Recurrent episodes of hypoglycemia impair sympathoadrenal counterregulatory responses (CRRs) to a subsequent episode of hypoglycemia. For individuals with type 1 diabetes, this markedly increases (by 25-fold) the risk of severe hypoglycemia and is a major limitation to optimal insulin therapy. The mechanisms through which this maladaptive response occurs remain unknown. The corticotrophin-releasing factor (CRF) family of neuropeptides and their receptors (CRFR1 and CRFR2) play a critical role in regulating the neuroendocrine stress response. Here we show in the Sprague-Dawley rat that direct in vivo application to the ventromedial hypothalamus (VMH), a key glucose-sensing region, of urocortin I (UCN I), an endogenous CRFR2 agonist, suppressed (~55–60%), whereas CRF, a predominantly CRFR1 agonist, amplified (~50–70%) CRR to hypoglycemia. UCN I was shown to directly alter the glucose sensitivity of VMH glucose-sensing neurons in whole-cell current clamp recordings in brain slices. Interestingly, the suppressive effect of UCN I–mediated CRFR2 activation persisted for at least 24 hours after in vivo VMH microinjection. Our data suggest that regulation of the CRR is largely determined by the interaction between CRFR2-mediated suppression and CRFR1-mediated activation in the VMH.
Rory J. McCrimmon, Zhentao Song, Haiying Cheng, Ewan C. McNay, Catherine Weikart-Yeckel, Xiaoning Fan, Vanessa H. Routh, Robert S. Sherwin
Stuart P. Weisberg, Deborah Hunter, Reid Huber, Jacob Lemieux, Sarah Slaymaker, Kris Vaddi, Israel Charo, Rudolph L. Leibel, Anthony W. Ferrante Jr.
Safe induction of autoantigen-specific long-term tolerance is the “holy grail” for the treatment of autoimmune diseases. In animal models of type 1 diabetes, oral or i.n. immunization with islet antigens induces Tregs that are capable of bystander suppression. However, such interventions are only effective early in the prediabetic phase. Here, we demonstrate that a novel combination treatment with anti-CD3ε–specific antibody and i.n. proinsulin peptide can reverse recent-onset diabetes in 2 murine diabetes models with much higher efficacy than with monotherapy with anti-CD3 or antigen alone. In vivo, expansion of CD25+Foxp3+ and insulin-specific Tregs producing IL-10, TGF-β, and IL-4 was strongly enhanced. These cells could transfer dominant tolerance to immunocompetent recent-onset diabetic recipients and suppressed heterologous autoaggressive CD8 responses. Thus, combining a systemic immune modulator with antigen-specific Treg induction is more efficacious in reverting diabetes. Since Tregs act site-specifically, this strategy should also be expected to reduce the potential for systemic side effects.
Damien Bresson, Lisa Togher, Evelyn Rodrigo, Yali Chen, Jeffrey A. Bluestone, Kevan C. Herold, Matthias von Herrath
Short-term overfeeding blunts the central effects of fatty acids on food intake and glucose production. This acquired defect in nutrient sensing could contribute to the rapid onset of hyperphagia and insulin resistance in this model. Here we examined whether central inhibition of lipid oxidation is sufficient to restore the hypothalamic levels of long-chain fatty acyl-CoAs (LCFA-CoAs) and to normalize food intake and glucose homeostasis in overfed rats. To this end, we targeted the liver isoform of carnitine palmitoyltransferase-1 (encoded by the CPT1A gene) by infusing either a sequence-specific ribozyme against CPT1A or an isoform-selective inhibitor of CPT1A activity in the third cerebral ventricle or in the mediobasal hypothalamus (MBH). Inhibition of CPT1A activity normalized the hypothalamic levels of LCFA-CoAs and markedly inhibited feeding behavior and hepatic glucose fluxes in overfed rats. Thus central inhibition of lipid oxidation is sufficient to restore hypothalamic lipid sensing as well as glucose and energy homeostasis in this model and may be an effective approach to the treatment of diet-induced obesity and insulin resistance.
Alessandro Pocai, Tony K.T. Lam, Silvana Obici, Roger Gutierrez-Juarez, Evan D. Muse, Arduino Arduini, Luciano Rossetti
The C-C motif chemokine receptor–2 (CCR2) regulates monocyte and macrophage recruitment and is necessary for macrophage-dependent inflammatory responses and the development of atherosclerosis. Although adipose tissue expression and circulating concentrations of CCL2 (also known as MCP1), a high-affinity ligand for CCR2, are elevated in obesity, the role of CCR2 in metabolic disorders, including insulin resistance, hepatic steatosis, and inflammation associated with obesity, has not been studied. To determine what role CCR2 plays in the development of metabolic phenotypes, we studied the effects of Ccr2 genotype on the development of obesity and its associated phenotypes. Genetic deficiency in Ccr2 reduced food intake and attenuated the development of obesity in mice fed a high-fat diet. In obese mice matched for adiposity, Ccr2 deficiency reduced macrophage content and the inflammatory profile of adipose tissue, increased adiponectin expression, ameliorated hepatic steatosis, and improved systemic glucose homeostasis and insulin sensitivity. In mice with established obesity, short-term treatment with a pharmacological antagonist of CCR2 lowered macrophage content of adipose tissue and improved insulin sensitivity without significantly altering body mass or improving hepatic steatosis. These data suggest that CCR2 influences the development of obesity and associated adipose tissue inflammation and systemic insulin resistance and plays a role in the maintenance of adipose tissue macrophages and insulin resistance once obesity and its metabolic consequences are established.
Stuart P. Weisberg, Deborah Hunter, Reid Huber, Jacob Lemieux, Sarah Slaymaker, Kris Vaddi, Israel Charo, Rudolph L. Leibel, Anthony W. Ferrante Jr.
Insulin receptor substrates, including Irs1 and Irs2, integrate insulin and IGF receptor signals with heterologous pathways to coordinate growth and metabolism. Since Irs2 is thought to be especially important in hepatic nutrient homeostasis, we deleted Irs1 from hepatocytes of WT mice (called LKO) or genetically insulin-resistant Irs1–/– mice (called LKO::Irs1–/–). Viable LKO::Irs1–/– mice were 70% smaller than WT or LKO mice, and 40% smaller than Irs1–/– mice. Hepatic insulin receptors were functional in all the mice, but insulin signaling via the Akt—FoxO1 pathway was reduced in Irs1–/– and LKO liver, and undetected in LKO::Irs1–/– liver; however, Gsk3β phosphorylation (Ser9) and hepatic glycogen stores were nearly normal in all of the mice. LKO and Irs1–/– mice developed insulin resistance and glucose intolerance that never progressed to diabetes, whereas LKO::Irs1–/– mice developed hyperglycemia and hyperinsulinemia immediately after birth. Regardless, few hepatic genes changed expression significantly in Irs1–/– or LKO mice, whereas hundreds of genes changed in LKO::Irs1–/– mice — including elevated levels of Pck1, G6pc, Ppargc1, Pparg, and Igfbp1. Thus, signals delivered by Irs1 or Irs2 regulate hepatic gene expression that coordinates glucose homeostasis and systemic growth.
Xiaocheng Dong, Sunmin Park, Xueying Lin, Kyle Copps, Xianjin Yi, Morris F. White
Using an siRNA-based screen, we identified the transcriptional corepressor RIP140 as a negative regulator of insulin-responsive hexose uptake and oxidative metabolism in 3T3-L1 adipocytes. Affymetrix GeneChip profiling revealed that RIP140 depletion upregulates the expression of clusters of genes in the pathways of glucose uptake, glycolysis, TCA cycle, fatty acid oxidation, mitochondrial biogenesis, and oxidative phosphorylation in these cells. Conversely, we show that reexpression of RIP140 in mouse embryonic fibroblasts derived from RIP140-null mice downregulates expression of many of these same genes. Consistent with these microarray data, RIP140 gene silencing in cultured adipocytes increased both conversion of [14C]glucose to CO2 and mitochondrial oxygen consumption. RIP140-null mice, previously reported to resist weight gain on a high-fat diet, are shown here to display enhanced glucose tolerance and enhanced responsiveness to insulin compared with matched wild-type mice upon high-fat feeding. Mechanistically, RIP140 was found to require the nuclear receptor ERRα to regulate hexose uptake and mitochondrial proteins SDHB and CoxVb, although it likely acts through other nuclear receptors as well. We conclude that RIP140 is a major suppressor of adipocyte oxidative metabolism and mitochondrial biogenesis, as well as a negative regulator of whole-body glucose tolerance and energy expenditure in mice.
Aimee M. Powelka, Asha Seth, Joseph V. Virbasius, Evangelos Kiskinis, Sarah M. Nicoloro, Adilson Guilherme, Xiaoqing Tang, Juerg Straubhaar, Andrew D. Cherniack, Malcolm G. Parker, Michael P. Czech
We have generated mice that carry a neuron-specific leptin receptor (LEPR) transgene whose expression is driven by the rat synapsin I promoter synapsin–LEPR B (SYN-LEPR-B). We have also generated mice that are compound hemizygotes for the transgenes SYN-LEPR-B and neuron-specific enolase–LEPR B (NSE-LEPR-B). We observed a degree of correction in db/db mice that are hemizygous (Syn db/db) and homozygous (Syn/Syn db/db) for the SYN-LEPR-B transgene similar to that previously reported for the NSE-LEPR-B transgene. We also show complete correction of the obesity and related phenotypes of db/db mice that are hemizygous for both NSE-LEPR-B and SYN-LEPR-B transgenes (Nse+Syn db/db). Body composition, insulin sensitivity, and cold tolerance were completely normalized in Nse+Syn db/db mice at 12 weeks of age compared with lean controls. In situ hybridization for LEPR B isoform expression in Nse+Syn db/db mice showed robust expression in the energy homeostasis–relevant regions of the hypothalamus. Expression of 3 neuropeptide genes, agouti-related peptide (Agrp), neuropeptide Y (Npy), and proopiomelanocortin (Pomc), was fully normalized in dual transgenic db/db mice. The 2 transgenes in concert conferred normal fertility to male and female db/db mice. Male mice with partial peripheral deletion of Lepr, induced in the periweaning phase, did not show alterations in body composition or mass. In summary, we show that brain-specific leptin signaling is sufficient to reverse the obesity, diabetes, and infertility of db/db mice.
Carl de Luca, Timothy J. Kowalski, Yiying Zhang, Joel K. Elmquist, Charlotte Lee, Manfred W. Kilimann, Thomas Ludwig, Shun-Mei Liu, Streamson C. Chua Jr.
Activation of inflammatory pathways may contribute to the beginning and the progression of both atherosclerosis and type 2 diabetes. Here we report a novel interaction between insulin action and control of inflammation, resulting in glucose intolerance and vascular inflammation and amenable to therapeutic modulation. In insulin receptor heterozygous (Insr+/–) mice, we identified the deficiency of tissue inhibitor of metalloproteinase 3 (Timp3, an inhibitor of both TNF-α–converting enzyme [TACE] and MMPs) as a common bond between glucose intolerance and vascular inflammation. Among Insr+/– mice, those that develop diabetes have reduced Timp3 and increased TACE activity. Unchecked TACE activity causes an increase in levels of soluble TNF-α, which subsequently promotes diabetes and vascular inflammation. Double heterozygous Insr+/–Timp3+/– mice develop mild hyperglycemia and hyperinsulinemia at 3 months and overt glucose intolerance and hyperinsulinemia at 6 months. A therapeutic role for Timp3/TACE modulation is supported by the observation that pharmacological inhibition of TACE led to marked reduction of hyperglycemia and vascular inflammation in Insr+/– diabetic mice, as well as by the observation of increased insulin sensitivity in Tace+/– mice compared with WT mice. Our results suggest that an interplay between reduced insulin action and unchecked TACE activity promotes diabetes and vascular inflammation.
Massimo Federici, Marta L. Hribal, Rossella Menghini, Hiroko Kanno, Valentina Marchetti, Ottavia Porzio, Susan W. Sunnarborg, Stefano Rizza, Matteo Serino, Veronica Cunsolo, Davide Lauro, Alessandro Mauriello, David S. Smookler, Paolo Sbraccia, Giorgio Sesti, David C. Lee, Rama Khokha, Domenico Accili, Renato Lauro
Recovery of the mitochondrial inner membrane potential (ΔΨm) is a key determinant of postischemic functional recovery of the heart. Mitochondrial ROS-induced ROS release causes the collapse of ΔΨm and the destabilization of the action potential (AP) through a mechanism involving a mitochondrial inner membrane anion channel (IMAC) modulated by the mitochondrial benzodiazepine receptor (mBzR). Here, we test the hypothesis that this mechanism contributes to spatiotemporal heterogeneity of ΔΨm during ischemia-reperfusion (IR), thereby promoting abnormal electrical activation and arrhythmias in the whole heart. High-resolution optical AP mapping was performed in perfused guinea pig hearts subjected to 30 minutes of global ischemia followed by reperfusion. Typical electrophysiological responses, including progressive AP shortening followed by membrane inexcitablity in ischemia and ventricular fibrillation upon reperfusion, were observed in control hearts. These responses were reduced or eliminated by treatment with the mBzR antagonist 4′-chlorodiazepam (4′-Cl-DZP), which blocks depolarization of ΔΨm. When applied throughout the IR protocol, 4′-Cl-DZP blunted AP shortening and prevented reperfusion arrhythmias. Inhibition of ventricular fibrillation was also achieved by bolus infusion of 4′-Cl-DZP just before reperfusion. Conversely, treatment with an agonist of the mBzR that promotes ΔΨm depolarization exacerbated IR-induced electrophysiological changes and failed to prevent arrhythmias. The effects of these compounds were consistent with their actions on IMAC and ΔΨm. These findings directly link instability of ΔΨm to the heterogeneous electrophysiological substrate of the postischemic heart and highlight the mitochondrial membrane as a new therapeutic target for arrhythmia prevention in ischemic heart disease.
Fadi G. Akar, Miguel A. Aon, Gordon F. Tomaselli, Brian O’Rourke