Diabetic hyperglycemia increases ischemic brain damage in experimental animals and humans. The mechanisms are unclear but may involve enhanced apoptosis in penumbral regions. Estrogen is an established neuroprotectant in experimental stroke. Our previous study demonstrated that female diabetic db/db mice suffered less damage following cerebral hypoxia-ischemia (H/I) than male db/db mice. Here we investigated the effects of diabetes and estrogen apoptotic gene expression following H/I. Female db/db and nondiabetic (+/?) mice were ovariectomized (OVX) and treated with estrogen or vehicle prior to H/I; brains were analyzed for damage and bcl-2 family gene expression. OVX increased ischemic damage in +/? mice; estrogen reduced tissue injury and enhanced antiapoptotic gene expression (bcl-2 and bfl-1). db/db mice demonstrated more damage, without increased bcl-2 mRNA; bfl-1 expression appeared at 48 hours of recovery associated with infarction. To our knowledge, this is the first description of bfl-1 in the brain with localization to microglia and macrophages. Early induction of bfl-1 expression in +/? mouse brain was associated with microglia; delayed bfl-1 expression in diabetic brain was in macrophages bordering the infarct. Furthermore, estrogen replacement stimulated early postischemic expression of bcl-2 and bfl-1 and reduced damage in normoglycemic animals but failed to protect the diabetic brain.
Liqun Zhang, Aji Nair, Kyle Krady, Christopher Corpe, Robert H. Bonneau, Ian A. Simpson, Susan J. Vannucci
Obesity alters adipose tissue metabolic and endocrine function and leads to an increased release of fatty acids, hormones, and proinflammatory molecules that contribute to obesity associated complications. To further characterize the changes that occur in adipose tissue with increasing adiposity, we profiled transcript expression in perigonadal adipose tissue from groups of mice in which adiposity varied due to sex, diet, and the obesity-related mutations agouti (Ay) and obese (Lepob). We found that the expression of 1,304 transcripts correlated significantly with body mass. Of the 100 most significantly correlated genes, 30% encoded proteins that are characteristic of macrophages and are positively correlated with body mass. Immunohistochemical analysis of perigonadal, perirenal, mesenteric, and subcutaneous adipose tissue revealed that the percentage of cells expressing the macrophage marker F4/80 (F4/80+) was significantly and positively correlated with both adipocyte size and body mass. Similar relationships were found in human subcutaneous adipose tissue stained for the macrophage antigen CD68. Bone marrow transplant studies and quantitation of macrophage number in adipose tissue from macrophage-deficient (Csf1op/op) mice suggest that these F4/80+ cells are CSF-1 dependent, bone marrow–derived adipose tissue macrophages. Expression analysis of macrophage and nonmacrophage cell populations isolated from adipose tissue demonstrates that adipose tissue macrophages are responsible for almost all adipose tissue TNF-α expression and significant amounts of iNOS and IL-6 expression. Adipose tissue macrophage numbers increase in obesity and participate in inflammatory pathways that are activated in adipose tissues of obese individuals.
Stuart P. Weisberg, Daniel McCann, Manisha Desai, Michael Rosenbaum, Rudolph L. Leibel, Anthony W. Ferrante Jr.
Insulin resistance arises from the inability of insulin to act normally in regulating nutrient metabolism in peripheral tissues. Increasing evidence from human population studies and animal research has established correlative as well as causative links between chronic inflammation and insulin resistance. However, the underlying molecular pathways are largely unknown. In this report, we show that many inflammation and macrophage-specific genes are dramatically upregulated in white adipose tissue (WAT) in mouse models of genetic and high-fat diet-induced obesity (DIO). The upregulation is progressively increased in WAT of mice with DIO and precedes a dramatic increase in circulating-insulin level. Upon treatment with rosiglitazone, an insulin-sensitizing drug, these macrophage-originated genes are downregulated. Histologically, there is evidence of significant infiltration of macrophages, but not neutrophils and lymphocytes, into WAT of obese mice, with signs of adipocyte lipolysis and formation of multinucleate giant cells. These data suggest that macrophages in WAT play an active role in morbid obesity and that macrophage-related inflammatory activities may contribute to the pathogenesis of obesity-induced insulin resistance. We propose that obesity-related insulin resistance is, at least in part, a chronic inflammatory disease initiated in adipose tissue.
Haiyan Xu, Glenn T. Barnes, Qing Yang, Guo Tan, Daseng Yang, Chieh J. Chou, Jason Sole, Andrew Nichols, Jeffrey S. Ross, Louis A. Tartaglia, Hong Chen
Failure to secrete adequate amounts of insulin in response to increasing concentrations of glucose is an important feature of type 2 diabetes. The mechanism for loss of glucose responsiveness is unknown. Uncoupling protein 2 (UCP2), by virtue of its mitochondrial proton leak activity and consequent negative effect on ATP production, impairs glucose-stimulated insulin secretion. Of interest, it has recently been shown that superoxide, when added to isolated mitochondria, activates UCP2-mediated proton leak. Since obesity and chronic hyperglycemia increase mitochondrial superoxide production, as well as UCP2 expression in pancreatic β cells, a superoxide-UCP2 pathway could contribute importantly to obesity- and hyperglycemia-induced β cell dysfunction. This study demonstrates that endogenously produced mitochondrial superoxide activates UCP2-mediated proton leak, thus lowering ATP levels and impairing glucose-stimulated insulin secretion. Furthermore, hyperglycemia- and obesity-induced loss of glucose responsiveness is prevented by reduction of mitochondrial superoxide production or gene knockout of UCP2. Importantly, reduction of superoxide has no beneficial effect in the absence of UCP2, and superoxide levels are increased further in the absence of UCP2, demonstrating that the adverse effects of superoxide on β cell glucose sensing are caused by activation of UCP2. Therefore, superoxide-mediated activation of UCP2 could play an important role in the pathogenesis of β cell dysfunction and type 2 diabetes.
Stefan Krauss, Chen-Yu Zhang, Luca Scorrano, Louise T. Dalgaard, Julie St-Pierre, Shane T. Grey, Bradford B. Lowell
The insulin receptor substrate-2 (Irs2) branch of the insulin/IGF signaling system coordinates peripheral insulin action and pancreatic β cell function, so mice lacking Irs2 display similarities to humans with type 2 diabetes. Here we show that β cell–specific expression of Irs2 at a low or a high level delivered a graded physiologic response that promoted β cell growth, survival, and insulin secretion that prevented diabetes in Irs2–/– mice, obese mice, and streptozotocin-treated mice; and that upon transplantation, the transgenic islets cured diabetes more effectively than WT islets. Thus, pharmacological approaches that promote Irs2 expression in β cells, especially specific cAMP agonists, could be rational treatments for β cell failure and diabetes.
Anita M. Hennige, Deborah J. Burks, Umut Ozcan, Rohit N. Kulkarni, Jing Ye, Sunmin Park, Markus Schubert, Tracey L. Fisher, Matt A. Dow, Rebecca Leshan, Mark Zakaria, Mahmud Mossa-Basha, Morris F. White
In this report, we show that hyperglycemia-induced overproduction of superoxide by the mitochondrial electron transport chain activates the three major pathways of hyperglycemic damage found in aortic endothelial cells by inhibiting GAPDH activity. In bovine aortic endothelial cells, GAPDH antisense oligonucleotides activated each of the pathways of hyperglycemic vascular damage in cells cultured in 5 mM glucose to the same extent as that induced by culturing cells in 30 mM glucose. Hyperglycemia-induced GAPDH inhibition was found to be a consequence of poly(ADP-ribosyl)ation of GAPDH by poly(ADP-ribose) polymerase (PARP), which was activated by DNA strand breaks produced by mitochondrial superoxide overproduction. Both the hyperglycemia-induced decrease in activity of GAPDH and its poly(ADP-ribosyl)ation were prevented by overexpression of either uncoupling protein–1 (UCP-1) or manganese superoxide dismutase (MnSOD), which decrease hyperglycemia-induced superoxide. Overexpression of UCP-1 or MnSOD also prevented hyperglycemia-induced DNA strand breaks and activation of PARP. Hyperglycemia-induced activation of each of the pathways of vascular damage was abolished by blocking PARP activity with the competitive PARP inhibitors PJ34 or INO-1001. Elevated glucose increased poly(ADP-ribosyl)ation of GAPDH in WT aortae, but not in the aortae from PARP-1–deficient mice. Thus, inhibition of PARP blocks hyperglycemia-induced activation of multiple pathways of vascular damage.
Xueliang Du, Takeshi Matsumura, Diane Edelstein, Luciano Rossetti, Zsuzsanna Zsengellér, Csaba Szabó, Michael Brownlee
Activation of peroxisome proliferator-activated receptor γ (PPARγ) by thiazolidinediones (TZDs) improves insulin resistance by increasing insulin-stimulated glucose disposal in skeletal muscle. It remains debatable whether the effect of TZDs on muscle is direct or indirect via adipose tissue. We therefore generated mice with muscle-specific PPARγ knockout (MuPPARγKO) using Cre/loxP recombination. Interestingly, MuPPARγKO mice developed excess adiposity despite reduced dietary intake. Although insulin-stimulated glucose uptake in muscle was not impaired, MuPPARγKO mice had whole-body insulin resistance with a 36% reduction (P < 0.05) in the glucose infusion rate required to maintain euglycemia during hyperinsulinemic clamp, primarily due to dramatic impairment in hepatic insulin action. When placed on a high-fat diet, MuPPARγKO mice developed hyperinsulinemia and impaired glucose homeostasis identical to controls. Simultaneous treatment with TZD ameliorated these high fat–induced defects in MuPPARγKO mice to a degree identical to controls. There was also altered expression of several lipid metabolism genes in the muscle of MuPPARγKO mice. Thus, muscle PPARγ is not required for the antidiabetic effects of TZDs, but has a hitherto unsuspected role for maintenance of normal adiposity, whole-body insulin sensitivity, and hepatic insulin action. The tissue crosstalk mediating these effects is perhaps due to altered lipid metabolism in muscle.
Andrew W. Norris, Lihong Chen, Simon J. Fisher, Ildiko Szanto, Michael Ristow, Alison C. Jozsi, Michael F. Hirshman, Evan D. Rosen, Laurie J. Goodyear, Frank J. Gonzalez, Bruce M. Spiegelman, C. Ronald Kahn
Diabetes is caused by an absolute (type 1) or relative (type 2) deficiency of insulin-producing β cells. We have disrupted expression of the mitochondrial protein frataxin selectively in pancreatic β cells. Mice were born healthy but subsequently developed impaired glucose tolerance progressing to overt diabetes mellitus. These observations were explained by impairment of insulin secretion due to a loss of β cell mass in knockout animals. This phenotype was preceded by elevated levels of reactive oxygen species in knockout islets, an increased frequency of apoptosis, and a decreased number of proliferating β cells. Hence, disruption of the frataxin gene in pancreatic β cells causes diabetes following cellular growth arrest and apoptosis, paralleled by an increase in reactive oxygen species in islets. These observations might provide insight into the deterioration of β cell function observed in different subtypes of diabetes in humans.
Michael Ristow, Hindrik Mulder, Doreen Pomplun, Tim J. Schulz, Katrin Müller-Schmehl, Anja Krause, Malin Fex, Hélène Puccio, Jörg Müller, Frank Isken, Joachim Spranger, Dirk Müller-Wieland, Mark A. Magnuson, Matthias Möhlig, Michel Koenig, Andreas F.H. Pfeiffer
The cannabinoid receptor type 1 (CB1) and its endogenous ligands, the endocannabinoids, are involved in the regulation of food intake. Here we show that the lack of CB1 in mice with a disrupted CB1 gene causes hypophagia and leanness. As compared with WT (CB1+/+) littermates, mice lacking CB1 (CB1–/–) exhibited reduced spontaneous caloric intake and, as a consequence of reduced total fat mass, decreased body weight. In young CB1–/– mice, the lean phenotype is predominantly caused by decreased caloric intake, whereas in adult CB1–/– mice, metabolic factors appear to contribute to the lean phenotype. No significant differences between genotypes were detected regarding locomotor activity, body temperature, or energy expenditure. Hypothalamic CB1 mRNA was found to be coexpressed with neuropeptides known to modulate food intake, such as corticotropin-releasing hormone (CRH), cocaine-amphetamine–regulated transcript (CART), melanin-concentrating hormone (MCH), and prepro-orexin, indicating a possible role for endocannabinoid receptors within central networks governing appetite. CB1–/– mice showed significantly increased CRH mRNA levels in the paraventricular nucleus and reduced CART mRNA levels in the dorsomedial and lateral hypothalamic areas. CB1 was also detected in epidydimal mouse adipocytes, and CB1-specific activation enhanced lipogenesis in primary adipocyte cultures. Our results indicate that the cannabinoid system is an essential endogenous regulator of energy homeostasis via central orexigenic as well as peripheral lipogenic mechanisms and might therefore represent a promising target to treat diseases characterized by impaired energy balance.
Daniela Cota, Giovanni Marsicano, Matthias Tschöp, Yvonne Grübler, Cornelia Flachskamm, Mirjam Schubert, Dorothee Auer, Alexander Yassouridis, Christa Thöne-Reineke, Sylvia Ortmann, Federica Tomassoni, Cristina Cervino, Enzo Nisoli, Astrid C.E. Linthorst, Renato Pasquali, Beat Lutz, Günter K. Stalla, Uberto Pagotto
Hepatocyte nuclear factors-3 (Foxa-1–3) are winged forkhead transcription factors that regulate gene expression in the liver and pancreatic islets and are required for normal metabolism. Here we show that Foxa-2 is expressed in preadipocytes and induced de novo in adipocytes of genetic and diet-induced rodent models of obesity. In preadipocytes Foxa-2 inhibits adipocyte differentiation by activating transcription of the Pref-1 gene. Foxa-2 and Pref-1 expression can be enhanced in primary preadipocytes by growth hormone, suggesting that the antiadipogenic activity of growth hormone is mediated by Foxa-2. In differentiated adipocytes Foxa-2 expression leads to induction of gene expression involved in glucose and fat metabolism, including glucose transporter-4, hexokinase-2, muscle-pyruvate kinase, hormone-sensitive lipase, and uncoupling proteins-2 and -3. Diet-induced obese mice with haploinsufficiency in Foxa-2 (Foxa-2+/–) develop increased adiposity compared with wild-type littermates as a result of decreased energy expenditure. Furthermore, adipocytes of these Foxa-2+/– mice exhibit defects in glucose uptake and metabolism. These data suggest that Foxa-2 plays an important role as a physiological regulator of adipocyte differentiation and metabolism.
Christian Wolfrum, David Q. Shih, Satoru Kuwajima, Andrew W. Norris, C. Ronald Kahn, Markus Stoffel
The serine/threonine kinase Akt/PKB plays key roles in the regulation of cell growth, survival, and metabolism. It remains unclear, however, whether the functions of individual Akt/PKB isoforms are distinct. To investigate the function of Akt2/PKBβ, mice lacking this isoform were generated. Both male and female Akt2/PKBβ-null mice exhibit mild growth deficiency and an age-dependent loss of adipose tissue or lipoatrophy, with all observed adipose depots dramatically reduced by 22 weeks of age. Akt2/PKBβ-deficient mice are insulin resistant with elevated plasma triglycerides. In addition, Akt2/PKBβ-deficient mice exhibit fed and fasting hyperglycemia, hyperinsulinemia, glucose intolerance, and impaired muscle glucose uptake. In males, insulin resistance progresses to a severe form of diabetes accompanied by pancreatic β cell failure. In contrast, female Akt2/PKBβ-deficient mice remain mildly hyperglycemic and hyperinsulinemic until at least one year of age. Thus, Akt2/PKBβ-deficient mice exhibit growth deficiency similar to that reported previously for mice lacking Akt1/PKBα, indicating that both Akt2/PKBβ and Akt1/PKBα participate in the regulation of growth. The marked hyperglycemia and loss of pancreatic β cells and adipose tissue in Akt2/PKBβ-deficient mice suggest that Akt2/PKBβ plays critical roles in glucose metabolism and the development or maintenance of proper adipose tissue and islet mass for which other Akt/PKB isoforms are unable to fully compensate.
Robert S. Garofalo, Stephen J. Orena, Kristina Rafidi, Anthony J. Torchia, Jeffrey L. Stock, Audrey L. Hildebrandt, Timothy Coskran, Shawn C. Black, Dominique J. Brees, Joan R. Wicks, John D. McNeish, Kevin G. Coleman
Recent evidence suggests the existence of a hepatoportal vein glucose sensor, whose activation leads to enhanced glucose use in skeletal muscle, heart, and brown adipose tissue. The mechanism leading to this increase in whole body glucose clearance is not known, but previous data suggest that it is insulin independent. Here, we sought to further determine the portal sensor signaling pathway by selectively evaluating its dependence on muscle GLUT4, insulin receptor, and the evolutionarily conserved sensor of metabolic stress, AMP-activated protein kinase (AMPK). We demonstrate that the increase in muscle glucose use was suppressed in mice lacking the expression of GLUT4 in the organ muscle. In contrast, glucose use was stimulated normally in mice with muscle-specific inactivation of the insulin receptor gene, confirming independence from insulin-signaling pathways. Most importantly, the muscle glucose use in response to activation of the hepatoportal vein glucose sensor was completely dependent on the activity of AMPK, because enhanced hexose disposal was prevented by expression of a dominant negative AMPK in muscle. These data demonstrate that the portal sensor induces glucose use and development of hypoglycemia independently of insulin action, but by a mechanism that requires activation of the AMPK and the presence of GLUT4.
Rémy Burcelin, Valerie Crivelli, Christophe Perrin, Anabela Da Costa, James Mu, Barbara B. Kahn, Morris J. Birnbaum, C. Ronald Kahn, Peter Vollenweider, Bernard Thorens
Bone marrow or hematopoietic stem cell transplantation is a potential treatment for autoimmune disease. The clinical application of this approach is, however, limited by the risks associated with allogeneic transplantation. In contrast, syngeneic transplantation would be safe and have wide clinical application. Because T cell tolerance can be induced by presenting antigen on resting antigen-presenting cells (APCs), we reasoned that hematopoietic stem cells engineered to express autoantigen in resting APCs could be used to prevent autoimmune disease. Proinsulin is a major autoantigen associated with pancreatic β cell destruction in humans with type 1 diabetes (T1D) and in autoimmune NOD mice. Here, we demonstrate that syngeneic transplantation of hematopoietic stem cells encoding proinsulin transgenically targeted to APCs totally prevents the development of spontaneous autoimmune diabetes in NOD mice. This antigen-specific immunotherapeutic strategy could be applied to prevent T1D and other autoimmune diseases in humans.
Raymond J. Steptoe, Janine M. Ritchie, Leonard C. Harrison
Insulin is a major target of the autoimmune response associated with destruction of pancreatic β cells in type 1 diabetes. A peptide that spans the junction of the insulin B chain and the connecting (C) peptide in proinsulin has been reported to stimulate T cells from humans at risk for type 1 diabetes and autoimmune diabetes–prone NOD mice. Here we show that proinsulin B24–C36 peptide binds to I-Ag7, the MHC class II molecule of the NOD mouse, and, after intranasal administration, induces regulatory CD4+ T cells that, in the absence of CD8+ T cells, block the adoptive transfer of diabetes. Curiously, however, intranasal B24–C36 did not inhibit development of spontaneous diabetes in treated mice. We then determined that B24–C36, and its core sequence B25–C34, bind to Kd, the NOD mouse MHC class I molecule, and elicit CD8+ CTLs. When the CD8+ T lymphocyte epitope was truncated at the C34 valine anchor residue for binding to Kd, the residual CD4+ T cell epitope, B24–C32/33, significantly inhibited diabetes development after a single intranasal dose. This study identifies a novel CTL epitope in proinsulin and demonstrates that the therapeutic potential of a “tolerogenic” autoantigen peptide can be compromised by the presence of an integral CTL epitope.
Nathan R. Martinez, Petra Augstein, Antonis K. Moustakas, George K. Papadopoulos, Silvia Gregori, Luciano Adorini, David C. Jackson, Leonard C. Harrison
Protein targeting to glycogen (PTG) is a scaffolding protein that targets protein phosphatase 1α (PP1α) to glycogen, and links it to enzymes involved in glycogen synthesis and degradation. We generated mice that possess a heterozygous deletion of the PTG gene. These mice have reduced glycogen stores in adipose tissue, liver, heart, and skeletal muscle, corresponding with decreased glycogen synthase activity and glycogen synthesis rate. Although young PTG heterozygous mice initially demonstrate normal glucose tolerance, progressive glucose intolerance, hyperinsulinemia, and insulin resistance develop with aging. Insulin resistance in older PTG heterozygous mice correlates with a significant increase in muscle triglyceride content, with a corresponding attenuation of insulin receptor signaling. These data suggest that PTG plays a critical role in glycogen synthesis and is necessary to maintain the appropriate metabolic balance for the partitioning of fuel substrates between glycogen and lipid.
Sean M. Crosson, Ahmir Khan, John Printen, Jeffrey E. Pessin, Alan R. Saltiel
Mice with 50% Pdx1, a homeobox gene critical for pancreatic development, had worsening glucose tolerance with age and reduced insulin release in response to glucose, KCl, and arginine from the perfused pancreas. Surprisingly, insulin secretion in perifusion or static incubation experiments in response to glucose and other secretagogues was similar in islets isolated from Pdx1+/– mice compared with Pdx1+/+ littermate controls. Glucose sensing and islet Ca2+ responses were also normal. Depolarization-evoked exocytosis and Ca2+ currents in single Pdx1+/– cells were not different from controls, arguing against a ubiquitous β cell stimulus-secretion coupling defect. However, isolated Pdx1+/– islets and dispersed β cells were significantly more susceptible to apoptosis at basal glucose concentrations than Pdx1+/+ islets. BclXL and Bcl-2 expression were reduced in Pdx1+/– islets. In vivo, increased apoptosis was associated with abnormal islet architecture, positive TUNEL, active caspase-3, and lymphocyte infiltration. Although similar in young mice, both β cell mass and islet number failed to increase with age and were approximately 50% less than controls by one year. These results suggest that an increase in apoptosis, with abnormal regulation of islet number and β cell mass, represents a key mechanism whereby partial PDX1 deficiency leads to an organ-level defect in insulin secretion and diabetes.
James D. Johnson, Noreen T. Ahmed, Dan S. Luciani, Zhiqiang Han, Hung Tran, Jun Fujita, Stanley Misler, Helena Edlund, Kenneth S. Polonsky
Adipose tissue lipolysis supplies circulating FFAs, which largely meet lipid fuel needs; however, excess FFAs, can contribute to the adverse health consequences of obesity. Because “normal” FFA release has not been well defined, average (mean of 4 days) basal FFA release and its potential regulation factors were measured in 50 lean and obese adults (25 women). Resting energy expenditure (REE), but not body composition, predicted most of the interindividual variation in FFA release. There was a significant, positive linear relationship between palmitate release and REE; however, women released approximately 40% more FFA than men relative to REE. Neither plasma palmitate concentrations nor respiratory quotient by indirect calorimetry differed between men and women. Glucose release rates were not different in men and women whether related to REE or fat free mass. These findings indicate that nonoxidative FFA clearance is greater in women than in men. This could be an advantage at times of increased fuel needs. We conclude that “normal” adipose tissue lipolysis is different in men and women and that the fuel export role of adipose tissue in obesity will need to be reassessed.
Søren Nielsen, ZengKui Guo, Jeanine B. Albu, Samuel Klein, Peter C. O’Brien, Michael D. Jensen
Bone marrow harbors cells that have the capacity to differentiate into cells of nonhematopoietic tissues of neuronal, endothelial, epithelial, and muscular phenotype. Here we demonstrate that bone marrow–derived cells populate pancreatic islets of Langerhans. Bone marrow cells from male mice that express, using a CRE-LoxP system, an enhanced green fluorescent protein (EGFP) if the insulin gene is actively transcribed were transplanted into lethally irradiated recipient female mice. Four to six weeks after transplantation, recipient mice revealed Y chromosome and EGFP double-positive cells in their pancreatic islets. Neither bone marrow cells nor circulating peripheral blood nucleated cells of donor or recipient mice had any detectable EGFP. EGFP-positive cells purified from islets express insulin, glucose transporter 2 (GLUT2), and transcription factors typically found in pancreatic β cells. Furthermore, in vitro these bone marrow–derived cells exhibit — as do pancreatic β cells — glucose-dependent and incretin-enhanced insulin secretion. These results indicate that bone marrow harbors cells that have the capacity to differentiate into functionally competent pancreatic endocrine β cells and that represent a source for cell-based treatment of diabetes mellitus. The results generated with the CRE-LoxP system also suggest that in vivo cell fusion is an unlikely explanation for the “transdifferentiation” of bone marrow–derived cells into differentiated cell phenotypes.
Andreea Ianus, George G. Holz, Neil D. Theise, Mehboob A. Hussain
To elucidate the function of PPARγ in leptin-deficient mouse (ob/ob) liver, a PPARγ liver-null mouse on an ob/ob background, ob/ob-PPARγ(fl/fl)AlbCre+, was produced using a floxed PPARγ allele, PPARγ(fl/fl), and Cre recombinase under control of the albumin promoter (AlbCre). The liver of ob/ob-PPARγ(fl/fl)AlbCre+ mice had a deletion of exon 2 and a corresponding loss of full-length PPARγ mRNA and protein. The PPARγ-deficient liver in ob/ob mice was smaller and had a dramatically decreased triglyceride (TG) content compared with equivalent mice lacking the AlbCre transgene (ob/ob-PPARγ(fl/fl)AlbCre–). Messenger RNA levels of the hepatic lipogenic genes, fatty acid synthase, acetyl-CoA carboxylase, and stearoyl-CoA desaturase-1, were reduced in ob/ob-PPARγ(fl/fl)AlbCre+ mice, and the levels of serum TG and FFA in ob/ob-PPARγ(fl/fl)AlbCre+ mice were significantly higher than in the control ob/ob-PPARγ(fl/fl)AlbCre– mice. Rosiglitazone treatment exacerbated the fatty liver in ob/ob-PPARγ(fl/fl)AlbCre– mice compared with livers from nonobese Cre– mice; there was no effect of rosiglitazone in ob/ob-PPARγ(fl/fl)AlbCre+ mice. The deficiency of hepatic PPARγ further aggravated the severity of diabetes in ob/ob mice due to decreased insulin sensitivity in muscle and fat. These data indicate that hepatic PPARγ plays a critical role in the regulation of TG content and in the homeostasis of blood glucose and insulin resistance in steatotic diabetic mice.
Kimihiko Matsusue, Martin Haluzik, Gilles Lambert, Sun-Hee Yim, Oksana Gavrilova, Jerrold M. Ward, Bryan Brewer Jr., Marc L. Reitman, Frank J. Gonzalez
Hedgehog proteins modulate development and patterning of the embryonic nervous system. As expression of desert hedgehog and the hedgehog receptor, patched-1, persist in the postnatal and adult peripheral nerves, the hedgehog pathway may have a role in maturation and maintenance of the peripheral nervous system in normal and disease states. We measured desert hedgehog expression in the peripheral nerve of maturing diabetic rats and found that diabetes caused a significant reduction in desert hedgehog mRNA. Treating diabetic rats with a sonic hedgehog–IgG fusion protein fully restored motor- and sensory-nerve conduction velocities and maintained the axonal caliber of large myelinated fibers. Diabetes-induced deficits in retrograde transport of nerve growth factor and sciatic-nerve levels of calcitonin gene–related product and neuropeptide Y were also ameliorated by treatment with the sonic hedgehog–IgG fusion protein, as was thermal hypoalgesia in the paw. These studies implicate disruption of normal hedgehog function in the etiology of diabetes-induced peripheral-nerve dysfunction and indicate that delivery of exogenous hedgehog proteins may have therapeutic potential for the treatment of diabetic neuropathy.
Nigel A. Calcutt, Karen L. Allendoerfer, Andrew P. Mizisin, Alicia Middlemas, Jason D. Freshwater, Monica Burgers, Rigel Ranciato, Jean-Dominique Delcroix, Frederick R. Taylor, Renee Shapiro, Kathy Strauch, Henryk Dudek, Thomas M. Engber, Alphonse Galdes, Lee L. Rubin, David R. Tomlinson