AMPK and Friends: Central Regulators of β Cell Biology

Molecular mechanisms linking type 2 diabetes mellitus and late-onset Alzheimer's disease: A systematic review and qualitative meta-analysis

Research evidence indicating common metabolic mechanisms through which type 2 diabetes mellitus (T2DM) increases risk of late-onset Alzheimer's dementia (LOAD) has accumulated over recent decades. The aim of this systematic review is to provide a comprehensive review of common mechanisms, which have hitherto been discussed in separate perspectives, and to assemble and evaluate candidate loci and epigenetic modifications contributing to polygenic risk linkages between T2DM and LOAD. For the systematic review on pathophysiological mechanisms, both human and animal studies up to December 2023 are included. For the qualitative meta-analysis of genomic bases, human association studies were examined; for epigenetic mechanisms, data from human studies and animal models were accepted. Papers describing pathophysiological studies were identified in databases, and further literature gathered from cited work. For genomic and epigenomic studies, literature mining was conducted by formalised search codes using Boolean operators in search engines, and augmented by GeneRif citations in Entrez Gene, and other sources (WikiGenes, etc.). For the systematic review of pathophysiological mechanisms, 923 publications were evaluated, and 138 gene loci extracted for testing candidate risk linkages. 3 57 publications were evaluated for genomic association and descriptions of epigenomic modifications. Overall accumulated results highlight insulin signalling, inflammation and inflammasome pathways, proteolysis, gluconeogenesis and glycolysis, glycosylation, lipoprotein metabolism and oxidation, cell cycle regulation or survival, autophagic-lysosomal pathways, and energy. Documented findings suggest interplay between brain insulin resistance, neuroinflammation, insult compensatory mechanisms, and peripheral metabolic dysregulation in T2DM and LOAD linkage. The results allow for more streamlined longitudinal studies of T2DM-LOAD risk linkages.

Enhancing β-cell function and identity in type 2 diabetes: The protective role of Coptis deltoidea C. Y. Cheng et Hsiao via glucose metabolism modulation and AMPK signaling activation

BACKGROUND

Abnormalities in glucose metabolism may be the underlying cause of β-cell dysfunction and identity impairment resulting from high glucose exposure. In China, Coptis deltoidea C. Y. Cheng et Hsiao (YL) has demonstrated remarkable hypoglycemic effects.

HYPOTHESIS/PURPOSE

To investigate the hypoglycemic effect of YL and determine the mechanism of YL in treating diabetes.

METHODS

A type 2 diabetes mouse model was used to investigate the pharmacodynamics of YL. YL was administrated once daily for 8 weeks. The hypoglycemic effect of YL was assessed by fasting blood glucose, an oral glucose tolerance test, insulin levels, and other indexes. The underlying mechanism of YL was examined by targeting glucose metabolomics, western blotting, and qRT-PCR. Subsequently, the binding capacity between predicted AMP-activated protein kinase (AMPK) and important components of YL (Cop, Ber, and Epi) were validated by molecular docking and surface plasmon resonance. Then, in AMPK knockdown MIN6 cells, the mechanisms of Cop, Ber, and Epi were inversely confirmed through evaluations encompassing glucose-stimulated insulin secretion, markers indicative of β-cell identity, and the examination of glycolytic genes and products.

RESULTS

YL (0.9 g/kg) treatment exerted notable hypoglycemic effects and protected the structural integrity and identity of pancreatic β-cells. Metabolomic analysis revealed that YL inhibited the hyperactivated glycolysis pathway in diabetic mice, thereby regulating the products of the tricarboxylic acid cycle. KEGG enrichment revealed the intimate relationship of this process with the AMPK signaling pathway. Cop, Ber, and Epi in YL displayed high binding affinities for AMPK protein. These compounds played a pivotal role in preserving the identity of pancreatic β-cells and amplifying insulin secretion. The mechanism underlying this process involved inhibition of glucose uptake, lowering intracellular lactate levels, and elevating acetyl coenzyme A and ATP levels through AMPK signaling. The use of a glycolytic inhibitor corroborated that attenuation of glycolysis restored β-cell identity and function.

CONCLUSION

YL demonstrates significant hypoglycemic efficacy. We elucidated the potential mechanisms underlying the protective effects of YL and its active constituents on β-cell function and identity by observing glucose metabolism processes in pancreatic tissue and cells. In this intricate process, AMPK plays a pivotal regulatory role.

Metabolic disorders in prediabetes: From mechanisms to therapeutic management

Diabetes, one of the world's top ten diseases, is known for its high mortality and complication rates and low cure rate. Prediabetes precedes the onset of diabetes, during which effective treatment can reduce diabetes risk. Prediabetes risk factors include high-calorie and high-fat diets, sedentary lifestyles, and stress. Consequences may include considerable damage to vital organs, including the retina, liver, and kidneys. Interventions for treating prediabetes include a healthy lifestyle diet and pharmacological treatments. However, while these options are effective in the short term, they may fail due to the difficulty of long-term implementation. Medications may also be used to treat prediabetes. This review examines prediabetic treatments, particularly metformin, glucagon-like peptide-1 receptor agonists, sodium glucose cotransporter 2 inhibitors, vitamin D, and herbal medicines. Given the remarkable impact of prediabetes on the progression of diabetes mellitus, it is crucial to intervene promptly and effectively to regulate prediabetes. However, the current body of research on prediabetes is limited, and there is considerable confusion surrounding clinically relevant medications. This paper aims to provide a comprehensive summary of the pathogenesis of pre-diabetes mellitus and its associated therapeutic drugs. The ultimate goal is to facilitate the clinical utilization of medications and achieve efficient and timely control of diabetes mellitus.

Mitochondrial bioenergetics, metabolism, and beyond in pancreatic β-cells and diabetes

In Type 1 and Type 2 diabetes, pancreatic β-cell survival and function are impaired. Additional etiologies of diabetes include dysfunction in insulin-sensing hepatic, muscle, and adipose tissues as well as immune cells. An important determinant of metabolic health across these various tissues is mitochondria function and structure. This review focuses on the role of mitochondria in diabetes pathogenesis, with a specific emphasis on pancreatic β-cells. These dynamic organelles are obligate for β-cell survival, function, replication, insulin production, and control over insulin release. Therefore, it is not surprising that mitochondria are severely defective in diabetic contexts. Mitochondrial dysfunction poses challenges to assess in cause-effect studies, prompting us to assemble and deliberate the evidence for mitochondria dysfunction as a cause or consequence of diabetes. Understanding the precise molecular mechanisms underlying mitochondrial dysfunction in diabetes and identifying therapeutic strategies to restore mitochondrial homeostasis and enhance β-cell function are active and expanding areas of research. In summary, this review examines the multidimensional role of mitochondria in diabetes, focusing on pancreatic β-cells and highlighting the significance of mitochondrial metabolism, bioenergetics, calcium, dynamics, and mitophagy in the pathophysiology of diabetes. We describe the effects of diabetes-related gluco/lipotoxic, oxidative and inflammation stress on β-cell mitochondria, as well as the role played by mitochondria on the pathologic outcomes of these stress paradigms. By examining these aspects, we provide updated insights and highlight areas where further research is required for a deeper molecular understanding of the role of mitochondria in β-cells and diabetes.

BRSK2 in pancreatic β cells promotes hyperinsulinemia-coupled insulin resistance and its genetic variants are associated with human type 2 diabetes

Brain-specific serine/threonine-protein kinase 2 (BRSK2) plays critical roles in insulin secretion and β-cell biology. However, whether BRSK2 is associated with human type 2 diabetes mellitus (T2DM) has not been determined. Here, we report that BRSK2 genetic variants are closely related to worsening glucose metabolism due to hyperinsulinemia and insulin resistance in the Chinese population. BRSK2 protein levels are significantly elevated in β cells from T2DM patients and high-fat diet (HFD)-fed mice due to enhanced protein stability. Mice with inducible β-cell-specific Brsk2 knockout (βKO) exhibit normal metabolism with a high potential for insulin secretion under chow-diet conditions. Moreover, βKO mice are protected from HFD-induced hyperinsulinemia, obesity, insulin resistance, and glucose intolerance. Conversely, gain-of-function BRSK2 in mature β cells reversibly triggers hyperglycemia due to β-cell hypersecretion-coupled insulin resistance. Mechanistically, BRSK2 senses lipid signals and induces basal insulin secretion in a kinase-dependent manner. The enhanced basal insulin secretion drives insulin resistance and β-cell exhaustion and thus the onset of T2DM in mice fed an HFD or with gain-of-function BRSK2 in β cells. These findings reveal that BRSK2 links hyperinsulinemia to systematic insulin resistance via interplay between β cells and insulin-sensitive tissues in the populations carrying human genetic variants or under nutrient-overload conditions.

Bile acid metabolism regulatory network orchestrates bone homeostasis

Bile acids (BAs), synthesized in the liver and modified by the gut microbiota, have been widely appreciated not only as simple lipid emulsifiers, but also as complex metabolic regulators and momentous signaling molecules, which play prominent roles in the complex interaction among several metabolic systems. Recent studies have drawn us eyes on the diverse physiological functions of BAs, to enlarge the knowledge about the "gut-bone" axis due to the participation about the gut microbiota-derived BAs to modulate bone homeostasis at physiological and pathological stations. In this review, we have summarized the metabolic processes of BAs and highlighted the crucial roles of BAs targeting bile acid-activated receptors, promoting the proliferation and differentiation of osteoblasts (OBs), inhibiting the activity of osteoclasts (OCs), as well as reducing articular cartilage degradation, thus facilitating bone repair. In addition, we have also focused on the bidirectional effects of BA signaling networks in coordinating the dynamic balance of bone matrix and demonstrated the promising effects of BAs on the development or treatment for pathological bone diseases. In a word, further clinical applications targeting BA metabolism or modulating gut metabolome and related derivatives may be developed as effective therapeutic strategies for bone destruction diseases.

Control of human pancreatic beta cell kinome by glucagon-like peptide-1 receptor biased agonism

AIM

To determine the kinase activity profiles of human pancreatic beta cells downstream of glucagon-like peptide-1 receptor (GLP-1R) balanced versus biased agonist stimulations.

MATERIALS AND METHODS

This study analysed the kinomic profiles of human EndoC-βh1 cells following vehicle and GLP-1R stimulation with the pharmacological agonist exendin-4, as well as exendin-4-based biased derivatives exendin-phe1 and exendin-asp3 for acute (10-minute) versus sustained (120-minute) responses, using PamChip protein tyrosine kinase and serine/threonine kinase assays. The raw data were filtered and normalized using BioNavigator. The kinase analyses were conducted with R, mainly including kinase-substrate mapping and Kyoto Encyclopedia of Genes and Genomes pathway analysis.

RESULTS

The present analysis reveals that kinomic responses are distinct for acute versus sustained GLP-1R agonist exposure, with individual responses associated with agonists presenting specific bias profiles. According to pathway analysis, several kinases, including JNKs, PKCs, INSR and LKB1, are important GLP-1R signalling mediators, constituting potential targets for further research on biased GLP-1R downstream signalling.

CONCLUSION

The results from this study suggest that differentially biased exendin-phe1 and exendin-asp3 can modulate distinct kinase interaction networks. Further understanding of these mechanisms will have important implications for the selection of appropriate anti-type 2 diabetes therapies with optimized downstream kinomic profiles.

Signaling pathways and intervention for therapy of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) represents one of the fastest growing epidemic metabolic disorders worldwide and is a strong contributor for a broad range of comorbidities, including vascular, visual, neurological, kidney, and liver diseases. Moreover, recent data suggest a mutual interplay between T2DM and Corona Virus Disease 2019 (COVID-19). T2DM is characterized by insulin resistance (IR) and pancreatic β cell dysfunction. Pioneering discoveries throughout the past few decades have established notable links between signaling pathways and T2DM pathogenesis and therapy. Importantly, a number of signaling pathways substantially control the advancement of core pathological changes in T2DM, including IR and β cell dysfunction, as well as additional pathogenic disturbances. Accordingly, an improved understanding of these signaling pathways sheds light on tractable targets and strategies for developing and repurposing critical therapies to treat T2DM and its complications. In this review, we provide a brief overview of the history of T2DM and signaling pathways, and offer a systematic update on the role and mechanism of key signaling pathways underlying the onset, development, and progression of T2DM. In this content, we also summarize current therapeutic drugs/agents associated with signaling pathways for the treatment of T2DM and its complications, and discuss some implications and directions to the future of this field.

Venom Peptides, Polyphenols and Alkaloids: Are They the Next Antidiabetics That Will Preserve β-Cell Mass and Function in Type 2 Diabetes?

Improvement of insulin secretion by pancreatic β-cells and preservation of their mass are the current challenges that future antidiabetic drugs should meet for achieving efficient and long-term glycemic control in patients with type 2 diabetes (T2D). The successful development of glucagon-like peptide 1 (GLP-1) analogues, derived from the saliva of a lizard from the Helodermatidae family, has provided the proof of concept that antidiabetic drugs directly targeting pancreatic β-cells can emerge from venomous animals. The literature reporting on the antidiabetic effects of medicinal plants suggests that they contain some promising active substances such as polyphenols and alkaloids, which could be active as insulin secretagogues and β-cell protectors. In this review, we discuss the potential of several polyphenols, alkaloids and venom peptides from snake, frogs, scorpions and cone snails. These molecules could contribute to the development of new efficient antidiabetic medicines targeting β-cells, which would tackle the progression of the disease.

Overexpression of TRIM32 promotes pancreatic β-cell autophagic cell death through Akt/mTOR pathway under high glucose conditions

Type 2 diabetes mellitus (T2DM) is a growing worldwide epidemic and is characterized by progressive pancreatic β-cell dysfunction and insulin resistance. Tripartite motif protein 32 (TRIM32) belongs to the TRIM family protein and has been shown to be involve in insulin resistance in skeletal muscle and the liver. However, the effect of TRIM32 on pancreatic β-cell dysfunction and its mechanism remains unknown. In the current study, we found that serum TRIM32 concentrations of T2DM in patients were significantly elevated compared to those in healthy controls, which indicated that TRIM32 might be used as a diagnostic biomarker in T2DM patients. In INS-1 cells, exposure to high glucose (HG) conditions caused a significant elevation in TRIM32 expression and TRIM32 was located in the nucleus. Overexpression of TRIM32 in INS-1 cells exacerbated the effects of HG-induced autophagy and impaired insulin secretion. In contrast, the silencing of TRIM32 produced the opposite effect. Furthermore, TRIM32 overexpression decreased the phosphorylation levels of Akt and mTOR under HG conditions. However, the activation of Akt/mTOR by MHY1485 reversed the effects of TRIM32 on HG-treated INS-1 cells. Collectively, the present results suggested that TRIM32 participates in the development of T2DM by modulating autophagic cell death and insulin secretion, which might occur through the Akt/mTOR pathway. Thus, TRIM32 might be a promising target in T2DM therapy.

Maturation of beta cells: lessons from in vivo and in vitro models

The ability to maintain normoglycaemia, through glucose-sensitive insulin release, is a key aspect of postnatal beta cell function. However, terminally differentiated beta cell identity does not necessarily imply functional maturity. Beta cell maturation is therefore a continuation of beta cell development, albeit a process that occurs postnatally in mammals. Although many important features have been identified in the study of beta cell maturation, as of yet no unified mechanistic model of beta cell functional maturity exists. Here, we review recent findings about the underlying mechanisms of beta cell functional maturation. These findings include systemic hormonal and nutritional triggers that operate through energy-sensing machinery shifts within beta cells, resulting in primed metabolic states that allow for appropriate glucose trafficking and, ultimately, insulin release. We also draw attention to the expansive synergistic nature of these pathways and emphasise that beta cell maturation is dependent on overlapping regulatory and metabolic networks.

It's What and When You Eat: An Overview of Transcriptional and Epigenetic Responses to Dietary Perturbations in Pancreatic Islets

Our ever-changing modern environment is a significant contributor to the increased prevalence of many chronic diseases, and particularly, type 2 diabetes mellitus (T2DM). Although the modern era has ushered in numerous changes to our daily living conditions, changes in "what" and "when" we eat appear to disproportionately fuel the rise of T2DM. The pancreatic islet is a key biological controller of an organism's glucose homeostasis and thus plays an outsized role to coordinate the response to environmental factors to preserve euglycemia through a delicate balance of endocrine outputs. Both successful and failed adaptation to dynamic environmental stimuli has been postulated to occur due to changes in the transcriptional and epigenetic regulation of pathways associated with islet secretory function and survival. Therefore, in this review we examined and evaluated the current evidence elucidating the key epigenetic mechanisms and transcriptional programs underlying the islet's coordinated response to the interaction between the timing and the composition of dietary nutrients common to modern lifestyles. With the explosion of next generation sequencing, along with the development of novel informatic and -omic approaches, future work will continue to unravel the environmental-epigenetic relationship in islet biology with the goal of identifying transcriptional and epigenetic targets associated with islet perturbations in T2DM.

The RING-domain E3 ubiquitin ligase RNF146 promotes cardiac hypertrophy by suppressing the LKB1/AMPK signaling pathway

The RING-domain E3 ubiquitin ligase RNF146 is an enzyme that plays an important role in ubiquitin-proteasomal protein degradation and participates in various pathophysiological processes. However, its role in cardiac hypertrophy is unclear. In the present work, thoracic transverse aortic constriction (TAC) was performed in transgenic mice with RNF146 knockout mice (KO) and wild-type mice, and neonatal rat cardiomyocytes (NRCMs) were subjected to angiotensin II (Ang II) stimulation to induce cardiac hypertrophy in vitro and in vivo. RNF146 expression was significantly increased in hypertrophied murine hearts and Ang II-stimulated NRCMs. RNF146-KO mice and knockdown of RNF146 NRCMs attenuated TAC- or Ang II-stimulated cardiac hypertrophy. Conversely, enforced expression of RNF146 aggravated these changes. Mechanistically, we found that RNF146 KO or knockdown increased the activation of the AMP-activated protein kinase (AMPK) pathway. Furthermore, we found that RNF146 KO or knockdown decreased ubiquitination of Liver kinase B1 (LKB1), which promoted the activation of the AMPK pathway in a dependent manner. In conclusion, RNF146 targets LKB1 protein for ubiquitin-proteasome degradation in cardiomyocytes and subsequently promotes cardiac hypertrophy by suppressing the activation of the AMPK signaling pathway.

Decoding the chemical composition and pharmacological mechanisms of Jiedu Tongluo Tiaogan Formula using high-performance liquid chromatography coupled with network pharmacology-based investigation

Type 2 diabetes mellitus (T2DM), a chronic low-grade inflammatory disease with high morbidity and mortality, is a serious threat to public health. Previously we demonstrated that a traditional Chinese medicine formulation, Jiedu Tongluo Tiaogan Formula (JDTL), exerted a favorable hypoglycemic effect due to unknown molecular mechanisms involving interactions among JDTL compounds and various cellular components. This study aimed to explore JDTL mechanisms for alleviating hyperglycemia using an integrated strategy incorporating system pharmacology, bioinformatics analysis, and experimental verification. This strategy entailed initial elucidation of JDTL chemical composition using fingerprint analysis via high performance liquid chromatography (HPLC). Next, functions of putative shared target genes and associated pathways were deduced using GO and KEGG pathway enrichment and molecular docking analyses. Ultimately, targets associated with JTDL anti-T2DM effects were found to be functionally associated with biological functions related to lipopolysaccharide and cytokine receptor binding. These results implicated PI3K-Akt signaling pathway involvement in JDTL anti-T2DM effects, as this pathway had been previously shown to play significant roles in glucose and lipid metabolism-related diseases. Furthermore, addition of JDTL to INS-1 and HepG2 cell cultures stimulated cellular mRNA-level and protein-level expression leading to enhanced production of IRS1, Akt, and PI3K. In summary, here JDTL bioactive ingredients, potential targets, and molecular mechanisms underlying JDTL anti-T2DM effects were identified using a multi-component, multi-target, and multi-channel analytical approach, thus providing an important scientific foundation to facilitate development of new drugs mechanistic strategies for preventing and treating T2DM.

Association between AMPKα1 gene polymorphisms and gestational diabetes in the Chinese population: A case-control study

AIM

The aim is to examine the association between seven candidate single nucleotide polymorphisms in AMPKα1 and gestational diabetes in Chinese people.

METHOD

We used a matched nested case-control study design, individuals including 334 participants with gestational diabetes and 334 healthy pregnant women. Confirmed 334 gestational diabetes cases and maternal age and district of residence matched controls (1:1) were enrolled. We examined seven candidate single nucleotide polymorphisms in AMPKα1 gene and the risk of gestational diabetes. The associations were estimated in Co-dominant, Dominant, Recessive, and Alleles models. The odds ratios (ORs) and their 95% confidence intervals (95% CI) were estimated by unconditional logistical regression as a measure of the associations between genotypes and gestational diabetes adjusting for maternal age, prepregnancy body mass index (BMI), fetal sex and parity.

RESULT

At the gene level, we found that AMPKα1 was associated with gestational diabetes (p = 0.008). After adjusting the covariates and multiple comparison correction, AMPKα1 (rsc1002424, rs10053664, rs13361707) polymorphisms were associated with the risk of gestational diabetes. In addition, gestational diabetes was related to the AAGGA haplotype comprising rs1002424, rs2570091, rs10053664, rs13361707 and rs3805486 in the haplotype models (p = 0.011).

CONCLUSIONS

This study provides evidence that the AMPKα1 genotypes (rs1002424 G/A, rs10053664 A/G, rs13361707 A/G) and the haplotype (AAGGA) are relevant genetic factors in a Chinese population with gestational diabetes.

Fighting Diabetes Mellitus: Pharmacological and Non-pharmacological Approaches

BACKGROUND

The increasing worldwide prevalence of diabetes mellitus confers heavy public health issues and points to a large medical need for effective and novel anti-diabetic approaches with negligible adverse effects. Developing effective and novel anti-diabetic approaches to curb diabetes is one of the most foremost scientific challenges.

OBJECTIVES

This article aims to provide an overview of current pharmacological and non-pharmacological approaches available for the management of diabetes mellitus.

METHODS

Research articles that focused on pharmacological and non-pharmacological interventions for diabetes were collected from various search engines such as Science Direct and Scopus, using keywords like diabetes, glucagon-like peptide-1, glucose homeostasis, etc. Results: We review in detail several key pathways and pharmacological targets (e.g., the G protein-coupled receptors- cyclic adenosine monophosphate, 5'-adenosine monophosphate-activated protein kinase, sodium-glucose cotransporters 2, and peroxisome proliferator activated-receptor gamma signaling pathways) that are vital in the regulation of glucose homeostasis. The currently approved diabetes medications, the pharmacological potentials of naturally occurring compounds as promising interventions for diabetes, and the non-pharmacological methods designed to mitigate diabetes are summarized and discussed.

CONCLUSION

Pharmacological-based approaches such as insulin, metformin, sodium-glucose cotransporters 2 inhibitor, sulfonylureas, glucagon-like peptide-1 receptor agonists, and dipeptidyl peptidase IV inhibitors represent the most important strategies in diabetes management. These approved diabetes medications work via targeting the central signaling pathways related to the etiology of diabetes. Non-pharmacological approaches, including dietary modification, increased physical activity, and microbiota-based therapy are the other cornerstones for diabetes treatment. Pharmacological-based approaches may be incorporated when lifestyle modification alone is insufficient to achieve positive outcomes.

Nutrients men-TOR β-Cells to Adulthood

A major trigger of adult β-cell insulin secretion is glucose. In a recent issue of Cell Metabolism, Helman and colleagues show that in fetuses insulin secretion depends on the activation of mTOR by amino acids and that reducing amino acids promotes maturation of β-cells derived from pluripotent stem cells.

Protein Kinases Signaling in Pancreatic Beta-cells Death and Type 2 Diabetes

Type 2 diabetes (T2D) is a worldwide serious public health problem. Insulin resistance and β-cell failure are the two major components of T2D pathology. In addition to defective endoplasmic reticulum (ER) stress signaling due to glucolipotoxicity, β-cell dysfunction or β-cell death initiates the deleterious vicious cycle observed in T2D. Although the primary cause is still unknown, overnutrition that contributes to the induction of the state of low-grade inflammation, and the activation of various protein kinases-related metabolic pathways are main factors leading to T2D. In this chapter following subjects, which have critical checkpoints regarding β-cell fate and protein kinases pathways are discussed; hyperglycemia-induced β-cell failure, chronic accumulation of unfolded protein in β-cells, the effect of intracellular reactive oxygen species (ROS) signaling to insulin secretion, excessive saturated free fatty acid-induced β-cell apoptosis, mitophagy dysfunction, proinflammatory responses and insulin resistance, and the reprogramming of β-cell for differentiation or dedifferentiation in T2D. There is much debate about selecting proposed therapeutic strategies to maintain or enhance optimal β-cell viability for adequate insulin secretion in T2D. However, in order to achieve an effective solution in the treatment of T2D, more intensive clinical trials are required on newer therapeutic options based on protein kinases signaling pathways.

Transcriptomic and Quantitative Proteomic Profiling Reveals Signaling Pathways Critical for Pancreatic Islet Maturation

Pancreatic β-cell dysfunction and reduced insulin secretion play a key role in the pathogenesis of diabetes. Fetal and neonatal islets are functionally immature and have blunted glucose responsiveness and decreased insulin secretion in response to stimuli and are far more proliferative. However, the mechanisms underlying functional immaturity are not well understood. Pancreatic islets are composed of a mixture of different cell types, and the microenvironment of islets and interactions between these cell types are critical for β-cell development and maturation. RNA sequencing and quantitative proteomic data from intact islets isolated from fetal (embryonic day 19) and 2-week-old Sprague-Dawley rats were integrated to compare their gene and protein expression profiles. Ingenuity Pathway Analysis (IPA) was also applied to elucidate pathways and upstream regulators modulating functional maturation of islets. By integrating transcriptome and proteomic data, 917 differentially expressed genes/proteins were identified with a false discovery rate of less than 0.05. A total of 411 and 506 of them were upregulated and downregulated in the 2-week-old islets, respectively. IPA revealed novel critical pathways associated with functional maturation of islets, such as AMPK (adenosine monophosphate-activated protein kinase) and aryl hydrocarbon receptor signaling, as well as the importance of lipid homeostasis/signaling and neuronal function. Furthermore, we also identified many proteins enriched either in fetal or 2-week-old islets related to extracellular matrix and cell communication, suggesting that these pathways play critical roles in islet maturation. Our present study identified novel pathways for mature islet function in addition to confirming previously reported mechanisms, and provided new mechanistic insights for future research on diabetes prevention and treatment.

AMPK Profiling in Rodent and Human Pancreatic Beta-Cells under Nutrient-Rich Metabolic Stress

Chronic exposure of pancreatic β-cells to elevated nutrient levels impairs their function and potentially induces apoptosis. Like in other cell types, AMPK is activated in β-cells under conditions of nutrient deprivation, while little is known on AMPK responses to metabolic stresses. Here, we first reviewed recent studies on the role of AMPK activation in β-cells. Then, we investigated the expression profile of AMPK pathways in β-cells following metabolic stresses. INS-1E β-cells and human islets were exposed for 3 days to glucose (5.5–25 mM), palmitate or oleate (0.4 mM), and fructose (5.5 mM). Following these treatments, we analyzed transcript levels of INS-1E β-cells by qRT-PCR and of human islets by RNA-Seq; with a special focus on AMPK-associated genes, such as the AMPK catalytic subunits α1 (Prkaa1) and α2 (Prkaa2). AMPKα and pAMPKα were also evaluated at the protein level by immunoblotting. Chronic exposure to the different metabolic stresses, known to alter glucose-stimulated insulin secretion, did not change AMPK expression, either in insulinoma cells or in human islets. Expression profile of the six AMPK subunits was marginally modified by the different diabetogenic conditions. However, the expression of some upstream kinases and downstream AMPK targets, including K-ATP channel subunits, exhibited stress-specific signatures. Interestingly, at the protein level, chronic fructose treatment favored fasting-like phenotype in human islets, as witnessed by AMPK activation. Collectively, previously published and present data indicate that, in the β-cell, AMPK activation might be implicated in the pre-diabetic state, potentially as a protective mechanism.

Lipid-associated metabolic signalling networks in pancreatic beta cell function

Significant advances have been made in deciphering the mechanisms underlying fuel-stimulated insulin secretion by pancreatic beta cells. The contribution of the triggering/ATP-sensitive potassium (K_ATP)-dependent Ca²⁺ signalling and K_ATP-independent amplification pathways, that include anaplerosis and lipid signalling of glucose-stimulated insulin secretion (GSIS), are well established. A proposed model included a key role for a metabolic partitioning 'switch', the acetyl-CoA carboxylase (ACC)/malonyl-CoA/carnitine palmitoyltransferase-1 (CPT-1) axis, in beta cell glucose and fatty acid signalling for insulin secretion. This model has gained overwhelming support from a number of studies in recent years and is now refined through its link to the glycerolipid/NEFA cycle that provides lipid signals through its lipolysis arm. Furthermore, acetyl-CoA carboxylase may also control beta cell growth. Here we review the evidence supporting a role for the ACC/malonyl-CoA/CPT-1 axis in the control of GSIS and its particular importance under conditions of elevated fatty acids (e.g. fasting, excess nutrients, hyperlipidaemia and diabetes). We also document how it is linked to a more global lipid signalling system that includes the glycerolipid/NEFA cycle.

Milk exosomal miRNAs: potential drivers of AMPK-to-mTORC1 switching in β-cell de-differentiation of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) steadily increases in prevalence since the 1950's, the period of widespread distribution of refrigerated pasteurized cow's milk. Whereas breastfeeding protects against the development of T2DM in later life, accumulating epidemiological evidence underlines the role of cow's milk consumption in T2DM. Recent studies in rodent models demonstrate that during the breastfeeding period pancreatic β-cells are metabolically immature and preferentially proliferate by activation of mechanistic target of rapamycin complex 1 (mTORC1) and suppression of AMP-activated protein kinase (AMPK). Weaning determines a metabolic switch of β-cells from a proliferating, immature phenotype with low insulin secretion to a differentiated mature phenotype with glucose-stimulated insulin secretion, less proliferation, reduced mTORC1- but increased AMPK activity. Translational evidence presented in this perspective implies for the first time that termination of milk miRNA transfer is the driver of this metabolic switch. miRNA-148a is a key inhibitor of AMPK and phosphatase and tensin homolog, crucial suppressors of mTORC1. β-Cells of diabetic patients return to the postnatal phenotype with high mTORC1 and low AMPK activity, explained by continuous transfer of bovine milk miRNAs to the human milk consumer. Bovine milk miRNA-148a apparently promotes β-cell de-differentiation to the immature mTORC1-high/AMPK-low phenotype with functional impairments in insulin secretion, increased mTORC1-driven endoplasmic reticulum stress, reduced autophagy and early β-cell apoptosis. In contrast to pasteurized cow's milk, milk's miRNAs are inactivated by bacterial fermentation, boiling and ultra-heat treatment and are missing in current infant formula. Persistent milk miRNA signaling adds a new perspective to the pathogenesis of T2DM and explains the protective role of breastfeeding but the diabetogenic effect of continued milk miRNA signaling by persistent consumption of pasteurized cow's milk.

The relevance of AMP-activated protein kinase in insulin-secreting β cells: a potential target for improving β cell function?

AMP-activated protein kinase (AMPK) is present in different kinds of metabolically active cells. AMPK is an important intracellular energy sensor and plays a relevant role in whole-body energy homeostasis. AMPK is activated, among others, in response to glucose deprivation, caloric restriction and increased physical activity. Upon activation, AMPK affects metabolic pathways leading to increased formation of ATP and simultaneously reducing ATP-consuming processes. AMPK is also expressed in pancreatic β cells and is largely regulated by glucose, which is the main physiological stimulator of insulin secretion. Results of in vitro studies clearly show that glucose-induced insulin release is associated with a concomitant inhibition of AMPK in β cells. However, pharmacological activation of AMPK significantly potentiates the insulin-secretory response of β cells to glucose and to some other stimuli. This effect is primarily due to increased intracellular calcium concentrations. AMPK is also involved in the regulation of gene expression and may protect β cells against glucolipotoxic conditions. It was shown that in pancreatic islets of humans with type 2 diabetes, AMPK is downregulated. Moreover, studies with animal models demonstrated impaired link between glucose and AMPK activity in pancreatic islet cells. These data suggest that AMPK may be a target for compounds improving the functionality of β cells. However, more studies are required to better elucidate the relevance of AMPK in the (patho)physiology of the insulin-secreting cells.

β-Cell Maturation and Identity in Health and Disease

The exponential increase of patients with diabetes mellitus urges for novel therapeutic strategies to reduce the socioeconomic burden of this disease. The loss or dysfunction of insulin-producing β-cells, in patients with type 1 and type 2 diabetes respectively, put these cells at the center of the disease initiation and progression. Therefore, major efforts have been taken to restore the β-cell mass by cell-replacement or regeneration approaches. Implementing novel therapies requires deciphering the developmental mechanisms that generate β-cells and determine the acquisition of their physiological phenotype. In this review, we summarize the current understanding of the mechanisms that coordinate the postnatal maturation of β-cells and define their functional identity. Furthermore, we discuss different routes by which β-cells lose their features and functionality in type 1 and 2 diabetic conditions. We then focus on potential mechanisms to restore the functionality of those β-cell populations that have lost their functional phenotype. Finally, we discuss the recent progress and remaining challenges facing the generation of functional mature β-cells from stem cells for cell-replacement therapy for diabetes treatment.

Expression of messenger RNA encoding two cellular metabolic regulators, AMP-activated protein kinase (AMPK) and O-GlcNAc transferase (OGT), in channel catfish: Their tissue distribution and relationship with changes in food intake

AMP-activated protein kinase (AMPK) is considered as the master cellular metabolism regulator that activates various proteins, including O-GlcNAc transferase (OGT). Physiological roles of AMPK and OGT, including the relationship between their mRNA expression and food intake, are poorly understood in channel catfish. This study examined the tissue distribution of AMPK and OGT mRNA and changes in their expression in response to changes in food intake in channel catfish. Expression of all AMPK subunit and OGT mRNA was detectable in the whole brain, liver, heart, spleen, white muscle, and kidney of channel catfish. The OGT mRNA was highly localized in the brain compared to other tissues. 28-day fasting increased hepatic expression of AMPK α1, β1, and OGT mRNA while refeeding fish for 14 days after the 14-day fast decreased their expression to the level similar to that of fish that were fed daily. No changes were noted in the expression of muscle and brain AMPK mRNA or OGT mRNA by fasting and refeeding. Hepatic AMPK α1, α2 and β1 mRNA decreased in response to increased feeding frequency, whereas no changes in the expression of AMPK or OGT mRNA were noted in the brain or the muscle. Results of the current study indicated that the hepatic expression of AMPK and OGT mRNA appeared to be more sensitive to changes in food intake in channel catfish. However, further studies are needed to clearly demonstrate if food intake influences the expression of AMPK and OGT mRNA in various tissues, including the hypothalamus.

Effect of sodium-glucose cotransporter 2 inhibitor, empagliflozin, and α-glucosidase inhibitor, voglibose, on hepatic steatosis in an animal model of type 2 diabetes

OBJECTIVE

We investigated the effects of sodium-glucose cotransporter 2 inhibitor, empagliflozin, and α-glucosidase inhibitor, voglibose, on hepatic steatosis in an animal model of type 2 diabetes (T2DM).

METHODS

Empagliflozin (OLETF-EMPA) or voglibose (OLETF-VOG) was administered to Otsuka Long-Evans Tokushima fatty (OLETF) rats once daily for 12 weeks. Control Long-Evans Tokushima Otsuka (LETO) and OLETF (OLETF-C) rats received saline.

RESULTS

Blood glucose levels were significantly suppressed in OLETF-EMPA and OLETF-VOG compared with the OLETF-C group. The liver fat content was significantly higher in the OLETF-C group than in the OLETF-EMPA and OLETF-VOG. Hepatic gene expressions involved in gluconeogenesis (glucose 6-phosphatase [G6Pase], fructose-1,6-bisphosphatase [FBP1], and phosphoenolpyruvate carboxykinase [PEPCK]) and lipogenesis (acetyl-CoA carboxylase [ACC], fatty acid synthase [FAS], and sterol regulatory element-binding transcription factor 1c [SREBP-1c]) were significantly decreased in the OLETF-EMPA group compared with other OLETF groups (OLETF-C and OLETF-VOG). Sirtuin 1 (SIRT1) expression level and SIRT1 activity were markedly reduced in OLETF-C rats; however, its expression increased in the OLETF-EMPA and OLETF-VOG. AMP-activated protein kinase (AMPK) phosphorylation level was remarkably increased by empagliflozin treatment in OLETF rats compared with other OLETF groups. Long-term empagliflozin and voglibose treatment reduced hepatic steatosis with suppression of gluconeogenesis and lipogenesis pathway in OLETF rats.

CONCLUSION

We suggest that this metabolic improvement might be related to SIRT1 and AMPK pathway in T2DM. But empagliflozin is thought to have more advantage to prevent hepatic steatosis than voglibose in T2DM.

The LKB1-AMPK and mTORC1 Metabolic Signaling Networks in Schwann Cells Control Axon Integrity and Myelination: Assembling and upholding nerves by metabolic signaling in Schwann cells

The Liver kinase B1 with its downstream target AMP activated protein kinase (LKB1-AMPK), and the key nutrient sensor mammalian target of rapamycin complex 1 (mTORC1) form two signaling systems that coordinate metabolic and cellular activity with changes in the environment in order to preserve homeostasis. For example, nutritional fluctuations rapidly feed back on these signaling systems and thereby affect cell-specific functions. Recent studies have started to reveal important roles of these strategic metabolic regulators in Schwann cells for the trophic support and myelination of axons. Because aberrant intermediate metabolism along with mitochondrial dysfunction in Schwann cells is mechanistically linked to nerve abnormalities found in acquired and inherited peripheral neuropathies, manipulation of the LKB1-AMPK, and mTORC1 signaling hubs may be a worthwhile therapeutic target to mitigate nerve damage in disease. Here, recent advances in our understanding of LKB1-AMPK and mTORC1 functions in Schwann cells are covered, and future research areas for this key metabolic signaling network are proposed.

Molecular aspects of pancreatic β-cell dysfunction: Oxidative stress, microRNA, and long noncoding RNA

Metabolic syndrome is known as a frequent precursor of type 2 diabetes mellitus (T2D). This disease could affect 8% of the people worldwide. Given that pancreatic β-cell dysfunction and loss have central roles in the initiation and progression of the disease, the understanding of cellular and molecular pathways associated with pancreatic β-cell dysfunction can provide more information about the underlying pathways involved in T2D. Multiple lines evidence indicated that oxidative stress, microRNA, and long noncoding RNA play significant roles in various steps of diseases. Oxidative stress is one of the important factors involved in T2D pathogenesis. This could affect the function and survival of the β cell via activation or inhibition of several processes and targets, such as receptor-signal transduction, enzyme activity, gene expression, ion channel transport, and apoptosis. Besides oxidative stress, microRNAs and noncoding RNAs have emerged as epigenetic regulators that could affect pancreatic β-cell dysfunction. These molecules exert their effects via targeting a variety of cellular and molecular pathways involved in T2D pathogenesis. Here, we summarized the molecular aspects of pancreatic β-cell dysfunction. Moreover, we highlighted the roles of oxidative stress, microRNAs, and noncoding RNAs in pancreatic β-cell dysfunction.

So Many Roads: the Multifaceted Regulation of Autophagy Induction

Autophagy is an evolutionary conserved, degradative process from single-cell eukaryotes, such as Saccharomyces cerevisiae, to higher mammals, such as humans. The regulation of autophagy has been elucidated through the combined study of yeast, Caenorhabditis elegans, mice, Drosophila melanogaster, and humans. MTOR, the major negative regulator of autophagy, and activating nutrient kinases, such as 5'-AMP-activated protein kinase (AMPK), interact with the autophagy regulatory complex: ULK1/2, RB1CC1, ATG13, and ATG101. The ULK1/2 complex induces autophagy by phosphorylating downstream autophagy complexes, such as the BECN1 PIK3 signaling complex that leads to the creation of LC3+ autophagosomes. We highlight in this review various reports of autophagy induction that are independent of these regulators. We discuss reports of MTOR-independent, AMPK-independent, ULK1/2-independent, and BECN1-PIK3C3-independent autophagy. We illustrate that autophagy induction and the components required vary by the nature of the induction signal and type of cell and do not always require canonical members of the autophagy signaling pathway. We illustrate that rather than thinking of autophagy as a linear pathway, it is better to think of autophagy induction as an interconnecting web of key regulators, many of which can induce autophagy through different requirements depending on the type and length of induction signals.

Activation of TGR5 promotes osteoblastic cell differentiation and mineralization

Impairment of normal osteoblast differentiation has been associated with bone loss-related disorders, such as osteoporosis. Takeda G-protein coupled receptor 5 (TGR5) has been identified as an important modulator of bile acid and energy homeostasis. Little information regarding the effects of TGR5 on osteoblastic bone formation and matrix mineralization has been reported before. In the current study, we found that TGR5 was expressed in osteoblast-like cell line MC3T3-E1 cells. Osteogenic medium (OM) stimulation promoted the expression of TGR5 in a dose-dependent manner. Notably, treatment with the specific TGR5 agonist GPBARA increased ALP activity, matrix mineralization, and expressions of osteoblastic differentiation marker genes, such as ALP, OCN, and Osx, by promoting the expression of Runx-2. Silencing of TGR5 by transfection with TGR5 siRNA abolished these effects. Also, we found that the AMPK/eNOS pathway was involved in this process. Blockage of AMPK activation using its specific inhibitor compound C abolished the effect of GPBARA-induced increase in ALP activity, matrix mineralization, and expressions of osteoblastic differentiation marker genes. The obtained results provide a new insight into the physiological function of TGR5 in bone formation and suggest that TGR5 might be a novel therapeutic target for bone diseases.