrocyte-derived neurotrophic factor with hyperlipidemia in patients with or without type 2 diabetes mellitus

PURPOSE

This study was conducted to determine the relationship between mesencephalic astrocyte-derived neurotrophic factor (MANF) and lipid metabolism with or without type 2 diabetes mellitus (T2DM).

METHODS

Human serum samples were collected from 58 normal controls (NC), 40 subjects with hyperlipidemia (HLD) without T2DM, and 42 subjects with HLD and T2DM. Their MANF levels were detected using an enzyme-linked immunosorbent assay (ELISA). Subgroup analysis was performed in the group with HLD and T2DM based on fasting blood glucose (FBG) > 8.22 vs. FBG ≤ 8.22. Furthermore, the relationship between MANF levels and lipid indices was analyzed.

RESULTS

Serum MANF levels were found to be significantly higher in the HLD group, both with and without T2DM (5.62 (3.59-7.11) and 4.21 (2.87-6.11)), both P < 0.001, than in the NC (2.81(1.81-4.01). MANF levels were higher in those with FBG > 8.22 than that in those with FBG ≤ 8.22. In addition, in the HLD without T2DM group, MANF levels were negatively correlated with total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and age, while LDL-C and age were independently related to MANF levels. The area under the curve (AUC) in the ROC analysis of MANF for the diagnosis of HLD without T2DM and HLD with T2DM was 0.709 and 0.841, respectively (P < 0.001).

CONCLUSION

Serum MANF levels increased in the HLD with or without T2DM groups and was associated with lipid and glucose metabolism. MANF may be a useful marker for predicting the development of dyslipidemia in T2DM.

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.

Endoplasmic reticulum stress as the basis of obesity and metabolic diseases: focus on adipose tissue, liver, and pancreas

Obesity challenges lipid and carbohydrate metabolism. The resulting glucolipotoxicity  causes endoplasmic reticulum (ER) dysfunction, provoking the accumulation of immature proteins, which triggers the unfolded protein reaction (UPR) as an attempt to reestablish ER homeostasis. When the three branches of UPR fail to correct the unfolded/misfolded proteins, ER stress happens. Excessive dietary saturated fatty acids or fructose exhibit the same impact on the ER stress, induced by excessive ectopic fat accumulation or rising blood glucose levels, and meta-inflammation. These metabolic abnormalities can alleviate through dietary interventions. Many pathways are disrupted in adipose tissue, liver, and pancreas during ER stress, compromising browning and thermogenesis, favoring hepatic lipogenesis, and impairing glucose-stimulated insulin secretion within pancreatic beta cells. As a result, ER stress takes part in obesity, hepatic steatosis, and diabetes pathogenesis, arising as a potential target to treat or even prevent metabolic diseases. The scientific community seeks strategies to alleviate ER stress by avoiding inflammation, apoptosis, lipogenesis suppression, and insulin sensitivity augmentation through pharmacological and non-pharmacological interventions. This comprehensive review aimed to describe the contribution of excessive dietary fat or sugar to ER stress and the impact of this adverse cellular environment on adipose tissue, liver, and pancreas function.

Mesencephalic astrocyte-derived neurotrophic factor alleviates alcohol induced hepatic steatosis via activating Stat3-mediated autophagy

Alcoholic fatty liver disease (AFLD) is induced by alcohol consumption and may progress to more severe liver diseases such as alcoholic steatohepatitis, fibrosis and cirrhosis, and even hepatocellular carcinoma. Mesencephalic astrocyte-derived neurotrophic factor (MANF) participates in maintaining lipid homeostasis. However, the role of MANF in the pathogenesis of AFLD remains unclear. We established an AFLD mouse model following the US National Institute on Alcohol Abuse and Alcoholism procedure. Both mRNA and protein levels of MANF were significantly increased in the chronic binge alcohol feeding model. Liver-specific knockout of MANF aggravated hepatic lipid accumulation. Similarly, liver-specific overexpression of MANF alleviated AFLD in mouse livers. MANF affected hepatic lipid metabolism by modulating autophagy. The levels of LC3-II and Atg5-Atg12 were decreased in mouse livers with MANF liver-specific knockout and increased with MANF liver-specific overexpression. Furthermore, MANF changed the phosphorylation of Stat3 and its nuclear localization. MANF may have a protective role in the development of AFLD.

Morus alba leaves ethanol extract protects pancreatic islet cells against dysfunction and death by inducing autophagy in type 2 diabetes

BACKGROUND

Protection of pancreatic islet cells against dysfunction or death by regulating autophagy is considered to be an effective method for treatment of type 2 diabetes mellitus (T2DM). Morus alba leaves (mulberry leaves), a popular herbal medicine, have been used for prevention of T2DM since ancient times.

PURPOSE

This study aimed to clarify whether Morus alba leaves ethanol extract (MLE) could protect islet cells in vivo and in vitro by regulating autophagy in T2DM, and explore the possible mechanism of action.

METHODS

The main chemical constituents in MLE were analyzed by HPLC. The T2DM rat model was induced via high-fat diet combined with peritoneal injection of low-dose streptozotocin, and MLE was administered by oral gavage. Fasting blood glucose (FBG) and plasma insulin were measured, and homeostatic model assessment of β cell function (HOMA-β) and insulin resistance (HOMA-IR) were determined. The histomorphology of pancreas islets was evaluated by haematoxylin and eosin staining. In palmitic acid (PA)-stressed INS-1 rat insulinoma cells, cell viability was assayed by an MTT method. Expression of the autophagy-related proteins LC3 I/II, p62, p-AMPK and p-mTOR in islet tissues and INS-1 cells was evaluated by western blotting or immunohistochemistry analysis.

RESULTS

The four main chemical constituents in MLE were identified as chlorogenic acid, rutin, isoquercitrin and quercitrin. MLE ameliorated hyperglycemia, insulin resistance and dyslipidemia of T2DM rats with prominent therapeutic effect. Further study indicated that MLE observably improved islet function, alleviated islet injury of T2DM rats, and inhibited PA-induced INS-1 cell death. On the other hand, MLE significantly induced autophagy in islet cells both in vivo and in vitro, and autophagy inhibitors abolished its therapeutic effect on T2DM rats and protective effect on islet cells. Apart from this, MLE markedly activated the AMPK/mTOR pathway in INS-1 cells, and the AMPK inhibitor prevented the autophagy induction ability of MLE.

CONCLUSION

Together, MLE could protect islet cells against dysfunction and death by inducing AMPK/mTOR-mediated autophagy in T2DM, and these findings provide a new perspective for understanding the treatment mechanism of Morus alba leaves against T2DM.

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

Type 2 diabetes mellitus (T2DM) is characterized by insulin resistance and a progressive loss in mass and function of pancreatic β-cells. In T2DM, lipotoxicity leads to β-cells dysfunction and decreases its number. Autophagy serves a crucial role in maintaining the normal islet architecture and the function of β-cells. Moreover, glucagon-like peptide-1 (GLP-1) and its analogs have beneficial roles in pancreatic β-cells. However, the protective effects of GLP-1 agents on palmitate (PA)-induced pancreatic β-cells and their underlying mechanisms are not fully elucidated. Forkhead box O1 (FoxO1) can prevent pancreatic β-cells from apoptosis. Whether GLP-1 protects against PA-induced β-cells injury via FoxO1 remains unknown. The present study exposed INS-1 cells to PA to establish a T2DM injury model. Cell viability was evaluated using a Cell Counting Kit-8 assay, and apoptosis was determined via western blotting. Furthermore, autophagy was examined using western blotting, immunofluorescence and transmission electron microscopy. Silencing FoxO1 was used to inhibit the activities of FoxO1. The results suggested that the GLP-1 analog liraglutide enhanced the cell viability, inhibited the protein expression of cleaved caspase-3 and increased the expression levels of microtubule-associated protein 1 light chain3 (LC3) II/I, and FoxO1 in INS-1 cells. The autophagy inhibitor chloroquine inhibited the protective effects of liraglutide on INS-1 cells. Silencing of FoxO1 decreased the expression levels of LC3-II and attenuated the protection of liraglutide on the viability of INS-1 cells. In conclusion, the results indicated that liraglutide ameliorated the PA-induced islet β-cells injury via the upregulation of autophagy-mediated by FoxO1.

Trophic activities of endoplasmic reticulum proteins CDNF and MANF

Mesencephalic astrocyte-derived neurotrophic factor (MANF) and cerebral dopamine neurotrophic factor (CDNF) are endoplasmic reticulum (ER) luminal proteins that confer trophic activities in a wide range of tissues under diverse pathological conditions. Despite initially being classified as neurotrophic factors, neither protein structurally nor functionally resembles bona fide neurotrophic factors. Their highly homologous structures comprise a unique globular, saposin-like domain within the N-terminus joined by a flexible linker to a C-terminus containing a SAP-like domain, CXXC motif and an ER retention sequence. Neurotrophic factors exert effects by binding to cognate receptors in the plasma membrane; however, no cell surface receptors have been identified for MANF and CDNF. Both can act as unfolded protein response (UPR) genes that modulate the UPR and inflammatory processes. The trophic activity of MANF and CDNF extends beyond the central nervous system with MANF being crucial for the development of pancreatic β cells and both have trophic effects in a variety of diseases related to the liver, heart, skeletal tissue, kidney and peripheral nervous system. In this article, the unique features of MANF and CDNF, such as their structure and mechanisms of action related to ER stress and inflammation, will be reviewed. Recently identified interactions with lipids and membrane trafficking will also be described. Lastly, their function and therapeutic potential in different diseases including a recent clinical trial using CDNF to treat Parkinson's disease will be discussed. Collectively, this review will highlight MANF and CDNF as broad-acting trophic factors that regulate functions of the endoplasmic reticulum.