Rapamycin toxicity in MIN6 cells and rat and human islets is mediated by the inhibition of mTOR complex 2 (mTORC2)

Immunosuppressive drug combinations after kidney transplantation and post-transplant diabetes: A systematic review and meta-analysis

Post-transplant diabetes mellitus (PTDM) is a frequent complication after kidney transplantation (KT). This systematic review investigated the effect of different immunosuppressive regimens on the risk of PTDM. We performed a systematic literature search in MEDLINE and CENTRAL for randomized controlled trials (RCTs) that included KT recipients with any immunosuppression and reported PTDM outcomes up to 1 October 2023. The analysis included 125 RCTs. We found no differences in PTDM risk within induction therapies. In de novo KT, there was an increased risk of developing PTDM with tacrolimus versus cyclosporin (RR 1.71, 95%CI [1.38-2.11]). No differences were observed between tacrolimus+mammalian target of rapamycin inhibitor (mTORi) and tacrolimus+MMF/MPA, but there was a tendency towards a higher risk of PTDM in the cyclosporin+mTORi group (RR 1.42, 95%CI [0.99-2.04]). Conversion from cyclosporin to an mTORi increased PTDM risk (RR 1.89, 95%CI [1.18-3.03]). De novo belatacept compared with a calcineurin inhibitor resulted in 50% lower risk of PTDM (RR 0.50, 95%CI [0.32-0.79]). Steroid avoidance resulted in 31% lower PTDM risk (RR 0.69, 95%CI [0.57-0.83]), whereas steroid withdrawal resulted in no differences. Immunosuppression should be decided on an individual basis, carefully weighing the risk of future PTDM and rejection.

Dysregulation of autophagy activation induced by atorvastatin contributes to new-onset diabetes mellitus in western diet-fed mice

BACKGROUND AND AIMS

The incidence of statin-induced new-onset diabetes (NOD) is increasing but its underlying mechanisms remain unclear. We aimed to investigate the effects of various doses of atorvastatin (ATO)-induced autophagy on the development of NOD.

METHODS AND RESULTS

The isolated rat islets and MIN6 cells-treated with ATO, exhibited impaired glucose-stimulated insulin secretion, reduced insulin content, and induced apoptosis. Additionally, autophagy was induced at all doses (in vitro: 5, 10, 20 μM; in vivo: 10, 15, 20 mg/kg) in ATO-treated MIN6 cells or western diet (WD)-fed mice. In contrast to normal glucose-tolerant mice administered a low-dose (10 mg/kg) ATO, those treated with high-doses (15 or 20 mg/kg) exhibited impaired glucose tolerance. Furthermore, high-dose ATO-treated mice showed decreased β-cell mass and increased apoptosis compared to that of vehicle-treated mice. We also observed that the number of vesicophagous cells in the pancreas of 20 mg/kg ATO-treated WD-fed mice was higher than in vehicle-treated WD-fed mice. Inhibiting autophagy using 3-methyladenine (3-MA) and siAtg5 improved glucose tolerance in vivo and in vitro by preventing apoptotic β-cell death and restoring insulin granules.

CONCLUSION

These results indicate that high doses of ATO induced hyperactivated autophagy in pancreatic cells, leading to impaired insulin storage, decreased cell viability, and reduced functional cell mass, ultimately resulting in NOD development.

Diabetic Kidney Disease in Post-Kidney Transplant Patients

Post-transplant diabetes mellitus (PTDM) is a common occurrence in post-kidney transplantation and is associated with greater mortality, allograft failure, and increased risk of infections. The primary goal in the management of PTDM is to achieve glycemic control to minimize the risk of complications while balancing the need for immunosuppression to maintain the health of the transplanted kidney. This review summarizes the effects of maintenance immunosuppression and therapeutic options among kidney transplant recipients. Patients with PTDM are at increased risk of diabetic kidney disease development; therefore, in this review, we focus on evidence supporting the use of novel antidiabetic agents and discuss their benefits and potential side effects in detail.

Advanced Delivery Strategies for Immunotherapy in Type I Diabetes Mellitus

Type 1 diabetes mellitus (T1DM) has been defined as an autoimmune disease characterised by immune-mediated destruction of the pancreatic β cells, leading to absolute insulin deficiency and hyperglycaemia. Current research has increasingly focused on immunotherapy based on immunosuppression and regulation to rescue T-cell-mediated β-cell destruction. Although T1DM immunotherapeutic drugs are constantly under clinical and preclinical development, several key challenges remain, including low response rates and difficulty in maintaining therapeutic effects. Advanced drug delivery strategies can effectively harness immunotherapies and improve their potency while reducing their adverse effects. In this review, we briefly introduce the mechanisms of T1DM immunotherapy and focus on the current research status of the integration of the delivery techniques in T1DM immunotherapy. Furthermore, we critically analyse the challenges and future directions of T1DM immunotherapy.

mTOR-inhibitors and post-transplant diabetes mellitus: a link still debated in kidney transplantation

The mammalian target of rapamycin inhibitors (mTOR-Is, Sirolimus, and Everolimus) are immunosuppressive drugs widely employed in kidney transplantation. Their main mechanism of action includes the inhibition of a serine/threonine kinase with a pivotal role in cellular metabolism and in various eukaryotic biological functions (including proteins and lipids synthesis, autophagy, cell survival, cytoskeleton organization, lipogenesis, and gluconeogenesis). Moreover, as well described, the inhibition of the mTOR pathway may also contribute to the development of the post-transplant diabetes mellitus (PTDM), a major clinical complication that may dramatically impact allograft survival (by accelerating the development of the chronic allograft damage) and increase the risk of severe systemic comorbidities. Several factors may contribute to this condition, but the reduction of the beta-cell mass, the impairment of the insulin secretion and resistance, and the induction of glucose intolerance may play a pivotal role. However, although the results of several in vitro and in animal models, the real impact of mTOR-Is on PTDM is still debated and the entire biological machinery is poorly recognized. Therefore, to better elucidate the impact of the mTOR-Is on the risk of PTDM in kidney transplant recipients and to potentially uncover future research topics (particularly for the clinical translational research), we decided to review the available literature evidence regarding this important clinical association. In our opinion, based on the published reports, we cannot draw any conclusion and PTDM remains a challenge. However, also in this case, the administration of the lowest possible dose of mTOR-I should also be recommended.

Kaempferol sensitizes cell proliferation inhibition in oxaliplatin-resistant colon cancer cells

Resolution to chemoresistance is a major challenge in patients with advanced-stage malignancies. Thus, identification of action points and elucidation of molecular mechanisms for chemoresist human cancer are necessary to overcome this challenge. In this study, we provide important evidence that kaempferol targeting RSKs might be a strategy to reduce the oxaliplatin-resistant colon cancer cells. We found that MAPK and PI3K-AKT signaling were increased in oxaliplatin (Ox)-resistant HCT116 (HCT116-Ox^R) cells compared to Ox-sensitive HCT116 (HCT116-Ox^S) cells. Comparison of cell sensitivities using SP600125 (JNK inhibitor), SB206580 (p38 kinase inhibitor), or MK-2206 (AKT inhibitor) revealed that cell proliferation inhibition was strongly observed in HT29 cells compared to that in HCT116 cells in both Ox^S and Ox^R cells. Interestingly, SP600125, SB206580, and MK-2206 treatment showed higher cell proliferation inhibition in Ox^S cells than that in Ox^R cells in both HCT116 and HT29 cells, except following treatments with 10 µM of SP600125, and 30 µM of SB206580. In comparison to magnolin and aschantin, kaempferol showed the strongest inhibitory effect on cell proliferation in both HCT116 and HT29 cells. Importantly, HCT116- and HT29-Ox^R cells showed higher sensitivities to cell proliferation inhibition than those of HCT116- and HT29-Ox^S cells, resulting in the accumulation of cells at the G₂/M-phases of the cell cycle. Finally, we showed that AP-1 transactivation activity was markedly decreased by kaempferol in HCT116- and HT29-Ox^R cells compared to the activity levels in HCT116- and HT29-Ox^S cells. Taken together, the results demonstrate that kaempferol-mediated AP-1 inhibition might be an important signaling mechanism to resolve the chemoresistance of Ox-resistant colon cancer cells.

Dissecting the biology of mTORC1 beyond rapamycin

[Figure: see text].

Regulation of mRNA Translation by Hormone Receptors in Breast and Prostate Cancer

Simple Summary

The estrogen and androgen receptors (ER, AR) are key oncogenic drivers and therapeutic targets in breast and prostate cancer, respectively. These receptors bind to DNA and regulate gene expression but emerging evidence indicates that they also play important roles in controlling the process of mRNA translation, which dictates cellular protein production. Here, we review the mechanisms by which abnormal activities of ER and AR can dysregulate mRNA translation in breast and prostate cancer cells. Specifically, we explore how the intricate cellular signalling pathways that keep mRNA translation in check are perturbed by aberrant ER and AR signalling, which can lead to enhanced cancer cell growth. We also discuss the potential of targeting mRNA translation as a strategy to treat patients with breast and prostate cancer.

Abstract

Breast and prostate cancer are the second and third leading causes of death amongst all cancer types, respectively. Pathogenesis of these malignancies is characterised by dysregulation of sex hormone signalling pathways, mediated by the estrogen receptor-α (ER) in breast cancer and androgen receptor (AR) in prostate cancer. ER and AR are transcription factors whose aberrant function drives oncogenic transcriptional programs to promote cancer growth and progression. While ER/AR are known to stimulate cell growth and survival by modulating gene transcription, emerging findings indicate that their effects in neoplasia are also mediated by dysregulation of protein synthesis (i.e., mRNA translation). This suggests that ER/AR can coordinately perturb both transcriptional and translational programs, resulting in the establishment of proteomes that promote malignancy. In this review, we will discuss relatively understudied aspects of ER and AR activity in regulating protein synthesis as well as the potential of targeting mRNA translation in breast and prostate cancer.

A Novel Stable Isotope Approach Demonstrates Surprising Degree of Age-Related Decline in Skeletal Muscle Collagen Proteostasis

Age-related deterioration in turnover of collagen proteins accelerates extracellular matrix fibrosis and hinders adaptation to external stimuli. This project sought to understand factors that increase skeletal muscle fibrosis with age by studying what we term the dynamic protein pool. We hypothesized that the dynamic protein pool size of muscle collagen decreases with age, thus indicating a decrease in proteostatic maintenance (ie, ability to maintain proteostasis), and that failure to account for these changes impacts the interpretation of tracer-measured synthesis rates. We used deuterium oxide (D₂O) labeling for up to 60 days in adult (6 months) and old (23 months) mice. The dynamic protein pool in adult skeletal muscle was 65% in tibialis anterior (TA), but only 28% in gastrocnemius (Gastroc). In aged muscle, the dynamic protein pool was further decreased to only 35% and 14% for TA and Gastroc, respectively. We showed that this loss in dynamic pool size was associated with increases in markers of fibrosis and decreased proteostatic maintenance. We demonstrate that aged muscle has higher rates of collagen protein synthesis and lower rates of collagen protein breakdown, which causes collagen accumulation. We further demonstrated that the normal assumption of complete protein renewal and the standard practice of taking a single sample with isotope labeling have profound impacts on interpretation of the genesis of fibrosis. Strategies to maintain muscle function with aging should focus on the dynamic protein pool with attention to methodological strategies to assess those changes.

Roles of mTOR in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease and the number of patients affected is increasing worldwide. Thus, there is a need to establish a new treatment for DKD to improve the renal prognosis of diabetic patients. Recently, it has shown that intracellular metabolic abnormalities are involved in the pathogenesis of DKD. In particular, the activity of mechanistic target of rapamycin complex 1 (mTORC1), a nutrient-sensing signaling molecule, is hyperactivated in various organs of diabetic patients, which suggests the involvement of excessive mTORC1 activation in the pathogenesis of diabetes. In DKD, hyperactivated mTORC1 may be involved in the pathogenesis of podocyte damage, which causes proteinuria, and tubular cell injury that decreases renal function. Therefore, elucidating the role of mTORC1 in DKD and developing new therapeutic agents that suppress mTORC1 hyperactivity may shed new light on DKD treatments in the future.

Regulation and metabolic functions of mTORC1 and mTORC2

Cells metabolize nutrients for biosynthetic and bioenergetic needs to fuel growth and proliferation. The uptake of nutrients from the environment and their intracellular metabolism is a highly controlled process that involves cross talk between growth signaling and metabolic pathways. Despite constant fluctuations in nutrient availability and environmental signals, normal cells restore metabolic homeostasis to maintain cellular functions and prevent disease. A central signaling molecule that integrates growth with metabolism is the mechanistic target of rapamycin (mTOR). mTOR is a protein kinase that responds to levels of nutrients and growth signals. mTOR forms two protein complexes, mTORC1, which is sensitive to rapamycin, and mTORC2, which is not directly inhibited by this drug. Rapamycin has facilitated the discovery of the various functions of mTORC1 in metabolism. Genetic models that disrupt either mTORC1 or mTORC2 have expanded our knowledge of their cellular, tissue, as well as systemic functions in metabolism. Nevertheless, our knowledge of the regulation and functions of mTORC2, particularly in metabolism, has lagged behind. Since mTOR is an important target for cancer, aging, and other metabolism-related pathologies, understanding the distinct and overlapping regulation and functions of the two mTOR complexes is vital for the development of more effective therapeutic strategies. This review discusses the key discoveries and recent findings on the regulation and metabolic functions of the mTOR complexes. We highlight findings from cancer models but also discuss other examples of the mTOR-mediated metabolic reprogramming occurring in stem and immune cells, type 2 diabetes/obesity, neurodegenerative disorders, and aging.

mTOR-targeted cancer therapy: great target but disappointing clinical outcomes, why?

The mammalian target of rapamycin (mTOR) critically regulates several essential biological functions, such as cell growth, metabolism, survival, and immune response by forming two important complexes, namely, mTOR complex 1 (mTORC1) and complex 2 (mTORC2). mTOR signaling is often dysregulated in cancers and has been considered an attractive cancer therapeutic target. Great efforts have been made to develop efficacious mTOR inhibitors, particularly mTOR kinase inhibitors, which suppress mTORC1 and mTORC2; however, major success has not been achieved. With the strong scientific rationale, the intriguing question is why cancers are insensitive or not responsive to mTOR-targeted cancer therapy in clinics. Beyond early findings on induced activation of PI3K/Akt, MEK/ERK, and Mnk/eIF4E survival signaling pathways that compromise the efficacy of rapalog-based cancer therapy, recent findings on the essential role of GSK3 in mediating cancer cell response to mTOR inhibitors and mTORC1 inhibition-induced upregulation of PD-L1 in cancer cells may provide some explanations. These new findings may also offer us the opportunity to rationally utilize mTOR inhibitors in cancer therapy. Further elucidation of the biology of complicated mTOR networks may bring us the hope to develop effective therapeutic strategies with mTOR inhibitors against cancer.

γ-aminobutyric acid stimulates β-cell proliferation through the mTORC1/p70S6K pathway, an effect amplified by Ly49, a novel γ-aminobutyric acid type A receptor positive allosteric modulator

AIM

To examine the mechanism of action of γ-aminobutyric acid (GABA) on β-cell proliferation and investigate if co-treatment with Ly49, a novel GABA type A receptor positive allosteric modulator (GABA_A -R PAM), amplifies this effect.

METHODS

Human or mouse islets were co-treated for 4-5 days with GABA and selected receptor or cell signalling pathway modulators. Immunofluorescence was used to determine protein co-localization, cell number or proliferation, and islet size. Osmotic minipumps were surgically implanted in mice to assess Ly49 effects on pancreatic β-cells.

RESULTS

Amplification of GABA_A -R signalling enhanced GABA-stimulated β-cell proliferation in cultured mouse islets. Co-treatment of GABA with an inhibitor specific for PI3K, mTORC1/2, or p70S6K, abolished GABA-stimulated β-cell proliferation in mouse and human islets. Nuclear p-Akt^Ser473 and p-p70S6K^{Thr421/Ser424} expression in pancreatic β-cells was increased in GABA-treated mice compared with vehicle-treated mice, an effect augmented with GABA and Ly49 co-treatment. Mice co-treated with GABA and Ly49 exhibited enhanced β-cell area and proliferation compared with GABA-treated mice. Furthermore, S961 injection (an insulin receptor antagonist) resulted in enhanced plasma insulin in GABA and Ly49 co-treated mice compared with GABA-treated mice. Importantly, GABA co-treated with Ly49 increased β-cell proliferation in human islets providing a potential application for human subjects.

CONCLUSIONS

We show that GABA stimulates β-cell proliferation via the PI3K/mTORC1/p70S6K pathway in both mouse and human islets. Furthermore, we show that Ly49 enhances the β-cell regenerative effects of GABA, showing potential in the intervention of diabetes.

In Silico Analyses and Cytotoxicity Study of Asiaticoside and Asiatic Acid from Malaysian Plant as Potential mTOR Inhibitors

Natural products remain a popular alternative treatment for many ailments in various countries. This study aimed to screen for potential mammalian target of rapamycin (mTOR) inhibitors from Malaysian natural substance, using the Natural Product Discovery database, and to determine the IC₅₀ of the selected mTOR inhibitors against UMB1949 cell line. The crystallographic structure of the molecular target (mTOR) was obtained from Protein Data Bank, with Protein Data Bank (PDB) ID: 4DRI. Everolimus, an mTOR inhibitor, was used as a standard compound for the comparative analysis. Computational docking approach was performed, using AutoDock Vina (screening) and AutoDock 4.2.6 (analysis). Based on our analysis, asiaticoside and its derivative, asiatic acid, both from Centella asiatica, revealed optimum-binding affinities with mTOR that were comparable to our standard compound. The effect of asiaticoside and asiatic acid on mTOR inhibition was validated with UMB1949 cell line, and their IC₅₀ values were 300 and 60 µM, respectively, compared to everolimus (29.5 µM). Interestingly, this is the first study of asiaticoside and asiatic acid against tuberous sclerosis complex (TSC) disease model by targeting mTOR. These results, coupled with our in silico findings, should prompt further studies, to clarify the mode of action, safety, and efficacy of these compounds as mTOR inhibitors.

Chemical Biology Toolbox for Studying Pancreatic Islet Function - A Perspective

The islets of Langerhans represent one of the many complex endocrine organs in mammals. Traditionally, islet function is studied by a mixture of physiological, cell biological, and molecular biological methods. Recently, novel techniques stemming from the ever-increasing toolbox provided by chemical laboratories have been added to the repertoire. Many emerging techniques will soon be available to manipulate and monitor islet function at the single-cell level and potentially in intact model animals, as well as in isolated human islets. Here, we review the most current small-molecule-based and genetically encoded molecular tool sets available to study islet function. We provide an outlook regarding future tool developments that will impact islet research, with a special focus on the interplay between different islet cell types.

Atorvastatin Targets the Islet Mevalonate Pathway to Dysregulate mTOR Signaling and Reduce β-Cell Functional Mass

Statins are cholesterol-lowering agents that increase the incidence of diabetes and impair glucose tolerance via their detrimental effects on nonhepatic tissues, such as pancreatic islets, but the underlying mechanism has not been determined. In atorvastatin (ator)-treated high-fat diet-fed mice, we found reduced pancreatic β-cell size and β-cell mass, fewer mature insulin granules, and reduced insulin secretion and glucose tolerance. Transcriptome profiling of primary pancreatic islets showed that ator inhibited the expression of pancreatic transcription factor, mechanistic target of rapamycin (mTOR) signaling, and small G protein (sGP) genes. Supplementation of the mevalonate pathway intermediate geranylgeranyl pyrophosphate (GGPP), which is produced by 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, significantly restored the attenuated mTOR activity, v-maf musculoaponeurotic fibrosarcoma oncogene homolog A (MafA) expression, and β-cell function after ator, lovastatin, rosuvastatin, and fluvastatin treatment; this effect was potentially mediated by sGP prenylation. Rab5a, the sGP in pancreatic islets most affected by ator treatment, was found to positively regulate mTOR signaling and β-cell function. Rab5a knockdown mimicked the effect of ator treatment on β-cells. Thus, ator impairs β-cell function by regulating sGPs, for example, Rab5a, which subsequently attenuates islet mTOR signaling and reduces functional β-cell mass. GGPP supplementation could constitute a new approach for preventing statin-induced hyperglycemia.

Epimagnolin targeting on an active pocket of mammalian target of rapamycin suppressed cell transformation and colony growth of lung cancer cells

Mammalian target of rapamycin (mTOR) has a pivotal role in carcinogenesis and cancer cell proliferation in diverse human cancers. In this study, we observed that epimagnolin, a natural compound abundantly found in Shin-Yi, suppressed cell proliferation by inhibition of epidermal growth factor (EGF)-induced G1/S cell-cycle phase transition in JB6 Cl41 cells. Interestingly, epimagnolin suppressed EGF-induced Akt phosphorylation strongly at Ser473 and weakly at Thr308 without alteration of phosphorylation of MAPK/ERK kinases (MEKs), extracellular signal-regulated kinase (ERKs), and RSK1, resulting in abrogation of the phosphorylation of GSK3β at Ser9 and p70S6K at Thr389. Moreover, we found that epimagnolin suppressed c-Jun phosphorylation at Ser63/73, resulting in the inhibition of activator protein 1 (AP-1) transactivation activity. Computational docking indicated that epimagnolin targeted an active pocket of the mTOR kinase domain by forming three hydrogen bonds and three hydrophobic interactions. The prediction was confirmed by using in vitro kinase and adenosine triphosphate-bead competition assays. The inhibition of mTOR kinase activity resulted in the suppression of anchorage-independent cell transformation. Importantly, epimagnolin efficiently suppressed cell proliferation and anchorage-independent colony growth of H1650 rather than H460 lung cancer cells with dependency of total and phosphorylated protein levels of mTOR and Akt. Inhibitory signaling of epimagnolin on cell proliferation of lung cancer cells was observed mainly in mTOR-Akt-p70S6K and mTOR-Akt-GSK3β-AP-1, which was similar to that shown in JB6 Cl41 cells. Taken together, our results indicate that epimagnolin potentiates as chemopreventive or therapeutic agents by direct active pocket targeting of mTOR kinase, resulting in sensitizing cancer cells harboring enhanced phosphorylation of the mTORC2-Akt-p70S6k signaling pathway.

A Chromatin-Mimetic Nanomedicine for Therapeutic Tolerance Induction

The undesirable immune response poses a life-threatening challenge to human health. It not only deteriorates the therapeutic performance of biologic drugs but also contributes to various diseases such as allergies and autoimmune diseases. Inspired by the role of chromatin in the maintenance of natural immune tolerance, here we report a DNA-protein polymeric nanocomplex that can mimic the tolerogenic function of chromatin and induce an immune tolerance to its protein cargos. We first proved that the chromatin-mimetic nanomedicine loaded with keyhole limpet hemocyanin (KLH), a highly immunogenic model protein, could elicit a durable antigen-specific immune tolerance to KLH lasting for at least five weeks in mice. Following the proof-of-concept study, we demonstrated that this nanomedicine could be applied to improve the safety and efficacy of a biologic drug, PEGylated uricase, by attenuating the relevant antibody (Ab) responses. Moreover, we also demonstrated that prophylactic treatments with this nanomedicine could tolerize the immune system with the allergen of ovalbumin (OVA) and thus inhibit the occurrence of airway inflammation in an OVA-induced allergic asthma murine model. Collectively, our work illustrates a nature-inspired concept of immune tolerance induction and establishes a useful tool to specifically suppress unwanted immune responses for therapeutic purposes.

The effects of AICAR and rapamycin on mitochondrial function in immortalized mitochondrial DNA mutator murine embryonic fibroblasts

Mitochondrial DNA mutations accumulate with age and may play a role in stem cell aging as suggested by the premature aging phenotype of mitochondrial DNA polymerase gamma (POLG) exonuclease-deficient mice. Therefore, E1A immortalized murine embryonic fibroblasts (MEFs) from POLG exonuclease-deficient and wild-type (WT) mice were constructed. Surprisingly, when some E1A immortalized MEF lines were cultured in pyruvate-containing media they slowly became addicted to the pyruvate. The POLG exonuclease-deficient MEFs were more sensitive to several mitochondrial inhibitors and showed increased reactive oxygen species (ROS) production under standard conditions. When cultured in pyruvate-containing media, POLG exonuclease-deficient MEFs showed decreased oxygen consumption compared to controls. Increased AMP-activated protein kinase (AMPK) signaling and decreased mammalian target of rapamycin (mTOR) signaling delayed aging and influenced mitochondrial function. Therefore, the effects of 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), an AMPK activator, or rapamycin, an mTOR inhibitor, on measures of mitochondrial function were determined. Rapamycin treatment transiently increased respiration only in WT MEFs and, under most conditions, increased ATP levels. Short term AICAR treatment transiently increased ROS production and, under most conditions, decreased ATP levels. Chronic AICAR treatment decreased respiration and ROS production in WT MEFs. These results demonstrate the context-dependent effects of AICAR and rapamycin on mitochondrial function.

Summary: A novel mitochondrial DNA mutator murine embryonic fibroblast cell line was created and the effects of the anti-aging compounds rapamycin and AICAR on energy metabolism in these cells was determined.

Design, synthesis and activity of Mnk1 and Mnk2 selective inhibitors containing thieno[2,3-d]pyrimidine scaffold

The mitogen-activated protein kinase-interacting kinases 1 and 2 (MNK1 and MNK2) phosphorylate eukaryotic initiation factor 4E (eIF4E) and play important roles in promoting tumorigenesis and metabolic disease. Thus, inhibiting these enzymes might be valuable in the treatment of such conditions. We designed and synthesized a series of 4-((4-fluoro-2-isopropoxyphenyl)amino)-5-methylthieno[2,3-d]pyrimidine derivatives, and evaluated their inhibitory activity against the MNKs. We found 15 compounds that were active as MNK inhibitors and that one in particular, designated MNK-7g, which was potent against MNK1 and substantially more potent against MNK2. The compound MNK-7g did not affect other signaling pathways tested and had no adverse effects on cell viability. As expected from earlier studies, MNK-7g also inhibited cell migration. Therefore, the compound MNK-7g, which forms an ionic bond with Asp226 in MNK2 and possesses a substituted aniline in a thieno[2,3-d] pyrimidine structure, is a promising starting point for the future development of novel drugs for treating or managing cancer and metabolic disease.

mTOR Inhibitor Therapy and Metabolic Consequences: Where Do We Stand?

mTOR (mechanistic target of rapamycin) protein kinase acts as a central integrator of nutrient signaling pathways. Besides the immunosuppressive role after solid organ transplantations or in the treatment of some cancers, another promising role of mTOR inhibitor as an antiaging therapeutic has emerged in the recent years. Acute or intermittent rapamycin treatment has some resemblance to calorie restriction in metabolic effects such as an increased insulin sensitivity. However, the chronic inhibition of mTOR by macrolide rapamycin or other rapalogs has been associated with glucose intolerance and insulin resistance and may even provoke type II diabetes. These metabolic adverse effects limit the use of mTOR inhibitors. Metformin is a widely used drug for the treatment of type 2 diabetes which activates AMP-activated protein kinase (AMPK), acting as calorie restriction mimetic. In addition to the glucose-lowering effect resulting from the decreased hepatic glucose production and increased glucose utilization, metformin induces fatty acid oxidations. Here, we review the recent advances in our understanding of the metabolic consequences regarding glucose metabolism induced by mTOR inhibitors and compare them to the metabolic profile provoked by metformin use. We further suggest metformin use concurrent with rapalogs in order to pharmacologically address the impaired glucose metabolism and prevent the development of new-onset diabetes mellitus after solid organ transplantations induced by the chronic rapalog treatment.

Who does TORC2 talk to?

The target of rapamycin (TOR) is a protein kinase that, by forming complexes with partner proteins, governs diverse cellular signalling networks to regulate a wide range of processes. TOR thus plays central roles in maintaining normal cellular functions and, when dysregulated, in diverse diseases. TOR forms two distinct types of multiprotein complexes (TOR complexes 1 and 2, TORC1 and TORC2). TORC1 and TORC2 differ in their composition, their control and their substrates, so that they play quite distinct roles in cellular physiology. Much effort has been focused on deciphering the detailed regulatory links within the TOR pathways and the structure and control of TOR complexes. In this review, we summarize recent advances in understanding mammalian (m) TORC2, its structure, its regulation, and its substrates, which link TORC2 signalling to the control of cell functions. It is now clear that TORC2 regulates several aspects of cell metabolism, including lipogenesis and glucose transport. It also regulates gene transcription, the cytoskeleton, and the activity of a subset of other protein kinases.

Everolimus Directly Suppresses Insulin Secretion Independently of Cell Growth Inhibition

Everolimus, an orally administered mammalian target of rapamycin inhibitor, has been widely used as an immunosuppressant and an anticancer agent. Whereas everolimus can control recurrent hypoglycemia in patients with insulinoma, possibly through tumor regression and/or the direct inhibition of insulin secretion, time-dependent changes in serum insulin levels caused by everolimus still remain unclear. Here we report a clinical case of a patient with metastatic insulinoma, in which frequent monitoring of serum insulin levels demonstrated rapid and substantial changes in insulin secretion levels, a few days after the discontinuation as well as the readministration of everolimus. To further confirm the direct effect of everolimus on β-cell function, we performed in vitro experiments using mouse insulinoma cells (MIN6) and human induced pluripotent stem cell (hiPSC)–derived insulin-producing cells and found that everolimus significantly suppressed glucose-stimulated insulin secretion in both MIN6 cells and hiPSC–derived insulin-producing cells. Thus, both a patient with metastatic insulinoma and in vitro experiments demonstrated that everolimus directly suppresses insulin secretion, independently of its tumor regression effect.

Cardioprotective effects of dietary rapamycin on adult female C57BLKS/J-Leprdb mice

Rapamycin (RAPA), an inhibitor of mTORC signaling, has been shown to extend life span in mice and other organisms. Recently, animal and human studies have suggested that inhibition of mTORC signaling can alleviate or prevent the development of cardiomyopathy. In view of this, we used a murine model of type 2 diabetes (T2D), BKS-Leprdb , to determine whether RAPA treatment can mitigate the development of T2D-induced cardiomyopathy in adult mice. Female BKS-Leprdb mice fed diet supplemented with RAPA from 11 to 27 weeks of age showed reduced weight gain and significant reductions of fat and lean mass compared with untreated mice. No differences in plasma glucose or insulin levels were observed between groups; however, RAPA-treated mice were more insulin sensitive (P < 0.01) than untreated mice. Urine albumin/creatinine ratio was lower in RAPA-treated mice, suggesting reduced diabetic nephropathy and improved kidney function. Echocardiography showed significantly reduced left ventricular wall thickness in mice treated with RAPA compared with untreated mice (P = 0.02) that was consistent with reduced heart weight/tibia length ratios, reduced myocyte size and cardiac fibrosis measured by histomorphology, and reduced mRNA expression of Col1a1, a marker for cardiomyopathy. Our results suggest that inhibition of mTORC signaling is a plausible strategy for ameliorating complications of obesity and T2D, including cardiomyopathy.

mTORC2 Signaling: A Path for Pancreatic β Cell's Growth and Function

The mechanistic target of rapamycin (mTOR) signaling pathway is an evolutionary conserved pathway that senses signals from nutrients and growth factors to regulate cell growth, metabolism and survival. mTOR acts in two biochemically and functionally distinct complexes, mTOR complex 1 (mTORC1) and 2 (mTORC2), which differ in terms of regulatory mechanisms, substrate specificity and functional outputs. While mTORC1 signaling has been extensively studied in islet/β-cell biology, recent findings demonstrate a distinct role for mTORC2 in the regulation of pancreatic β-cell function and mass. mTORC2, a key component of the growth factor receptor signaling, is declined in β cells under diabetogenic conditions and in pancreatic islets from patients with type 2 diabetes. β cell-selective mTORC2 inactivation leads to glucose intolerance and acceleration of diabetes as a result of reduced β-cell mass, proliferation and impaired glucose-stimulated insulin secretion. Thereby, many mTORC2 targets, such as AKT, PKC, FOXO1, MST1 and cell cycle regulators, play an important role in β-cell survival and function. This indicates mTORC2 as important pathway for the maintenance of β-cell homeostasis, particularly to sustain proper β-cell compensatory response in the presence of nutrient overload and metabolic demand. This review summarizes recent emerging advances on the contribution of mTORC2 and its associated signaling on the regulation of glucose metabolism and functional β-cell mass under physiological and pathophysiological conditions in type 2 diabetes.

mTORC1 Signaling: A Double-Edged Sword in Diabetic β Cells

The mechanistic target of rapamycin complex 1 (mTORC1) is a central regulator of metabolic and nutrient cues that integrates environmental inputs into downstream signaling pathways to control cellular metabolism, growth, and survival. While numerous in vitro and in vivo studies reported the positive functions of mTORC1 in the regulation of β cell survival and proliferation under physiological conditions, more recent work demonstrates the opposite in the long term; this is exemplified by the constitutive inappropriate hyper-activation of mTORC1 in diabetic islets or β cells under conditions of increased β cell stress and metabolic demands. These recent findings uncover mTORC1's importance as an emerging significant player in the development and progression of β cell failure in type 2 diabetes and suggest that mTORC1 may act as a "double edge sword" in the regulation of β cell mass and function in response to metabolic stress such as nutrient overload and insulin resistance.

Human antibody-based chemically induced dimerizers for cell therapeutic applications

Chemically induced dimerizers (CIDs) have emerged as one of the most powerful tools to artificially regulate signaling pathways in cells; however, currently available CID systems lack the properties desired for use in regulating cellular therapies. Here, we report the development of human antibody-based chemically induced dimerizers (AbCIDs) from known small-molecule-protein complexes by selecting for synthetic antibodies that recognize the chemical epitope created by the bound small molecule. We demonstrate this concept by generating three antibodies that are highly selective for the BCL-xL/ABT-737 complex over BCL-xL alone. We show the potential of AbCIDs to be applied to regulating human cell therapies by using them to induce CRISPRa-mediated gene expression and to regulate CAR T-cell activation. We believe that the AbCIDs generated in this study will find application in regulating cell therapies, and that the general method of AbCID development may lead to the creation of many new and orthogonal CIDs.

Sirolimus induces depletion of intracellular calcium stores and mitochondrial dysfunction in pancreatic beta cells

Sirolimus (rapamycin) is an immunosuppressive drug used in transplantation. One of its major side effects is the increased risk of diabetes mellitus; however, the exact mechanisms underlying such association have not been elucidated. Here we show that sirolimus impairs glucose-stimulated insulin secretion both in human and murine pancreatic islets and in clonal β cells in a dose- and time-dependent manner. Importantly, we demonstrate that sirolimus markedly depletes calcium (Ca²⁺) content in the endoplasmic reticulum and significantly decreases glucose-stimulated mitochondrial Ca²⁺ uptake. Crucially, the reduced mitochondrial Ca²⁺ uptake is mirrored by a significant impairment in mitochondrial respiration. Taken together, our findings indicate that sirolimus causes depletion of intracellular Ca²⁺ stores and alters mitochondrial fitness, eventually leading to decreased insulin release. Our results provide a novel molecular mechanism underlying the increased incidence of diabetes mellitus in patients treated with this drug.

Angiotensin II Causes β-Cell Dysfunction Through an ER Stress-Induced Proinflammatory Response

The metabolic syndrome is associated with an increase in the activation of the renin angiotensin system, whose inhibition reduces the incidence of new-onset diabetes. Importantly, angiotensin II (AngII), independently of its vasoconstrictor action, causes β-cell inflammation and dysfunction, which may be an early step in the development of type 2 diabetes. The aim of this study was to determine how AngII causes β-cell dysfunction. Islets of Langerhans were isolated from C57BL/6J mice that had been infused with AngII in the presence or absence of taurine-conjugated ursodeoxycholic acid (TUDCA) and effects on endoplasmic reticulum (ER) stress, inflammation, and β-cell function determined. The mechanism of action of AngII was further investigated using isolated murine islets and clonal β cells. We show that AngII triggers ER stress, an increase in the messenger RNA expression of proinflammatory cytokines, and promotes β-cell dysfunction in murine islets of Langerhans both in vivo and ex vivo. These effects were significantly attenuated by TUDCA, an inhibitor of ER stress. We also show that AngII-induced ER stress is required for the increased expression of proinflammatory cytokines and is caused by reactive oxygen species and IP3 receptor activation. These data reveal that the induction of ER stress is critical for AngII-induced β-cell dysfunction and indicates how therapies that promote ER homeostasis may be beneficial in the prevention of type 2 diabetes.

Inhibiting 4EBP1 in Glioblastoma

Glioblastoma is the most common and aggressive adult brain cancer. Tumors show frequent dysregulation of the PI3K-mTOR pathway. Although a number of small molecules target the PI3K-AKT-mTOR axis, their preclinical and clinical efficacy has been limited. Reasons for treatment failure include poor penetration of agents into the brain and observations that blockade of PI3K or AKT minimally affects downstream mTOR activity in glioma. Clinical trials using allosteric mTOR inhibitors (rapamycin and rapalogs) to treat patients with glioblastoma have also been unsuccessful or uncertain, in part, because rapamycin inefficiently blocks the mTORC1 target 4EBP1 and feeds back to activate PI3K-AKT signaling. Inhibitors of the mTOR kinase (TORKi) such as TAK-228/MLN0128 interact orthosterically with the ATP- and substrate-binding pocket of mTOR kinase, efficiently block 4EBP1 in vitro, and are currently being investigated in the clinical trials. Preclinical studies suggest that TORKi have poor residence times of mTOR kinase, and our data suggest that this poor pharmacology translates into disappointing efficacy in glioblastoma xenografts. RapaLink-1, a TORKi linked to rapamycin, represents a drug with improved pharmacology against 4EBP1. In this review, we clarify the importance of 4EBP1 as a biomarker for the efficacy of PI3K-AKT-mTOR inhibitors in glioblastoma. We also review mechanistic data by which RapaLink-1 blocks p-4EBP1 and discuss future clinical strategies for 4EBP1 inhibition in glioblastoma. Clin Cancer Res; 24(1); 14-21. ©2017 AACR.

mTOR inhibitors in cancer therapy

The mammalian target of rapamycin, mTOR, plays key roles in cell growth and proliferation, acting at the catalytic subunit of two protein kinase complexes: mTOR complexes 1 and 2 (mTORC1/2). mTORC1 signaling is switched on by several oncogenic signaling pathways and is accordingly hyperactive in the majority of cancers. Inhibiting mTORC1 signaling has therefore attracted great attention as an anti-cancer therapy. However, progress in using inhibitors of mTOR signaling as therapeutic agents in oncology has been limited by a number of factors, including the fact that the classic mTOR inhibitor, rapamycin, inhibits only some of the effects of mTOR; the existence of several feedback loops; and the crucial importance of mTOR in normal physiology.

Toxicity of rapamycin and its derivatives to pancreatic islets

The development of islet transplantation has been promoted by the proposal of the Edmonton protocol. Rapamycin, as a recommended immunosuppressive medicine of the Edmonton protocol, has been getting extraordinarily popular. At the same time, derivatives of rapamycin (everolimus, deforolimus, zotarolimus and temsirolimus) have also garnered great interest. While the immunosuppressive and anti-cancer effects of rapalogs were being discussed actively, researchers discovered their cytotoxic effect on pancreatic islets. Whether they could be ideal drugs for anti-rejection after islet transplantation needs further study. This review aims to elucidate the function and application of rapalogs as well as their toxicity to pancreatic islets.

The Mechanistic Target of Rapamycin: The Grand ConducTOR of Metabolism and Aging

Since the discovery that rapamycin, a small molecule inhibitor of the protein kinase mTOR (mechanistic target of rapamycin), can extend the lifespan of model organisms including mice, interest in understanding the physiological role and molecular targets of this pathway has surged. While mTOR was already well known as a regulator of growth and protein translation, it is now clear that mTOR functions as a central coordinator of organismal metabolism in response to both environmental and hormonal signals. This review discusses recent developments in our understanding of how mTOR signaling is regulated by nutrients and the role of the mTOR signaling pathway in key metabolic tissues. Finally, we discuss the molecular basis for the negative metabolic side effects associated with rapamycin treatment, which may serve as barriers to the adoption of rapamycin or similar compounds for the treatment of diseases of aging and metabolism.

GSK3 is required for rapalogs to induce degradation of some oncogenic proteins and to suppress cancer cell growth

The single-agent activity of rapalogs (rapamycin and its analogues) in most tumor types has been modest at best. The underlying mechanisms are largely unclear. In this report, we have uncovered a critical role of GSK3 in regulating degradation of some oncogenic proteins induced by rapalogs and cell sensitivity to rapalogs. The basal level of GSK3 activity was positively correlated with cell sensitivity of lung cancer cell lines to rapalogs. GSK3 inhibition antagonized rapamycin's growth inhibitory effects both in vitro and in vivo, while enforced activation of GSK3β sensitized cells to rapamycin. GSK3 inhibition rescued rapamcyin-induced reduction of several oncogenic proteins such as cyclin D1, Mcl-1 and c-Myc, without interfering with the ability of rapamycin to suppress mTORC1 signaling and cap binding. Interestingly, rapamycin induces proteasomal degradation of these oncogenic proteins, as evidenced by their decreased stabilities induced by rapamcyin and rescue of their reduction by proteasomal inhibition. Moreover, acute or short-time rapamycin treatment dissociated not only raptor, but also rictor from mTOR in several tested cell lines, suggesting inhibition of both mTORC1 and mTORC2. Thus, induction of GSK3-dependent degradation of these oncogenic proteins is likely secondary to mTORC2 inhibition; this effect should be critical for rapamycin to exert its anticancer activity.

Treatment with Tacrolimus and Sirolimus Reveals No Additional Adverse Effects on Human Islets In Vitro Compared to Each Drug Alone but They Are Reduced by Adding Glucocorticoids

Tacrolimus and sirolimus are important immunosuppressive drugs used in human islet transplantation; however, they are linked to detrimental effects on islets and reduction of long-term graft function. Few studies investigate the direct effects of these drugs combined in parallel with single drug exposure. Human islets were treated with or without tacrolimus (30 μg/L), sirolimus (30 μg/L), or a combination thereof for 24 hrs. Islet function as well as apoptosis was assessed by glucose-stimulated insulin secretion (GSIS) and Cell Death ELISA. Proinflammatory cytokines were analysed by qRT-PCR and Bio-Plex. Islets exposed to the combination of sirolimus and tacrolimus were treated with or without methylprednisolone (1000 μg/L) and the expression of the proinflammatory cytokines was investigated. We found the following: (i) No additive reduction in function and viability in islets existed when tacrolimus and sirolimus were combined compared to the single drug. (ii) Increased expression of proinflammatory cytokines mRNA and protein levels in islets took place. (iii) Methylprednisolone significantly decreased the proinflammatory response in islets induced by the drug combination. Although human islets are prone to direct toxic effect of tacrolimus and sirolimus, we found no additive effects of the drug combination. Short-term exposure of glucocorticoids could effectively reduce the proinflammatory response in human islets induced by the combination of tacrolimus and sirolimus.

The cannabinoid CB1 receptor and mTORC1 signalling pathways interact to modulate glucose homeostasis in mice

The endocannabinoid system (ECS) is an intercellular signalling mechanism that is present in the islets of Langerhans and plays a role in the modulation of insulin secretion and expansion of the β-cell mass. The downstream signalling pathways mediating these effects are poorly understood. Mammalian target of rapamycin complex 1 (mTORC1) signalling is a key intracellular pathway involved in energy homeostasis and is known to importantly affect the physiology of pancreatic islets. We investigated the possible relationship between cannabinoid type 1 (CB₁) receptor signalling and the mTORC1 pathway in the endocrine pancreas of mice by using pharmacological analysis as well as mice genetically lacking the CB₁ receptor or the downstream target of mTORC1, the kinase p70S6K1. In vitro static secretion experiments on islets, western blotting, and in vivo glucose and insulin tolerance tests were performed. The CB₁ receptor antagonist rimonabant decreased glucose-stimulated insulin secretion (GSIS) at 0.1 µM while increasing phosphorylation of p70S6K1 and ribosomal protein S6 (rpS6) within the islets. Specific pharmacological blockade of mTORC1 by 3 nM rapamycin, as well as genetic deletion of p70S6K1, impaired the CB₁-antagonist-mediated decrease in GSIS. In vivo experiments showed that 3 mg/kg body weight rimonabant decreased insulin levels and induced glucose intolerance in lean mice without altering peripheral insulin sensitivity; this effect was prevented by peripheral administration of low doses of rapamycin (0.1 mg/kg body weight), which increased insulin sensitivity. These findings suggest a functional interaction between the ECS and the mTORC1 pathway within the endocrine pancreas and at the whole-organism level, which could have implications for the development of new therapeutic approaches for pancreatic β-cell diseases.

Summary: Evidence supporting a functional interaction between the endocannabinoid system and the mTORC1 pathway within the endocrine pancreas, which could have implications for the development of new therapeutic approaches for diabetes.

Moderate calorie restriction to achieve normal weight reverses β-cell dysfunction in diet-induced obese mice: involvement of autophagy

Background

Severe calorie restriction (CR) is shown to improve or even reverse β-cell dysfunction in patients with obesity and type 2 diabetes mellitus. However, whether mild to moderate CR can reverse β-cell dysfunction induced by obesity and the underlying mechanism remain unclear. Autophagy plays an important role in maintaining mass, architecture and function of β-cells. While the impact of CR on β-cell autophagy is unknown. This study aims to investigate the effects of moderate CR on β-cell function and autophagy activity in diet-induced obese (DIO) mice.

Methods

DIO C57BL/6 mice were subjected to 3 weeks of switching to normal chow (HF → NC group) or normal chow with 40 % CR (HF → NC CR group). Then hematoxylin-eosin and immunohistochemistry staining were performed to observe β-cell morphology. β-cell function was evaluated by intraperitoneal glucose tolerance test in vivo and static GSIS (glucose-stimulated insulin secretion) in isolated islets. β-cell autophagy activity was determined by transmission electron microscope and western blot.

Results

In the HF → NC CR group, CR normalized body weights, completely restored glucose tolerance, early-phase and second-phase insulin secretion, insulin sensitivity, and islet size. CR also normalized insulin content and glucose-stimulated insulin secretion in isolated islets in vitro. Furthermore, β-cell autophagy level was increased in the HF → NC CR group, but AMPK phosphorylation remained unchanged. Although HF → NC mice achieved moderate weight loss and normal glucose tolerance, their insulin secretion was not improved compared with obese control mice, and additionally, β-cell autophagy was not activated in these mice.

Conclusions

Moderate (40 %) CR to achieve normal weight reversed β-cell dysfunction and insulin resistance, and restored glucose homeostasis in DIO mice. Furthermore, the up-regulation of β-cell autophagy may play a role in this process, independent of AMPK activation.

Beneficial Effects of Early mTORC1 Inhibition after Traumatic Brain Injury

The mammalian target of rapamycin complex 1 (mTORC1) signaling pathway mediates many aspects of cell growth and regeneration and is upregulated after moderate to severe traumatic brain injury (TBI). The significance of this increased signaling event for recovery of brain function is presently unclear. We analyzed the time course and cell specificity of mTORC1 signal activation in the mouse hippocampus after moderate controlled cortical impact (CCI) and identified an early neuronal peak of activity that occurs within a few hours after injury. We suppressed this peak activity by a single injection of the mTORC1 inhibitor rapamycin 1 h after CCI and showed that this acute treatment significantly diminishes the extent of neuronal death, astrogliosis, and cognitive impairment 1-3 days after injury. Our findings suggest that the early neuronal peak of mTORC1 activity after TBI is deleterious to brain function, and that acute, early intervention with mTORC1 inhibitors after injury may represent an effective form of treatment to improve recovery in human patients.

Sirolimus therapy in a patient with severe hyperinsulinaemic hypoglycaemia due to a compound heterozygous ABCC8 gene mutation

INTRODUCTION

Hyperinsulinaemic hypoglycaemia (HH) is the most common cause of severe and persistent hypoglycaemia in neonates. The treatment of severe diazoxide unresponsive HH involves near total pancreatectomy. Mammalian target of rapamycin (mTOR) is a protein kinase that regulates cellular proliferation. mTOR inhibitors are used in cancer patients and recently found to be effective in the treatment of insulinoma and HH patients.

CASE

A 36 weeks large for gestational age neonate presented with severe hypoglycaemia on day 1 of life. The hypoglycaemia screen confirmed HH and genetic testing revealed compound heterozygous ABCC8 mutation, confirming diffuse disease. He was unresponsive to the maximal dose of diazoxide (15 mg/kg/day), hence needed treatment with higher concentration of intravenous glucose (25 mg/kg/min), intravenous glucagon and subcutaneous octreotide (30 μg/kg/day) infusions to maintain normoglycaemia. Sirolimus, a mTOR inhibitor, was commenced at 9 weeks of age following which he showed a marked improvement in his glycaemic control. After 4 weeks of sirolimus therapy, he was discharged home on subcutaneous octreotide injection (20 μg/kg/day) and oral sirolimus, thereby avoiding the need for a near total pancreatectomy.

CONCLUSION

We report the first case of compound heterozygous ABCC8 mutation causing severe diffuse HH that responded to therapy with a mTOR inhibitor.

The MAP kinase-interacting kinases regulate cell migration, vimentin expression and eIF4E/CYFIP1 binding

The MAP kinase-interacting kinases (Mnk1 and Mnk2) are activated by ERK and are best known for phosphorylating the translation initiation factor eIF4E. Genetic knockout of the Mnks impaired the migration of embryonic fibroblasts both in two-dimensional wound-healing experiments and in three-dimensional migration assays. Furthermore, a novel and selective Mnk inhibitor, Mnk-I1, which potently blocks eIF4E phosphorylation, blocked the migration of fibroblasts and cancer cells, without exerting ‘off-target’ effects on other signalling pathways such as Erk. Mnk-I1 or genetic knockout of the Mnks decreased the expression of vimentin, a marker of mesenchymal cells, without affecting vimentin mRNA levels. Vimentin protein levels were much lower in Mnk1/2-knockout cells than in controls, although mRNA levels were similar. Our data suggest that the Mnks regulate the translation of the vimentin mRNA and the stability of the vimentin protein. Inhibition or genetic knockout of the Mnks increased the binding of eIF4E to the cytoplasmic FMRP-interacting protein 1 (CYFIP1), which binds the fragile-X mental retardation protein, FMRP, a translational repressor. Since FMRP binds mRNAs for proteins involved in metastasis, the Mnk-dependent release of CYFIP1 from eIF4E is expected to release the repression of translation of FMRP-bound mRNAs, potentially providing a molecular mechanism for the control of cell migration by the Mnks. As Mnk1/2 are not essential for viability, inhibition of the Mnks may be a useful approach to tackling cancer metastasis, a key process contributing to mortality in cancer patients.

Protection of pancreatic β-cells against glucotoxicity by short-term treatment with GLP-1

Glucagon-like peptide-1 (GLP-1) reduces pancreatic β-cell apoptosis in type 2 diabetes. Glucotoxiciy is a main cause of β-cell apoptosis in type 2 diabetes. The aims of this study were to investigate the anti-apoptotic mechanisms of GLP-1 against glucotoxicity and whether physiological short-term treatment with GLP-1 can protect β-cells from glucotoxicity-induced apoptosis. GLP-1 treatment for only 30 min alleviated high glucose-induced β-cell apoptosis. The effect of GLP-1 was related with phosphoinositide 3-kinase (PI3K)/AKT-S473 phosphorylation. The increase in pAKT-S473 led to suppression of FoxO-1. GLP-1-induced AKT-S473 activation and FoxO-1 suppression were abolished by the selective inactivation of mTOR complex (mTORC) 2 using small interfering RNA directed towards the rapamycin-insensitive companion of mTOR. The protective effect of GLP-1 on β-cell apoptosis was also abolished by the selective inactivation of mTORC2. Hence, the protective effect of GLP-1 against glucotoxicity may be mediated by FoxO-1 suppression through the PI3K/mTORC2/AKT-S473 phosphorylation. This report provides evidence that short-term treatment with GLP-1 is beneficial to protect against glucotoxicity-induced β-cell apoptosis.

GABAergic system in the endocrine pancreas: a new target for diabetes treatment

Excessive loss of functional pancreatic β-cell mass, mainly due to apoptosis, is a major factor in the development of hyperglycemia in both type 1 and type 2 diabetes (T1D and T2D). In T1D, β-cells are destroyed by immunological mechanisms. In T2D, while metabolic factors are known to contribute to β-cell failure and subsequent apoptosis, mounting evidence suggests that islet inflammation also plays an important role in the loss of β-cell mass. Therefore, it is of great importance for clinical intervention to develop new therapies. γ-Aminobutyric acid (GABA), a major neurotransmitter, is also produced by islet β-cells, where it functions as an important intraislet transmitter in regulating islet-cell secretion and function. Importantly, recent studies performed in rodents, including in vivo studies of xenotransplanted human islets, reveal that GABA exerts β-cell regenerative effects. Moreover, it protects β-cells against apoptosis induced by cytokines, drugs, and other stresses, and has anti-inflammatory and immunoregulatory activities. It ameliorates the manifestations of diabetes in preclinical models, suggesting potential applications for the treatment of diabetic patients. This review outlines the actions of GABA relevant to β-cell regeneration, including its signaling mechanisms and potential interactions with other mediators. These studies increase our understanding of the regenerative processes of pancreatic β-cells, and help pave the way for the development of regenerative medicine for diabetes.

Current models of mammalian target of rapamycin complex 1 (mTORC1) activation by growth factors and amino acids

Mammalian target of rapamycin (mTOR), which is now referred to as mechanistic target of rapamycin, integrates many signals, including those from growth factors, energy status, stress, and amino acids, to regulate cell growth and proliferation, protein synthesis, protein degradation, and other physiological and biochemical processes. The mTOR-Rheb-TSC-TBC complex co-localizes to the lysosome and the phosphorylation of TSC-TBC effects the dissociation of the complex from the lysosome and activates Rheb. GTP-bound Rheb potentiates the catalytic activity of mTORC1. Under conditions with growth factors and amino acids, v-ATPase, Ragulator, Rag GTPase, Rheb, hVps34, PLD1, and PA have important but disparate effects on mTORC1 activation. In this review, we introduce five models of mTORC1 activation by growth factors and amino acids to provide a comprehensive theoretical foundation for future research.

Pancreatic β-cell failure mediated by mTORC1 hyperactivity and autophagic impairment

Hyperactivation of the mammalian target of rapamycin complex 1 (mTORC1) in β-cells is usually found as a consequence of increased metabolic load. Although it plays an essential role in β-cell compensatory mechanisms, mTORC1 negatively regulates autophagy. Using a mouse model with β-cell-specific deletion of Tsc2 (βTsc2(-/-)) and, consequently, mTORC1 hyperactivation, we focused on the role that chronic mTORC1 hyperactivation might have on β-cell failure. mTORC1 hyperactivation drove an early increase in β-cell mass that later declined, triggering hyperglycemia. Apoptosis and endoplasmic reticulum stress markers were found in islets of older βTsc2(-/-) mice as well as accumulation of p62/SQSTM1 and an impaired autophagic response. Mitochondrial mass was increased in β-cells of βTsc2(-/-) mice, but mitophagy was also impaired under these circumstances. We provide evidence of β-cell autophagy impairment as a link between mTORC1 hyperactivation and mitochondrial dysfunction that probably contributes to β-cell failure.