Rapamycin induces glucose intolerance in mice by reducing islet mass, insulin content, and insulin sensitivity. J Mol Med (Berl). 2012;90:575-585. [PMID: 22105852 DOI: 10.1007/s00109-011-0834-3]

Low-dose interleukin-2 therapy: a driver of an imbalance between immune tolerance and autoimmunity

For many years, the role of interleukin-2 (IL-2) in autoimmune responses was established as a cytokine possessing strong pro-inflammatory activity. Studies of the past few years have changed our knowledge on IL-2 in autoimmune chronic inflammation, suggesting its protective role, when administered at low-doses. The disrupted balance between regulatory and effector T cells (Tregs and Teffs, respectively) is a characteristic of autoimmune diseases, and is dependent on homeostatic cytokines, including IL-2. Actually, inherent defects in the IL-2 signaling pathway and/or levels leading to Treg compromised function and numbers as well as Th17 expansion have been attributed to autoimmune disorders. In this review, we discuss the role of IL-2 in the pathogenesis of autoimmune diseases. In particular, we highlight the impact of the dysregulated IL-2 pathway on disruption of the Treg/Th17 balance, reversal of which appears to be a possible mechanism of the low-dose IL-2 treatment. The negative effects of IL-2 on the differentiation of follicular helper T cells (Tfh) and pathogenic Th17 cells, both of which contribute to autoimmunity, is emphasized in the paper as well. We also compare the current IL-2-based therapies of animal and human subjects with immune-mediated diseases aimed at boosting the Treg population, which is the most IL-2-dependent cell subset desirable for sufficient control of autoimmunity. New perspectives of therapeutic approaches focused on selective delivery of IL-2 to inflamed tissues, thus allowing local activity of IL-2 to be combined with its reduced systemic and pleiotropic toxicity, are also proposed in this paper.

HRES-1/Rab4-mediated depletion of Drp1 impairs mitochondrial homeostasis and represents a target for treatment in SLE

OBJECTIVE

Accumulation of mitochondria underlies T-cell dysfunction in systemic lupus erythematosus (SLE). Mitochondrial turnover involves endosomal traffic regulated by HRES-1/Rab4, a small GTPase that is overexpressed in lupus T cells. Therefore, we investigated whether (1) HRES-1/Rab4 impacts mitochondrial homeostasis and (2) Rab geranylgeranyl transferase inhibitor 3-PEHPC blocks mitochondrial accumulation in T cells, autoimmunity and disease development in lupus-prone mice.

METHODS

Mitochondria were evaluated in peripheral blood lymphocytes (PBL) of 38 SLE patients and 21 healthy controls and mouse models by flow cytometry, microscopy and western blot. MRL/lpr mice were treated with 125 μg/kg 3-PEHPC or 1 mg/kg rapamycin for 10 weeks, from 4 weeks of age. Disease was monitored by antinuclear antibody (ANA) production, proteinuria, and renal histology.

RESULTS

Overexpression of HRES-1/Rab4 increased the mitochondrial mass of PBL (1.4-fold; p=0.019) and Jurkat cells (2-fold; p=0.000016) and depleted the mitophagy initiator protein Drp1 both in human (-49%; p=0.01) and mouse lymphocytes (-41%; p=0.03). Drp1 protein levels were profoundly diminished in PBL of SLE patients (-86±3%; p=0.012). T cells of 4-week-old MRL/lpr mice exhibited 4.7-fold over-expression of Rab4A (p=0.0002), the murine homologue of HRES-1/Rab4, and depletion of Drp1 that preceded the accumulation of mitochondria, ANA production and nephritis. 3-PEHPC increased Drp1 (p=0.03) and reduced mitochondrial mass in T cells (p=0.02) and diminished ANA production (p=0.021), proteinuria (p=0.00004), and nephritis scores of lupus-prone mice (p<0.001).

CONCLUSIONS

These data reveal a pathogenic role for HRES-1/Rab4-mediated Drp1 depletion and identify endocytic control of mitophagy as a treatment target in SLE.

Acute mTOR inhibition induces insulin resistance and alters substrate utilization in vivo

The effect of acute inhibition of both mTORC1 and mTORC2 on metabolism is unknown. A single injection of the mTOR kinase inhibitor, AZD8055, induced a transient, yet marked increase in fat oxidation and insulin resistance in mice, whereas the mTORC1 inhibitor rapamycin had no effect. AZD8055, but not rapamycin reduced insulin-stimulated glucose uptake into incubated muscles, despite normal GLUT4 translocation in muscle cells. AZD8055 inhibited glycolysis in MEF cells. Abrogation of mTORC2 activity by SIN1 deletion impaired glycolysis and AZD8055 had no effect in SIN1 KO MEFs. Re-expression of wildtype SIN1 rescued glycolysis. Glucose intolerance following AZD8055 administration was absent in mice lacking the mTORC2 subunit Rictor in muscle, and in vivo glucose uptake into Rictor-deficient muscle was reduced despite normal Akt activity. Taken together, acute mTOR inhibition is detrimental to glucose homeostasis in part by blocking muscle mTORC2, indicating its importance in muscle metabolism in vivo.

Chronic rapamycin treatment causes diabetes in male mice

Current evidence indicates that the mammalian target of rapamycin inhibitor rapamycin both increases longevity and, seemingly contradictorily, impairs glucose homeostasis. Most studies exploring the dimensions of this paradox have been based on rapamycin treatment in mice for up to 20 wk. We sought to better understand the metabolic effects of oral rapamycin over a substantially longer period of time in HET3 mice. We observed that treatment with rapamycin for 52 wk induced diabetes in male mice, characterized by hyperglycemia, significant urine glucose levels, and severe glucose and pyruvate intolerance. Glucose intolerance occurred in male mice by 4 wk on rapamycin and could be only partially reversed with cessation of rapamycin treatment. Female mice developed moderate glucose intolerance over 1 yr of rapamycin treatment, but not diabetes. The role of sex hormones in the differential development of diabetic symptoms in male and female mice was further explored. HET3 mice treated with rapamycin for 52 wk were gonadectomized and monitored over 10 wk. Castrated male mice remained glucose intolerant, while ovariectomized females developed significant glucose intolerance over the same time period. Subsequent replacement of 17β-estradiol (E2) in ovariectomized females promoted a recovery of glucose tolerance over a 4-wk period, suggesting the protective role of E2 against rapamycin-induced diabetes. These results indicate that 1) oral rapamycin treatment causes diabetes in male mice, 2) the diabetes is partially reversible with cessation of treatment, and 3) E2 plays a protective role against the development of rapamycin-induced diabetes.

Engineered hair follicle mesenchymal stem cells overexpressing controlled-release insulin reverse hyperglycemia in mice with type L diabetes

Genetically engineered stem cells that overexpress genes encoding therapeutic products can be exploited to correct metabolic disorders by repairing and regenerating diseased organs or restoring their function. Hair follicles are readily accessible and serve as a rich source of autologous stem cells for cell-based gene therapy. Here we isolated mesenchymal stem cells from human hair follicles (HF-MSCs) and engineered them to overexpress the human insulin gene and release human insulin in a time- and dose-dependent manner in response to rapamycin. The engineered HF-MSCs retained their characteristic cell surface markers and retained their potential to differentiate into adipocytes and osteoblasts. When mice with streptozotocin-induced type 1 diabetes were engrafted with these engineered HF-MSCs, these cells expressed and released a dose of human insulin, dramatically reversed hyperglycemia, and significantly reduced death rate. Moreover, the engineered HF-MSCs did not form detectable tumors throughout the 120-day animal tests in our experiment. Our results show that HF-MSCs can be used to safely and efficiently express therapeutic transgenes and therefore show promise for cell-based gene therapy of human disease.

Dyrk1a haploinsufficiency induces diabetes in mice through decreased pancreatic beta cell mass

AIMS/HYPOTHESIS

Growth factors and nutrients are important regulators of pancreatic beta cell mass and function. However, the signalling pathways by which these factors modulate these processes have not yet been fully elucidated. DYRK1A (also named minibrain/MNB) is a member of the dual-specificity tyrosine phosphorylation-regulated kinase (DYRK) family that has been conserved across evolution. A significant amount of data implicates DYRK1A in brain growth and function, as well as in neurodegenerative processes in Alzheimer's disease and Down's syndrome. We investigated here whether DYRK1A would be an attractive candidate for beta cell growth modulation.

METHODS

To study the role of DYRK1A in beta cell growth, we used Dyrk1a-deficient mice.

RESULTS

We show that DYRK1A is expressed in pancreatic islets and provide evidence that changes in Dyrk1a gene dosage in mice strongly modulate glycaemia and circulating insulin levels. Specifically, Dyrk1a-haploinsufficient mice show severe glucose intolerance, reduced beta cell mass and decreased beta cell proliferation.

CONCLUSIONS/INTERPRETATION

Taken together, our data indicate that DYRK1A is a critical kinase for beta cell growth as Dyrk1a-haploinsufficient mice show a diabetic profile.

Beneficial metabolic effects of rapamycin are associated with enhanced regulatory cells in diet-induced obese mice

The “mechanistic target of rapamycin” (mTOR) is a central controller of growth, proliferation and/or motility of various cell-types ranging from adipocytes to immune cells, thereby linking metabolism and immunity. mTOR signaling is overactivated in obesity, promoting inflammation and insulin resistance. Therefore, great interest exists in the development of mTOR inhibitors as therapeutic drugs for obesity or diabetes. However, despite a plethora of studies characterizing the metabolic consequences of mTOR inhibition in rodent models, its impact on immune changes associated with the obese condition has never been questioned so far. To address this, we used a mouse model of high-fat diet (HFD)-fed mice with and without pharmacologic mTOR inhibition by rapamycin. Rapamycin was weekly administrated to HFD-fed C57BL/6 mice for 22 weeks. Metabolic effects were determined by glucose and insulin tolerance tests and by indirect calorimetry measures of energy expenditure. Inflammatory response and immune cell populations were characterized in blood, adipose tissue and liver. In parallel, the activities of both mTOR complexes (e. g. mTORC1 and mTORC2) were determined in adipose tissue, muscle and liver. We show that rapamycin-treated mice are leaner, have enhanced energy expenditure and are protected against insulin resistance. These beneficial metabolic effects of rapamycin were associated to significant changes of the inflammatory profiles of both adipose tissue and liver. Importantly, immune cells with regulatory functions such as regulatory T-cells (Tregs) and myeloid-derived suppressor cells (MDSCs) were increased in adipose tissue. These rapamycin-triggered metabolic and immune effects resulted from mTORC1 inhibition whilst mTORC2 activity was intact. Taken together, our results reinforce the notion that controlling immune regulatory cells in metabolic tissues is crucial to maintain a proper metabolic status and, more generally, comfort the need to search for novel pharmacological inhibitors of the mTOR signaling pathway to prevent and/or treat metabolic diseases.

In vitro and in vivo evaluation of Rapamycin-eluting nanofibers coated on cardia stents

Diagram of the process used to fabricate non-biodegradable metal stents with an outer layer of Rapa-loaded fibrous membrane using the electrospinning process. With the release of Rapa, the stents are expected to inhibit fibroblast proliferation and tissue hyperplasia, therefore treating a benign cardia stricture.

Everolimus dramatically improves glycemic control in unresectable metastatic insulinoma: a case report

Hypoglycemia poses a significant management challenge in patients with unresectable metastatic insulinoma. A 57-year-old woman with pancreatic neuroendocrine tumor with multiple liver metastases was referred to our institution. During the clinical course of pancreatic neuroendocrine tumor, she had experienced palpitations, cold sweats and faintness between meals that indicated her tumors had attained the characteristics of an insulinoma, and her quality of life was impacted by frequent hypoglycemic episodes which could not be prevented by conventional therapies. Shortly after the approval of everolimus for pancreatic neuroendocrine tumor in Japan, we began oral administration at 10 mg per day, which produced a rapid and substantial improvement in glycemic control. The serum insulin level decreased dramatically despite the tumor size remaining stable on computed tomography evaluation. Despite a dose reduction of everolimus to 5 mg per day in response to the adverse reaction of interstitial pneumonitis and a subsequent moderate increase in the serum insulin level, the patient has maintained normoglycemia for a year. Everolimus might represent the treatment of choice for unresectable insulinoma in terms of not only tumor stabilization but also glycemic control.

TOR-centric view on insulin resistance and diabetic complications: perspective for endocrinologists and gerontologists

This article is addressed to endocrinologists treating patients with diabetic complications as well as to basic scientists studying an elusive link between diseases and aging. It answers some challenging questions. What is the link between insulin resistance (IR), cellular aging and diseases? Why complications such as retinopathy may paradoxically precede the onset of type II diabetes. Why intensive insulin therapy may initially worsen retinopathy. How nutrient- and insulin-sensing mammalian target of rapamycin (mTOR) pathway can drive insulin resistance and diabetic complications. And how rapamycin, at rational doses and schedules, may prevent IR, retinopathy, nephropathy and beta-cell failure, without causing side effects.

Low-dose interleukin 2 in patients with type 1 diabetes: a phase 1/2 randomised, double-blind, placebo-controlled trial

BACKGROUND

An improper balance of regulatory/effector T (Treg/Teff) cells is central to the development of autoimmune diseases, including type 1 diabetes. We previously showed that low-dose interleukin 2 (IL2) induced Treg cell expansion and activation and clinical improvement in patients with hepatitis-C-virus-induced vasculitis. We aimed to establish which low doses of IL2 would be safe and induce Treg cells in patients with type 1 diabetes, considering that: (1) type 1 diabetes might be linked to alteration of the IL2/IL2R activation pathway; (2) activation of pathogenic Teff cells by IL2 could exacerbate disease; and (3) the safety of low-dose IL2 is not known in type 1 diabetes.

METHODS

This was a single-centre phase 1/2 study. 24 adult patients (18-55 years) with established insulin-dependent type 1 diabetes and at least one diabetes-related autoantibody were enrolled and randomly assigned (in a 1:1:1:1 ratio, by computer-generated randomisation list, with block size four) to placebo or IL2 at 0.33 MIU/day, 1 MIU/day, or 3 MIU/day for a 5-day course and were followed up for 60 days. All investigators and participants were masked to assignment. The primary outcome was change in Treg cells, measured by flow cytometry, and expressed as a percentage of CD4+ T cells, from day 1 to day 60. This trial is registered with ClinicalTrials.gov, number NCT01353833.

FINDINGS

Six patients were assigned to each group between June 1, 2011, and Feb 3, 2012. IL2 was well tolerated at all doses, with no serious adverse events. However, there was a dose-response association for non-serious adverse events during the treatment phase (days 1-6); one patient in the placebo group, three patients in the 0.33 MIU group, five patients in the 1 MIU group, and six patients in the 3 MIU group had non-serious adverse events. The most common adverse events in the treatment phase were injection-site reaction (no patients with placebo vs three patients with 0.33 MIU and 1 MIU vs two patients with 3 MIU) and influenza-like syndrome (no patients with placebo vs one patient with 0.33 MIU and 1 MIU vs four patients with 3 MIU). After the treatment phase, adverse events did not differ between groups. IL2 did not induce deleterious changes in glucose-metabolism variables. IL2 induced a dose-dependent increase in the proportion of Treg cells, significant at all doses compared with placebo (placebo mean increase 0.5% [SD 0.4]; 0.33 MIU 2.8% [1.2], p=0.0039; 1 MIU 3.9% [1.8], p=0.0039; 3 MIU 4.8% [1.9] p=0.0039).

INTERPRETATION

We have defined a well-tolerated and immunologically effective dose range of IL2 for application to type 1 diabetes therapy and prevention, which could be relevant to other disorders in which a Treg cell increase would be desirable.

Validation of a pretransplant risk score for new-onset diabetes after kidney transplantation

OBJECTIVE

Identification of patients at high risk for new-onset diabetes after kidney transplantation (NODAT) will facilitate clinical trials for its prevention.

RESEARCH DESIGN AND METHODS

We previously described a pretransplant predictive risk model for NODAT using seven pretransplant variables (age, planned use of maintenance corticosteroids, prescription for gout medicine, BMI, fasting glucose, fasting triglycerides, and family history of diabetes). We have now applied the initial model to a cohort of 474 transplant recipients from another center for validation. We performed two analyses in the validation cohort. The first was a standard model with variables derived from the original study. The second was a summary score model, in which the sum of dichotomized variables (all the variables dichotomized at clinically relevant cut points) was used to categorize, individuals into low (0-1), intermediate (2, 3), or high (4-7) risk groups. We also conducted a combined database analyses, merging the initial and validation cohorts (n=792) to obtain better estimates for a prediction equation.

RESULTS

Although the frequency of several risk factors differed significantly between the two cohorts, the models performed similarly in each cohort. Using the summary score model, incidences of NODAT in low-risk, medium-risk, and high-risk groups in the initial cohort were 12, 29, and 56%, and in the validation cohort incidences were 11, 29, and 51%.

CONCLUSIONS

A pretransplant model for NODAT, including many type 2 diabetes risk factors, predicted NODAT in the validation cohort.

Late-life rapamycin treatment reverses age-related heart dysfunction

Rapamycin has been shown to extend lifespan in numerous model organisms including mice, with the most dramatic longevity effects reported in females. However, little is known about the functional ramifications of this longevity-enhancing paradigm in mammalian tissues. We treated 24-month-old female C57BL/6J mice with rapamycin for 3 months and determined health outcomes via a variety of noninvasive measures of cardiovascular, skeletal, and metabolic health for individual mice. We determined that while rapamycin has mild transient metabolic effects, there are significant benefits to late-life cardiovascular function with a reversal or attenuation of age-related changes in the heart. RNA-seq analysis of cardiac tissue after treatment indicated inflammatory, metabolic, and antihypertrophic expression changes in cardiac tissue as potential mechanisms mediating the functional improvement. Rapamycin treatment also resulted in beneficial behavioral, skeletal, and motor changes in these mice compared with those fed a control diet. From these findings, we propose that late-life rapamycin therapy not only extends the lifespan of mammals, but also confers functional benefits to a number of tissues and mechanistically implicates an improvement in contractile function and antihypertrophic signaling in the aged heart with a reduction in age-related inflammation.

Post-prandial regulation of hepatic glucokinase and lipogenesis requires the activation of TORC1 signalling in rainbow trout (Oncorhynchus mykiss)

To assess the potential involvement of TORC1 (target of rapamycin complex 1) signalling in the regulation of post-prandial hepatic lipid and glucose metabolism-related gene expression in trout, we employed intraperitoneal administration of rapamycin to achieve an acute inhibition of the TOR pathway. Our results reveal that rapamycin inhibits the phosphorylation of TORC1 and its downstream effectors (S6K1, S6 and 4E-BP1), without affecting Akt and the Akt substrates Forkhead-box Class O1 (FoxO1) and glycogen synthase kinase 3α/β (GSK 3α/β). These results indicate that acute administration of rapamycin in trout leads to the inhibition of TORC1 activation. No effect is observed on the expression of genes involved in gluconeogenesis, glycolysis and fatty acid oxidation, but hepatic TORC1 inhibition results in decreased sterol regulatory element binding protein 1c (SREBP1c) gene expression and suppressed fatty acid synthase (FAS) and glucokinase (GK) at gene expression and activity levels, indicating that FAS and GK activity is controlled at a transcriptional level in a TORC1-dependent manner. This study demonstrates for the first time in fish that post-prandial regulation of hepatic lipogenesis and glucokinase in rainbow trout requires the activation of TORC1 signalling.

The required beta cell research for improving treatment of type 2 diabetes

In healthy individuals, insulin resistance is associated with physiological conditions such as pregnancy or body weight gain and triggers an increase in beta cell number and insulin secretion capacity to preserve normoglycaemia. Failure of this beta cell compensation capacity is a fundamental cause of diabetic hyperglycaemia. Incomplete understanding of the molecular mechanisms controlling the plasticity of adult beta cells mechanisms and how these cells fail during the pathogenesis of diabetes strongly limits the ability to develop new beta cell-specific therapies. Here, current knowledge of the signalling pathways controlling beta cell plasticity is reviewed, and possible directions for future research are discussed.

SAD-A kinase controls islet β-cell size and function as a mediator of mTORC1 signaling

The mammalian target of rapamycin (mTOR) plays an important role in controlling islet β-cell function. However, the underlying molecular mechanisms remain poorly elucidated. Synapses of amphids defective kinase-A (SAD-A) is a 5' adenosine monophosphate-activated protein kinase-related protein kinase that is exclusively expressed in pancreas and brain. In this study, we investigated a role of the kinase in regulating pancreatic β-cell morphology and function as a mediator of mTOR complex 1 (mTORC1) signaling. We show that global SAD-A deletion leads to defective glucose-stimulated insulin secretion and petite islets, which are reminiscent of the defects in mice with global deletion of ribosomal protein S6 kinase 1, a downstream target of mTORC1. Consistent with these findings, selective deletion of SAD-A in pancreas decreased islet β-cell size, whereas SAD-A overexpression significantly increased the size of mouse insulinomas cell lines β-cells. In direct support of SAD-A as a unique mediator of mTORC1 signaling in islet β-cells, we demonstrate that glucose dramatically stimulated SAD-A protein translation in isolated mouse islets, which was potently inhibited by rapamycin, an inhibitor of mTORC1. Moreover, the 5'-untranslated region of SAD-A mRNA is highly structured and requires mTORC1 signaling for its translation initiation. Together, these findings identified SAD-A as a unique pancreas-specific effector protein of mTORC1 signaling.

Young and old genetically heterogeneous HET3 mice on a rapamycin diet are glucose intolerant but insulin sensitive

Rapamycin, an inhibitor of the mechanistic target of rapamycin (mTOR) signaling pathway, extends the life span of yeast, worms, flies, and mice. Interventions that promote longevity are often correlated with increased insulin sensitivity, and it therefore is surprising that chronic rapamycin treatment of mice, rats, and humans is associated with insulin resistance (J Am Soc Nephrol., 19, 2008, 1411; Diabetes, 00, 2010, 00; Science, 335, 2012, 1638). We examined the effect of dietary rapamycin treatment on glucose homeostasis and insulin resistance in the genetically heterogeneous HET3 mouse strain, a strain in which dietary rapamycin robustly extends mean and maximum life span. We find that rapamycin treatment leads to glucose intolerance in both young and old HET3 mice, but in contrast to the previously reported effect of injected rapamycin in C57BL/6 mice, HET3 mice treated with dietary rapamycin responded normally in an insulin tolerance test. To gauge the overall consequences of rapamycin treatment on average blood glucose levels, we measured HBA1c. Dietary rapamycin increased HBA1c over the first 3 weeks of treatment in young animals, but the effect was lost by 3 months, and no effect was detected in older animals. Our results demonstrate that the extended life span of HET3 mice on a rapamycin diet occurs in the absence of major changes in insulin sensitivity and highlight the importance of strain background and delivery method in testing effects of longevity interventions.

Evidence for rapamycin toxicity in pancreatic β-cells and a review of the underlying molecular mechanisms

Rapamycin is used frequently in both transplantation and oncology. Although historically thought to have little diabetogenic effect, there is growing evidence of β-cell toxicity. This Review draws evidence for rapamycin toxicity from clinical studies of islet and renal transplantation, and of rapamycin as an anticancer agent, as well as from experimental studies. Together, these studies provide evidence that rapamycin has significant detrimental effects on β-cell function and survival and peripheral insulin resistance. The mechanism of action of rapamycin is via inhibition of mammalian target of rapamycin (mTOR). This Review describes the complex mTOR signaling pathways, which control vital cellular functions including mRNA translation, cell proliferation, cell growth, differentiation, angiogenesis, and apoptosis, and examines molecular mechanisms for rapamycin toxicity in β-cells. These mechanisms include reductions in β-cell size, mass, proliferation and insulin secretion alongside increases in apoptosis, autophagy, and peripheral insulin resistance. These data bring into question the use of rapamycin as an immunosuppressant in islet transplantation and as a second-line agent in other transplant recipients developing new-onset diabetes after transplantation with calcineurin inhibitors. It also highlights the importance of close monitoring of blood glucose levels in patients taking rapamycin as an anticancer treatment, particularly those with preexisting glucose intolerance.

Can new-onset diabetes after kidney transplant be prevented?

Because the negative consequences of new-onset diabetes mellitus after transplantation (NODAT) diminish the significant gains of kidney transplantation, it is imperative to develop clinical interventions to reduce the incidence of NODAT. In this review, we discuss whether intensive lifestyle interventions that delay or prevent type 2 diabetes mellitus may decrease the incidence of NODAT. We examine the literature pertaining to incidence and timing of onset of NODAT, as well as the risk factors and pathophysiology that NODAT shares with type 2 diabetes mellitus, namely pathways related to increased insulin resistance and decreased insulin secretion. Our central hypothesis is that NODAT results from the same metabolic risk factors that underlie type 2 diabetes mellitus. These risk factors are altered and enhanced by transplantation, "tipping" some transplant recipients with seemingly normal glucose homeostasis before transplant toward the development of NODAT. We describe the diabetogenic properties of transplant immunosuppressive drugs. We describe novel methods of prevention that are being explored, including resting the pancreatic β-cells by administration of basal insulin during the period immediately after transplant. On the basis of the current evidence, we propose that intensive lifestyle modification, adapted for individuals with chronic kidney disease or end-stage renal disease, as well as resting pancreatic β-cells during the immediate postoperative period, may lower the incidence of NODAT.

Molecular and genetic crosstalks between mTOR and ERRα are key determinants of rapamycin-induced nonalcoholic fatty liver

mTOR and ERRα are key regulators of common metabolic processes, including lipid homeostasis. However, it is currently unknown whether these factors cooperate in the control of metabolism. ChIP-sequencing analyses of mouse liver reveal that mTOR occupies regulatory regions of genes on a genome-wide scale including enrichment at genes shared with ERRα that are involved in the TCA cycle and lipid biosynthesis. Genetic ablation of ERRα and rapamycin treatment, alone or in combination, alter the expression of these genes and induce the accumulation of TCA metabolites. As a consequence, both genetic and pharmacological inhibition of ERRα activity exacerbates hepatic hyperlipidemia observed in rapamycin-treated mice. We further show that mTOR regulates ERRα activity through ubiquitin-mediated degradation via transcriptional control of the ubiquitin-proteasome pathway. Our work expands the role of mTOR action in metabolism and highlights the existence of a potent mTOR/ERRα regulatory axis with significant clinical impact.

Calcineurin inhibition and new-onset diabetes mellitus after transplantation

New-onset diabetes after transplantation independently increases the risk of cardiovascular disease, infections, and graft loss and decreases patient survival. The required balance between insulin sensitivity/resistance and insulin secretion is necessary to maintain normal glucose metabolism. Calcineurin inhibitors are standard immunosuppression drugs used after transplantation and have been implicated in the development of new-onset diabetes after transplantation partially by pancreatic β-cell apoptosis and resultant decrease in insulin secretion. The ability of muscle to take up glucose is critical to blood glucose homeostasis. Skeletal muscle is quantitatively the most important tissue in the body for insulin-stimulated glucose disposal and is composed of diverse myofibers that vary in their properties between healthy and insulin-resistant muscle. Various signaling pathways are responsible for remodeling of skeletal muscle, and among these is the calcineurin/nuclear factor of activated T-cell pathway. The mechanism of action of the calcineurin inhibitors is to bind in a complex with a binding protein to calcineurin and inhibit its dephosphorylation and activation of nuclear factor of activated T cells. In this review, we will provide a detailed discussion of the hypothesis that inhibition of calcineurin in tissues involved in insulin sensitivity/resistance could be at least partially responsible for the diabetogenicity seen with the use of calcineurin inhibitors.

Resveratrol potentiates rapamycin to prevent hyperinsulinemia and obesity in male mice on high fat diet

High doses of rapamycin, an antiaging agent, can prevent obesity in mice on high fat diet (HFD). Obesity is usually associated with hyperinsulinemia. Here, we showed that rapamycin given orally, at doses that did not affect weight gain in male mice on HFD, tended to decrease fasting insulin levels. Addition of resveratrol, which alone did not affect insulin levels, potentiated the effect of rapamycin, so that the combination decreased obesity and prevented hyperinsulinemia. Neither rapamycin nor resveratrol, and their combination affected fasting levels of glucose (despite lowering insulin levels), implying that the combination might prevent insulin resistance. We and others previously reported that resveratrol at high doses inhibited the mTOR (Target of Rapamycin) pathway in cell culture. Yet, as we confirmed here, this effect was observed only at super-pharmacological concentrations. At pharmacological concentrations, resveratrol did not exert ‘rapamycin-like effects' on cellular senescence and did not inhibit the mTOR pathway in vitro, indicating nonoverlapping therapeutic mechanisms of actions of rapamycin and resveratrol in vivo. Although, like rapamycin, resveratrol decreased insulin-induced HIF-1-dependent transcription in cell culture, resveratrol did not inhibit mTOR at the same concentrations. Given distinct mechanisms of action of rapamycin and resveratrol at clinically relevant doses, their combination warrants further investigation as a potential antiaging, antiobesity and antidiabetic modality.

Rapamycin ameliorates age-dependent obesity associated with increased mTOR signaling in hypothalamic POMC neurons

VIDEO ABSTRACT

The prevalence of obesity in older people is the leading cause of metabolic syndromes. Central neurons serving as homeostatic sensors for body-weight control include hypothalamic neurons that express pro-opiomelanocortin (POMC) or neuropeptide-Y (NPY) and agouti-related protein (AgRP). Here, we report an age-dependent increase of mammalian target of rapamycin (mTOR) signaling in POMC neurons that elevates the ATP-sensitive potassium (K(ATP)) channel activity cell-autonomously to silence POMC neurons. Systemic or intracerebral administration of the mTOR inhibitor rapamycin causes weight loss in old mice. Intracerebral rapamycin infusion into old mice enhances the excitability and neurite projection of POMC neurons, thereby causing a reduction of food intake and body weight. Conversely, young mice lacking the mTOR-negative regulator TSC1 in POMC neurons, but not those lacking TSC1 in NPY/AgRP neurons, were obese. Our study reveals that an increase in mTOR signaling in hypothalamic POMC neurons contributes to age-dependent obesity.

The combined deletion of S6K1 and Akt2 deteriorates glycemic control in a high-fat diet

Signaling downstream of mechanistic target of rapamycin complexes 1 and 2 (mTORC1 and mTORC2) controls specific and distinct aspects of insulin action and nutrient homeostasis in an interconnected and as yet unclear way. Mice lacking the mTORC1 substrate S6 kinase 1 (S6K1) maintain proper glycemic control with a high-fat diet. This phenotype is accompanied by insulin hypersensitivity, Akt- and AMP-activated kinase upregulation, and increased lipolysis in adipose tissue and skeletal muscle. Here, we show that, when S6K1 inactivation is combined with the deletion of the mTORC2 substrate Akt2, glucose homeostasis is compromised due to defects in both insulin action and β-cell function. After a high-fat diet, the S6K1(-/-) Akt2(-/-) double-mutant mice do not become obese, though they are severely hyperglycemic. Our data demonstrate that S6K1 is required for pancreatic β-cell growth and function during adaptation to insulin resistance states. Strikingly, the inactivation of two targets of mTOR and phosphatidylinositol 3-kinase signaling is sufficient to reproduce major hallmarks of type 2 diabetes.

Once again on rapamycin-induced insulin resistance and longevity: despite of or owing to

Calorie restriction (CR), which deactivates the nutrient-sensing mTOR pathway, slows down aging and prevents age-related diseases such as type II diabetes. Compared with CR, rapamycin more efficiently inhibits mTOR. Noteworthy, severe CR and starvation cause a reversible condition known as "starvation diabetes." As was already discussed, chronic administration of rapamycin can cause a similar condition in some animal models. A recent paper published in Science reported that chronic treatment with rapamycin causes a diabetes-like condition in mice by indirectly inhibiting mTOR complex 2. Here I introduce the notion of benevolent diabetes and discuss whether starvation-like effects of chronic high dose treatment with rapamycin are an obstacle for its use as an anti-aging drug.